Assessment of a rock planar slide along an expressway in Vietnam

Tóm tắt

This paper presents an assessment of a rock planar slide, which took place at km 108 along the Tien Yen-Mong Cai expressway, an extension of the Halong-Vandon expressway in Vietnam. Half of the expressway has been covered by a large volume of rock deposit after its movement. The height of the slope in this study is 16 m and its width is 200 m. The main head scarp is about 11 m high. The sliding angle of the failure surface is from 12÷150. The stratigraphy mostly consists of weathered jointed siltstone, which is located in the upper part of the Ha Coi formation (J1-2hc2). The sedimentary rocks are thick bedded, fine-grained sandstones interbedded with medium-bedded chocolate pink siltstones or thin-bedded shales. In general, they are medium to thick bedded with the thickness of rock layer from 0.3÷0.8 m. The upper rock layer is the 9b-1 layer with RQD = 0÷36% whereas the lower one is the 9b-2 layer with RQD = 0÷92%. The topsoil layer is 0.5÷2.5 m thick. Rockplane and Plaxis computer softwares were adopted to perform stability analysis of the slope. Results showed that the overall factor of safety of the slope before treatment is lower than 1.0, which is in good agreement with the instability of the slope. In order to apply the countermeasures, part of the slope will be first excavated with an angle of 450. Then, the prestressed ground anchor system will be installed. After treatment, the overall factor of safety of the slope was increased to larger than 1.30, which meets the requirement by the Vietnam code