Abstract As a result of excavation and unloading of foundation pit，the state of passive zone soil body in front of diaphragm wall was transformed from the normal consolidation to the overconsolidation. At the same time，the indexes of consolidated undrained triaxial shear test(CU) of cohesive soil will be changed，therefore，the calculational theory of elastic foundation beam could be modified. Based on the relationship among over- consolidation ratio(OCR)，undrained shear strength and overburden pressure，the relationship between undrained shear strength and CU indexes was introduced and a function used to solve the CU indexes of overconsolidated soil in condition of several layers was derived gradually. Then the function was applied to the “m” method calculation theory of elastic foundation beam. A new modified m value calculational method was set up which considers the effect of the overconsolidated cohesive soil in the passive zone after excavation and unloading step by step. The result of finite element calculation of Wuhan Yangtze River tunnel indicates that CU indexes and m value of each cohesive soil layer in a certain depth below the excavated surface both increase in different degrees with increasing of OCR value. In particular，the indexes and value in silt increase greatly. In addition，the displacement of diaphragm wall calculated by the new modified method was close to the actual measurement results.
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Received: 16 May 2009
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