Study On Supporting Technique Of Expansive Soil Foundation Pit In Cheng Du

With the rapid economic development and urbanization, and lots of high buildings stands out. As there is a saying "great oaks grows from little acorns", the stability of foundation pit plays a decisive role in the engineering project. As one of the many designers and construction personnel in Chengdu, the author knows the issues about expansive soil are the main difficulty of engineering construction. Therefore, based on the research and summary on the relevant subjects, firstly the main properties and performance characteristics of Chengdu expansive soil are concluded; and then, stability analysis of pit slope using the limit equilibrium method are conducted and the safety factors are researched, including parameters sensitivity study, effect law of tension fracture and support effect at different locations; finally, based on examples of successful supporting engineering, comprehensive of security, economic and technological aspects, appropriate supporting technology are summed on different depths of expansive soil foundation. The main conclusions can be drawn as follows:(1) Parameters sensitivity analysis of expansive soil shows that, the main controlling factor of stability of slope are its height, cohesion of strength parameters has a greater impact. than friction angle:(2) Effect analysis of tension fracture shows that, with the development of fracture, it have different impact phases, which the depth affecting on the overall stability of pit slope can be used to decide the warning value, and the depth when slope have minimum safety factors can be used to decide the most unfavorable reference value:(3) Comparative analysis of supporting effect shows that, the base lock pin support design is the most economical way, the lower 1/3 of slope height is the most effective location and the higher 1/3 of slope height are not recommended to place the supporting;(4) Examples analysis of pit in depth of less than 5m shows that, the conjunction measures of anchor and sprayed stress relief grooves plus dwarf wall (foot wall height of not more than 0.5m) approach are suitable, the bolt (Soil nails) in clay layer should only consider setting barbs, not grouting;(5) Examples analysis of pit in depth of 5m～10m shows that, the supporting with unloading groove binding anchor spray heightening foot wall (foot wall height 0.5m～1.0m range) supporting manner, clay layer bolt (soil nails) only consider setting barbs, not grouting, are suitable when the clay layer is less than 5m and locating at the lower part of slope. Otherwise, it should adopt the measures of piles and shoring;(6) Examples analysis of pit in depth of more than 10m shows that, it is more appropriate to adopt the supporting of anchored piles.