A Study On Seepage Control Issues Of Anti-uplift Method For Underground Structures Based On Intercepting And Discharging Water

The underground structures need to bear the action of underground water pressure.With the increasing depth and width of underground structures,the seepage environment becomes more and more complex,and the anti-uplift problem becomes more and more prominent.The passive anti-uplift measures designed in a relatively conservative way may also fail.In this condition,the active anti-uplift method based on intercepting and discharging underground water(IDUW)can be used as an important supplement to the passive anti-uplift method.However,the research work on the key theories and technical problems of the IDUW method is not perfect at present,which has become an obstacle to its popularization and application.Therefore,this paper firstly introduces the concept,structure and application prospect of the IDUW method,expounds several key problems existing in the application of this method,and summarizes relevant literature.The problems of relief well clogging,durability of cutoff wall and seepage field calculation,which are most concerned by engineers and technicians,have been deeply studied.The specific contents are as follows:(1)Research on constriction size distribution(CSD)and permeability characteristics of no-fines concrete.Based on the Silveira model,a simplified algorithm of CSD for no-fines concrete is proposed by using probability method,which reflects the effect of cement slurry on aggregate wrapping and pore filling.The standard cubic specimen of no-fines concrete was made for slicing test.The test results show that there is little difference in the number of pores between the specimens with the same aggregate,and the cement slurry tends to concentrate into small and fine pores.In addition,based on the permeability test and sand injection test,the law of seepage and the law of decrease and recovery of permeability in the no-fines concrete are obtained.(2)Research on retention and clogging performance of no-fines concrete.A sand flume model was designed and made in the laboratory.Uniform sand,continuously graded sand and discontinuously graded sand were used as the base soil,respectively,and no-fines concrete specimen was used as filter to carry out seepage test.In order to improve the retention performance of no-fines concrete for unstable soil,the test of transitional filter was carried out.The long-term permeability of sand and no-fines concrete system was also tested.Based on the testing results and literature data,the filtration patterns of no-fines concrete interface is described,and the geometric and hydraulic conditions of preventing clogging of no-fines concrete are discussed.(3)Durability definition of cutoff wall and research on crack leakage variation process of cutoff wall.It is pointed out that the key to maintain the durability of cutoff wall is that the crack leakage remains constant for a long time or decreases gradually.A self-made sand flume model was used to simulate the cutoff wall with crack.The test results show that when there is suitable backfill at the downstream of the crack,the crack will occur a phenomenon of "self-healing".Moreover,sand gradation,crack length,hydraulic conditions and other factors have an impact on crack leakage.(4)Seepage field analysis under the IDUW condition and introduction of engineering case.In the environment of IDUW,a simplified calculation method for the total flow rate of the relief wells and the hydraulic head values of the characteristic points are proposed when the influence of the cutoff wall leakage and the flow around the end of cutoff wall is considered.The far field boundary of hydraulic head under various topographic conditions is determined.Finally,an engineering case of the IDUW method is introduced,and its success and shortcomings in application are summarized.The research in this paper shows that the IDUW method can form a relatively closed seepage field,significantly reduce the total discharging flow rate and the impact on the surrounding environment.Relief wells making of no-fines concrete with large diameter have strong permeable capacity.When the appropriate interfacial ratio(size ratio between the constriction of no-fines concrete and the diameter of base soil)is set,and hydraulic conditions are limited and interference is reduced,the relief wells are almost free of clogging.The large diameter of relief wells also provides a possibility for later cleaning and maintenance.In the non-corrosive environment,the durability of the cutoff wall is determined by the variation of crack leakage.When the crack outlet is properly backfilled and the hydraulic conditions are stable,the crack leakage will gradually decrease,resulting in the phenomenon of "self-healing",thus guaranteeing the durability of the cutoff wall.