受动力打桩影响的泥岩宏细观力学特性室内试验研究

Laboratory test on macroscopic and mesoscopic mechanicalproperties of mudstone affected by driven pile

基于原状、受动力打桩影响的桩周泥岩的扫描电子显微镜(SEM)试验和室内单轴抗压试验,分析桩周扰动泥岩和原状泥岩的细观结构,揭示原状泥岩及桩周扰动泥岩单轴抗压强度的演变规律,并与泥岩的点荷载试验结果进行对比;同时开展桩周扰动泥岩三轴压缩试验,明确桩周扰动泥岩抗剪强度的演化特征,将试验获得的内摩擦角与由图像处理软件确定破裂面角度ψ推算出的内摩擦角进行对比。研究结果表明:受动力打桩影响和受静载试验破坏的泥岩出现了二次损伤,与原状泥岩相比发生了结构性损伤;选用合适的SEM图像放大倍数能够反映完整的损伤裂隙;与原状泥岩相比,桩周扰动泥岩的单轴抗压强度平均值降低28.2%,且试验得到的泥岩单轴抗压强度低于工程勘察报告的推荐值;三轴试验测得的桩周扰动泥岩抗剪强度指标c=217.2 kPa、φ=21.6°,与图形处理软件所确定的内摩擦角φs=23.2°相近。

The scanning electron microscope(SEM)tests and laboratory uniaxial compression tests were carried out on the mudstone and undisturbed mudstone around the pile affected by dynamic piling.The mesostructure of disturbed mudstone and undisturbed mudstone around pile was analyzed.The evolution law of uniaxial compressive strength of undisturbed mudstone and disturbed mudstone around pile was proposed and compared with the point load test results of mudstone.The evolution characteristics of the shear strength of disturbed mudstone were determined by triaxial compression test.The internal friction angle obtained by the experiment was compared with that derived from the angleψof fracture surface determined by image processing software.The results show that the mudstone affected by driven pile and static load test has secondary damage.Compared with the undisturbed mudstone,structural damage occurs.Proper SEM image magnification can reflect the complete damaged crack.The average uniaxial compressive strength of the disturbed mudstone around the pile is 28.2%lower than that of the undisturbed mudstone,and the uniaxial compressive strength obtained by the test is lower than the recommended value given by the engineering investigation report.The shear strength of disturbed mudstone around pile measured by triaxial test is c=217.2 kPa andφ=21.6°.Theφis similar to the internal friction angleφs=23.2°determined by the graphic processing software.