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对于地铁车站、地下管道沟槽等狭窄基坑,其被动区土体宽度有限,不满足半无限体的假定,采用经典的库仑、朗肯土压力理论计算挡墙被动土压力是不合适的。首先建立了无黏性土中狭窄基坑刚性挡墙的有限元分析模型,研究了挡墙相对平移时不同宽度土体的被动滑裂面的分布规律;借鉴库仑平面土楔假定,建立了狭窄基坑刚性平动挡墙被动土压力的理论计算模型,推导了被动极限状态下滑裂面倾角及被动土压力系数的解析公式;再采用水平薄层单元法,得到了被动土压力分布、土压力合力作用点高度的理论公式。结合算例,深入研究了这种工程背景下挡墙被动滑裂面倾角的影响因素,以及被动土压力合力、土压力分布及合力作用点位置与经典库仑土压力理论的差别,与数值计算结果的对比验证了该理论方法的合理性。研究发现,当被动区土体宽度小于满足半无限体的临界值、且墙土摩擦角大于0时,被动滑裂面倾角大于传统库仑被动滑裂面倾角,被动土压力大于经典库仑解,合力作用点高度则小于库仑解,且基坑越窄,墙土摩擦角越大,其差别越大。
For the narrow foundation pit such as metro station and underground pipe trench, the passive earth pressure is limited and does not satisfy the assumption of semi-infinite body. It is unsuitable to calculate the passive earth pressure of retaining wall by the classical Coulomb and Rankine earth pressure theory. Firstly, the finite element analysis model of the rigid retaining wall of the non-cohesive soil is established, and the distribution of the passive slip surface of soils with different widths is studied. The Coulomb flat earth wedge hypothesis is used to establish the stenosis The theoretical calculation model of the passive earth pressure of the rigid translation retaining wall in the foundation pit is deduced, and the analytic formula of the slip angle and the passive earth pressure coefficient under the passive limit state is deduced. Using the horizontal thin-layer element method, the passive earth pressure distribution, the earth pressure The theoretical formula of the point of joint force. Combined with an example, the influencing factors of passive slip surface slip angle of retaining wall under such engineering background and the differences between passive earth pressure force distribution, earth pressure distribution and the location of the resultant force and the classical Coulomb earth pressure theory are studied. The numerical results The comparison verifies the rationality of the theoretical method. It is found that when the width of passive soil is less than the critical value of semi-infinite body and the friction angle of wall soil is greater than 0, the dip of passive slip plane is larger than that of traditional Coulomb passive slip plane. The passive earth pressure is larger than classical Coulomb solution, The action point height is less than the Coulomb solution, and the more narrow foundation pit, the greater the friction angle of the wall soil, the greater the difference.