EXCAVATION-INDUCED BEHAVIOR OF A RETAINING STRUCTURE USING DOUBLE-ROWED MICROPILES IN SOFT CLAY
YU Feng1，LIU Nianwu2，FANG Kai2
(1. School of Civil Engineering and Architecture，Zhejiang Sci-Tech University，Hangzhou，Zhejiang 310018，China； 2. Institute of Geotechnical Engineering，Zhejiang University，Hangzhou，Zhejiang 310058，China)
Abstract：Double-rowed micropiles，usually served as excavation-supporting structures，have advantages such as convenient construction and satisfying lateral stiffness. In order to provide better understanding of their field performance，we investigate a full-scale retaining structure with 88 micropiles arrayed in two rows. The structure is instrumented to measure the lateral displacement，earth pressure and pile stress during excavation. The field-test results and associated numerical analyses show that the displacement of pile shaft increases with the increasing excavation depth and the maximum displacement is captured near the excavation surface. A non-zero bending moment is recorded at the pile head and the excavation depth decides the magnitude and distribution of the bending moment. The earth pressure imposed on the back-row piles can be transferred to the front ones through the upper connecting beam and the soil between the two pile rows. As the excavation proceeds，the earth pressure between the two pile rows decreases gradually above the excavation surface but increases below the surface. The measured pressures lie between the results calculated by the volume-scaling factor method and the elastic foundation beam method. Furthermore，both the active earth pressure acted on the back-row piles and the passive pressure at the bottom of pit are related to the displacement of pile shafts. The measured passive earth pressure is in good agreement with the predicted value of the elastic foundation beam method.
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2013, Vol. 32 
