The Study On The Application Of Vertical Cut-off Wall In The Seepage Controlling Technology In Dongting Lake Dykes

The cut-off wall, also named as the continuous diaphragm wall, is a kind of anti-seepage construction in the form of wall built by pouring concrete into continuous pores made in loose and water-permeable base. Its water-blocking function makes it widely applied in water course projects, irrigation projects, hydropower projects and other projects that require base anti-seepage treatment. However, further research and exploration need to be done to see whether the cut-off wall, with its load bearing mechanism and design and computing theories, is able to be applied to prevent seepage in Dongting Lake's dykes due to the complex geological condition of Dongting Lake area and correspondingly complex construction technology. This paper, based on study of domestic and international researches on related topic, gives rather in-depth analysis to the anti-seepage issue of Dongting Lake's dykes with a case study on the Zhoujiawan Anti-Seepage Project at Xinmin Embankment in Ningxiang County, Changsha City. Through analyses on related theories, actual applications and site testing results, a rather systematic discussion is made on the anti-seepage mechanism as well as the related computing method and construction technology of vertical cut-off walls in the sand and gravel dyke bases in Dongting Lake area.The paper starts with a brief introduction of the basic facts about the dykes in Dongting Lake area as well as the key features of the anti-seepage technology applied in these dykes. Then finite element computation and analysis model is built for the sand and gravel dyke bases in Dongting Lake area with simulation of possible scenarios during project construction and analyses on corresponding anti-seepage solutions. Special analyses and study have been done on the penetration depth of the vertical cut-off wall in the sand and gravel dyke base and in the non-permeable dyke base, as well as the relationship between the penetration depth and the position and size of the maximum penetration slope of the dyke base. With seepage flow charts based on such analyses, in-depth discussion is then made on the anti-seepage theory of the vertical cut-off wall. Also, because of the lack of information on experiments with the vertical cut-off wall in Dongting Lake area, the author designed by himself a series of comparative experiments involving different water levels, different material proportions and different socketed depths in order to illustrate the features of the functionality of the vertical anti-seepage wall in sand and gravel dyke bases in Dongting Lake area. Rather comprehensive discussion is also made on the vertical cut-off wall construction technology as well as on-site quality monitoring methods through analysis on actual project applications. At the end of the paper, a case study on the Zhoujiawan Anti-Seepage Project at Xinmin Embankment is offered because this project utilized the methods introduced in this paper with proven good effects through on-site monitoring and testing.