Preliminary exploration of tests on effect of micro-immersion on negative skin friction of pile foundation

In order to solve the problem of negative skin friction of pile foundation in collapsible loess areas, a new idea is proposed to improve the bearing capacity of pile foundation by immersion of the soil around the pile to eliminate part of the loess collapsibility in the process of pile foundation construction. Taking it as a starting point, the concept of micro-immersion is introduced, and the field tests are designed. A preliminary exploration is made on the distribution characteristics and development laws of negative skin friction of pile side under different geological conditions and the degree of micro-immersion. The results show that the high technology of pressure circulation grouting forming pile can achieve micro-immersion of soil around the pile to make it pre-collapse at first, and it can enhance the moisture content of soil significantly within the scope of certain depth below leakage layer and form strong immersion sections, and then it may lead to re-collapsibility and cause negative friction. The discontinuous distribution of the leakage slurry layer in the soil layer results in discontinuous collapsibility of the soil around the pile after the pile is loaded, and the negative skin friction of the pile side shows a staggered distribution along its length. With the gradual increase of the degree of micro-immersion, the positive friction resistance of the pile side is gradually weakened, and the ultimate bearing capacity of the single pile decreases gradually. At the same time, the negative skin friction of the pile side increases gradually, but the increase is small and the value is small. Finally, the shortcomings of this experiment are pointed out and the future research is prospected.