基于统一强度准则的桩侧卸荷缩孔弹塑性解析解

Elastoplastic Analytical Solutions for Borehole Contraction of Bored Piles by Boring Unloading Based on Unified Strength Theory

为对灌注桩卸荷缩孔过程进行定量预测,采用统一强度屈服准则并结合非相关联流动法则,推导了桩侧卸荷缩孔大应变和小应变弹塑性解析解,并分析土体中主应力系数、土体剪胀角、土性参数等对桩侧卸荷缩孔解析值的影响,结果表明:中主应力系数b、土体内摩擦角φ值越大,土体剪胀角ψ值越小,越有利于灌注桩孔壁稳定性;采用Mohr-Coulomb屈服准则以及当孔壁土体进入塑性状态后采用小应变解所得结果均偏向于保守;中主应力系数b越大,对应的圆柱孔孔壁沿径向同一位置处的径向应力和孔壁最大环向应力值越大,而同一位置处的孔周位移越小;孔壁最大环向应力出现位置随着b值的增大而逐渐靠近圆柱孔孔壁,而孔壁最大环向应力增长幅度随着b值的增大而减小;采用大应变解和小应变解分析圆柱孔卸荷缩孔孔周应力场和位移场分布规律皆可满足要求。研究成果可应用于灌注桩成孔开挖过程中孔壁土体稳定性以及灌注桩承载特性的定量分析。

To quantitatively predict the process of unloading for bored piles,combining the unified strength theory(UST)with the non-associated flow rule,the elastoplastic analytical solutions of large strain and small strain for borehole contraction of bored piles were derived.And the influence of intermediate principal stress,dilatancy angle and parameters of piles on analytical values in the borehole contraction process were analyzed.The result indicated that the larger the coefficients of intermediate principal stress b and the internal friction angle of soilφwere,the smaller the dilatancy angleψof soil was,and the better the stability of borehole walls of bored piles was.The solutions based on the Mohr-Coulomb yield criterion and the small strain theory in a plastic state of borehole wall soil were both conservative.The larger the coefficient of intermediate principal stress b was,the larger the radial stress and the maximum circumferential stress at the same position of cylindrical borehole wall were,and the smaller the radial displacement at the same position was.With the increase in the coefficients of intermediate principal stress b,the maximum circumferential stress gradually approached the borehole wall,simultaneously,the increment of the maximum circumferential stress decreased with the increase in the coefficient of intermediate principal stress b.Both solutions for soil stress and displacement fields around the cylindrical borehole in the process of borehole contraction due to unloading by large and small strain theories all meet the requirements.The findings could be applied to the quantitative analysis for the stability of borehole wall soil during boring and the bearing characteristics of bored piles.