# Impact of Rock Mass Strength Anisotropy with Depth on Slope Stability Under Excavation Disturbance
###### Abstract  
In open-pit excavations, overburden rock mass is disturbed by processes like blasting and mechanical excavation, leading to a reduction in mechanical properties. Accounting for this disturbance is essential for ensuring slope stability, optimizing costs, and maintaining feasibility. The Hoek-Brown failure criterion, a widely used empirical method in rock mechanics, incorporates the disturbance factor to reflect the reduction in rock mass strength after disturbance. This study reviews five approaches from the literature regarding the role of disturbance in rock mechanics, focusing on its impact on the factor of safety and the volume of rock mass above the potential failure surface. Additionally, an \"S\" shaped decay formulation was proposed as an alternative to existing equations. A key consideration is the transitional disturbance effect, which reflects the gradual change from a fully disturbed rock mass near the excavation surface to an undisturbed rock mass with increasing depth. Among the examined approaches, the \"S\" shaped decay equation, informed by insights from previous studies, appears to be the most realistic. One approach assumes the disturbance factor is highest at the surface due to the removal of blasted rock, leading to a fully disturbed rock mass in front of the excavation face. The disturbance then decreases with depth, transitioning to an undisturbed condition depending on the excavation method. Even when the rock mass is homogeneous and isotropic in joint properties, excavation induces anisotropy in mass strength, causing overall strength to increase with depth. This study also investigates the effect of anisotropic strength behavior resulting from the disturbance factor. For incorporating transitional disturbance in the design stage, both circular and combined failure mechanisms should be considered for a comprehensive understanding of slope stability. d 2020 2020  
samples can be prepared, the equipment to perform the related laboratory investigations is generally not commonly available in conventional rock mechanics laboratories. To overcome these difficulties, researchers have focused on empirical tools for designing engineering projects involving rock masses, especially after the early 1950s [1, 2, 3, 4, 5]. Due to the simple and ease accessible input parameters used in the [PERSON] and Brown empirical strength criterion, it has been preserved its popularity in rock mechanics since it was introduced to the rock mechanics literature in 1980. By their nature, empirical tools are continuously updated and modified by considering new data and new cases. Due to its openness to the improvement of the empirical tools, the disturbance factor ranging a value from undisturbed to completely disturbed rock mass condition was first introduced to the literature by [PERSON] and [PERSON] [6]. Their approach was subsequently adopted to the criterion by [PERSON] and co-authors as originators of the criterion who incorporated the disturbance factor into their criterion, with classification ranging from an undisturbed (D = 0) to a completely disturbed (D = 1) rock mass [4]. [PERSON] [7] offered a technical note outlining recommendations for selecting and applying the disturbance factor in various projects. The degree of disturbance naturally decreases to the undisturbed rock mass condition from the excavation surface to a certain depth depending on the excavation method. Due to difficulties in collecting real data, especially in terms of failed rock mass cases, there are few studies from the past to the present on the effects of transitional rock mass disturbance from surface to depth on the stability of slope excavation and the location of potential failure surfaces [8, 9, 10, 11, 12, 13, 14]. These studies have provided important contributions to the perspectives on the use of transitional rock mass disturbances.