Underground Construction and Ground Movement

Researches on rock dynamics for underground development, mainly focusing on an underground project of ammunition storage in Singapore, have been carried out. The researches include the study of dynamic properties of rock material (strength, modulus, constitutive relations and failure criteria), dynamic normal and shear properties of rock joints, shock wave propagation across joints and through the rock masses, and dynamic response of the rock mass and structures in rock using the discrete element method. The results obtained from the research works provide the necessary input to the design and construction of the cavern project.

The rapid development of underground constructions in China has raised many new issues for the research works on rock mechanics and engineering. Some of them are very significant for the recent engineering practices. This paper mainly presents the research works carried out on two issues, i.e., (1) stability analysis of the surrounding rock of large span underground structures built in complex geological condition, (2) deformation behavior and support mechanism of deep-buried long and large rock tunnel. The stability analysis is applied to the huge caverns at the Longtan Hydroelectric Power Station. Numerical simulations on the behavior of the layered rock mass with steep dip angle are presented. A back analysis method to obtain the initial rock stress and material parameters and to predict the deformation of the surrounding rock mass is established, in which the geological statistics method is employed to estimate the variation range of the Young's modulus and the u-t curves measured in situ are used to determine the time-dependant parameters of the surrounding rock mass. The back analysis can be conducted efficiently and the fitness function converges quickly. The main aspects related to the second topic are discussed. Laboratory tests to reveal the effect of rock bolts are also presented. Furthermore, the importance of the research works is emphasized at the end of the paper.

Crosshole tomography field data was collected on bridge foundation sites in Pennsylvania, in close proximity to geotechnical boring locations. Profiles determined from these field measurements were plotted against drilling data, and these comparisons revealed ability of crosshole wave velocities to differentiate overburden soil from rock. In addition, foundation construction data was collected and compared with crosshole test results determined prior to construction. In particular, pile tip elevations at driving refusal were compared with crosshole test results. From these data it appears that seismic wave tomograms can characterize the soil/rock interface, and that it is possible to predict expected design pile lengths based upon a measured seismic wave velocity tomogram. It can be concluded from these site comparisons that geophysical techniques such as seismic crosshole tomography can provide important additional information to site characterization for bridge foundations in karst terrane.

Cavity effects on the bearing capacity of footing foundation were investigated analytically using two dimensional elasto-plastic Finite Element Method (FEM). Several factors, such as cavity location, shapes of footing and cavity, cavity size and soil type, affect the bearing capacity of footing foundation. In present study, the effect of a single cavity on bearing capacity of footing foundations was analyzed for various conditions. The failure mechanism of ground was also examined in the study. In the FEM analyses, the geomaterial was assumed as an elastic- perfectly plastic material. The analytical results indicate that there exists a critical region for a cavity under the footing foundation, and the bearing capacity is significantly affected by the cavity only when the cavity is within the critical region. In addition, based on the above results of FEM analyses, a simple and practical calculation method is proposed for the cavity effect on the bearing capacity of footing foundation.

Land subsidence due to the groundwater withdrawal is attributed to a significant amount of large destructions and distresses on the industrial and residential facilities as well as the urban infrastructures. In order to protect these facilities, it is necessary to predict the future development of land subsidence based on present state. Many researchers proposed different approaches to predict the land subsidence due to the groundwater withdrawal according to the different geological conditions and the groundwater withdrawal practices. This paper classifies these methods into five categories according to the theories and the assumptive models: (1) statistics methods, (2) 1D numerical method, (3) quisi-3D seepage model, (4) 3D seepage model, (5) fully coupled model. In China, the former four categories are presently employed in prediction practice and their advantages and disadvantages are discussed. In the future prediction activities, more sophisticated model with fully-coupled analysis in 3D condition is recommended.

In China, carbonate rocks cover an area of 3.443 million km squared, which consist of 36% of the nation's territory. It is not unusual to encounter karst related problems in tunnel construction. It is a difficult problem to build tunnels in complex karstified area. Strong and complex karstification makes it dangerous because water inrush is common during tunneling. About 50% of the built tunnels had the water inrush problems. The newly built Yuanliangshan Tunnel on Yu-Huai railway line crosses the karstified area, many times of water inrush occurred and caused big damage. Now, a railway line from Wanzhou to Yichang crosses the strong karstified area, there are 127 tunnels and most are karst tunnels, of which 10 are large karst tunnels and several tunnels such as Bieyancao and Qiyueshan tunnels had experienced water inrush. Thus, water inrush has become a big obstacle in tunnel construction in karst area. In this paper, the performance of karst cavities with high pressurized water are studied due to their possible dangerous and frequent burst or collapse. A model is developed to predict the critical thickness of the water-bearing rock between the karst rock cavity and the tunnel. Based on this model, the cause of the water inrush from Yuanliangshan Tunnel in Tongmangling section is analyzed. Proposed model can also predict the water inrush phenomenon. As another example, the proposed model is applied to forecast the water inrush of Qiyueshan Tunnel in order to ensure the safety in tunnel construction.

Dewatering of groundwater can cause significant ground displacement and deformation. Severely, the ground movement may affect the safety of the adjoining structures. In this article, ground movement induced by dewatering of groundwater is considered as a stochastic process and surrounding soil and rock are treated as a stochastic medium. Based on the theory of stochastic media, a procedure is developed to predict ground movement induced by dewatering of groundwater. In addition, the theory is satisfactorily applied in the practical engineering areas such as the foundation excavations and subways.

Construction dewatering-induced settlements on surrounding buildings/structures and roads/pavements have been observed by engineers. To understand the potential impact, a geohydrological study was carried out at a project site in the City of Toronto, Ontario. Results indicated that the potential impacts are strongly related to the phreatic surface change of the project site. The range of impact area, the depth of drawndown, the change in pore water pressure and the induced settlements are functions of pumping discharge, soil type and compositions, and varied with shoring type and dewatering device. Reducing the quantity and duration of dewatering, minimizing drawdown and limiting influence area are three important ways to mitigate the potential impacts of construction dewatering.

Bridges, grade separation retaining walls, and noise walls are common structure types in a highway system. Due to the unique subsurface condition of Karst terrain, the stability of residual soils that overlay the cavitose limestone bedrock is often the critical factor to determine the foundation selection. The stability mechanism of residual soil over the karst limestone rock is summarized based on more than 120 field-observed sinkhole collapse events in the eastern United States. Also, factors affecting the stability of residual soils are discussed. The majority of sinkhole events that occurred near the highway structures were triggered by unusual amounts of precipitation. The classification of SPT Low Blow Count material near the soil-carbonate rock interface is important to identify the subsurface sinkhole features.

An expanding population has increased the likelihood of ground water supply contamination, the risks to constructed facilities, the cost of construction, and the difficulty of handling stormwater under current Federal regulation at "karst" sites. Geotechnical and geohydrological practitioners often underestimate the problems created by developing land underlain by solutioned carbonates. Both conventional and unconventional exploratory tools can be used to investigate a "karstic" subsurface, including satellite imagery, aerial photography, ground reconnaissance, geologic map ping, test pits, test probes, test borings, aquifer tests, slug tests, and dye tracing. Geophysical investigations, unless performed with an understanding of the high variability of the subsurface, are often unsatisfactory. The requirements of municipal ordinances may govern the nature of an investigation. Remediation is possible. The more frequently used remedial techniques include grouting, pin or pipe piles, caissons, dynamic compaction, and reverse filter sinkhole filling. Whether a regulator, developer, geotechnical professional or citizen, karst poses a problem that is difficult to deal with properly and economically no matter the locale.

The use of graded rock fill is a cost-effective means of sinkhole repair, providing a stable platform for infrastructure while allowing controlled flow of surface water into the sinkhole throat. Typically, the sinkhole is excavated and large diameter (0.25 to 0.5 m) shot rock aggregate is dumped down the excavated throat of the sinkhole. This paper discusses the two-dimensional modeling of the placement of shot rock using the Discrete Element Method, where the aggregate placement is assumed to be similar to granular materials flowing through a hopper. The stability is investigated for a range of rock particle and sinkhole throat radii. It is demonstrated that for a given throat radius, there exists a range of particles sizes that could be either stable or unstable depending upon how the particles arrange during the dumping procedure. The gradual transition from unstable to stable behavior is best described by a logistic regression.

The construction process of twin tunnel is very complex, and the different construction schemes will cause obviously different mechanical behavior, so it is necessary to make optimal analysis of construction schemes for twin tunnel. In this paper, a finite element forward analysis and back analysis program for twin tunnel is established, which can simulate the construction process under the three-heading construction method and benching tunneling construction method, the settlement of crown and ground, stress of the middle wall and the stability of the surrounding rock are analyzed and compared by back analyzed parameters of the surrounding rock, then the advantages of the two methods are compared and practical construction scheme is optimized.

In recent years, grouting behind the lining of shield tunnels is an important way to control the settlement of tunnels in areas of soft soil. One of the main concerns is how to evaluate the quality of this grouting. When ground penetrating radar (GPR) is used to detect the quality of grouting behind segment at the tail of shield tunnel, it is very important to ascertain the velocity of electromagnetic wave (EMW) to obtain accurate results. In this study, a network analytic instrument is initially used to detect the permittivities of different grouting materials, as this could affect results of the GPR. Permittivity is exponentially related to detecting frequency, for different mixture ratios and curing periods of grouting materials. From the results, we find that permittivity varies with detecting frequency, moisture content, and curing period. In particular, moisture content is the most important factor affecting dielectric character. Model and in-situ tests have been carried out. This study demonstrates that it is important to adopt different permittivity values according to different choices of detecting frequency. It is also important to more accurately interpret the grouting effect behind the lining of shield tunnels for GPR.

The jacking technology of underpass bridges has been adopted abroad under railway and highway line. In order to provide reliable basis of design for the construction of underpass bridges, this study simulates the interaction between the underpass bridge structure and the soil in the jacking process by using of FEM method. 3D modeling method is adopted to simulate the displacement and stress in both the structure and the surrounding soil. The numerical simulation results indicate that the displacement and the stress in front of the box structure are largely affected by the length of the structure.

The east anchorage of E-Gong-Yan Suspension Bridge in Chongqing City is a tunnel style anchorage and located in soft rock masses. In the paper a model test of anchorage structure scaled 1:12.5 in field is described. Firstly, the instrumentation layout, observation procedure and the main results of the test are introduced. Then the engineering significance of the measurements obtained from the test is explained and the safety factor of the global stability for the anchorage structures together with the surrounding rock masses is analyzed by using dynamic programming technique and 3D elasto-plastic finite element computation. It is shown from having monitored of displacements since the bridge was opened to traffic in 1999 that the tunnel anchorage is in a good condition. The model test has played an important role for the success of the design and construction of the bridge.

Considering limitation of the current design method of open caisson when it is applied to an ultra-deep one, the nonlinear three-dimensional finite element method is employed for the first time to analyze time-varying stress mechanism of the structure system during subsidence process after subsidence checking computations have been done. Spatial stresses of the open caisson-stratum system are calculated under 28 operating modes which are divided according to the construction procedure during subsidence process and integral structural analyses of the open caisson are carried out at the final designed elevation. The results of these previous researches indicate that, for ultra-deep open caisson, the stress ranges of the local domains of sidewalls can be underestimated by the present numeration method of structural strength; the secondary stresses of the upper linkage sections which have a tendency of descending will keep stationary eventually; the emphasis of checking computations should be the longitudinal bend of side and partition walls; the vertical loads are the major factors influencing the stress and deformation behaviors; the current checking calculation methods and constructional measures of cutting curb need to be adjusted. All the conclusions attempt to make reference to subsidence design and construction of other similar projects.

In this paper, an assessment method for structure damage due to shield tunneling was proposed based on risk analysis. Firstly the relationship between ground surface settlement due to shield tunneling in soft soil and closer building structure was established. The general impact distribution curves of structure were obtained. Thus it is possible to use clear physical parameters of soil and structure to perform the risk analysis of the bearing risk bodies. Secondly the structure was classified into large stiffness and small stiffness building. The grade of damage and the corresponding impacts of building structure were denoted by the gradient of building and the width of crack. And therefore the function between ground settlement and building structure impact by tunneling was acquired. Finally, a case study in Shanghai Metro presented a good beginning application of risk analysis.

The Municipal City of Shanghai has become the focus as the International Financial Centre of the People Republic of China. The rapid urban development involves construction of infrastructure and property developments at geometric scale. It is inevitable that some of these constructions being carried out above existing metro tunnels; it becomes more critical when deep excavations are involved. This paper is to study how the "Time-Space Effects Theory" can be applied as a mean of counter measures to minimize tunnel upheaving effect during overlying excavations. Hence, ensure the safe operations of metro lines.

The concept of Submerged Floating Tunnel (SFT) can date back to the 19th century. Norway, Italy, Japan and some other countries have carried out the pertinence research over 30 years and SFT has obtained an increasing attention in recent years. There are some limits by our current research on tether structure which was an important member in SFT. In this paper, the author did some researches on the tether structure in the fluid condition and obtains some useful conclusions on the characteristic of tether structure under the influence of vortex-excited vibration. As results, this paper deduce an analytical equation on lock-in velocity under assumed computing model; Calculate the spectrum of lock-in velocity based on the geometric and physical characteristics of tether which has been selected ahead, then analyze the results and obtain the condition of vortex-excited vibration.

This paper investigates the effect of lubrication stability against frictional forces in pipe jacking. Friction tests at the interface between the pipe and the lubricant material were performed. Based on the testing results a three dimensional analysis was carried out using FLAC3D code. The results show that lower frictional resistance and about 17% increase in jacking efficiency are expected by using more stable lubrication material.

The soft soil within the pipe roof ahead of excavation face was generally reinforced for retaining the face stability, but the Beihong-Road tunnel in Shanghai constructed recently is the first case to adopt pipe roof method without reinforcing the saturated soft soil. It is made of 80 phi 970 steel pipes with interlocks forming a rectangular type of pipe curtain. Stability of the excavation face and the controlling of ground settlement during construction are obtained by box grid and steel pipe roof. The heave of ground surface is produced during the box grid extruding into the soil as culvert box jacking forward. To study the mechanism of pipe roof, such as ground heave magnitude, range, uplift force and steel pipe flexural rigidity, pipe roof is simplified as longitudinal grade beam. The pipes ahead of grid bear uplift force within the range of passive sliding zone, and other parts of them lay on elastic foundation. This model can calculate heave magnitude, range and uplift force, etc.

It is unavoidable that during Double-O-Tube (DOT) shield tunnel construction, direction will deviated from the pre-designated places. The deviation includes rolling, pitching, and yawing. This paper presents the causes of deviations at first, including (1) inherent factors of shield machine itself such as manufacturing errors and unbalance tube weight at two sides, (2) subsoil conditions such as non-uniformity, (3) problems happened in construction operation. The deviation not only influences the final central-line position of tunnel but also causes the environmental problems such as large surface settlement over tunnel. Therefore, it is necessary to rectify the deviation during construction in order to build high quality tunnel. For the DOT tunnel, direction control includes rolling control, pitching control, and yawing control. The controlling methods are presented and discussed in details according to the field data during a DOT metro tunnel construction of Shanghai Metro line 6.

A numerical program based on a 3-D Finite-Difference-Method has been developed in order to simulate the air losses in compressed air tunneling. The program contains an automatic advance sequence and takes into account the strong non-linear air- and water conductivity-functions of the unsaturated ground. The developed program was used to investigate the effect of a varying overburden on the air losses for NATM-tunnels. The use of bulkheads has been analyzed for the top-cover method. The conducted case studies show that it is favorable to drive compressed air tunnels in direction of decreasing overburden (if the overburden is variable) and that the use of intermediate bulkheads in top-cover tunneling in order to reduce air losses is limited.

To satisfy the rapid development of economy and transportation, the super cross-section highway tunnel with lower flat-ratio, such as four-lane road tunnel, seems very demanding and its low flat-ratio make it difficult to be constructed under traditional tunnel support system. To break out present status, an innovated "pre-built support" system was investigated thoroughly, which characterized by an innovative idea of installing support system before excavation, and with the consideration of economical and technical aspects, an implementation of this system suggested here is a "pre-stressed" way which incorporates the support system in surrounding rock. It was found that this "pre-built support" system can greatly improve the stability of super cross-section tunnel. Detailed analysis of the stability of super cross-section tunnel without and with the "pre-built support" has been put forward in this paper. Results from both numerical analysis and analogical model experiment have proved the effectiveness of this innovated "pre-built support" system for the stability of super cross-section highway tunnel.

Based on the background of crossing-river twin-tube shield tunneling in Shanghai, a 3D FEM model of twin-tube Shield tunnel, which bears water pressure, was developed, and the whole excavating and supporting process were simulated by elasto-plastic finite element method. Circumstance with different tunnel distance was analyzed, and the research emphases the interaction rules between the two tunnels. The reasonable parameter of tunnel distance was drawn, which can be the references for optimal design. The internal force, deformation of antecedent-building tunnel and load applying to it were monitored during the course of construction. Monitored results and optimal results of numerical simulation were compared and analyzed. The significant results obtained provide a better understanding of excavation process of twin-tube tunnel, and it is helpful in similar constructions in future.

There are a lot of discontinuous planes in rock mass of Longtan hydropower station site. It is of practical value to make certain whether there are movable blocks on excavation planes and judge their stability. Block theory is an effective method to analyze the stability of fractured rigid rock masses with faults and joints. By detailed investigation of the rock mass data. Stereo-analytical method for Block theory is used to analyze stability of Longtan hydropower station underground power-house, and the distribution of the discontinuities induced by the excavation is systematically evaluated. Obvious statistical distribution result of the movable blocks is given, and helpful advice for designing schemes for reinforcing moveable blocks is put forward. Thus, this method provides a reference to design effective reinforcing schemes.

In the construction of Shanghai Subway Line No.2, the interval tunnel, from people's park station to middle Henan road station, will have to pass beneath the running subway line No.1. It is only 12 meters after the shield machine had departed from the starting shaft that the Subway line No.2 will intersect with old Subway line No.1 with an angle of 85 degrees, as shown in Figure 1. What is more, the minimum net distance between the tunnel invert of Subway line No.1 and the tunnel crown of Subway line No.2 is only 1 meter. This is the first case of tunnel excavation in close proximity in Shanghai City, which also puts forward the severe challenge to most engineers and technicians. In order to study the safety and stability of Subway line No.1 during the tunneling process, a 3D numerical model for this case is presented in this paper. According to the calculation results, the law of ground movement and the construction influence on Subway line No.1 are analyzed. At the same time, some useful conclusions and advice are provided, which can also be referenced by some other similar projects in future.

The roof of two adjacent underground chambers is simplified to beam with build-in ends mechanical model, and blasting vibration load is simplified to harmonic wave. The catastrophic model of double cusp for underground chambers destabilization induced by blasting vibration has been established under the circumstances of considering deadweight of the beam, and the condition of destabilization has been worked out. The critical safety thickness of the roof between underground chambers has been confirmed according to the destabilization condition. Research results show that the destabilization of underground chambers is not only dependent on the amplitude and frequency of blasting vibration load, but also related to deadweight load and internal attribute of structures. It is accordant to testing results and some related research results of blasting seismic effect. The research results gotten in the paper can offer references for arranging underground chambers reasonably and preventing disasters of underground engineering, etc.

Beneath an urban environment there are many tunnels carrying roads and railways. At the same time urban development involves the construction of high-rise buildings that require deep foundation. The influence of bored piles on existing tunnel is a common interaction problem especially in soft ground of Shanghai. This paper assesses the influence of pile group on existing tunnels using the finite-element method due to the lack of theoretical method to calculate the settlement field around piles. In the first part of paper 2-D plane strain approach is used to analyze the response of a tunnel to loading of piles located on one side of the tunnel. Some parametric studies including foundation layouts and clear distance between piles and existing tunnels are carried out. Then a case study of Pacific Square II which minimum distance between pile foundation from No.1 subway in Shanghai is only 15m is introduced. The predictions of numerical simulations are compared with field measurements. The loading of piles causes global downward movement and squatting of the tunnel lining. The crown settlement of tunnel lining reduces with the increasing of S₁, (the spacing along the pile rows), S₂ (the spacing between the pile rows) and S₃ (the minimum spacing between the pile rows and the tunnel). The horizontal displacement of tunnel lining is much smaller than vertical displacement. The bending moment distribution behaves clockwise rotation due to pile loading.

To investigate the mechanical behaviors of steel fibre reinforced concrete (SFRC) segments which are firstly used in the test section of the Shanghai Rail Transit Project Line 6, and to propose some useful suggestions for design and construction, a numerical analysis and field test are conducted. The contents of this study involve: (1) the behaviors of the segments against the jacking force, (2) the occurrence and development of cracks, the distribution of stress and strain of segment body, and (3) the distribution of stress and strain in circumferential joints of lining. The results show that safety against the jacking force of shield and the distribution of tensile strain in segment body and joint meet the requirement of design and construction. No cracks have been found in segments under the construction load. This indicates that the steel fibre provides the concrete of the segment with an improved crack resistance. It should be noticed that, although there is no cracks, the maximum tensile strain of rabbets of circumferential joints is much larger than the critical strain of the concrete. It is suggested that the rabbets should be reinforced in design.

Thirty-three experiments were performed in a scale of 1:6th tunnel model. The purpose of the experiments was to investigate the behaviours of smoke propagation and temperature distribution and to propose an effective ventilation measure during fire fighting in a long sized road tunnel. As a fire source, an oil pool was used. The temperature, air velocity and pressure in the tunnel were recorded continuously. The results showed that the temperature, pressure and smoke flow in the tunnel varying significantly with the ventilation measures. Also, the proper ventilation measures could rapidly reduce the temperature for fire fighter and victims and improve air quality and visibility within the tunnel. In addition, the basic ventilation measure was experimentally established.

Total weight of overburden is usually considered in calculation of vertical earth pressures on shield tunnel lining segments unless the arching effect of soil above tunnel can be justified. Theoretical approach has been used to estimate the vertical earth pressures on tunnels with soil arching effect. Previous studies on field monitoring data indicate that measured vertical earth pressures on tunnel linings account for only 40 to 50 percents of the total overburden, except for cases in very soft clay formation. Moreover, the measured vertical earth pressures are usually lower than the theoretical estimates. In this paper, a numerical study using a software package (FLAC) is conducted on the earth pressure distribution on shield tunnels considering the tunnel construction and various overburden thicknesses. The results indicate the vertical earth pressures on linings of shield tunnels at depths of 20m, 25m, and 30m in T2 zone of Taipei area are respectively 45%, 46%, and 42% of corresponding total overburden pressures. Furthermore, the estimated lateral earth pressure coefficient is close to K_a.

This paper presents an analytical solution for the prediction of internal forces of a jointed segmental precast DOT (Double-O-tube) lining. The `force method' is used to determine the internal forces of DOT lining. The comparison is also made between the numerical results and analytical solution under the same condition. And the analytical solution makes a good agreement with the numerical results.

A road tunnel with 669m long has been built under the airport taxiway in Shanghai Pudong International Airport; With the effect of the additional loads including airplane, the tunnel project is mainly related to the uneven settlement between the tunnel structure and soft ground at its two sides, which is caused by the settlement of the deep soft soil. In this study, a reasonable design technical program had been brought forward. Moreover, considering the uneven settlement between the tunnel structure and soft ground at its two sides, soil-cement pile was adopted to improve the foundation of the tunnel at the sides and the bottom. At last, a prediction study on settlement and an analysis of the survey in-situ were carried out in the road tunnel and the foundation surrounding, and these two results are approximate. The result of this study provides the scientific and feasible basis of design for the construction of road tunnels under the airport taxiways in soft ground.

A geo-material failure process analysis, considering the coupling of stress distribution, fluid flow, and element damage evolution, has been used to investigate the mechanisms of crack initiation and propagation around a 2-D cylindrical cavity in heterogeneous stiff soils during grouting. Numerical simulations were performed using the specifically developed computer software F-RFPA2D. The results indicate the analysis is a powerful tool for the studying of soil behavior during fracture grouting. Moreover, they give us a better understanding of the crack initiation and propagation mechanisms during hydrofracturing.

This paper presents an evaluation of three branches of analytical and semi-analytical predictions of ground movements induced by shallow tunneling in soils. These three branches of theoretical solutions are based on basic solutions, simplified theory of elasticity, and stochastic medium conceptualization, respectively, and they represent the contemporary theoretical treatments of the subject without resorting to sophisticated numerical methods. Their formulations, physical assumptions, expressions and applications are analyzed. The solutions evolved from basic solutions are all in the form of tunnel deformation characterization multiplied by transfer function; the solutions derived from using simplified theory of elasticity involve certain inconsistencies and ambiguities; and the semi-analytical solution based on stochastic medium theory bears strong resemblance, in terms of both fitting parameters and functional form, to a well-known family of empirical formulas. Comparative calculations reveal that these solutions may yield rather discrepant predictions of ground surface settlement, suggesting caution for proper actual applications.

To investigate the influence of existing building load on the deformation and earth pressure of the ground in shallow tunneling, two-dimensional model tests and numerical analyses are carried out. A stack of aluminum rods is used in the 2D model tests. Flat and piled raft foundations supporting an initial dead load are modeled in the laboratory tests and numerical analyses. For the sake of comparison the laboratory tests and numerical simulations for tunneling in the initially undisturbed ground condition (i.e. green field) are performed as well. In the finite element analyses, an elastoplastic constitutive model named subloading tij model is used. The observed and computed results for the ground with existing building load are compared with those for the green field condition.

Traditional fault tree analyses use single probability to represent each basic event. However, it is unrealistic to evaluate the occurrence of a top event by using a crisp value without considering inherent uncertainty and imprecision each basic event has. The fuzzy set theory can be used to deal with this kind of phenomenon. A triangular fuzzy number is introduced to represent the failure probability of a basic event. Fuzzy fault tree algorithm is developed by the lambda-cut method. The fuzzy failure probability of SMW retaining structures in deep excavations is calculated by a fuzzy fault tree. Main basic events affecting the occurrence probability of the top event are verified by a sensitivity analysis, which can be applied in the risk analysis of SMW retaining structures in deep excavations. Compared with the traditional fault tree analysis, the fuzzy fault tree method can get the failure possibility distribution of SMW retaining structures in deep excavations.

Controlling the displacements of foundation pit walls and supporting structures is one of the most effective measures for ensuring safety of foundation pit construction. Because of it, the accurate displacement computation of foundation pit walls and supporting structures is paid great attention by geotechnical engineers. In this paper, the three-dimensional displacement field of Deping Station foundation pit, which is part of Shanghai Track Traffic Line 6 project, is computed by means of ANSYS software. The computed result is contrasted with BP (back propagation) neural network predicted data. Basing on the computed results, fuzzy control theory is applied to construction pre-control. The application effect is satisfactory. The research result of current paper is very helpful for geotechnical construction.

It is demonstrated in the paper that the loading and boundary condition of the classic plasticity problem corresponding to an inverted sheet extrusion through a square die is equivalent to the bearing capacity of equally spaced multiple strip footings on cohesive soils. Furthermore, the same solution is shown to be appropriate to estimate the pile spacing/cut depth relationship for unlagged soldier pile systems.

This paper describes novel developments of tools for predicting, monitoring, and controlling ground movements associated with excavations in urban areas. The paper describes developments in the following areas (1) Laser scanning for developing an accurate record of construction activities, (2) Intelligent, self-updating numerical models to compute anticipated ground movements, and to learn from field observations, and (3) integration of heterogeneous data using a GIS based system. These new technologies are illustrated using excavations in the Chicago area.

The actual earth pressure exerted on a strutted soil support system in cohesionless soil has been hard to measure. Apparent Earth Pressure (AEP) diagrams are commonly used to design strutted excavations. An AEP diagram is a function of a soil angle of internal friction (φ') and its bias. Also, the bias in an AEP diagram was estimated using a simplified linear earth pressure diagram. The analysis resulted in recommended load factors applied to AEP and reliability levels in the design of a strutted excavation in cohesionless soils.

The observational method, proposed by Peck in 1967, is often used to assist in predicting the wall deflection in various stages of deep excavation. Here, a back-analysis using finite element method is usually carried out to "update" soil parameters so that the after-the-fact prediction of the response at the current stage of excavation matches the measured response such as wall deflection. However, it is time consuming and requires much effort and considerable engineering judgment. This paper presents an alternative using artificial neural network (ANN) to predict the wall deflection in the next stage of excavation based on the observed response in the prior stages.

The paper presents analytical and numerical approaches to the evaluation of the depth of the influence zone; the term influence zone is assigned to the region where the load has substantial influence on the deformation of the soil skeleton. The approach relies on the analytical solution based on the analysis of Westergard subspace assuming elastic material response. The depth of the influence zone must also be taken into account in the back analysis of the soil parameters, e.g. the deformation modulus. The necessity of this is shown by rigid plate field load tests. The standard back analysis based on the Boussinesq half space theory provides unreal data when the load of the plate is not sufficient and the depth of influence zone is small. It is caused by geostatic stress. Due to excavation (e.g. in the deep hole) the soil is significantly over-consolidated and the small surcharge deforms only thin upper layer of the subsoil. Boussinesq formula should be accepted if the depth of influence zone reaches approximately two and half times higher than width of footing.

In this paper, a new empirical method is developed by which the surface settlement profile can be accurately estimated. The new empirical method is an extension of the Hsieh and Ou method, which showed that the surface settlement profile could be reasonably constructed if the maximum surface settlement (δ_vm) was known. However, there is no reliable method to predict δ_vm with good accuracy. To this end, a simple procedure is established by which δ_vm can be accurately estimated from the maximum wall deflection (δ_hm). This procedure includes two elements: 1) an empirical equation for estimating the ratio of δ_vm over δ_hm (R = δ_vm/δ_hm), and 2) a means to determine δ_hm. Since the latter can be accurately estimated with a routine finite element or finite difference analysis, the focus of the paper is on the former. To this end, a set of empirical equations for the ratio R is developed. The accuracy of the proposed method is verified with well-documented case histories of braced excavation.

Deep soil mixing (DSM) has been widely used in the design of excavation supports. This paper introduces a circular retaining structure using DSM to shore a deep soft clay excavation. The diameter of circular excavation is 42.117 m and the depth of the excavation is 10.7 m. The geology of the site comprises fill (3–4 m), soft clay (12–22 m) and silty clay (12–23m). The circular retaining structure is formed by nine rows of DSM columns. The DSM columns have a diameter of 550 mm and are overlapped with a minimum length of 150mm in both tangential and radial directions. In order to increase the whole rigidity of the circular retaining structure, another row of minipiles are inserted into the fourth row of DSM columns. Field monitoring data shows such circular retaining structure functions well during and after the excavation. Compared with other shoring systems, such circular retaining structure is more economical.

During the dry excavation of deep foundation pit, groundwater must be pumped within and/or around the pit and the seepage of groundwater forms a groundwater level depression cone around the pit. Drawdown of the groundwater level will cause the increase of effective stress of soft soil. Thus, the soft clay will consolidate and settlement will occur within and/or around the pit. This paper presents a case history on the settlement within and around an unexcavated pit due to groundwater pumping. Before excavation the groundwater was pumped for 260 days and about 0.33 m settlement with in the pit was observed. In order to analyze the variations of groundwater level, seepage in the subsoil, and ground surface settlement, a 3D finite element model, considering groundwater seepage and calculation of ground settlement in one process, was adopted. The analytical result indicates that by using the geotechnical investigated parameters the proposed method can simulate the field measurement value well.

This paper presents a case history of a deep excavation for a building foundation in soft deposit in Shanghai. This deep excavation is of particular interest because it was constructed using the united methods: bottom-up method in the main building part and top-down method in the annex building part. The excavated area is about 7000 square meters. The depth of excavation in the main building part is 13.5 m and in the annex building part is 12.0 m. The excavation was retained by diaphragm wall with a thickness of 0.8 m. Three levels of reinforced concrete bracing structures were installed to support the wall at the part which was constructed by bottom-up method. Wall displacement, axial forces of the struts, and displacements of the props were monitored during the excavation. At last, field monitored results were analyzed in details.

The foundation pit of Zhongsheng Commercial Centre Building was constructed using top-down method. The one-pile-supporting-on-column mode was adopted in the foundation excavation and basement construction, which means a higher capacity of piles to sustain the total load imposed by the building structure and the temporary constructing loads. Base grouting technique was used improve the bearing capacity of the conventional bored piles that are usually constructed using bentonite slurry. In order to verify the effectiveness of base grouting, static load tests were conducted on three base grouted piles and three conventional bored piles, those of 48m long and embedded into sand. The load-settlements, distribution of the skin friction and pile toe resistance are presented and compared. By not only increasing the pile end bearing and the basal stiffness but also increasing the skin friction, base grouting significantly improved the overall performance of the pile.

A series of three-dimensional finite-element analyses have been made to simulate deep excavation in soft soils with an elasto-viscoplastic constitutive relationship using top-down construction (TDC). For a particular substructure geometry and certain ground conditions, the settlement variation due to change of construction sequences and/ or pillar pile supporting system, is especially presented and discussed. On the whole, with TDC the settlement of basement floor is spherical, and it develops as construction progresses. In addition, different construction sequences obviously affect the settlement of pillars and walls, and different pillar pile supporting system has influence on the magnitude and distribution of differential settlement between pillars and walls.

This paper involves a foundation pit about 10.0 m in depth. The main problems in choosing a supporting system for excavation are difficult geological conditions and pipelines around the pit. Pile-anchor structures (bored piles and pre-stressed anchors) were used as the shoring system in the east, the south and a part of the west of the foundation pit to restrain displacements. The composite soil nailing walls (jet grouting piles combined with soil nailing) were adopted as the supporting system in the north and west of the foundation pit. Jet grouting piles were chosen both as a cut-off wall and a tool to reinforce the soil mass. The design calculation method of the pile-anchor structure and the composite soil nailing walls are presented. The structural characteristics of bored piles, pre-stressed anchors, cut-off walls and soil nails are also introduced. The results of monitoring in excavating the pit demonstrated excellent stability of the foundation pit.

This paper presents unpublished data on the largest excavation and retaining structure of the "pile curtain" type already constructed in the Center of Brazil, more specifically at the city of Brasilia. This city is characterized by having a tropical, unsaturated, collapsible sandy clay soil known as the Brasilia "porous" clay. These soil characteristics are reproduced, with some differences, in most areas of the Brazilian Central Plateau. Hence, the paper briefly discusses about project details and presents the simplified design approach adopted for the retaining structure, that was carried out with the Geofine software package. This case history is also under scrutiny of an on-going research thesis, which aims the interpretation of its instrumented results and the establishment of more refined numerical analyses.