Investigation on measurement methods and distribution characteristics of negative skin friction of piles in high-fill ground of mountainous areas

This study proposes a method to measure pile skin friction by observing the stress in the main reinforcement of foundation piles using strain gauges and monitoring the axial forces through water immersion of the fill around the pile. The high-fill foundation filler exhibits significant spatial variability, leading to interlaced positive and negative skin friction distributions along the depth and multiple neutral points in the in-situ test results. The properties of the filler directly influence the neutral point depth ratio. Under the self-weight load of the upper fill, the lower fill is compacted and generated positive skin friction. After consolidation settlement in duced by water immersion, the positive skin friction transforms into negative skin friction. In the test area, the weighted average negative skin friction values within the weak soil layer around three piles are 14.6 kPa, 25.4 kPa, and 9.1 kPa, with corresponding negative skin friction coefficients of 0.133, 0.097, and 0.104.