桩板式路基引扩孔灌浆后植入桩的承载特性

Bearing Characteristics of Implanted Pile After Pre-bored Grouting in Pile-slab Subgrade

为了探明桩板路基结构中引扩孔灌浆后植入预制混凝土桩的承载特性和荷载传递机制,以G3W德阳-上饶高速公路合肥至枞阳段桩板路基桩基工程为依托,开展了2组不同扩孔条件下孔内灌入砂浆后植入预制桩的静载荷试验。考虑植入桩中内部芯桩、外围砂浆固结体与周围土三者的相互作用,基于界面剪切试验,揭示了芯桩-砂浆界面、砂浆-土界面剪切性能的非线性,并分别建立了砂浆-土界面双曲线剪切模型和芯桩混凝土-砂浆界面弹性-破坏剪切模型。在此基础上,构建了引扩孔灌浆后植入桩三维数值分析模型。现场载荷试验结果验证了数值模型的可靠性,并对引扩孔灌浆后植入桩的荷载传递机制和影响因素进行了数值分析。结果表明:引扩孔灌浆后植入桩桩端荷载约为桩顶总荷载的20%,整体表现为端承摩擦桩的承载特性;外围较高强度水泥砂浆可有效将芯桩荷载传递至周围土,能起到扩径增强的作用;试验工况下芯桩-包裹砂浆界面阻力沿桩长呈两端大、中间小的分布特点,而包裹砂浆-土界面阻力随深度呈逐渐增大变化趋势;外围砂浆厚度的增加有利于提升传统预制管桩承载性能,但其厚度不宜过大,厚径比宜为0.2~0.5,以充分发挥内芯预制桩承载特性和芯桩-砂浆的协同作用。

To investigate the bearing characteristics and load transfer mechanism of implanted pile after pre-bored grouting in pile-slab subgrade structure,relying on the pile project of pile-slab subgrade in Hefei-Zongyang section of G3W Dezhou-Shangrao expressway,two sets of field load test are conducted.Two groups of static load tests of precast implanted pile after pre-bored grouting under different reaming conditions are carried out.Considering the interaction among implanted pile inner core,outer cement mortar,and surrounding soil,the nonlinear mechanical behaviors of core pile-cement mortar interface and cement mortar-soil interface are revealed through a series of interface shear tests.A hyperbolic model and an elastic-failure model are adopted to characterize the shear behaviors of cement mortar-soil interface and core pile-cement mortar interface respectively.Based on this,a three-dimensional numerical analysis model is conducted for implanted pile after pre-bored grouting.The numerical model is verified by comparing the calculations with field test result,and further extended to reveal the load transfer behaviors of implanted pile after pre-bored grouting.The result indicates that the load at the end of implanted pile after pre-bored grouting is about 20%of the total load at the top of pile.the bearing characteristics of end-bearing friction pile is shown on the whole.The outer cement mortar with high-strength can effectively transfer core pile load to surrounding soil,and play a role in expanding core pile diameter.Under test conditions,the interface resistance between core pile and wrapped mortar is large at both ends and small in the middle along pile length,while the interfacial resistance between cement mortar and soil gradually increase with depth.Increasing the thickness of outer cement mortar is beneficial for improving the bearing performance of traditional precast concrete tubular pile.However,the thickness of outer cement mortar should not be too large,which is supposed to be 0.2-0.5 for effectively utilizing the synergistic effect of inner core precast pile bearing characteristics and core pile-cement mortar.