Determining the inclination angles of anchor bolts for sliding and toppling failures: a case study of İzmir, Türkiye

When anchors are installed along or close to discontinuity surfaces in a jointed rock slope, it is very difficult for them to bond to the rock mass. The correct orientation of rock anchors should be selected for precise design. Hence, using stereographic projection to reveal the geometrical relationships among the slope face, discontinuities, and anchor bolts is vital. In support measures, the inclination of the anchor bolt is affected by many factors, such as the feasibility and difficulty of construction. Therefore, it should be based on the analysis results of stereographic projection. This study aims to determine the most suitable anchor inclination angle based on geometrical information using stereographic projection techniques to provide the stability to excavation slopes. Remarkable stereographic projection images such as “an opened umbrella” and “an upside-down umbrella” for planar and toppling failures, respectively, were obtained. The most suitable anchor inclination angles for both planar and toppling failures were determined by investigating the largest acute angle between the discontinuity plane and the anchor bolt on the stereographic projection. Additionally, a computer program based on basic geometric relations was developed to determine the most suitable inclination angle for rock anchors installed perpendicular to the slope face. Using both stereographic projection techniques and computer software, the most suitable anchor inclination angles for planar slides and toppling failures were determined to be 17° and 11°, respectively. However, this method may not be reliable in determining the suitable inclination angle of rock anchors in highly fractured rock masses.