A numerical study of cone penetration tests in granular assemblies.

摘要

The Discrete Element Method (DEM) was used in this study to simulate the cone penetration test (CPT) in granular soil. The granular soil was numerically simulated as a two dimensional particulate assembly. Soil particles were simulated as two dimensional disks. 3,000 disks were initially placed in a hopper. The disks were pluviated into a rectangular container. The numerical assemblies with desired state of stress and varying overconsolidation ratios (OCR) were obtained under Ko condition. The results of Ko consolidation test and biaxial compression tests showed that DEM simulation can reliably simulate the behavior of granular soil.; A 12,000-disk specimen was created by stacking four 3,000-disk assemblies together. A constant stress conditions (BC1) or zero strain conditions (BC3) were applied in the horizontal direction of the 12,000-disk specimen in order to simulate the calibration chamber tests. By coupling DEM with the Boundary Element Method (BEM), a new boundary condition (BC5) was developed which represents the field condition more closely. A series of simulated cone penetration tests were performed in specimens with various OCR values and boundary conditions. From the results of simulated penetration tests, measurements were made to evaluate tip resistance, sleeve friction resistance, strain, stress, displacements field as well as soil fabric around the cone.; This study confirmed that the cone resistance {dollar}qsb{lcub}c{rcub}{dollar} increases with increasing OCR up to a value equal to about 8. Boundary condition BC1 seems to represent the field condition more closely than BC3. The effect of initial fabric on the {dollar}qsb{lcub}c{rcub}{dollar} was found to be less significant compared to other effects such as the state of stress, density and stress history. The lateral stress measured from the region above cone tip was not sensitive to the lateral in-situ stress in different OCR specimens. These findings are confirmed by the previous experimental research. Complex strain fields were found around the cone and the soil dilation below the cone tip was observed in the simulations. The local failure around the cone tip in higher OCR specimens seems to reduce the {dollar}qsb{lcub}c{rcub}{dollar} value. This issue should be studied further. The magnitude of stress near the cone face was comparable with the {dollar}qsb{lcub}c{rcub}{dollar} value in various OCR specimens. Evaluation of stresses inside disks during penetration indicates a possibility of crushing of the fine particles during the penetration. The particle crushing will result in a lower {dollar}qsb{lcub}c{rcub}{dollar} value. The results of this study can be used for more accurate interpretation of CPT measurements and better understanding of cone penetration mechanism in granular soil. (Abstract shortened by UMI.)