CASE STUDIES OF ROCK-SOCKETED PILES

摘要

This paper presents the results of load tests on a large number of instrumented bored piles socketed in sedimentary rocks and granite in Singapore. Many of these piles were load tested to at least 2.5 times the respective working load. The ultimate unit shaft friction values obtained in the rocks are correlated to the unconfined compressive strength of the rock by means of the rock socket adhesion factor. In cases where unconfmed compressive strength of the rocks is not available, the unconfined compressive strength is obtained indirectly from other rock parameters such as pressuremeter test data, standard penetration resistance values and point load strength values. Illustrative examples presented in this paper show that pressuremeter test can be a viable alternative to determine the strength of fractured rocks. For weak rock with unconfined compressive strength below 5 MPa, the measured adhesion factors agree reasonably well with those proposed by several existing design methods. For rocks with unconfined compressive strength above 5 MPa, the measured adhesion factors are considerably lower than those proposed by existing design methods. It is believed such rocks have been significantly weakened by chiselling during pile installation.