Main engineering geological problems in the 1st-stage project of West-line for transfering water from Southern to Northern China

The project of water transfer in western area of China,aimed at resolving the lack of water in Northwest China,is one of the important water conservancy projects through which the water of upper stream of Yangtze River is transferred to the upper stream of Yellow River.The 1st\|stage project,with an elevation of 3500m,is located at the east edge of Qinghai\|Tibet Plateau where geological conditions are very complex and the tectonic movements are developed frequently.The area has a unique system of crust deformation and structural stress.The water transfer project focuses on diverting water from the branch of Daduhe River and Yalongjiang River,namely Akehe River,Ma'erqu River,Dukehe River,Daqu River and Niqu River,to the Jiaqu River,a branch of Yellow River.The main engineering geological problems,including the active faults,deep\|seated long tunnels,reservoir geological problems and frozen soil\|induced damage,are discussed based on the preliminary field and in\|situ data. 1 Active faults\;There are 15 active faults in the western area of water transfer,in which Yushu Fault,Sangrima Fault,South Elinghu Fault,South Gande Fault and Xianshuihe Fault have strong influence on the project.Active faults not only affect the stability of water\|transferring tunnels,but also affect the regional tectonic stability of the area. 2 Engineering geological problems of deep\|seated long tunnels\;The deep\|seated long tunnels have a total length of 244km and a depth ranging between 300m and 600m.Running through areas of different geological units,the tunnels encountered many engineering problems such as high geostresses,rock burst,geo\|thermal abnormal and high\|pressure water blasting etc.inevitably.The overlaid rock mass of slightly metamorphosed Triassic sandstone is 300～600m in thickness,resulting in high geostresses.According to the stress measurement,the maximal principal stresses are: σ\-1 =6 0～11\^7MPa, σ\-2 varies within the range of 1\^0～6\^0MPa,and σ\-3 0\^3～4 3MPa.The background of high stress provides an environment for rock burst.\;Geo\|thermal gradient in the area is between 18～26℃/km,averaging 22℃/km.In the process of tunnel excavation,geo\|thermal temperature may reach 20～25℃,as a result,geo\|thermal abnormal may occur.Besides,the high\|pressure water blasting threatens the safety of deep\|seated tunnels as a result of the development of regional tectonics,neotectonics,and the structure of fold. 3 Engineering problems of reservoirs\;The geological problems include reservoir\|induced earthquake and bank stability after the construction of the reservoirs.The factors of dimension of reservoir,structural condition,geo\|stresses and earthquake activity are propitious to the development of reservoir\|induced earthquake.The comprehensive results indicate that the reservoir\|induced earthquake may reach middle intensity of M \-s=4\^5～6\^0.Furthermore,the deformation modes of bank slope are mostly rock\|fall and landslide.Statistical results show that the rock\|fall and landslide are mostly developed in the elevation ranging from 350m to 600m. 4 Problems of special soil\;The special soil existing in the area refers to frozen soil.The physico\|mechanical properties of the frozen soil change with the soil distribution and geo\|stresses.Attention should be given to frozen soil damage in this project of water transfer.