The Group Effect on Negative Skin Friction on Piles

Abstract

When piles are constructed in consolidating ground, negative skin friction (NSF) is induced as a result of the downward movement of the soil relative to the pile. Model tests on negative skin friction on pile groups in sand were designed and conducted. Pile stress, pile top displacement and layered settlement of soil were tested under different kinds of surcharge load. The results indicate that when surrounding load increases from 20kPa to 120kPa, the neutral plane of the single pile varies from 0.8 L (length of pile in sand) to 0.95 L. Pile head settlement and negative skin friction under side load were smaller compared with the results of the test under surrounding load, while the location of neutral plane was higher. NSF and neutral plane depth increase sequentially in order of interior pile, interior-perimeter pile, corner-perimeter pile and corner pile for the pile group under side load. Based on the test results, the group effect is not obvious when pile spacing reaches 5 times pile diameter.