动力打桩桩周泥岩损伤特性与损伤模型

Damage characteristics and damage model for mudstone around driven pile

针对泥岩地基同施工场地条件下动力打入桩的承载力差异性大且部分打入桩承载力不足等异常现象,文章开展了桩周0.2m处打桩前后的桩周泥岩单轴抗压强度对比试验,和打桩后的桩端中风化泥岩三轴压缩试验,明确打桩后桩周泥岩的损伤特性,基于统计损伤理论建立考虑受打桩影响的桩周泥岩损伤本构模型,并对泥岩地基打入桩的承载性能进行探讨。研究表明:打桩后桩周0.2m处泥岩强度平均损伤28.2%,弹性模量平均损伤41.4%;桩端中风化泥岩损伤后抗剪强度参数平均值为c=217.2kPa、φ=21.6°,φ仅是同场地原状强风化和全风化泥岩的49.1%和51.4%;打桩后桩周泥岩应力-应变曲线的损伤模型计算值的与实测值吻合较好,验证模型的合理性;泥岩地基打入桩承载力异常特征为桩端受力小,但桩端沉降显著,静载破坏时桩端阻力的平均占比为5.25%;动力打桩对桩周泥岩的损伤是泥岩地基打入桩承载力异常的重要原因;泥岩地基打入桩的设计计算与数值模拟采用原状泥岩力学参数不合理,泥岩损伤后不易恢复,建议按损伤特性赋予参数。研究结果对泥岩地基打入桩的设计、施工、承载力评价有较强的参考价值。

In view of the insufficient bearing capacity of dynamic driven pile in mudstone foundation,uniaxial and triaxial compression tests of mudstone around the pile 0.2 m were carried out before and after driving.Based on the statistical damage theory,the damage constitutive model of mudstone affected by pile driving is established.Combined with the field tests data,the bearing capacity of the driven pile and the damage characteristics of the mudstone around the pile are explored.The results show that the average damage of mudstone strength and elastic modulus at 0.2 m around pile is 28.2%and 41.4%respectively.The average shear strength parameters of the moderately weathered mudstone at the pile end after damage are c=217.2 kPa andφ=21.6°,andφis only 49.1%and 51.4%of the undisturbed strongly weathered and fully weathered mudstone in the same site.The calculated value of the damage model of the stress⁃strain curve of the mudstone around the pile after driving is in good agreement with the measured value,which verifies the rationality of the model.The characteristic of abnormal bearing capacity is that the pile end bears little force but the settlement displacement of the pile end is significant.The damage of mudstone around the pile caused by dynamic driving is one of the important reasons for the abnormal bearing capacity of driven pile.Mudstone is not easy to recover after damage.It is unreasonable for the mudstone’s undisturbed mechanical parameters to be used to design and calculate the driven pile of mudstone bearing layer,and recommended to reduce the undisturbed parameters of mudstone according to the damage characteristics.The research results could provide reference for the design,construction and calculation of driven piles in mudstone foundation。