Experimental Study On The Effect Of Suspended Seepage Controlling Wall To Control Seepage Failure

Seepage failure is one of the high frequent disasters for dike engineering during flood season. At present, a number of ripe vertical cut off techniques have been widely used in levee project, and many rich experiences have been accumulated in the treatment of diseased levee project. The vertical seepage controlling technique has been widely used in levee project, and it is the main reinforcing methods for seepage preventing. The seepage controlling wall is one of the techniques of vertical seepage controlling method, and it can be divided into three types: closed seepage controlling wall, semi-closed seepage controlling wall and suspended seepage controlling wall.The research of seepage preventing indicates that the foundation of the middle and lower reaches of Yangtze Rive is mostly composed of dual subsoil layers which is often soft clay and lacks reliable methods to prevent seepage. The middle and lower reaches of Yangtze Rive has been widen and reinforced, but there are still some hidden troubles, for example, disorder embankment soil, small degree of compaction, lower construction quality, lower criterion of controlling flood, serious leakage of dike foundation, sever eroding of embankment slope, badly destroyed by the human being, demolishing and aging of the buildings that across the embankment, long-time and continuous settlement and so on.On the basis of the characteristics of the middle and lower reaches of Yangtze Rive, a seepage sandbox has been made to simulate the specialty of the dual subsoil layers. The tests have been done indoors and the functions of suspended seepage controlling wall in preventing seepage failure have been discussed. The following are the main contents.The soil that is used in the test is from the south bank of NanKing dike of Yangtze Rive. The upper layer is composed of silt clay and the under layer is composed of silt. The soil is same to that of the local spot, so the hydraulic factors of seepage failure is also the same. The tests of the two kinds of soil have been carried out which are specific gravity, coefficient of permeability, particle size analysis, liquid limit and plastic limit. The results indicate that the silt lacks middle particles and the particle size is symmetrical which can easily leads to seepage deformation. The hydraulic conductibility of silt is 20 times that of the silt clay. Under the function of high water level during flood season, great hydraulic pressure can be easily produced under the bottom of the silt clay layer which can cause some disasters to happen. So, some effective measures must be taken to prevent dangers.Based on the foundation characteristics of Yangtze Rive embankment, a seepage sandbox has been manufactured which is made of plexiglass. It is 2 meters long, 1 meter high, and 10 centimeters wide. Silt clay and silt are put into the sandbox. It can be used to analyze the characteristics of seepage failure and the function of suspended seepage controlling wall which is used to prevent seepage failure. The actual hydraulic gradient is simulated by changing the deepness of the suspended seepage controlling wall which is composed of silt clay. The mechanical composition and dry density of the soil are same to that of the local spot, so the critical hydraulic gradient and the effect of preventing seepage are consistent with that of local spot.During the time of the tests indoors, the tests which have different depths of suspended seepage controlling wall have been done. For the dual subsoil foundation which are composed of silt clay upside and silt subside, sand spring occurs at the feeble spots, then contact erosion occurs at the face that silt clay and silt integrate. When the water level rises continuously and exceeds the critical water level, the seepage channel develops from downstream to upstream, and runs through the whole soil. At this time, the seepage failure occurs. Research indicates that under the function of suspended seepage controlling wall, the qualification of seepage failure has been improved, for example, the water level rises greatly, critical apparent hydraulic gradient increases obviously, the seepage quantity reduces distinctly and the pore-water pressure changes evidently. The results of the research are that the suspended seepage controlling wall can effectively block the seepage failure, at the same time, it is constructed easily and acceptable in economy, so it is worth applying in project.