Effect Of Cementation Solution Parameters On MICP Reinforced Silt

Microbially induced carbonate precipitation(MICP)has high reaction efficiency,easy control,good environmental tolerance,and has great potential to surpass traditional foundation treatments.Most of the nutrient solutions and cementation solutions used in existing MICP studies are analytical grade reagents,which are expensive and not conducive to large-scale application and promotion.In order to better control the cost and promote the application,it is necessary to study the feasibility of using industrial grade reagents for MICP reinforcement of soil.The parameters of cementation solution have always been one of the important factors of MICP reinforcement effect,the concentration,interval time and number of infiltration rounds may affect the production of calcium carbonate,crystal form,crystal size and spatial distribution in MICP reaction.Especially in the current research on fine-grained soil reinforcement,the problem of uneven reinforcement is generally faced,which has a great impact on the final reinforcement effect of MICP,and poor reinforcement uniformity has become an important difficulty and challenge that restricts the further application.Based on this,in this paper,the influence of cementation solution parameters on the reinforcement effect of silt is experimented by MICP.Specifically,the solution experiment and silty reinforcement experiment are carried out by using industrial grade nutrient solution to culture bacteria and industrial grade calcium chloride as the source of cemented calcium.Its main contents include: the effects of urea concentration,calcium ion concentration,solute concentration ratio and calcium source purity on bacterial urease activity and calcium carbonate production through solution experiments;The effects of cementation solution concentration,number of infiltration rounds and interval time on the reinforcement effect of silt are studied by pre-mixing and surface infiltration method.By changing the dry density and multi-concentration combined with infiltration,the method of effectively improving the uniformity of silt reinforcement is studied.The main conclusions are as follows:(1)Feasibility study of using industrial grade reagents to culture bacteria and as a source of cemented calcium.The use of industrial grade nutrient solution to culture Sporosarcina pasteurii had no significant effect on the growth of bacteria.Using industrial grade calcium chloride as calcium source will slightly reduce calcium carbonate production,but the gap with analytical grade calcium chloride is acceptable and still maintains a high calcium carbonate productivity.(2)Study on the influence of cementation solution parameters on MICP reaction in solution environment.Appropriately increasing urea concentration can enhance bacterial urease activity,but should not be too high.Calcium ion concentration inhibits bacterial urease activity.The dosage of urea in the cementation solution should not be lower than the dosage of calcium chloride,and the solute concentration ratio should be 1:1.(3)Study on the influence of infiltration rounds and interval time on MICP reinforced silt.Increasing the number of infiltration rounds can increase the strength and the calcium carbonate production,but the effect on high cementation solution concentration is limited.The increase of the interval time does not have a direct impact on the strength,and the interval time of 12 h can already achieve a better reinforcement effect.(4)Study on the effect of cementation solution concentration on the uniformity of MICP reinforced silt.The uniformity of silt reinforcement is mainly affected by cementation solution concentration.When the concentration is lower than 1mol/L,calcium carbonate production generated in the upper part is more than that in the lower part,the failure mode is lower shear failure.When the concentration is 1mol/L,the distribution of calcium carbonate is relatively uniform,the failure mode is overall shear failure.When the concentration is higher than 1mol/L,calcium carbonate production in the upper part is less than that in the lower part,the failure mode is upper shear failure.(5)Study on methods to improve the uniformity of MICP reinforced silt.Increasing the dry density of the silt can improve the uniformity of the reinforced silt,so that the upper calcium carbonate production percentage at higher cementation concentration increases,and the overall strength increases.The treatment of multi-concentration cementation solution had a significant effect on the strength and the calcium carbonate production percentage,which could improve the uniformity of calcium carbonate distribution during MICP reinforcement of silt,and obtain higher calcium carbonate production percentage,thereby improving the strength.