Evaluation method for self-weight collapsible deformation of large thickness loess foundation

The collapse deformation of loess is a key issue in foundation engineering. A large number of field water immersion test results and corresponding laboratory compression test ones are comparatively analyzed so as to investigate the relationship between the measured and computed collapses under overburden pressure. The test condition differences such as stress, water seepage, air seepage, stratigraphic texture and soil behavior between field and laboratory tests as well as different regions of test sites are considered. The results show that the correction factor of computed collapse under overburden pressure for loess in the western region of Liupan Mountains is 2.0, while in the eastern region of Liupan Mountains, the northern Shaanxi Province and the western Shanxi Province it is 1.7, in the Guanzhong Plain it is 1.2, and in other regions it is 0.4. The changing characteristics of the coefficient of collapsibility and the collapse deformation under overburden pressure and the stratigraphic texture with depth at a typical site are analyzed. Furthermore, the mean coefficients of collapsibility under overburden pressure of in-situ measurements within different depth ranges are compared with the corresponding weighted mean ones of laboratory measurements. It is seen that the weighted mean coefficients of collapsibility under overburden pressure for loess at depths of 0 to 10 m, 10 to 15 m, 15 to 20 m are 0.015, 0.020 and 0.025 respectively. The threshold coefficients of collapsibility under overburden pressure are determined when collapse deformation under overburden pressure occurs at loess site with large depths, which increase with depth. The in-situ collapse deformation of Q2 loess stratum under overburden pressure at different sites in Guanzhong Plain is commonly smaller than 7.0 cm. However, the collapsible loess under overburden pressure with a larger depth in this region is commonly Q₂ loess. Its averaged coefficient of collapsibility under overburden pressure at different sites is about 0.029, so the threshold coefficient of collapsibility for the Q₂ loess can be taken as 0.025.