The self-weight collapsible characteristics of loess in Xi'an urban area

Based on the results of 12 large loess test pits immersion tests and indoor collapsibility tests conducted during the construction process of Xi'an Rail Transit Engineering, the self-weight collapsible deformation characteristics of loess in Xi'an urban area were systematically studied. The results show that: 1) Within the urban area of Xi'an, the collapse of each landform unit, from strong to weak, is in the following order: Weibei Loess Plateau>Chanhe Tertiary Terrace>pluvial tableland>loess ridge and depressiona>Shaoling Plateau (Duling Plateau, Shenhe Plateau), and Weihe Tertiary Terrace. The self-weight collapsible loess site accounts for 50% of the total number of test sites, and the maximum depth of the self-weight collapsible bottom limit is 20m; The loess plateau in the southern part of the city is a non self-weight collapsible site, which is different from previous indoor experiments. 2) The deformation of the self-weight collapse occurs mainly in the Q3 loess layer. Based on immersion tests, the bottom boundary of self-weight collapse is mostly located in the Q3 ancient soil layer. Only Q2 losses in two sets of tests showed weak collapse. The uniform correction coefficient provided for in the current regulations for the Guanzhong region overestimates the collapsibility of Q2 losses. 3) Distinguishing between geomorphic units and sedimentary ages of strata, recommended values for self-weight collapsible deformation correction coefficients of loess in Xi'an urban area were provided. 4) The measured area of settlement diffusion due to loess immersion and collapse is typically related to the depth and amount of self-weight collapse. It usually does not exceed 1.0 times the radius of the test pit and 1.0 times the measured collapsible limit depth. This can serve as a boundary for water accumulation around the project. 5) The development process of loess collapsible deformation mainly includes five stages: rapid deformation, slow deformation, stable deformation, rapid deformation after water interruption, and stable deformation after water interruption. The larger the measured self-weight collapses, the greater the daily settlement rate during the sinking phase. The maximum consolidation settlement after water interruption is 95.1mm.