卸荷损伤节理岩体疲劳特性与水岩耦合流变特性研究

The mechanical characteristics of jointed rock under the condition of unloading are significantly different from that of under the condition of loading，and the unloading would cause sharp degradation of rock mass quality. There is less research results about the damage characteristics of jointed rock under the unloading condition so far，and they are not involve the affection of long-term loading and multi cycle factors that acting on the mechanical characteristics of jointed rock. Many scientific physical and mechanical tests will be carried out in this project，and the mechanical characteristics of jointed rock will be studied which with different degrees damage under the influence of various factors. Using CT scanning，ultrasonic testing and SEM testing，the unloading damage degree is quantitative analyzed. The fatigue and aging characteristics of damage jointed rock under cycle and long-term loading conditions are studied. The influence rules of rock deformation and strength parameters are investigated under the action of unloading quantity，cycle times， water stress，soaking time，pH and other factors. The damage failure evolving mechanism of jointed rock in complex conditions is revealed， and the nonlinear damage constitutive model which can describe rheological and fatigue characteristics of rock are proposed. The research results can provide technical reference for the design and construction of excavation engineering.

节理岩体在加载与卸荷条件下，力学特性显著不同，卸荷将导致岩体质量急剧劣化，现阶段对于节理岩体卸荷条件下的损伤特性研究较少，且未考虑长期荷载和多种循环作用对卸荷损伤节理岩体力学特性的影响。本项目拟开展系统的物理力学试验，研究经历不同程度卸荷损伤后，节理岩体在多种因素影响下的力学特性：采用CT扫描、声波测试、电镜扫描等先进技术，对岩样卸荷后内部损伤程度进行定量地分析；开展不同程度卸荷损伤岩样的疲劳特性（主要考虑干湿循环、冻融循环、加卸荷循环三种因素）与水岩耦合流变力学特性试验，研究损伤岩体循环与长期载荷条件下的疲劳特征与时效特性，探讨卸荷量、循环次数、水压力、浸泡时间、溶液酸碱度等因素对岩体变形与强度参数的影响规律；揭示卸荷损伤岩体复杂因素影响下的损伤破裂演化机理，分别建立能描述岩体长期流变特征与循环疲劳特性的非线性损伤本构模型。研究成果可为开挖工程设计和建设提供技术参考。

本项目基于大量试验，考虑不同卸荷量损伤及多种工程中常见的影响因素（循环加卸载、干湿循环、循环冻融、流变），较为全面系统的研究了卸荷损伤节理岩体在不同因素作用下的应力应变特征、破坏机理及强度、变形参数的变化规律。研究结果表明：1）随着卸荷量的增加，节理岩体的波速、峰值强度、弹性模量与变形模量都有所降低，泊松比和破坏程度逐渐增加，卸荷损伤对节理岩体力学性质有较大的削弱作用；2）随着循环频率的增加，卸荷损伤岩样的峰值强度呈现出先增加，后减小的变化趋势，循环加卸载频率越高，岩样破碎程度越严重；卸荷损伤岩样在循环加卸载下的应力应变曲线滞回环表现为由疏松到密集，然后再从密集到破坏前的疏松，随着卸荷量的增大，滞回环面积、动弹性模量、阻尼比和阻尼系数有所下降，动泊松比有所升高；低幅值的循环加卸载对岩样的压密作用明显，并使得岩样的峰值强度大幅提高，随上限应力比的增加，峰值强度与峰值强度增长比都呈现先增加后降低的二次函数变化趋势。3）同一岩样在经过不同次数的干湿循环作用以后，纵波波速均有较为明显的降低，且干湿循环次数越多，岩样波速下降的量越大；干湿循环作用对岩样的峰值应变影响十分显著，随着干湿循环次数的增加，岩样的峰值应变明显减小；4）随着冻融循环次数增加，岩样逐渐裂化，抗冻性逐渐降低；单轴和三轴抗压强度逐渐降低，轴向应变逐渐变大；不同冻融次数岩样的三轴峰前卸荷应力-应变曲线均出现了明显的压密阶段和弹性阶段，具有一定的脆性特征；5）流变破坏的严重程度较常规三轴压缩破坏更大，产生的次生裂纹更多，在长期的荷载作用时，岩石内部的微裂隙得以充分扩展而产生宏观位移，破坏程度更加彻底，甚至破坏后不再具有整体性；随着卸荷损伤程度的加深和孔隙水压的增大，岩样的峰值强度和长期强度逐渐降低，最大可降低20%左右；6）基于完整岩样和卸荷损伤岩样常规三轴加载试验，结合损伤力学和Weibull统计分布理论，建立损伤本构模型，计算得到了weibull分布的参数F0和n，并将试验得到的应力-应变曲线与损伤本构模型计算的应力-应变曲线进行对比，发现吻合度较高。