Abstract
In the geogenetic overburden excavation of underground space projects (such as comprehensive pipe corridors or subways), the foundation stress is in an unloading state. The effect(s) from the unloading on the coefficient of subsidence in the loess area should be considered. In this study, to explore the effect of unloading on the collapsibility of loess, the collapsible loess in the Guanzhong area was considered as the research object. An expression for the unloading collapse coefficient was established based on the unloading stress ratio, unloading collapse ratio, and other parameters. The influence of the unloading on the loess collapse coefficient was studied using an indoor collapsibility test, and the function form and parameters for the expression were determined. As combined with the field test, the accuracy of the expression for the unloading coefficient was verified based on the test value for the specific collapsibility, calculated value for the specific collapsibility, and calculated value for the unloading collapsibility.
Highlights
Unloading collapse coefficient δxsUnloading collapse coefficient is always smaller than the constant pressure collapse coefficient
Zhu et al [10] analyzed the influences of eight soil property indexes on the collapse coefficient and established a regression equation for the loess collapse coefficient and each influencing factor
Owing to the limitations of laboratory tests, field tests can simulate an actual project relatively well, and the test results are relatively reliable. erefore, many scholars have studied the collapsibility of collapsible loess through field experiments
Summary
Unloading collapse coefficient is always smaller than the constant pressure collapse coefficient. E unloading curve slope inflection point is taken as the unloading collapse limit point, and the corresponding pressure is the limit pressure If the collapse coefficient remains as 0.015, that is, as the limit for judging collapsibility, it can be found that the difference between the calculated initial pressure of the collapsibility and test value will not exceed 5%. Indoor tests were conducted to obtain the collapse coefficient. e unloading collapse coefficient and total collapsibility were calculated as shown in Tables 7 and 8, and the self-weight collapse coefficient and self-weight collapsibility were calculated as shown in Tables 9 and 10
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