Recent Advancement in Soil Behavior, in Situ Test Methods, Pile Foundations, and Tunneling: Selected Papers from the 2009 GeoHunan International Conference

In this paper, swell pressures of the compacted expansive soil of Guangxi Province are investigated by a series of swelling laboratory tests with different initial moisture contents and dry density. The relationships of swell pressure with initial moisture content and dry density are established. The method to calculate the expansive characteristics is obtained when the water contents and total stress levels are changed. These relationships can be used in practical expansive soils engineering.

Soft soil is widely distributed in the world. With the increase in construction of highways and railways on soft soil, the treatment of soft soil subgrade is becoming more and more extensive. Based on the reinforcement effects of glass fiber, the possibility of applying glass fiber to strengthen soft soil subgrade is discussed in this paper. More than 100 groups of cement soil samples' laboratory testing results are presented and compared. The analysis of test results indicates that glass fiber mixed in cement soil can improve the strength and deformation characteristic of cement soil in a certain degree. It could also be used as a possible replacement of soft soil subgrade. The findings are a new contribution to the soft soil subgrade treatment techniques.

Featured by its high strength and good water stability, coarse-grained soil can be mixed with clay and used as fine-property filler in embankment construction. However, the mixing ratio is usually difficult to determine. If the coarse-grained soil content is excessively high, the embankment is prone to crack or damage because of cohesion deficiency. On the contrary, if the coarse-grained soil content is too low, its high strength can not be utilized effectively, which may result in strength deficiency and excessive settlement. Based on field survey and laboratory test results, this paper has made deep analysis on the strength mechanism of glacial sediment coarse-grained soil, and the reasonable mixing ratio of coarse-grained soil and clay soil has been discussed.

A difficult problem for tunneling in red strata soils in Guangzhou subway is that the mud cakes are easily formed in the cut face of shield machine. It has frequently induced ground failures and collapse accidents. The microstructures of red soil are studied using SEM (scanning electron microscope). The SEM tests disclose the important microstructures of red strata minerals such as micro-lamina tactoid, petal-shape and micro-porosity. The mechanism of water-induced red strata swelling damage and high-viscosity characteristics are then investigated. The disclosed microstructure and micro-porous properties provide the evidences for understanding the mechanical behavior of Guangzhou swelling red strata soils. Furthermore, the chemical foamed-soil modification tests for red soils are presented. Experiments on foam modified red soils disclose the relationship between permeability and fluidity for foamed red soils and sandy soils in subway engineering. This research is helpful for applying foamed soil to stabilize the tunneling face and to prevent ground seepage damage in shield tunneling construction.

To investigate the variation of K₀, the coefficient of lateral earth pressure at rest, with initial saturation degree (S_r) and constant radial stress (σ_rc), a series of K₀ consolidation tests were conducted on expansive soil samples under different saturation and stress conditions using a stress-path triaxial system equipped with Hall-effect transducer. The coefficient K₀ of every sample were obtained by strictly confining radial strain and evenly increasing radial stress to a given value with a slow and steady speed. The test results showed that the curve axial stress-radial stress exhibits nonlinear under small saturation degree; K₀ of samples in different saturation and stress state ranged from 0.22 to 0.72 and increased with increase of initial saturation degree and radial stress.

This paper describes an aggregate imaging based Discrete Element Modeling (DEM) methodology successfully employed to model both clean and coal dust fouled railroad ballast behavior. Laboratory direct shear box tests were conducted on granite type clean and fouled ballast aggregate samples. The size, shape and angularity properties of the aggregate particles were obtained through image analysis. Accordingly, direct shear box DEM simulations were conducted for different aggregate contact friction conditions. Both the clean ballast behavior and the heavily fouled case of coal dust filling completely all the voids in ballast were adequately modeled using the DEM approach by assigning a lower contact friction angle as the controlling discrete element model parameter in the latter case. In accordance with the direct shear test results, much lower shear stress-shear deformation curves, i.e., lower shear strengths, were predicted the coal dust fouled case using the DEM simulations.

Traditionally, the formulas of critical edge pressure p_cr and critical load p_1/4 are developed by assuming coefficient of earth pressure at rest K₀ equal 1. It means that the geostatic stress is treated as hydrostatic stress. This assumption leads to an increase in lateral load of subsoil and results in a higher bearing capacity of subsoil. In the paper, a MATLAB program is used to find the numerical solution of bearing capacity of soil for K₀ ≠ 1. The proposed method overcomes some shortcomings of the methods available in the literature for K₀ ≠ 1. The influence of shear strength parameters of soil on the critical load is investigated.

Generally, it is very difficult to obtain the undisturbed soil and keep it in the undisturbed state in practice. In this paper the residual shear strength of Grey-white expansive soil of Ningming was studied based on the analysis of the influencing factors of residual shear strength of expansive soil. The test results of undisturbed samples, compacted samples and samples prepared by static compaction conducted by strain-controlled repeated direct shear test were compared, which show that the differences of the peak shear strengths are very large but the differences of the residual shear strengths are very small. By the comparison and analysis of the test results, it is more reasonable and practical to use the residual shear strength of static compaction sample to represent that of undisturbed sample. Therefore, the residual shear strength (c=10.53 kPa, φ=11.55°) of samples prepared by static compaction can be taken as that of Ningming Grey-white expansive soil.

A lightweight fill was produced by blending expanded polystyrene (EPS) beads and sands in proportions. Such formed granular geomaterials, known as sand-EPS lightweight fills, have potentials of being lightweight compared to traditional fills, thus are suitable for many infrastructure works where less overburdens are expected, e.g., utilities trench backfills. Consolidated drained triaxial compression (TC) tests were conducted on the lightweight fills to observe materials' stress-strain relationships, specifically, the stress-strain variations associated with the mixing ratios of EPS beads. EPS beads were incorporated into the mixtures based on their mass ratios over sands, i.e., 0.5%, 1.5% and 2.5%. It was found that confining pressures and mixing proportions played important roles in affecting the stress-strain behaviors of lightweight fills. The materials underwent shear contraction, which is related to the inclusion of EPS beads. The constitutive law of the lightweight fills was derived based on Cam-clay model and modified Cam-clay model, and verified by the test results.

This paper investigated the densification effects of deep dynamic compaction (DDC) and vibratory compaction on loose saturated sands, which was based on two well-documented case histories. This investigation was carried out by examining pre- and post-compaction cone penetration testing (CPT) results. The CPT results indicated that under the same design earthquake excitation, the sands treated by DDC were densified to the level of resisting potential liquefaction, while, the sands were still liquefiable after vibratory compaction.

Spectral Analysis of Surface Waves (SASW) is a non-destructive method for determining the stiffness profile of pavement sites. The method consists of generation, measurement, and processing of dispersive elastic waves in layered systems. The test is performed on the pavement surface at low strain level, where the elastic properties are considered independent of strain amplitude. During an SASW test, an impact source was used to generate energy at various frequencies. Two vertical acceleration transducers are set up to detect the energy transmitted through the testing media. By recording signals in digitised form using a data acquisition system and processing them, surface wave velocities can be determined by constructing a dispersion curve. Through forward modeling, the shear wave velocities can be obtained, which can be related to the variation of stiffness with depth. This paper presents the results of two case studies for near-surface profiling of two different asphalt pavement sites.

An integrity testing for stone columns was attempted using crosshole S-wave logging. The method is conceptionally quite similar to the crosshole sonic logging (CSL) for drilled piers. The critical difference in the logging is the use of s-wave rather than p-wave, which is used in CSL, because s-wave is the only wave sensing the stiffness of slower unbounded materials than water. An electro-mechanical source, which can generate reversed S-wave signals, was utilized in the logging. The stone column was delineated from the S-wave travel times across the stone column, and taking S-wave velocities of the crushed stone and surrounding soil into account. The volume calculated from the diametrical variance delineated is very close to the actual quantity of the stone filled.

A new s-wave probe, called "MudFork", has been recently developed and is used in accurate measurements of shear wave velocities of soft soils. The probe is composed of two bender elements mounted on a "fork" having two blades, one element perturbing ground and the other one monitoring seismic waves, and can be penetrated using SPT(standard penetration test) rods pushed with a routine boring machine. To expand its use to estimate undrained shear strength and density, an attempt to correlate shear wave velocity to those properties was made at normally consolidated silt near Incheon, Korea. A simple linear relationship between shear strength and shear wave velocity was obtained, and a tentative relationship between density and shear wave velocity was also defined.

Soil strength, type, and moisture content are needed for site characterization applications and to assess the load carrying capacity of soil in construction control applications. Currently, no portable, automatic, easy-to-use field methods exist to measure the required soil parameters. In this paper, we describe a new instrument that integrates and extends two proven technologies, the cone penetrometer (CPT) and dynamic cone penetrometer (DCP). A portable Rapid Soil Characterization System is under development to perform near surface assessments to determine trafficability for heavy vehicles and aircraft. In the construction control context, the new device has the potential to eliminate errors in the measurement of soil strength due to soil type and moisture effects. A fully automatic prototype system has undergone limited field demonstration at the USACE facility in Vicksburg, MS. Preliminary laboratory and field test results indicate that the required soil geotechnical parameters can be extracted from dynamic penetration data, providing a near surface instrument that can provide accurate soil strength assessment to a depth of one meter.

Based on the limit analysis and nonlinear Mohr-Coulomb failure criterion, the ultimate pull-out capacity of horizontal plate anchors is calculated, in which the type of anchors and the corresponding failure mechanism are taken into consideration. The ultimate pullout capacity is obtained by a nonlinear sequential quadratic programming algorithm, and the theoretical results are compared with the available results presented in the existing literatures. The relationship between the nonlinear parameter and the ultimate pullout capacity is analyzed. The shape modification factors for different kind of anchors are given through a multiple nonlinear regression method.

This paper provides the fundamentals, capabilities and limitations of the seismic surface-wave method as applied to in-situ testing of pavement and foundation and represents the results obtained from its recent applications in a number of projects. These applications include characterization of flexible pavement layers during construction, monitoring of early-age strength development of Portland cement concrete and evaluation of soil foundations. The issues on understanding the results from surface-wave tests and how to incorporate them in those requirements adopted in most existing specifications or common practices are discussed.

Through the analysis of the common roadbed and pavement diseases such as cavity beneath slab and pumping, and their current treatment situation, the author proposed the idea of improving and resuming the loading capacity and waterproof performance of highway through intercalating a waterproof bonding layer between base and slab. The author has developed a new composite grouting material composed of an environmentally friendly powdery inorganic component and an emulsified bitumen component to solve the technical issue of the pressure grouting of emulsified bitumen. Their practices show that the material can combine the excellent waterproofing behavior of bitumen and the high-strength of cement and adjust its rigidity to be suitable for different road structures. Through the grouting treatment by the new material, the stress state of roadbed and slab can be significantly improved and the carrying capacity can be resumed at reasonable cost/performance ratio.

In order to ensure that the nodes are distributed uniformly in the definition domain of calculation points, the uniform experiment design is introduced in the meshless method, which can make the nodes distribution uniform in the domain. Using uniform designs table, distributes these nodes, the interpolation function is built by those nodes, and dispersant equations are founded by the Galerkin Method. According to this concept, a programme based on uniform design is made. In order to verify the theory and programme, a load test of pile foundation is chosen to provide calculation data. The calculated results accord with survey data on-the-spot and show that it's possible that the uniform design may be applied in the nodes distribution in meshless method. And the calculation result obtained by less nodes is precise, based on the meshless method using uniform design. Because the radius of influence domain is decreased, the computer workload is greatly reduced.

Embankment construction on soft clay can result in the development of significant lateral ground movement. When the pile is installed adjacent to this unstable embankment, it may experience unexpected lateral passive loading along its length and may cause the integrity problem of the superstructure. A lot of numerical and experimental research works have been conducted for better understanding of the behavior of passively loaded pile. However, the nonlinear response of piles subjected to horizontal ground movement is difficult to analyze with two-dimensional technique since the passively loaded piles are truly three-dimensional problem. In order to investigate the complex soil-pile interaction, the three-dimensional finite element analysis was employed in this study. The passive p-δ curves are presented to account for a nonlinear response of piles as the common p-y curves may not properly describe the actual behavior of piles subjected to lateral ground movement. It was found that the generated p-δ curves were dependent on pile spacing; when pile spacing decreased the passive p-δ curves stiffened, whereas the active p-y curves softened. A better understanding of behavior of passively loaded piles adjacent to an embankment constructed on soft Bangkok clay was achieved.

An analytical model is proposed to evaluate the pile skin friction at the pile-soil interface and analyze P-s curve of single pile. The model is based on the exponential transfer function technique and allows back-analysis to be carried out easily. The calculated skin friction results is in good agreement with the measured ones and the accuracy of the proposed method has been verified by an example in Xiao et al.'s (2002) work. Then the transfer model is implemented into differential equation of pile-soil interaction, and after being iterated by computer simulation, the calculated P-s curve is in very good agreement with the results of Xiao et al. (2002) and Carrubba (1997). Parameters are initially obtained from lab experiment and subsequently modified by fitting the Carrubba's (1997) pile head displacements to computer simulation.

Piled embankments has technical and economical advantages over other soft ground improvement methods. The load transfer mechanism in piled embankments is referred to as arching effect. Piled embankments are generally related to the advantage of soil arching effects of granular soil. Most of present research on piled embankments is focusing on the soil arching effect, but there is lack of investigation on the vertical stress distribution in the inner soil arching under embankments. In this paper a new analytic solution called multi-arching theory is applied to investigate the behavior of soil arching. The solution shows the stress distribution in piled embankments as follows; the vertical stress above the soil arching increased as geostatic state, and inside of the soil arching the vertical stress decreased nonlinearly, which reflects the mechanism of soil arching effect and the vertical stress distribution in piled embankments. The theoretical solutions show good agreements with model test data. The results demonstrate that the distribution of vertical stress in embankments is helpful in understanding the behavior of piled embankments.

The effect of micropiles on soil reinforcement under static and dynamic loadings was studied. Embankment on untreated soil and treated soil by micropiles were modeled using the finite element code PLAXIS. The displacement caused by embankment static loading and acceleration of the embankment caused by seismic loading were calculated and compared. It was found that micropiles treated soil can greatly reduce the settlement of the embankment and mitigate seismic response of the embankment. The results of this study provide valuable information about the design and application of micropiles.

Based on the vertical static load test results on a test pile, located in the soft soil, the load transfer mechanism and bearing behavior of super-long filling piles is first discussed. Then, a method of predicting the axial bearing capacity of super-long piles by the pile top settlement is advised. By introducing the linear elastic-fully plastic model and tri-broken-line model to fit the development of shaft resistance and tip resistance respectively, analytical solutions of axial load capacity is derived under elastic stage of the subsoil. Finally, the present method is applied to analyze the data from the test pile, from which good agreement between the predicted and measured pile top load-settlement curves is found. The results also show that buckling stability analysis and deformation checks are necessary for super-long filling piles, and the axial bearing capacity of super-long piles should be controlled by the allowable settlement on the pile top.

The influence of four independent variables of Y-shaped cross section configuration on flexural behavior was analyzed by flexural factor of section and area ratio according to actual load on Y-shaped vibro-pile under three conditions, i.e., sharp-angled location of cross section, concave arc position and typical tension point. Flexural behavior under above three conditions is quite different and it changes with variation law of four independent variables of the cross section. The same template radian exists while the other three independent variables are defined, so that flexural behavior under conditions of sharp-angled position and typical tension point reaches the minimum value. Solution of corresponding template radian of the minimum value of flexural behavior has been introduced by utilizing the mathematical analysis software, Mathematica.

With development of piling technology, various pile sectional configurations are adopted in the pile industry practice. The soil stresses induced by the piles of various sectional configurations are significantly different. In this paper, the solutions for the induced soil stresses were proposed for Y-shaped pile, closed- and open-ended pipe piles, triangular-shaped pile, rectangular pile, and square pile. The calculation of soil stresses is based on the Mindlin stress solution and Geddes methodology for derivation of soil stresses. It is assumed that the pile end bearing and shaft resistance are uniformly distributed across the pile tip area and shaft perimeter, respectively. The numerical software Mathematica (Nintegrate) was used to provide integrations to the derived theoretical solutions.

Based on field tests on the new developed grouted gravel pile, the bearing performance, working mechanism and improvement effect on the adjacent ground were studied. The variation of pore water pressure, pile-soil stress ratio, ground surface settlement, layered settlement, and lateral displacement of improved zone adjacent to grouted gravel pile were monitored and presented in this paper. It indicates that the properties of adjacent soil surrounding both pile body and pile toe were improved due to the infiltration and cementation of cement grout, therefore both shaft friction and end bearing resistance were remarkably increased and apparently the ultimate bearing capacity was increased.

To reduce the noise in learning samples while using BP neural network to predict the bearing capacity of pile foundation, a self-organizing map neural network was adopted to classify the collected pile samples in the paper. Firstly, to maintain the SOM network at a stable situation, pile samples were discriminated into symbol codes and character codes, and a new coding model of pile character was established, by which a SOM neural network's weight formula of reduction was derived. Then, clustering of pile samples were shown by calibrating the maximum response cell of the self-organizing map neural network. Finally, case studies using the clustered samples as input vector to a BP network were presented, and the results showed that it was a good alternative approach for estimating the bearing capacity of pile foundation by using the improved solution with the characters of simplicity.

This paper presents geotechnical issues and our design approaches for the Upper Oso Reservoir Bridge Widening located along State Route 241 in Mission Viejo, California. The total bridge length is approximately 1540 feet (470 m). The foundations of the existing bridge structures consist of 36-inch (0.91 m) diameter cast-in-drilled-hole (CIDH) piles and driven steel H-piles. The subsurface materials at the bridge site were investigated by a field exploration program. Key geotechnical design involved development of new seismic design parameters and acceleration response spectra for an Upper Level Earthquake (ULE) and a Lower Level Earthquake (LLE); evaluation of new fill and liquefaction-induced settlements on the existing and new foundations; pile foundation modeling and capacity assessment; abutment slope seismic stability and deformation.

Stone column is an economical treatment method in embankment engineering. Controlling potential bearing capacity failure is a challenging problem in this design technique. A modified bearing capacity calculation method which takes the influence of time into account is presented by utilizing two-dimension consolidation theory. Also, a case study to validate the proposed method and to study the time effect on the bearing capacity of stone column foundation system is also presented in this paper. The analytical result shows that the bearing capacity of stone column composite foundation increases with increase in time. It is therefore suggested that the time effect on the bearing capacity of the composite foundation formed by stone columns should be taken into account in embankment engineering for the economical and optimal design.

Three-dimensional nonlinear finite element simulations are becoming increasingly feasible for transportation geotechnical applications. This paper presents a robust and versatile framework that helps streamline the use of finite elements for seismic response of soil-structure systems. In this regard, a Windows-based graphical-user-interface OpenSeesPL is developed for pile-ground interaction analyses. Particularly suited to seismic applications, the open-source computational platform OpenSees is employed throughout. OpenSeesPL allows convenient studies of three-dimensional seismic (earthquake) and/or push-over pile analyses. Various ground modification scenarios may be also addressed by appropriate specification of the material within the pile zone. To illustrate the capabilities of OpenSeesPL, two studies are presented in this paper. Lateral spreading effects on pile foundations are modeled, followed by an investigation of ground remediation in a mildly sloping silt stratum. Along with the insights gained from these studies, the reported effort aims to highlight the analysis framework capabilities and range of potential applications.

Through analyzing the process of tunnel construction using the finite element method, we conclude the regularization of ground surface movement, and take a contrastive analysis with the analysis result of ground surface movement and deformation by using the stochastic medium theory. The research shows that stochastic medium theory is adopt to predict the ground surface movement and deformation of crushed surrounding rock tunnel; the value of subsidence on the tunnel axis is maximal, and far away from the axis direction the value of subsidence decreases; the ground surface horizontal displacement on the cross section of mountain tunnel increases with the increase of distance from the central axis of tunnel, the value arrives the maximum at the point of inflection, after that decreases; when the mountain tunnel depth increases, the area of influence of ground surface movement and deformation enlarges and the strength of influence weakens. The actual ground surface movement of this tunnel by monitoring proves the reliability of this research.

Failure mechanisms of homogenous rock slopes were investigated within the upper bound theorem of limit analysis. In rich water zone, the effective stress analysis of saturated slopes is considered. The corresponding charts for different types of rocks are presented for practical use. From the results, it is found that the stability factors increase with the increasing rock strength, and that the nonlinear parameter and rock types have important effects on failure mechanisms. According to the results, new equations for determining the stability factors are proposed.

As in urban areas, construction of tunnel inevitably leads to ground movements. These must be carefully predicted if there is a risk of settlement damage to nearby structures. How to identify the real danger is the basis of quantitative risk analysis of buildings. Due to various conditions, it is impossible to undertake a risk assessment of each building. In the process of excavation, the mechanism of interaction of the tunnel and adjacent structures is very complicated because ground movements are affected by a lot of factors, such as the formation conditions, the tunnel section depth and size, foundation type and geometric characteristics of adjacent building, and relative position, etc. So, a practical and reliable quantitative model with concise, clear physical meaning of the parameters is in need. Referencing the quantitative risk assessment methodology of petrochemical plant, tunnel safety risk identification model could be established and it can be quickly and reliably identify the high-risk buildings.

Liuyang River tunnel, one of the longest tunnels in Wuhan-Guangzhou railway passenger dedicated line, encountered low overburden, weak rock and crowded surface buildings in exit. If incorrect excavation method was tacked, it will cause serious damages to the environment and buildings. As it belongs to large-section excavation, for which cross section area surpasses 150 m². In order to avoid oversize subsidence by excavation of the large cross section, field monitoring including stratum displacement and three dimensional deformations were carried out. Combined field monitoring with numerical analysis, stratum displacement distributed rule in large cross section tunnel excavation process was observed, which showed that the construction process is safe.

The double side drift method, CRD and CD method are widely adopted for super large cross-section excavation for tunnel in weak rock in China. Further, it is shown good adaptability because of the extensive application in highway, railway, especially in urban underground facilities. However, there are also some problems in work efficiency, structure safety and engineering management and so on. It is necessary to make optimization of construction methods under these conditions. In this paper these shortcomings for double side drift, CRD and CD methods are detailed. The work efficiency, load conversion mechanism and the influence on tunnel structure, and construction management are discussed. Then suggestions for tunnel excavation determination in such conditions are put forward. It is shown that if auxiliary measures are adopted first, partial excavation could be abandoned. Even full-face excavation may be feasible. The principle proposed in this paper has been used in practice, which is proved once more for tunnel excavation in soft and weak surrounding ground.

Pipe-roof has been adopted extensively as pre-support in tunnel construction. The vertical deformations of the pipe-roofs in the entrance of Liuyanghe Tunnel are monitored by installation of a series of strain gauges to investigate the mechanical behavior of the pipe-roofs during the tunnel excavation. Based on the monitoring results, the mechanical characteristics and the evaluation of the reinforced effect of pipe-roof in the construction process were analyzed.

In present engineering design, rock mass is simply treated as an isotropic material and their strength parameters are given by decreasing those of intact rock through joint connectivity, which is introduced to reflect the integrity of rock mass separated by joints. This method may be acceptable for most jointed rockmass. But for some sedimentary or metamorphic rocks, such as shales, sandstones, slates, phyllites and schists, are characterized by inherent anisotropy due to the existence of the preferentially oriented weakness plane. In this study, the influences of the anisotropic properties of rockmass on the deformation and stability of tunnel are analyzed by the site monitoring and numerical calculation. A detailed investigation on the engineering geological conditions of the horizontal stratified strata in Queerxi Highway Tunnel was carried out. The deformation and the surrounding rock pressure are monitored, and then field measuring results and distributing law are summarized. The results show that anisotropy of rockmass has remarkable influence on the deformation properties and stability of tunnel in stratified jointed rockmass.

Two dimensional dynamical finite element and effective stress method were used to analyze dynamical response of Qifenghu Lake earth-rock dam during earthquake. During analysis, the floodwater level in the upriver is 198.5 meter and 180 meter in the downriver. Peak acceleration of earthquake was 0.275g and it lasted 10s. Calculation results showed that pore water pressure after earthquake was as near twice as that before earthquake. Some region in the central clay wall and the silt groundsill where pore water pressure is equal to lateral consolidation pressure was found. This will endanger the stability of the dam. Through analyzing dynamical response of nodes on the dam surface, we find that absolute peak acceleration and peak displacement of D and E node in the middle of the dam is greater than others.

A rigid block failure mechanism of shallow rectangular tunnel is proposed to calculate the needed support pressure σ_T for tunnel stability using upper bound solution. The velocity discontinuities in the side wall of the shallow rectangular tunnel of the failure mechanism occur in both radial and tangent directions. Formula for calculating support pressure σ_T using upper bound solution are deduced based on the presented failure mechanism, and the calculation program is compiled. It is shown that the proposed rigid block failure mechanism can be used effectively to analyze the stability problems of shallow rectangular tunnel using upper bound solution.

The double down-side drifts construction method was put forward in a shallow-buried weak tunnel. Its construction behavior was studied by numerical simulation using MIDAS. Results show: (1) this method can improve tunnel load, the key construction step is arch ring excavation and core soil is good to tunnel steady; (2) weak parts mainly locate wall foot and crown foot of drifts, crown foot of tunnel and the connections; (3) reinforcement of soil under the drifts has no apparent effect on improving rock deformation and support load. From an economical and safety point of view, main parts to be reinforced are drifts (its foot depth, connection parts with tunnel, and its corners); core soil should be kept if rock is unsteady and needs reinforcing.

Sequential excavation method is often used in urban tunnel construction. Based on the stochastic medium theory and according to the stratum deformation caused by element excavation, the stratum deformation united calculating equation under this excavation method is studied, which can take into account the development course of the deformation with the different tunnel section excavation. Then the time-space rules of the stratum deformation caused by tunnel excavation with different division of cross-section are discussed. The maximum of stratum deformation and curvature arise after some part of the whole tunnel, rather than the whole tunnel section has been excavated. Double-sidewalls heading excavation method has more control effect on stratum deformation than central departure excavation method. The study achievement can provide scientific basis for controlling the stratum deformation caused by tunnel construction, and protecting the safety of the buildings and pipelines around the tunnel.

Deformation of surrounding rock during tunnel excavation could be regarded as a time sequence. In this paper, the auto regressive moving average (ARMA) process of tunnel deformation prediction during construction, which can, to some extent, modulate model parameters according to the input and output data, adjust them to its optimal values in some statistical conditions through the iterative algorithm. Firstly, the raw monitoring data is dealt with by difference operation (d=1) and the stationary error time series is obtained. Secondly, the randomicity and the stabilization of the error series have been analyzed to confirm the feasibility of ARMA model. Both the autocorrelation function (ACF) and partial autocorrelation function (PACF) of the error series are tested, and the order of model ARMA is obtained based on the AIC criterion. Finally, the method of least square is adopted for parameter estimation. As a test, this modeling is used to predict the surface settlement of a Shenzhen metro line 2 of China. The results of engineering case indicate that ARMA is reliable in deformation prediction. In addition, the new-information model idea has been put into the model to achieve the real-time forecast of settlement.

Multi-waterproof measures are adopted to highway tunnel, where waterproof membrane is the most vital link between initial lining and final lining during waterproof system. In light of plenty of field monitoring data by compress sensors, the article presents phase and position of the maximal compress stress of waterproof membrane during pouring final lining, and different calculation formula of analyzing self-weight stress and temperature stress of concrete. The article also presents tensile stress condition under surrounding rock bad extra-excavation and stress calculation by finite element method (FEM) of nonlinear hardening constitutive model. The mechanic characteristic contributes to applied value for simplifying reliability assessment parameters and conducting safety construction for waterproof membrane.

Based on the Chenjiaqiao tunnel project, the construction process of tunnel under different surrounding rock conditions and with various construction methods is analyzed with MIDAS program. The mechanical behavior under complex process of construction and the optimization of the construction process of multi-arch tunnel are studied by the analysis of the monitoring measured data and the numerical analysis results. The main contents of the research contain: The 3D elastoplastic model of multi-arch tunnel is set up, which contains Grade III, IV and V surrounding rock. The stress of the surrounding rock and the supporting structure at typical excavation stage under above three excavation methods are simulated and analyzed. The monitoring data is analyzed and compared with the simulated data. The reasonable distance between the working faces of the right and left tunnel is obtained.