# Impact of Rock Mass Strength Anisotropy with Depth on Slope Stability Under Excavation Disturbance
## 6 Conclusions  
The disturbance factor, introduced by [PERSON] and [PERSON] [6], was incorporated into the Hoek-Brown failure criterion, which is commonly used to assess the strength of jointed rock masses under an excavation-induced disturbance. This factor was subsequently similarly adopted by the original developers of the criterion. However, there remains some uncertainty about the application of the disturbance factor, particularly in deep slope excavations, and only a limited number of suggestions are available in the literature regarding its use. In addition to the five approaches from the literature, a new decay formulation is proposed in this study. Initially, the six approaches mentioned in the literature were applied to a hypothetical slope model, and the results were discussed in terms of slope stability and the volume of rock mass above the potential failure surface. As expected, different factors of safety were obtained from each approach considered in this study. However, the use of a single disturbance factor in AP1 for the entire rock mass, from the surface to depth, can be viewed as an indirect conservative contributor to the factor of safety. Furthermore, as a simple assumption, [PERSON] and [PERSON] [8] divide in situ rock masses into three groups, disregarding the transitional disturbance effects. Their proposal for assessing the possible thickness of disturbed rock mass zones appears to be both reliable and practical for application. Conceptually, the approach proposed by [PERSON] et al. [10] is the first applicable method due to its use of a transitional disturbance zone that extends from the surface to the in situ (undisturbed) rock mass. However, a zone of completely disturbed rock mass (D = 1) at the surface overlies a transitional disturbance zone, which eventually leads to the in situ (undisturbed) rock mass (D = 0). As noted by [PERSON] and [PERSON] [8], the completely disturbed rock mass zone can be removed through excavation. It appears that the completely disturbed rock mass zone will be removed during the excavation of benches. Additionally, [PERSON] and [PERSON] [6] preferred using the completely disturbed rock mass condition (D = 1) to define the strength of dump rock masses, such as spoil piles, due to the nearly cohesionless shear failure envelope derived from the Hoek-Brown criterion. The fourth approach, which is a minor improvement to [PERSON] et al. 's [10] approach by combining it with [PERSON] and [PERSON]'s [8] approach, seems more acceptable than AP1, AP2, and AP3. This is because [PERSON] et al. [14] considered D = Df at the surface, reflecting the removal of blasted rock (fully disturbed rock mass) during excavation in front of the blasted damaged rock. On the other hand, AP5 ([PERSON] and [PERSON] [21]) and AP6 (this study) consider continuous decay equations extending from the surface of the slope to the undisturbed depth limit (UDL). Therefore, conceptually, both AP5 and AP6 are better able to represent on-site conditions. AP6 has an advantage due to the use of DfL for determining the extremum point, which satisfies the yielded rock mass of approximately 90% \(\pm\) 5, consistent with the southeast wall of the HVC Lornex Pit and the northeast of the HVC Valley Pit cases studied by [PERSON] et al. [10]. The impact of rock mass strength anisotropy with a depth on slope stability under an excavation disturbance was analyzed using a combined failure surface approach. The results of the slope stability analysis indicate that the overall stability can be influenced by both circular and elliptical failure surfaces, owing to the anisotropic nature of rock mass strength under excavation disturbances. As a result, both circular and combined failure surface analyses should be conducted in stability evaluations to more accurately assess the depth of potential failure surfaces. Geology can be complex in nature and, as noted by [PERSON] [11], substantial spatial variability may significantly affect the factor of safety and the design of slopes.