MULTI-BLOCK UPPER BOUND METHOD FOR BASAL HEAVE STABILITY ANALYSIS OF BRACED EXCAVATIONS IN CLAY
QIN Huilai1，2，3，HUANG Maosong1，2，MA Shaokun4
(1. Department of Geotechnical Engineering，Tongji University，Shanghai 200092，China；2. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education，Tongji University，Shanghai 200092，China；3. Department of Geotechnical Engineering，China Institute of Water Resources and Hydropower Research，Beijing 100048，China；4. Guangxi University， Nanning，Guangxi 530004，China)
Abstract：Multi-block upper bound method is employed to analyze basal heave stability of braced excavations in undrained clay. For this purpose，the kinematically admissible multi-block failure mechanism is proposed firstly. Based on the proposed multi-block failure mechanism，the energy equation of the upper bound method is deduced again. To examine the application of the multi-block upper bound method in basal heave stability analysis，a lot of comparisons have been made with other existent solutions according to some true cases and the influential factors on the basal heave stability. These factors include the width of the foundation pit，the embedment of the hard stratum，the friction between the wall and soil，the insert depth of the wall and the strength nonhomogeneity. The existent solutions adopted include the upper bound solutions obtained by Terzaghi¢s mode and Prandtl¢s mode，and the Faheem¢s solutions obtained by the finite element method with strength reduction technique，and the Ukritchon¢s solutions obtained by the limit analysis finite element method. According to the comparisons，it can be found that the multi-block upper bound method gives the optimum solutions among the upper bound methods. It can also be found that the solutions given by the multi-block upper bound method are close to those obtained by the upper bound finite element method. It should be noted that the multi-block upper bound method is easy to program and needs less workload. Based on the calculations and comparisons，it may be found that the application of proposed multi-block upper bound method is successful.
