Tunneling and Underground Construction

According to the structural characteristics and static equilibrium of the joints, an immersed tube tunnel, three-dimensional, nonlinear stiffness mechanical model is established. What's more, the harmonious relation for deformation and stress-strain relations of GINA and OMEGA gasket are analyzed. By using this model, the different operating modes of the joints can be divided and identified by the relative displacement of the shear key. In addition, the mechanical characteristics of joints and the nonlinear relation between the joint displacement and internal force are further revealed.

In underground powerhouses' construction, the stability evaluation of the surrounding rock of underground caverns is a fundamental problem. In this paper, the influence of different rise-span ratio and lateral pressure coefficient towards the stability of crown of surrounding rock is studied. On the basis of the maximum tensile criterion, the stability of crown of surrounding rock is evaluated and the predicator formula of reasonable rise-span ratio is proposed. The paper comes to the conclusion that: (1) when rise-span ratio is set, compressive stress at the top of the crown decreases when lateral pressure coefficient goes down; and (2)when the lateral pressure coefficient is set, compressive stress at the top of the crown decreases when rise-span ratio goes down. With appropriateness and reliability, the prediction formula of reasonable rise-span ratio guarantees the stability of surrounding rock of crown and provides scientific foundation for the preliminary confirmation of reasonable rise-span ratio of crown.

Ground vibrations generated from the pile driving process using impact hammers can have adverse effects on adjacent structures. Several factors contribute to the vibration levels, including the soil types, distance from the structures, and energy levels of the hammer. Depending upon the type of structure, regulatory authorities often impose restrictions on the allowable vibration level, typically in terms of peak particle velocity. Only a few methods are available to estimate the ground vibration levels due to pile driving. This paper presents the results of the vibration monitoring during the driving of six 406-mm-diameter, open-ended steel pipe piles and two H-piles (HP 360 x 174) using hydraulic impact hammers in medium dense to very dense, silty sands. Final penetration depths varied from 18 to 21 m. Six geophones were installed at the locations of each pile to monitor the vibration levels. The actual pile driving energy transferred to the pile was monitored using pile driving analyzer (PDA). The relationship between peak particle velocity and scaled distance was developed and compared against the methods available in literature.

In Sarawak, estuarine structures (such as jetties and wharves) are usually supported on pile foundations due presence of very soft and deep sedimentary soils. The response of the ground and the piles to the tidal fluctuation (on the order of 4 to 7 m) is very complex. The evaluation of the lateral stability of piles is usually neglected in design. As a result, there have been many incidents of failure or lateral movement of bridges, jetties and wharves. The formulation of a model to analyze the soil-pile system under such a complex situation requires data on ground movement and pore water pressure changes due to tidal fluctuation. Piezometers and ABS inclinometer casing have been installed on the banks of a site where a bridge construction is proposed. Instrumentation has also been made to monitor the lateral movement of a pile installed in the riverbed. The piezometers and inclinometers are being monitored regularly. Similar instrumentation and monitoring have been carried out at another site where a jetty is proposed to be constructed. The paper explains the background of the study, soil conditions at the sites, details of instrumentation, results of measurement, and the interpretations.

Geosynthetic-reinforced slopes have the advantages of easy construction, low construction cost, short construction period, better deformation tolerance, earthwork amount balance and good seismic resistance ability. Therefore, a great number of geosynthetic-reinforced slopes have been used to improve the slope stability in Taiwan. However, during the Taiwan 921 Chi-Chi earthquake, some geosynthetic-reinforced slopes were destroyed. In order to understand the performance of the seismic behavior of the geosynthetic-reinforced slope affected by the earthquake, this study set an earthquake monitoring system to record actual seismic data of a geosynthetic-reinforced slope built in FoGuang University, Taiwan. The monitoring system adopts newly developed seismic instruments which have the advantages of: a variety of seismic interpretation schemes, easy to use, low cost, high temperature resistance, and waterproof. In fact, it is similar to, but different from the traditional earthquake monitoring system with seismic instruments setting in structure. The recorded seismic data can be further used to verify the dynamic simulation analysis to confirm the seismic response of geosynthetic-reinforced slopes under different magnitude scale earthquakes. It is hopeful that this study can provide earthquake resistance information for geotechnical engineers during the design phase.

Internal erosion and soil piping are caused by the migration of fine soil particles through a skeleton of coarse grains or by progressive mass movement of soil grains under the tractive forces produced by concentrated subsurface flow, which may lead to the failure of dams and levees. The ability of the Vision Cone Penetrometer (VisCPT) to record internal erosion and soil piping in the laboratory and in-situ has previously been reported. The present paper focuses on developing a video-processing algorithm to quantify the soil particle motions. An optical flow technique is adopted to compute particle migration velocity fields. This makes it feasible to detect, track and quantify the movement of soil particles by the VisCPT. The research defines the eroded area percentage (EAP) and the sum of the absolute velocities of mobilized fine soil particles (SAV) which may eventually be used to quantify soil erosion and piping susceptibility.

For compaction works, it is necessary to spot-check the density of compacted backfill, usually by means of the sand cone test. However, this method is time-consuming. A light-weight deflectometer (LWD) developed for evaluation of surface stiffness may be employed to estimate the degree of compaction. In this study, the following tests were performed on a lateritic soil: (i) modified Proctor compaction test to determine the optimum water content (w_opt) and the corresponding maximum dry density (ρ_d,max); (ii) California Bearing Ratio (CBR) tests on specimens prepared at w_opt; (iii) sand cone tests to find the field density and, therefore, the degree of compaction (D_c); and (iv) LWD tests to find the surface stiffness (k_LWD). While gradually increasing the compaction effort in a test pit, sand cone and LWD tests were performed on the compacted soil. It was found that there are relevant correlations between the D_c and %CBR and the k_LWD. When these correlations are known, the LWD test can be an alternative for indirectly evaluating D_c and %CBR for compaction control.

This paper presents the results of the load testing program designed to confirm the vertical design capacity and/or to determine the ultimate vertical load carrying capacity of the drilled shafts for the New Jersey Turnpike Interchange 6 to 9 Widening Program Section II, presently under construction in New Jersey, USA. The results of the load testing are correlated with the results of the design capacity empirically derived using AASHTO Bridge Design Specifications. This paper also discusses the installation procedures and load-testing programs involving O-Cell Test. Finally, recommendations regarding design and construction of drilled shafts are presented based on the results of the static load test.

This paper evaluates three lateral load tests performed on 406 mm (16-inch) diameter auger cast piles (ACP). The lateral deflection values of the ACP measured in the field are compared with the lateral deflection values of the ACP predicted using a commercial computer program, LPile. The predictions were made assuming the linear, as well as the non-linear, variation of the flexural stiffness of ACP. A sensitivity analysis was performed to determine the effect of various soil parameters on the lateral deflection of the ACP. The sensitivity analysis indicated that soil layers at a depth of about 0.3 times the length of the pile (i.e., 0.30L, where L = length of the pile) or greater has a negligible effect on the lateral deflection of the ACP. Based on the results of the lateral load test data of ACP, it is determined that the measured response of ACP to lateral load is somewhere in between the responses predicted using the linear and non-linear flexural stiffness of ACP. Further, reliable prediction of lateral displacement is not possible without knowing the accurate values of modulus of elasticity of pile material.

This paper presents centrifuge experiment data related to the problem of tunnelling-induced ground displacement in sand. The paper focuses on the examination of the effect that relative density has on greenfield soil displacements above tunnels in sandy ground. Data from a series of plane strain centrifuge tests on tunnels in silica sand are presented. The relative density of the sand ranged from 50% to 90% in the tests. The soil displacement data were obtained using an imaged-based deformation measurement technique and examined to determine features of greenfield settlement, both surface and subsurface. The effect that relative density has on the settlement trough shape is demonstrated and discussed.

In the past, only displacement, stress, size and distribution of plastic zone can be obtained when analyzing the stability of jointed rock tunnel. Neither the location and range of the failure surface could be found, nor the quantitative critera of safety factor be obtained. Quantitative analysis of the stability of a jointed rock tunnel is deduced in this paper by model test and numerical analysis. Failure state and safety factor of the jointed rock tunnel are calculated by using FEM strength reduction. The results show that joint obliquity α has a greater impact on the location of failure surface. If α=0°, failure surface distributes symmetrically on both sides. If α=30° and 45°, failure surface rotates with the change of joint obliquity correspondingly and distributes in the up-down parts of the joint. If α≥60°, failure surface transfers to the vault and the foots of the sidewall mainly because of gravity. In particular, if α=90°, a failure surface can be formed in the middle of vault. The safety factor results show that safety factors reduce in different degrees in jointed rock tunnel compared with homogenous tunnel; but, joint obliquity has little impact on the safety factor. With the reduction of joint spacing and strength, the safety factor decreases.

Considering a horse-shaped deep tunnel subjected to far-field stresses and lining inner pressure, a complex variable solution is presented in this paper to describe the stress and displacement distribution around the surrounding rock mass. The solution is implemented in the platform of MATLAB and then verified by numerical simulation in the platform of FLAC3D. In addition, the influences of far-field stresses and lining inner pressure on the stress and convergence along tunnel perimeter are discussed through case study.

The damage of interlaid rock caused by blasting will affect the stability of the adjacent adjoining rock and tunnel lining directly, especially in the small interval tunnel. Based on the construction of Shizishan Tunnel in Nanping, Fujian Province, some detailed monitoring for the blasting vibrations in surrounding rock mass and tunnel lining were carried out. According to the measured data, the dynamic mechanics parameters of adjoining rock were back-analyzed through numerical simulations. The velocity distribution characteristics of interlaid rock vibration in three directions were well studied. Then, some conclusions about the interrelation of this three-direction velocity can been drawn which could provide some reference to the blasting controlling in the small interval tunnel.

The utilization of great, deep, underground space (50 m below ground surface) is becoming increasingly important; thus, it becomes very necessary to study the pressure and deformation for the great, deep, underground structures. In this paper, a series of finite element analysis was adopted to simulate the construction process of new pneumatic caisson and diaphragm wall for the great, deep, underground structure. Based on the numerical results, the distributions of earth pressure and soil displacements surrounding the deep underground structures were studied. Compared to the shallow underground structures, the characteristics of earth pressure surrounding the deep underground structures were analyzed.

The relationship between subsurface settlement and ground volume loss caused by the excavation of a new tunnel underneath the existing tunnel was analyzed and identified based on Mair's theory. Subsurface settlements were determined by equations and a 3-D finite element numerical modeling. The settlement and ground volume loss control measurements for the tunneling-induced settlements in the existing tunnel were proposed and demonstrated by using 3-D finite element analysis. The large pipe-shed (LPS) ground stabilization was utilized to perform ground stabilization prior to the new tunnel excavation. The effects of using LPS ground stabilization on ground volume loss control were evaluated by comparing with non-LPS tunneling situations. The results indicate that the LPS ground stabilization can significantly reduce the settlement of an existing tunnel caused by the excavation of a new tunnel, and the ground volume loss method has proven to be an effective approach to estimate the effects of LPS ground stabilization.

Assessing the potential of building damage is a critical issue for existing and new building projects. Simple analytical approaches up to now are still mainly considered to assess the vulnerability of structures. This paper presents a new approach based on a small-scale physical model (1/40 scale factor on the dimensions) under normal gravity. It has been designed for developing and validating experimentally new methods of prediction of damages to masonry structures induced by subsidence (generally resulting from underground excavations of tunnels and mines). The analogical soil is homogenous sand, allowing the realization of different simulations. The masonry structure consists of walls built with wood pieces without cohesion (mortar) and resting on an elastic foundation. The vertical displacements are applied through the use of an electro-mechanical jack. The technique of digital image correlation (DIC) is used to measure accurately the displacements and the deformations of the structure. The identification of the damage level is based on the crack width resulting from different vertical displacements. A specific algorithm has been developed to quantify the strain of joints. The total length of opened cracks appears to be a more relevant indicator of damage than the maximum width of cracks. The damage evolution with the vertical displacement can be divided into an initial linear part and a subsequent non-linear part. Guidelines are suggested for the assessment of the masonry damages due to underground excavations.

Previous theoretical solutions for tunneling-induced ground movements are usually based on the boundary condition of uniform radial displacement at the cavity opening. There has been little investigation into the problem of non-uniform convergence deformation pattern. Actually, excavation convergence is highly non-uniform with more crown settlement and less invert heave. The displacement controlled boundary element solution is presented and the oval-shaped ground deformation pattern is imposed to the tunnel opening boundary to consider the non-uniform convergence characters. The applicability of the proposed solution is checked with the field observations and other analytical methods and centrifuge test data. Generally good agreement of the predicted ground deformations can be seen with the compared verifications. It may provide a certain basis to draw up correctly protective measurements of geotechnical environments influenced by subway tunneling in soft soils.

This paper studies the ground subsidence due to the tunneling in sands. The relationship between tunnel volume loss ratio and subsurface soil volume loss ratio is obtained by analyzing the test data. This relationship is then introduced into existing empirical methods to establish the surface settlement trough caused by tunneling in sands. Compared with the geotechnical centrifugal test data, the equation can provide reasonable results under the condition of the construction level nowadays. The finding of the relationship between tunnel volume loss ratio and subsurface settlement trough volume loss ratio makes it possible to calculate the surface and subsurface settlement troughs using empirical method.

This paper presents a new geotechnical design concept - robust geotechnical design (RGD) - which seeks to minimize the variation of the tunnel circumferential performance to the uncertainty of geotechnical parameters (which is a measure of design robustness) in addition to meeting the requirements of safety and cost efficiency. To this end, uncertain geotechnical parameters are represented as fuzzy sets (or more specifically, fuzzy numbers) to copy with the scarcity of data, which provides an adequate measure of the uncertainties when the knowledge is incomplete or data is limited. Given fuzzy input parameters, the circumferential performance of a shield-driven tunnel is uncertain and logically expressed as a fuzzy factor of safety, Based upon which the failure probabilities and robustness of the tunnel circumferential performance can be computed in the RGD framework. Finally, to aid in the selection of the optimal design that maximizes robustness and minimizes cost simultaneously while the safety is brought to the target level, non-dominated optimization is performed and a Pareto front is obtained. the knee point located on the Pareto front is further identified and recommended as the optimal design, showing the best compromise between robustness and cost. The proposed RGD methodology of shield-driven tunnels is deterministic in nature. Through an illustrative design example presented, the effectiveness and significance of the proposed RGD methodology in the design of shield-driven tunnels for the circumferential performance is demonstrated.

The construction of tunnels is booming in China in recent decades. However, the degradation of concrete lining in tunnels seems inevitable, and the challenges in the repair and maintenance in urban metro structures confront engineers daily. The concept of self-healing in concrete was proposed over a decade ago. Concretes with microencapsulated healing agents are very appealing due to the advantages of self-healing, adaptivity to concrete, and the potentiality of controllable, quantifiable healing. The focus of this paper is to summarize the motivation of using self-healing materials and to classify the investigations on the microcapsule-enabled concrete in terms of its components and properties. Relative materials, experiments and theories have been reviewed. Some important factors of microcapsule-enabled, self-healing, underground concrete in urban metro structures are discussed too.

Based on the specialties of the drilling augers, the piling equipment and the construction techniques of soil displacement screw piles (known as SDS piles), two groups of full-scale load tests between SDS piles and half screw piles (known as HS piles) were carried out in Weihai City, China. Besides the tests, the differences of mechanical behaviors and the bearing-deformation performances between the two types of piling system are further analyzed. Moreover, the mechanical properties and technical advantages of SDS piles are also discussed in detail. The investigations show that SDS piles have more technical advantages than HS piles in the aspects of bearing and deformation characteristics.

Observation and Measurement of displacements at the crown of the tunnel is an integral part of New Austrian Tunneling Method (NATM) in complex rock masses to verify the construction parameters, support systems and safety requirements. However, the prediction of ground conditions ahead of an advancing tunnel face is also an application, often less explored in the field by site engineers. Literature suggests displacement vector orientation is a good indicator of weak ground or fault/shear zones ahead of the tunnel face. There has been no quantification between the vector orientation and the properties of the weaker ground ahead. An attempt is made to quantify the effect of the properties of the weaker ground on the vector orientation numerically. The model results are initially compared with analytical solutions, followed by benchmarking with the results of other researchers. The factors which affect the vector orientation are the diameter of the tunnel, stiffness ratio of the rocks and in situ stress ratio. The effect of each of these parameters is studied independently. A correlation between the vector orientation and the variation in ground conditions is then established to predict the properties of the weaker ground ahead of the advancing tunnel face.

For the super-shallow embedded tunnel - like a ground-penetrating shield tunnel (GPST) - the internal force and deformation of the lining are quite different from the normal ones. This paper adopts the nonlinear shell spring model to simulate the behavior of a lining. Taking the configuration of lining joints into consideration, a 3D numerical model was taken to calculate the stiffness of longitudinal joints and the lining behavior is further analyzed. The results show that in super-shallow embedded tunnel, the moment is larger while the axial force is smaller compared with the general one. Also, the bending stiffness of the longitudinal seam joints becomes smaller and behaves non-linearly. What's more, the shell spring model is compared with the mean ring method. The contrast analysis shows that, for conventional tunnels, the internal force calculated by a nonlinear shell spring model is close to the results bythemean ring model; but, the deformation values aresignificantly different. Therefore, it is necessary to consider the non-linear joints stiffness in the calculation of the super-shallow embedded tunnel.

In this paper - based on monitoring data from 18 deep excavation cases in soft soil areas in Shanghai - the depth of basal heave (H_R), the width of settlement zone (B_s), the maximum ground settlement (δ_vm) and lateral deflection of retaining wall (δ_hm) are studied. First, it is found that H_R is the depth where the unloading ratio is 0.15. Second, B_s is found to be closely related to the volume of excavation and the depth of basal heave. Then, two simple methods are proposed for the prediction of B_s. Last, the relation between maximum deformation and construction time is studied and the objective construction time is suggested.

The embedded depth ratio of multi-pivot retaining walls is a very important parameter in the design of deep excavations. Taking an excavation in the Suzhou subway as an example, the relationship between the deformation and internal forces and the embedded depth of the retaining wall was analyzed for the purpose of determining the rational embedded depth. The maximum lateral displacement of retaining walls and the maximum surface settlement does not reduce endlessly with deepening the embedded depth. It is little affected by the increase of embedded depth when the embedment reaches a certain depth. The internal forces of the retaining structure increase or decrease first and then stabilize when the embedded depth ratio reaches a certain value. Based on these analyses, the ratio of wall embedded depth to excavation depth in Suzhou City was proposed in the range of 0.7 to 0.8. This reference range not only can guarantee the stability of deep excavation, but also can reduce the construction cost.

This paper investigates the 3D excavation-induced ground and building's settlements by means of 3D numerical simulations. The effects of the excavation responses are studied with and without considering the nearby building. This paper proposes a simplified simulation technique (capturing the plastic behavior of the structure to enhance the realistic modeling of the structure) in which the excavation model and the structure model are decoupled and considered by two separate numerical programs. An iteration scheme is developed to bridge the two models. The results show that the proposed analytical scheme is feasible and the convergence can be reached within several iterations. It allows more in-depth investigation on the structure response such as where the plastic hinge or high potential of damage may occur in the structure. This study also provides valuable insights not only on the interaction characteristics of the soil and the structure adjacent to an excavation site, but also on the effect on the excavation behavior due to inelastic behavior of the adjacent structure.

During the assembly stage of precast segmental tunnel linings, the segments are often subjected to impact and concentrated loads. Since plain concrete is a quasi-brittle material exhibiting low tensile strength and fracture toughness, concrete damages - in the form of cracking and spalling - are very likely to occur on the periphery of the segments. By the addition of steel fibers into the concrete matrix, the robustness and ductility of this quasi-brittle material can be significantly enhanced due to the crack-bridging effect of fibers. To simulate the segments subjected to concentrated loads in small-scale, partial-area loading tests were carried out on plain and fiber concrete prisms under laboratory conditions. The principal variables investigated in this paper were fiber reinforcement, area ratio and loading eccentricity. The effects of those variables on the load-bearing capacity, failure mode and crack pattern were analyzed and discussed. From the experimental results, it was found that the presence of steel fibers led to a remarkable increase of the load-bearing capacity of concrete and changed its failure mode from a brittle to a ductile one. Increasing the area ratio or loading eccentricity also had significant influence on the bearing strength and failure pattern.

Deformation prediction is one of the core contents in the design of the gravity retaining walls in Shanghai soft soil. Geotechnical design engineers used to rely on numerical analysis and beam on elastic foundation analysis to calculate the lateral displacement of a gravity retaining wall. However, both methods are too complicated to be used and they are not suitable for engineers. In this paper, the lateral displacement function of a gravity retaining wall was normalized through four excavations in Shanghai. The simplified formula of lateral displacement of a gravity retaining wall was derived through the principle of minimum potential energy. The simplified calculation method of horizontal deformation of a gravity retaining wall was verified by ten case histories in Shanghai.

A 30-m-deep foundation pit is excavated into 10-m-thick weathered granite strata in Shenzhen, China. The upper ground over weathered granite is a 20-m strata composed of loose sandy soil and clayey soil with high water content. To evaluate the impact on the surroundings caused by the excavation of the pit, a numerical simulation is performed by finite element method (FEM). Taking account of the interaction of excavation process, retaining structures and soil, simulation is conducted for the process of progressive excavation, support system assembling, and disassembling. Simulation results agree well with measured values and meet the requirements of construction criterion. The FEM model offers an available analysis method for the deformation prediction and design of similar ultra-deep excavation in Shenzhen.

The behaviour of existing cast iron tunnels subjected to ground movements induced by new tunnelling works is a much discussed topic. In many cases, new tunnels in highly populated urban cities like London will need to be constructed underneath a dense network of existing tunnels to avoid them. The construction of new tunnels, however, inevitably results in ground deformations that are transmitted to adjacent existing structures. The response of existing cast iron tunnels to tunnelling-induced deformation is not well understood. Practicing engineers are faced with significant uncertainties about their response. This paper presents a case study in which multiple monitoring technologies have been deployed in a section at an existing cast iron tunnel in London underneath which a new, much larger tunnel is being constructed. The new tunnel is being excavated parallel with, and directly below the existing tunnel for a length of approximately 100m. Instrumentation technologies deployed in a 40-m-long section within the 100m zone include analogue linear displacement transducers, fibre optics, digital tilt sensors, video extensometer and digital image correlation, laser scanning and photogrammetry. The multi-technology deployments in this case study are presented in a unified dashboard system specifically developed for this project. They provide an ideal scenario to investigate the detailed cast iron tunnel response using independent data sets. They also provide an exceptional opportunity, within the dashboard system, to use these data sets to understand the capabilities of the associated technologies when compared and contrasted against each other. The dashboard system can provide practicing engineers with the ability to understand tunnels' response accurately and rapidly and, hence, potentially provide significant time and cost savings for complex infrastructure projects.

Shield tunnels are widely used in the Shanghai metro system, which has numerous joints and is buried in saturated soft soil. Therefore, seepage is the most common failure event of tunnel structures. In the present work, a methodology to estimate the reliability of shield tunnel joint was proposed. This methodology contains a two-level hierarchical reliability evaluation. The first level estimation can give the probability distribution function of the seepage frequency as well as the interval estimation of the distribution parameters using MCMC technique and bootstrap based on prior information of tunnel performance so that the epistemic uncertainty can be taken into consideration. The second level estimation can provide the reliability index of the tunnel joint at a specified location along the tunnel structure. To have a more realistic estimation of reliability index, the advanced first order reliability method, combined with Bayesian inferential structure, was employed. The longitudinal curvature radius of tunnel structure was considered as posterior information. The proposed approach has also been validated with data extracted from the Shanghai metro system with direct inspection and measurement.

Shallow buried tunnels are commonly seen in engineering practice. To understand the failure mechanism of a shallow buried tunnel is of significance in engineering practice. There is a reasonable judging index lacking in tunnel stability. The strength reduction method (SRM) gained limited status of geotechnical materials by reducing the computation parameters. Then, the failure zone can be obtained and shown. Finally, a safety factor can be obtained by this progress. This method has been used in slope stability analysis. The usage of this method is a new field. Based on shallow tunnel computation model under different cover depth, the SRM method is adopted in finding the safety factor of shallow buried tunnels. The displacement curve, changing with the strength reduction factor, is drawn and the catastrophe point is found as the safety factor. Further, in comparison with the failure criteria of plastic zone connection and non-convergence, and also compared with model tests, failure mechanism of shallow buried tunnels is analyzed. Specialty of these safety factors is discussed and it is proved that they maintain accordance. This research is significant for a tunnel safety factors study.

Combining the project practice of deep foundation pit excavation under railway trestle in coastal soft clay region, numerical calculation methods are used to analyse the excavation impact on the structural dynamic property and the deformation of the operating railway trestle over it. Monitoring data of the foundation pit and railway trestle are statistically analyzed. Based on the analysis above, protection and control countermeasures of operating railway trestles over deep excavation are presented, which could be reference for design and construction of railway stations and foundation pit engineering

The influencing factors of shield tunneling pattern, tool disposition, efficiency, construction process and parameters of shield tunneling are mainly discussed from five aspects - physical and mechanical properties, structure, construction and water abundance of complex strata - which vary a lot from one type to another. Therefore, it is necessary to master the classification of the complex strata and its influence on shield tunneling accurately. This paper attempts to put forward a set of classification processes and methods based on geological features of complex strata of Guangzhou and Shenzhen area. The complex strata is clustered into six groups (A~F). Then, each group is clustered into four subclasses (I~IV) according to main influencing factors of penetration rate (PR) and face self-stability. This method is of certain guiding significance for shield construction and the study of stratum adaptability.

In this study, three-dimensional elastic-plastic numerical analyses are conducted to investigate the influences of tunnel excavation on existing loaded piles. The displacement controlled model (DCM) was used to simulate the tunneling- induced volume loss effects. Numerical simulations are performed which concern the construction of the tunnel in presence of the pile foundations. Analysis is carried out for both free-field and MJS consolidation project. Results of numerical simulations show that tunneling induces significant displacement in adjacent piles. The MJS pre-consolidation can effectively improve the pile behaviors. Due to the rigorous control of the project, the uplift of piles was induced and the maximum horizontal displacement of piles occurred nearby the tunnel crown.

With the development of urban construction, the excavation area of a foundation pit becomes larger, the depth becomes deeper, and the surrounding environment becomes more complex, which requires higher environment risk control. As a new construction method,thepit-divided method becomes more and more prevalent in the foundation pit. The designed new site of Shanghai International Dance Center is located at the center of Hongqiao historical protection area. With the large excavation area, irregular shape, complex surroundings, the Yan'an viaduct on the southern side, the metro line 10 on the northern side, and the six historical conservation buildings around, there is great difficulty for design and construction. By numerical simulation, this paper draws a conclusion that the pit-divided method has obvious effect on control of the surrounding environment around the pit, which provides scientific guidance for design and construction of the pit.

Doolayi Tunnel, located in Toyserkan, is one of the strategic tunnels that connect Hamedan to the western provinces of Iran. This tunnel was excavated in proximity to the Sannandaj-Sirjan active fault and is exposed to landslide hornfels stone and groundwater. It means that, due to the occurrence of possible destructive earthquakes in this region. tunnel demolition - as a result of undesirable geology conditions - is definite. In this article, dynamic behavior of a tunnel is studied by FLAC 3D V3.00 software. Moreover, an optimum arrangement of rock bolt and reinforced Shotcrete is proposed to be able to have the most stability against accompanied effects of quake and groundwater. The results of this study indicate that the use of a composite system - in addition to making dynamic stability of the tunnel - significantly decreases displacement, swelling, settlement, stress and shear stress.

For monopile, where single pile carries all the lateral forces and moments, predicting top displacement and slope with reasonable accuracy becomes important in design practice. In this study, linear Winkler's (1867) model is created in which monopile is modelled using beam-column element with roller support at its bottom and surrounding soil is represented by linear springs. Matlock's (1970) recommendation has been used to calculate soil spring constant from its Young's modulus estimated through shear modulus. Deflection of simulated pile has been compared for various recommendations of G_max estimation through SPT values. Predicted deflection showed large variation questioning its accuracy. Since average strain level of the soil during loading is actually unknown, one can assume any strain level to find a desired value of G to match the same deflection for any of those G_max correlations. Similar analysis showed a large variation in the strain level expected in different correlations. This creates discomfort in taking design decisions and requires finding a way to approximately calculate the applicable average strain level corresponding to the induced deformations at various depths of monopile.

This study elucidated the field tests on behaviors of the spread foundations with centrically vertical pier, vertical but offset pier, and battered pier in geogrid-plannar-reinforced Aeolian sand under a combination of uplift and lateral loadings, which was compared with the parallel studies of the same foundations in Aeolian sand. The site conditions, the arrangement of reinforcing geogrid, and the load tests were documented comprehensively. A dimensionless breakout factor was presented to reflect the difference of foundation types. Under a combination of uplift and lateral loadings, the uplift-displacement curve exhibited a two-phase behavior, while the corresponding lateral displacement gradually increased with the load, apparently without two-phase behavior. Under a combination of uplift and lateral loadings, the foundation type had an obvious effect on the load-displacement behaviors. The spread foundations with vertical, but offset, pier or battered pier could have a better load-bearing capacity than that of the foundations with centrically vertical pier. Due to the higher tensile capacity of the geogrid and the frictional resistance between the geogrid and the sand mass, the geogird-reinforced Aeolian sand could behave as a much stiffer system to improve the uplift and lateral bearing capacity of the spread foundations.

The key parameters for waterproofing ability of segment joint of shield-driven tunnel - such as waterproof rule of segment joint, water resistance of gasket, and the value of assembly force of ethylene-propylene-diene monomer (EPDM) rubber gasket - have always been the research focuses in this field. This paper studied these key parameters for Nanjing Weisan Road passing river tunnel project through the new high water pressure, automatic loading device. The test results indicated: (1) waterproofing ability and variation law of EPDM rubber gasket in ‘—'shaped test are quite different from those of ‘T' shaped test; (2) waterproofing ability of EPDM rubber gasket is largely related to its assembly force and average contact stress based on optimizing section form of gasket; and (3) hardness, section form and filling ratio of gasket have significant impacts on its waterproofing performance. Finally, based on the test results, this paper summarized significant rules and several beneficial conclusions for the design and analysis of segment joint waterproofing of shield-driven tunnel.

The annular gap between segment lining and bedrock, caused by tunnel driving, must be filled instantaneously with an adequate grouting mortar. The decisive requirements for such grouts are, on the one hand, optimal flow properties lasting for several hours and sufficient stability and, on the other hand, a rapid development of shear strength immediately after grouting. The latter is normally achieved by dewatering under pressurization into the surrounding soil. Thus, two contradictory requirements are demanded for such grouts. The dewatering behavior of these grouts, which is significantly influenced by their constituents, is an important key factor. The correlation of these properties has been studied in systematic and extensive tests. The comprised grout mixtures are also performed in accordance with real design concepts to ensure an adequate application in practice. For this purpose, a test set-up was developed, simulating the conditions within annular gaps up to 18 cm in width. The amount of filterable water, including temporal effects, has been determined. Additionally, the development of shear strength by the dewatering effect has been examined at dewatered grouts. The investigations were carried out on typical grout mixtures with different variations of parameters (e.g. fly ash: additive ratio). From the results, the main influencing parameters on the dewatering behavior and development of shear strength could be defined. Consequently, well-proved mixtures can be recommended for further purpose.

Joint opening width is a major indicator to assess the safety of concrete segmental linings. A new joint mechanical model is briefly introduced. Full-scale tests of the segmental lining joint of Shanghai Metro Line 13, subjected to both sagging moment and hogging moment, indicate that the joint model is capable of describing the joint behavior more accurately. Moreover, the joint opening width in different stress states can be obtained and the limit joint opening width can be quantified. The joint model is then used to investigate the influences of tunnel depth, segment thickness, pre-tightening force of bolt, and soil stiffness on the limit joint opening width. Parametric studies show that the limit joint opening width is dependent on the stress state of the joint. The limit joint opening width obtained in this study could be potentially used as a safety indicator for concrete segmental linings.

Polymer support fluids have been successfully used for the construction of bored piles (drilled shafts) and diaphragm walls for many years and yet, there is currently little guidance on the interpretation of their rheological properties from viscometer test results. In particular, there is confusion about the choice of an appropriate rheological model for this type of fluid. The use of oilfield units by some has also added to the confusion. To promote the use of SI units, this paper summarizes conversion factors that can be used to present viscometer data in a more uniform manner. Simple rheological concepts and instrument-specific equations are also given for those unfamiliar with the issues. Viscometer test results for two polymer fluids are then used to illustrate the application of the power-law model over the shear-rate range achievable with a typical direct-indicating viscometer.

Estimation of small-strain stiffness of soil by in-situ tests is more effective and reliable than other methods which were derived from resistance-based correlation or laboratory testing. In this paper, based on the theory of elasticity, an innovative technique in terms of small-strain stiffness was suggested to estimate the allowable bearing capacity of shallow foundation. In order to evaluate the proposed method, a series case history was studied, including the loading tests and seismic geophysical tests. These field measurements were compared with the predicted values. The result indicated that the proposed method in this study could be effectively used to predict the allowable bearing capacity of footing on granular soils and is much more accurate than the SPT- or CPT-based predictions.

Existing pile foundations supporting high-speed railways - especially those embedded in soft clays - are undoubtedly affected by the nearby embankment construction or excavation activity. The distance between the surcharge load point and an existing bridge pile foundation (d) is an important factor affecting the internal forces and displacements of the foundation system. Three-dimensional finite element models were created to investigate the behavior of a bridge pile foundation supporting a high-speed railway in China under the surcharge load. The analysis results compare well with the field data. The study results indicate that the internal forces and horizontal displacements of piles decrease with the increase of d. When d is less than 4 times of soft clay depth (h), the horizontal displacements of pile groups decrease linearly and rapidly with the increase of d/h ratio. When d is larger than 4h, the horizontal displacements of pile foundations decrease at a lesser degree with the increase of d/h ratio. Suitable d value can be determined based on the maximum allowable displacement of the superstructure under the normal operating condition.

This study provides a case history of a large-diameter shield tunnel (D = 15.43 m) in Shanghai soft clay through field measurement and finite element analysis (FEA). Two elevated bridges - Yixian elevated road and Metro Line 3 - were supported by multiple pile groups and multi-crossed by a large-diameter slurry shield machine. The two bridges were first crossed by the shield machine during the south-bound tunneling, and then crossed during the north-bound tunneling by the same shield machine. The minimum clearance between the shield skin and piles is 1 m. Field measurement on the movement of the pile groups during the tunneling process - including the vertical, longitudinal transverse, and lateral transverse displacement - was carried out for both bridges. The finite element (FE) software program, ABAQUS, is used to investigate the movement of the pile groups during the multi-crossing by the slurry shield. A full, three-dimensional FE model is generated without considering upper structures of the two bridges. Most of the relevant factors in tunneling are taken into consideration in the FE models, including:slurry pressure, grouting pressure, grouting material hardening and soil-pile interaction. A modified Cam clay (MCC) model is adopted in simulating the soft clay in Shanghai involved in this tunnel project. The FE results are compared with the field data to provide a better understanding of the disturbance of pile groups caused by the crossing tunneling process.

Steel pipe-jacking is widely used in water supply and other pipeline projects because of its low environmental impact and high construction efficiency. The tradeoff between economic benefits and engineering safety renders the wall thickness of such pipes becoming increasingly thinner. Meanwhile, the stratum and surrounding environment become more complex. The buckling of steel jacking pipes is considerably different from the conventional buckling problems due to the pipe-soil interactive behavior. For instance, the stratum provides constraining effect on the outward deflection; whereas, the non-uniform stratum may lead to the reduction in the critical elastic buckling load. Steel jacking pipes are subjected to these complicated loads so that the buckling phenomenon sometime occurs on the pipes. In this paper, the elastic buckling behavior of steel jacking pipes is analyzed by introducing the Winkler Foundation Model. The steel jacking pipes are modeled as cylindrical shells with two simply supported ends. Buckling eigen value analysis is conducted for such a model subjected to the axial force. The friction resistance is neglected due to the application of grouting. The surrounding soil is modeled as a series of closely spaced, mutually independent, and linear elastic spring elements. The influences of various parameters are discussed using the numerical analysis. Results obtained will inform the design of an economic and efficient steel jacking pipe.

Aiming at the foundation pit in soft soil areas which has underlying hard soil and confined aquifer, the 3D finite element calculation model of the plastic deformation failure of inrushing of the foundation pit was used to analyze the influence of inducing factors (confined water head, length and width size of the pit) on inrushing plastic deformation failure of the pit. The results show that the uplift deformation and inrushing plastic deformation failure of the soil beneath the pit are nonlinearly proportional to the confined water head and the width of the pit, the higher the water head or the wider the pit, the larger the uplift deformation of the soil beneath the pit, and the greater the possibility and extent of inrushing plastic deformation failure of the soil beneath the pit. However, the influence of the length of the pit on the uplift deformation and inrushing plastic deformation failure of the soil beneath the pit is small, and it is a non-sensitive factor. Finally, some suggestions helpful for design and construction of the pit with confined water are given in this paper.

With the unceasing development of metro construction, multi-line overlapped shield tunnels in soft soil are being built as a complex spatial distribution. When the existing tunnel is traversed by a new one, the construction will result in ground settlement and, meanwhile, will exert an adverse effect on the existing tunnel. For two kinds of typical construction methods of up-crossing and under-crossing, 3D-elastoplastic FEM was applied to analyze the dynamic construction process. A modified Gaussian Equation was proposed to predict ground settlement according to some parts of the results. The results show that, when the interval among all tunnels is in the influenced range, a secondary disturbance is to be caused by shield advance and greater influence will be exercised on the existing tunnel. During the construction of up-crossing, ground settlement turns to be larger, and the existing tunnel has a tendency of upward moving. But under-crossing leads to a smaller settlement with a tendency of subsidence. The research results can provide a theoretical basis and prophase guidance for similar projects in the future.

The composite segment has been used in the deep, long, large, and multi-cross-section shield tunnels of the subway, underground road, underground pedestrian passage and underground reservoir, etc. However, the mechanical behavior of the composite segment is not clarified because the structural type is complicated. Meanwhile, the selected structure model and parameters are not reasonable. Therefore, the designed composite segment lining of a shield tunnel has disadvantages in terms of safety and economy. The stiffness reduction method is proposed for considering confined effect, interface slip, local buckling and damage. The proposed design method can be used to solve the coupling of multi-material and composite segment under multi-scale, and is suitable for a rational design of the composite segment because of improving the convergence of computations and having high precision and clear physical significance.

A series of laboratory radial drainage odometer tests was conducted to investigate the deformation behaviour of clayey soils under the combined effect of vacuum pressure and surcharge loading. A parameter, K_w, defined as the ratio of effective horizontal stress on the inner wall of the consolidation ring to the vertical effective stress in the soil sample, is used to determine the tendency of the lateral displacement of the soil sample (i.e., inward or outward). A dimensionless parameter, α, is defined as a function of surcharge loading rate (SLR) and the rate of consolidation of a prefabricated vertical drain (PVD) improved deposits, has been introduced as a control parameter for K_w value which corresponds to the end of surcharge load application. Based on the test results, the α - K_w relationships have been proposed to determine the surcharge loading rate (SLR), with which the lateral displacement of the ground can be minimized.

In some of the Portuguese harbors, geology is characterized by alternating layers of limestone and marls, the so-called karstification. This paper presents two case studies regarding the geotechnical aspects of harbor structures founded in karst formations. The first case refers to the reinforced concrete piles of a quay wall founded in karst limestone. The second case discusses some problems related to the execution of an anchored retaining wall and the way it was used to guarantee that the bond length was not in a karst zone.

This study is conducted to make detailed comparisons and discussion of different dilution standards of pollutants in tunnels based on domestic specifications JTJ026.1-1999 and PIARC2012 (World Road Association). From three aspects (the method for calculating required air volume in tunnel ventilation, emission of vehicles, and admissible in-tunnel concentrations of toxic gases) this paper has made a comparative analysis between domestic specification JTJ026.1-1999 and PIARC2012. Taking the Donghu tunnel in WuHan for instance, the research calculates the required airflow volume in the Donghu tunnel based on the two different sets mentioned above. The calculation results show that there is a huge gap between the two sets for tunnel ventilation. The results of field measurement in Yan'an Donglu Tunnel also prove that the concentration of CO is relatively low, in fact. JTJ026.1-1999 is conservative in reduction coefficient of CO. Nitrogen oxides and non-exhaust particulate matter emissions are becoming dominant factors instead of CO in calculating required air volume for normal operation of tunnel. In order to keep pace with future traffic volume and vehicle emission standards in China, domestic specifications should be improved in terms of vehicle emissions and threshold value of toxic gases so as to make calculation for required air volume in tunnel more reasonable and economical.

A series of laboratory tests was carried out to investigate the shear strength between geomembrane/geotextile and geomembrane/soil interfaces. These tests were conducted with a new test method which enabled repeating shear strength between soil body and cover system components under various normal stresses. The reduction of peak and residual shear strengths of the interface were investigated by conducting the test repeatedly on a same geomembrane/geotextile interface under constant normal stress. The stacking process of the landfill was simulated by testing interface samples under increasing normal stresses. The analysis results obtained from the tests demonstrate significant variation of the interface strength.

In past decades, a rigid block dynamic response has been monitored with shake table tests by many scholars to investigate how the transition develops from static to kinetic friction. The dynamic characteristics of the interface can be obtained after analyzing the test data. However, in a real life situation, the dynamic response of the upper structure is unknown, which makes it difficult for us to get access to the dynamic characteristics of the interface. In this article, we focus on how to get dynamic shear properties of the interface under the condition of known seismic wave, which will have many implications on better evaluation of the dynamic stability of interfaces. In a slip-slip phenomenon, existing models may estimate friction coefficient acceptably, where as they are unsuitable for stick-slip phenomenon because of the yielded large error. To calculate the sliding velocity of a slider when only the property of seismic waves is available, this research puts forward an improved interface friction model for stick-slip phenomenon, and introduces a method to determine interface friction coefficient. The model was first validated in geotextile-wood and wood-wood interfaces. The numerical results were then compared to actual experimental data obtained from a rigid block sliding along an inclined plane subjected to base harmonic acceleration. This model was applied to a soil-geotextile interface, which manifests that the simulated results are closed to the test. The findings will encourage an extension of this new method to a more general seismic loading case.

This paper evaluates the significance of slope facing on the stability and deformation behaviour of soil-nailed slopes subjected to seepage. A short series of centrifuge tests was performed to study the behaviour of 5V:1H soil-nailed slopes with and without slope facing by maintaining the model slope height (240 mm) with horizontal back slope, nail inclination of 10° with horizontal and model nail spacing of 60 mm x 60 mm constant at 30 gravities. The effect of flexible, as well as stiff, facing on the performance of soil-nailed slopes was also studied. All models were instrumented with displacement and pore water pressure transducers, and markers were digitized to arrive at displacement vectors with rising ground water table during centrifuge tests. It was observed that the slope facing prevents the local failure of the soil between the nails. Soil-nailed slope without facing was found to experience face failure due to bearing failure at slope surface and nail head surface, as well as due to build-up of excess pore water pressure at the toe region after 8.5 days of the seepage. Soil-nailed slope with woven geotextile (flexible) facing experienced 0.18 m of crest settlement and bulging of facing was observed in between nail heads. However, a soil-nailed slope with an aluminium facing was found to sustain large settlements and showed improved deformation behaviour at the onset of seepage. Further, finite element analyses of the slope models - with and without slope facing - were found to be in good agreement with those of physically observed centrifuge test results.

The uneven settlement of a subway tunnel will aggravate the tunnel defects which may threaten the safety operation of the metro and increase the maintenance cost greatly. A series of in-situ testing and monitoring works in the future two years are being conducted in the tunnel between Zuibaichi Station and Songjiangnan Station of the Shanghai No. 9 subway line. Monitoring systems are divided into two parts, the system which is for monitoring the mechanics of the tunnel structure and the system which is for measuring the characteristics of the silty soft clay during the train operation. The monitoring system for tunnel structure has been fixed on the tunnel structure, including lining, ballast and track vibration acceleration sensors. The dynamics characteristics data of the silty soft clay will be detected by some vibration acceleration sensors, displacement meters, and pore-water pressure meters which have been drilled on both sides of the tunnel. Through these measurements, the deformation characteristics and change regulation of silty soft clay under train vibration will be studied and can offer valuable information for the subway tunnel maintenance department. In this paper, the design of the monitoring solution will be discussed in detail and some typical measured data will be analyzed.

The steel sheet pile walls have been widely used in the temporary and permanent foundation pit projects due to their advantages of reutilization, fast speed in construction, and saving excavation and materials. They are varied in sectional shapes such as channel, I-beam, U-shape and H-shape. The present site monitoring data shows that the earth pressures against the extruding portion and the denting portion of steel sheet pile walls are different. The nonuniform distribution of transversal earth pressure due to the corrugated shape of steel sheet pile walls cannot be ignored. This paper aims to study the effects of sectional shape of sheet pile walls on the wall deformation mode and distribution of earth pressures on both sides of retaining walls by using centrifuge model tests. Two cross-sections of sheet pile walls, planar and "concave" walls, are used. The whole process - from the deformation to failure after excavation - is captured. By comparing the earth pressure and wall deformation under two different sheet pile walls, the effects of sectional shape of sheet pile walls are studied.

Experimental study on model micropiles was undertaken in field conditions to ascertain pullout capacity of vertical micropile under oblique loads. Micropiles of 25-mm diameter and embedded lengths of 300 mm, 400 mm and 600 mm (L/D-12, -16 and -24) were auger-drilled and casted in silty sand (SM soil). Reinforcement in the form of 10-mm Tor steel bar was provided at the center of each borehole. Thoroughly mixed neat cement water grout of 0.45 w/c ratio was poured into boreholes under gravity through a pipe. Ample cured micropiles were tested under incremental pullout loads applied at 0-, 5-, 10-, 15-, 20-, 30-, 45- and 90-degree inclinations with respect to axis of micropiles i.e. vertical. For each load inclination, ultimate pullout capacity was determined from load-deformation curves and was also calculated theoretically. Test results indicate that ultimate pullout capacity increases with increase in L/D ratio and decreases as load inclination increases with micropile axis. Load inclination, at which mode of failure changes from axial to lateral (i.e. critical angle), was found between 5-10 degrees with axis of micropile. Lateral pullout capacity is obtained at 25-30% of the axial pullout capacity.

A series of centrifuge model tests was conducted to investigate the deformation and failure behavior of the foundation pit during construction period using the geotechnical centrifuge at Tsinghua University. The excavation and seepage processes were simulated in the centrifuge model tests for a reasonable consideration of the construction of the foundation pit. A few earth pressure cells were buried on the retaining wall to measure the earth pressure in the process of excavation and seepage. Several pore pressure transducers were installed in the soil to observe the pore pressure response. An image-based displacement measurement system (Zhang et al. 2005; Zhang et al. 2007; Zhang et al. 2009) was used to capture the images and measure the displacement field of the soil accordingly.

Piles are subjected to various loads (vertical, lateral and uplift) simultaneously rather than independently. This indicates that the combined loading analysis is essential to understanding the actual pile behavior rather than independent loading -namely, vertical-compressive, vertical-uplift and lateral loading. However, it is observed that the understanding of pile behaviour in combined loading is simulated with a combination of vertical-compressive and lateral; but, the vertical-uplift with lateral loading has not been simulated. Hence, an experimental program is carefully planned to understand the interaction of the soil-pile system to combined uplift and lateral loading in loose to medium-densesand (RD = 40%). Aluminium model piles with different length-to-diameter ratios are used in the testing. Tests were conducted to measure pile behaviour under independent uplift and lateral loadings to assess their ultimate capacities, respectively. Then, lateral load tests were conducted by keeping the constant uplift load on pile head, to study the effect of uplift load on lateral behaviour of piles embedded in sand. Tests were conducted for different magnitudes of constant uplift load, i.e. 40%, 60% and 80% of ultimate load. It is observed from the results that there is significant variation in lateral load-pile head deflection behaviour as well as the ultimate lateral capacity under combined loading compared to independent and independent loading, which need to be considered appropriately in the practical design.

The artificial ground freezing method is widely used in the construction of cross-passage of shield tunnel. The excessive frost heave force may induce damage of the segments around the cross-passage. However, due to lack of in-situ monitoring data, no suitable frost heave force is specified in the tunnel design codes. In this paper, a careful in-situ monitoring was carried out with new PAD type earth pressure gauge in Shanghai Yangtze River Tunnel. First, the main characteristics of PAD type earth pressure gauge and the installation method were introduced. Then, the automatic data logging system and the layout of measure points were described. The careful installation ensures good working of all 5 gauges and that reliable data were obtained. The data showed that the maximum measured frost heave force of Shanghai Yangtze River Tunnel was much smaller than expected. It should be related to the countermeasure of pressure release hole, which reduced the heave pressure dramatically.

A series of centrifuge tests of composite structure with scattered piles and soil nailing (PSN) were carried out by Tongji University. Based on the results of 13 group tests, the failure modes of PSN structure and the effecting law of parameters, including pile spacing and soil nailing, were explored. The results showed that the failure modes of PSN structure could be mainly expressed as three forms. When the soil nails were longer than 2H/3 (H was excavation depth of pit) or the pile space was larger than 8D (D was pile diameter), the pit supporting structure with PSN was dominated by soil nailing and the failure of PSN structure was similar to pit supporting structure with soil nailing. On the other hand, when the soil nails were shorter than H/3 or the pile space was smaller than 4D, the PSN structure was dominated by scattered row piles and the failure of PSN structure was similar to pit supporting structure with scattered row piles. The failure modes of other kinds of PSN structures were multiple failure modes controlled by both soil nailing and scattered row piles, which were presented as the failure of soil nail wall following by soil instability between piles.

The lateral bearing characteristic of pile is complex for the soil-pile interaction. The field static loading test is scarce. Based on the project of the DongtiaoxiBridge in Huzhou City, a field test was carried out in order to study lateral bearing capacity of pile. The soft soil (including back-filled soil), silt clay and muddy clay are distributed in the site area, and the depth of the clay is more than 40m. For testing the axial force of pile and the distribution of bending moment under lateral load, reinforcement meter was welded to the steel cage at different levels before the bored pile was constructed. The inclinometer casing was used to obtain the lateral displacement distribution of pile along the depth. The result shows that the lateral bearing capacity of pile is more than 1100 kN, and the displacement at loaded point is only 2.66 mm. The maximum bending moment of pile is about 4 m below the soil surface. The bending moment transfers to the deeper location with the increase of the horizontal load, and the bend deformation only occurs in the upper 1/6 of pile length. The ground coefficient decreases and the decrease extent is smaller as the lateral deformation increases.

As a new reinforcement method, using a new composite structure to reinforce the segment has such advantages as lightweight, fast, high strength, safety and durability. The new composite structure is a kind of prefabricated component and can be produced largely in the factory. This paper focuses on the mechanical behavior and failure form of the RC segment reinforced with the new structure. The ultimate bearing capacity and the deformation properties of the reinforced segment are better than the universal segment. The new composite structure breaks away from the segment without breaking before the failure of the segment. The concrete crushes after yielding and the bolt yield sand breaks due to the stress redistributing. The results indicate that the new composite structure can improve the bearing capacity and the deformation properties of the segment significantly. The separation between the segment and the new composite structure is caused by the failure of the binder. Improving the bond properties between the new composite structure and segment may be a feasible method to increase the ultimate bearing capacity of the reinforced segment.

One important method for studying natural ventilation is a model experiment. However, the mutual relationships between traffic flow and inner airflow in tunnel are quite complex (Zhong, et. al., 2008). Based on the Donghu Tunnel in Wuhan, which is under construction, the paper analyzes the analogical conditions for model and prototype and deduces the similitude criterion numbers. Indications are that the experiment similitude of fluid and solid flow should be ensured at the same time. The way to convert model data to the actual tunnel is explained. The ventilation effect in the natural tunnel is evaluated as having certain theoretic and engineering instructional meaning on natural ventilation in urban tunnel with top openings.

Liquefaction and associated ground failures have been commonly observed in past major earthquakes across the world. A lesson learned from two major earthquakes in Alaska was that the freezing of ground crust has great influence on bridge pile foundation behaviors during lateral spreading. Based on a typical bridge from the ADOT&PF bridge inventory, supported on commonly used pile foundations that penetrate a liquefiable sand layer, two finite element (FE) models of the same soil-foundation system were created - one, named "frozen case" (with a frozen ground crust), representing the typical winter conditions in Alaska, and the other named "unfrozen case" (with an unfrozen ground crust) representing the summer conditions in Alaska. Both models have liquefiable soils underlying the ground crust, and the ground crust has a small slope angle that is common in a bridge site. Soil reactions and pile response are analyzed by fluid-solid coupled FE modeling. Results are presented for both the frozen and unfrozen conditions to illustrate the key characteristics of pile performance in liquefiable soils underlying a frozen crust.

Much research has been done on pile response to deep excavation construction in soft soil. However, the behavior of the pile and pile groups due to deep excavation in multilayered conditions of soils overlying rock(defined as soil-rock formations in this paper) is still unclear. This study performed a series of 2D numerical studies of pile response due to deep excavation. Firstly, the numerical model was verified through a case history in China and the comparison of computed results to monitoring data showed good agreements. Secondly, the effects on the pile response of several parameters were studied, including stratigraphic distribution, distance to the retaining wall, pile length, excavation depth, and stiffness of retaining wall and pile. The results presented in this study can be used as a first approximation for cases in which the deep excavation is located very near the pile and pile groups.

Analyses of diaphragm wall deflections and undrained side resistance for drilled shafts rely on the use of empirical methods due to an inadequate understanding of the physical phenomena involved in these highly nonlinear, multivariate problems. Various advanced computational learning tools, such as artificial neural networks (ANN), have been increasingly used. However, neural networks have been criticized for the long training process. This paper explores the use of a fairly simple, nonparametric regression algorithm known as multivariate adaptive regression splines (MARS) to mathematically model multivariate, nonlinear problems through two numerical case studies. The main advantages of MARS are highlighted. First, the MARS methodology is described. MARS models of diaphragm wall deflections and undrained side resistance for drilled shafts are then presented.

In this study, combined with an engineering case, nonlinear finite element (FE) analysis is adopted to explore the mechanism of a deep soft soil foundation pit supported by bamboo soil nails and bamboo piles in rows. Firstly, a plain strain model is built to analyze the stability of the pit excavated with a slope with 45° inclination angle and without a retaining system. It reveals that its factor of safety is so small that effective retaining measures should be taken. In order to reasonably analyze the working mechanism of this particular retaining structure, a high-fidelity simulation is carried out in the Super Computing Center of Fujian Province using three-dimensional (3-D) FE methods. That is to say, bamboo soil nails are modeled with solid elements instead of structural elements. In addition, the dense bamboo piles in rows are modeled with the equivalent diaphragm wall. Coulomb's frictions between the soils and bamboos, as well as soils and diaphragm wall, are considered. Mohr-Coulomb's constitutive model and strength reduction finite element technique are employed in the numerical analysis. In order to decrease the computational costs, displacement constraint and its release method are adopted to simulate the process before and after excavation. The study shows that an appropriate stability and structure analysis method for foundation pits supported by this kind of structure is presented. The research outcomes will facilitate this sort of environment-friendly, energy-saving and cost-saving retaining structure to be widely used in excavation engineering.

Researchers have put forward a new pre-supporting technique, the freeze-sealing pipe roof method (FSPR), combining the pipe-roofing method and artificial ground freezing method (AGF). The Gongbei Tunnel, a major part in the Zhuhai Link of the Hong Kong-Zhuhai-Macao Bridge, is going to employ the FSPR method for the first time in China. We created an innovative freezing scheme with three kinds of freezing tubes (normal, enhancing and limiting) for the FSPR method. In this paper, the temperature field of the scheme in the active freeze period is analyzed by numerical simulation in order to ensure the validity and feasibility. The characteristics of frozen soil wall have been studied for different strata and controllable parameters. The results show that FSPR can form a frozen soil wall quickly and keep it stable in the different soil layers. In addition, it is indicated that the freezing effect is flexible and controllable.

The excavation face stability of shield tunnel under seepage condition was studied by 3D numerical simulation. By using elasto-plastic deformation/seepage finite element analysis, the deformation process when support pressure reduces from earth pressure at rest to limit state under seepage condition was obtained, and the failure mechanism of tunnel face and the limit support pressure were determined. The influence of the cohesion and friction angle of soil on the failure mechanism of tunnel face and limit support pressure under specific water table line were investigated. The results showed that the soil strength parameters affect the value of limit support pressure; however, only the friction angle of soil would change the failure mechanism obviously, but the soil cohesion would not. Furthermore, the influence of the water level change which is caused by tide on the face stability was studied. The results showed that the change of water table leads to the redistribution of pore water pressure around the tunnel face and results in the fluctuation of the limit support pressure.

The numerical simulation method has become one of the most important assistant approaches for engineering design. But for the model scope of the overlying strata of deep-buried tunnel, there's no consensus which could be accepted by the whole geotechnical engineering industry; and, in most cases, the boundary of the model is determined by experience. In this paper, the influence of overlying strata' simulation on stress and deformation field of surrounding rock mass is studied through the 2D and 3D finite element method. The diameter, depth and section shape are all taken into account. Finally, a reasonable simulating scope of the overlying strata is proposed which may provide some reference for deep-buried tunnel's numerical simulation.

The accurate shape and position of cavities in an underground mine are important factors that could affect the reliability of numerical modeling analysis used to assess the stability of such structures. The traditional numerical stability analysis of underground mine openings either considers the cavity shape as a regular geometric object, which is determined during the design phase, or uses a simple model created for analysis purposes, both of which affect the accuracy of numerical simulation results. In this paper, a cavity monitoring system (CMS) survey is carried out to obtain the actual three-dimensional shape and the true position of mining excavations. The 3D digital terrain model (DTM) of the suite of mining cavities is then created in the mine design software Surpac. A new and integrated approach to determine the stability of the underground cavity based on the DTM and FLAC models is presented. A case study conducted in an underground copper mine confirms the efficiency and reliability of the proposed method.

In soft, partially or fully saturated ground conditions, machine-driven tunnel construction causes short- and long-term ground deformations resulting from the disturbance of the virgin stress state of the soil and changes in the pore water conditions. These variations are, in turn, influenced by the heading face support, shield skin friction and by the gap grouting. Realistic large-scale 3D simulations are, therefore, increasingly required to investigate the interaction between machine-driven tunnel construction and the surrounding soil in order to provide reliable estimates of the expected settlements and associated risks of damage for existing structures, respectively, in particular in urban tunneling projects. If performed properly, these simulations involve complex interactions between individual components of the numerical model. The presented paper is concerned with recent advances in the process-oriented adaptive computational simulation of the excavation and steering processes in mechanized tunneling in soft soils using the finite element method. A novel automated adaptive mesh-refinement procedure is proposed to allow a refined resolution of the region of interest in the vicinity of the tunnel face during the TBM advancement. This procedure allows for an accurate assessment of the tunnel face stability and for the investigation of the immediate soil deformation and pore pressure changes around the tunnel. Furthermore, selected aspects of the numerical treatment - such as the stabilization of low order, two-phase, finite elements and the sub-stepping schemes inherent in the numerical integration of elasto-plastic models -,are also addressed in the presentation.

The excavation process ofearth-pressure balance (EPB) shield machines involves the cutting of the ground at the tunnel face and the transport of the soil paste in the excavation chamber. For the numerical simulation of these two processes, a computational strategy, characterized by the coupling of two partial models using the discrete element method (DEM) and the finite element method (FEM) has been developed (Wessels et al., 2013). Excavation is simulated using DEM, with the fracture process being represented by the release of interaction forces between the particles. The transport of the excavated soil mixed with the soil conditioning foam, yielding a pasty soil-foam mixture within the pressure chamber, is simulated by means of a two-phase fluid model in Eulerian description. The two momentum and mixture mass equations are discretized in time by the characteristic-based split method (CBS) (Zienkiewicz et al., 2005). The phase volume fraction equations are solved using upwind weighting functions according to the improved Mizukami-Hughes method (Knobloch, 2006). The proposed model is applied to a coupled analysis of the excavation and transport-mixing flow inside a simplified pressure chamber with foam injections. The mixing process, due to the rotation in the chamber, is preliminarily investigated by the mixing flow in a 2D cavity test case.

Based on results of pile load tests, this paper demonstrated the procedure of employing the finite element method (FEM) to predict the behavior of bored piles - especially the defective piles - in some special situations. The main aspects of the FEM simulation of the defective behaviors were explored. The pile defects caused by geotechnical- and construction-related problems were discussed and a procedure for tracing the causes of these defects was proposed. This paper suggests detecting the defects at pile shaft and/or piling base by controlling interface parameters. To verify the feasibility of the proposed procedure, two case studies on defective piles were thoroughly investigated. The first case is about a bored pile in granular soil and the second one is for a rock socket. Good agreement between predicted and measured responses was observed.

With the development of construction in cities and the exploitation of underground space, increasing excavation projects are conducted right above subway stations. Such excavation leads to ground settlement, deep-level strata heave near the excavation area, and the consequent uplift of the subway tunnels. To decrease the influence of foundation pit excavation on the metro tunnel in the foundation pit project, a numerical model was established based on the foundation pit engineering of the traffic hinge of the Tianjin West Railway Station project. The concordance between the simulation analysis values and monitoring practice results validated the feasibility of the numerical analytical method. This research will provide a guideline for application in the metro development of Tianjin. The method and research ideas are reasonable, scientific, and could provide beneficial references to similar projects.

The behavior of a single pile subject to excavation-induced soil movement is investigated using the explicit finite difference code, FLAC^3D. The Modified-Cam Clay Constitutive Model was employed to model the non-linear stress-strain soil behavior, and the pile was assumed to have linear elastic behavior. The interface model incorporated in FLAC^3D code was used to simulate the soil/pile contact. The built-in ‘fish' language was used to calculate the data demanded. The results given by the numerical analysis indicate that the pile deflection, bending moment and lateral soil pressure increase with increasing excavation depth and decrease with the increasing distance from the excavation face. The retaining wall stiffness, the pile stiffness, the pile head condition and the length of pile exert important effect on the pile response. Compared with the above, the effect of the axial load on the pile response is less. The research finding was compared with other published case history and reasonably good agreement was found between them.

The underground metro station of the International Passenger Transportation Center and the Baiyulan Square, sharing a same diaphragm wall as retaining structure, are two deep excavations with the maximum excavation depths of 13.8 m and 21.1 m, respectively. Due to the overall construction arrangement, the shallow excavation (i.e., the metro station) must be finished before the construction of the square, so the potential adverse impact caused by the following excavation is remarkable. In this paper, 2D FEM simulation with the Cam-Clay Constitutive Model is carried out to investigate the interactive behavior of the two adjacent excavations. Lateral wall deformation and ground settlement are analyzed to reveal the characteristics of interactive impact on the retaining structures and surrounding environment. Then, the influences of wall depth and thickness on structure displacements are investigated. Field-measured data are presented which show the similar deformation performance obtained by the numerical method.

In a power plant, two shield tunnels were constructed for circulating cooling water under the Yangtze River. During the construction of one line, a collapse occurred because of the abundance of methane in the ground. Artificial ground freezing (AGF) was adopted to recover the collapsed tunnel. A working platform was built above the river to facilitate ground freezing. The frozen soil wall (temporary ice bulkhead) formed in freezing was watertight and strong, providing temporary support before the concrete permanent bulkhead was constructed. This paper describes the design of chosen recovery option and the use of ground freezing which provides a safe environment for the permanent bulkhead construction and later works.

Retaining walls are constructed to withstand earth pressure and lateral thrust due to backfilling, surcharge pressures from foundations of adjacent structures, and traffic-induced loading. Reduction in earth pressure and lateral thrust on these walls, by providing compressible geo-inclusion, helps to economize the project cost. In the present study, small-scale experiments were carried out for cases of retaining wall without geofoam, with 10D (10 kg/m³ density) geofoam and 15D geofoam. Results of earth pressure distribution, backfill surface settlement and EPS geofoam compression under effect of three different surcharge pressures (viz. 10 kPa, 30 kPa and 50 kPa) are obtained. Reductions of 25.3% and 21.8% in lateral thrust were observed with 10D and 15D geofoam inclusions, respectively. Maximum geofoam compression in the range of 0.68 mm and 0.38 mm were observed for 10D and 15D geofoam, respectively. The surface settlement in the range of 1.8 mm, 2 mm and 2.6 mm were observed for cases of nofoam, 15D and 10D geofoam inclusions, respectively. The results of numerical analysis using finite element analysis code (PLAXIS) for a full-scale retaining wall revealed that, though geofoam of lower density helped to reduce more lateral thrust, considering serviceability and geofoam compression, minimum geofoam density of 15D is preferable.

Parameters from piezocone test (CPTU) are commonly used for soil profiling and geostratigraphy, along with the parameters used for assessment of geotechnical design. CPTU provides near-continuous measurements of tip resistance, sleeve friction and pore pressure at the shoulder, or face, or shaft of the cone. The dissipation results in CPTU soundings are used to evaluate the coefficient of consolidation and permeability of soil at intermittent depth. Recently, however, several approaches based on CPTU data to assessing the hydraulic conductivity of soils continuously are developed to avoid the time-consuming dissipation of excess pore pressure. This paper presents an experiment, centered on the use of piezocone tests, to determine the flow characteristics of cohesive soils on the engineering background of design of a transformer substation in Lianyungang, China. Three methods (two continuous and one discontinuous) are applied to obtain the coefficient of permeability of soils, and the results are compared with those from laboratory tests. This study confirmed the potential for use of piezocone tests to obtain valid predictions for flow characteristics of soils.

The GPR method is always used to locate embedded pipes. However, it is hard to determine their diameters, especially when the underground pipe is full of a lossy medium (as water, oil or gas) in the operation period. This paper first puts forward a new method for probing and interpreting the diameter of underground pipeline filled with the lossy medium. By means of the GPR, the shape of a certain circle can be determined by the coordinates of three points on this circle. Moreover, the operation procedure of this method is listed in detail. Lastly, this method is applied to detect the diameters of the underground pipelines in the model experiment of the actual project. The measurement value is approximately consistent with the real value. This demonstrates that the proposed method achieves good results.

The waveform inversion method was used to reveal the physical and mechanical properties of underground medium, which comprehensively utilized the amplitude, travel time and phase of wave field. A typical stratified medium model in geotechnical engineering investigation was established for grasping the intermediate medium properties. In forward calculation, response waveforms were achieved by the finite-difference time domain (FDTD) method; and, in inversion analysis, the least squares method was adopted. From the response waveforms, it is found that the higher the P-wave velocity of the intermediate layer is, the smaller the amplitude of response waveform is; while the thicker the intermediate layer is, the more waveform phase is deferred. The feasibility and accuracy ofthe waveform inversion method was verified. Furthermore, this method was used in the detection of grouting quality of immersed tube tunnel. Based on the waveform data collected on site, the P-wave velocity and thickness of the grouting layer were revealed by inverse calculation and the grouting quality was effectively evaluated.

The methodology of non-invasive geophysical investigation has been widely used in different fields such as geology, ground water, and petroleum exploration. In geotechnical engineering, geophysical techniques offer unique means of site characterization. However, how to produce preferred high-resolution data for imaging and monitoring in different scenarios remains a challenge. In this paper, new approaches are advanced aimed for high-resolution geo-imaging and monitoring based on the concept of electromagnetic theory and the method of Green's function. The Green's function can be used to solve inhomogeneous differential equations subject to specific boundary conditions. This approach can be combined with the traditional electrical resistivity tomography (ERT) to map sub-surface properties and monitoring evolution of spatial variability. The scenarios where this method can be applied include static situations and dynamic situations such as during earthquakes and landslides.

The Wulukou subway station No. 6, located in the city of Chongqing, has a crossing section of 326 m² and a span of 24.54 m. The maximum of buried depth is about 14 m and the minimum is about 4 m. An improved method of tunnel construction - the "interlaid rock wall" method - was put forward for the typical tunnels with shallow buried depth and large crossing section. The numerical simulation and field monitoring were introduced together to verify the feasibility of the improved method by comparing the double side drift method. Some results have been obtained as follows. The safety during tunnel construction can be ensured with the "interlaid rock wall" method. The improved construction method was more effective than the conventional one as double-sided drift method. Therefore, the "interlaid rock wall" method is very suitable for the kind of tunnel with shallow buried depth and large crossing section.

Numerical analyses are performed on a routine basis in practical geotechnical engineering to assess the deformation behaviour of tunnels - in particular, for near-surface tunnels - in soils where the influence on existing infrastructure (such as buildings, deep foundations and adjacent tunnels) has to be evaluated. In addition, it becomes increasingly common to use results from numerical analysis as basis for designing the support measures for the tunnel. When doing so, the strongly nonlinear material behaviour of shotcrete - namely, the increase of stiffness and strength with time - should be taken into account, in particular when the excavated cross-section is subdivided into several construction stages involving temporary shotcrete structures with high stress concentrations near corners. In this paper, a new constitutive model for shotcrete is applied in the numerical analysis of a complex underground railway station. It could be shown that significant differences in lining stresses are obtained when employing the newly developed constitutive model for shotcrete. However, the overall deformation behaviour is not significantly influenced by the shotcrete model.

In Beijing, dewatering has been strictly prohibited in foundation-pit excavation since March 1, 2008. Therefore, the deep foundation pit has to be constructed underground water level, which makes the construction of the water-resistant curtain and anchor quite difficult in granular soil. This paper introduces the construction of a foundation pit of underground garage with the excavation depth of 20.6 m. By improving construction techniques, a water-resistant curtain was constructed with good performance under a water head of up to 6 m in a granular soil layer with high permeability. The anchoring force is guaranteed in the case that cement slurry is lost after the water-resistant curtain is perforated underground water level. The project is a successful example of foundation pit engineering construction in the Beijing area.

To optimize the design of blasting excavation and construction of the subway station in Chongqing, FEM dynamics research was carried out based on ANSYS/LS-DYNA. It analyzed the vibration velocity of the etaining pile, air shaft and tunnel structure caused by blasting during the excavation process, and proposed a reasonable scheme to reduce blasting vibration. Both numerical simulation values and the field monitoring data illustrate the same attenuation law. That is, the blasting impact on the structure can be effectively reduced by optimized design. Setting a damping isolation belt is a relatively effective method for damping blasting impact. The achievements of numerical analysis and construction scheme could be references for the similar deep pit excavation design in urban area.

A case of shield tunnel crossing under an operating metro is studied in this paper. The existing tunnel was in operation and the new shield tunnel was close to the existing one. The existing tunnel was closed to launching shaft, so the passing was in launching phase. The earth pressure balance had not yet been reached in the launching phase, and the boring face was unstable. Studies revealed that ground loss and water loss - which can cause the structure a great displacement or even failure - were the biggest threats to the existing tunnel. Therefore, a special outer sleeve which was used for TBM launching was fixed in the tunnel portal. The TBM can be sealed in launching phase by using the sleeve. At the same time, such countermeasures as ground improvement, adjustment of boring parameters and information feedback construction were employed. The monitored data showed that the countermeasures can effectively reduce the loss of ground and water and ensure safety of the existing tunnel.

Particle image velocimetry (PIV) technology is a kind of non-intrusive, instantaneous, dynamic technique to measure the planar distribution of velocity in the fluid based on the cross-correlation. By applying PIV technology to the pullout test of horizontal reinforcement with ribs-sand interface, sand particle movements can be measured in the process of testing from the mesoscopic view. Meso-characteristics of displacement vector near the interface will be discussed. Furthermore, a quantitative analysis is made of the changes of horizontal and vertical displacement with pullout displacement. Thereby, interface interaction mechanism of 3D reinforcement-sand is further revealed from a microscopic viewpoint. The result showed that the vertical inclusions of the reinforcement played important roles in interface characteristics. The movement of sand particles formed a flow field. The failure surface was wavy-shaped between the two ribs. Horizontal displacement was larger than vertical displacement of sand particles near the interface. The impact area of 3D reinforcement was larger than that of traditional horizontal reinforcement. The pullout resistance acting on the front rib was larger than that on the second rib.

The loading on the tools of a TBM can usually only be estimated through the global thrust force, which gives a typical force of about 250 kN for 17''-discs. The actual loading, however, is highly variable with peak loads that can be many times the nominal load. In the present paper, the development and implementation of a method which makes it possible to measure disc forces in-situ and in real time is presented. It turns out that the measured forces are unevenly distributed over the area of the face and can be correlated with geological/geotechnical features in the face. Furthermore, a method is presented which makes it possible to document the face photographically. Single images or videos are combined into an overall image by means of digital image processing. The quality of the pictures obtained in this way provides a significant improvement in the geological documentation of TBM drives.

Much attention has been paid in the past to study the potential impact of piled foundations onto existing tunnels in the vicinity. However, relatively less study has been done to investigate the performance/behaviour of existing foundation piles due to tunnelling works. This paper presents a case study of an instrumented low-rise building founded on piles at Circle Line Stage 3 (CCL3) in Singapore. The CCL 3 comprised the construction of five underground train stations connected by 5.7-km long-running twin tunnels. The building's protective strategy and monitoring results of vertical and lateral ground movement, vertical building movement and pile down drag force due to tunnelling works are presented in this paper. A comparison of the predicted values using the three-dimensional finite element method (FEM) program with the measured monitoring results is also discussed. A sensitive analysis with different soil/rock constituted models in the numerical modeling was also carried out. The monitoring results indicated that a significant down drag force was measured in the piles although the ground movement due to tunnelling was relatively small. The analysis results show that the numerical modelling based on a linear elastic soil/rock constituted model may over-estimate the movements and the forces on the pile under the effect of tunnelling works.

The need for multi-storey buildings and underground structures such as subway and metro systems in large cities often requires deep excavations. This paper reports on a study of a multi-anchored deep excavation of a business center construction in Istanbul. Five different critical cross-sections were determined and analyzed. The maximum excavation depth was 21.6 m. The support system of the wall consists of anchors and soil nailing. The lateral wall movements were monitored with inclinometers placed inside the wall, and the measurements were compared with the results of finite element (FE) analysis conducted using PLAXIS to evaluate the in situ wall behavior. The measured results were compatible with FE results. The mean values of the maximum lateral displacements of walls vary from 0.11% H to 0.317% H, where H is the excavation depth. Regression analysis was performed using this study's results and some database collection reported by the researchers. It can be said that this study's results are consistent with those reported by the researchers.

In this paper, the construction and performance of a deep metro station excavation is presented. Top-down construction method has to be used in this deep excavation as it is located under the high speed railway, and the potential deformations of both structures and railway subgrade are extremely large. In order to reduce the deformations and ensure safety during the construction, several design and construction measures were taken including the thickening diaphragm walls, two additional temporary concrete struts, large area of soil improvement, and dense drilled piles. Additionally, a novel excavation method is used to improve construction efficiency. Field performance data were collected (i.e., lateral wall deflections, vertical displacements of diaphragm wall, middle slabs and railway subgrade, and support system loads). Results are comprehensively analyzed and show that the deformations of structures and railway subgrade are controlled within limited range.

Results of ground anchors load measurement are presented. A 7.5-m-deep excavation was carried out for a 2-level basement building in Poland. A sheet pile wall with one level of ground anchors was designed to ensure the excavation stability. A number of anchors were equipped with vibrating wire load cells. The loads were measured at two locations with 3 anchors instrumented at each location. At one of the locations, intensive site traffic was observed. At the other location, the area behind the wall was operated by building equipment. The differences in soil conditions at both points were moderate. The anchor loads were relatively constant during the anchor life and only slight dependence on the excavation depth and site operations behind the wall was observed. The anchor forces at the site were primarily the effect of the lock-off load. Soil conditions, excavation depth, and traffic impact are secondary and they induce anchor load variation by ca 20%.

Estimating soil pressure acting on the tunnel lining accurately is critical to study the mechanical behavior of shield tunnels. The evaluation of internal forces can also contribute to the understanding of the mechanical behavior of segmental lining. This paper presents observed ground pressures and internal forces of the Shanghai Yangtze River Tunnel, which is a large cross-section tunnel with an outer diameter of 15.0 m. The observed ground pressures of the tunnel show obvious sinusoidal fluctuations with the water level of the Yangtze River. The observed ground pressures are closer to the values given by Terzaghi's formula. This means that soil arch still exists although the buried depths are only about 1.5D (D represents the diameter of the tunnel). The observed bending moments are generally greater than theoretical ones, and measured hoop forces are approximately twice as much as theoretical results. This indicates that internal forces calculated by conventional models could only reveal the stress related to the ground load. Observed internal forces could be greater than calculated internal forces because assembling stress is not included.

Based on the stress tests of soldier Piles, ring Beam and Anchor tiebacks (PBA), and the hole displacement observation on Wangjing Soho construction site, the development process of the internal force caused by spatial member interaction has been revealed. It reflects the differences from mechanic principals of the traditional design method, such as elastic foundation beam or equivalence beam of limit equilibrium state. Practical tests showed that soldier piles were under the combination state of compression and bending, and were proved safe because of low stress; while the top ring beam was under the combination state of tension and bending, and the tensile stress might come to the elastic stress limit, which has much relationship to the anchor arrangement. So, the design of the top ring beam should be regarded as one of the key controls of the construction. The actual tested tieback tensile force reached 150~220KN, only half of the design value.