The Experiment And Study On Resilience Character Of Unloading Foundation Pit

With the great development of urban construction, more and more deep and large foundation pits are applied to the construction of multi-story basement, underground stores and parks under high buildings, and the scale and depth become larger and larger. The application and development period of foundation pit is not long in our country, although some experience and theories are accumulated and summed, more theories and practice are needed to improve the practical Geotechnical Engineering.Heave of foundation pit base is studied by laboratory test in this article. Special undisturbed soil samples are collected from the construction field, loading and unloading processes are simulated by K₀ test in laboratory. The staged loading is imposed according to preconsolidation loading. Unloading is done by stage after a certain time of consolidation, the resilience value and corresponding lateral pressure are recorded during different loading. Unloading modulus and lateral pressure coefficients are gotten according to the relation between the unloading amount with resielence amount and lateral pressure amount. Critical effect depth and ultimate effect depth of unloading resilience are get by analyzing the relations between unloading ratio and lateral pressure coefficients, unloading ratio and resilience modulus, and lateral stress relaxation method. The relations between unloading ratio and lateral pressure coefficients, unloading ratio and resilience modulus are analyzed with regression method. The relation between stability time of resilence and pit depth is analyzed by using of the relation between unloading ratio and t₉₀. Finally, part of test parameter is applied in numerical calculation to analyze the unloading resilience value of pit bottom and mid-post pile, and the results of resilience value are analyzed and compared with the result of empirical formula calculation and measurement.Critical effect depth, high resilience zone, resilience modulus of part typical soil in Shanghai and the result of excavation should be done quickly at the last one-third part are get by test, Practicality of resilience modulus is proved by its application in numerical calculation, All of results can be applied to the design and construction in deep and large foundation pits.