Special Issue of Professor WANG Jianhua JIANG Xia，HUANG Wei, SUN Qiyan
In order to investigate the deformation characteristics and load transfer mechanism of deep excavation, a numerical model considering the process of stepped excavating and soil nailing was established by FLAC 3D. The lateral displacement of excavation surface and outside soil, the shear strain increment of soil, and the axial force distribution of nail were analyzed. The results show that, the maximum lateral displacement appears close to slope toe, meanwhile, outside corner is the most disadvantageous location of deflection, and the multilevel platforms have positive effects on controlling soil deformation. Tensile failure and shear failure are the two main failure modes of excavation slope. The location of potential sliding surface can be indicated by shear strain increment contour, and the location moves toward the outside end of soil nail due to soil nail reinforcement effects. The maximum axial force of soil nail appears near the middle and the relative minimum value near the two ends, and the distribution of maximum axial force agrees well with the potential sliding surface.
The load model and its design method of a pipe are to be improved. Based on the South Line project of sewage treatment in Shanghai, the performance of inner diameter of 4 m jacking pipe was studied by numerical simulation. The variation of contact pressure between pipe and soil during construction was analyzed, and the influence of covering soil depth was then discussed. The differences of the load model from "the technical specification for pipe jacking of water supply and sewerage engineering" were researched, and the differences of the internal forces were compared. The results show that soil arch effect is strengthened with increasing of cover soil depth, while the distribution of contact pressure is more uniform than the codes. Therefore, the active earth pressure is conservative to calculate lateral pressure, and the subgrade reaction could be also more uniformed. The bending moment of pipe will decrease while the axis force increase if the load model is improved, which would optimize the design method of pipe.
The vertical bearing mechanism of screw piles was studied by the model test and numerical analysis. The results of the analysis show that the bearing capacity of the screw piles depends on the soil shear strength and a shear zone along the pile will take place in the surrounding soil under ultimate load. Parameter analysis was presented including the pile-soil interface properties, the soil shear strength, and the design parameters of the screw pile. The parameter study indicates that the key factors influence the vertical bearing capacity of screw piles are the soil shear strength, the screw pitch and the width of screw. A calculation method was obtained based on the field test and numerical results.
On the background of 500 kV Shanghai Expo underground substation, a fluid-structure coupling FEM analysis of dewatering and excavation was made based on the Biot's consolidation theory. A pumping test was simulated to determine soil parameters by back-analysis of displacement and pore pressure. A fluid-structure coupling model was built to analyze dewatering and excavation with steady analysis method and birth-death element method respectively. Seepage and stress fields were solved at the same time. With comparison of the calculated and measured values, the fluid-structure coupling method used in the analysis of dewatering and excavation was proved to be correct and feasible.
The three dimensional finite element model was built up to simulate an over size and deep excavation traversing shield tunnels, and the effects on surroundings and tunnel heave due to excavation were analyzed. From monitored retaining wall horizontal displacements and tunnel heave, a simplex method was employed for back- analysis of soil parameters. According to the back-analysis program based on simplex method, optimized soil parameters were attained after finite element analysis. The final tunnel heave was predicted by the optimized soil parameters. The results show that the predicted tunnel heave is close to monitored data, which guarantees the effectiveness of back analysis by this paper.
The natural element method (NEM) is a novel numerical computational method for solving partial differential equation. It is built upon the notion of the natural neighbor interpolation, which is based on Voronoi diagram and Delaunay triangulation. This paper focused on its application in solving Biot consolidation equation. The discrete form of control equation was obtained with classical variation principle; the algorithm routine for 2D condition was also elaborated. The results of numerical examples show that the results of NEM are in concordance with the analytical solution and the precision is higher than that of FEM.
Model test was performed to investigate the propagation and decay of impact-load induced vibration in sandy soil, and the effect of vibration screening panel was furthermore studied. The results show that the polystyrene wave-absorbing panel placed at the boundary of test box is effective in controlling the boundary reflection of vibration waves. The impact-load induced vibration decays rapidly with the increase of distance from the load point, and the attenuation of peak acceleration along horizontal, vertical and diagonal direction can be well fitted by the function of amax=kR-β. Polystyrene screening panel, behind which vibration can be reduced, has the negative effect of intensifying the vibration just before it, this may be caused by the reflecting of vibration wave at the screening panel.
The buckling of steel jacking-pipe under complex loads has been an important factor in construction because of the increasing of diameter and jacking distance. Numerical analysis on the buckling of long steel jacking pipe, whose distance-diameter ratio is larger than 100, is studied in this paper with finite element method (FEM). The first buckling mode of pipe-jacking under different loads are obtained by the buckle analysis. By introducing the first mode as the initial imperfection, the elastic-plastic buckling behavior of steel pipes is analyzed with the RIKS method. Both the buckling mode and ultimate load of buckling of the steel jacking pipe are discussed, and the buckling phenomenon in practice is verified. Parametric analysis shows that the stability of steel pipe can be improved by reducing friction and face resistance of pipe-jacking, and the jacking load of the pipes with high confining pressure should be carefully controlled.
The case histories of deformations due to the deep excavations for some metro stations in Shanghai soft soil deposits were presented and discussed. The statistics show that the ratio of the maximum lateral displacement of the retaining structures to the excavation depth ranges from 0.04% to 0.6%, and the mean value is about 0.3%. The deformation of the retaining structures develops a clearly deep-bulging profile as the excavations continue, and the maximum lateral displacement of the retaining structures usually appears between 1.5 m above the excavation surface and 7 m below the excavation surface. The ratio of the maximum surface ground settlement to the excavation depth lies between the range 0.05% to 0.7%, and the ratio of the maximum surface ground settlement to the maximum lateral displacement of retaining structures falls within the range 0.4 to 1. The construction method of cast-in-place piles combined with compaction grouting for cutting off groundwater is generally proved to be more effective in controlling deformation of deep excavations than diaphragm wall or SMW method.
The soft soil creep (SSC) model was adopted to simulate the whole process of a deep foundation pit with different construction conditions. Comparisons of the effect of different construction technologies on the deformation of foundation pit and the surroundings were made. The results show that the deformation features of the foundation pit under both construction technologies are similar. The top-down channel-type construction technology is more effective on controlling the deformation of the enclosure structures, and has less impact on the surrounding by decreasing the ground settlement, the lateral displacement of soil outside the pit and the upheaval mount of soil at the pit bottom. While considering the train load, with top-down channel-type construction technology, the deformation of the railway subgrade is safe.
The load-transfer method (t-z method) is easy to calculate and can be used in design practice. The most important thing of using the t-z method is the determination of the load-transfer parameters. The uncertainties of the two parameters in the hyperbolic load-transfer function of pile foundation were investigated. Data of seven static load tests with strain gauges, twelve static load tests without strain gauges together with 75 load tests at a single site in Shanghai were collected. Statistical analyses were conducted for both measured and back-calculated parameters for different soil layers. It was found that the uncertainties of the back-calculated values are close to those of the measured ones. The parameters a and b are negatively correlated. Compared with basic soil properties such as unit weight and shear strength parameters, the COVs of the load transfer parameters are greater. According to the Kolmogorov-Smirnov (K-S) test at a significance level of 5%, the normal distribution for both parameters can not be rejected.
A new risk evaluation method of deep excavation was presented by considering the correlation of multiple parameters. The load transfer and deformation of retaining structure and surrounding soil were analyzed to discuss the correlation mechanism of different parameters during deep excavation. The quantitative relationship among these parameters was determined by the statistical analysis. A multi-parameter risk evaluation method and software were then proposed based on the correlation analysis of multiple parameters. The presented method was applied in a case of metro station in Shanghai. The results show that some risk during construction which can not be warned by the traditional methods is found in the new method.
A series of finite element method (FEM) analysis were carried out to study the seismic response of the nuclear low pressure cylinder and condenser, based on the code for seismic design of building. Seismic response characteristics of the nuclear low pressure cylinder and condenser were obtained through the seismic time history analysis and spectrum analysis. The results show that the seismic response of the nuclear low pressure cylinder and condenser presents some vibration model features of plate structures, and has a better aseismic performance than general building.
A fully coupled numerical model was presented to analyze the process of dissipation of the excess pore water pressure and solid skeleton deformation based on the poroelastic governing equations. The numerical model was verified against a two-dimensional consolidation of homogeneous unsaturated soil. The numerical results show that the non-homogeneity has its own importance not only during the process of dissipation of the excess pore water pressure but also for solid skeleton deformation. As the gradient of soil modulus increases, dissipation rate of excess pore water pressure increases and the amplitude of the soil's deformation decreases in the initial compaction stage and final steady stage.
A three-dimensional finite element model based on viscoelastic boundaries was developed to effectively capture the dynamic behavior of the metro transfer hall hub of the People's Square. Dynamic characteristics of the underground structure during vibration induced by dismantling temporary reinforced-concrete supporting system were studied, resorting to the Newmark method. In-situ monitoring data were used to calibrate the proposed method in this paper. The results show dynamic characteristics of the underground structure under vibration loading are accurately simulated by the presented model based on viscoelastic boundaries, and thus spurious reflections on the interface of soil and structure can be effectively eliminated. Prediction on the possibility of structural resonance under vibration loading can also be made by the proposed model, which is of benefit to decision making of engineering design and construction.
Based on two-phase u-p theory for saturated soil, a new constitutive model based on the super/ sub-loading surface and anisotropy was utilized to analyze the dynamic responds of a sandy seabed under the combined wave and current loadings. Firstly, a poro-elastoplastic model for a sandy seabed was established. The mechanics of oscillatory excess pore water pressure in seabed and residual excess pore pressure due to wave/ current were discussed and the liquefaction depth which changes correspondingly was obtained. A comparison between the elastic and elatoplastic sandy seabed's dynamic responds to wave/current loading was also presented.
Based on the Biot's dynamic coupled consolidation theory, the scaled boundary finite-element method was developed to correctly model the dynamic unbounded far-field boundary of three-dimensional (3D) fully saturated soil in this paper. Body forces and surface tractions were considered in the derivation. The concept of similarity, the compatibility equation, Biot's coupled consolidation equations, and the Galerkin's weighted-residual method were used to derive the formulation for the governing equations. The main difference from the single-phase version was the presence of pore water pressures as additional parameters to be solved, in addition to the displacements, strain and stress which were incorporated into the static-stiffness matrices by producing fully coupled matrices. Solving the resulting equations yielded a boundary condition satisfying the far-field radiation condition exactly. The computed solutions were exact in a radial direction (perpendicular to the boundary and pointing towards infinity), while converging to the exact solution in the finite element sense in the circumferential direction parallel to the soil-structure boundary interface.
Annular reinforcing steel bar stress and pipe-soil contact pressure during pipe-jacking were monitored on the spot. The differences of the active contact pressure from the related research results were analyzed. The results show that when the pipe is pulled in the stable slurry interface which has been already formed, and since the test pipe was pulled into the tunnel bore, the distribution of contact pressure tends to be uniform and remain stable. But the contact pressure will increase suddenly when grouting, and return to normal gradually after stopping pulling. The lateral force of the pipe is also stable, though not big, mainly showing compressive stress, whose changing is controlled by pipeline axial deviation and grouting. Therefore, the pipe is in a state of eccentric compression in the test. Compared with the results of the field test, the specification is rather conservative. Besides, the active distribution of contact pressure is close to the load model developed by Lei Han, which can be used to optimize pipeline structure design.
The water pressure on the surface of the seabed was obtained with the cnoidal wave theory usually employed in coastal regions to analyze the interaction between the structures and waves. Dynamic responses induced by the cnoidal water waves in seabed sediments were investigated with numerical methods. Parametric studies were conducted to indicate the influences of the elastic constants, seepage characteristics and the compressibility of the pore water in analytical and numerical calculations. The results show that the excess pore pressures are extensively affected by the compressibility of the pore water and the seepage coefficient, whereas the anisotropy of the soil permeability has little impact on the pore pressure. The shear modulus and the Poisson's ratio used in the calculation also have some effect on the response of the seabed.
It is relatively difficlut to determine the parameters adopted in numerical simulation of excavation due to the non-uniformity and uncertainties of soil. In this paper, an inverse analysis method for deep excavation based on the Pareto multiobjective optimization was proposed. The excavation process was first simulated in ABAQUS. A multialgorithm genetically adaptive multiobjective method (AMALGAM) was then invoked by Matlab to identify the soil parameters in excavation with multiple types of field observations. The proposed method was applied to the analysis of a well-instrumented deep well to predict the wall deflection, as well as the ground surface settlement in following excavation with acceptable accuracy. In addition, the nine soil parameters obtained from the inverse analysis on Changshou Road Station excavation were presented, which probably could be uesd as reference for other excavations.
Analysis of soil counterforce and displacement of circular caisson pipe jacking project was made under the effect of different top edge using the site monitoring method as well as the comparative validation of distribution pattern of resistance of different open caisson using finite element numerical simulation methods. The results show that the distribution pattern of resistance of open caisson is approximated by a straight line which mutates in the depth of the caisson bottom due to the stiffness of the floor at large and reaches the maximum at the foot. The displacement of soil occurs less but as a whole under the jacking force. Simultaneously, the rationality of less than the active state was verified in the case that the soil of open caisson produces a smaller displacement under the caisson sinking back below the front wall of the active state which gives the variation of inking back soil reactions with the different distance.
Three-dimensional limit analysis was utilized to determine the stability of the convex corner in a slurry-supported trench. Analytical solutions were derived for the safety factor of the convex corner stability in a slurry-supported trench. The failure surface has the shape of logarithm helicoids, with outline profile defined by a log-spiral curve. Power expressions were obtained for dissipation rate, gravity and slurry pressure. By solving the energy balance equation, the equation of safety factor for convex corner stability was obtained. The slurry weight ratio, the slurry surface depth, the angle of internal friction and other parameters were discussed. The result indicates that the stability factor increases with increasing slurry and soil bulk density ratio, cohesion, friction angle, but it decreases with decreasing slurry level depth and trench depth ratio, trench width and depth ratio.
A finite element model for theoretical analysis was established to study the effect of slurry pressure on soil deformation control during pipe-jacking construction. Based on the comparison of measured data and finite element results, the influences of pore pressure and soil deformation during the construction process were discussed. The soil disturbance around pipe-jacking with different slurry pressures was analyzed, based on which the concept of pore pressure change rate was proposed. Taking the results of soil deformation and disturbance analysis into consideration, it is suggested that in practical engineering, the slurry pressure should be 1.1 times the overlying earth pressure, which has less impacts on the surrounding environment. This conclusion can provide reference for future similar pipe-jacking constructions.
Closely constructed excavations will influence the stress and deformation of adjacent existing underground structures. In this paper, the non-linear numerical analysis of plane finite element was applied to predict the movement of a construction of foundation pit in Shanghai to verify its applicability. Parametric studies were performed to investigate the influence of width of pits and the distance of the two pits on deformation of soil between two excavations. The relationship of optimal distance between excavations and the width of excavations was derived. The influence of the distance between the tunnel and the excavation on the deformation of tunnel was also analyzed. The results show that the settlement of shield tunnel is less than that of its neighboring soil. The shallow tunnel heaves during the excavation. The amount of heave is reduced for the tunnel more distant away from the excavation.
A consolidation model for saturated-unsaturated soil was formulated in axisymmetric cylindrical coordinates to simulate the hydraulic head changes and land deformations of circular excavations caused by well pumping. The transverse isotropic properties with respect to both hydraulic and mechanical properties were considered, so were the effects of underground structures. Based on this model, two groups of pumping-recovery tests performed on a circular excavation were simulated to study the effects of transverse isotropy related to Young's modulus and initial saturated hydraulic conductivity on hydraulic heads and soil displacements. The result shows that as Young's modulus increases, hydraulic head changes get easier and soil displacements get smaller. As initial saturated hydraulic conductivity increases, both hydraulic head changes and soil displacements get smaller.
A data model considering parameter fusion was presented by studying the relation among the geometric, physical and mechanical parameters of different entities during excavation. Based on C++ and the object-oriented program development method, a data structure reflecting the entity class hierarchy was introduced to develop a 3D modeling and risk pre-warning software for deep excavation. By using the 3D modeling software, the geometric and mechanical model of deep excavation was unified. The software was applied to the deep excavation of the metro station at Hanzhong Road in Shanghai, and the results show that the presented data model reflects the relation among different entities well and is effective in detecting potential risks during excavation.
In this paper, based on Biot's theory, a numerical model for wave-seabed-pipeline dynamic response was established to investigate seabed instability failure. The seabed was treated as porous medium. The model simulated the distribution of pore pressure and effective stress, and the process of liquefaction around buried pipeline under various wave loads were investigated. Partly dynamic (u-p) formulations for the wave-induced response of the seabed with pipeline were adopted. In partly dynamic analysis, the u-p formulation in which both displacement and pore pressure were field variables was adopted considering the acceleration of soil skeleton while neglecting the inertial terms associated with pore water. Using COMSOL Multiphysics, a parametric study, including the permeability, degree of saturation, buried depth and wave height was conducted to investigate the seabed response. Then, a criterion for liquefied state was used and the possibility of wave-induced liquefaction occurring in porous seabed was studied.
The stability of layered seabed subjected to combined wave and current loading was studied by numerical model based on Biot's consolidation theory. The numerical results reveal that the existence of following current not only aggravates the possibility of liquefaction, but also increases the depth of shear failure. As a treatment, higher permeable soils layered upon seabed composed of low permeable soil will decrease the potential possibility of liquefaction as well as help to prevent original seabed from shear failure.
Unloading effect of the deep excavation would decrease the pile's bearing capacity and increase the tensile in pile shaft. A novel test system which can control the soil stress state was developed to study the pile-soil interactive behavior. In this novel system, the normal stress on the pile-soil interface is applied by the air pressure in the triaxial cell. The soil stress along the pile axis and the movement of model pile are controlled by the double piston. The pore pressure and water flow in the soil sample are adjusted by the two water cannels on the test cell. With the monitoring part of the system, the total shear force on the interface, the relative movement of the pile, and the deformation of the soil layer can be measured during tests. The triaxial interface tests show that the limit friction resistance and friction coefficient increase with the increase of the confining pressure, and the displacement of soil also increases with the increase of the confininig pressure.
CEL (Coupled Eulerian-Lagrangian) method was used to model the pile penetration process in soft clay. Firstly, effective stress method was used in the Vumat subroutine to calculate excess pore pressure. Comparison of the experiment results (by odometer test and triaxial test) with the numerical tests demonstrated the reliability of the Vumat subroutine. The subroutine was implemented in the CEL method of Abaqus/Explicit. Pile jacking process in soft clay under undrained conditions was simulated. The soil movements, horizontal displacement, horizontal stress, excess pore pressure were analyzed. The analysis results show that the CEL method which considers excess pore pressures can simulate well the installation effects caused by pile jacking in soft clay.
Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was employed to investigate the deformation characteristics of a staged excavated and supported foundation pit. Modified Cam-clay model was adopted to model the soil behavior and the interaction between soils and retaining structures was also taken into account in the numerical model. The deflection of retaining walls, the settlement of ground surface, the heave of excavation bottom, and the movement of the deep strata outside the excavation were analyzed. The ground surface settlement curves of the numerical model are basically consistent with the empirical ones from the existing literatures, so its feasibility is proved. The numerical results provide a useful reference for the design and construction of similar deep excavation projects.
Based on the random field theory, a random finite element model of coupled unsaturated consolidation in spatial random soils was established using the covariance matrix decomposition method and Monte Carlo simulation method. The effects of spatial variability of Young's modulus and saturated permeability were investigated. The results show that the mean and standard deviation of the settlement are significantly affected by the coefficient of variation of Young's modulus, and COVE. When COVE increases, the mean and standard deviation of the settlement increase, which means the uncertainty of the settlement are increased due to the spatial variability of Young's modulus. When the correlation length of Young's modulus δlnE decreases, the standard deviation of excess pore water pressure and the surface settlement decrease due to the increased spatial averaging effect. The spatial averaging effect is more significant when the thickness of soil layer is smaller than δlnE. In general, the effect of spatial variability of ks is much less significant than that of elastic modulus, which mainly affects the unsaturated consolidation in process.
In a foundation pit group project, complex excavation stages and large number of monitor data can be encountered, so that the operators are hard to handle the analysis of the interactive impact of the excavation processes on the adjacent foundation pits. To resolve this problem, an analysis system was developed to monitor data and construct information in a foundation pit group synchronously and dynamically. The system used Microsoft SQL Server to facilitate the classification and management of the information of constructions and instrumentations, the time related fields were selected as the reference for the synchronous analysis. The visualized modeling for the excavation processes and the monitor data was conducted through the secondary development of Microsoft Visio and Excel, respectively. A console application was utilized to link and control these models. The system was applied in the synchronous and dynamic analysis of the construction processes and the monitor data in the project of Shanghai Expo foundation pit group, and exposed the interactive impact characteristics of the adjacent excavations in a global and local time/space domain. The system provided an efficient means for the analysis and verification of theories of the interactive impact in the excavation of foundation pit groups.
A statically admissible stress field was constructed by using nonlinear optimization sequential quadratic programming (SQP) algorithm and FEM. Based on the rigid plastic assumption for soil materials, adopting lower bound theorem, the bearing capacity of rectangular surface footing was calculated. The example indicates that the application of SQP algorithm is successful.
Artificial recharge in deep strata is an effective method to prevent land subsidence, and make the deep strata upheave to some extent. The pile foundations of elevated road are relatively deep so that the deformation of deep strata will greatly affect the elevated road. Using the numerical method, the elevated pile and the behavior of the surrounding soil at pumping and recharge loads were simulated and its deformation characteristics were discussed based on the coupled theory. The result shows that groundwater pumping can cause a large settlement of elevated road, while the artificial recharge can control the settlement effectively. Regional land subsidence is smaller than the elevated settlement, but the deformation tendency matches the elevated road well. Besides, based on an engineering project, the long-term deformation characteristic of elevated road at underground water recharge was simulated. The study shows that numerical results agree with the filed data, and the deformation characteristics of elevated piles are mainly influenced by deep strata. Using parameter analysis, the basic laws of elevated deformation were obtained, providing reference for the prediction of long-term settlement of elevated piles.
Large span double-row steel sheet piles were constructed in marine environments to serve as cofferdams of dry dock projects. Due to the construction of the dock excavation, considerable deformation of the cofferdam could occur. The deformation of the large span double-row steel sheet piles was measured during construction of a large scale dock project in Shanghai. Extensive field performance data were collected including lateral survey data and lateral inclinometer data. Construction procedures were summarized and correlated with monitoring data. The measured data were analyzed to investigate the deformation performance of the large span double-row steel sheet piles. A 2D finite-element method was also performed to study the effect of the soil reinforcement technology on deformation control of the double-row steel sheet piles.
A practical numerical example is used to simulate the excavation process of a deep foundation pit in Shanghai, and the rationality of the model is verified by comparing with the measured data. The cross wall between tunnel and diaphragm wall is studied and the influence of cross wall is discussed. By analyzing the vertical displacement of adjacent walls and the displacement of soil on both sides of diaphragm walls, the interaction principle between diaphragm wall and tunnel or diaphragm wall and soil is obtained. The force distribution of the wall in the excavation process is used to reveal the influence principle of adjacent deep excavation on underground structure (cut-and-cover tunnel). The results show that the uplift of the tunnel is mainly caused by the uplift of the nearby diaphragm wall. The influence of the diaphragm wall on the cut-and-cover tunnel is obviously greater than that of the surrounding soil. Under the influence of deep excavation, the reason for the diaphragm wall uplifting is that the friction force in the foundation pit is larger than that of outside the pit.
The double lines strengthening elastic-plastic model was developed by simplifying the concrete constitutive law according to Saenz formula. The formulae for the model parameters were given. The structural analysis procedure Algor was taken to conduct the linear elastic and elastic-plastic FEM analysis on the joints of segments. The strain distribution of segment, the displacement of joints, the rotary angle of joints and the tensile force of joint bolts were given. The comparison between FEM calculation and test results was made, which shows that the finite element analysis results correspond with the test results. The FEM analysis results can bean effective measure to observe the distribution patterns of the strain and stress.
According to the basic solution of semi-infinite elasticity subjected to horizontal loading presented by Muki, boundary conditions and continuous conditions between layers, the basic solution for twolayer elastic half space was derived. The displacement and stress of arbitrary point within the elasticity were also inferred. Thus, exact working property of laterally loaded piles will be obtained by applying these solutions. Several numerical examples were given. The results are well coincident with Mindlin's solution and Davies & Banerjee's computing results.
Circumferential and longitudinal strain of steel jacking pipe which is buried in deep soft soil and jacked with long distance was monitored on the spot to study internal force of pipe under construction and temperature load. The results show that internal force of a fixed section changes little due to jacking distance. For different sections, the one that is closer to the jacking machine head is affected less by jacking force. Compressive stress predominates in longitudinal direction, and is mainly affected by jacking force. However, circumferential stress is mainly due to buried depth, and maybe tensile with deep buried on top of pipe. Circumferential stress and longitudinal stress are coupling especially with large buried depth. Eccentricity of jacking force has a great effect on internal force of pipe. When jacking force is applied, longitudinal stress changes by a large margin, and returns to steady after jacking force removed. The stress in pipe can reach 25 MPa caused by 6 ℃ temperature difference, which hardly influences the using of the pipe. There is little distinction between longitudinal stress and circumferential stress. However, extreme range of temperature should be valued, and may cause destroying.
Special Issue of Professor WANG Jianhua
