地震作用下微型桩加固堆积体边坡的响应特征与荷载传递机制

Micropile is one of the most effective structures used to prevent the shallow landslide induced by earthquake. However, the interaction mechanism between micropile group and soil under seismic load is still not clear. To date, no sound framework for estimating the earthquake load on micropile group has been reported in the slope reinforcement. Under the background of disaster prevention in earthquake-induced shallow deposit landslide, a series of centrifuge shaking table modelling tests will be conducted to study the distribution form of seismic contact load between soil and pile in prototype scale. Based on the tests results, the structure-soil-interaction forces and load distribution ratios in each row of the micropile group are obtained. Then, numerical analysis will be conducted to simulate the centrifuge tests. The validity of the numerical analysis is calibrated by comparing the calculations with the tests results. Moreover, multiple factors and levels parametric sensitivity analysis of the pile-soil system will be performed by the numerical simulations. The three most sensitive factors are taken into account in determining the distribution form and magnitude of the dynamic load between pile and soil. On the basis of the above results and simulations, comprehensive analysis of centrifugal shaking table modelling tests and numerical analysis will be performed. The transfer mechanism of dynamic load between deposit slope and micropile group under seismic excitations is revealed by introducing the dynamic contact stress envelope during whole process of the seismic response. Finally, a process based on the pressure method is introduced in calculating the earthquake induced force in micropile group. The results of this research project can provide some theoretical and technical support for micropile aseismic design used in the deposit slope reinforcement.

微型桩是治理地震浅层滑坡的有效支挡结构之一，目前对其地震作用下桩土间的相互作用机理尚不明确，缺少成熟的抗震计算方法。本项目以堆积体地震浅层滑坡灾害防治为工程背景，基于离心振动台模型试验，通过连续输入多级地震荷载，实时量测桩土间的动接触应力以及微型桩的桩身应力时程曲线，定量描述桩土间的地震动接触应力以及微型桩体系内部各排桩之间的荷载分配比例，确定原型堆积体边坡与微型桩间的地震动接触应力分布形式。通过对离心模型试验的模拟来验证优化数值分析方法，进一步采用数值模拟进行多因素多水平因子的敏感性分析，明晰桩土间动荷载大小与分布形式的主要影响因素。在此基础上，综合分析离心振动台模型试验与数值分析的结果，阐明地震作用下堆积体边坡与微型桩间的动荷载传递机制，得到全过程响应的各排桩之间最不利动接触应力的包络线，基于压力法推导微型桩体系的地震内力计算方法，为微型桩边坡加固体系抗震设计提供理论技术支持。

本项目以堆积体地震浅层滑坡灾害防治为工程背景，从认知地震荷载下微型桩体系加固堆积体边坡的桩土相互作用机理出发，开展了堆积体力学特性三轴试验，获取了相关物理力学参数，进一步针对典型工况，开展了基于离心振动台模型试验的微型桩体系加固堆积体边坡地震响应研究，得到了微型桩体系加固堆积体边坡的加速度响应与变形特性，明晰了地震作用下堆积体与微型桩体系间的动荷载传递模式；通过数值模拟结果与模型试验数据获得了堆积体边坡岩土体与微型桩体系之间的动接触应力的分布规律，找出了影响微型桩体系-堆积体相互作用的主要因素，通过桩顶刚性框架使微型桩形成一个整体联系的体系，将加强微型桩体系之间、桩与土之间的联系，形成共同体协同作用，更大程度发挥了群桩抗震支护的效果。在相同加固横截面积的条件下，与大直径抗滑桩相比，采用多根抗滑桩加固方式时，坡体下滑时分散了土体的塑性分布区域，从而能改善桩土之间的受力特性；最后综合离心振动台模型试验、动力数值分析的结果，凝练简化了地震荷载下微型桩体系的桩土接触应力分布形式，确定了地震荷载下的桩身内力，发现在不设置连梁时，前排微型桩比后排微型桩承担了更大的荷载；设置连梁以后，前排桩与后排桩承担的荷载则迅速接近，得到了微型桩体系内各排桩间的地震滑坡推力分配比例。本研究将为微型桩体系加固堆积体边坡的抗震设计提供研究参考，为防治地震滑坡灾害等提供技术支撑。