Construction Materials And Technology Of Concrete Cutoff Wall In100M Level Deep Overburden Foundation

Hydropower industry is developing vigorously in Western China, with many hydropower projects of different sizes having been constructed. Because of the complex geological conditions in the west, however, the problem concerning dam foundation seepage has to be overcome in the construction of many hydropower stations. Dam foundation seepage control can be classified into two types, horizontal seepage control and vertical seepage control, while for the latter, curtain grouting and cut-off wall are two anti-seepage technologies most frequently employed. Cut-off wal is preferred for seepage control in the construction of a dam on the overburden of over one hundred meters. In China, cut-off wall of100metres is still the first, so in the construction of such cut-off wall in the deep overburden, many technical difficulties must be overcome, which include the features of the concrete pouring cut-off wall, properties of slurry stablizing the wall, construction technology and productive test of hole and grooveThe concrete mixture pouring cut-off wall should have high workability, rheology, durability and mechanical property. To meet the above requirements, two concrete mixes were chosen for the experiment according to the engineering experience. The results showed that the slump, impermeability, and compressive strength all can meet the technical requirements of the dam foundation concrete cut-off wall. And then through the comparison experiment, a concrete mix of low compressive strength and high water-cement ratio is optimised to carry out experiments about slump loss, setting time and other property indicators. The results indicate that this new concrete mix still can meet the technical requirements of concrete placement of the cut-off wall, and this mix is chosen for the project.MMH mud with excellent property of stablizing wall was chosen for the construction of the slot at one-hundred-meters level. Research about the MMH mud showed that MMH mud owns properties of high rheology, resistibility to salt pollution, and a strong solid wall property verified through experiments.Research about the effects of CMC upon MMH mud property, foud that low concentration led to viscosity reduction, while high concentration caused viscosifying effect. Therefore, MMH mud with such mixing ratio can fulfill the capacity of stablizing wall and carrying rock powder.Combined construction method was adopted in the construction process, according to the characteristics of the strata and depth of the hole. On the basis of drill-clamshell method (two-drill one-clamshell method, three-drill two-clamshell method), the sub-processes, sub-strata of the drill grasping alternately,drilling split alternately and drill grasping burst alternately orderly and efficient construction methods, which combines the advantages of various construction methods and can be effectively employed in construction with the areas covered by ultra-deep sand and gravel cover layer in which large boulders, boulders and cemented strata coexist.Productive test of cut-off wall was carried out with the above materials and technologies, by which the cut-off wall at one-hundred-meters level was successfully completed, fulfilling the technical requirements through quality test indoor and on site.