CENTRIFUGE MODEL STUDY OF PILES SOCKETED IN SOFT ROCK

Abstract

The research reported herein is concerned with the centrifuge model testing of piles socketed in soft rocks having uniaxial strengths below 12 MPa. Gypsum cement was employed as the pseudo-rock to obtain the desirable range of rock strength. Aluminium tubing with a roughened surface having an equivalent structural stiffness as that of a solid concrete pile was used to simulate the piles. By comparing the centrifuge model test results with those obtained from conventional small-scale models, the latter will overpredict the ultimate unit shaft resistance as the magnitude of friction mobilized along the pile socket depends upon the confining pressure and lateral stiffness of surrounding rocks in the rock socket. In general, the shaft and base resistances obtained from the centrifuge test results agree with predictions from existing design methods whose formulations are derived from load tests on piles in the field. The second part of the research work is to examine the effect of weakness planes in the rock mass on pile capacity. It is noted that for piles having major weakness planes below their base, very little base resistance can be mobilized.