砂岩依時性力學特性研究及應用
Date Issued
2005
Date
2005
Author(s)
蔡立盛
DOI
zh-TW
Abstract
Due to a special geological background in Taiwan, several unsuccessful cases, concerned with tunneling through special strata, had been occurred. Calamities, induced by severe squeezing and raveling, were encountered during tunnel construction, and it increases the cost and the construction time of the project. Base on the previous study, squeezing problem may be caused by the following mechanics characteristic of sandstones, including wetting deterioration, shear dilation, and significant creep behavior.
In order to evaluate the immediately and time-dependent deformational characteristics of Sandstone, five kinds of sandstone in western Taiwan were selected as experimental materials in this research. A series of hydrostatic and triaxial compressive tests were performed through pure shear stress path loading to distinguish deformation resulted from pure hydrostatic stress or pure shear stress. Especially in triaxial compressive test, the creep test was performed as well by following a step-wise loading procedure. Afterward the measured deformations were decomposed into elastic and irreversible, included plastic and creep part, components. In addition, further discussions on the relation between yield surface, plastic potential surface and viscoplastic potential surface were conducted. The results indicate that, (1) similar to other soil-like geo-materials, the sandstone has plastic and viscoplastic strain before the stress path reaching the failure envelope, and significant volumetric dilation is induced especially when stress path approaching the failure envelope; (2) apparent coupling behavior exists volumetric strain not only relates to shear stress but also involved in volumetric stress; (3) similar direction exists between plastic flow and viscoplastic flow; (4) base on irreversible stress work theory, the behavior of sandstone is satisfied with the associate flow rule, e.g. the yield surface ,plastic potential surface and viscoplastic potential surface are all the same one.
According to the test results, an elastic/viscoplastic constitutive model is proposed, and it comprises nonlinear elastic deformation, related to Hyperelastic model, and viscoplastic deformation, modified from Cristescu (1994). After comparing the experimental results with the predictions, it is shown that the proposed model reveals well the elastic, plastic and creep behaviors of sandstone under hydrostatic and triaxial loadings.
Given the distinct deformation behavior of sandston, especially shear dilation, influences of such behavior on the tunnel sidewall deformation was assessed by numerical analysis using finite element code. The numerical analysis indicates that the tunnel leads to a greatest inward displacement, which is resulted from the shear dilation prior to failure state.
Subjects
砂岩
塑性
黏塑性
sandstone
plastic
viscoplastic
Type
thesis
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