Experimental Study On Solidification Of River Bank Protection By Microbial Mixing And Percolating Sand

Riparian collapse is a form of channel evolution which exists in alluvial rivers.The frequent occurrence of river bank collapse will seriously threaten the safety of river dike,river regime stability,navigation development and coastal infrastructure,and cause a large amount of land loss on both sides of river.The traditional rigid revetment does great harm to the environment because it cuts off the connection between surface water and groundwater,and the plant measures are affected by many factors,so the revetment efficiency is low.As a new soil improvement technology,microbially induced calcite precipitation（MICP）,which has emerged in recent years,has the advantages of simple principle,convenient operation,high cementation efficiency and environmental friendliness.It has a certain application prospect in the application of river bank protection.This paper discusses the feasibility of MICP technology in ecological revetment,and finally draws the following conclusions:（1）The number of microorganisms was proportional to urease activity,and the p H of microorganisms decreased first and then increased.There is little difference in the mineralization time of solution mineralization tests with different concentrations of cementing fluid,but the mineralization efficiency decreases with the increase of concentration,and the p H of reaction fluid with different concentrations only decreases instantly and stabilizes to about 7.0 when the solution is mixed,which has little influence on the environment.The experimental results show that the optimal cementing fluid concentration is 2.0M,which has high Ca²⁺utilization rate and calcium carbonate production.（2）MICP sand column solidification was carried out by mixing and percolating.In the initial stage,the reactant of mixing solidification has a higher utilization rate and can fill part of the pores.The subsequent infiltration can obviously improve the soil properties and produce sufficient calcium carbonate.After curing,the maximum compressive strength of the sample is 1.86mpa,and the maximum calcium carbonate content is 16.89%.Among the variables studied,particle size has an obvious effect on the curing effect.Fine particles are easy to block and the upper limit of strength is not high,while the calcium carbonate content of coarse particles is gradually accelerated after mixing,and the overall uniformity is good and the strength is high.The mixing ratio has little effect on curing effect.In addition,the disintegration rate and water absorption rate of the sample in still water decreased significantly after curing by four filtration cycles.The disintegration rate and water absorption rate of the sample decreased to a minimum of no more than 2%and 9.26%after 10 cycles of wetting and drying,which decreased by about 50%compared with that of the uncured sand.The results show that the optimal working condition is 0.30～0.60mm particle size sand,mixing ratio 2:8,after mixing again percolation curing 4 times.（3）Application of microbial curing technology in riparian protection,after curing the banks less curing original slope erosion resistance effect is obvious,not curing clay slope after soaking by high water level of water in the process of collapse,and then has a little influence on water cycle of slope shape,may after the slope between18～20°,and the slope is slow,may degree is smaller,the smaller amount of slope foot forward.After 5 cycles of water level,the solidified slope body has no bank collapse.The total content of calcium carbonate in the three slope solidified layers is above 15%.When the slope is steep,the content of calcium carbonate is higher at the foot of the slope,while when the slope is slow,the content of calcium carbonate accumulates in the middle and upper part of the slope.And the three slope curing layers all have good permeability.Finally,the microbiological percolation solidified sandy slope is more likely to be blocked than the solidified layer of viscous slope,and the solidified slope body calcium carbonate distribution is not uniform.