Abstract
Soil structure has significant influences on the mechanical behaviors of natural soils, although it is rarely considered in previous cavity expansion analyses. This paper presents an undrained elastoplastic solution for cylindrical cavity expansion in structured soils, considering the destructuration effects. Firstly, a structural ratio was defined to denote the degree of the initial structure, and the Structured Cam Clay (SCC) model was employed to describe the subsequent stress-induced destructuration, including the structure degradation and crushing. Secondly, combined with the large strain theory, the considered problem was formulated as a system of first-order differential equations, which can be solved in a simplified procedure with the introduced auxiliary variable. Finally, the significance and efficiency of the present solution was demonstrated by comparing with the previous solutions, and parametric studies were also conducted to investigate the effects of soil structure and destructuration on the cavity expansion process. The results show that the soil structure has pronounced effects on the mechanical behavior of structured soils around the cavity. For structured soils, a cavity pressure that is larger than the corresponding reconstituted soils when the cavity expands to the same radius is required, and the effective stresses first increase to a peak value before decreasing rapidly with soil structure degradation and crushing. The same final critical state is reached for soils with different degrees of the initial structure, which indicates that the soil structure is completely destroyed during the cavity expansion. With the increase of the destructuring index, the soil structure was destroyed more rapidly, and the stress release during the plastic deformation became more significant. Moreover, the present solution was applied in the jacking of a casing during the sand compact pile installation and in situ self-boring pressuremeter (SBPM) tests, which indicates that the present solution provides an effective theoretical tool for predicting the behavior of natural structured soils around the cavity.
Highlights
Cavity expansion theory provides a useful, accurate, and simple tool for modelling many complex geotechnical problems [1], such as the interpretation of the results of pressuremeter and cone penetration tests [2–4], the estimation of stress responses around installed piles [5–7], as well as the stability and deformation analyses for wellbore drilling and tunnel excavation [8–11]
The present solution was compared with the previous solutions both in reconstituted and structured soils [22,36]
For the problem of cylindrical cavity expansion in naturally structured soils, an undrained elastoplastic solution was presented by using the Structured Cam Clay (SCC) model of Carter and Liu [37]
Summary
Cavity expansion theory provides a useful, accurate, and simple tool for modelling many complex geotechnical problems [1], such as the interpretation of the results of pressuremeter and cone penetration tests [2–4], the estimation of stress responses around installed piles [5–7], as well as the stability and deformation analyses for wellbore drilling and tunnel excavation [8–11]. Sivasithamparam and Castro [31] extended their anisotropic solution [25] by incorporating the effects of structure on the soil behavior by updating the employed constitutive model from the S-CLAY1 [32] to the S-CLAY1S model [33] This solution is at the cost of complexity, though the better results can be obtained. The jacking of a casing during the sand compact pile installation and in situ self-boring pressuremeter (SBPM) tests were analyzed to illustrate the applicability of the present solution
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