预应力混凝土连续梁裂缝分析及控制

通过分析预应力混凝土连续梁桥在施工和使用过程中出现的一些主要裂缝产生的原因,针对性地提出了预防和控制裂缝的措施。

钢筋砼构件受力分析与圆柱边节点抗裂度计算

笔者依据试验结果,分析了钢筋混凝土构件的结构受力性质,结合实际工作经验,对圆柱边节点的抗裂度进行了理论分析和计算。

溃水溃沙多源信息评价与生产布局优化研究

针对我国现阶段煤矿溃水溃沙灾害预测评价方法单一、防治手段被动等问题,以薄基岩、厚松散层矿井为研究对象,从影响溃水溃沙致灾的主控因素出发,提出了以“沙层厚度、基采比、溃沙裂缝带发育高度、基岩风化指数、单位涌水量、饱水沙层厚度、渗透系数、采动影响指数”为指标的溃水溃沙危险性多源信息分区方法,建立了“区域转局部、高位截流接续”的超前生产布局优化模式,研究成果在神东矿区隆德煤矿成功应用,提高了煤矿溃水溃沙预警评价的精准度,为超前主动解决溃水溃沙问题提供了新理念。

大东一干渠新2#隧洞加固工程施工

引大东一干渠新 2 #隧洞由于地震张裂缝隙发育 ,针对不同程度的裂缝 ,采取不同的处理措施及施工工艺 ,既保证了工程的安全运行 ,又减少了不必要的投资。

Experimental study of seepage characteristics of single rock fracture based on stress states and stress history

Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture. The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure. With the increasing in the confining pressure,the permeability of the fracture decreases,but the decreasing rate is changeing. During the unloading process,the fracture seepage velocity cannot be fully recovered to the size of the loading process. Therefore,in the unloading process of the confining pressure,the recovery of fracture permeability shows obvious hysteresis effects. The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure. In each cycle,the evolution character of the flow rate with the confining pressure remains unchanged. These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state.

The effect of the fracture distribution on CO_2 injection into a coal seam

The effect of the fracture distribution on CO 2 injection into coal seams was studied with a heterogeneous model having dual porosity to represent both the primary medium (the coal matrix) and the secondary medium (the fractures) under variable stress conditions. A numerical generation method and a digital image processing method were used to model the heterogeneous fracture distribution in the coal. The model solutions demonstrate that: (1) the fractures are the main channel for gas flow and their distribution has an important impact on the gas injection rate; (2) the fractures only affect the injection rate of CO 2 into the coal but not the final storage amount; (3) when gas is injected into coal the fractures will first expand and then close due to the changing effective stresses and the adsorption induced swelling of coal grains. This fully coupled dual-porosity model with a heterogeneous fracture distribution provides a way to predict the CO 2 injection into a coal seam.

Unsaturated expansive soil fissure characteristics combined with engineering behaviors

The relationship among the surface fissure ratio, moisture content, seepage coefficient and deformation modulus of field unsaturated expansive soil in Nanning, Guangxi Province, China, was obtained by a direct or indirect method. Digital images of expansive soil of the surface fissure with different moisture contents were analyzed with the binarization statistic method. In addition, the fissure fractal dimension was computed with a self-compiled program. Combined with in situ seepage and loading plate tests, the relationship among the surface fissure ratio, moisture content, seepage coefficient and deformation modulus was initially established. The surface fissure ratio and moisture content show a linear relation, ＂y=-0.019 1x＋1.028 5＂ for rufous expansive soil and ＂y=-0.07 1x＋2.610 5＂ for grey expansive soil. Soil initial seepage coefficient and surface fissure ratio show a power function relation, ＂y=1× 10^-9exp（15.472x）＂ for rufous expansive soil and ＂y=5× 10^-7exp（4.209 6x）＂ for grey expansive soil. Grey expansive soil deformation modulus and surface fissure ratio show a power fimction relation of ＂y=3.935 7exp（0.993 6x）＂. Based on the binarization and fractal dimension methods, the results show that the surface fissure statistics can depict the fissure distribution in the view of two dimensions. And the evolvement behaviors of permeability and the deformation modulus can indirectly describe the developing state of the fissure. The analysis reflects that the engineering behaviors of unsaturated expansive soil are objectively influenced by fissure.

Void Morphology in 3-D Braided Preform/phenolic Composites

Improved Resin Transfer Molding (RTM) technology and equipment were established.Void content and morphology of the 3-D braided preform/phenolic composite were investigated using different RTM processes.The results showed that void content of the vacuum and compression co-assisted RTM process was the lowest.Void morphologies of the specimen cross-section were analyzed with metallographic microscope.In traditional RTM process,the crack of cross-section was in evidence.In vacuum assisted RTM process,the void shape was divided into three categories:irregular crack,triangle,rotundity and ellipse.The most voids distributed in resin rich areas and were observed as large void based on equivalent diameter.In compression assisted RTM,vacuum and compression co-assisted RTM process,the polygonal voids mostly existed inter tows.Void size was mainly intermediate and small based equivalent diameter separately.

Numerical Modeling of the Effect of Crack Parameters on Attenuation Anisotropy

Propagation through stress-aligned fluid-filled cracks and other inclusions have been claimed to be the cause of azimuthal anisotropy observed in the crust and upper mantle.This paper examines the behavior of seismic waves attenuation caused by the internal structure of rock mass,and in particular,the internal geometry of the distribution of fluid-filled openings Systematic research on the effect of crack parameters,such as crack density,crack aspect ratio(the ratio of crack thickness to crack diameter),pore fluid properties(particularly pore fluid velocity),VP/VS ratio of the matrix material and seismic wave frequency on attenuation anisotropy has been conducted based on Hudson's crack theory.The result shows that the crack density,aspect ratio,material filler,seismic wave frequency,and P-wave and shear wave velocity in the background of rock mass,and especially frequency has great effect on attenuation curves.Numerical research can help us know the effect of crack parameters and is a good supplement for laboratory modeling.However,attenuation is less well understood because of the great sensitivity of attenuation to details of the internal geometry.Some small changes in the characteristics of pore fluid viscosity,pore fluids containing gas and liquid phases and pore fluids containing clay can each alter attenuation coefficients by orders of magnitude.Some parameters controlling attenuation are therefore necessary to make reasonable estimations,and anisotropic attenuation is worth studying further.

Reservoir space types and the factors influencing the characteristics of spherulite in rhyolite

Oil-gas reservoir space types involving spherulite in pyromeride rocks are common in the Lower Cretaceous Shangkuli Formation, the Hailar Basin, China. The main types include interspherulite fissures, interlayer fissures, intraspherulite concentric rings and net microcracks, cavity pores, dissolution pores, and devitrification pores. The first two were found to restrict the effective plane porosity of interspherulite. Devitrification microporosities, microcracks, cavity pores, and spherulite diameter influence the effective plane porosity of intraspherulite. The degree of dissolution is determined by the degree of development and the type of intraspherulite microcracks. Another important role of ring and net microcracks is to connect devitrification pores to form a pore and fissure network. Finally, chilling contraction plays an important role in the form and development of interspherulite fissures, microcracks, and cavity pores. The diameter of spherulite restricts chilling contraction, especially when the diameter is between the common spherulites and lithophysae, thus benefiting microcrack and cavity pore formation. To summarize, devitrification microporosities represent excellent oil reservoir space, while offering micro-channels for the movement of formation water and organic fluids. However, the inclusion of microcracks improves this capacity.

Determination of critical slip surface of fractured rock slopes based on fracture orientation data

The critical slip surface of a fractured rock slope tends to extend along the fractures.Thus,fracture orientation plays a critical role in determining the critical slip surface.Based on fracture orientation data,this paper examines the critical slip surfaces of fractured rock slopes.Given that the surface of a fractured rock slope extends along the fracture surfaces,or the wedges,with each composed of two arbitrary fractures,the critical slip surface is determined via stochastic dynamics.In addition,a fracture frequency method is proposed as a means of analyzing the critical slip surface.According to this method,the critical slip surface slips in whichever direction has the lowest fracture frequency.Based on the stochastic dynamics method and the fracture frequency method,the critical slip surface of the slope is finally determined,that is,the critical slip surface takes the form of a plane passing the slope toe with a dip of 120° and a dip angle of 45°.

An experimental investigation on the mechanism of fluid flow through single rough fracture of rock

The structure of fractures in nature rock appears irregular and induces complicated seepage flow behavior.The mechanism and quantitative description of fluid flow through rock fractures is a difficult subject that has been greatly concerned in the fields of geotechnical,mining,geological,and petroleum engineering.In order to probe the mechanism of fluid flow and the effects of rough structures,we conducted a few laboratory tests of fluid flow through single rough fractures,in which the Weierstrass-Mandelbrot fractal function and PMMA material were employed to produce the fracture models with various fractal roughnesses.A high-speed video camera was employed to record the fluid flow through the entire single rough fracture with a constant hydraulic pressure.The properties of fluid flow varying with the fracture roughness and the influences of the rough structure were analyzed.The components of flow resistance of a single rough fracture were discussed.A fractal model was proposed to relate the fluid resistance to the fracture roughness.A fractal equivalent permeability coefficient of a single rough fracture was formulated.This study aims to provide an experimental basis and reference for better understanding and quantitatively relating the fluid flow properties to the structures of rock fractures.

A unified theory for elastic wave propagation through porous media containing cracks-An extension of Biot's poroelastic wave theory

Rocks in earth＇s crust usually contain both pores and cracks. This phenomenon significantly affects the propagation of elastic waves in earth. This study describes a unified elastic wave theory for porous rock media containing cracks. The new theory extends the classic Biot＇s poroelastic wave theory to include the effects of cracks. The effect of cracks on rock＇s elastic prop- erty is introduced using a crack-dependent dry bulk modulus. Another important frequency-dependent effect is the ＂squirt flow＂ phenomenon in the cracked porous rock. The analytical results of the new theory demonstrate not only reduction of elas- tic moduli due to cracks but also significant elastic wave attenuation and dispersion due to squirt flow. The theory shows that the effects of cracks are controlled by two most important parameters of a cracked solid： crack density and aspect ratio. An appealing feature of the new theory is its maintenance of the main characteristics of Biot＇s theory, predicting the characteristics of Blot＇s slow wave and the effects of permeability on elastic wave propagation. As an application example, the theory cor- rectly simulates the change of elastic wave velocity with gas saturation in a field data set. Compared to Biot theory, the new theory has a broader application scope in the measurement of rock properties of earth＇s shallow crust using seismic/acoustic waves.