| Enzyme Induced Carbonate Precipitation(EICP)reinforcement is a new sand solidification technology that has emerged rapidly in recent years.Its environmental protection and high efficiency provide a new green curing method for solidifying sand.EICP reaction speed is fast and changes greatly.Without intervention and regulation,uneven carbonate deposition will inevitably occur,resulting in poor homogeneity of solidified soil and obvious hole roar effect.The phenomenon that the strength of soil reinforced by EICP is difficult to achieve the desired effect repeatedly restricts and disturbs the popularization and application of this method.At the same time,because the urease activity is obviously affected by temperature,the change of ambient temperature changes the soil temperature,and then affects the stability of urease activity,leading to the rapid or slow process of EICP reaction,and the unstable production of calcium carbonate,which makes the field application effect is not good,or even uncontrollable,and limits the application effect of EICP.In this paper,the regulation of urease activity and the adaptive regulation of calcium carbonate production during EICP curing at different temperatures were studied.The study adopted targeted regulation methods: 1.Control urease activity and calcium carbonate output rate to ensure the stability of calcium carbonate output and the uniformity of soil reinforcement,and improve the reinforcement effect of EICP;2.The intensity regulation rules of EICP sand fixing samples at different temperatures were obtained.The thesis research has achieved good results,and the research work mainly includes:(1)The change rule of urease activity and the rate of EICP to produce calcium carbonate at different temperatures was studied,the EICP sand solidification process was determined,and the EICP sand solidification test was completed.The temperature increase can greatly improve the instantaneous activity of urease and the deposition rate of calcium carbonate,but the aging of urease activity will shorten,especially when the temperature is higher than 60℃,urease will enter the state of rapid inactivation,affecting the overall effect of soil reinforcement.(2)Through experimental studies,urease inhibitor A was used to regulate urease activity,and the EICP sand fixation regulation test was completed at 30-75℃,which improved the uniformity of EICP sand fixation at different temperatures.The optimal extraction conditions of inhibitor A were p H 7 or 8 and 15 min at room temperature.When the temperature is 30-75℃,the urease activity,the calcification rate of EICP and the final calcification rate can be controlled by adding different mass fractions of inhibitor A to make the calcification reaction more uniform.The relationship between the dosage of inhibitor A and the regulation of urease activity and calcification rate was established.From the control effect,the sand curing uniformity is better when the temperature is 30-55℃.When the temperature is 60-75℃,the solidification uniformity of sand is poor.After curing,the calcium carbonate content of sand decreases and its stability is poor.(3)The combined curing method of inhibitor and reducing agent was used to improve the content and uniformity of calcium carbonate in soil,and the effect of urease reducing agent B was studied to strengthen sand fixation performance at high temperature.The changing rule of urease activity and EICP calcium carbonate production rate was obtained by controlling the different dosage of reducing agent B.The combination of inhibitor and reducing agent to solidify sand at high temperature can effectively improve the uniformity and compactness of solidified soil,and reduce the permeability of soil.The maximum unconfined compressive strength of soil is increased by50%-130%,and the permeability coefficient is reduced by one or two orders of magnitude.(4)The curing methods of inhibitor-stabilizer(30-55℃)and inhibitor-reducing agent-stabilizer(60-75℃)were used to increase the amount of carbonate precipitation in soil,study the effect of adding stabilizer C,determine the best dosage of stabilizer C,improve the stability of solidified soil,and further strengthen the sand-fixing properties at different temperatures.Inhibitor curing and combined curing methods can improve the curing effect of sand,but the content of calcium carbonate is low and the stability is poor.On this basis,the application research of stabilizer was carried out,and it was found that the sand cementing effect was the best when the content of stabilizer C was 20%.The addition of stabilizer C does not affect the effect of inhibitor sand fixation and combined sand fixation,thus enlarging the applicable temperature range of EICP sand fixation.The combined curing method of EICP-stabilizer can increase the content of carbonate,reduce the permeability coefficient of soil and improve the strength of soil.The maximum unconfined compressive strength of soil is higher than 2MPa at all temperatures. |
PDF Full Text Request