Jingpei Li

Simplified Method for Calculating Active Earth Pressure on Rigid Retaining Walls Considering the Arching Effect under Translational Mode

AbstractBased on the limit-equilibrium concept, a new method for calculating the active earth pressure acting on a rigid retaining wall that moves horizontally away from soil mass is proposed. Using this method, the trajectory of the minor principal stress resulting from the soil arching effect in retained soil mass is considered, and the arc-shaped axis of the minor principal stress is approximated to a linear axis using the improved horizontal flat-element method. The effects of soil’s internal frictional angle, its unit weight, the wall–soil friction angle relative to the active earth pressure, and the point of application of the resultant active earth pressure are investigated. Finally, the proposed method is applied to two existing tests for rigid retaining walls with different heights. A comparison of the predicted and measured values shows that the proposed method yields satisfactory results.

Analysis of Undrained Cylindrical Cavity Expansion Considering Three-Dimensional Strength of Soils

AbstractUndrained cylindrical cavity-expansion solutions that were based on the modified Cam-clay model have been widely used to predict and interpret geotechnical problems, such as pile installation, and in pressuremeter tests in saturated clay. However, the yield and failure of soils around the cavity might not be properly modeled by the extended Mises criterion adopted in the modified Cam-clay model. To consider the three-dimensional mechanical properties of soils during cavity expansion, an analytical solution with the spatially mobilized plane criterion-based Cam-clay model is derived for the undrained cylindrical cavity-expansion problem by using the stress-transformed method. The presented solution is verified by two well-documented pile-installation tests and is compared with the modified Cam-clay model–based solutions in detail. The results show that the prediction from the presented solution is closer to the actual stress field induced by the undrained cylindrical cavity expansion. However, the ...

Interpretation of cone resistance and pore-water pressure in clay with a modified spherical cavity expansion solution

A theoretical approach to interpreting the cone penetration resistance and the pore-water pressure measured on the face of the cone during piezocone tests of clays is proposed. The mechanism for the penetration of the piezocone is assumed to be spherical cavity expansion in modified Cam clay critical-state soil. Using large strain theory, the spherical cavity expansion problem is reduced to solving a system of first-order ordinary differential equations for effective stresses in the plastic zone. By taking the normal and shear stresses acting on the cone face to be the ultimate cavity expansion pressure and the effective friction at the cone–soil interface, respectively, the cone resistance was evaluated at force equilibrium. The pore-water pressures induced by cone penetration include components caused by changes in normal and shear stresses, for which the normal term can be predicted by integrating the radial equilibrium equation in terms of total stress. As it is based on an exact constitutive relationship, the present method takes more factors (such as the effects of interface shear and the traditional overconsolidation ratio) into account than other methods of tackling this problem. Comparisons between the predicted and measured values of cone resistance and pore-water pressure at different well-documented sites are in good agreement for most relatively homogeneous low- and medium-sensitivity clay sites.

Analytical Solutions of Spherical Cavity Expansion Near a Slope due to Pile Installation

Based on the hypothesis that the penetration of a single pile can be simulated by a series of spherical cavity expansions, this paper presents an analytical solution of cavity expansion near the sloping ground. Compared with the cavity expansion in the half-space, the sloping free boundary has been taken into account as well as the horizontal free boundary. The sloping and horizontal free surfaces are considered by the introduction of a virtual image technique, the harmonic function, and the Boussinesq solution. The results show that the sloping free boundary and the variation of the inclination angle have pronounced influences on the distribution of the stress and displacement induced by the spherical cavity expansion. The present solution provides a simplified and realistic theoretical method to predict the soil behaviors around the spherical cavity near the sloping ground. The approach can also be used for the determination of the inclination angle of the slope according to the maximum permissible displacement.

Service Life Prediction of Underground Concrete Pipeline in Chloride Contaminated Soils

This paper develops a theoretical model to predict the service life of concrete pipelines in contaminated soils. The service life of concrete pipeline is divided into four stages: the chloride ion diffusion stage, the initial corrosive stress generation stage, the initial crack generation stage and the crack propagation stage. For the first stage, the equation for chloride diffusion is formulated and solved analytically by using the integral transform method. For the other stages, the concrete around a corroding steel reinforcing bar is modeled by a thick-walled cylinder with a wall thickness be equal to the thinnest concrete cover. The concrete pipeline is supposed to reach the end of service life when the crack width exceeds the maximum allowable value at the limit state. The proposed model is validated by comparing the predictions with the numerical simulation results. The analysis results demonstrate that the soil pressure and the concrete cover thickness have significant effects on the service life of concrete pipelines exposed to the chloride contaminated soils.

Analysis of Time-Dependent Bearing Capacity of a Driven Pile in Clayey Soils by Total Stress Method

AbstractThis paper proposes an analytical approach to evaluate the time-dependent bearing capacity of a driven pile in clayey soils by taking the pile installation and subsequent reconsolidation effects into consideration. The process of pile installation is modeled by undrained expansion of a spherical cavity at the pile tip and a cylindrical cavity around the pile shaft. The cavity expansion solution, which is based on a K0-consolidated anisotropic modified Cam-clay model (K0-AMCC), is used to capture the pile installation effects. After pile installation, the dissipation of the excess pore water and the increase of the effective stress in the surrounding soil are evaluated by the radial consolidation theory. Based on the effective stress, the strength of the remolded soil is quantified by the modified Cam-clay (MCC) model and the spatially mobilized plane (SMP) criterion. With the three-dimensional strength of the surrounding soil, the time-dependent bearing capacity of the driven pile is evaluated by ...

Deformation of Subway Tunnels Affected by Adjacent Excavation: In-situ Monitoring and Centrifugal Model Test

The basement excavation will change the initial stress equilibrium of the surrounding soil and hence result in surface subsidence and strata movement. The adjacent subway tunnels would be inevitably influenced by the basement excavation in the dense urban environment. Based on the excavation engineering of Wufangyuan project in Shanghai, the effects of excavation on adjacent subway tunnels are studied by monitoring data and centrifugal model test in this paper. Detailed discussions are performed to investigate the different excavation partitions and excavation sequences. The deformations of an adjacent tunnel under different construction conditions are obtained and the comparisons between the tests are conducted. The results indicate that the excavation of the soil in the areas closer to the tunnel induced greater additional settlements and additional convergence. Some of the construction technologies were employed to reduce the deformation of adjacent tunnels including setting a small partition in the foundation excavation close to the tunnel, excavating the small partition after the completion of the main body of foundation excavation as well as enhancing the support in the direction perpendicular to the tunnel.

Modified approach to evaluation of undrained shear strength from piezocone tests in soft clays

ABSTRACT This paper proposes a modified-theoretical approach to interpreting the undrained shear strength from piezocone tests in clays. Assuming the shear and normal stresses on the cone face to be the friction at the cone–soil interface and the ultimate expansion pressure, respectively, an expression of the tip resistance is first derived at force equilibrium. The undrained shear strength is then determined by combining the derived expression of tip resistance with the formulation for pore pressure at the cone shoulder position. Many factors, such as the penetration rate and the cone roughness, are considered in this model. Different shaped model penetrometers, including cone- and ball-shaped ones, are adopted in centrifuge tests to investigate the validity of the proposed method. The undrained shear strength estimated from the piezocone test is found to agree well with that from ball penetrometer test. Case studies are also presented to show the application of the proposed method. Comparisons between the predicted and measured values of undrained shear strength indicate that the proposed approach is generally applicable for nonfissured clays, especially intact clays.

Drained Elastoplastic Solution for Cylindrical Cavity Expansion in K0-Consolidated Anisotropic Soil

AbstractThis paper presents a semianalytical solution for drained expansion of a cylindrical cavity in K0-consolidated clay. The solution is derived based on the K0-based anisotropic modified Cam-c...