【作者】 方磊；

【导师】 曹日红； 雍伟勋；

【作者基本信息】 中南大学 ， 工程硕士（专业学位）， 2023， 硕士

【摘要】 目前越来越多的地下工程项目岩体在热冷循环作用下发生损伤劣化与力学性能退化,进而影响整个岩体工程项目的稳定性,如隧道火灾、核废料深埋地质处理、煤炭地下气化开采、地热资源的开发等。为揭示冷热循环作用下岩体损伤劣化机理及断裂特性,本文主要从实验室试验和理论分析两方面进行了相关研究。研究内容和结论如下:(1)开展了砂岩试样的加热-自然冷却循环试验和单轴压缩试验,揭示了加热-自然冷却循环作用对砂岩试件强度、形变特征、微观结构和破坏模式的影响。结果表明,热冷循环作用下砂岩试样的峰值强度不断退化;其微观结构表现为晶间微裂纹间距增加和晶内微裂纹数量增加,宏观破坏模式由剪切破坏逐渐变为劈裂破坏;荷载作用下的形变特征变化为裂纹闭合阶段随着热冷循环次数的增加逐渐增大。(2)砂岩试样的声发射振铃累积计数特征表明其荷载作用下孔隙压密阶段随着热冷循环次数增加而增大,微裂纹稳定扩展阶段随着热冷循环次数的增加而减小,荷载作用下微孔隙和裂纹闭合越困难。基于RA-AF裂纹破裂模式识别技术,得到砂岩试样在热冷循环作用下裂纹破裂模式由剪切破裂向拉伸破裂变化。(3)基于应变等效原理推导了热冷循环处理后砂岩试样在荷载作用下的损伤统计本构模型,结合其应力应变曲线形状变化特征,对模型进行了修正。最后利用实验数据对模型进行了验证,并与已有相关理论模型对比分析了本文模型的可靠性。(4)利用核磁共振技术获取了不同加热-水冷循环作用下花岗岩内部孔隙率与孔径分布,揭示了微观孔隙结构特征随加热温度和循环次数的演化规律。结果表明温度400℃以上时,热冷循环作用对微孔径分布和渗透率影响较大;总的来说花岗岩试样孔隙率均随着循环次数的增加而增大。(5)开展了加热-水冷循环作用下花岗岩试样的断裂特性研究,计算了不同循环次数的断裂韧度、声发射b值与断口面的分形维数D_F,揭示了断裂韧性、断裂破坏扰动以及断口面粗糙度随循环次数的变化规律。结果表明随着循环次数增加,花岗岩断裂韧性减小,断裂破坏扰动变化与温度有关,其断口面的粗糙度增大。图55幅,表6个,参考文献114篇更多还原

【Abstract】 At present,more and more underground engineering rock mass has damage deterioration and mechanical property degradation under the action of thermal-cooling(T-C)cycling,which affects the stability of the whole rock mass engineering project.Such as tunnel fire,nuclear waste buried deep geological treatment,underground coal gaification mining,geothermal resources development.To reveal the mechanism of rock mass damage and deterioration and fracture property under the action of T-C cycling,this paper mainly conducted relevant research from two aspects:laboratory test and theoretical analysis.The research contents and conclusions as follows:(1)The thermal-natural cooling(T-NC)cycle treatments and uniaxial compression tests of sandstone specimens were carried out,and the influence of T-NC cycle on the strength,deformation characteristics,microstructure and failure mode of sandstone specimens was revealed.The results show that the peak strength of sandstone samples degenerated continuously under the action of T-C cycling,the microstructure shows that the spacing of intergranular microcracks and the number of transgranular microcracks increase,and the macroscopic failure mode gradually changes from shear failure to split failure.The deformation characteristics of the crack under load increased gradually with the increase of T-C cycles.(2)The acoustic emission ringing cumulative counting characteristics of sandstone show that the pore compaction stage increases with the increase of T-C cycles,and the microcrack stable growth stage decreases with the increase of T-C cycles,and the micropores and cracks are more difficult to close under the load.Based on the RA-AF crack rupture pattern recognition technique,it is obtained that the crack rupture mode of sandstone samples changes from shear to tensile rupture under the action of T-C cycling.(3)Based on the principle of strain equivalence,the statistical constitutive model of damage of sandstone samples under load after T-C cycle treatments was derived.This constitutive model was modified according to the shape change characteristics of stress-strain curves.Finally,proposed model was verified by experimental data,and the reliability of proposed model was analyzed by comparing with the existing theoretical models.(4)The internal porosity and pore size distribution of granite under different thermal-water cooling(T-WC)cycles were obtained by nuclear magnetic resonance technology,and the evolution of pore structure characteristics with heating temperature and cycle times was revealed.The results show that the micropore distribution and permeability are significantly affected by T-C cycles at temperatures above 400℃.Generally speaking,granite samples porosity increases with the increase of cycle times.(5)The fracture properties of granite samples under the action of T-WC cycles were studied.The AE b values,fracture toughness and the fractal dimension of fracture surface D_Fwere calculated for different cycles,and the variation rules of fracture toughness,fracture disturbance and fracture surface roughness with cycles were revealed.The results show that with the increase of T-C cycles,the fracture toughness of granite decreases,the change of fracture disturbance was related to temperature,and the roughness of the fracture surface increases.更多还原