Field investigation and numerical simulation on rockfalls in Zhangmu Town, Tibet, China

Zhangmu Town in Tibet of China, which lies in the southern piedmont of the median Himalayas, is a small but strategically important port of trade exchange between China and Nepal. Many rockfall events have occurred in Zhangmu since 1970, resulting in huge economic losses and serious influence on the bilateral trade. We conducted a detailed field investigation on the high and steep slope in Zhangmu Town, and analyzed the distribution features, stability, failure modes and evolution of dangerous rocks of potential rockfalls. Then we numerically simulated the movement path, velocity and accumulation forms of the rockfall with PFC 3D program. The results indicated that the dangerous rock belt could be divided into three sections, namely, unstable section, slightly stable section and basically stable section. It was estimated that the rock debris and single dangerous rock would be unstable in the case of earthquakes or rainstorms. Due to the terrain constraints, the fallen rocks would scatter near the mouth of the Zhangmu ditch and in the Buqu River through multiple times of rolling, collision-induced diversion and bouncing. Without reinforcement, the rockfall could cause serious damage to the car parks, gas stations and National Highway 318 along the line from Zhangmu Town to Zhangmu ditch. Based on the field survey and numerical simulation, we recommended rockfall removal and interception as the major prevention measures, and protective sheds as auxiliary measure.