Creep behaviour and constitutive model of coal filled with gas

Coal exhibits different creep behaviours when filled with different amounts of gas. Creep tests of coal filled with 0 and 0.5 MPa gas were performed, and strain under different axial stress was compared.The three creep constitutive models which were analysed using the method fitting experimental data for determining which creep model can reflect the creep process of the test best. The results show that the deformation of coal filled with 0.5 MPa gas is more higher than that of coal filled with 0 MPa gas under the same axial stress. Gas plays a positive effect on the deformation of coal process and will accelerate creep process. And gas will reduce coal intensity and change coal creep properties.Compared with Nishihara Model and Extensional Nishihara Model, Burgers Model can reflect the three stages of creep process of coal filled with gas better. The research results can contribute to reveal coal and gas outburst mechanism.     

粉砂质泥岩蠕变特性与非线性黏弹塑性本构模型

针对边坡、隧道工程中粉砂质泥岩长期稳定性问题,采用DZSZ-150型多场耦合岩石三轴压力试验机,利用粉砂质泥岩相似材料试样,开展不同围压下粉砂质泥岩蠕变试验。根据蠕变试验结果建立可描述粉砂质泥岩蠕变全过程的非线性黏弹塑性本构模型,以7 MPa围压下蠕变试验结果为例,对所提出的蠕变本构模型进行合理性和可行性验证。结果表明：试样的稳态蠕变速率与偏应力大小有关,随着偏应力的增加,试样稳态蠕变速率与偏应力之间符合指数函数关系;在加速蠕变阶段的蠕变速率相对低偏应力水平下减速蠕变和稳态蠕变速率明显要增大很多,且非常短时间内就发生了蠕变破坏;提出一种描述粉砂质泥岩全蠕变过程的非线性黏弹塑性本构模型,该模型能描述粉砂质泥岩蠕变-破坏全过程的蠕变变形规律,反映了粉砂质泥岩在不同偏应力水平作用下的蠕变特性,克服了经典模型中无法准确描述加速蠕变过程的难题。     

芒硝蠕变特性及本构模型研究

利用RLW-2000岩石流变试验机对芒硝开展了三轴压缩蠕变试验。试验结果显示,同一围压下,随轴向应力增大,芒硝蠕变变形量和稳态蠕变率均随之增加,而各级荷载加载过程中芒硝变形模量不断减小;芒硝蠕变过程具有非线性特征,且随蠕变时间延长,芒硝屈服强度逐渐降低。以分数阶粘滞体代替广义Kelvin模型中的经典粘滞体,建立了分数阶广义Kelvin模型;针对其蠕变方程形式复杂、应用不便的缺点对其进行了简化,将简化后的分数阶广义Kelvin模型与Heard稳态蠕变模型相结合,构建了一种新的非线性蠕变本构模型,并利用芒硝蠕变试验结果反演了模型参数。结果表明,拟合曲线和试验结果吻合良好,说明该模型能够较好的描述芒硝的蠕变特性。     

三轴压缩下粉砂质泥岩蠕变力学特性试验研究

为揭示三峡地区巴东组二段粉砂质泥岩的蠕变力学特性,采用RLJW-2000岩石流变伺服仪对饱和粉砂质泥岩进行了三轴压缩蠕变试验。试验在分级加载条件下进行,试验围压为1 MPa。基于试验结果,定量研究了粉砂质泥岩蠕变过程中轴向蠕应变与径向蠕应变的差异、轴向蠕变速率与径向蠕变速率的差异,得出了岩石的长期强度。研究结果表明:1)在各级应力水平下,试样径向蠕应变占径向总应变的比例始终比轴向蠕应变占轴向总应变的比例大,岩石的径向蠕变效应更明显。2)在破裂应力水平下,岩石径向蠕变比轴向蠕变先进入加速蠕变阶段,径向的初始蠕变速率、稳态蠕变速率以及加速蠕变速率均高于轴向相应的蠕变速率,以径向蠕变特征来判别粉砂质泥岩是否发生蠕变破坏更合理。工程实践中,应加强对岩石径向蠕变特性的监测工作,这对于工程失稳的预测预报更有意义。3)粉砂质泥岩的长期强度仅为其瞬时强度的74.4%,长期强度折减较大。4)试验中获得的长期强度实际上应为粉砂质泥岩的径向长期强度,径向先发生蠕变破坏从而导致试样破坏。     

Experimental study on the deformation behaviour,energy evolution law and failure mechanism of tectonic coal subjected to cyclic loadsOA

Compared to intact coal, tectonic coal exhibits unique characteristics. The deformation behaviours under cyclic loading with different confining pressures and loading rates are monitored by MTS815 test system,and the mechanical and energy properties are analysed using experimental data. The results show that the stress–strain curve could be divided into four stages in a single cycle. The elastic strain and elastic energy density increase linearly with deviatoric stress and are proportional to th...     

孔隙压力作用下泥岩三轴蠕变实验研究

在具有孔隙压力系统的岩石三轴蠕变仪上,对泥岩进行了考虑孔隙压力作用的三轴蠕变实验.实验中不仅考虑了轴压σ₁和围压σ₃对蠕变的影响,而且考虑了孔隙压力p在泥岩蠕变过程中产生的重要影响.通过不同应力水平下的蠕变实验,对比含孔隙压力和不含孔隙压力的蠕变实验曲线,表明当轴压σ₁和围压σ₃一定时,随着孔隙压力p的增加,蠕变变形量将会减小,在稳态蠕变阶段的应变率也会减小,在一定程度上会延长蠕变三个阶段的蠕变时间.并采用经典蠕变模型对实验结果进行分析.     

轴压水压耦合作用下裂隙砂岩蠕变特性

在水利水电、水底隧道等岩土工程建设中,伴有初始损伤的岩石材料长期处于轴压水压耦合环境下,严重影响岩土工程的长期稳定性.为保证处于轴压水压耦合环境下岩土工程的长期稳定性,以预加载制备的裂隙砂岩岩样为研究对象,利用特制的流固耦合多通道岩石流变系统,开展轴压水压耦合作用下裂隙砂岩单级加载蠕变试验及其蠕变模型研究,主要分析压力...     

饱和软粘土的流变和循环流变试验研究

分别对上海淤泥质饱和软粘土进行了长期流变和循环流变试验,得出其在不同围压、不同偏压和不同动应力作用下的变形规律。结果显示,围压相同时,偏压比大,试样的流变变形大,而偏压比相同时,围压大,流变变形也大;循环流变试验总体规律和流变试验相同,但经过一个循环加载阶段之后,随后的流变变形则很小。这些结论对今后软土地区高速公路、铁路和地铁建设提供一些帮助。     

煤岩固—气耦合的流变力学分析

为分析煤与瓦斯延迟突出机理,讨论了煤层瓦斯流动特性,认为游离瓦斯和吸附瓦斯、突出空洞内的瓦斯和突出空洞附近煤体中的瓦斯均在煤与瓦斯突出过程中起重要作用,因而提出原煤吸附瓦斯贡献系数k并建立了煤层瓦斯流动的质量守恒方程;基于煤岩流变力学实验,提出了讨论煤岩流变力学性质的广义弹粘塑性组合模型。最后,建立了可以用来研究煤与瓦斯延迟突出机理的含瓦斯煤固－气耦合分析的数学模型。     

掺砾黏土蠕变性质的三轴试验

为分析掺砾量、围压和应力水平对掺砾黏土蠕变性质和规律的影响,对以不同黏土和砾混合比备制的掺砾黏土进行了不同围压和不同应力水平下的三轴排水蠕变试验。土样掺砾量分别为30%、40%、50%和70％,试验围压50kPa~200kPa,应力水平0.21~1.04。试验结果表明掺砾黏土受荷后发生较明显的瞬时变形和蠕变变形,其蠕变变形将趋于一稳定值;蠕变变形随应力水平和围压的增大而增大,随掺砾量的增加而减小。提出一个三参数经验蠕变方程以表示掺砾黏土的应力水平-轴向应变-时间关系,其中轴向应变-时间关系和应力水平-轴向应变关系以双曲线方程表示,并分析了模型参数的意义和取值。     

软土的等效时间线剪切流变模型

为反映软土剪切流变的非线性特性,建立剪切流变模型,修正了Singh-Mitchell提出的指数型剪切蠕变经验公式,使之适用于低修正应力水平工况.根据黏塑性剪应变-耗散剪应力-等效时间之间的关系方程推导出黏塑性剪应变速率与剪应力和黏塑性剪应变之间的函数表达式.把该表达式和剪切弹性模型相结合,建立了剪切弹黏塑性模型.以此模型为基础,不但获得了有效围压恒定时单级和多级荷载作用下的剪切流变解析解,而且还获得了有效围压和剪应力均随时间变化时的剪切流变积分解答.结果表明,流变模型能够较好地定量模拟三轴固结排水试验中多级加载作用下的剪切蠕变发展过程,合理地反映剪应变随修正应力水平(或剪应力)、有效围压和持续时间等影响因素变化的流变规律.     

粉砂质泥岩的三轴蠕变试验研究

为了揭示分布于北天山中西部的志留系上统紫红色粉砂质泥岩的蠕变特性,为拟建于此的某深埋越岭特长隧洞的设计、施工,以及长期稳定问题评价提供依据,通过钻孔取样进行了三轴蠕变试验研究。试验在5台岩石三轴蠕变试验机上进行,围压分别为0、5、10、20、30 MPa。试验取得以下主要成果：1）揭示了这类黏土岩的蠕变特性可用西原模型加以描述,并由此建立了蠕变本构方程;2）采用曲线求参法求解了各流变参数;3）采用叠加原理与等时曲线法获得了岩石的长期强度;4）各蠕变参数随围压的升高而增大,长期强度较瞬时强度降低的幅度亦随围     

堆石蠕变与颗粒破碎特性三轴试验

为分析堆石的蠕变规律和研究颗粒破碎与蠕变的关系,对某堆石料进行了不同应力水平和围压下的大型三轴排水蠕变试验。蠕变试验后通过筛分试验测量了堆石的颗粒破碎程度。结果表明堆石的蠕变变形与应力水平和围压有关;轴向蠕变和体积蠕变随应力水平的增大而增大,应力水平相同时则随围压增大而增大。堆石的应变一时间关系可用幂函数表示,轴向应变一应力关系和体积应变一应力关系分别满足双曲线函数和线性比例函数。随应力水平和围压的增大,堆石颗粒破碎增多。堆石颗粒破碎可用相对颗粒破碎指数度量,其与轴向蠕变和体积蠕变近似呈线性比例关系。     

不同围压下茅口灰岩渐进性破坏的试验研究

利用MTS815电液伺服控制刚性试验机进行不同围压下茅口灰岩三轴压缩试验,通过计算绘得相应裂隙体积应变图,分析得出裂纹起始应力、裂纹破坏应力。结果表明:随着围压的增大,应力门槛值均呈非线性增长态势,当围压超过17 MPa时,裂纹起始应力、裂纹破坏应力分别增加48.5%和20.1%,茅口灰岩延性开始增强;裂纹破坏应力为峰值强度的64%~75%,三轴压缩下茅口灰岩裂隙不稳定发展阶段较长;环向应变值随围压增大而增大,当轴力超过裂纹破坏应力进入裂隙不稳定发展阶段,环向应变增大2.7~3.2倍,用环向-轴向应力应变曲线图能较好的反映岩石应力门槛值。     

基于砂岩蠕变试验的非线性蠕变模型辨识研究

为了研究砂岩的蠕变特性,利用全自动三轴伺服仪对砂岩试样进行10 MPa围压下的常规三轴试验和蠕变试验。为有效描述蠕变全过程,提出了一种含分数阶导数的非线性蠕变模型并进行验证。结果表明:在蠕变衰减、稳定阶段,试样环向蠕变速率和轴向蠕变速率比较接近;在蠕变加速阶段,试样的蠕变速率迅速增大,环向较轴向先发生加速蠕变,且环向加速蠕变速率更大,稳定蠕变速率随着应力水平的增大而增大,环向稳定蠕变速率增幅较轴向大,可见环向蠕变速率受应力水平影响更大,建立的含分数阶导数的非线性蠕变模型能较好模拟蠕变全过程,具有较高的准确性。     

Mechanical property and permeability of raw coal containing methane under unloading confining pressure

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal–hydrological–mechanical coupling of coal containing methane, an experimental study was carried out to investigate mechanical property and gas permeability of raw coal, under the situation of conventional triaxial compression and unloading confining pressure tests in different gas pressure conditions. Triaxial unloading confining pressure process was reducing confining pressure while increasing axial pressure. The research results show that, compared with the peak intensity of conventional triaxial loading, the ultimate strength of coal samples of triaxial unloading confining pressure was lower, deformation under loading was far less than unloading, dilation caused by unloading was more obvious than loading. The change trend of volumetric strain would embody change of gas permeability of coal, the permeability first reduced along with volumetric strain increase, and then raised with volume strain decrease, furthermore, the change trends of permeability of coal before and after destruction were different in the stage of decreasing volume strain due to the effect of gas pressure. When gas pressure was greater, the effective confining pressure was smaller, and the radial deformation produced by unloading was greater. When the unloading failed confining pressure difference was smaller, coal would be easier to get unstable failure.     

Viscoelasto-plastic rheological experiment under circular increment step load and unload and nonlinear creep model of soft rocks

The viscoelastic-plastic creep experiments on soft ore-rock in Jinchuan Mine III were performed under circular increment step load and unload. The experimental data were analyzed according to instantaneous elastic strain, visco-elastic strain, instantaneous plastic strain and visco-plastic strain. The result shows that instantaneous deformation modulus tends to increase with the increase of creep stress; soft rocks enhance the ability to resist instantaneous elastic deformation and instantaneous plastic deformation during the multi-level of load and unload in the cyclic process. In respect of specimen JC1099, the ratio of visco-elastic strain to visco-plastic strain varies from 3.15 to 6.58, and the ratio has decreasing tendency with stress increase as a whole; creep deformation tends to be a steady state at low stress level; soft rocks creep usually embodies accelerated creep properties at high stress level. With the damaging variable and the hardening function introduced, a nonlinear creep model of soft rocks is established, in which the decay creep is described by the nonlinear hardening function H of viscidity coefficient. The model can describe the accelerated creep of soft rocks since the nonlinear damaging evolvement variable D of deformation parameter of rocks is introduced. Three stages of soft rocks creep can be described with the uniform creep equation in the nonlinear creep model. With this nonlinear creep model applied to the creep experiments of the ore-rock of Jinchuan Mine III, the nonlinear creep model’s curves are in good agreement with experimental data. Foundation item: Project(2007CB209400) supported by the Major State Basic Research and Development Program of China; Project(50774093) supported by the National Natural Science Foundation of China; Project(200801) supported by Open Research Fund of Hunan Provincial Key of Safe Mining Techniques of Coal Mines     

煤和瓦斯突出机理的流变假说

目前煤和瓦斯突出机理的假说,都是在弹性力学基础上建立的,缺少时间因素,难于完满地解释突出的发生发展过程。作者通过对含瓦斯煤样在三维受力状态下流变特性的研究,得出了含瓦斯煤样蠕变行为的数学模型,能够比较好地阐明突出的机理。实验表明,突出煤和非突出煤其流变行为并无本质区别,只要条件具备,各类煤层都有产生突出的可能。含瓦斯煤蠕变方程的导出为建立广义的突出危险综合指标提供了基础。     

北山花岗岩短长期常规三轴力学特性试验研究

为研究北山花岗岩的物理力学特性，开展了常规三轴、蠕变和松弛试验，研究过程与结论如下：（1）开展北山花岗岩在不同围压条件下的常规三轴压缩试验，对比分析试样的变形和破坏形式等力学特征，得出北山花岗岩岩石破坏时的不可恢复变形较小，且随着围压增大未出现脆-延性转变现象的结论；（2）开展北山花岗岩单级蠕变试验及不同围压条件下的多级蠕变试验，分析不同偏应力的形变和单级蠕变的蠕变速率，得出北山花岗岩的蠕变形式为非稳定蠕变，其应变曲线出现了典型的蠕变三阶段特征的结论；（3）开展北山花岗岩单级应力松弛试验及循环松弛试验，分析偏应力的变化规律，得出北山花岗岩在应力松弛过程的初始松弛阶段，其偏应力下降速率很快，在较短时间内即能够达到稳定状态的结论。     

Creep properties and permeability evolution in triaxial rheological tests of hard rock in dam foundation

Triaxial creep tests were carried out under seepage pressure by using rock servo-controlled triaxial rheology testing equipment. Based on experimental results, rock rheological properties influenced by seepage-stress coupling were studied, and variations of seepage rate with time in complete creep processes of rock were analyzed. It is shown that, when the applied stress is less than failure stress level, the creep deformation is not obvious, and its main form is steady-state creep. When applied stress level is greater than or less than but close to fracture stress, it is easier to see the increase of creep deformation and the more obvious accelerative creep characteristics. The circumferential creep deformation is obviously higher than the axial creep deformation. At the stage of steady-state creep, the average of seepage flow rate is about 4.7×10⁻⁹ m/s at confining pressure (σ ₃) of 2 MPa, and is about 3.9×10⁻⁹ m/s at σ ₃ of 6 MPa. It is seen that the seepage flow rate at σ ₃ of 2 MPa in this case is obviously larger than that at σ ₃ of 6 MPa. At the stage of creep acceleration, the seepage flow rate is markedly increased with the increase of time. The variation of rock permeability is directly connected to the growth and evolution of creep crack. It is suggested that the permeability coefficient in complete creep processes of rock is not a constant, but is a function of rock creep strain, confining pressure, damage variable and pore water pressure. The results can be considered to provide a reliable reference for the establishment of rock rheological model and parameter identification.