Gravitational stresses in anisotropic rock masses with inclined strata

This paper presents closed-form solutions for the stress field induced by gravity in generally anisotropic, orthotropic and transversely isotropic rock masses. These rocks are assumed to be homogeneous and linearly elastic continua with strata inclined with respect to a horizontal ground surface. It is found that the stress field is multiaxial. The vertical stress is always a principal stress and is equal to the weight of the overlying material. The horizontal stresses are strongly correlated to the rock mass fabric. The expressions for the gravity-induced horizontal stresses are different for rock masses deforming under conditions of no lateral strain and no lateral displacement (uniaxial strain). The gravity-induced horizontal stresses depend on several parameters such as the type, degree and orientation of the rock anisotropy with respect to the ground surface. It is found that depending on the value of those parameters, and constrained by the thermodynamic requirement that the strain energy of the rock must always be positive-definite, the gravity induced horizontal stresses can be larger, equal or less than the vertical stress. Furthermore, for a certain range of elastic properties of a transversely isotropic rock mass with inclined strata only, it is thermodynamically admissible for the horizontal stress parallel to the dip direction of the strata to be tensile.     

中国煤矿井下地应力数据库及地应力分布规律

收集了采用井下小孔径水压致裂地应力测量装置获得的煤矿地应力数据，以及其他采用应力解除法、水压致裂法等获得的煤矿地应力数据，共计1 357条。在此基础上建立了“中国煤矿井下地应力数据库”，绘制了中国煤矿矿区地应力分布图。分析了我国煤矿井下地应力分布特征和主要影响因素，取得以下研究成果:① 埋深是影响煤矿井下地应力的重要因素。垂直应力总体上随埋深增加不断增大，但数据存在一定的离散性。最大、最小水平主应力总体上也与埋深呈正相关关系，但数据离散性更大。② 在浅部煤矿，地应力类型主要为逆断型应力状态(σH>σh>σV);在千米深井，主要为正断型应力状态(σV>σH>σh);介于两者之间主要为走滑型应力状态(σH>σV>σh)。③ 水平应力与垂直应力的比值(包括最大、最小水平主应力与垂直应力的比值;平均水平主应力与垂直应力的比值;最大水平主应力与最小水平主应力之差与垂直应力的比值)，埋深越小，这些比值离散性越大，分布范围越广。随着埋深增加，比值的离散性和范围越来越小，并逐渐趋于某一定值。④ 粉砂岩、细砂岩、泥质砂岩和泥岩4类岩性地应力数据统计结果表明，总体上，岩石强度越高，承受的水平应力越大。⑤ 弹性模量较大的岩石，水平应力较高;弹性模量较低的松软破碎岩层，水平应力较低。     

Modeling simulation of deformation in a blocky geomedium during origination of earthquake

The paper focuses on two models of an earthquake—the dilatancy model and the consolidation and stick-slip model. Experimental basis for the research was measurements of stress-strain state in a granular medium with a movable plate that simulated edges and surfaces of a tectonic fault. The dilatancy model showed the lift of the granular material and the respective accumulation of potential energy. The second model showed that a share of the accumulated energy is elastic energy produced in a blocky medium due to sliding resistance on the surface of faults. The curves of shear stresses and displacements, obtained in soft loading of the plate, showed the stick-slip mechanism with displacement discontinuities and partial drops of stresses. The maximum displacement discontinuity and the highest dynamics on the curves correspond to the maximum value of the accumulated elastic energy which is then released on the descending branch of the curve.     

可控冲击矛钻进轨迹理论分析

首先对被研究对象冲击矛及土体作出了若干假设,并在此基础上建立起力学模型,然后找出研究对象所有受力并对它们进行分析、简化,最后从力学的角度对可控冲击矛钻进轨迹进行了分析.     

裂隙充填对岩体单轴压缩力学性能及锚固效应的影响

用相似材料试件研究了裂隙不同充填物对节理岩体单轴压缩力学性能及锚固效应的影响。对裂隙含不同充填物节理岩体相似材料无锚及有锚试件进行了单轴压缩试验及数值研究,分析了不同充填物对节理岩体单轴压缩力学性能及锚固效应的影响。研究得到：充填物弹性模量在一定范围内,含充填节理岩体抗压强度峰值随着充填物弹性模量的提高而提高;充填物与基体材料弹性模量越接近,无锚含充填节理岩体试件的峰后塑性越好,但充填物对加锚试件的峰后塑性影响很小;充填物与基体材料弹性模量差值越大,试件峰后应力-应变曲线应力下降速率越快;当裂隙充填物弹性模量低于基体材料时,试件内沿受力方向出现拉应力,拉应力的峰值及分布区域随充填物弹性模量的降低而增大。     

Influence of Microplasticity on the Static and Dynamic Elastic Moduli of Rocks

Using the analysis of experimental data as the base, it is shown that the difference in the values of static and dynamic elastic moduli of rocks is governed by viscoelastic and microplastic mechanisms of deformation, provided the stresses do not exceed the proportionality limit.     

Statistical Model of Rock Failure under Compression

Based on the analysis of the elastic stresses between two shear cracks in the biaxial compression field, the conditions of crack joining are determined. The simulated statistical model is proposed for the development of shear failure in solid body under compression.     

Pillar failure by axial splitting in brittle rocks

An analytical approximate elastic model is presented of the pillar failure mechanism in the case of multiple underground openings in brittle rocks by parallel equidistant vertical splitting cracks forming slabs, which are assumed to buckle. The failure region is considered to be elliptical in shape with the major axis growing as failure proceeds parallel to the minimum applied principal stress. A modified solution for the potential energy loss due to the presence of an elliptical hole in an infinite elastic space was derived in order to account for multiple openings. This solution, which yields the failure initiation stress and the crack spacing, was achieved by inserting configuration correction factors estimated by considering certain limiting conditions. In order to obtain simple approximate formulae and after considering the blast damage effect, equivalent effective circular holes are assumed for the case of square openings and elliptical holes for the case of rectangular openings. Next, the stable mode of pillar failure was formulated based on the observation that the weak inclusion of the axially split rock mass reduces the stresses for some distance inside the pillar. The stable model was obtained first by computing the elastic stresses outside the failure zone using a circular approximation and then applying a stability criterion based on Huber's classical fracture hypothesis. Comparison of the theoretical results with field data concerning a bauxite mine using room and pillar have indicated reasonable agreement. Furthermore, the scale effect exhibited by the strength and the axial splitting crack spacing was predicted sufficiently well by the above model.     

Estimating remaining life of underground tunnel concrete lining by convergence measurements

The authors propose a procedure for estimating stresses, load bearing capacity and remaining life of lining in long-term operated underground tunnels using the analytical calculations based on solving the plane elastic problem on stress-strain state of a non-circular variable-thickness ring restraining a hole in a linearly deformed medium, and by the in situ measurement data.     

塑料板夹层双层井壁的轴对称变形分析

针对特殊地层中的塑料板夹层双层井壁结构,应用空间轴对称问题的弹性理论建立了相应的受力分析方法。综合运用线性叠加原理、弹性通解、Fourier方法等理论,获得了该双层井壁在一般荷载条件下的一组圣维南解。通过算例分析了内壁、外壁厚度的改变对井壁环向、径向及轴向正应力的影响,并利用第四强度理论分析了立井安全性的变化。结果表明：仅增加内壁厚度对井筒内、外壁安全性的提高均不显著;仅增加外壁厚度对井筒内壁安全性的改善较小,但对于井筒薄弱环节外壁安全性的提高则较为显著。     

Modeling evolution of damage in rock specimens under loading

Based on the integrated analysis of micro-strains obtained using white light specklephotography method in Brazilian Test of rock specimens and analytically calculated elastic fields of stresses and strains, the authors show that there exist significant correlation dependences between the damage in a certain domain of a rock specimen and the level of the external load. Given a verified geomechanical model describing properly evolution of stresses in a rock specimen, this fact offers pre-requisites for estimation of damage in different areas of a rock specimen by monitoring condition only in one of such areas.     

Modeling Deformation Processes in Self-Stressed Rock Specimens

The authors use mathematical model of structurally inhomogeneous rocks to describe the property of rocks to accumulate and release potential elastic energy. The finite element algorithm and bundled software are developed to solve plane boundary-value geomechanical problems. The article presents calculations of deformation of self-stress rock specimens. It is shown that the deformation curve depends both on the elastoplastic properties of the specimens and on their natural self-balanced stresses. Depending on sign, the stresses can either increase or decrease the limit load under which the specimens fail.     

高速齿轮离心应力的估算

从高速齿轮结构特点出发 ,提出了计算离心应力的近似模型。作者以弹塑性力学为基础 ,推导出了齿轮轴和整体式齿轮的离心应力计算公式 ,得到了其弹性极限转速的表达式。计算实例表明 ,在高速齿轮传动设计中建议考虑离心应力的影响。     

巷道围岩支护系统粘弹性分析蠕变柔量法

以圆形巷道为例，讨论了围岩支护系统应力与变形的时间效应，建立了巷道围岩支护系统粘弹性分析的一种新方法——蠕变柔量法，得到围岩支护系统的适用于反问题的粘弹性应力解与位移解．对于反问题，巷道围岩支护系统的新的粘弹性分析方法，使有支护和无支护围岩可以依据相同的粘弹性反分析的解析方法，识别围岩的力学模型和反演力学参数．解决了粘弹性位移反分析解析方法实用化中的一个重要问题     

Numerical modeling of elastic energy accumulation and release in structurally heterogeneous geomaterials

The approach to numerical modeling of specimen loading considered by the authors using the discrete element method enables describing ability of rocks to accumulate and release elastic energy. The model specimen is a package of particles characterized by viscoelastic interaction with dry friction. The outer layer particles are connected by elastic springs. On the whole, the model specimen is an element of a medium capable of accumulating a part of energy of deformation in the form of internal self-balanced stresses. Numerical modeling of the specimen compression is performed, and the accumulated energy is assessed. It is shown that clusters form in the medium, and sliding along the boundaries of these clusters causes discontinuities in deformation curve. Also, the discontinuities are possible under stress relaxation after unitary dynamic effect on the specimen. There is a good agreement between the numerical and experimental results.     

Calculating stresses in support and sidewall rocks in stagewise face drivage in long excavations

The issues of calculation of stresses and strains in the elements of support and in rock mass in stagewise drivage of a production face are under discussion. In order to take into account the sequence of mining and support installation, it is required to solve problems on extra stresses due to small cross-section drivage. Geomechanical estimation of support and rocks used the method based on single formation of stiffness matrix to describe rock mass prior to mining start. Sequential drivage of excavations and change of mechanical properties in the calculation system are modeled using initial stress procedure. The author calculates two scenarios of mining with stagewise face drivage under conditions of elastic deformation of rocks and support and analyzes behavior of stress redistribution in elements of support being installed in stages. It is shown that mining sequence considerably influences stresses in the support elements upon the drivage completion. The scenario of mining with initial installation of sideways support elements results in increased tensile stresses in the support as against the scenario when the underroof space is first mined out and supported.     

气动冲击器活塞的非线性有限元分析

应用有限元软件ANSYS,建立了非线性接触有限元分析模型,分析了活塞与钻头碰撞的整个过程,得出了各个时刻的应力应变情况,以及关键节点的密塞斯应力和径向位移随时间的变化曲线。活塞应力最大的位置与活塞经常断裂处相吻合。     

Deformation of Rock Mass in the Vicinity of Underground Opening at Great Depth

Journal of Mining Science - The article discusses natural stress field variation with depth. Rocks are assumed to be elastic. Increase in the stress level results in higher principal shear stresses...     

Stress-strain state of a rock sample with cuts

The singular integral equation is derived for evaluation of normal stresses along the extension of cuts in an elastic domain. The exact solution is found. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 25–31, November–December, 2005.