The “Active Fault Survey and Stress Measurement along the Golmud-Lhasa Railway”, which crosses the central Tibetan Plateau, is one of the key projects undertaken for the China Geological Survey (CGS). The project started in January, 2001 and ended in December, 2003, and included its major contents as active fault survey, in-situ stress measurement of tunnels, prospecting of geological hazards and evaluation of engineering stability along the railway. The CGS Department of Hydrogeology and Environmental Geology managed and supervised the project, and Institute of Geomechanics of Chinese Academy of Geological Sciences (CAGS) conducted the project. The Railway Ministry of China sponsored the project, and First Academy of Railway Prospecting and Railway Design provided direction and supervision to the project. The Ministry of Land and Resources (MLR) and Chinese Academy of Geological Sciences (CAGS) also gave support and help to the project.

 Task and Aim: Task of the project includes exploration for active faults and geological hazards, measurement of stress in tunnels and evaluation of engineering sites along the Golmud-Lhasa Railway, all aimed at providing detailed geological data for designing, engineering construction and hazard protection along the new railway.

General Plan: The project is planed to survey active faults and geological hazards by large-scale mapping, field trenching, geophysical profiling and chronological dating, to analyze stress fields of tunnels by in-situ stress measurement and numerical modeling, and to evaluate stability of construction sites and degree of hazard from active faults along the Golmud-Lhasa Railway. The project was required to provide detailed geological reports, maps of active faults at different scales and reasonable suggestions for decreasing the geological hazards for design departments of the Golmud-Lhasa Railway.

Contents and Methods: The investigation consisted of several parts: (1) Survey of active faults: remote sensing images, 1:2000 mapping and trenching are used to determine position, strike, offset, property, displacement and other features of active faults along the Golmud-Lhasa Railway. Quaternary profiling and thermoluminescent (TL), Photoluninescent (OSL), U-series and ¹⁴C dating are used for studying times and slip rates of active faulting and evaluation of potential hazards of active faults to engineering facilities along the Railway. (2) Survey of geological hazards in permafrost areas: migrating pingos, landslides, mudflows, surface fractures and heterogeneous freezing deformation along the Golmud-Lhasa Railway are studied by field trenching and measurement in different seasons during 2001-2003, to provide abundant data to understand their formation, evolution and potential hazard. (3) Geophysical exploration of active faults: shallow depth seismic reflection, conductivity profile and radioactive α measurement are used to detect active faults along the Golmud-Lhasa Railway. (4) In-situ stress measurement: in-situ stress is measured in tunnels across the Kunlun Mts., Fenghuoshan Mts. and mountains in southeast of Yangbajain basin and their vicinity to calculate stress fields of the tunnels by numerical modeling and provide key data for design of long tunnels. (5) Assessment of crustal stability along the Golmud-Lhasa Railway: an overall assessment of the crustal stability is carried out after integrating the data from active fault survey, in-situ stress measurement, geological hazard exploration and numerical modeling of stress fields. The slip rate of active fault, magnitude of earthquake, temperature of hot springs and tectonic strain from numerical modeling are used as key factors in grading the stability of the crust at engineering construction sites.

 Data Acquisition and Reports: The project compiled a 1:2000 map of active faults and geological hazards along the Golmud-Lhasa Railway, a 1:100000 map of ETM remote sensing image and 1:100000 map of active faults along the Golmud-Lhasa Railway. Reports were prepared on the Survey of Active Faults along the Golmud-Lhasa Railway and In-situ Stress Measurement and numerical modeling of the railway tunnels. These data have been adopted and applied to engineering design of the Railway by the authorized design agency, the First Academy of Railway Prospecting and Railway Design. The project also submitted special reports on migrating pingos at the 83rd, 85^th and 86^thHighway stations and potential hazard caused by yak herds on the railway to administrative agency of the Golmud-Lhasa Railway and the First Academy of Railway Prospecting and Railway Design. These reports together with reasonable suggestions were adopted and applied to engineering measurements to reduce or eliminate the potential hazard.