Stability analysis of expansive soil landslide based on homogenization theory and upper limit analysis

Under the forces of expansive soil and landslides, the construction of the tunnel entrance is more likely to cause engineering disasters, such as surface cracking and landslides. The application of micro piles in the tunnel has advantages over anti slide piles. Based on the homogenization theory and upper limit analysis, this study calculates the stability of expansive soil landslide at the entrance of an expressway tunnel, and evaluates the treatment effect of different combinations of micro pile groups and cutting-unloading. In the calculation, to improve the calculation efficiency, the micro pile groups and soil around the piles are equivalent to the plus solid conforming to the Mohr-Coulomb strength criterion based on the homogenization theory. the results then are verified by monitoring the landslide deformation after the cutting and micro pile group reinforcement treatment in the field. This study indicates that compared with the strength parameters of soil, the internal friction angle of equivalent reinforcement remains constant, and the cohesion increases from 26 kPa to 85.36 kPa. The evaluated landslide stability before and after treatment show that the sliding surface of the landslide extends from the rock-soil interface above the landslide to the front of the tunnel portal without treatment; when only using micro pile group reinforcement, the landslide safety factor is about 1.17, and the sliding surface extends from the rock-soil interface to the tunnel portal; when only using both micro pile group reinforcement and cutting-unloading, the safety factor increases from 1.26 to 1.28, and the upper edge of the sliding surface moves forward from the rock-soil interface. The field deformation monitoring shows that the deformation of surface and deep soil are less than 3 mm, which can keep the landslide stable, and also verifies the effectiveness of the calculation method. This study provides beneficial information for similar projects.