非挤土预制管桩-注浆体-土体界面的相互作用机理及抗震性能研究

To overcome the potential material damage or environmental pollution of the traditional displacement piling techniques, drilling with PHC pipe cased piles (DPC piles) have attracted increasing attention in the rapid urbanization construction projects of China with its superior ability to adapt to geology, which widens the scope of PHC piles with large diameter 800 mm - 1400 mm to stiff solum or rocks. As a kind of replacement pile, the lateral friction resistance of the precast pile can be increased by grouting the gap between the outer surface of the precast pile and the inner wall of the borehole, which is the fundamental difference between DPC and other piling techniques. Therefore, this project is devoted to the research on interaction and seismic performance of replacement precast pile-cement paste-soil system by combining mechanics, foundation engineering and earthquake engineering during the whole lifecycle of the pile foundation (including design, construction and performance assessment). We plan to establish a theoretical prediction method for the mechanical properties of cement paste, reveal the the influence of grouting interface on the mechanical performance of the pile foundation by comparing the bearing capacity and failure modes of DPC piles with typical displacement piles, and promote the analytical models to calculate the bearing capacity and assess the seismic performance of the pile-cement paste-soil system based on the dynamic characteristics of the system and quasi-static simplification method. The results can provide theoretical basis for the improvement and promotion of replacement pipe piles with large diameter from performance evaluation, design optimization to construction guidance.

随钻跟管桩技术克服了传统预制管桩沉桩工艺对桩身质量的影响和可能造成的环境污染，其超强的地质适应能力也使大直径(800-1400 mm)PHC管桩在内陆坚硬土层或岩层成为了可能，在我国高速城市化建设工程中具有相当广阔的应用前景。针对此类非挤土预制管桩通过桩侧后注浆提高摩阻力的技术特点（即与其他成桩工艺的本质区别），本项目交叉融合力学、基础工程、岩土工程等学科及管桩基础的设计、施工和性能评估全寿命过程，开展管桩-注浆体-土体界面的相互作用机理及抗震性能的研究。本项目拟建立一套预估注浆体力学性能的理论方法；通过与典型挤土桩承载机理和失效模式的对比，揭示注浆界面对基础力学性能的影响规律；并建立管桩-注浆体-土体体系在的承载力计算方法和基于体系动力学特性和准静态简化方法的抗震性能评估理论；从而从性能评估、优化设计和指导施工等方面为大直径非挤土预制管桩基础的完善和推广提供理论基础。

以随钻跟管桩为代表的后注浆非挤土技术在钻进的同时利用PHC管桩本身进行钻孔护壁，沉桩终了在管桩外壁和孔壁间通过水泥浆粘结，施工文明，机械化程度高，其超强的地层适应能力也使其具有相当广阔的应用前景。本项目针对随钻跟管桩的施工工艺，以注浆界面为主线研究随钻跟管桩基础在服役状态下的承载机理和抗震性能，主要取得了以下研究成果：. 1）通过有限元模拟对注浆流动过程进行了数值模拟，揭示了注浆工艺对注浆体成型的影响机理；通过随钻跟管桩-土接触面作用机制分析和破坏模式的大型直剪试验研究，明确了破坏面位于注浆体-土体层的破坏模式，揭示了注浆加固机制，构建了可描述应变软化的修正剑桥模型应力应变方程预估注浆体力学性能； . 2）利用内聚力模型模拟随钻跟管桩基础中管桩—注浆体—土体的相互作用机理，建立了通过原位静载试验数据拟合注浆界面剪切强度的方法；系统分析了位移加载和力加载情况下静载试验曲线的基本规律和相关力学机理，揭示了桩侧注浆界面的强度和施工过程中桩侧土的模量衰减对随钻跟管桩基础的竖向极限承载力和失效模式的影响机理和调控规律；揭示了竖向载荷能够减小主动土压力区注浆界面的剪应力水平从而一定程度增大随钻跟管桩水平承载力的力学机理，并建立了不同桩侧土模量以及竖向载荷水平下桩基础失效模式相图，并分析了对应水平承载力的演化趋势。. 3）搭建了一套模拟随钻跟管桩施工工艺的振动台模型试验平台，通过试验揭示了因桩头承台处挤土效应不再明显以及桩测摩阻力分布因动载荷而产生不可逆附加弯矩使得后注浆预制管桩的抗震表现优于传统挤土桩的力学机理；发现了群桩基础间连通的间隙在注浆后的刚度突变会引起桩身明显的弯矩集中及动载后不可逆的桩侧摩阻力编号；同时系统研究了土层条件、地震波谱、桩头约束、群桩效应和上部载荷等因素对桩基础抗震性能的影响规律。.研究成果为随钻跟管桩基础的设计、工艺优化、抗震性能评估提供了分析、试验方法和可靠的实验依据和理论指导。