Optimization study of PP-PAM composite modified microbial solidified expansive soil based on response surface method
[Objective]The microbial-induced calcium carbonate precipitation technology(MICP)can effectively improve the strength of expansive soil,as well as reduce the expansion and shrinkage of expansive soil,however,there are some problems such as obvious brittleness,and high disintegration during the early curing period.In order to further improve the brittle failure of microbial solidified expansive soil and the high amount of disintegration in the early stage of conservation,[Methods]In this study,the effects of adding polypropylene fiber(PP)and polyacrylamide(PAM)on the failure mode and water stability of microbial solidified expansive soil were studied on the basis of microbial solidified expansive soil.With the fiber length,fiber content,and polyacrylamide content as the influencing factors,and with the unconfined compressive strength and disintegration a-mount as the response values,the Box-Behnken Design response surface method was used to conduct the condition optimization test,based on the above research a response surface regression model was established.The effects of the length of polypropylene fiber,the amount of polypropylene fiber,polyacrylamide,and their interaction on the comprehensive indexes of strength and dis-integration of microbe-cured expansive soil were studied.[Results]The result show that the addition of polypropylene fiber reduces the brittleness when the microbial curing and expanded soil is destroyed,improves the strength of the soil,and reduces the disintegration of the expanded soil.However,with the increase of fiber length,the disintegration amount increases gradually;the addition of polyacrylamide reduces the disintegration of expansive soil but decreases the soil strength.[Conclusion]In the test range of influencing factors,the highest unconfined compressive strength and the lowest disintegration amount were taken as the principle,and the optimal ratio was obtained by Box-Behnken response surface method:the length of polypropylene fiber was 9 mm,the content was 0.5％,and the content of polyacrylamide was 0.12％.Under this ratio,the unconfined compressive strength of the composite solidified soil was 1.24 MPa,which was increased by 29.57％compared with the optimization period,and the disintegration amount was only 0.34％,which decreased by 99.07％compared with the optimization period.
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