Stability analysis method for perilous rock by fracture mechanics

Perilous rock is a type of geological disaster in mountainous areas. Research concerning perilous rock ruptures focuses on the expanding of control fissures in perilous rock under load action. Taking the control fissure in perilous rock as one crevice in a sample, a method employing fracture mechanics is established to calculate the union fracture strength factor along the rupture orientation at the terminus of a control fissure in perilous rock. The union fracture strength factor is a function of both the first and second type fracture strength factors. We define the ratio between the fracture tendency of rock and the union fracture strength factor as the stability coefficient of perilous rock. Further, it simplifies the rupture mechanism of sliding, falling, and toppling perilous rock as pressure shear and tension shear ruptures. We establish methods for calculating the first and second type fracture strength factors. The applications show that the stability status identified by the method is more reasonable and sensitive.     

Mechanical Illation for Chained Regularity of Perilous Rock

Chained regularity of perilous rock is mainly a describtion for the avalanche order of the group perilous rock. The core of the study on chained regularity of perilous rock is to confirm the avalanche time of each perilous rock suffering from different lo     

A massive development mechanism and countermeasures for perilous rocks in the Three Gorges Reservoir area of P. R. China: The example of the Taibaiyan cliff at Wanzhou

Perilous rock is a dominant geological hazard in Three Gorges Reservoir area of P. R. China. The Taibaiyan cliff at Wanzhou is a representative case of massive perilous rocks in the area. Using this cliff as an example, the conditions triggering massive perilous rocks were studied and described. This included examining the following three conditions: alternating layers of mudstone and sandstone; steep landforms such as cliffs or scarps; and intense rainfall. The massive development mechanism for perilous rocks was discussed, including micro chained pattern gradual and interval evolution from the bottom to the summit of the cliffs individually as perilous rock, and a macro chained pattern evolving stage by stage from the cliff face backward up the mountain. In some respects, rock cells below sandstone in cliffs serves as the pulsating valve of the massive development mechanism for perilous rock. In any micro chained pattern, perilous rock situated on summits is the easiest to rupture due to the fissure pressure. For any single perilous rock, two load compositions were derived. In addition, methods for analyzing perilous rock stability were established in detail using the limit equilibrium principle. Two key techniques, a union scheme that both supports and anchors and a union scheme that nails and anchors, are proposed in light of the massive development mechanism for perilous rock.     

A Fracture Mechanics Solution for Control Fissures in Perilous Rock under Seepage Stress

Crack propagation of control fissures in perilous rock under loads is a key process in the failure of perilous rock. Based on the loading mechanism, the control fissures are classified into compression shear and tension shear types. By introducing a model of seepage stress, the calculating principle of the stress intensity factor and the propagation orientation of control fissure under seepage stress are put forward using fracture mechanics methods. Using Shoulishan perilous rock in the Wanzhou district of Chongqing, P. R. China, as an example, the calculated results show that there is an obvious increase of the stress intensity factor. The influence of hydrostatic pressure and hydrodynamic pressure also are analyzed.     

复合岩体的TBM破岩机理数值模拟

为了指导TBM刀盘刀具的研制和不同地质条件下刀盘刀具的选型,TBM破岩机理的研究成为核心。在TBM滚刀的作用下,岩体中裂纹的生成、扩展和连接规律是深刻理解TBM破岩机理的前提,因此,TBM滚刀破岩机理的研究具有重要的工程应用价值。目前,TBM滚刀破岩机理的研究主要集中在单一岩体中,但在TBM施工过程中会遇到各种复杂的地质条件。笔者采用离散元方法,研究了复合岩体的破岩机理,复合岩体中岩片的形成不同于单一岩体,其裂纹的最终连接是由起裂于复合岩体交界面上的微裂纹的扩展,将两滚刀之间的赫兹裂纹连接,最终形成岩片。因此,在一定情况下复合岩体更有利于TBM隧道施工。     

基于随机场的岩石边坡三维稳定性分析

基于随机场理论,考虑了岩石材料属性的空间变异性对岩石边坡稳定性的影响,将边坡主滑面上的摩擦系数和粘聚力视为高斯随机变量,确定了主滑面上的摩擦系数和粘聚力的均值、方差和协方差,获得了两个随机量之间的相关系数和互相关长度。在此基础上,对岩石边坡进行了三维稳定性分析,确定了岩石边坡的稳定系数和失效概率。数值计算结果表明,摩擦系数和粘聚力的空间变异性对边坡稳定性有重要影响。     

Experimental study on acoustic emission characteristics of coal rock at different confining pressure

This paper conducts experimental investigation on acoustic emission(AE) characteristics of coal rock at uniaxial and triaxial compression by MTS815 rock mechanics test system. The results show that the variation of AE has tendency effect at uniaxial compression and confining pressure experiments. We indicate that AE signal decreases significantly in the elastic stage, and the relatively quiet period of AE before the specimens failure is not obvious under confining pressure. The AE amplitude distribution with time and its envelope line can indirectly reflect the trend of stress. The AE events peak stress and elastic modulus decrease with the temperature increase, and the value of m which reflects the cumulative distribution of amplitude increases as the confining pressure rises. The results also show that the AE frequency distributes in three frequency domains, and the proportions of dominant frequency significantly increase while the specimens are broken.     

Analysis on rock cross-cut coal uncovering using high pressure water jet slotting in close distance seam group

Safe production and procedures at the driving face are restricted in mines of Guizhou province by the long periods required for rock cross-cut coal uncovering in high gas coal seam group. A new method is proposed to solve this problem using high pressure water jet slotting in penetration boreholes. This is proposed to increase the gas desorption rate and reduce drilling hole, which will shorten the cycle of rock cross-cut coal uncovering. Numerical simulation is used to compare the pressure relief effects of different slotting methods in penetration boreholes. The results show that the pressure relief effect of slotting all coal seams is more ideal. Field application indicates that high pressure water jet slotting has good effect of the pressure relief in coal seam group. The drilling number is reduced by 30, the drilling length is shortened by 610 m and the standard time of gas pre-pumping decreases by 39 days.     

Rock classification method for tunnel boring machine

In order to study the geological factors which impact penetrating rate of tunnel boring machine (TBM), this paper uses three-dimensional discrete element model 3DEC to build simulated models on rock fragment by TBM cutter. It analyzes the influence of different geological conditions on TBM penetrating rate and classified the surrounding rock in west route of south-to-north transfer project according to the drill ability of TBM in surrounding rock. The results show that the penetrating rate of TBM is closely related to the mechanical properties of rock and joint conditions in rock mass. In certain extent, TBM penetrating rate will be increased with the decrease of rock strength or closely distributed joints. TBM penetrating rate will be decreased with the increase of rock strength or rarely distributed joint. Another result is that the surrounding rock by TBM penetrating can be divided into three classes based on the drill ability of TBM in surrounding rock, which can guide the TBM penetrating.     

Chaotic behavior of stick slip in rock bursts

Two types of rock bursts, strain rock bursts and fault-slip rock bursts, are defined briefly in terms of their instability mechanisms. Justification for stick-slip instability to account for a fault-slip rock burst is presented. A model we call     

基于磁性标签石块的桥墩局部冲刷监测方法

针对桥墩局部冲刷监测存在服役环境恶劣、传感器需粗放式布设等特点,提出基于磁性标签石块的桥墩局部冲刷监测方法。桥墩局部冲刷监测系统,包括磁性标签石块和磁力梯度仪。磁性标签石块采用磁性标签浇筑成混凝土石块,通过运动自由度缩减的方式,避免了基于优化搜索的磁场梯度反演中的非线性和不适定性的问题,采用磁场梯度反演磁性标签石块的三维运动,实现桥墩局部冲刷的动态监测。在磁性标签石块的模拟定位试验中,最大误差为0.2 m,最大相对误差为5%,满足桥墩局部冲刷监测的要求。磁场梯度、磁场梯度张量不变量及张量的模量均与冲刷位移场高度相关,可直接用于冲刷监测的早期预警。     

Elasto-plastic analysis on surrounding rock of roadways based on seepage, strain softening and dilatancy

According to seepage body force, strain softening and rupture expansion of rock mass, elastic-plastic mechanics theory, distribution laws of stress and displacement of surrounding rock in seepage field are derived, and relationships between different zonation range of the surrounding rocks, pore water pressure, strain softening and rupture expansion are established. The results show that the pore water pressure and rupture expansion rock mass have a more obvious impact on the surrounding rock rupture area than the plastic zone. Both the plastic zone and the rupture area are larger when the seepage field is considered. The impact of strain softening on both the plastic zone and the rupture zone of surrounding rock is very significant, and both seepage and strain softening rupture expansion affect deformation of surrounding rock of roadways obviously. It provides certain reference values for the roadway support engineering in seepage field.     

Analysis on stress wave effect during the process ofrock breaking by pulsed jet

A mathematical model of rock breaking under pulsed jet is established by introducing the Johnson-Holmquist-Concrete constitutive relation and the smoothed particle hydrodynamics method. Based on this model, the formation, propagation and attenuation of stress wave during rock breaking by pulsed jet are simulated. The relations between pressure and time at different points on rock surface and the curve of peak stress wave versus distance to action spot are obtained. Destruction behaviors of rock under pulsed jet and effects on stress wave effect from jet velocity and lithology are studied according to the above calculation results, analysis results show that stress wave effect of pulsed jet acts locally and the peak stress wave shrinks sharply as the acting distance increases. The rock breaking mechanism of stress wave is tensile failure during the high speed process of load-unload. Power and effect range of stress wave is in high direct proportion with jet velocity. There is a threshold velocity before the macroscopic failure. Rocks of different lithologies have different destruction types under pulsed stress wave of pulsed jet. Destruction type of low strength rock like sandstone is crack propagation under the tensile stress during the high speed process of load-unload, while the destruction type of high strength brittle rocks like granite and limestone is vertical failure of stress concentration.     

Laboratory similar model test investigation of prestressed anchor rope strengthened slope fractured rock mass

Now in the highway construction of the mountain area, fractured rock mass slope always strengthened by the anchor rope. In order to investigate the strengthen effect of the slope fractured rock mass strengthened by the prestressed anchor rope, laboratory similar model test was designed and preceded. By the self-made facilities, a new method of modeling prestressed anchor rope was used in the test. Nylon ropes and the aluminum flakes were used to model the anchor rope and discrete rock mass joints. Gypsum based mix material was used to model rock. According to the real slope engineering site circumstances, six sorts of different disposed prestressed nylon rope strengthened model specimens and the specimens without prestressed nylon rope were made by the similar theory. With the test results, the strength and deformation properties of different model specimens were investigated. Comparison to different anchor effects of the different model specimens was made. The final analysis shows that in order to make full use of the anchor rope's strengthen ability, anchor rope should be disposed perpendicularly to the fracture structure rock mass's main joint direction and should be placed in the upper or top area of the fractured rock mass slope.     

直墙拱形巷道围岩应力场分析

为得出直墙拱形巷道围岩应力分布规律,应用复变函数弹性理论推导了直墙拱形巷道围岩应力分布的解析表达式。对直墙拱形巷道边界的围岩应力和巷道水平线方向的围岩应力分布规律进行分析,并考虑直墙拱形巷道断面高宽比和侧压系数对其影响规律。研究表明：在不同巷道断面高宽比、侧压系数下,直墙拱形巷道围岩应力集中区域主要集中在直墙底部底角处、拱形顶板中点附近和底板中部3个位置。不同巷道断面高宽比下,直墙拱形巷道沿水平线的应力分布规律基本相同。侧压系数大于1时,采用巷道断面高宽比小于1较有利于巷道稳定;侧压系数小于等于1时,采用巷道断面高宽比大于1较有利于巷道稳定。     

Reflected Wave Isotraveling Time Circle and Its Application in Inverting Jointed Rock Masses

Joints are crucial factors in rock masses engineering,so using stress waves to invert joint attitude is a valuable practice.The stress wave emitted from a vibration source is reflected by joints and returns to the ground.A formula to calculate the reflected wave travel time was deduced using analytic geometry theory.In the formula,a direct relationship was established between a joint's real dip angle,real dip direction and the travel time at test spots on the ground.The reflected wave's isotravel time circle described by the formula has a clear conception and a definite meaning.Using the program on the MATLAB platform,this formula can be applied to invert the joint attitude by searching the center of the circle based on the measured travel time at the testing spots around the wave source.     

盐岩水平储气库的相似模拟建腔和长期稳定性分析

利用地下盐穴作为油气储库是一种常见的方法。但由于中国地下盐矿层状盐岩居多,特点是单层厚度薄,不溶物含量高,因此单井造腔腔型控制难度大,造腔速度慢。根据双井对流建库方法,通过实验模拟建造的水平盐穴为模型基础,依据湖北云应地区盐矿地质条件和盐岩的物理力学性质,数值模拟其在不同埋深情况下建造后腔体长期运行体积收缩情况。通过实验发现采用双井对流造腔方法建设储气库是可行的,腔体的形状可以通过流量和油液分界面来控制。对地下盐岩水平储气库的岩石长期蠕变模拟发现,水平储气库随着埋深越大相同蠕变期内条件下腔体的体积收缩率和腔体周边塑性变形区体积也越大,同时使用寿命也越短。     

Development and application of a new plain strain apparatusfor testing rock like materials

We present the development, fabrication and use of a new apparatus for testing rock like material in plain strain stat. A major feature of the plain strain apparatus is the confining pressure applied in the pressure vessel rated to 20 MPa. The rectangular     

Damage Model of Rock and the Damage Energy Index of Rockburst

Based on research of brittle rock mechanical experiment, damage model was established by damage mechanics theory. Furthermore, interior energy transformation of rock is analyzed from the point of view of damage mechanics. By analyzing the energy transformation of rock burst, the new conception of damage energy index of rock burst is put forward. The condition of rock burst is also established.     

A NEW IDEA FOR PROTECTING ROCK AROUND UNDERGROUND EXCAVATION-STUDIES OF SOFTENING SURROUNDING ROCK METHOD

This paper advances a new idea for protecting rock around underground excavation, based on the analyese of movements of surrounding rock,then studies the sloting in surrounding rock-a kind of softening technique for surrounding rock by means of BEM and modle tests. It is proved that this method is useful and effective.