The Research For Lateral Pressure Of Expansive Soil Deep Foundation Pit Slope

Expansive soil is mainly composed of strong hydrophilic clay minerals (such as montmorillonite, illite and kaolinite).It is high plastic clay with the special expansion structure, and a strong swell-shrink, multi fissure and strength attenuation characteristics Through the investigation of the swelling soil foundation pit in Chengdu area, after the rainfall, the foundation ditch will appear deformation or big cracks, due to rainfall and water seepage of pipeline. The expansive force is the main reason leading to the loss of stability of foundation pit. However, in the relative standards about the expansive soil, there is no clear regulation about the lateral pressure distribution. It is unable to consider the effect of expansion force in the supporting design, resulting in foundation pit support design can not meet the engineering requirement. This paper focuses on the research of the lateral pressure of expansive soil foundation pit slope, which aims to explore the influence of swelling force on lateral pressure, and provides the basis for the design of supporting structure. The article’s main research contents and conclusions are as follows:(1) Combined with the relevant literature of expansive soil and the swelling stress, using the knowledge of unsaturated soil mechanics and thermodynamic, expansion stress calculation formula is derived, △Pπ= k1n(?). With the water content curve changing with depth in soil, analysis of the expansive stress distribution in the semi infinite space is feasible.(2) The expansive soil slope is divided into areas, combined with the humidity field theory, the moisture distribution in expansive soil foundation pit slope is discussed. The expansive stress changing with depth in expansive soil slope is nearly irregular trapezoid.(3) Using Mohr-Kulun strength theory and the limit equilibrium condition. Considering the effect of expansive stress, active earth pressure and passive earth pressure formula is derived. Respectively,(4) Taking the foundation pit project in longtansi for example, using the calculation method in this paper, the expansive stress and lateral pressure of the slope is obtained. The results prove that the expansive force has great influence on the lateral pressure of slope. In supporting design calculations, if considering the expansive force, the displacement at the top of pit, the displacement at the bottom of pit and the embedded depth are larger, therefore the expansive force should be considered.