Geology and Slope Stability Analysis using Markland Method on Road Segment of Piyungan – Patuk, Sleman and Gunungkidul Regencies, Yogyakarta Special Region, Indonesia

摘要

Road segment of Piyungan - Patuk is a part of Yogyakarta - Wonosari highway, fairly dense traversed byvehicles, from bicycles to buses and trucks. This road crosses hilly topography, causing its sides bounded by quite steepslopes or cliffs. Steep slopes and cliffs are potential to create mass movement. Geologic condition of the surroundingarea is built of various volcanic lithology such as breccia, siltstone, sandstone and tuff. There are also geologicstructures of joints and faults that affect the stability of the slopes around this road. Slope stability analysis for roadsegment of Piyungan – Patuk was conducted by applying Markland method. Laboratory testings were done todetermine the mechanical and physical properties of rocks that influence the slope strength. Results of the testings showthat cohesion and friction angle of volcanic breccia are c = 20.0441 kg/cm2 and f = 56.38?; cohesion and friction angleof sandstone are cr = 0.6862 kg/cm2, cp = 4.6037 kg/cm2, fr = 26.37?, and fp = 32.79?; cohesion and friction angle oftuff is cr = 1.677 kg/cm2, cp = 7.5553 kg/cm2, fr = 17.85?, and fp = 24.19?. Based on the analysis, some slopes in thestudy area are potential to move. The movements can be classified into rock fall, debris fall, and rock slides with thesliding plane categorized as planar and wedge. On the other hand, landslide prone zones in the study area can bedivided into: Areas with high vulnerability, Areas with moderate vulnerability, and Areas with low vulnerability. Areasprone to landslide should be managed by a series of measures, among others understand natural phenomena,recognizing symptoms of avalanche, attempting to reduce the risk, and land use regulation. The management activitiesshould involve all stakeholders in an integrated manner of implementation.