Quaternary fault activity and engineering effects along the Peikucuo-Gilong segment of the China-Nepal railway

Abstract

The project site of the China-Nepal railway is just located on the tectonic boundary zone where the Indian plate collides with the Eurasian plate. The active faults and their engineering influences have become the important problems faced by the railway route selection design of the China-Nepal Railway. In particular, the Peikucuo-Gilong segment not only crosses the active rift with complex north-south trending active faults system, but also includes the Malashan crossing section, facing relatively complex engineering geological problems related to the active faults. Through remote sensing interpretation, field survey, paleoseismic research, and quantitative limit of fault slip rate, we found that the railway route selection and design of the Peikucuo-Gilong segment mainly involves 6 nearly north-south trending normal faults with obvious differences in activity age and activity intensity in the southern section of the Pekucuo-Cuoqin rift valley. Among these faults, the Gangpengqing fault zone belongs to the the Holocene active fault, which is the most important active fault affecting the railway route selection and design. Paleoseismic research and quantitative analysis of the faults activity rate further indicate that the frequency of large earthquakes in the Gangpengqing fault is relatively low. The recent early and late paleoseismic events occurred before about （11050 ± 30） a B.P. and between about （4950 ± 30） a B.P. and （4800 ± 30） a B.P., respectively, with a recurrence interval of more than 6000 years. The average vertical activity rate since the Late Pleistocene should be between 0.14 and 0.31 mm/a, which limits that if a surface dislocation occurs during the engineering life of the fault, and the vertical dislocation amplitude should be between 0.7 and 1.6 m. Based on the evaluation results of the active faults and its engineering impact in the Peikucuo-Gilong segment of the China-Nepal railway, it is considered that the engineering route selection and design of the Malashan crossing section in this area can be compared and selected from two different schemes of the tunnel straight through the southern Peiku Tso and the north way through the Mulincuo graben. At the same time, attention should be paid to the possible uneven ground settlement when the subgrade crosses the Langqiangcuo fault and the Quzongle fault, as well as the possible adverse engineering geological problems, such as the surrounding rock instability and fracture permeability when the tunnel crosses the Jilong fault. In addition, if the tunnel is used to cross the Gangpengqing fault zone which has been actived in Holocene, the engineering preventive measures shall be given in the line design according to the possible risk of surface dislocation.

Keywords

• tibetan plateau
• rift of southern tibet
• active fault
• paleo-earthquake
• engineering stability