Experimental Study on Grouting Effect of Combined Post-Grouting Piles in Cohesive Soil

To study the grouting effect of pile end and pile side combined post-grouting technology in cohesive soil, the self-balancing static load test was carried out on two bored piles with length of 56.5 m and diameter of 1.5 m in a bridge pile foundation project, and the test results before and after the combined cement grouting were compared and analyzed. The influences of combined grouting on ultimate load-bearing ability, pile axial force, pile side friction, pile end resistance, and settlement reduction of bored piles in cohesive soil were studied. The findings revealed that the ultimate load-bearing abilities of combined grouting piles in cohesive soil improved by 32.99∼38.42 % as compared with before grouting, the corresponding settlement was effectively controlled, and the grouting effect was remarkable. Combined post-grouting enhanced the soil layer strengths of pile tip soil and pile side soil, improved the condition of pile-soil contact surface, and greatly increased the pile end resistance and pile side friction. The pile end resistances increased by 96.90∼98.61 % and pile side frictions increased by 23.63∼29.70 %, which causes the pile axial force to decay faster along the piles and also has an obvious influence on load transfer characteristic of the test piles. However, in some stages, the reinforcement effect of post-grouting on the soil stiffness of pile side was not obvious or even deteriorated, which reflected the instability of the reinforcement effect of post-grouting technology.