Slope mass rating-based analysis to assess rockfall hazard on Yogyakarta Southern Mountain, Indonesia

Karlina Triana,Koko Hermawan

doi:10.1186/s40677-020-00164-w

Abstract

In the Parangtritis Beach tourism area located in the Southern Mountain of Yogyakarta, karst hills were excavated to build the main accessing road and produce some of long and very steep slopes along the sides of the road. But still, there was none of the slope reinforcement installed along the road. Meanwhile, at several nearby locations within Southern Mountain, rockfall incidents have occurred many times even caused casualties. The potential of rockfall hazard also could be found in the main road of Parangtritis Beach as the study area. The purpose of this study is to determine the rockfall hazard assessment along the main road using Slope Mass Rating (SMR) analysis with the additional parameter of the slope height and the rock block size. The necessary data obtained by direct measurement and laboratory test. Geomechanics analysis, stereographic projection analysis, and hazard parameters weighting were carried out to produce the Rockfall Hazard Zonation Map of the study area. Based on 17 measurement stations, there are 4 (four) rockfall hazard classes in the study area, i.e., very low, low, moderate, and high. The class of very low, which also included road segments without slope, has the largest percentages of 83.83%, followed by the classes of moderate, low, and high with the percentage of 7.16%, 4.28%, and 4,19%, respectively. SMR was assumed as the most significant parameter that influences the rockfall hazard zonation. Historical rockfall points were overlaid over the Rockfall Hazard Zonation Map to validate the predicted hazard zones. Since 91.23% of the rockfall occurred in the moderate and high hazard classes, the zonation map considered reliable to predict future rockfall. This study also identified several landslide potential zones and provides the recommendation of slope reinforcement to be installed in the study area.

Highlights

Rockfall is one type of mass movement that occurred in the form of rock lumps collapsed from a slope and happens quickly both vertically and sub-vertically (Budetta 2004; Goodman 1989)
Geological setting The study area is included in a series of Southern Mountains hills along the west to the east of the south coast of Java, and the northern part of the area is encountered by a lowland known as Solo Lane
Geological structures founded on the Geology Map of Yogyakarta sheet (Rahardjo et al 1977) are joints, faults, and folds

Summary

Introduction

Rockfall is one type of mass movement that occurred in the form of rock lumps collapsed from a slope and happens quickly both vertically and sub-vertically (Budetta 2004; Goodman 1989). The rockfall incidents have occurred several times in Yogyakarta. Hizbaron et al (2010) have identified 16 rockfall events that occurred in 1970–2009 in Yogyakarta and Triana and Hermawan Geoenvironmental Disasters (2020) 7:24 discovered that the high vulnerability area of rockfall was located along the transportation route. A rockfall incident occurred in 2011 on Yogyakarta Southern Mountain hills that fell into settlements and caused casualties (Mustopo 2015). The rockfall incident occurred again in 2015 on Sadranan Beach and caused fatalities (Jatmikotomo et al 2015). Located within the Southern Mountain hills area, Parangtritis Road as the study area of this present study surely cannot get away from this dangerous threat of rockfall

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