Abstract

This paper aims to assess rockfall susceptibility along the road leading to the Giants Castle Nature Reserve, in the northern Drakensberg, South Africa, which is a main attraction, for tourists due to immense natural beauty of the reserve area and the important rock art, found in the caves formed in Clarens formation sandstone. Rockfall susceptibility analysis involved mapping of rockfall accumulation zones, field surveying of boulders, rockfall run-out zones. The Oregon Rockfall Hazard Rating System (ORHS) provided the basis for initial screening of susceptible zones, ranked as high hazard segments. Preliminary, rockfall estimation of run out zones, was performed using CONEFALL, Quantera© and 2- dimensional analysis using Rockfall, Rocscience©, to study run out distance, bounce height, kinetic energy, and translational velocity. According to the results of the modelling, barriers in height 8–10 m with capacities ranging from 1,500 to 2,400 KJ are suggested as protective measures.

1 Introduction

Rock falls are classified as a form of rapid mass movement that commonly involves, the independent, movement of an individual rock fragment that was detached from an extruding bedrock surface. The movement of a rock fall is characterized by high energy, and high mobility indicating that even relatively small rock fragments can pose a substantial hazard (Evans & Hungr 1993). The rock fragment undergoes severe energy dissipation, as it interacts with the slope material, and this friction, between the two surfaces, results, in the rock fragment stopping at the base of the talus slope or in many cases further than the base (Evans & Hungr 1993). The process of a rock fragment becoming detached from an extruding bedrock surface can be divided into both geological factors and trigger mechanisms. The major geological factors controlling the detachment of a rock fragment from a bedrock surface include the general lithology, weathering degree and spacing as well as the orientation of discontinuities (Selby 1993, Dorren 2003). Rockfall trigger mechanisms refer to the process, which may initiate the movement of rock fragments. Rockfall protection approaches include quantitative hazard and rick assessment, as well as the design of structural countermeasures. Many analytical approaches are introduced to simulate rockfall trajectories. Providing highly reliable modeling inputs to rockfall protection remains a difficult task, because of the complexity and intrinsic stochastic nature of rockfall physics and the uncertainty of all relevant parameters. Employing probabilistic simulations has proven to be an effective and acceptable method for systematically handling the uncertainties. This paper aims to assess and analyse rockfall susceptibility along the main road leading to the Giants Castle Nature Reserve, in the northern Drakensberg, South Africa.

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