# Impact of Rock Mass Strength Anisotropy with Depth on Slope Stability Under Excavation Disturbance
## 4 Slope Stability Evaluations of a Hypothetical Slope Model

Table 1: The assumed geomechanical properties of the limestone and mudstone rock masses (the values of m\({}_{\mathbf{i}}\) were selected from [PERSON]’s recommendations based on type of rock material). Figure 4: A view from an open pit mine slope benches of mudstone overlie a limestone rock mass (photo taken by [PERSON], 13 September 2022). In the first approach (AP1), the disturbance factors selected for the limestone and mudstone rock masses (D = 0.9 and D = 0.7, respectively) were applied to the entire rock mass. [PERSON] and [PERSON] [8] defined three rock mass groups after blasting, considering the degree of disturbance from the surface toward the depth, such as blasted rock, blast-damaged rock, and in situ rock. In the second approach (AP2), only the blast-damaged rock (disturbed rock mass condition, D = 0.9 and D = 0.7 for limestone and mudstone rock masses, respectively) overlying in situ rock (undisturbed rock mass condition, D = 0) was used in the hypothetical slope model. This choice is based on the researchers' suggestion that the blasted rock would be excavated and removed after blasting operations. These operations were considered to lie between \"large production blast, confined and with little or no control: T = 2 to 2.5 H\" and \"production blast with no control but blasting to a free face: T = 1 to 1.5 H\", according to [PERSON] and [PERSON]'s [8] recommendations. Therefore, the thickness of the blast-damaged (disturbed) limestone rock mass (T) remaining above the undisturbed rock mass after excavation of the blasted rock mass was evaluated as equal to 2 H. mass, T = 0.5 was preferred, considering the ease of excavation by ripper and/or digging. Accordingly, when a bench height equal to 10 m was considered, the T values for limestone and mudstone rock masses were determined to be 20 m and 5 m, respectively. The transitional disturbance of the rock mass proposed by [PERSON] et al. [10], which is the third approach (AP3), defines a fully disturbed rock mass condition (D = 1) to a depth of FDL and assumes that the disturbance effect attenuates to an undisturbed rock mass (D = 0) within a depth of UDL. While UDL is assumed to be equal to the height of the overall slope profile, FDL can be calculated as a percentage of the height of the overall slope profile based on the rock mass properties rated in the rock mass disturbance rating (DR) classification proposed by [PERSON] et al. [10]. The DR values for the limestone and mudstone rock masses were 15.5 and 7.5, respectively, according to the rock mass disturbance rating evaluation given in Table 2. While the UDL used was 100 m, considering the height of the overall slope profile, the FDL values for the limestone and mudstone rock masses were determined as 15.5 m and 7.5 m, respectively, by using the DR values and the height of the overall slope profile. The last approach used in this study was a modification of [PERSON] et al. 's [10] method  
Figure 5: Hypothetical slope model used in the slope stability evaluations. by [PERSON] et al. [14]. The D\({}_{\text{f}}\) values for the limestone and mudstone rock masses were 0.9 and 0.7, respectively, with the same thicknesses of disturbed rock masses (DfL) from the surface, 15.5 m for limestone and 7.5 m for mudstone, as determined by [PERSON] et al. [10]. As explained above, the value of k as a constant in the equations proposed by [PERSON] and [PERSON] [21] (AP5), and derived in this study (AP6), is used to control the shape of the decay curve. In AP6, while the k values for limestone and mudstone were determined by using the DFL, which is equal to 15.5 m and 7.5 m, respectively, the UDL was taken as 100 m, the same as with AP3 and AP4. The value of k in AP5 is considered to be 1 and 0.5 for limestone and mudstone after matching the curve, as much as possible, to the one used in AP6.