【作者】 王伟；

【导师】 王汉鹏；

【作者基本信息】 山东大学 ， 岩土工程， 2023， 博士

【摘要】 富煤贫油少气是我国的国情,以煤为主的能源结构短期内难以根本改变,目前煤炭平均开采深度以每年10～25m的速度增加,因此深部煤炭资源是我国能源安全的重要保障。然而深部煤岩体常处于高地应力、高地温、高瓦斯压力等耦合赋存环境,同时频繁受到断层滑移、岩层破断、采掘开挖、爆破振动等扰动影响,造成煤与瓦斯突出灾害频发,危害巨大。深部煤与瓦斯突出致灾机理与防治技术已成为世界性难题与研究热点。目前相关研究多集中于探索煤岩体、地应力、瓦斯压力的气固耦合作用机理或者煤岩体、地应力、冲击荷载的动静叠加作用机理,且多通过霍普金森压杆施加单次高应变率冲击荷载开展研究。综合考虑气固耦合作用以及中低应变率循环冲击动载与地应力静载叠加作用的煤与瓦斯突出致灾机理研究相对匮乏。本文首先研发了多应变率动静叠加岩石力学试验系统,并利用该试验系统研究了不同循环冲击荷载(次数、频率、峰值)、静载应力阶段、吸附瓦斯压力等参量下的煤体损伤演化规律与破坏失稳特征,进而结合理论分析与试验结果,建立了循环冲击扰动下预静载含瓦斯煤体气-固耦合动力学模型,最终利用物理模拟与数值模拟等手段探索了循环冲击扰动下预静载含瓦斯煤体耦合损伤致灾机理。具体成果如下:(1)研发的多应变率动静叠加岩石力学试验系统攻克了多应变率动静荷载单面叠加与静载快速补偿、冲击荷载高频循环加载、蠕变荷载自动平衡加载、动静叠加条件下高压气体密封及气压恒定、试验过程多元信息耦合采集、多种加载装置集成控制等关键技术难题,最终实现了试件表面重力蠕变(<10-4 s-1)、液压静载(10-4～10-2 s-1)、液压脉冲动载(10-2～100 s-1)、循环落锤冲击动载(100～102 s-1)的多应变率动静叠加,并可形成高压气体赋存环境,从而获得煤岩体在气固耦合及动静叠加作用下的物理力学特性。(2)开展了不同瓦斯压力、静载应力阶段、单次冲击峰值耦合作用试验,获得了煤体多种力学参数损伤演化规律;在高气压密封腔室内安装无频闪高亮光源,满足了高速摄像光线要求,获得了煤体表面裂隙发育特征;收集破坏后的煤体碎块,获得了煤体破碎块度分形演化特征。结果表明:1)随着瓦斯压力、静载应力阶段、单次冲击峰值的增大,煤体损伤逐渐增强,裂隙发育及失稳破坏模式趋于复杂,一般由斜面剪切破坏或者竖向拉伸破坏向局部或者整体爆裂破坏演化,煤体损伤敏感性排序为:静载应力阶段>单次冲击峰值>瓦斯压力。2)以弹性模量为衡量指标,动静叠加荷载对煤体同时产生强化作用与损伤作用,在压密阶段以强化作用为主,在塑性阶段以损伤作用为主,且动载损伤作用存在显著应变率强化效应。(3)获得了不同循环/持续冲击次数、频率、峰值作用下,预静载含瓦斯煤体多种力学参数损伤演化规律以及表面裂隙、破碎块度的分形演化特征,结果表明:1)循环冲击指定次数时,随着冲击次数、峰值的增大或者冲击频率的减小,煤体损伤逐渐增强,裂隙发育及失稳破坏模式趋于复杂。相同冲击峰值下,冲击频率的损伤敏感性大于冲击次数。2)持续冲击直至煤体破坏时,累积残余应变随冲击次数增大呈现倒S型演化模式,表明煤体损伤经历快速孕育→平缓发展→高速扩张贯通→宏观破碎的演化过程。3)持续冲击直至煤体破坏时,冲击频率越大,单次冲击造成的损伤越小,单次冲击在煤体内积聚的能量越多,最终累积冲击次数与累积能量越大,最终破坏越剧烈。(4)基于试验结果建立了瓦斯吸附损伤因子演化模型;基于煤体微元强度Weibull分布假设及试验结果建立了静载损伤因子演化模型;以Logistic方程的逆函数为基础,基于试验数据及理论分析建立了含冲击次数、频率、峰值等参量的循环冲击损伤因子演化模型。以广义开尔文体为基础构建了组合型时效损伤本构框架,结合上述三种损伤演化模型,建立了循环冲击扰动下预静载含瓦斯煤体组合型时效耦合损伤本构模型,进而以渗透率及孔隙率随应变的演化关系为桥梁,将损伤本构模型与煤体内瓦斯渗流模型相结合,最终创建循环冲击扰动下预静载含瓦斯煤体气-固耦合动力学模型。(5)开展了工程尺度巷道掘进揭煤扰动诱发煤与瓦斯突出模型试验,获得了与事故现场相似的突出现象与多物理量演化数据。以模型试验为背景,利用气-固耦合动力学模型开展数值分析,并通过调整冲击损伤模型常数,使数值分析获取的多物理量演化规律与模型试验一致,从而构建了适用于工程尺度的动力学模型参数体系。通过数值分析获取了不同瓦斯压力、垂直应力、冲击峰值与频率下工程尺度多物理场耦合演化规律,进而探索了多因素耦合损伤致灾机理。结果表明:瓦斯压力及垂直应力越大,相同冲击次数下冲击峰值越大、冲击频率越小,煤岩层损伤峰值及损伤集中范围越大,突出危险性越高。研究成果将有助于细化完善复杂地质条件下的煤与瓦斯突出致灾机理,助力深部煤炭资源安全高效开采。更多还原

【Abstract】 Rich coal,poor oil and little gas are the national conditions of China,the coal-based energy structure is difficult to change in the short term,and the average mining depth of coal is increasing at the rate of 10-25m per year.Therefore,the mining of deep coal resources is an important guarantee for China’s energy security.However,during deep coal mining,the coal and rock mass are often in the multi-phase and multi-field coupling environment of high stress,high temperature,high gas-liquid pressure,etc.In addition,fault slip,rock fracture,mining and excavation,blasting vibration,etc.frequently affect the coal and rock mass.That resulting in the frequent occurrence of nonlinear,high-energy coal and rock dynamic disasters such as coal and gas outburst.The disaster mechanism and prevention technology of deep coal and gas outburst has become a worldwide problem and research hotspot.At present,most relevant researches focus on exploring the gas solid coupling mechanism of coal,geostress and gas pressure or the dynamic static superposition mechanism of coal,geostress and impact load,and most researches were applying single high strain rate impact load through Split Hopkinson Pressure Bar.The study on the mechanism of coal and gas outburst,which considers the gas solid coupling effect and the superposition of medium low strain rate cyclic impact dynamic load and geostress static load,is relatively scarce.This paper developed a dynamic static superposition rock mechanics test system,and used this test system to study the damage evolution law and failure instability characteristics of coal under different cyclic impact load,static load stress stage,adsorbed gas pressure.The gas solid coupling dynamic model of pre static loaded gas-adsorbed coal under cyclic impact disturbance was established.Finally,explored the coupling damage mechanism of pre static loaded gas-adsorbed coal under cyclic impact disturbance.The main achievements are as follows:(1)The multi strain rate dynamic static superposition rock mechanics test system has overcome six key technical problems.This including single side superposition of multi strain rate dynamic and static loads and rapid compensation of static loads,high-frequency cyclic impact loading,automatic balanced loading of creep loads,high-pressure gas seal and constant air pressure,multiple information coupling collection,and integrated control of multiple loading devices.Finally,the multi strain rate dynamic and static superposition of gravity creep(<10-4 s-1),hydraulic static load(10-4～10-2 s-1),hydraulic pulse dynamic load(10-2～100 s-1),and cyclic drop hammer impact dynamic load(100～102 s-1)was realized,and the high-pressure gas-liquid occurrence environment can be formed.Thus obtaining the physical and mechanical properties of coal and rock masses under gas-solid coupling and dynamic static superposition(2)Conducted tests on different gas pressures,static stress stages,and single impact peak,and obtained the damage evolution laws of various mechanical parameters of the coal body.Installing a non-flickering high brightness light source in a high-pressure sealed chamber that meets the requirements of high-speed camera,and then obtains the development characteristics of coal surface cracks.Collect the damaged coal fragments,and then obtain the fractal evolution characteristics of coal fragmentation.The results show that:1)With the increase of gas pressure,static load stress stages and peak impact load,the coal damage gradually increases,and the fracture development and instability failure mode tend to be complex.Evolution from single slope shear failure or vertical tensile failure to local burst or global burst failure.The order of coal damage sensitivity is static stress stage>single peak impact load>gas pressure.2)The dynamic and static superimposed loads have both strengthening and damage effects on the coal.The strengthening effect is dominant in the compaction stage and the damage effect is dominant in the plastic stage,and the dynamic load damage effect has a strain rate effect.(3)Through tests,obtained the damage law of various mechanical parameters of coal and the fractal evolution law of surface crack and fragmentation under different cycle/continuous impact number,frequency and peak value.The results show that:1)With the increase of impact number,peak value or the decrease of impact frequency,the coal damage gradually increases,and the fracture development and instability failure mode tend to be complex.Under the same impact peak,the damage sensitivity of impact frequency is greater than the number of impacts.2)During continuously applying impact load until the instability and failure,the cumulative residual strain presents an inverted S-shaped evolution mode,and the damage of coal body undergoes the evolution process of rapid inoculation→gentle development→high-speed expansion and penetration→macro crushing.3)In the continuous impact loading until the failure test,the greater the impact frequency,the smaller the damage caused by a single impact,the more energy accumulated in the coal by a single impact,the greater the final cumulative impact number and cumulative energy,and the more severe the final failure.(4)Based on the test results,the evolution model of gas-adsorbed damage factor was established.Based on Weibull distribution assumption of coal microelement strength,the evolution model of static load damage factor was established.Based on the inverse function of the Logistic equation,the evolution relationship of the cyclic impact damage factor with the impact number,impact frequency and impact peak value was established.Based on the generalized Kelvin body,a combined damage constitutive framework was constructed.Combining the three aforementioned damage evolution models,a coupled damage constitutive model for pre-loaded gas-containing coal under cyclic impact disturbance was established.Using the relationship between permeability and porosity evolution with strain to combine the damage constitutive model with the gas flow model.Finally,formed a gas-solid coupled dynamic model for pre-loaded gas-containing coal under cyclic impact disturbance.(5)Conducted an engineering scale tunnel excavation induced coal and gas outburst model experiment,and outburst phenomena and multi physical evolution data were similar to the accident site.Taking model experiments as the background,using the gas-solid coupling dynamic model conducted numerical analysis.By adjusting the constant of impact damage model,obtained the evolution laws of multiple physical quantities that consistent with model experiments,thus constructing a dynamic model parameter system suitable for engineering scale.Through numerical analysis,obtained the multi physical fields coupling evolution law under different gas pressures,vertical stresses,peak value of impact load,and then explored the mechanism of multi factor coupled damage causing disasters.The results show that the greater the gas pressure and vertical stress,the greater the impact peak and the smaller the frequency under the same impact loading times,the more severe the damage to coal and rock layers,and the higher the risk of outburst.更多还原