Research On Key Technology Of Plastic Concrete Impervious Wall In Deep Overburden Layer During Construction And Operation Period

With the rapid development of hydropower industry in C hina and the construction of many water conservancy projects,plastic concrete impervious wall is more and more widely used in dam foundation as an economical and effective anti-seepage measure.The rapid development of water conservancy construction has put forward higher requirements for the technology of concrete impervious wall in the area of super deep overburden in the impervious engineering such as reinforcement of reservoir and seepage prevent ion and reinforcement of levee.Therefore,how to ensure the construction quality of the impervious wall and the impervious performance of the embankment（earth-rock dam）is becoming more and more important.At present,the construction of ultra-deep plastic concrete impervious wall mostly depends on the previous engineering experience,especially in the areas with deep overburden and poor geological conditions,the construction period of the plastic concrete impervious wall is short of theoretical guidance.There are many seepage deformation problems during operation.It is urgent to solve a series of key technical problems on the basis of theoretical analysis and engineering practice.In this paper,numerical simulation is used as the main theoretical analysis method to grasp the characteristics that the depth of underground impervious wall of Jingjiang embankment is over 85 m L,the geological conditions are poor,and the wall material is plastic concrete.In this paper,the key problems in the construction period of the impervious wall are analyzed.The key problems during the construction of the cutoff wall,such as extubation and demoulding technology,and seepage field of the embankment during the operation period are simulated.According to the seepage field simulation results,the wall materials and the proportion of the plastic concrete cutoff wall are selected.The results show that:1)During the numerical simulation of seepage field of embankment,there is an obvious tendency of sudden drop of pore water pressure through the cutoff wall,which indicates that the impermeable wall plays a certain role in the impermeability of embankment.When other parameters such as water head in front of the embankment are not changed,the impermeability increases with the decrease of permeability coefficient of the cutoff wall,the position of the embankment’s infiltration line,the height of the overflow point and the maximum velocity of flow decrease.The seepage flow behind the embankment and the seepage slope behind the embankment also become smaller.When the permeability coefficient of the cutoff wall is constant,the maximum velocity increases with the increase of the water head in front of the embankment.The maximum velocity is generally located at the o verflow point at the foot of the embankment downstream,and the position of the embankment infiltration line rises,and the height of the overflow point rises.The single wide seepage flow and the infiltration slope increase with it.2)According to the numerical simulation results of seepage field,this project needs to adopt the wall material whose permeability coefficient k is about 0.52×10^-5cm/s to meet the impermeability requirement.In this paper,plastic concrete is chosen as the wall material,compared with ordinary concrete.The utility model has the advantages of good anti-seepage effect and can adapt to the deformation of the foundation.Limiting the range of permeability coefficient of plastic concrete(k≤n×10^-6cm/s（1≤n<10）can effectively improve the impermeability of levees and save some engineering cost.Finally,the construction mix ratio of plastic concrete is put forward in combination with the laboratory results.3)Combined with the plastic concrete of the selected wall material and considering the law of early strength variation,the difficulties and key problems in construction,I.e.,the determination of the time of drawing joint pipe are selected to study.The extubation time of joint pipe is affected by many factors,including e nvironmental condition,load condition,construction condition,etc.After pouring concrete,pipe can be pulled out earlier,which can avoid drawing difficulty or even casting pipe caused by concrete solidification.There is plenty of time to stabilize the concrete without the concrete collapsing after extubation due to external loads.For the 85 m ultra-deep impervious wall of Jingjiang embankment,the maximum compressive stress of 5.12 MPA,the maximum tensile stress of 1.77 MPa,and the maximum compressive strain of 1.06E-03 are within the permissible range under the condition that the concrete pouring surface and the bottom end of the joint pipe are maintained at 12 m,the maximum compressive stress is 5.12 MPA,the maximum tensile stress is 1.77 MPA,and the maximum compressive strain is 1.06E-03.The overall stability and deformation of the concrete are obviously better than that of the first pouring of 15m and 18m,so it is considered that the extubation of plastic concrete after 4 hours can meet the requirements.Firstly,the seepage field of embankment under different working conditions is simulated in this paper.Combined with the simulation results,plastic concrete is selected to meet the requirements of wall impermeability.Combined with the laboratory results,the construction mix ratio of plastic concrete is put forward,and then considering the rule of early strength change of the selected plastic concrete,the time of extubation during the construction period of the super deep dike cutoff wall is studied and determined.It has certain reference value for improving the construction quality and impervious performance of ultra deep impervious wall.