CLASSIFIED ANALYSIS OF CSAMT SECTION IN EMBEDDED TUNNEL EXPLORATION AT ABA SECTION OF FIRST STAGE OF WEST LINE PROJECT OF SOUTH-TO-NORTH WATER TRANSFER
Abstract:The first stage of the west route project of the South-to-North Water Transfer,which diverts water from the upper Yangtze River into the upper Yellow River,is located in the east edge of Qinghai—Tibet Plateau where the regional geological conditions are very complex. Active faults are distributed over the project zone,and strata are strongly folded. Through CSAMT exploration,the distribution of faults and groundwater are qualitatively analyzed;and the stability of embedded is evaluated. According to regional geology background,sedimentary rock modes and condition and physical features of rocks,the characters of CSAMT section to explore the strata structure,fault and groundwater condition are analyzed. The CSAMT section is classified into 4 types,accounting for 54.75 percent,38.75 percent,3.75 percent,2.75 percent respectively in the 40 kilometer long surveying line. Each mode reflects different geological condition. For type 1 with wide high resistance area,CSAMT section changes sparsely and gradually,r :2 000–10 000 W· m. Type 2,wide low resistance area,CSAMT section also changes sparsely and gradually,but the resistance reduces from the ground surface to deep zone,r :1 000–50 W·m. For type 3 with wide high resistance area,the resistance increases from the ground surface to deep zone,r :50–1 000 W·m. For type 4 with low resistance strip,r<300 W·m. The geological interpretation is that the wide high resistance area(type 1 and type 3 ) reflects that the groundwater is not abundant in the sandrock and slate stratum. The large region of low resistance anomaly(type 2) reflects the hydraulic permeability and water reservoir of deep rocks are better than the superficial rocks. Low resistance anomaly depends on ground water conditions and lithologic characters,not on tectonic movement. Sandrock filled with water may appear low resistance anomaly. According to groundwater condition,when the tunnel is excavated,these low resistance anomaly made of moderate to thick-bedded sandrock may cause water gushing but the amount of water which may affect the safety of tunnel is not much. The low resistance strip (type 4)which reflects fault and its crushed belt will affect the excavation of tunnel.