Experimental Research And Mechanism Analysis On Interaction Of Water And Earth Pressures In Deep Foundation Pit

Calculating the value of load on the bracing structure rationally is one of the key contents of designing the foundation pit, as well as the important premise of safety and investment rationality of foundation pit. Lateral loads on bracing structure of foundation pit mainly include earth pressure and water pressure, and some other loads that work as lateral pressure on bracing structure through soil mass, such as vertical loads of peripheral buildings, construction loads, and so on. Therefore the calculating of water and earth pressure is key to adoption of the value of loads on bracing structure of foundation pit. However, there is no consensus on the acknowledgement to it in academic and engineering circles, with drastic debate between estimating water and earth pressures separately and together. This problem relates to the suitability of classic earth pressure theories, the interaction mechanism of water and erath pressures, existence mode of pore water pressure in soil, rational adoption of strength index during water and earth pressures calculations, and so on. Consequently, it is a significant and practical issue to deeply understand the interaction mechanism of water and erath pressure and rationally adopt calculating method and strength index.Based on aboved backgrounds, starting with the microstructure nature of clay, this dissertation studies the micromechanics of action of water and earth together. Experiments on pore water pressure transfer of different clays were conducted. Water and earth pressures are under long-term spot monitoring integrated with real project. Non-linear distribution theory of earth pressure was studied based on horizontal layer element model and soil arching effect theory. A non-linear earth pressure mode which is capable of reflecting displacement-time effect was advanced. Test installation simulating excavation working condition was designed, and representative soil samples were selected for model experiments. Based on the above research, many factors affecting water and earth pressure on the foundation pit were analyzed systematically. Contrast studies on estimating water and earth pressures separately and together were conducted integrated with typical calculations, and the result of calculation and real values were compared to evaluate its rationality.The main research content consists of:1. The inquiry of the microstructure nature of clay and its effects on macroscopic project character, the formation character of pores in the soil, existence mode and mutual transformation mechanism of pore water, the statement that groundwater destroys and reconstructs the soil microstructure through changing its chemical field and seepage field, followed by effects on macroscopic project character of soil mass, and in turn the change of soil structure nature affect the existence mode and seepage character of pore water in the soil, the development of the concept and estimating formula of "critical density", through which to discriminate whether compact clay can transfer pore water pressure and the concept mode of transport mechanism of transport mechanism of weak bound water in the soil, the analysis of micro mechanism of "initial hydraulic grade", and the conclusion that clay related to existing foundation pit project can generally transfer pore water pressure based on the above studies.2. Pore water pressure transference on many influences by selecting different clays and sand soil was experimented. The test result shows that: the transference rule of pore water pressure in the soil is restrained by many factors, among which the soil type and its structurenature pose the most remarkable influence, and the earth moisture content, compaction rate, the magnitudes of coefficient of permeability and continuing pressure environment also pose marked influence on hysteresis of pore pressure and head loss. In a word, at present it is common in the foundation pit projects that the time for pore pressure transference and the head loss during the transference for different soil mass...