软岩锚固界面剪切流变特性及其应用研究

It is showed in a large quantity of experiments and engineering practice that the failure of the great majority of anchor in soft surrounding rock happens in the interface between rock and soil mass and grouting body, namely, in the anchorage interface, which is the weak part of anchorage system. Meanwhile the instability of the anchorage system is a gradual process, which does not appear from the beginning. It is closely related to the rheological damage of rock and soil mass and anchorage interface. In order to reveal the shear rheological characteristic of soft rock anchorage interface,a new test system is designed for pulling creep test of prestressing anchor on the compression type.The pulling creep tests of indoor anchorage system is done in the laboratory to analyze the creep damage characteristics of soft rock anchorage interface, to explore the evolution regularity of anchorage interface creep, to put forward the creep damage variable that can reflect synthetic influence on interface character and time, and build the creep damage constitutive model. Based on elastic mechanics and rheology model theory, the load transfer time effect model of soft rock anchorage interface is set up to analyze the influence of shear creep of anchorage interface on load transfer. Using finite difference method, a calculation model that can consider rheological damage characteristic of anchorage intrface is set up,so as to analyze the regularity of axis force and prestress of anchor under soft surrounding rock with the time changing. Thereby it reveals the deformation mechanism of anchorage interface and the time effect characteristics of soft rock anchorage system that can provide a guidance for anchor engineering design and its long-term stability control.

大量的实验和工程实践表明，大多数软弱岩体中锚杆的失效发生在岩土体和注浆体的界面、即锚固界面上，这个界面是锚固系统的薄弱部分。同时锚固系统的失稳并不是一开始就出现的，而是一个渐变的过程，它与岩土体和锚固界面的流变损伤密切相关。为揭示软岩锚固界面剪切流变特性，本项目设计了一种新的压力型预应力锚固体蠕变拉拔试验装置。拟通过室内锚固系统拉拔蠕变试验，分析软岩锚固界面蠕变损伤特性和损伤演化规律，提出反映界面特性和时间因素综合影响的蠕变损伤变量，建立蠕变损伤本构模型。基于弹性力学和流变力学理论，建立软岩锚固界面荷载传递时效性模型，以分析界面剪切蠕变对荷载传递的影响。采用有限差分数值分析方法，建立考虑锚固界面流变损伤特性的有限差分计算模型，研究软弱岩体中锚杆轴力、预应力随时间的变化规律。从而揭示软岩锚固界面的受力变形机理和锚固系统的时效特性，为锚固工程的设计和长期稳定性控制提供指导。

本项目以RYL-600型微机控制三轴流变试验机为基础，设计了一种通用型锚固界面剪切流变试验装置，并获得了国家实用新型专利。锚固体试件的基体采用C20或C30的混凝土材料，锚杆选用直径12mm或16mm的四级螺纹钢，灌浆材料选用M7.5或M10的砂浆。采用该设备，进行了室内锚固系统拉拔蠕变试验，分析了锚杆轴力、第一界面剪应力和第二界面剪应力沿杆长的分布。试验结果表明，锚杆轴力由锚杆近端向远端急速衰减，第一界面和第二界面的平均剪应力由锚杆近端从0开始迅速增大，到达峰值点以后又迅速变小。第二界面的剪应变流变特征分为三个阶段：初始剪切流变阶段、稳定剪切流变阶段和加速剪切流变阶段。依据室内锚固界面流变试验结果，建立了反映软岩锚固界面粘弹塑性蠕变特性的六元件流变模型，采用数值分析法确定了流变本构模型参数。基于弹性力学和流变力学理论，建立了软岩锚固界面荷载传递时效性模型，推导了灌浆体周围岩土体全部处于弹性阶段、部分处于塑性阶段和部分进入滑移阶段时的考虑锚固界面流变的荷载传递函数的微分方程解，分析了界面剪切蠕变对荷载传递的影响。采用有限差分数值分析方法，建立考虑锚固界面流变损伤特性的有限差分计算模型，研究了软弱岩体中锚杆轴力、预应力随时间的变化规律，探讨了荷载条件、锚固体强度、锚固体长度、锚固体直径等对锚固体蠕变特征的影响。分析结果表明，同一测点剪应变随荷载的增加而增加，随锚固体强度、长度和直径的增大，界面的剪应变减小。