An empirical design method using Rock Mass Rating (RMR) and Slope Mass Rating (SMR) have been applied based on field observation and laboratories testing to assess the stability of rock mass and to design a rock slope. This procedure will be beneficial for gaining a better understanding of the influence of geological and rock strength parameters, and the mechanisms of rock failure. Field observations were carried out at five sections along the road way connecting Liwa–Krui, West Lampung, Sumatera, Indonesia, where some rock slope failures have occurred. Geologically, this area consists of andesitic (intrusion), volcanic breccias, and interbeded layers of sandstone and claystone. Tectonically this area has been strongly deformed and faulted by shearing forming complex geological structures. Rock core samples were drilled and tested in laboratory. The application of RMR and SMR system at the section LK-2 shows that the rock mass condition is fair, but it needs special care is required to ensure stability of the slope. The rock mass at three section LK-1, 4 and 5 indicated that the rock mass could be classified as good with recommended slope angle of between 65o–75o. Whereas the rock mass at section LK-3, could be classified as very good with recommended slope angle of between 75o- 89o. According to this classification system, the possible failure could be predicted and the supporting slopes could be estimated early in the life of the developing excavation.
The road connecting Liwa–Krui, West Lampung area, in which the study was carried out, includes the busiest road in West Lampung, Sumatra, Indonesia. Some short term measures at road section of Liwa–Krui, Km 9 to 12.5 have been taken by the Public Works Department to avoid the risk of rock failure during a road widening project.
