Experimental study on optimizing ratio of EICP solution to reinforce red mudstone filler based on response surface method

In order to explore the effects and mechanisms of the urease-induced calcium carbonate precipitation (EICP) technology on the solidification of red mudstone fillers, urease is extracted from soybean, and the ratio of EICP solution is optimized by the response surface method. The curing effects of EICP solution under the optimized ratio are tested through the unconfined compressive strength tests, expansion tests, permeability tests and crack development tests under wetting-drying cycles. The curing mechanism is explained by using the XRD, NMR and SEM tests. The results show that the optimized process parameters are as follows: the ratio of gum to enzyme is 1.5:1, the concentration of urease is 100 g/L and the concentration of cementing solution is 1.4 mol/L. The unconfined compressive strength of the sample under the optimized ratio is 55.21% higher than that of the plain soil. The free expansion rate and the loadless expansion rate decrease by 25.10% and 45.65%, respectively. The saturated permeability coefficient is reduced by 90.54%. The cracks of red mudstone filler samples are greatly reduced after wetting-drying cycles. The content of calcium carbonate in the red mudstone filler increases significantly after curing, and the generated calcium carbonate plays the role of pore filling and cementing soil particles, reducing the number of large and medium pores in the samples. The research results provide a reference for the engineering applications of the EICP technology in red mudstone filler.