基于CPTU测试的K_0固结黏土中静压桩时变承载力研究

基于空间滑动面(SMP)准则改进的K_0固结各向异性修正剑桥模型,考虑K_0固结饱和黏土初始应力各向异性、应力历史及应力诱发各向异性对土体三维力学特性的影响,推导了静压沉桩柱孔扩张问题的弹塑性解析解。在此基础上,根据桩侧土体应力状态与单剪试验中试样应力状态的相似性,结合桩周土轴对称固结理论提出采用孔压静力触探仪(CPTU)锥尖阻力、锥肩孔隙水压力及相应孔压消散数据预测静压桩时变承载力的理论方法。通过离心机模型试验实测结果和理论预测值的对比,验证了理论方法的有效性,研究了静压桩承载力随时间的变化规律。研究结果表明,本文理论预测方法避免了土体基本参数测定等繁琐过程,且可以较为合理地预测静压桩时变承载力;静压桩沉桩结束后其承载力在短时间内迅速增加,之后承载力增加幅度变缓且逐渐趋于稳定值;静压桩桩径越大,沉桩结束后承载力增加的速度越慢,承载力达到稳定值的时间越长。

Time-dependent bearing capacity of jacked piles in K0 consolidated clay based on CPTU tests

Based on the SMP criterion-based K₀ consolidated anisotropic Cam-clay model, an analytical solution to cylindrical cavity expansion for pile installation is derived. This solution incorporates the effects of the initial stress anisotropy, stress history and initial stress-induced anisotropy on the three-dimensional properties of K₀ consolidated clay. According to the similarity of the stress state between the soil adjacent to pile shaft and the soil sample in simple shear tests, a theoretical approach to predict the time-dependent bearing capacity of jacked piles is proposed. This method is based on the axisymmetrical consolidation theory, and the parameters required in this method are only the cone tip resistance, cone base pore water pressure and the corresponding dissipation data from the CPTU sounding. This theoretical approach is verified by the centrifugal model tests, and the time-dependent bearing capacity of jacked piles is studied. The results show that the proposed theoretical method can properly predict the time-dependent bearing capacity of jacked piles, and can avoid the complicated test process of soil properties. The bearing capacity increases rapidly in short time after the pile installation and gradually tends to a stable value. The larger the pile diameter is, the slower the bearing capacity increases and the longer the required time for bearing capacity reaching stable value.