层状盐岩及泥岩夹层动态力学特性对比试验研究

为对比研究盐岩和泥岩夹层的动态力学特性,以应城盐矿的盐岩及泥岩夹层为研究对象,利用带围压的分离式Hopkinson(SHPB)试验装置,进行不同围压(5,15,25 MPa)下的动载冲击试验研究,分析盐岩和泥岩夹层动力特性的围压效应与应变率效应,基于联合的热活化与黏性机制相互竞争的材料强度–应变率依赖的简化模型拟合出盐岩及泥岩夹层的动力强度公式。研究结果表明:(1)盐岩和泥岩夹层均属于率敏感性材料,其峰值应力和延性随应变率的增大而增加,但低围压(如5 MPa)作用下应变率强化效应较高围压(如25 MPa)作用下更加显著;(2)盐岩和泥岩夹层在动力荷载条件下的力学行为的围压效应没有静力荷载条件下明显,动力放大系数(DIF)随着围压增加而减小,泥岩夹层的围压效应要小于盐岩的围压效应;(3)动力强度计算公式拟合效果较好,盐岩平均相对误差为2.51%,泥岩夹层平均相对误差为6.58%。     

Fractal property of spatial distribution of acoustic emissions during the failure process of bedded rock salt

A rock mechanics test system and the acoustic emission (AE) test system were employed to perform experiments on bedded rock salt samples under uniaxial compression and indirect tension. Based on the basic theory of fractal geometry, a column covering method is proposed to analyze the fractal property of the spatial distribution of acoustic emissions during the rock damage and failure process. The experimental results indicate obvious differences in failure features for different parts of a sample due to the structural differences in bedded rock salt. The consistency between the failure state and the AE spatial distribution is confirmed. The relationships of the stress and energy release with the fractal dimension of the AE spatial distribution are established. An increase in the fractal dimension corresponds to a decrease in the stress and an increase in the energy release, which is consistent with the theoretical analysis. When the fractal dimension obtained from uniaxial compression and indirect tensile tests is less than 2.20 and 2.57, respectively, the stresses in the bedded rock salt sample are over 80% of the peak stress. A great amount of accumulated damage occurs, leading to the global failure of the bedded rock salt sample. Therefore, it is possible to forecast the failure state of bedded rock salt by inspecting the variation between the stress or the energy release and the fractal dimension of the AE spatial distribution.     

岩盐时效特性实验研究

本文通过对盐岩单轴、三轴的强度与蠕变实验结果的分析,研究了应力状态对盐岩的强度及其时间相关性特征的影响。分析结果表明:盐岩是一种软岩,围压对盐岩力学性质影响较大;初始蠕变极限可以表示成稳态蠕变率的函数。通过实验获得的蠕变曲线和岩石参数,回归出了盐岩的蠕变本构方程,结果表明该方程能较好的模拟实验结果。     

Assessment of the properties of polycrystalline rock salt synthesized under nominally dry and wet conditions

Polycrystalline rock salt’s compression is a function of applied stresses,exposure duration to the applied stresses,ambient temperature,and water content.Rock salt’s compressional behavior under different conditions and its effects on the specimens’mechanical properties have been investigated in the literature.However,the one-dimensional(1D)compression behavior of polycrystalline rock salt at various water contents and how the specimen’s compression at different water contents further affects its physical and mechanical properties are not fully understood yet.In this study,polycrystalline rock salt specimens were prepared under nominally dry and wet conditions and some of the dry and wet specimens were annealed after the preparation.The relationship between the porosity of the specimens and the logarithm of the applied axial stresses during the 1D compression was found to follow a linear relationship after reaching unique critical porosities of 32%and 37%for the dry and wet specimens,respectively.Unloading and reloading the specimens did not result in any major changes in the porosity of the specimens.The specimens compressed under wet condition showed an average final porosity of 2.6%compared to 6.9%for the dry specimens.The dry and wet specimens that were annealed after the compression exhibited a lower porosity in comparison to the dry and wet specimens,respectively.Unconfined compression experiments on the specimens showed dry and wet specimens possess averaged unconfined compressive strengths(σ_u)of 64.3 and 16.2 MPa,respectively.Annealing decreased σ_uof the dry specimens to 39.6 MPa and increased σ_uof the wet specimens to 41 MPa.     

杂质盐岩渗透特性试验研究

利用四川大学THMC岩石三轴试验系统,针对中国天然气储库杂质盐岩开展全过程渗透试验研究,并通过试验结果拟合出同时考虑围压、扩容体积应变以及杂质含量的多因素耦合杂质盐岩渗透模型。研究表明:杂质含量、杂质分布及成分对盐岩渗透性均有显著影响,不同杂质含量盐岩损伤恢复后渗透率均有所降低,其塑性变形可分为2个阶段,I阶段渗透率增长迅速,II阶段渗透率增速减缓甚至渗透率下降,盐岩破坏后渗透率明显增大,残余阶段能维持在相对稳定的水平;低渗夹层制约盐岩垂向渗透性,而泥质成分盐岩较钙芒硝质盐岩渗透率更低。由拟合的多因素耦合渗透模型可得到:围压越高渗透率越低,扩容体积应变越大渗透率越高。当杂质含量大于0.46时,渗透率随杂质含量的增大而增大,当杂质含量小于0.46时,渗透率随杂质含量的增大而减小。     

Experiments on mechanical properties of salt rocks under cyclic loading

The primary purpose of underground gas storages is to provide gas for seasonal consumptions or strategic reserve.The periodical operations of gas injection and extraction lead to cyclic loading on the walls and surrounding rocks of gas storages.To investigate the mechanical behaviors of different host rocks in bedded salt deposit,laboratory experiments were conducted on the samples of rock salt,thenardite,glauberite and gypsum.The mechanical properties of rock samples under monotonic and cyclic loadings were studied.Testing results show that,under monotonic loading,the uniaxial compressive stress(UCS) of glauberite is the largest(17.3 MPa),while that of rock salt is the smallest(14.0 MPa).The UCSs of thenardite and gypsum are 16.3 and 14.6 MPa,respectively.The maximum strain at the peak strength of rock salt(halite) is much greater than those of the other three rocks.The elastic moduli of halite,thenardite,glauberite and gypsum are 3.0,4.2,5.1 and 6.8 GPa,respectively.Under cyclic loading,the peak strengths of the rock specimens are deteriorated except for rock salt.The peak strengths of thenardite,glauberite and gypsum decrease by 33.7%,19.1% and 35.5%,respectively;and the strains of the three rocks at the peak strengths are almost the same.However,the strain of rock salt at the peak strength increases by 1.98%,twice more than that under monotonic loading.Under monotonic loading,deformation of the tested rock salt,thenardite and glauberite shows in an elastoplastic style.However,it changes to a ductile style under cyclic loading.Brittle deformation and failure are only observed for gypsum.The results should be helpful for engineering design and operation of gas storage in bedded salt deposit.     

利用Hou/Lux本构模型考虑蠕变破坏标准和损伤改进盐岩储存硐库的设计(英文)

损伤力学和新材料模型 (包括结构损伤 )引入到盐岩硐库的设计概念中 ,能够减少以前知识和计算模型的不足。在保持同样安全的情况下 ,新模型能为设计更经济的盐岩储存硐库建立科学基础。本文通过一个实际例子 ,对Asse盐矿 (德国 )的一个原形储存硐库进行了承载性能和最小容许内压的计算验证 ,并把使用Hou Lux模型和Lubby2模型的计算结果进行了对比。比较结果显示 ,新材料模型有许多优点 ,如 :通过减少内压 ,储存硐库的围岩应力重分布、扩容、损伤、软化及片帮区域等均得到改善。     

损伤盐岩短期自恢复特性试验研究

为了解盐岩在产生损伤以后的力学性质以及在恒温环境下的短期自恢复特性,设计了盐岩剪切损伤后的自恢复试验,研究了损伤盐岩相关力学参数随恢复时间的变化规律。试验结果表明,自恢复对盐岩内摩擦角的恢复作用明显,而对黏聚力的恢复不明显;在恢复的初期,损伤盐岩抗剪强度随之降低,继续恢复则会出现相对增强,最终会进入长期恢复阶段,趋于稳定;经一定时间的恢复以后,损伤盐岩的抗变形能力有所增强的同时,其变形能力也有所增强;对盐岩损伤自恢复的研究可以分为长期和短期,试验中两者的分界点为7 d左右。通过对盐岩损伤自愈合的理论进行讨论分析,可以知道盐岩的自恢复并不是简单的力学性质的增强,更体现在综合性质的改善,同时伴随部分力学性质的劣化;通过对损伤变量的拟合,可以看出试件的损伤值在自愈合过程中的发展变化规律。     

天然气盐岩洞室群长期存储能力

对某天然气存储场盐岩洞室群的长期变形进行了三维有限元法流变分析。盐岩洞室周边附近区域内围岩的应力较低,其分布呈现出抽水井附近的水压力特征。当达到设计使用年限(80a)时,该天然气存储场内单一洞室的剩余存储能力保有初始存储能力的29.1%。进一步研究表明,当洞室间距较大时,单一洞室的剩余存储能力较大。间距400m的洞室群中单一洞室的剩余存储能力比间距280m的大5%～10%。     

Thermal and mechanical behaviour of refrigerated caverns in hard rock

One key issue in the design of unlined caverns for low temperature products is understanding the disturbance of the rock fracture network. Increasing aperture and extension of fractures inevitably affect the rock mass stability, the heat loss from stored products, and the risk of ice growth in cases when water invades the cavern. Consequently, it is essential that the designer of a refrigerated cavern has appropriate knowledge of the coupled thermal and mechanical behaviour of the fractured rock mass. Chalmers University of Technology in Gothenburg, Sweden has for several years, carried out research in the field of mechanical and physical phenomena of rock masses subjected to low temperatures. The main investigation was performed in a pilot scale cavern in hard rock, constructed as a vertical cylinder with a diameter of 7 m and a height of 15 m. The facility was equipped with comprehensive instrumentation, including approximately 200 temperature gauges and 140 deformation gauges. In the test, the temperature in the cavern was reduced in a stepwise manner to −40 °C, with comprehensive monitoring of relevant parameters such as relative humidity, air and rock temperature, rock strain, rock fracture aperture, cavern convergence and rock mass deformation. Prior to the field test, major efforts were made to predict the field results by analytical and numerical methods. The essential results of the theoretical analyses and the actual measurements of thermal and mechanical behaviour of the cavern are given in this paper.     

高温后无烟煤静动态压缩力学特性研究

为探究温度对煤岩静、动态力学特性的影响规律,首先采用箱式氛围炉在准真空环境下对直径50 mm,高度分别为100和50 mm的2组无烟煤试样进行8种温度水平的热处理(20℃~500℃),然后分别利用液压伺服试验机和分离式Hopkinson压杆对2组试样进行静态单轴压缩和动态冲击试验。此外,还通过扫描电镜和压汞试验获得各种温度后煤样的SEM图像、孔隙率及孔径分布。结果表明,煤样热损伤以300℃为界分为2个阶段,分别以解吸、热破裂等物理反应和热解化学反应为主,孔隙率逐步变大且中大孔占比逐渐增加;煤岩承载和抗变形能力都随温度升高而逐步劣化,第二阶段衰减趋势较第一阶段急剧,500℃后的静、动态抗压强度分别降至常温时的8.41%和16.94%。静载条件下煤样宏观力学性能的温度敏感性比动态冲击时显著,抗压强度和弹性模量的动态增强因子随温度的变化规律不一致。     

Effect of rock mechanical properties on electromagnetic radiation mechanism of rock fracturing

The influence of rock mechanical properties on the electromagnetic radiation(EMR) mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of rock fracturing considering the fracture factor,elastic modulus,Poisson's ratio,radiation distance and crack length is derived based on the Hertz oscillator array assumption.An experimental system,including an electromagnetic shielding module,an EMR signal induction and transmission module,a signal recording module and a loading module,is developed to understand the EMR characteristics of four different rocks.The validity of the EMR theoretical model is verified and the relationships between the rock cracking morphology and the EMR waveform,amplitude and frequency are revealed.It is found that rock mechanical properties have obvious influences on the EMR waveform,amplitude and frequency during rock fracturing.This study provides a better understanding on the EMR mechanism of rock fracturing and can help to improve the accuracy of rock disaster prediction based on EMR.     

层状岩体的抗剪强度力学特性研究

基于摩尔—库仑准则研究了单结构面岩体的力学特性,对不同形态结构面的抗剪强度进行了分析,得出了不同形态结构面剪切强度公式,并指出结构面上产生的切向力大于结构面的摩擦力且克服了剪胀压力的影响是导致岩体结构面发生剪切方向的变形和破坏的原因。     

Estimating the relation between surface roughness and mechanical properties of rock joints

Discontinuities in rock masses have an important influence on deformational behaviour of blocky rock systems. For a single rock joint, the roughness of its surface is of paramount importance to its mechanical and hydraulic properties, such as friction angle, shear strength, and dilatancy/aperture. Many methods have been used to characterize the surface roughness of rock joints, such as joint roughness coefficients (JRC), root mean square (RMS) value, structure function (SF) etc. However, most of these methods can only be used in the 2-D models. In this study, we carried out direct shear experiments on rock joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, and measured the surfaces of rock joints before and after shearing, using a 3-D laser scanning profilometer system. By using a 3-D fractal evaluation method of roughness characterization, the projective covering method (PCM) and a direct shear apparatus of high accuracy, the relation between mechanical properties of rock joints under different boundary conditions and the change of their fractal dimensions in both 2-D and 3-D models have been examined, which gives a new approach to accurately evaluate the evolution of roughness of rock joint surfaces and its influence on the hydro-mechanical behaviours of rock joints.     

Numerical modeling of thermally-induced fractures in a large rock salt mass

Numerical modeling of thermally-induced fractures is a concern for many geo-structures including deep underground energy storage caverns. In this paper, we present the numerical simulation of a large-scale cooling experiment performed in an underground rock salt mine. The theory of fracture mechanics was embedded in the extended finite element code used. The results provide reliable information on fracture location and fracture geometry. Moreover, the timing of the fracture onset, as well as the stress redistribution due to fracture propagation, is highlighted. The conclusions of this numerical approach can be used to improve the design of rock salt caverns in order to guarantee their integrity in terms of both their tightness and stability.     

基于能量耗散原理的盐岩动力特性及破坏特征分析

 为研究盐岩的动力特性和破坏特征,利用带围压的分离式Hopkinson压杆(SHPB)试验装置,对盐岩进行不同围压(5,15和25 MPa)下的冲击试验,并基于能量耗散原理来研究盐岩动态力学性能以及破坏特征,分析整个试验过程中的能量传递与转化,探究围压和输入能量对试件吸能及破坏的影响。研究结果表明：在同一围压下,随着入射能的增加,盐岩硬化效应越明显,表现为能量反射率增高而透射能和吸收能降低;在相同或相近的入射能下,随着围压的升高盐岩的流塑性变得越明显,但在动力荷载下盐岩由流塑性向脆性转变,最后发生脆性破坏;随着吸收能的增加,盐岩的峰值应力因围压不同而表现出不同的变化趋势,低围压时,吸收能越大,峰值应力越高,而高围压时,吸收能越大,峰值应力却越小;在有围压状态下,盐岩的冲击破坏形态与其他的脆性岩石相似,但在破坏机制上存在很大差异。     

盐岩层中天然气存储洞室围岩长期变形特征

采用有限差分法软件FLAC3D对一天然气存储地下盐岩洞室围岩的流变数值分析表明,由于盐岩的大流变特性,盐岩层中的稳定应力场具有静水压力的特征,这一点对围岩的稳定有十分重要的意义。在设计平均天然气内压6MPa条件下,当达到设计使用年限(80a)时,洞室的剩余存储能力仍保有初始存储能力的27 5%。考虑模型尺寸效应及模型边界条件的影响,计算结果为相对保守的可靠估计。     

温度和应力循环作用下花岗岩力学特性变化规律试验研究

采用多功能岩石高温三轴试验机,对花岗岩试件进行温度上限为100℃～600℃、应力上限分别为各温度下70%和85%单轴抗压强度的温度和应力循环试验,揭示温度和应力循环过程中花岗岩力学特性的变化规律,研究表明:(1)随循环次数增加,花岗岩弹性模量逐渐增大,每次循环加载的上限应变总体呈减小趋势,与应力上限为70%单轴抗压强度相比,应力上限为85%单轴抗压强度时上限应变的降低程度更大;(2)除600℃外,试件经温度和应力循环作用后的单轴抗压强度都大于对应实时温度下的强度值,其中循环温度上限为300℃时,其强度值增幅最大,在循环应力上限为70%与85%抗压强度条件下,增幅分别达到57.1%和50.9%;(3)经温度和应力循环后,花岗岩试件的强度产生明显变化,而峰值应变与实时温度下的峰值应变相差不大,说明从变形条件研究岩石的稳定性比强度条件研究岩石的稳定性更符合试验规律。研究结果对受温度和应力循环作用的深部岩石工程的稳定性研究有一定的借鉴价值。     

Empirical equations between characteristic impedance and mechanical properties of rocks

Based on a great number of experimental data on various mechanical properties of rock in the literature, six empirical equations between the characteristic impedance (product of density and P-wave velocity) and mechanical properties of rock are proposed. These properties include uniaxial compressive strength, tensile strength, shear strength, mode I fracture toughness, Young's modulus, and Poisson's ratio. These empirical equations show that the values of the aforementioned properties increase with increase in characteristic impedance. It also implies that the characteristic impedance of rock may be considered as an index to represent the main properties of rock. In this sense, it is possible to consider using characteristic impedance to classify rock masses for studies in the future.