Three-dimensional Analysis On Seepage And Stability Of Water Storage Modification Of Silt Dam

As one of the three"highlights"projects in the Loess Plateau,the silt dam has played an important role in controlling soil erosion,improving the ecological environment and developing the agricultural and fishery industries,and has very obvious ecological and social benefits.In order to alleviate the shortage of water resources in impoverished mountainous areas,technical research on water storage improvement of silt dams is being carried out.Silt dams have poor anti-seepage conditions and do not have the capacity to store water.The analysis of seepage and dam slope stability before and after the silt dam reconstruction is the basis of the water storage reconstruction.At present,most studies on the seepage and stability of silt dams use two-dimensional models.For silt dams with strong three-dimensionality,the analysis results are different from the actual situation.It is necessary to carry out three-dimensional seepage and stability analysis.The river channel at the dam site of Xiaogou is narrow,and its cross-section varies greatly along the axis of the dam.It is appropriate to use a three-dimensional method for analysis.This paper uses ABAQUS software to establish a three-dimensional model,combined with the principle of fluid-solid coupling and strength reduction,to check the seepage and slope stability of the silt dam and analyze its three-dimensional characteristics.The specific research content and conclusions are as follows:（1）Consult relevant documents and comprehensively review the seepage and stability analysis methods of earth-rock dams and silt dams.（2）Verify the two-dimensional fluid-solid coupling model,and analyze the difference between the two and three-dimensional model calculation results.（3）Consider the coupling of stress field and seepage field,and adopt the strength reduction method to analyze the seepage and stability of the original Xiaogou silt dam at the design flood level.The original dam body is a homogeneous earth dam with poor seepage prevention conditions.The seepage flow after impoundment is 1.20×10^-5m³/s,and the overflow point of the infiltration line is 11.54 m.The downstream overflow point is prone to runoff damage.The downstream slope is subject to seepage pressure to produce a certain displacement,which adversely affects its stability.After strength reduction,the stability safety factor of the dam is 1.200,which does not meet the requirements of the specification and requires anti-seepage modification.（4）In order to make the renovated silt dam meet the requirements of the design code for earth-rock dams,combined with the previous research results,this paper adopts the geomembrane renovation plan:add geomembrane impervious body in the upstream,set slope drainage downstream,and increase the dam The roof width is 6 m,and the upper and lower slope coefficients of the slowing down are 2.5 and 2.0 respectively.（5）The seepage and stability calculations of the dam after the geomembrane transformation are carried out in the completion period,the stable seepage period and the earthquake under normal operating conditions:（1）Completion period:During the completion period,the upstream and downstream slopes of the dam slowed down and were not affected by seepage water.The stability of the upstream and downstream slopes of the dam was good.（2）Stabilization period of seepage:The anti-seepage effect of the geomembrane is good,so that the infiltration line changes sharply before and after the geomembrane,from 18 m to 6m.The hydraulic slope inside the dam is small,and the seepage flow is reduced to 1.00e×10^-6m3/s,the height of seepage overflow point is 0.22 m.After water storage,the displacement of the upstream slope of the dam is mainly caused by hydrostatic pressure.The maximum displacement is 0.097 m.The displacement of the rest of the dam is relatively small.The downstream slope stability safety factor is 2.068.（3）Earthquake under normal operating conditions:the quasi-static method is used to calculate the stability safety factor of the dam under a magnitude 7 earthquake load.The stability of the upstream and downstream dam slopes is reduced after being affected by the seismic inertial force.The stability safety factor of the downstream dam slope is 1.230.The upstream dam slope still maintains a high safety level under the horizontal reaction force due to the hydrostatic pressure.The coefficient is 2.150.（6）The calculation results of the seepage field and stress field before and after the reconstruction of the Xiaogou silt dam show that due to the interaction between the lateral flow and the soil,the overall wettability line,horizontal displacement,and instability of the silt dam are slippery.The fracture surfaces show obvious three-dimensional characteristics,and the most unfavorable area near the center section of the silt dam should be given special attention.