Abstract
Fractured rocks are a type of complex media that widely exist in various projects including energy, hydraulic, and underground space engineering, whose permeability properties are a hotspot in current rock mechanics domain. Aiming at investigating the seepage characteristics of the fracture surfaces in different rock strata, uniaxial compressive test and permeability test were performed on single-fracture homogenous and heterogeneous rocks. Specifically, rock’s physical and mechanical parameters were measured in uniaxial tests while the initial width of the single fracture was determined through CT scanning. In combination with test results and the calculation model of the displacement of single-fracture heterogeneous rock under triaxial stress condition, the calculation formula of the permeability coefficient of single-fracture heterogeneous rock was derived. Results show that hydraulic pressure in the fracture can affect the permeability coefficient of the fractured rock. Hydraulic fracturing effect occurred with the increase of hydraulic pressure in the fracture, which then generates slight normal deformations of the rock masses on both two sides of the fracture surface, decreases the contact area in the fracture, and leads to the increases of both fracture width and permeability coefficient. For single-fracture rock, the lithological properties of the rock masses on both two sides of the fracture surface impose significant effects on the permeability coefficient. Under same hydraulic pressure and confining pressure, the permeability coefficient of single-fracture coarse sandstone is greatest, followed by that of single-fracture heterogeneous rock, and finally by single-fracture fine sandstone. Theoretical calculation results agree well with the test results, suggesting that the derived theoretical formula can adequately describe the variation tendencies of permeability coefficient with confining pressure and hydraulic pressure in the fracture.
Highlights
Seepage in fractured rocks can significantly affect construction stability in underground engineering [1,2,3], foundation engineering [4, 5], and rock-soil bodies on side slopes [6,7,8]
Assuming Δdt denotes the overall displacement of the fractured rock, Δdf denotes the normal displacement of the fracture surface, and Δdr denotes the normal displacement of the rock, normal deformation of the fracture surface can be written as
As the applied normal stress exceeded 10 MPa, hydraulic pressure in the fracture was relatively smaller compared with normal stress and the gas width only equaled to the residual gap width; because of the existence of high confining pressure, normal deformation of the rock on both two sides of the fracture surface was fairly limited under the action of hydraulic pressure in the fracture, thereby leading to slightly varying fracture width
Summary
Seepage in fractured rocks can significantly affect construction stability in underground engineering [1,2,3], foundation engineering [4, 5], and rock-soil bodies on side slopes [6,7,8]. Under long-term seismic load, construction-induced disturbance, and temperature effect, original fractures develop steadily and rock is gradually cut into several structural surfaces by the fracture network [9,10,11]. Different rocks undergo different deformations because of the existence of the structural surfaces, and the formed structure surfaces act as main seepage channels of underground water. Permeability coefficient and permeability tensor are two main parameters that are widely sued for describing the permeability of fractured rocks [12,13,14], which are generally determined by theoretical calculation [15,16,17,18], field measurement [19], or laboratory test [20,21,22,23]. Natural fractures are coarse to varying degrees, whose widths always change under external loading, thereby inducing the change of permeability coefficient
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
