| There is a great potential of development in western part of China because of the abundant hydropower there. However, the deep overburden there has become a problem, namely, the thickness is over 30 meters. Therefore, the evaluation of engineering geologic characteristics has come out to be one of the most difficult problems.Qizong hydropower station of Jinsha River, is reservoir with high dam of which the highest dam is over 356 meters, was built by valley area. The thickness of riverbed and terrace of hydro-junction area is from 60～127 meters and the origin of it is rather complex including the factors of impact, debris flow deposits and colluviation. Completely excavation can not be realized, no matter form the technical or economic aspect, in that the over thick of the overburden. Thus, the core of engineering geologic problems there is the suitability of building high dam in deep overburden.On the basis of researching data, local in-situ tests, laboratory tests and so on, there is an analysis of the spatial distribution situation of all layers of soil, forming reasons, engineering characteristics. Finally, a comprehensive evaluation of stability against sliding, deformation stability, seepage stability and liquefication of sandy soil of overburden of dam foundation came out.According to origin of the deep overburden in Qizong hydropower, it can be divided into 3 major layers and 5 sub layers. There are :①gravel (broken stone) with in fine sand or silty caly layer (al+fglQ3), its physical and mechanical properties was good, r=2.2～2.3g/cm3, e=0.25～0.??R]=0.6～0.9MPa, E0=50～70MPa, K=1.0×10-1～1.0×10-3cm/s;②-1 gravel (broken stone) with fine sand or silty caly layer (al+fgl+sefQ3), r=2.15～2.25g/cm3, e=0.25～0.3, [R]=0.4～0.6MPa, E0=25～40MPa, K=1.0×10-5～1.0×10-4cm/s;②-2 fine sand layer (alQ3), its physical and mechanical properties was poor, r=1.8～2.1g/cm3, e=0.7～0.8, [R]=0.2～0.25MPa, E0=10～15MPa, K=2.0×10-5～1.0×10-3cm/s;③-1 boulders and gravel (broken stone) layer (alQ4), r=2.1～2.2g/cm3, e=0.3～0.45, [R]=0.4～0.7MPa, E0=30～50MPa, K=2.0×10-1～3.0×100cm/s;③-2 sand and silty sand layer (alQ4), its physical and mechanical properties was poor r=1.8～2.0g/cm3, e=0.45～0.7, [R]=0.15～0.2MPa, E0=8～12MPa, K=7.0×10-4～1.0×10-3cm/s.In a word, the totality of river bed overburden of Qizong hydropower station's downstream dam site is in good condition, it's stability against sliding Satisfies the request, though some problems do exist, such as cobble and gravel infiltration, large amount settlement deformation of overburden, liquefiable sand layer and so on. However, such problems can be solved through engineering treatment measures and the dam foundation of overburden may own the conditions of building high core type rockfill dam.
|
PDF Full Text Request