Determination of Shear Strength Modification Factors in Drilled Shaft

현장타설말뚝의 전단강도 조정계수 결정법

An experimental study is described in which a 305-mm-diameter instrumented drilled shaft was installed in a moderately expansive clay soil during the dry season and monitored over a period of about 18 months. The purpose of the study was In investigate the effects of seasonal moisture changes in the soil on the shear stresses imposed on the sides of the drilled shaft and movements of the shaft head. The soil in the vicinity of the test shaft was instrumented to measure suction and ground surface movement and the relation between suction, total stress and shear strength of the soil at the test site was determined through laboratory triaxial compression testing. Daily rainfall and temperatures were also monitored at the test site, the National Geotechnical Experimentation Site at the University of Houston, where control on surface grading and vegetation existed. Over the course of the study induced unit side shear values of up to 54 kPa were measured in the test shaft. A simple computational model was developed that related observed suction changes to unit side shear induced by the expansion of the soil through the use of the laboratory suction-total stress-shear strength relation.

팽창토에 설치된 직경 305 mm 현장타설말뚝의 18개월간에 걸친 거동을 관찰하였다. 계절적 함수량 변화에 따른 말뚝주변 흙의 부피 변화가 발생시킨 말뚝의 인발력을 측정하였고, 측정한 인발력에서 말뚝 단위 표면적당의 전단 응력을 계산하였다. 본 실험 말뚝에서는 최대 전단 응력은 54 kPa이 계산되었다.