Study On Cement-based Seepage Grouting Composite Materials For Earth-rock Dam

Seepage-induced deformation in earth-fill and rock-fill dams significantly affect engineering safety and can result in additional cost on the required mitigation measures.At present,grouting impermeable materials used in hydraulic engineering are cement slurry and chemical grout.Chemical grouts have not been widely used due to high cost and poor durability,some may even have toxicity which would produces some pollution of groundwater.Compared to chemical grout,cement slurry has some advantages such as low cost,high strength and so on.However,cement grouting has been greatly affected due to the existing limitations,such as the poor fluidity and low stone rate.In this paper,according to the design requirements of anti-seepage grouting and the damaged condition of earth dam and trans-dam culvert,two materials are developed through a series of experiments.We used Portland cement as the basic material of composite single-fluid grouting materials and backfill fly ash and bentonite in cement as the water reducing agent and expansive agent respectively.Laboratory tests concentrate on investigating the three concerned physical properties of the examined grouting materials,i.e.setting time,the slurry fluidity and concretion,under different mixture proportions of the backfilled materials.Based on the experimentally obtained results and SEM,appropriate material mixture proportions are given as cement:fly ash:bentonite=70:25:5,with 5%expansive agent is added in the slurry.In particular,experimental results show that bentonite increases the stone rate of grouting and therefore improve the slurry stability,but it reduces the slurry fluidity.On the other hand,the addition of appropriate amount of fly ash improves the slurry fluidity,which can increase the grouting efficiency.However,as the proportions of the fly ash and bentonite increase,the concretion strength reduces.It is therefore suggested to quantitatively control the mixture proportions of the backfilled materials in order to achieve an optimum strengthening effect.Composite cement-water glass double grout is based on the traditional cement-water glass double grout with some fly ash and bentonite added in the slurry.The composite double slurry has improved the disadvantages of traditional double slurry like poor stability without changing its short setting time and early high compressive strength.In this paper,a series of composite double slurry under different volume ratios of cement and water glass were researched,and their slurry gelling time and the physical properties of the stones were analyzed,and combined with the result of SEM,appropriate material mixture proportions are given as cement:fly ash:bentonite=70:25:5,with volume ratio of cement and water glass are 2:1.We can conclude that the addition of water glass shortens slurry gelling time by a large margin.However,too much water glass leads to a sharply decrease of concretion properties,while too little water glass makes it hard to control its gelling time.Although the addition of fly ash increase slurry setting time and reduces concretion strength,a proper proportion of fly ash improves the slurry fluidity and lower the cost.According to the analysis of the earth and rock dam project,the following two cases may occur:first,seepage water may result in contact scouring between trans-dam culvert and dam which may lead to the flaking of concrete on the surface of culvert.As a result,the durability of trans-dam culvert will decrease.Second,seepage water may lead to uneven force on the upper and lower sides of trans-culvert which may cause uneven settlement and concrete cracking,it may even cause trans-dam culvert leakage.Based on different conditions,two different grouting schemes are made as followed:as with seepage water has small hydraulic gradient and only forms seepage channel,we reinforce the dam by split grouting with composite slurry;as with seepage water has large hydraulic gradient and forms piping,we reinforce the dam by split grouting with composite double slurry.The results in the paper are to be verified in Datun reservoir in Dezhou,Shandong province.And we will detect seepage-induced problem by GPR and TEM.As well as we find out the flaws,we will reinforce the dam by grouting.