冻拔与逆风荷载协同作用下微型灌注桩-土相互作用机理研究

As a common foundation type of PV power generation facilities, the micro bored pile suffers from uplift deformation, or even total failure due to the strong upwind-induced uplift load, lateral load and moment at the pile head, as well as the frost heave effect of surrounding soils during winter, while investigation on pile behaviors under such complex conditions is absent. This study aims to reveal the interaction mechanism of pile-soil system under combined loads by laboratory tests, numerical simulation and theoretical analysis. A multifunctional model test system is remolded for investigating the micro bored pile response under complex combined loading or under single factor’s effect, and the interaction mechanism between frost jacking and upwind is illuminated, as well as the factor levels accounting for the most unfavorable condition. The equivalent interface roughness serves as a bridge between model pile test and direct shear test of pile-soil interface. The shear characteristics of pile-soil interface under various factors and static/dynamic loading are obtained. Based on laboratory results, a pile-soil interaction model under complex loading condition is established, and the load transfer and displacement mode are analyzed, with the pile-soil interaction mechanism clarified under tangential forces of heaving and complex dynamic loads at the pile head. A method is proposed to predict the response of a micro bored pile exposed to both frost jacking and upwind. This study aims to improve the theoretical framework of pile response under complex conditions and design code.

强逆风作用在大尺寸轻型光伏板上时引起下部基础显著的上拔、水平及弯矩荷载，若叠加冬季地基土的冻胀效应，作为光伏支架常用基础的微型灌注桩极易发生上拔变形，甚至失稳破坏，而此类复杂条件下的桩基力学行为尚未得到研究。本项目采用室内试验、数值模拟和理论分析等手段对复杂荷载组合工况下桩-土相互作用机制开展研究：基于升级改造的多功能桩基模型试验系统，探究复杂荷载组合工况或单因素工况下微型灌注桩力学响应特性，明确冻拔和逆风的协同机理，掌握最不利工况因素组合；利用接触面等效粗糙度联系桩基模型试验与桩-土界面直剪试验，阐明多因素影响下桩-土界面静/动剪切特性；结合室内试验数据，建立复杂荷载组合工况下桩-土相互作用数值模型，分析荷载传递规律与位移模式，揭示切向冻胀力与复杂动荷载作用下桩-土相互作用机理，建立冻拔和逆风荷载组合工况下微型灌注桩力学响应计算方法。本项目可完善复杂条件下桩基响应理论与设计方法。

作为光伏发电设施的1种常见基础类型，微型钻孔灌注桩由于强烈逆风引起的上拔荷载、桩顶侧向荷载和弯矩，以及冬季桩周土体的冻胀效应，会产生上拔位移，直至桩基功能性失效，这种复杂工程环境下的桩基力学行为亟需进一步研究。项目采用室内试验、数值模拟和理论分析等手段研究了复杂荷载组合工况下桩-土相互作用机制。升级改造了多功能桩基模型试验系统，探究了复杂荷载组合工况或单因素工况下微型灌注桩力学响应特性，明确了冻拔和逆风的协同机理，掌握了最不利工况因素组合；利用接触面等效粗糙度联系桩基模型试验与桩-土界面直剪试验，阐明了多因素影响下桩-土界面静/动剪切特性；结合室内试验数据，建立了复杂荷载组合工况下桩-土相互作用数值模型，分析了荷载传递规律与位移模式，揭示了切向冻胀力与复杂动荷载作用下桩-土相互作用机理，建立了冻拔和逆风荷载组合工况下微型灌注桩力学响应计算方法。研究表明：当最大切向冻胀力与逆风荷载引起峰值竖向力之和小于桩基抗拔承载力时，桩基保持稳定；在寒季，最大切向冻胀力与逆风荷载引起峰值竖向力之和持续大于抗拔承载力时，桩基上拔位移持续发展；上拔合力非持续性超过抗拔承载力时，桩基上拔位移阶段性发展，当等效驱动力和阻力平衡时，上拔位移不再累积。试验测量值存在较大分散性，主要有两个原因：1）"切向冻胀力"和"界面冻结强度"概念混乱，2）测试条件和测试技术不统一。界面直剪试验结果往往未反映现场实际情况，试验研究宜确定室内和现场实测的相关性；当缺乏精确有效的界面剪切模型时，冻结和强逆风协同作用下的桩基数值仿真结果可能产生偏差；基于可靠性的设计方法在冻土地基微型灌注桩建设实践中应用前景广阔。本项目可完善季节性冻土区特殊场地微型灌注桩响应理论与设计方法。