高喷插芯组合单桩荷载传递简化计算分析

 高喷插芯组合桩(JPP桩)是由高压旋喷桩和预应力混凝土芯桩构成的一种新型组合桩。结合JPP桩不同的组合特点，采用理想弹塑性模型模拟桩侧土体的非线性，弹性模型模拟水泥土与芯桩界面的荷载传递特性，双折线函数模拟桩端土的硬化特性。基于荷载传递法，考虑水泥土与芯桩界面摩擦、水泥土或芯桩与桩周土界面摩擦，提出不同组合形式下JPP桩荷载传递的简化计算方法，并与模型试验结果进行对比，验证该计算方法的可行性和可靠性。采用提出的简化计算方法对JPP桩荷载传递机制进行分析，并对不同组合形式、不同水泥土厚度、不同水泥土弹性模量、不同刚度系数比等影响荷载传递的主要因素进行计算分析。分析结果得出：从承载力、沉降控制、经济角度综合考虑，分段组合承载效果最好；增加水泥土厚度可有效提高JPP桩承载力；JPP桩变形由高强度的芯桩控制，水泥土弹性模量的改变对JPP桩变形影响较小。

SIMPLIFIED CALCULATION AND ANALYSIS OF LOAD TRANSFER BEHAVIOR FOR SINGLE JPP

Jet grouting(JG) soil-cement-pile strengthened pile(JPP) is a new kind of composite pile composed of high pressure jet grouting pile and prestressed core pile. JPP has different combination forms depending on soil conditions as well as the bearing capacity requirements. Considering combination features of JPP，a perfect elasticplastic model is used to simulate nonlinear of soil around pile，and an elastic model is used to simulate load transfer behavior of interface between soil-cement and core pile，and a double broken line function is used to simulate hardening characteristics of soil under pile tip. Based on the load transfer method，taking into account interface friction betweent soil-cement and core pile，and interface friction between soil-cement or core pile and soil around pile，a simplified calculation method is presented to analyze load transfer of different combinations of JPPs. The feasibility and reliability of the method are verified by the model test results. Load transfer mechanism of JPP is analyzed by the proposed simplified calculation method；and the main factors of JPP load transfer，different combinations，different soil-cement thicknesses，different elastic moduli of soil-cement，and different stiffness coefficient ratios，are analyzed comparatively. The calculation results show that，in view of the bearing capacity，settlement control and costs，the sub-combination JPP has better bearing capacity；increaseing soil-cement thickness can effectively improve the bearing capacity of JPP；the deformation of JPP is controlled by high-strength core pile；elastic moduli of soil-cement are less affected on JPP deformation.