Abstract
An innovative method is proposed to prepare artificial columnar jointed rock masses (CJRM) with different columnar dip angles, and laboratory physical model tests are conducted to investigate anisotropic permeability and porosity characteristics of the prepared artificial CJRM. In the physical model experiment, permeability and porosity of artificial CJRM with different columnar dip angles is measured during three times cyclic loading and unloading of confinement pressure. Based on the results of the laboratory model tests, the Equivalent Continuum Media Model was applied to analyse anisotropic permeability of CJRM. The main conclusions are summarized as follows. In the first loading phase of confinement pressure, the impacts of confinement pressure on the anisotropic permeability of artificial CJRM, porosity, and the major and minor principle permeability coefficients (PPCs) are significant, while in the following stages of confinement pressure loading and unloading, the change of them is small, with stable value. Permeability of artificial CJRM gradually increases with rise of columnar dip angle, and the permeability anisotropy of artificial CJRM under low confinement pressure is higher than that under low confinement pressure.
Highlights
Columnar jointed rock masses (CJRM) as a type of jointed rock masses with distinct fractural structure that are developed due to the cooling shrinkage in the process of the overflow and eruption of volcanic lava are frequently encountered in civil and hydraulic engineering projects [1]
In order to avoid experimental errors that are caused by the discreteness of sample, three repetitive tests are conducted on artificial CJRM, and the average value of the three repetitive tests is taken as the final experimental results
Due to the existence of columnar joint structure, rock becomes easy to be compacted during the first-time loading of confinement pressure, and with unloading of confinement pressure, artificial CJRM keeps compacted status
Summary
Columnar jointed rock masses (CJRM) as a type of jointed rock masses with distinct fractural structure that are developed due to the cooling shrinkage in the process of the overflow and eruption of volcanic lava are frequently encountered in civil and hydraulic engineering projects [1]. Another problem which is the large discrepancy between hidden joints in natural CJRM causes the large discreteness of laboratory experimental results [11] Site experiments such as pumping tests and packer tests are often conducted by some researchers to investigate the permeability tensor of rock masses [12,13,14]. The investigation about the changing law of CJRM porosity during cyclic loading and unloading of confinement pressure is necessary to be conducted to explore the internal mechanism of anisotropic permeability variation of CJRM. En, based on the results of the physical model experiment, the anisotropic permeability and porosity change law of artificial CJRM during cyclic loading and unloading of confinement pressure is researched.
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