大厚度自重湿陷黄土湿陷变形评价方法的研究

黄土湿陷变形是地基工程的关键问题。依据大量的现场试坑浸水试验和室内湿陷性试验结果,区分不同黄土地区,分析了场地浸水自重湿陷变形实测值与计算值之间的关系,表明陇西地区、陇东—陕北—晋西地区、关中地区和其他地区自重湿陷变形计算值的修正系数分别为2.0,1.7,1.2,0.4。依据典型场地黄土自重湿陷系数、自重湿陷变形、地层结构随深度的变化特征,通过现场试验实测不同埋深黄土自重湿陷变形的平均自重湿陷系数与室内试验测试自重湿陷系数的加权平均值之间的关系,揭示0~10 m,10~15 m,15~20 m不同埋深范围黄土原位浸水产生自重湿陷变形时,对应的室内试验自重湿陷系数的加权平均值依次为0.015,0.020,0.025,确定了大厚度自重湿陷性黄土的自重湿陷系数起始门槛值。关中地区不同场地Q2黄土的自重湿陷变形实测值一般小于7.0 cm。该地区不同场地Q2黄土的自重湿陷系数的均值约为0.029,其自重湿陷系数的起始门槛值可取0.025。

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.