Study On The Deformation Characteristics And The Support Parameters Designment Of The Deep Foundation Pit In WuliDun Station Of Wuhan Metro

Nowadays, the spring up of the deep foundation projects of the subway station is accompanied with the new wave of the subway constuction in china. Moreover, these deep foundation pits are usually located in the downtown which has a dense population, heavy traffic and complex underground cables. Therefore, it is very important to design a reasonable reinforcement system which can guarantee the safety of the foundation pit, controll the deformation and economize the construction cost.Based on the background of WuLiDun metro Station, the deformation characteristics of the deep foundation pit and variation of the internal force of the reinforcement system during the excavation are studied in this paper. Besides, the parameters of the reinforcement system is optimized and two probably related parameters is combined to analyze their effects on the deformation, which provides a new method in parametric design of reinforcement system. The main issues conducted in this thesis are listed as follows.1. The characteristics of deformation in deep foundation pit and the variation of internal force in reinforcement system during excavation are analyzed in this paper. The deformation of the deep foundation pit and internal force of supporting system both increase with the increase of excavation depth. At the same time, the maximum bending moment and the maximum horizontal displacement of the pile are always at the same point of the pile and this point moves down gradually during excavation.2. The effect of soil parameters on the deformation of the deep foundation pit is analyzed in this paper. The elastic modulus has a great impact on the horizontal displacement of the pile when it is relatively low, however, the effect turns very small when it increases to three times of the compression modulus. On the contrary, the poisson’s ratio of the soil has great effect on the horizontal displacement of the pile when it is relatively high, but the effect can be neglected when it is less than0.2.3. The effect of length (H), diameter (Φ) of the pile, stiffness (kes) and brace pre axial force (F) of the inner supporting system on the deformation of the deep foundation pit and the internal force of the reinforcement system are analyzed in this paper. There exists an effective length (Hel) of the pile. If the length of the pile is below Hel, the longer the pile is, the less the horizontal displacement is. Meanwhile, Hel has relation to diameter of the pile. The larger the diameter is, the shorter the Hel is. When the length is short, the bending moment of the pile will change obviously with the increase of the length of the pile. But the change (increase or decrease) of the bending moment depends on diameter of the pile. There is an effective stiffness (kes) of the inner supporting system. When the stiffness is below kes, the larger the stiffness is, the less the horizontal displacement and the lower the bending moment of the pile is. kes has nothing to do with the diameter of pile. The horizontal displacement and the bending moment of the pile will both decrease with the increase of the brace pre axial force of the inner support system in a certain range.4. Considering the interaction of length and diameter of the pile, diameter of the pile and stiffness of inner supporting system, this paper adopted orthogonal test to analyze and compare the influence of0, H, kes, F on the horizontal displacement and the bending moment of the pile. Taking the horizontal displacement, the bending moment of the pile and the cost for reinforcement as evaluation index, the optimal level of these factors is determined.