Experimental Study On Bearing Characteristics Of MICP Post-Grouting Pile

In the traditional post-grouting method,cement concrete is usually used as the cementing material to be injected into the pile,so that the soil around the pile shaft can be strengthened,and this method can indirectly improve the bearing capacity of the pile.However,this method requires a series of complex construction techniques and special grouting equipment,and also causes pollution to the soil and the environment.In this paper,a new microbially induced calcite precipitation(MICP)grouting technique is proposed,which is pollution-free to the environment and has fast and efficient cementing ability.In this paper,two MICP(microbially induced calcite precipitation)post-grouting technologies were innovatively proposed and a series of model tests were carried out,including pile foundation model test under vertical load and pile foundation model test under horizontal load.The main point is to study the influence of MICP-grouting on end bearing capacity and lateral resistance character.Its main contents include:(1)In order to reveal the influence of MICP pile-toe grouting treatment on the vertical bearing capacity of model piles,two sets of model tests of concrete piles under vertical load were carried out in carbonate sand foundation(one set of tests was treated by microbial grouting,and the other set of tests were not treated by microbial grouting),and the strength of soil strengthened at different positions under the concrete pile toe after MICP grouting was measured,SEM images were used to show the MICP-cemented sand samples at different positions under the pile toe of MICP grouting model.The test results showed that :(1)the ultimate bearing capacity of model piles increased by 3.4 times and the ultimate toe bearing capacity of pile increased by 8.5times after the treatment of microbial grouting.(2)after the microbial grouting treatment,a bubble-shaped reinforcement range was formed under the pile end,with a depth of 25 cm.The strength of the strengthened soil at different spatial positions decreases with the increase of the distance from the pile toe.(3)SEM image shows that the higher the content of calcium carbonate,the stronger the cementing sand.In addition,in the process of microbial grouting,calcium carbonate crystal precipitation has three functions :(a)filling the pores in the particles;(b)act as a connector between sand particles;(c)covering the surface of sand particles.(2)In order to reveal the influence of MICP pile-shaft grouting treatment on the lateral load-bearing characteristics of model piles,two sets of model tests of concrete piles under vertical load were carried out in silica sand foundation(one set of tests was treated by microbial grouting,and the other set of tests were not treated by microbial grouting).After MICP grouting,the content of calcium carbonate at different positions around the concrete pile shaft was measured,and the test results showed that:(1)the ultimate lateral resistance of model piles increased by 1.5 times after microbial grouting treatment.Under the same lateral load after the microbial grouting treatment,the pile bending moment,the soil resistance of the pile shaft and the lateral displacement of the pile all decreased obviously.(2)the higher the content of calcium carbonate in strengthened sand,the better the deformation improvement effect of the pile at the corresponding position.The calcium carbonate content in strengthened sand then decreases along with the increase of soil depth and distance from pile shaft.The grouting reinforcement area on the side of microbial pile is the area above 580 mm away from the sand surface.