Comprehensive Analysis On The Relaxation Depth Of Foundation Leftbank Rock Excavation Of Dagangshan Hydropower Station On Dadu River

The DaGangshan Hydropower station on the Dadu river under construction in the dam,whose regional tectonic environment is special, and complex is ingredient, mainly with some fault and with some extension length and shape of the slow crack in gently and substrate fractures (structural joints), etc. In addition, yet developed many fai green dam dike , and faults developed in green dike two walls or fraser, which making the fai green dikes internal crushing serious. Arch dam foundation (shoulder) excavation will cause the slope rock mass, which cause the change of stress field of rock stress direction in excavation unloading is flabby, unloading differences are significant, the excavation stability problem is the main reason of the accident which cause arch dam safety. Based on the engineering geological research, rock stability of the DaGangShan Hydropower station on the dadu river dam, we sited tracking survey on the ladder rock excavation segment of the engineering geological characteristics of the dam, Mainly by the characteristics of fracture developing in irrigation and drainage hole foundation, the RQD of core and the lastic modulus variable model hole,wave velocity material as the foundation on EL1135~EL1040m, analysised and studied of the foundation rock excavation dam face left after unloading, determine the characteristics of unloading zones, and used the the 3D numerical simulation method of dam foundation excavation left face to simulated and analyzed, obtained the following main research results:(1)Based on the analysis of the field geological data of the DaGangshan Hydropower station, understanded the power station engineering geological conditions of the dam. According to the characteristics of the rock weathering of DaGang mountain, identified rock weathering standards and according to the standard will rock of the table inward failured divided into fully weathered zone, strongly weathered zone, weak weathered zone, the fresh breeze– mass. (2) Tracked the geological data on the foundation excavation on-site.And divide the rock quality of foundation surface by blasting holes before, after the explosion of the blasting waves and integrity rock mass coefficientof rock foundation surface integrity coefficient quality division.(3) First analyzes the unloading effect essence and relaxation mechanism theoretically, and second according to the geological survey data such as fracture characteristics of foundation surface of irrigation and drainage hole, the RQD of core and the lastic modulus variable model hole,wave velocity material as the foundation, to divide the depth caused by excavation unloading. Partitioning results showed that: depth of relaxation which using irrigation and drainage hole fracture characteristic parameters is largish, Irrigation and drainage hole for the excavation of the second artificial disturbance caused by rock mass is second unloading flabby, So depth of relaxation was greater. The depth of relaxation using variable model hole RQD, elastic modulus material and blasting holes into the depth of wave velocity data is in accord with flabby. In vertical direction, relaxation depth is nearly 1 meter or more metres, which were less than using irrigation and drainage hole fracture material qualitative partition of relaxation depth. Normally high elevation with depth were low elevation flabby, each largish elevation in dam axis with flabby near the depth is bigger, but in local appeared abnormalities which may be coused by dikes with the development of the emergence of or broken concerned.(4) Use the three-dimensional numerical simulation method to simulate the stress field of the left foundation. According to the natural state of stress test results to simulate flat adit left by fitting stre, again the calculated stress of the foundation after excavation. Based on Stress zoning and unloading zoning have relevance of principle, divided the depth of unloading face the left after the foundation rock for excavation, simulation results indicated that the unloading depth and previous analysis results are identical with each other(5) Analysis the causes of excavation unloading mechanism, With summarized that unloading of rockmass brae contour features and the correlation of lithologic features. In addition, excavation relaxation depth is also related with many human activities, such as the excavation blasting method, excavation depth, supporting measures etc.