Research On The Stability And Prevention Engineering Of Deposits On The Right Bank In Front Of The Dam At A Hydropower Station In The Upstream Region Of The Dadu River

A hydropower station project was built in Aba Tibetan and Qiang Autonomous Prefecture,Sichuan Province.A large overburden deposit is developed in front of the dam on the right bank.The overburden deposit consists of slope diluvial and colluvial deposits,which are overlying the slope diluvial deposits.At present,the hydropower station is under construction.After construction,the normal pool level of the reservoir will be 2788m,and the backwater height will be 18m.The slope diluvium will be in a saturated state,and some colluvial and slope deposits will also be in a saturated state.The decrease in soil strength after saturation reduces the stability of the accumulation body.Once the slope of the accumulation body becomes unstable,the collapse of more than 300000 m~3 will pose a significant threat to the normal operation of the hydropower station.The purpose of this paper is to study the stability changes of the accumulation body in front of the dam on the right bank of a hydropower station before and after impoundment.The main research methods used are limit equilibrium theory and FLAC3D numerical simulation,to conduct qualitative and quantitative analysis of the stability before and after impoundment.Then,carry out prevention and control engineering design for the accumulation and verify the prevention and control effect.Through the above research,the main research results obtained in this article are as follows:(1)Through the field geological survey,it is found that the overburden accumulation area in front of the dam on the right bank is a trough terrain,in which the loose overburden accumulation is developed and the underlying sand slate is developed.The overburden deposit is divided into two layers,the upper layer and the lower layer,with the volume of about 400000 m~3;It is covered with colluvial and slope deposits with a volume of more than 300000 m~3.There is no obvious deformation sign of the accumulation body in natural state,and the accumulation body is generally stable in natural state.However,after impoundment,the water level rises by about 18m,and the slope diluvium of the slope is in a saturated state,and part of the colluvium-deluvium is also in a saturated state,which greatly increases the unstable factors of the accumulation body.(2)The unbalanced thrust method,which is a part of the limit equilibrium method,is used to calculate the stability coefficient of the accumulation body.This method enables quantitative analysis of the stability of the accumulation body.The calculation results indicate that the accumulation body is stable under natural conditions.However,under water storage conditions,some part of the sliding surface of the accumulation body is in a relatively stable state,which does not comply with the relevant specifications.The accumulation body is situated in close proximity to the gate dam,which means that its stability has a significant impact on the dam.As the accumulation body is a side slope in front of the dam,it needs to be reinforced to meet the engineering requirements.(3)Numerical simulations using the FLAC3D software were conducted to investigate the natural and water storage states of an accumulation.The displacement and strain fields were compared between these two states.The simulation results indicate that impoundment significantly increases the displacement and maximum shear strain increment of the accumulation body,leading to the formation of potential sliding surfaces and slope instability in certain areas.Based on the results of the limit equilibrium method and the numerical simulations using FLAC3D,the location and depth of anchor cable layout and the required support for the potential sliding surface were determined.(4)Based on the calculation results obtained from the limit equilibrium method,support design was performed for the accumulation body.Following the reservoir impoundment,lattice prestressed anchor cables were arranged in the area where the soil mass of the accumulation body was in a saturated state.A total of 105 anchor cables were used,arranged in 3 rows with 35 cables in each row.Each anchor cable was prestressed with 1000 k N,and the accumulation body was supported in cooperation with the lattice.Using the limit equilibrium method,the safety factor of the slope after support was calculated.The results of the calculation showed that the accumulation body after support met the requirements of relevant specifications.Finally,a three-dimensional numerical simulation of the supported accumulation body was conducted using the FLAC3D numerical simulation software.The simulation results demonstrated that the prevention measures implemented were highly effective in strengthening the accumulation body.