| The stability of slope is one of the most concerned topics in large hydropower projects.Banda hydropower station is located in lancang river.The survey found that there were two large scale ductile shear zones and several alteration zone in the dam site area.The development of these zones worsen the engineering geological environment of the dam site area,and have great impact on stability of the excavation slope.In this paper,based on detailed engineering geological investigation,the structural characteristic of rock mass in the right bank slope was analysed,and the developmental characteristics of the ductile shear zone and the alteration zone were found out.Then,the stability of the right bank slope before and after the excavation was analysed,combined the rigid body limit equilibrium method and numerical simulation method.At the same time,the effects of the development of ductile shear zone and the alteration zone on the slope stability was discussed,and the specific contents and results are as follows:(1)Ductile shear zones are deep fault tectonic product,the rocks are ductile,but the ductile shear zones,exposed on the surface,were supergene reformation obviously,and rock fracture in ductile shear zones were much more than normal rock masses.The occurrence of ductile shear zones is 180°?240° ?60°?80° and is dipping toward to the inner slope.According to the microscopic observation,the movement direction of the ductile shear zones is the right lateral shear and dextral strike-slip.(2)Alteration rock mass are dotted and zonal distribution,and mainly shows sericitization,clay(kaolin,yili petrochemical and montmorillonitization),chloritization,carbonatization,etc.,and is controlled by ductile shear zones and fracture-fault activity.(3)In the survey of unloading cranny in adits,we found that the strong unloading depth increased exceedingly in elevation of 3000 m in PDS08 and weak unloading depth increased exceedingly in elevation of 3100 m in PDS06.The Universal Distinct Element Code was used to discuss these anomalies,and results shows that the slope unloading anomalies is related to the weak base effect of ductile shear zone and the alteration zone.(4)Through investigating the cracks in the adit,the structure characteristics of rock mass in he right bank of dam site was found out,which is divided into loose-cataclastic structure,cataclastic-block crack structure,mosaic-submassive structure and submassive-massive structure.(5)The BQ method was adopted to classification of rock mass quality in the right bank slope,which was divided into ?,?,?,? four categories,and refined? rock as ? 1 and ? 2 two classes.The ? class is mainly strongly weathered rock mass and strong alteration rock mass.The rock mass quality the ductile shear zone is slightly lower than normal rock mass.(6)Based on the existing experiment and combined with the relevant specification and similar engineering,the rock mass parameter of the right bank of dam site was gained in the case of considering the rock mass quality classification,and the rock mass parameter in ductile shear zones and the alteration zones is lower than that in normal rock mass.(7)Using rigid body limit equilibrium method to calculate slope stability on natural,rainstorm and earthquake state,the results show that the overall stability of the slope on the right bank is good,but stability is bad in the distribution area of loose cataclastic rock mass and the dumping of broken rock mass,and may be unstability under extreme conditions such as rainstorm state or earthquake state.(8)Through the numerical simulation analysis of water inlet excavation on the right bank slope,the stability is good under natural condition,but the minimum principal stress near slope table changes from compressive stresses to tensile stress after the secondary excavation,and the slope may be unstable with strong unloading rock mass bottom boundary as sliding surface and cut out from the ductile shear zone and the alteration zone in high elevation.(9)The development of ductile shear zones and the alteration zones degrades engineering geological environment of slope,formes the slope structure of a soft and a hard slope,strengthens the superficial reformation,accelerates the development speed of rock mass structure to the fragmentation,and causes the rock mass quality in the ductile shear zones and the alteration zones lower than normal rock mass.The ductile shear zones and the alteration zones are not as sliding boundary directly,but they degrades various control factors of the slope stability drastically,which has large influence on the stability. |
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