Engineering Geology Study On Weathered & Unloaded Granite Rock Mass In Incised Valley Of Yellow River Laxiwa Hydroelectric Station

Water conservacy and hydroelectric projects being programmed or constructed in incised river valley of southwest and northwest of China all relate to weathered and unloaded rockmass. It is very important and significant to study weathering and unloading for engineering design, parameter value choosing, rockmass quality classificatioarockmass excavation, foundation plane choosing, even project running.The dissertation is based on granite rockmass in Laxiwa hydroelectric station damsite, Yellow river. The essential cause inducing weather and unloading is distict difference between epigenetic-surface and deep condition. Firstly, the dissertation introduces the background conditions that are the base of damsite granite rockmass weathring and unloading; Secondly, the mechanism of the rockmass weathering and unloading is probed into; Thirdly, different degree weathered zones and load-off zones are compartmentalized.tastly, right rockmass which meet the dambase demand is choosed.Above-mentioned is the dissertation' s technical course which is clearly from base research to application research..The dissertation uses natural geology analyse method to offer reasons for why the weathered and unloaded degree is light, uses quantification analyse method to compartmentalize different weathered and load-off rockmass, and from part to whole, obtains the damsite rockmass weathered and unloaded characteristic of spatial distribution. The quantification indexes that token weathered degree are primary velocity, borehole RQD(rock quality designation), joint space, joint number and so on, and the unloading ones are primary velocity, joint opening, borehole penetrability and so on. The compartmentalization of different weathered and load-off zones according to quantification indexes tallies with the slope geo-stress computed by finite element method. The main conclusions and cognitions are as follows:(l)Rockmass weathering should be studied from either microcosmic and macrocosmic, microcosmic contain includes of mineralogy and of lithology, and in macrocosmic , weathering action damages integrality of rockmass,so studying rockmass structure can open out weathered degree of epigenetic-surface rockmass.(2]The dissertation sums up the characteristic indexes which can token weathered and unloaded degree, simultaneously, puts forth and summerizes several methods that classifies different weathered and relaxed zones of slope rockmass.(3)River valley epigenetic-surface reformation is controlled by rockmass structure , but weathering and unloading of rockmass is the direct cause which leads to different epigenetic-surface physical geology phenomena, for example, collapse, landslide, incline, dynam-relaxed and so on.(4)Blocky rockmass with the same age, same rock and same tectonic experience, has gradual change in weathered and unloaded degree, weathering and unloading of the intact damsite granite rockmass in accordance with the law. (S)weathering and unloading action which are the two main exogenous process is active in epigenetic-surface.so, although one is different with the other, they are associated with each other closely and are cntrolled by geostress and seepage fields. In fact, weak weathered zone corresponds to weak load-off one, strong weathered zone corresponds to strong load-off one in virtue of result of this dissertation.(6)Rock mass is a geologic body which is composed of rock and structural plane.and under the condition of geostress.temperature and seepage fields,correspondingly.studying weathering should pay attation to the aspects of rock,structural plane and fields.According to this.the author subdivises rockmass weathering into rock weathering and structural weathering, ulteriorly,the dissertation studies rockmass weathering from three aspects as follows:㏑ock weathering: aberrance degree of mineral and physical mechanical performance of weathered rock; ￤e have already knew that weathering action damage the integrity of rock mass,but few applies it to engineering practice.The dissertation is based...