The Study On Cantilever Pile Optimal Design Of Expansive Soil Foundation Pit Slope

In recent years, with the emergence of a large number of deep foundation engineering, the stability of deep foundation pit of expansive soil is getting more attention. Deep foundation pit in the city construction has characteristics of limited slope space, strict deformation requirement and complex underground condition, besides, with the increase of excavation depth, side slope gradually shows the trend of deeper and steeper. At present, the support design of deep foundation pit of expansive soil basically follow the conventional soil design theory, consequently lead to the damage of engineering.The soil foundation pit engineering in Chengdu was taken as the research object. In the test section of cantilever pile, the inclinometer, steel stress meter and other monitoring element were embedded, and the data of pile, pile soil displacement and variation of stresses were obtained. On the basis of it, the reason of pit deformation and pile damage was analyzed. Besides, the model of expansive stress distribution applicable to this foundation pit was obtained according to the study of the relationship of expansibility with percentage of moisture and the expansive stress increment, as well as referring to different expansion force model. Under three conditions of not considering the rainfall, considering the rainfall without the expansion force, and considering the rainfall with the expansion force, the foundation pit model was established and simulated by using FLAC 3D software to verify the feasibility of the proposed expansion force model. In addition, the factor of cantilever pile’s length, diameter and distance was simulated numerically to analyze the influence of pile parameters on the stability of the foundation pit, and optimize pile parameter on the basis of the simulation result.The following conclusions were obtained through the above analysis. In the support of foundation pit, the expansive soil can’t meet the requirement under the rainfall condition in accordance with conventional soil. To simulate foundation pit under different conditions by using numerical simulation software, it can know that the expansion force model proposed in this paper can applied to the foundation pit engineering. It shows that the expansive force can’t be ignored in the design of foundation. The parameters of pile suitable for the foundation pit can be obtained by optimizing the length, diameter and distance of cantilever pile with the numerical simulation software. The expansion force model established in this paper was loaded into the Lizheng design software to simulate, and then compared with the result of the numerical simulation software. Finally, it showed that the model has good practicability.