Abstract
Aspect ratio and crack density are essential parameters to understand the physical properties of porous-cracked rocks, although it is difficult to independently determine each parameter, as both are closely linked. The objective of this study is to propose a relationship between aspect ratio and crack density that can be used to solve for each through experimental and optimization methods. Two different constitutive equations are solved to create expressions explicitly defining aspect ratio and crack density, with all remaining variables arranged as functions of elastic wave velocity. Ten core specimens extracted from construction sites, with diameters of 46 mm, are subjected to artificial weathering to identify how their crack density and aspect ratio evolved with time. The artificial weathering process consisted of chemical and physical weathering cycles using saline solution and slake durability tests, respectively. Compressional and shear wave velocities are measured at every weathering step, and both aspect ratio and crack density are calculated. The random forest as an optimization method is selected to define the important score among input variables. The calculated aspect ratios and crack densities are converted into a crack porosity, the reliability of which is verified through percentage of crack porosity (~6%) in total porosity. This study demonstrates that the relationship between aspect ratio and crack density is robust and has wide-ranging applications in determining individual aspect ratio and crack density parameters in porous-cracked rock.
Highlights
Rocks undergo a range of weathering processes driven by changing environmental factors, such as climate, temperature, and precipitation
A relationship between crack aspect ratio and crack density was derived through combination of several constitutive equations, and subsequently verified by matching predicted and observed results from weathering experiments
Various parameters included in two constitutive equations were rearranged and simplified to define elastic wave velocity, with aspect ratio and crack density as the main variables to be solved
Summary
Rocks undergo a range of weathering processes driven by changing environmental factors, such as climate, temperature, and precipitation. Pore water pressure is assumed constant in all directions As a result, this theory has limited applicability to heterogeneous materials that may contain many cracks. This theory has limited applicability to heterogeneous materials that may contain many cracks This theory was developed further to generate a new Biot-consistent theory that related explicitly to porous rocks, as shown in Figure 1 [22,23]. This Biot-consistent theory uses three dependent variables (stress, strain, and fluid pressure) to model a canonical medium in which porosity and crack density are isotropic. Equant porosity (φep ) and crack density (ε) are defined in terms of the shear modulus (G), as follows:
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