The Evaluation Of The Geological Defects Features And Treatment Measures On The Foundation Rock Of Da Gang Shan Hydropower Station

A large number of projects show that the rock that always cannot be used forgood directly after the excavation of the dam foundation surface is little. There aremany geological defects found in the foundation rock, including faults zone, joints,and weak interlayers and so on, which make problems for the selection of thefoundation. These geological defects not only damage the original of the uniformityof the rock mass, decrease the rock mass quality and influence the deformation andstability of the whole arch dam and its abutment, which bring the enormous harm tothe safety of hydropower project. It is not suitable to remove these geological defectscompletely through deepening excavation depth with considering the economicrationality of engineering. Consequently, to think over if the weaker rock mass qualityof the excavated foundation after using the proper treatment can achieve therequirement of the foundation rock availability or not is very significant.The excavation work of the foundation of the Da Gang Shan hydropower stationhas been finished. And about60geological defects were revealed on the rock mass,such as slightly weathered granite, granite with fissure concentrated zones, faults andits fracture zone, broken diabase dikes and so on, which is main one of engineeringgeology issues existing in the dam foundation surface. Basing on the research of therock mass quality after foundation excavation, combining with the engineeringgeological condition of the foundation surface, the author make analysis primarily onthe aspects of the geological defects containing its space development characteristics,engineering geological characteristics, influence depth, engineering measures and itsfollowed test effect and so on. The main results and conclusions are as follows:(1) By analyzing the space distribution features the of the rock mass quality ofthe excavated foundation on its plane and sectional drawing, it shows that the dam foundation surface not only revealed the new faults and dikes, and also the change ofthe rock types on its space area. And compared with the design period, theconsequence indicate thatⅡrock mass outcropped area increases, Ⅲ1rock massreduces, and other rock types are basically the same as before, among which Ⅲ2rockmass mainly embodies on the new granite with fissure concentrated zones exposed inthe local foundation surface. Therefore, uncovered rock mass can meet requirementsof the foundation rock quality of the arch dam.(2) Based on the basic requirements of arch dam foundation, combined with theactual engineering geological conditions of the foundation surface, it is probable toconfirm the basic principles of the available rock mass. According to the spacedistribution characteristics of the rock mass quality of the excavation foundation, theconclusion shows that the rock mass in the940m elevation of the both side damfoundation can fit the bill of the available, but the riverbed dam foundation cannotattain it which must make some engineering measures.(3) Mainly four types’ geological defects have been exposed on the damfoundation rock mass, including slightly weathered granite, granite with fissureconcentrated zones, faults and its fracture zone, broken diabase dikes and so on.Through the research on the space distribution features of all kinds of geologicaldefects in the foundation surface,it is to analyze its effect on the rock mass quality(4) After combining kinds of geological defects space distribution characteristics,the writer make research on the engineering geological characteristics of thegeological defects from four respects such as strength, deformation, stability,permeability and so on. According to that analyze, it finds that slightly weatheredgranite and fissure concentrated zones making negative affect on the foundation rockmass are mainly embodied in the strength and deformation, however, faults andbroken diabase dikes are mainly embodied in the stability and permeability. Inaddition, the research explain that geological defects on the foundation surface owingweaker resistance to deformation are main these developing relatively concentratedand larger scale, on the basis of analyzing its physical mechanical characteristics andqualitative analysis on the deformation characteristics.(5) Through analyzing the Ⅲ2slightly weathered rock and fissure concentratedrock mass by the method of geophysical exploration, it indicate that the influencedepth of these two kinds of geological defects about5m. To attain the requirements ofthe foundation rock mass quality and improve the foundation uniformity, somedifferent engineering measures must be used to deal with the geological defects such as foundation clearing,concrete replacement, mechanical cutting, consolidationgrouting and so on, which must be selected with considering some factors like scale,characteristic, position of the defects.(6) Making use of numerical simulation to compute the stress changes and thedeformation characteristics of the foundation rock mass before and after dealing withgeological defects, the results show there is no significant stress concentrationphenomenon on the foundation rock mass with certain engineering measures. Inaddition, analyzing the deformation characteristics of the dam spandrel rock mass, itindicates that, under the normal loads, the deformation in every elevation rock massof the dam foundation is uniform relatively and the rock displacement direction isconsistent with the direction of arch abutment forces. Consequently, making someengineering measures for the geological defects is reasonable from above conclusions.(7) The effectiveness test after using some engineering measure for thegeological defects contains packer test, drill hole sound wave test combining drillingpanoramic images. The detection of14#dam section indicates that the grouting effectoverall is good, but the local does not meet the requirements which is suggested togrout again.