Width Of Fracture Zone Research Articles

Discovery of the Qinghe fault, the inner part of the Weihe graben, central China, and its geological significance

The Weihe graben is an active Cenozoic continental rift with frequent seismic activity. The previous work focused on the graben boundary faults, but less work has been conducted on the faults in the internal graben. The Weihe basin is an economically developed and densely populated area. Therefore, identifying these potential risks is significant for the evaluation of regional seismic hazards and to understand the evolution of continental rifts. Prior work used oil exploration methods to document a fault (we named it “Qinghe fault”) in the Qinghe river area of Sanyuan County, north of Xi’an. But the shallow structure and activity was not clear. Therefore, we carried out shallow seismic detection and borehole exploration, as well as a geological survey in the area. Based on seismic reflection profile and boreholes, the Qinghe fault is the main fault and with other secondary faults, together they constitute a typical Y-shaped structure, with a fracture zone width ∼4 km. Combined with the field survey, we provide evidence that the Qinghe fault is a Holocene active fault and capable of earthquakes of magnitude 5.2–5.5. The discovery of the Qinghe fault shows that the Weihe rift is active, and the faults inside the rift play an important role in tectonic deformation.

Study on the Safety Thickness of Rock Strata for Outburst Prevention in Deep Tunnel Based on Numerical Modeling and Backpropagation Neural Network

Water inrush and mud inrush pose a serious threat to safe construction in underground engineering, but it is very difficult to determine the safe distance of outburst prevention rock mass. Based on deep-buried tunnel engineering, this paper proposes a method to determine the safe distance from water inrush disaster between the tunnel and the fault fracture zone. This method combines numerical modeling and backpropagation (BP) neural network. By means of numerical simulation, the internal influence law of the water pressure, lateral pressure coefficient, fault fracture zone width, and tunnel burial depth on the surrounding rock is analyzed. The evolution law of the minimum safe strata thickness under a single variable and the correlation degree between minimum safe strata thickness and various disaster factors are revealed. Based on the BP neural network analysis of the simulation results and the measured data of Wulaofeng Tunnel, the calculated values of safe strata thicknesses of fault fracture zone (F10) were determined. The results show that the thickness of the safe rock strata increases with increasing water pressure, lateral pressure coefficient, fault fracture zone width, and tunnel burial depth. The minimum safe thickness of F10 of the tunnel ranges from 7.1 m to 7.4 m, and 10 m is reserved in the actual project. The calculated results are consistent with the reserved thickness value in the construction. This conclusion can provide a reference for similar projects.

Research on Floor Heave Mechanisms and Control Technology for Deep Dynamic Pressure Roadways

In order to study the influencing factors of floor deformation and floor heave mechanisms of deep mining roadways, this paper takes the deep dynamic pressure mining roadway of a mine as the engineering background and adopts a research method combining theoretical analyses, numerical simulations and field observations to study the influence of various factors on floor deformation and floor heave mechanisms. It is determined that the influencing factors on floor heave are a large buried depth, a long duration of dynamic pressure, unique characteristics of the surrounding rock and an insufficient support strength. A bearing mechanics model of the roadway floor beam is established, and it is determined that the displacement of the roadway floor is negatively correlated with the elastic modulus and floor thickness and positively correlated with the buried depth of roadway, the roadway width and the width of fracture zone. A numerical simulation method is used to study the influence of the original geological conditions, strengthening the elastic modulus of floor, strengthening the strength of the side wall rock and increasing the thickness of the floor rock on the displacement of the roadway floor. It is determined that increasing the thickness of floor rock controls the floor heave the most, followed by strengthening the elastic modulus of the floor rock and then strengthening the strength of the side walls. The results of the numerical simulation agree well with those of the theoretical analysis. After the control method of “bottom lifting + bottom angle bolt + floor bolt ” is adopted on site to treat the floor heave, the floor heave volume of the roadway is small during the service period of the 303 working face return air roadway, which meets the application requirements of the roadway. Meanwhile, the theoretical analysis and numerical simulation results are indirectly verified.

Heat control mechanism and productivity optimization of artificial fracture zone structure of dry hot rock in Gonghe Basin

Hydraulic fracturing is necessary to obtain geothermal energy from the hot dry rocks. The structure of the artificial fractures plays an important role in controlling the water and heat transport during the heat production. In this study, we analyzed the influence of the permeability and width of artificial fracture zone on the coupled heat and flow processes in the Gonghe Basin, China. The results showed that in the fractured reservoir with permeability lower than 5 D, the outflow temperature increases with the width of the fracture zones. This is because the injected cold water can sufficiently merge with the thermal water in the reservoir, and has a weak influence on the water temperature close to the extraction well. A special situation occurs in the horizontal reservoir with permeability higher than 10 D, where the outflow temperature decreases with the increase of fracture zone width, because the overall low temperature zone is increased due to the rapid diffusion of injected cold water. In the reservoir with horizontal fracture zone, outflow temperature decreases with the increase of the permeability, because the injected cold water easily arrives the production well. In contrast, in the vertical or tilted fracture reservoir, the outflow temperature increases with the permeability, because the free convection occurs strongly in the high-permeable reservoirs. A synthetic comparison suggested that under the same well distance, heat production is higher in the reservoirs with low-permeable horizontal fracture zone and with high-permeable vertical fracture zone, among other fracture zones.

The Study on Mechanical Strength of Titanium-Aluminum Dissimilar Butt Joints by Laser Welding-Brazing Process

Laser welding–brazing of 5A06 aluminum to Ti6Al4V titanium in a butt configuration was carried out to discuss the influences of welding parameters on dissimilar joint properties. The effects of laser offset, welding speed, and laser power on the spreading length of the molten aluminum liquid, interface fracture zone width (IFZW), fracture roughness, intermetallic compounds (IMCs) thickness, and tensile strength were also investigated. The microstructure and fracture of the joint were also studied. The results show that the tensile strength of the joint is not only influenced by the thickness and type of IMCs, but also influenced by the spreading ability of the aluminum liquid, the fracture area broken at the Ti/fusing zone (FZ) interface, and the relative area of the brittle and ductile fracture in FZ. A dissimilar butt joint with an IMC thickness of 2.79 μm was obtained by adjusting the laser offset, welding speed, and laser power to 500 μm, 11 mm/s and 1130 W, respectively. The maximum tensile strength of the joint was up to 183 MPa, which is equivalent to 83% of the tensile strength of the 5A06 aluminum alloy.

Analysis of Overlying Strata Movement and Disaster-Causing Effects of Coal Mining Face under the Action of Hard Thick Magmatic Rock

When the hard and thick key strata are located above the working face, the bed separation structure is easy to be formed after mining because of the high strength and integrity of the hard and thick key strata and the initial breaking step is large. After the hard, thick strata are broken, the overburden will be largely collapsed and unstable in a large area and the dynamic disaster is easily induced. In this study, considering the fundamental deformation and failure effect of coal seam, the development law of the bed separation and the fractures under hard and thick magmatic rocks and the mechanism of breaking induced disaster of hard and thick magmatic rocks are studied by similar simulation tests. The results of the study are as follows: (1) The similar material ratio of coal seam is obtained by low-strength orthogonal ratio test of similar materials of coal seam, that is, cement:sand:water:activated carbon:coal = 6:6:7:1.1:79.9. (2) The magmatic rocks play a role in shielding the development of the bed separation, which makes the bed separation beneath the magmatic rock in an unclosed state for a long time, providing space for the accumulation of gas and water. (3) The distribution pattern of the fracture zone shows different shapes as the advancing of working face and the fracture zone width of the rear of working face coal wall is larger than that of the front of the open-off. (4) The breaking of magmatic rocks will press the gas and water accumulated in the bed separation space below to rush towards the working face along the fracture zone at both ends of the goaf. The above results are verified through the drainage borehole gas jet accident in the Yangliu coal mine. The research results are of great significance for revealing the occurrence process of dynamic disasters and adopting scientific and reasonable preventive measures.

Zonal Disintegration Mechanism of Deep Rock Masses under Coupled High Axial Geostress and Blasting Load

Zonal disintegration phenomenon with alternative distribution of fracture zones and nonfracture zones is a characteristic failure in deep rock masses, especially for deep tunnel excavated by drill and blast method. To investigate the mechanism of zonal disintegration under coupled high axial geostress and blasting load, elastic stress field distribution for a circular tunnel in deep isotropic rock masses is obtained. Furthermore, Hoek‐Brown criterion is amended by considering blast‐induced damage effect. Both radial blasting load and blast‐induced damage effect are assumed to decay in a negative exponential function. Taking the deep tunnel of Dingji coal mine in China as engineering background, the number and width of fracture zones are determined by deduced elastic stress field and modified Hoek‐Brown criterion. Then numerical computation is conducted. Numerical computation results indicate that both the number and width of fracture zones mainly depend on high axial geostress and mechanical parameters of deep rock masses, and peak radial blasting load plays an important role in determining the width of fracture zone near the excavation.

Mechanical and fracture behavior of rock mass with parallel concentrated joints with different dip angle and number based on PFC simulation

Rock mass is an important engineering material. In hydropower engineering, rock mass of bank slope controlled the stability of an arch dam. However, mechanical characteristics of the rock mass are not only affected by lithology, but also joints. On the basis of field geological survey, this paper built rock mass material containing parallel concentrated joints with different dip angle, different number under different stress conditions by PFC (Particle Flow Code) numerical simulation. Next, we analyzed mechanical property and fracture features of this rock mass. The following achievements have been obtained through this research. (1) When dip angle of joints is 15° and 30°, with the increase of joints number, peak strength of rock mass has not changed much. But when dip angle increase to 45°, especially increase to 60° and 75°, peak strength of rock mass decreased obviously with the increase of joints number. (2) With the increase of confining stress, peak strengths of all rock mass have different degree of improvement, especially the rock mass with dip angle of 75°. (3) Under the condition of no confining stress, dip angle of joints is low and joint number is small, existence of joints has little influence on fracture mode of rock mass, but when joints number increase to 5, tensile deformation firstly happened at joints zone and further resulted in tension fracture of the whole rock mass. When dip angle of joints increases to 45°, fracture presented as shear along joints, and with increase of joints number, strength of rock mass is weakened caused by shear-tension fracture zone along joints. When dip angle of joints increases to 60° and 75°, deformation and fracture model presented as tension fracture zone along concentrated joints. (4) Influence of increase of confining stress on fracture modes is to weaken joints' control function and to reduce the width of fracture zone. Furthermore, increase of confining stress translated deformation mode from tension to shear.

The Relationship Between Thrust Faults and Structural Fractures in the Tarim Basin, China

It is a problem that how thrust faults control the distribution of structural fractures in the exploration and development of fracture oil-reservoirs. One section of fracture outcrops in Ordovician carbonites is measured in the north margin of Tarim Basin, and two sections cross the Fault I in the central Tarim Basin are measured and processed in the paper. The development rule of structural fractures can be depicted by the fracture density, and the fractures near fault can be divided into two regions: the fracture zone controlled by fault and the fracture zone controlled by regional stress field. The ratio of fault-controlled fracture zone width to the throw of thrust fault is a very important parameter to depict the development of fractures influenced by thrust fault. The ratio is related to the mechanism, scale and throw of the thrust fault. The width of fault-controlled fracture zone can be predicted based on the mechanism and throw of the thrust fault. It is very helpful to the exploration and development of fault-controlled fracture reservoirs. Key words: Structural fractures; Fault-controlled fracture zone; Thrust fault; Fracture density

Development of fractures in soft rock surrounding a roadway and their control

As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage roadway in a certain coal mine is so broken and loose that the supporting is very difficult. Based on comprehensive analysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks. Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture development. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.

Identification of key parameters controlling dissolved oxygen migration and attenuation in fractured crystalline rocks

In the crystalline rocks of the Canadian Shield, geochemical conditions are currently reducing at depths of 500–1000 m. However, during future glacial periods, altered hydrologic conditions could potentially result in enhanced recharge of glacial melt water containing a relatively high concentration of dissolved oxygen (O 2). It is therefore of interest to investigate the physical and geochemical processes, including naturally-occurring redox reactions, that may control O 2 ingress. In this study, the reactive transport code MIN3P is used in combination with 2 k factorial analyses to identify the most important parameters controlling oxygen migration and attenuation in fractured crystalline rocks. Scenarios considered are based on simplified conceptual models that include a single vertical fracture, or a fracture zone, contained within a rock matrix that extends from the ground surface to a depth of 500 m. Consistent with field observations, Fe(II)-bearing minerals are present in the fractures (i.e. chlorite) and the rock matrix (biotite and small quantities of pyrite). For the parameter ranges investigated, results indicate that for the single fracture case, the most influential factors controlling dissolved O 2 ingress are flow velocity in the fracture, fracture aperture, and the biotite reaction rate in the rock matrix. The most important parameters for the fracture zone simulations are flow velocity in the individual fractures, pO 2 in the recharge water, biotite reaction rate, and to a lesser degree the abundance and reactivity of chlorite in the fracture zone, and the fracture zone width. These parameters should therefore receive increased consideration during site characterization, and in the formulation of site-specific models intended to predict O 2 behavior in crystalline rocks.