Damage Constitutive Equation and Experiment of Layered Rock

The microcosmical study on many speciments of sedimentary rock by SEM and petrography theory show that rock is formed of microcrystalline and micropore with all kinds of forms.Therefrom the microstructure model of rock is established.Further the three dimensional nonlinear damage constitutive equation and damage evolution equation of layered rock including respective process of damage evolution,mechanical parameter,effective stresses,and unequal biaxial stress in different rocks are derived.The results of the experiment indicate that the theoretical curve is fairly close to the experimental curve.     

Step-by-step Method of Structural Damage Diagnosis

Base on the existing step-by-step structural damage diagnosis method, a three-step structural damage diagnosis method is developed. According to the analysis of the characteristic of genetic algorithm, a new idea of excluding the undamaged element by means of step-by-step evaluation is developed to deal with the damage diagnosis problem. In this method, sensitivity genetic algorithm is used to exclude the undamaged element step by step and residual force method is used to fix the damage district. According to the simulation research of a 2D framed structure, it is shown that the step-by-step structural damage diagnosis method can gain the ideal results when it's difficult for a single damage diagnosis method to get the good results. It is also indicated that sensitivity genetic algorithm is a good way to exclude the undamaged element step by step.     

The influence of initial internal structure of coal sample on gas flow characteristic

Three kinds of coal samples with different components are chosen as study objects.Density calculation and SEM are adopted to study their internal structures,and a self made triaxial gas seepage instrument is used to study their internal gas flow characteristics.The results show that internal structures of coal samples made of different particle size coal powders under identical external conditions are various,and nonlinearity is presented on the influence caused by fabric.Gas flow characteristic is complex in complete stress strain process,generally it firstly increases and then decreases,initial gas flow velocity is lower than the one after the failure of coal sample,and obvious hysteretic nature of gas flow characteristic is showed.The influence of gas flow characteristic caused by initial internal structure of coal sample is nonlinear and the stress sensitivity is high on the influence of gas flow characteristic caused by initial internal structure.The more complex the initial internal structure of the coal sample is,the lower the axial tress sensitivity is,and the higher the confining pressure sensitivity is.     

基于区间分析的框架结构不确定性损伤识别方法

考虑实际结构易受荷载、环境温度和测试噪声等不确定性因素的影响,笔者基于区间分析原理提出框架结构不确定性损伤识别方法。利用测试的结构加速度响应数据,建立向量自回归模型,并采用其系数矩阵主对角线的马氏距离作为损伤特征指标。基于粒子群算法建立区间优化求解方法,并与传统的区间组合法和区间叠加法对比。通过提出的区间重叠率指标和区间名义值分别实现损伤定位和损伤程度的识别。数值模拟和实验室框架结构试验结果表明,区间分析能在测试数据较少时实现损伤识别,为损伤识别在实际结构中的应用提供了理论基础和技术手段。     

Rockburst Hazard and Its Forcast and Treatments in Underground Engineering

Rockburst is a serious damage geologic hazard. According to the rockburst phenomenon in Erlangshan tunnel and the Jinping 2nd hydropower station and a large of rockburst data,this paper proposes that rockburst is a result that many factors synthesize. These factors include teconics ,epigenetic and superficial structure, wall-rock intensity, attitude of rocks, wall-rock state of stress, wall-rock deformation and underground engineering arrangement, etc. It is given that the mechanism of rockburst is a tension fracture damage under press.     

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.     

Generalized Damage Reliability and Sensitivity Analysis on Rolled-Concrete Gravity Dam

Based on fuzzy self-adapting stochastic damage model, the characteristics of generalized damage stress field on material crack tip are studied. The results express that the numerical algorithm is reliable. Sensitivity of rolled-concrete gravity dam under fuzzy-stochastic damage gaining is implemented by considering the spatial variation of material parameters. It is found that the compression strength of rolled-concrete is the governing index on gravity dam reliability. The activation simulations on fuzzy self-adapting stochastic damage model were carried by adopting different fuzzy distributions, which indicated the governing characteristics of the distribution on generalized damage evolution of rock-like material.     

Relationship between effective volumetric stress and permeability of gas-filled coal

Considering the damage effect of porous media under triaxial compression, the calculation formula of effective stress is modified. It is verified that the formula can very well describe complete stress-strain process of gas-filled coal under triaxial compression. The permeability experiments under triaxial compression show that the relationship between the effective volumetric stress and permeability of gas-filled coal samples is negative exponent before the peak stress. It is still exponentially after the peak point, but the coefficient changes. The permeability of the gas-filled coal samples changes in reverse direction with the effective volumetric stress, that is, the effective volumetric stress increases when the permeability decreases, and vice versa.     

Analysis of Damage Localization in Crack Weakened Rock Mass

Damage localization in crack weakened rock mass is closely related to the crack growth pattern. Bifurcation of the alternative evolution of cracks occurs when the cracks grow to some extent, then some cracks keep on growing while other ceased evolving. It is found that damage localization in crack weakened rock mass is caused by bifurcation of the crack growth pattern, and the initial location is also determined by the crack growth pattern. Based on the analysis on the bifurcation of crack growth pattern, the critical length of wing crack and the critical stress of damage localization in crack weakened rock mass are obtained. Subsequently, the onset location of damage localization is determined by using the eigenvalue and eigenvector of coefficient matrix, and crack interaction is also taken into account in this model. Finally, the relationship between the interval between columns and rows, the orientation of crack, confining stress and the critical stress of damage localization is defined in the example.     

Collapse Analysis of Steel Trussed Arch Structure Considering Damage Cumulative Effect

Based on an actual project, the ABAQUS material subroutine considering damage cumulative effect and member buckling was adopted to analyze the collapse process of steel trussed arch structure. The failure mechanism and the failure mode of such structure under severe earthquake conditions were studied. The results indicated that, under the action of severe earthquakes, the cumulative damage increased and structural stiffness declined, which leading to the structure failure. The damage cumulative effect caused the decrease of the member stress and the increase of nodal displacement and member strain. Subjected to seismic waves, the webs at the columns of the middle main truss failed at first; then the failure region extended along the out-of-plane direction of the main truss and extended from the column foot to the top of structure. After the earthquake, the webs at the one-quarter point of the main truss and the webs at columns with large slenderness ratio buckled. It will lead to early failure of part members if member buckling is considered. However, it has little effect on the failure mode of structure.     

A Stress Path Damage Constitutive Model for Sang

A hypothesis that the skeleton deformation of sand is only the deformation of the interfaces of grains, and the deformation characteristics including nonlinearity, plastic deformation and shear dilation are controlled by the sliding of interfaces of grains within skeleton, is presented.The contact between grains is classified as perfect contact and sliding contact in this paper.In the elastic deformation phase, the contact between grains is regarded as perfect contact.With the increase of shear stress, there are gradual conversions from perfect contacts to sliding contacts which are viewed of damages in this paper.Based on Mohr Coulomb law, a calculation method for the damage ratio is given according to the relative distance of the stress point to the initial damage line and failure line.On this basis, a damage constitutive model is proposed.The model properties can be conveniently obtained through conventional triaxial compression test and constant stress ratio consolidation test.Test results indicate that the model is capable of predicting deformation behavior for various conditions, including varying consolidation conditions and stress paths.     

Application of Improved Multi-population Genetic Algorithm to Damage Identification of Soil-wall System

The method of damage identification in soil-wall system was studied; a new approach based on improved multi-population genetic algorithm (IMGA) was developed. First, the simplified dynamic-detection model of soil-wall system was established, meanwhile, the theoretical analysis of characteristic equations in soil-wall system was conducted when soil in damage status. The objective function based on characteristic equations was established. Then, the improvements of multi-population genetic algorithm, including the adoption of real-valued representation, adaptive cross operator and adaptive mutation operator, were conducted. Finally, the localization and quantification of the soil-wall system damage were performed by IMGA with and without the consideration of noise, respectively. The results indicate that damage location and damage extent can be detected efficiently, and anti-noise performance is better.     

The Dynamic- Damage Variables of Jointed Rock Masses

This paper comprehensively reviews various damage variables of jointed rock masses and their meaning. The practical occasion of these variables is discussed. And the paper points out the significance of appling the dynamic- damage variable into rocks engineering.     

Identification of the Serious Damage in Superficial Part on Piles

Two kinds of singular signal's characteristics of upper part serious damage piles encountered in the examination of structural integrity of piles are presented. Based on vibration and wave theories, the principle of identifying the existence of the upper part serious damage piles and the method of identifying the damaged positions and severity of piles are worked out. The structure integrity of a pile including damage type and position should be identified by vibration theory of single severity of freedom from its oscillating signs of low frequency,and the damage type and position should be respectively detected by vibration theory and wave theory from the oscillating signs of high frequency. The method is of great practicability in engineering field.     

Spatial Structure Adjustment Strategies of the Coal Resource-Based Cities during the Mature Period: A Case Study of Pingdingshan

Coal cities are the main part of the resource-based cities in China, and the benign development of coal cities' spatial structure has a direct impact on these cities' future economic and social development, as well as the urban residents' welfare. Land use fragmentation is the most typical morphological characteristic of the coal city's spatial structure development. In this paper, Pingdingshan City of Henan Province in China is taken as an example. Through empirical analysis, the urban spatial structure development processes of a typical coal resource-based city in its mature period are illustrated, and the formation reasons and potential mechanism behind coal city land use fragmentation are explored, and the measurement method of land use fragmentation degree of the coal city is put forward. On the above basis, the appropriate adjustment strategies and methods aimed at the coal city spatial structure are found out and given. This study is a good guideline and reference for the spatial structure planning and land use planning of the coal city during the mature and declining period, which is of great help to the sustainable development and industrial structure transformation of the coal city. It also has certain reference significance for the coal city in the growth period.     

Effect of the Circulate Loading on the Deformation of Sanjome Andesite

By the experimental study about the effect of a circulate loading on the deformation and the Young's model of Sanjome andesite at the distinct strain rate in a low stress state, the viscoelasticity of Sanjome andesite in a low stress state is researched by means of the effect of the circulate loading on the deformation of rocks. It is found that the natural material such as rocks has obvious viscoelasticity, and the mechanical property of rocks has a direct bearing on the size, direction and loading rate, but also on the way of loading and the organization attribute of rocks.     

Stress wave effect in numerical simulation on rock breaking under high pressure water jet

The evolvement of rock damage struck by a high pressure water jet is characterized by nonlinear properties, thus making it a complicated dynamic problem. Based on a nonlinear finite element and elastic plasticity theory, a computational model was established. The dynamic load striking the rock by a high pressure water jet was simulated by the dynamic contact method. Furthermore, the propagation of a stress wave in the same rock was simulated at different impact velocities. The results show that the propagation velocity of a stress wave is proportional to the impact velocity of the high pressure water jet. The effects of a stress wave in sandstone and coal impacted by high pressure water jets of the same velocity were simulated.The effect of a stress wave in coal was stronger than in sandstone, while the region of propagation of stress wave in coal was smaller.     

Synthesis Mode of Stress and Strain for Complexus Theory of Geomaterials Damage

Although the constitutive model for geomaterial damage has developed significantly, there is still dispute regarding the synthesis mode of stress and strain for the complexus theory of geomaterials damage. The synthesis mode of stress and strain for the complexus theory of geomaterials damage was studied in depth in light of the basic concepts of continuum mechanics. A general synthesis mode of stress and strain for the complexus theory of geomaterials damagmall. The amount of sampling could sharply decrease by using the dual sampling method. During the comparison, the supporting role exaggeration of the line element, which is used in the FEM model to simulate the initial lining and rock bolt, was found by FEM simulation. The lining element reaction forces which were greater than usual were reported in FEM analysis results. Deeply Buried Tunnel Reliability Analysis was developed on the platform of ANSYS.     

Experimental study of coalbed methane seepage in fuxin basin

Taking raw coal samples collected from the wangying colliery in Fuxin basin as the research object, the experiment of coalbed methane seepage law is conducted by the triaxial osmoscope and the relationship between effective stress and coal permeability is presented. The experiment results indicate that the coal permeability is of stress sensitivity and tended to decline in exponent with the increment of effective stress, which is consistent with the former research results. The seepage flow curves from experiments demonstrate the nonlinear characteristics under different confining pressures and moisture contents, and it accurately reflecte the effect of coal body deformation on the coalbed methane seepage flow in the experimental process. Therefore considering the influence of effective stress on the coal body deformation, a new motion equation for the nonlinear percolation characteristic of coalbed methane is established. Moreover, the motion equation is correlated well with the experimental data, and the fitting correlation coefficients are above 99.6%.     

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.