Study On Seepage-stability Of Laterite-type Dams Under The Rising And Falling Of Reservoir Water Level

This paper is based on the National Natural Science Foundation of China subject---"Study on Yunnan Laterite Dam under Wetting-drying Cycle."(No.51568031)In view of leakage and stability of laterite dam,"Study on leakage and stability of laterite dam in rising and falling of reservoir water levels" is proposed.Considering the influence of time,speed and height of reservoir water level,the leakage and stability change of laterite damim in rising and falling of reservoir water level is studied by using finite element software---ABAQUS.The research may provide some reference for the prevention of leakage of the laterite dam and the improvement of the safety of it.The leakage of the laterite dam in the rising reservoir water level show that: with the increase of the rising time of reservoir water level,the reservoir water level rises correspondingly,the saturation area inside the dam gradually increases to the maximum value,and the saturation line gradually rises to the maximum value from upstream to downstream,the pore pressure and equipotential line in the dam gradually increase and tend to be stable,the hydraulic gradient gradually decreases and tends to be stable,the velocity in the dam first increases rapidly and then decreases slowly,and then tends to be stable,the velocity of leakage increases gradually to stable.With the increase of rate of water level rise,the hysteresis of water infiltration into the dam body is more obvious,and the saturation area is smaller.Therefore,the lower the saturation line is,the denser the equipotential line is,the greater the head loss is,and the faster the pore pressure and velocity increase.The stability of the laterite dam in the rising of reservoir water level shows that: with the increase of time of reservoir water rising,the reservoir water level rises correspondingly,the pore pressure inside the dam increases gradually,the maximum and minimum principal stresses gradually decrease and tend to be stable;the expansion displacement of the dam body increases gradually and tends to be stable due to the existence of hydrostatic pressure on the upstream side,The more serious the displacement of the dam to the downstream,and the soil wetting,the safety and stability coefficient of the dam gradually decreases and tends to be stable.With the increase of the rising rate of reservoir water level,the faster the change rate of stress and displacement is,the more obvious the "hysteresis" of water infiltration into the dam body,the smaller the saturated area is,the greater the maximum and minimum principal stress,the safety and stability coefficient is bigger with smaller displacement.The leakage characteristics of laterite dam in the falling of reservoir water level show that: with the increase of time of water level falling,the reservoir water level decreases correspondingly,and the phreatic line presents a convex shape which is high in the middle and low on both sides,and gradually drops to form a horizontal straight line;the water seeps from the highest point of the saturation line to the upstream and downstream dam slope,and the equipotential line becomes dense.With the decrease of reservoir water level,the pore pressure becomes smaller and smaller,the internal velocity of the dam decreases gradually,and the upstream dam slope water seeps outward,and the velocity increases gradually and tends to be stable.With the increase of drawdown rate of reservoir water level,the the faster the water leak from the dam body,and the change speed of phreatic line,pore pressure and velocity is faster.However,the influence of drawdown rate of reservoir water level in ABAQUS on the leakage characteristics of dam is small,which mainly depends on the dehumidification characteristics of soil.The closer the saturated area is to the saturation line,the faster the fluid velocity of it is.The stability of the laterite dam in the falling of reservoir water level shows that: with the increase of time of water level falling,the reservoir water level decreases correspondingly,the pore water pressure decreases gradually,the maximum and minimum principal stresses in the dam gradually increase and tend to be stable,and the upstream dam slope presents tensile stress;water in the dam loses and the the displacement of the dam decreases gradually and tends to be stable,and then rebounds to the upstream,and the safety stability coefficient increases gradually and tends to be stable.With the increase of drawdown rate of reservoir water level,the faster the water leaks out,the faster the change speed of stress and displacement is,but the influence on stress and displacement is little,and the safety and stability coefficient decreases slightly.