3D finite elements analysis of vertically loaded composite piled raft

Abstract

In recent years, a new type of foundation named composite piled raft foundation (also called long-short composite piled raft) has been developed. Where designing shallow foundations would mean unacceptable settlement, or other environmental risks exist which could impair the structure in the future, composite piled raft foundations could be used. Finite element method was applied to study the behavior of this type of foundation subjected to vertical loading. In order to determine an optimal pile arrangement pattern which yields the minimum settlement, various pile arrangements under different vertical stress levels were investigated. Results show that with increasing the vertical stress on the raft, the effectiveness of the arrangements of short and long piles become more visible. In addition, a new factor named “composite piled raft efficiency” (CPRE) has been defined which determines the efficiency of long-short piles arrangement in a composite piled raft foundation. This factor will increase when short piles take more axial stresses and long piles take less axial stresses. In addition, it is found that the changes in settlements for different long-short piles arrangement are in a well agreement with changes in values of CPRE ratio. Thus, CPRE ratio can be used as a factor to determine the efficiency of piles arrangements in composite piled raft foundation from the view point of reducing raft settlements.

Keywords

composite piled raft / settlement / composite piled raft efficiency / long-short pile arrangement / cushion

References

[1] PoulosH. Pile raft foundations: Design and applications [J]. Geotechnique, 2001, 51(2): 95-113

[2] DavisE, PoulosH. The analysis of piled raft systems [J]. Australia Geotechnique Journal, 197221-27

[3] BurlandJ, BromsB. Behavior of foundations and structures [C]. Proceeding 13th International Conference on Soil Mechanics and Foundation Engineering. Tokyo, 1977495-546

[4] CookeR. Piled raft foundation on stiff clays-A contribution to design philosophy [J]. Geotechnique, 1986, 36(2): 169-203

[5] ChowY, ThevendranV. Optimisation of pile groups [J]. Computers and Geotechnics, 1987, 4(1): 43-58

[6] RandolphM. Design methods of pile group and piled rafts: State-of-the-art report [C]. Proceeding 13th International Conference on soil Mechanics and Foundation Engineering. New Delhi, 199461-82

[7] HorikoshiK, RandolphM. Centrifuge modeling of piled raft foundation on clay [J]. Geotechnique, 1996, 46(4): 741-752

[8] TaL, SmallJ. Analysis of piled raft systems in layered soils [J]. International Journal for Numerical and Analytical Method in Geomechanics, 1996, 20(1): 57-72

[9] KimK, LeeS. Optimal pile arrangement for minimizing differential settlements in piled raft foundation [J]. Computers and Geotechnics, 2001, 28(2): 235-253

[10] ShahuJ, MadhavM, HayashiS. Analysis of soft ground-granular pile-granular mat system [J]. Computers and Geotechnics, 2001, 27(1): 45-62

[11] ZhaoM, ZhangL, YangM. Settlement calculation for long-short piled raft foundation [J]. Journal of Central South University of Technology, 2006, 13(6): 749-754

[12] LiangF, ChenL, ShiX. Numerical analysis of composite piled raft with cushion subjected to vertical load [J]. Computers and Geotechnics, 2003, 30(6): 443-453

[13] LiangF, ChenL, HanJ. Integral equation method for analysis of piled rafts with dissimilar piles under vertical loading [J]. Computers and Geotechnics, 2009, 36(3): 419-426

[14] WangX Z, ZhengJ J, YinJ H. On composite foundation with different vertical reinforcing elements under vertical loading: A physical model testing study [J]. Journal of Zhejiang University: Science A (Applied Physics & Engineering), 2010, 11(2): 80-87

[15] ZhengJ, AbushararS W, WangX. Three-dimensional nonlinear finite element modelling of composite foundation formed by CGF-lime piles [J]. Computers and Geotechnics, 2008, 35(4): 637-643