Research On Key Design Technique For Shallow Buried Tunnel Passing Through Expansive Soil In Hefei

At present, in the subway construction of our country some city’s subway has encountered expansive soil ground such as Nanning, Chengdu and Kunming and so on. There has an understanding defect of expansive soil engineering characteristics such as swell shrink characteristic and cranny property, and the expansive soil engineering characteristics vary in different region, then the code did not give the exactly design load of expansive tunnel, What’s more, expansive soil tunnel construction experience is insufficient. Because of above factor, tunnel collapse, lining spalling, bottom protrusion always happened in expansive soil tunnel.Therefore, it is of great significance to carry out the study on the design and construction technique of expansive soil tunnel in different region. The article based on the the shallow buried underground-cut section from the end of the test section of Hefei metro line 1 to YunGU road station, conducted the research as bellow:(1) Based on the fluid and thermal model of FLAC3D, get the distribution of water content by seepage calculation, then reduce the soil intensity parameter and apply additional expansive stress based on the water content, then put forward the seepage field-additional expansive stress field numerical method.(2) Based on the seepage field-additional expansive stress field numerical method and field measurement of ground settlement, confirmed the expansive soil tunnel failure model, modified the break angle and gave the critical buried depth of expansive soil tunnel, and analysed influence factors of additional expansive stress, based on above factors, the modified calculation method of the load of shallow-buried tunnel was put forward.(3) Analysed the stability of tunnel when take the leading ductule injecting, and confirmed the construction method by comparison of two construction method, finally the construction suggested values such as the excavation footage, double tunnel space and the distance of working face, was given.