Abstract: The southeast coast of China, particularly in Wenzhou, is characterized by soil strata comprising a thick layer of soft soil overlying an uneven pebble layer. In this region, post-grouting technique is frequently employed to enhance the bearing performance of bored piles. To assess the effectiveness of post-grouted piles in such strata, several model tests were carried out to analyze the impact of varying grouting volume on the bearing capacity of the piles. Subsequently, scanning electron microscope (SEM) tests were used to explore the distribution ranges of the grout in the pebble layer. Furthermore, the relationship between the diffusion range and the bearing capacity of piles was investigated. The results show that the grout effectively permeates the pebble around piles tip, and increasing the grouting volume expands the permeated range. The most significant improvement in pile bearing capacity occurs when the range is 3-4 times the pile diameter. An optimal grout volume level is identified, with the normalized value of the grout volume being approximately 2.8 for the model piles. The bearing capacity of the pile is no longer significantly increased once the normalized value of the grout volume is exceeded. Notably, the optimal grout volume closely aligns with the predicted result of Liu Jinli's formula[1]. The utilization of scanning electron microscopy proved instrumental in evaluating the effect of post-grouting in a soil layer characterized by a thick layer of soft soil overlying an inhomogeneous pebble layer.

Key words: pebble bearing layer, post-grouting at pile tip, grouting volume, static load test, scanning electron microscope (SEM), microscopic evaluation