Development of Three-Dimensional Finite Difference Analysis for Piled Raft Foundation under Vertical Loads

• Main Authors: Hsin-Wei Lien, 連心維
• Other Authors: Der-Wen Chang
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/b6ypv6

碩士 === 淡江大學 === 土木工程學系碩士班 === 106 === This study suggests a simplified computer-based program WEAPR-S (Wave Equation Analysis for Piled Raft foundation-Statics) to analyze the settlements of piled raft foundations subjected to vertical loads. This program is based on finite-difference solutions on two-dimensional deformations of the raft and one-dimensional deformations of the piles. Soil springs underneath the raft can be modeled by the axial stiffness of a rod or the Lysmer’s analog model. Equivalent stiffness of the pile-soil elements can be computed first and incorporated into the analysis. Validation of the proposed program was conducted with the 3D FEM analysis using Midas-GTS NX program. The effects of the structural and soil parameters in design were discussed for the applicability of such analysis. The study reveals that: 1. By using the rod stiffness for the soils underneath the raft and with appropriate area of the soils along foundation edge and optimal length of the rod, rational results can be obtained. 2. The optimal length used for the rod stiffness is dependent of the shear wave velocity of the soil. They are suggested in this study. 3. With the Lysmer’s analog model, the settlements at the center and the edge were found similar to FEM results, however the ones computed at the corner were much less than the FEM solution.4. The equivalent stiffness of the pile-soil elements using simplified models were found compatible with other models. 5. By using the Lysmer’s analog model, total area of the foundation must be counted before averaging. The soil stiffness needs to be modified to yield rational results. 6. Effects of the pile length, soil stiffness can be found rational by using the proposed analysis, however the effects of S/D were found incompatible to FEM solutions. This is due to the pile-to-pile interaction which needs to be examined more carefully in further studies.