考虑泥皮厚度的红层泥岩桩基承载力计算公式修正

Correction of Bearing Capacity Formula of Pile Foundation in Red Mudstone Considering Mudcake Thickness

通过室内桩-岩剪切试验、数值模拟及桩基模型试验,研究了泥皮厚度对红层泥岩桩基承载力的影响,提出了不同泥皮厚度下的红层泥岩桩基承载力修正系数,对红层泥岩桩基承载力计算公式进行了修正。为建立泥皮作用下的桩-岩接触面本构模型,进行了室内试验并发现:红层泥岩桩-岩接触面力学性状呈现应变软化特征;泥皮存在降低接触面峰残强度,峰值摩擦角和黏聚力分别降低47.7%和53.4%,残余摩擦角和黏聚力分别降低39.5%和34.4%。基于试验结果,建立桩-岩接触面应变软化本构模型,将其植入FLAC3D模拟不同泥皮厚度对桩基承载力的影响,结果表明:桩基承载力随泥皮厚度增加而减小,泥皮厚度超过50 mm时桩-岩相互作用由泥皮自身强度决定。根据计算结果分析桩基承载比与泥皮厚度关系,提出了承载力修正系数。在此基础上设计了一套室内桩基模型试验装置,验证了修正系数的合理性。

By indoor pile-rock shear test, numerical simulation and model test, the influence of mudcake thickness on bearing capacity of pile foundation in red mudstone is studied, the correction coefficients of the bearing capacity of pile foundation is proposed to amend the formula of the bearing capacity of pile foundation in red mudstone. For building the pile-rock interface constitutive model under the influence of mudcake, the indoor test is conducted. It is found that （1） the pile-rock interface mechanical in red mudstone has the characteristics of strain softening; （2） the existence of mudcake reduced peak strength and residual strength of the interface, the peak friction angle and cohesive force are reduced by 47.7% and 53.4% respectively, the residual friction angle and cohesive force are reduced by 39.5% and 34.4% respectively. The rock-pile interface strain softening constitutive model which has been established based on the results of pile-rock shear tests is implanted into FLAC3D to simulate the bearing capacity of pile foundation under different mudcake thicknesses. The result shows that the bearing capacity of pile foundation decreases with the increase of mudcake thickness, and the interaction of pile-rock is decided by its own strength of mudcake when the thickness is more than 50 mm. According to the calculation result, the relationship between the pile foundation bearing ratio and the mudcake thickness is analysed, and the correction coefficient of bearing capacity is put forward. The correction coefficient is verified by a self designed indoor model test device of pile foundation.