Effect of Rock Mass Structure and Block Size on the Slope Stability-Physical Modeling and Discrete Element Simulation

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.

Study on Mechanics Parameters of Unloaded Rock Mass about the Underground Powerhouse of Jin-ping Hydroelectric Station

After the excavation of Jinping underground cavern, a strong expansion appears along the unloading direction of the rock mass, mainly in the type of tensile rupture, accompanied by shear destruction, unloading resulted in significant deterioration of mechanical properties of rock. Based on the in-site investigation of rock mass structure, via analyzing the acoustic testing data, we identify the unloading range of the side walls and the division of rock types, and carry out with the solution of rock mechanical parameters about different unloading zone, providing geological foundation for the supporting design of the following design of the side walls, at the same time, providing reference for the selection of mechanical parameters of other underground excavation engineering with similar geological conditions.

Analysis of critical excavation depth for a jointed rock slope using a face-to-face discrete element method

The critical excavation depth of a jointed rock slope is an important problem in rock engineering. This paper studies the critical excavation depth for two idealized jointed rock slopes by employing a face-to-face discrete element method (DEM). The DEM is based on the discontinuity analysis which can consider anisotropic and discontinuous deformations due to joints and their orientations. It uses four lump-points at each surface of rock blocks to describe their interactions. The relationship between the critical excavation depth D-s and the natural slope angle alpha, the joint inclination angle theta as well as the strength parameters of the joints c(r) ,phi(r) is analyzed, and the critical excavation depth obtained with this DEM and the limit equilibrium method (LEM) is compared. Furthermore, effects of joints on the failure modes are compared between DEM simulations and experimental observations. It is found that the DEM predicts a lower critical excavation depth than the LEM if the joint structures in the rock mass are not ignored.

非均匀性对岩石破裂过程影响的研究

Rock heterogeneity plays an important role in rock fracturing processes. However, because fracturing is a dynamic process and it is very difficult to quantify materials' heterogeneity, most of the theories dealing with local failure were based on the homogeneity assumption, very few involving stress distribution heterogeneity and successive local failure due to rock heterogeneity. Therefore, based on various references, the author studied the laws and mechanism of influences of heterogeneity on rock fracturing processes, under the frame of the project "Study on Associate Mechanism between Rock Mass Fracture and Strength Failure", funded by Nation Natural Science Fund. the research consists of such aspects as size effect correction to rock fracture parameters, SEM (Scanning Electron Microscope) real-time observation on rock samples under different loads, micro-hardness testing, and numerical simulating based on microstructure. There are some important research results as followed: 1. Unifying formula for nonlinear and non-singularity correction, simplifying the complex process of correcting size effect on rock fracture toughness. 2. Using the methods of micro-hardness testing mineral grain and random jointing micrograph digitizing mineral slice, preliminarily solving the problems of numerical simulating and quantitatively describing the heterogeneous strength and its distribution rules, which has certain innovation and better practicability. 3. Based on SEM real-time observation, studying the micro-process of fracturing in marble, sandstone, granite, and mushroom stone samples with premanufactured cracks under tension, pure-shear and compression-shear conditions. Strength Failure was observed: there was some kind failure occurred before Fracture Failure in marble and sandstone samples with double cracks under pure-shearing. It is believed that the reason of strength failure developing is that stress concentrations is some locations are larger than that near the end of pre-manufactured cracks. 4. Based on the idea that rock macro-constitute is composed of complex microstructure, the promising method used to handle heterogeneity considers not only the heterogeneity of the rock medium, but also the heterogeneity of the rock structure. 5. Putting forward two types of rock strength failure: medium strength failure induced by heterogeneity of rock medium and structure strength failure induced by heterogeneity rock structure. 6. By evaluating potential fracture cell with proper failure priority, the numerical simulating method solved the problem of simulating the coextensive strength failure and fracture failure with convention strength failure rules. The result of numerical analysis shows that the influence of heterogeneity on rock fracturing processes is evident. The sinuosity of the rock fracture-propagation path, and the irregular fluctuation of loading displacement curve, is mainly controlled by the heterogeneity of rock medium.

基于工程地质力学的岩土工程加固理论、技术与实践

In the engineering reinforcement of-rock and soil mass, engineers must consider how to obtain better reinforcing effect at the cost of less reinforcing expense, which, in fact, is the aim of reinforcement design. In order to accomplish the purpose, they require not only researching the material used to reinforce and its structure, but also taking into account of several important geological factors, such as the structure and property of rock and soil mass. How to improve the reinforcing effect according to engineering geomechanical principle at the respect of the reinforcement of engineering soil and rock mass is studied and discussed in this paper. The author studies the theory, technology and practice of geotechnical reinforcement based on engineering geomechanics, taking example for the soil treatment of Zhengzhou Airport, the effect analysis of reinforcement to the slope on the left bank of Wuqiangxi Hydropower Station and the reinforcing design of the No. 102 Landslide and unique sand-slide slope on the Sichuan-Tibet Highway. The paper is comprised of two parts for the convenience of discussion. In the first part, from the first chapter to the fifth chapter, trying to perform the relevant research and application at the viewpoint of soil mass engineering geomechanics, the author mainly discusses the study of reinforcing soft ground soil through dynamical consolidation and its application. Then, in the second part, from the sixth chapter to the eleventh chapter, the study of new technologies in the rock slope reinforcement and their application are discussed. The author finds that not only better reinforcing effect can be gained in the research where the principle and method of rock mass engineering geomechanics is adopted, but also new reinforcing technologies can be put forward. Zhengzhou Airport is an important one in central plains. It lies on Yellow River alluvial deposit and the structure of stratum is complex and heterogeneous. The area of airport is very large, which can result in differential settlement easily, damage of airport and aircraft accident, whereas, there are no similar experiences to dispose the foundation, so the foundation treatment become a principal problem. During the process of treatment, the method of dynamic compaction was adopted after compared with other methods using the theory of synthetic integration. Dynamic compaction is an important method to consolidate foundation, which was successfully used in the foundation of Zhengzhou Airport. For fill foundation, controlling the thickness of fill so as to make the foundation treatment can reach the design demand and optimum thickness of the fill is a difficult problem. Considering this problem, the author proposed a calculation method to evaluate the thickness of fill. The method can consider not only the self-settlement of fill but also the settlement of the ground surface under applied load so as to ensure the settlement occurred during the using period can satisfy the design demand. It is proved that the method is correct after using it to choose reasonable energy of dynamic compaction to treat foundation. At the same time, in order to examine the effect of dynamic compaction, many monitor methods were adopted in the test such as static loading test, modulus of resilience test, deep pore pressure -test, static cone penetration test and the variation of the pore volume measurement. Through the tests, the author summarized the discipline of the accumulation and dissipation of pore pressure in Yellow River alluvial deposit under the action of dynamic compaction, gave a correct division of the property change of silt and clay under dynamic compaction, determined the bearing capacity of foundation after treatment and weighted the reinforcing effect of dynamic consolidation from the variation of the soil particle in microcosmic and the parameter of soil mass' density. It can be considered that the compactness of soil is in proportion to the energy of dynamic compaction. This conclusion provided a reference to the research of the "Problem of Soil Structure-the Central Problem of Soil Mechanics in 21 Century ". It is also important to strengthen rock mass for water conservancy and electric power engineering. Slip-resistance pile and anchoring adit full of reinforced concrete are usually adopted in engineering experience to strengthen rock mass and very important for engineering. But there also some deficiency such as the weakest section can't be highlighted, the monitor is inconvenient and the diameter of pile and adit is very large etc. The author and his supervisor professor Yangzhifa invented prestressed slip-resistance pile and prestressed anchoring adit full of reinforced concrete, utilizing the advantage that the prestressed structure has better anti-tensile characteristic (this invention is to be published). These inventions overcome the disadvantages of general slip-resistance pile and anchoring adit full of reinforced concrete and have the functions of engineering prospecting, strengthening, drainage and monitor simultaneous, so they have better strengthened effect and be more convenient for monitor and more economical than traditional methods. Drainage is an important factor in treatments of rock mass and slop. In view of the traditional drainage method that drainage pore often be clogged so as to resulted in incident, professor Yangzhifa invented the method and setting of guide penetration by fiber bundle. It would take good effect to use it in prestressed slip-resistance pile and anchoring adit full of reinforced concrete. In this paper, the author took example for anchoring adit full of reinforced concrete used to strengthen Wuqiangxi left bank to simulate the strengthened effect after consolidated by prestressed slip-resistance pile, took example for 102 landslide occurred along Sichuan-Tibet highway to simulate the application of slip-resistance pile and the new technology of drainage. At the same time the author proposed the treatment method of flowing sand in Sichuan-Tibet highway, which will benefit the study on strengthening similar engineering. There are five novelties in the paper with the author's theoretical study and engineering practice: 1. Summarizing the role of pore water pressure accumulation and dissipation of the Yellow River alluvial and diluvial soil under the action of dynamical consolidation, which has instructive significance in the engineering construction under the analogical engineering geological conditions in the future. It has not been researched by the predecessors. 2. Putting forward the concept of density D in microcosmic based on the microcosmical structure study of the soil sample. Adopting D to weight the reinforcing effect of dynamic consolidation is considered to be appropriate by the means of comparing the D values of Zhengzhou Airport's ground soil before with after dynamically consolidating reinforcement, so a more convenient balancing method can be provided for engineering practice. 3. According to the deep research into the soil mass engineering geology, engineering rock and soil science, soil mechanics, as well as considerable field experiments, improving the consolidating method in airport construction, from the conventional method, which is dynamically compactmg original ground surface firstly, then filling soil and dynamically layer-consolidating or layer-compacting at last to the upgraded method, which is performing dynamical consolidation after filling soil to place totally at the extent of the certain earth-filling depth. The result of the dynamical consolidation not only complies with the specifications, but also reduces the soil treatment investment by 10 million RMB. 4. Proposing the method for calculating the height of the filled soil by the means of estimating the potential displacement produced in the original ground surface and the filled earth soil under the possible load, selecting the appropriate dynamically-compacting power and determining the virtual height of the filled earth soil. The method is proved to be effective and scientific. 5. According to the thought of Engineering Geomechanics Metal-Synthetic Methodology (EGMS), patenting two inventions (to the stage of roclamation, with Professor Yang Zhi-fa, the cooperative tutor, and etc.) in which multi-functions, engineering geological investigation, reinforcement, drainage and strength remedy, are integrated all over in one body at the viewpoint of the breakage mechanism of the rock slope.

Application of Three-Dimensional Discrete Element Face-to-Face Contact Model with Fissure Water Pressure to Stability Analysis of Landslide in Panluo Iron Mine

Three-dimensional discrete element face-to-face contact model with fissure water pressure is established in this paper and the model is used to simulate three-stage process of landslide under fissure water pressure in the opencast mine, according to the actual state of landslide in Panluo iron mine where landslide happened in 1990 and was fathered in 1999. The calculation results show that fissure water pressure on the sliding surface is the main reason causing landslide and the local soft interlayer weakens the stability of slope. If the discrete element method adopts the same assumption as the limit equilibrium method, the results of two methods are in good agreement; while if the assumption is not adopted in the discrete element method, the critical phi numerically calculated is less than the one calculated by use of the limit equilibrium method for the same C. Thus, from an engineering point of view, the result from the discrete element model simulation is safer and has more widely application since the discrete element model takes into account the effect of rock mass structures.

断续节理岩体随机模型三维离散元数值模拟

针对断续节理岩体提出了一种随机计算模型.在该模型中,假设结构面的形状为正方形,通过岩体结构面的统计分布函数模拟结构面的空间随机分布.给出了随机节理模型的实现方法,对该随机模型的算法可靠性进行了验证.通过单向加载模拟试验研究了节理岩体破坏强度与节理倾角及节理连通率等因素的关系,并与极限平衡条件推导的理论结果进行了比较,分析了数值模拟结果与极限平衡理论结果的异同性,进而验证了节理随机计算模型的可靠性.同时,研究了节理连通率与岩体等效弹性模量之间的影响关系,给出了二者的影响关系式.

一种岩石概率型本构及其应用

在岩石材料非均匀特性的基础上,建立了弹塑性概率材料本构.认为材料单元的切线模量与破坏强度都是服从二参数Weibull分布的随机量,通过用户材料子程序将该本构导入到LS-DYNA3D中,推导了程序流程,分析了导入过程中的关键技术.算例验证表明,应用该本构模拟得出的现象与实验观测完全一致,这是确定性本构无法实现的.

清江茅坪滑坡白岩危岩体崩塌现场测量及其分析

位于茅坪滑坡体后缘的白岩危岩体于2002年8月24日发生了大规模的崩塌。崩落的块石落在滑坡体上，对滑坡体产生了加载作用，影响了该滑坡体的稳定性。为研究茅坪滑坡体的稳定性，有必要弄清滑坡体上崩落块石的堆积情况。论文在对清江隔河岩水库白岩危岩体崩塌现场调查的基础上，估算了崩塌岩体的体积，实地测量了岩体崩塌后堆积体表面块石的尺寸以及各块石空间位置坐标。对测量的结果进行了统计分析。根据所测量的块石尺寸、得到了崩落岩体的块体大小级配累积曲线图和各块石尺度出现的概率，从而阐明了各尺度崩落块石组合情况。根据各块石尺寸和各块石空间位置坐标、分析得到不同尺寸崩落块石落在滑坡体上的空间分布规律，从而为茅坪滑坡的进一步研究打下了基础。

应力波峰值变化与岩体结构关系的试验研究

选择了3种有代表性的岩体结构进行冲击试验,分析研究了波形最大峰值变化与岩体结构的关系.试验结果表明:震动峰值随空间衰减、震动峰值延时及其离散性变化均能有效反映岩体结构特点和受扰动程度,也能反映岩体的各向异性.

岩体中应力波幅值随时空衰减的关系

把岩石抽象为Kelvin-Voigt黏弹性体, 应用复数理论建立了应力波在岩石中传播时的振动频率和波动频率的关系, 在此基础上, 研究了岩石和含有一组平行结构面的岩体中应力波幅值随时间和随空间衰减的关系. 研究表明, 应力波在岩石的传播过程中, 频率是影响应力波幅值衰减的的主要因素; 应力波在含有1组平行结构面岩体的传播过程中, 由于结构面的存在, 影响了应力波能量的传播, 其幅值随时空衰减系数主要由结构面间距及其反射系数决定, 结构面间距减小和反射系数增加, 幅值随传播距离的衰减系数增加和随时间的衰减系数减小, 而结构面的黏性系数增加, 幅值随传播距离的衰减系数增加, 但随时间的衰减系数变化很小. 上述结论对岩体结构探测具有重要的指导意义

基于GSI的锦屏地下厂房岩体参数研究

工程开挖卸荷后岩体参数研究一直是工程界关注的焦点,是稳定性评价的基础性工作.本文以锦屏地下厂房开挖工程为背景,通过对上下游边墙不同桩号段开挖揭露的岩体进行工程地质岩组划分,进行了开挖后岩体质量评价并对其进行分类,通过在GSI(Geological Strength Index)评价体系中引入Jv(节理数/m3),使评价体系相对合理化,经回归分析,对不同风化程度的岩体进行了力学参数求解,发现内聚力及内摩擦角的计算值与建议值吻合较好

小湾电站坝基岩体卸荷工程地质力学研究

Dam is the key main works in the construction of water power. The success or failure of the construction of the dam mainly depends on the stability of the dam foundation. The double curvature arch dam-XiaoWan Dam is the highest one among the dams with the same type in the world, and the water thrust acted on it reaches ton, so the rock bearing capacity of dam foundation becomes more important. Because of the high and steep valley-side slope, the large scale of excavation and the complex body type of excavation, it is prominent that the problem of stress release of the rock mass in dam foundation. More great attentions should be paid for the stability and the degraded of rock properties of rock mass induced by the stress release. In this paper, the phenomena of stress release of rock mass in XiaoWan Dam foundation and its mechanisms were analyzed based on the collection of data, the detailed field engineering investigations, measurement of the rock mass and the 2D numerical calculations. The rock mass under the foundation is weak-weathered to intact, the quality of which is good. After excavation of the foundation, the rock mass near the slope surface occurred extend, stretch and stick-slip along original textures till the new fracture surface formed. Then platy structure of the rock mass takes on. The rock mass in the dam foundation occur resilience due to stress release towards free faces with the characteristics of time effect and localized deformation. In-situ measurements show that the rock mass near the surface are degraded. The stress release induced by excavation is a process of the interaction between engineering structures and geologic body. The stress release of rock mass in dam foundation is related to the changed degree of geometrical conditions. The rock near excavation surface failed nearly under uniaxial stresses. The bending-breaking mechanism of plate girder can interpret the failure model of the rock mass with platy structure in dam foundation slope. In essence, the stress release is the change of stress field including the change of directions and magnitudes of stress induced by excavation, which can induce the comedown of the safety margin. In this paper, the inducing conditions of stress release were calculated by numerical analyses. Moreover, from the point of view that the change of stress field, the coefficient of K, i.e. the variable load coefficient was proposed. Then the law of the change of it is interpreted. The distributional characteristics of fracture zone were expressed by the coefficient. The stress release of hard rock has the characteristic of localization. The measuring technique of sound wave can not reflect the small cracks in this kind of rock mass due to stress release. So, the spectral analysis method was proposed. At the same time, the application foreground in engineering of the Stockwell Time-Frequency- Spectrum method was discussed with a view to the limitation of it.

悬索桥隧道式锚碇与围岩系统的破坏模式研究

The anchorages are unparalleled structures only in a suspension bridge, and as main bearing facilities, play an important role in connecting the superstructures and the ground. The tunnel anchorage, as one alternative type of the anchorages, has more advantages over its counterpart, the gravity anchorage. With the tunnel anchorages adopted, not only can surface excavation be reduced to protect the environment, and natural condition of the rock be utilized and potential bearing capacity of surrounding rock be mobilized to save engineering cost, but also the technological predominance of auxiliary engineering measures, such as prestressed concrete, anchoring piles, rock anchors and collar beam between the two separated anchorages, can be easily cooperated to work together harmoniously under the circumstances of poor rock quality. There are plentiful high mountains and deep canyons in west part of China, and long-span bridge construction is inevitably encountered in order to realize leapfrogging development of the transportation infrastructure. Western mountainous areas usually possess the conditions for constructing tunnel anchorages, and therefore, the tunnel anchorages, which are conformed to the conception of resource conservative and sustainable society, extremely have application and popularization value in western underdeveloped region. The scientific and technological problem about the design, construction and operation of tunnel anchorages should be further investigated. Combining the engineering of western tunnel anchorages for the Balinghe Suspension Bridge, this paper probed into the survey method and in-situ test method for tunnel anchorages, scientific rock quality evaluation of surrounding rock to provide reasonable physical and mechanical parameters for design, construction and operation of tunnel anchorages, bearing capacity estimation for tunnel anchorage, deformation prediction of the anchorage-rockmass system, tunnel-anchorage slope stability analysis and the evaluation of excavation stability and degree of safety of the anchorage tunnel. The following outcomes were obtained: 1. Materials of tunnel anchorages of suspension bridge built (and in progress) at home and abroad were systematically sorted out, with the engineering geological condition and geomechanical property of surrounding rock around the anchorage tunnel, the design size of anchorages and the construction method of anchorage tunnel paid more emphasis on, to unveil the internal relationship between the engineering geological conditions of surrounding rock and the design size and axis angle of anchorages and provide references for future design, construction and study of tunnel anchorages. 2. Physical and mechanical parameters were recommended based on three domestic and foreign methods of rock quality evaluation. 3. In-situ tests, adopting the back-thrust method, of two kinds of reduced scale model, 1/30 and 1/20, for the tunnel anchorages were conducted in the declining exploration drift with rock mass at the test depth being the same as surrounding rock around real anchorages, and reliable field rockmass displacement data were acquired. Attenuation relation between the increment of distance from the anchorage and the decrement of rockmass displacement under maximum test load, and influential scope suffered by anchorage load were obtained. 4. Using similarity theory, the magnitude of real anchorage and rockmass displacement under design load and degree of safety of the anchorage system were deduced. Furthermore, inversion analysis to deformation modulus of slightly weathered dolomite rock, the surrounding rock of anchorage tunnel, was performed by the means of numerical simulation. 5. The influential law of the geometrical size to the limit bearing capacity of tunnel anchorage was studied. 6. Based on engineering geological survey data, accounting for the combination of strata layer and adverse discontinuities, the failure patterns of tunnel anchorage slope were divided into three modes: sliding of splay saddle pier slope, superficial-layer slippage, and deep-layer slippage. Using virtual work principle and taking anchorage load in account, the stability of the three kinds of failure patterns were analyzed in detail. 7. The step-by-step excavation of anchorage tunnel, the numerical overload and the staged decrement of rock strength parameters were numerically simulated to evaluate the excavation stability of surrounding rock around anchorage tunnel, the overload performance of tunnel anchorage, and the safety margin of strength parameters of the surrounding rock.