Damage Characteristics Analysis and Fractal Study of Shale With Prefabricated Fractures under Thermal-mechanical Coupling

To study the damage and failure of shale with different fracture inclination angles under uniaxial compression loading,in this work,RFPA2D-Thermal,a two-dimensional real failure process analysis software,was used for numerical simulation.Numerical simulation results show that quartz in shale mainly affects the tensile and compressive strength of shale by increasing rock brittleness.The coupling of temperature and pressure will cause lateral and volume destruction of shale,which enables the shale body to be more easily broken.Fracture inclination is the key factor affecting shale damage patterns.The failure mode of shale with low-and high-angle fractures is mainly shear failure,and the compressive strength does not vary with crack inclination.The damage mode of obliquely intersecting fractured shale is slip damage along the fracture face,the compressive strength decreases and then increases with the fracture inclination,and a minimum value exists.The acoustic emission simulation results of the damage process effectively reflect the accumulated internal damage and macroscopic crack appearance until fracture instability when the prefabricated fractured shale is subjected to uniaxial compressive loading.The crack inclinations of 0°and 120℃ corresponds to the most complex"N"shape damage mode.The crack inclinations of 30°and 60°,and the damage mode is an inverted"λ"shape.

Rock burst mechanism analysis in an advanced segment of gob-side entry under different dip angles of the seam and prevention technology

In order to investigate the frequent occurrences of rock burst in gob-side entry during the mining process of the mining zone No. 7, the mechanical model of main roof of fully-mechanized caving mining before breaking was established by the Winkler foundation beam theory, and the stress evolution law of surrounding rock with different dip angles of the seam during the mining process was analyzed by using FLAC3 D. The results show that: with the dip angle changing from 45° to 0°, the solid-coal side of gobside entry begins to form an L-shaped stress concentration zone at a dip angle of 30°, and the stress concentration degree goes to higher and higher levels. However, the stress concentration degree of the coalpillar side goes to lower and lower levels; the influence range and peak stress of the abutment at the lateral strata of adjacent gob increase with dip angle decreasing and reach a maximum value at a dip angle of 0°, but the tailgate is not affected; the abutment pressure superposition of two adjacent gobs leads to stress concentration further enhancing in both sides of gob-side entry. With the influence of strong mining disturbance, rock burst is easily induced by dynamic and static combined load in the advanced segment of gob-side entry. To achieve stability control similar to that in the roadway, the key control strategy is to reinforce surrounding rock and unload both sides. Accordingly, the large-diameter drilling and high-pressure water injection combined unloading and reinforced support cooperative control technology was proposed and applied in field test. The results of Electromagnetic Emission(EME) and field observation showed that unloading and surrounding rock control effect was obvious.

Effects of coal seam dip angle on the outburst in coal roadway excavation

The prevention and forecast of coal and gas outburst has always been one of the key issues in coal mining safety.By simulating the process of tunneling in coal seam with different dip angle through FLAC3D software,the dangerous zone in which outburst may occur and the probability of outburst near the working face were predicted through the distribution of stress,displacement and plastic zone.Then we discussed the size of unstable area in the surrounding rock through the distribution of stress and the variation curve of the displacement on the roadway wall.The results show that,with an increase of the coal seam dip angle,the risk of outburst in the working face rises gradually.And the dangerous areas in which may outburst occur moves to the upper part of coal seam.The size of unstable area in the surrounding rock increases with the increase of coal seam dip angle.

A preliminary analysis of arcuate structures-relationship of the island arc and deep-sea trench to the dip angle of Benioff zone

The origin of arcuate islands and deep-sea trenches has been studied for a long time and various interpretations have been proposed. In this paper, some analytical models are put forward from a geometrical viewpoint and then the theoretical dip angles of the underthrusting slabs of circum-Pacific island arcs are computed and compared with those of the Benioff zone. As a result, it is found that the dip angle of the underthrusting slab is one of the main factors determining the curvature of the arcuate structure. The authors consider that this result may contribute to the plate theory.

Determination of a Drawing Die's Cone Angle at a Small Compression Ratio Based on the Upper Bound Theory

The value of a drawing die＇s cone angle has great influence on wire drawing. In order to determine the optimum value of a drawing die＇ s cone angle, the plastic deformation power Wi, shear deformation power Wi and friction power of contact surface Wf were calculated using the upper bound theory with a reasonable and movement permitted velocity field according to the related characteristics. Then the relation between half cone angle and unit drawing force was obtained and it was compared with the result with the spherical velocity field. The relative error of the two near the optimal value is only about 0. 26% through comparing with existing calculated results. Finally, in an ABAQUS environment the finite element modal of the wire rod with 12. 5 mm diameter in first drawing pass was established and the axial drawing force in different cone angles was obtained using the ABAQUS/Explicit explicit integration method. The finite element method （FEM） results verify the results using the upper bound theory and this indicated that the velocity field and the relation between half cone angle and unit drawing force reasonable.

Strength and deformation characteristics of irregular columnar jointed rock mass: A combined experimental and theoretical study

The irregularity of jointed network poses a challenge to the determination of field mechanical param-eters of columnar jointed rock mass(CJRM),and a reasonable prediction of deformation and strength characteristics of CJRM is important for engineering construction.The Voronoi diagram and three-dimensional printing technology were used to make an irregular columnar jointed mold,and the irregular CJRM(ICJRM)specimens with different dip directions and dip angles were prepared.Uniaxial compression tests were performed,and the anisotropic strength and deformation characteristics of ICJRM were described.The failure modes and mechanisms were revealed in accordance with the final appearances of the ICJRM specimens.Based on the model test results,the empirical correlations for determining the field deformation and strength parameters of CJRM were derived using the dip angle and modified joint factor.The proposed empirical equations were used in the Baihetan Project,and the calculated mechanical parameters were compared with the field test results and those obtained from the tunneling quality index method.Results showed that the deformation parameters determined by the two proposed methods are all consistent with the field test results,and these two methods can also estimate the strength parameters effectively.

FEM Analysis of Effect of Die Angle on Tube Inversion Forming Process under Conical Die

Tube inversion including free deformation under conical die is an advanced forming process for manufacturing complicated thin-walled parts with high strength/weight ratio, high efficiency, and good flexibility for size changing.However, the successful reality of forming process, the change of deforming mode and shape and size of part formedare mainly on the die angle. Based on the analysis of the forming process, the model of rigid-plastic FEM (finiteelement method) is established and a numerical simulation system is developed. The effect of die angle on the tubeinversion forming process is investigated with the code developed. The results of the effect of half die angle on shapeof free deformation zone and on deforming load are obtained. There is an optimal die angle (about 75 deg), whichmakes the forming load minimum.

Effects of die angle on microstructures and mechanical properties of AZ31 magnesium alloy processed by equal channel angular pressing

AZ31 Mg alloy was prepared through equal channel angular pressing (ECAP) by Bc route in two different dies, in which the intersecting angles between channels are 90° and 120° respectively. Microstructures and tensile behaviors of the processed material at room temperature were investigated. The 90° die could provide more effective grain refinement in one pass of ECAP. But after multiple passes of deformation and when the total strain reached about 8, the alloy processed by the two dies acquired tiny homogeneous equiaxed grains with a mean size of 15 μm and possessed similar mechanical properties with a large ductility of above 45% and a yield strength of 100 MPa, which are much different from the ductility of 18% and the yield strength of 200 MPa for the conventionally extruded material. The X ray diffraction results show a great difference on peak of the basal plane (0001) between sections perpendicular and parallel to the extrusion direction for the conventionally extruded alloy but the difference lowers much for the ECAP processed alloy. The ultra fine grain microstructure and the texture or scattered orientation of the basal plane (0001) has the great effect on the alloys mechanical behavior.

Structural Study of the Kakobola Area and Its Surroundings by Detecting the Edges of Gravity Anomaly Sources

The area covered by this study is the county of Kakobola and its surroundings. Previous studies show that those related to the study of depths by the gravity method, using other techniques, are not always carried out until now. The main goal of this article is the gravimetric characterization of our area by other approach. The interest is not only to map the lineaments and to know their dip, but also to estimate the depths of these different anomalies. The methods used for this study are the first total horizontal derivative (FTHDT), tilt angle (TA), analytical signal (AS) and horizontal gradient magnitude (HGM). The processing of the complete Bouguer anomalies (CBA) data was done mainly through software. Data analysis using the semi-finished body depth method shows depths ranging from 7.49 m to 224.6 m. Data analysis using the AS method shows values ranging from 41.7 mGal/m to 510 mGal/m. The fractures and/or geological contacts in our study area show dips ranging from -73.73° to 68.16° and North-South orientation according to the tilt angle method. The FTHDT shows several lineaments, a NE oriented fracture of Kakobola and low dip values which suggest a tabular structure of the subsurface in our study area. According to the HGM, the study area shows several preferential directions of fractures and/or geological contacts whose the most frequent directions are the NNE-SSW and WNW.

Support-surrounding rock relationship and top-coal movement laws in large dip angle fully-mechanized caving face

When mining the fully-mechanized longwall caving face along strike, the unstable equipment, the low top-coal recovery ratio and the difficulty in controlling surrounding rock may occur due to large dip angle. Considering the effects of strike angle on support stability, the ‘‘support-surrounding rock"mechanical models of support topple and support slip were established in this paper. On the basis, the influencing factors of support stability were analyzed and the technical measures of controlling support and surrounding rock stability were put forward. Then the loose particles simulation experiment was conducted to analyze the impacts of caving directions and methods on the top-coal recovery in large dip angle fully-mechanized caving face. Finally, the ‘‘upward sequence and double-openings doublerounds" caving technology was determined. The research results are of great scientific significance and practical values to improve large dip thick seam mining technology.

Stability of High Slope Interbedded Strata with Low Dip Angle Constituted by Soft and Hard Rock Mass

Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft while the sandstone is hard and contains many opening or closing joints with a high dip angle. Some are nearly parallel and the others are nearly decussated with the trend of the slopes. Many natural slopes are in deformation or sliding because of those reasons. The stability of cutting slopes and supporting method to be taken for their stability in civil engineering are important. In this paper, the stability and deformation of the slopes are studied. The methods of analysis and support design principle are analyzed also. Finally, the method put forward is applied to study Fengdian high cutting slope in Sichuan section of the express way from Chengdu to Shanghai. The results indicate that the method is effective.

Applications of dip angle and coherence attributes to recognition of volcanic edifice in Songliao Basin

On the basis of the shape and inner structure of volcanic edifice,the dip angle and coherence were selected to recognize the buried volcanic edifices in Songliao Basin.Five volcanic edifices were recognized in both two methods in the first volcanic cycle of Yingcheng Formation and the prediction perfectly corresponds to the drilling results in well XS8 area.The results are satisfying when the prediction method were employed in the exploration and development of Qingshen gas field.

FINITE ELEMENT ANALYSIS AND EXPERIMENTAL STUDY OF THE METAL MULTIDIE IRONING PROCESS

Taking double-die ironing for example, the plastic deformation behavior of theworkpiece in multidie ironing process is analysed by the rigid-plastic finite element method(RPFEM).Considering the strain hardening of the material, the distrbutions of the effective strainrate and hydrostatic stress are obtained. Calculated results and the effect of die argles on thedeformation and ironing force are discussed. The companrson of calculated results with thcoe of ex-poriment shows a good agreement.

Determining relative block structure rating for rock erodibility evaluation in the case of non-orthogonal joint sets

The most commonly used method for assessing the hydraulic erodibility of rock is Annandale's method.This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten's index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to intact rock and rock mass, such as compressive strength of intact rock, rock block size, discontinuity shear strength and relative block structure. To quantify the relative block structure, Kirsten(1982) developed a mathematical expression that accounts for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing the relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonally fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint sets is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonally fractured system has a significant effect on Kirsten's index and, as a consequence, on the assessment of the hydraulic erodibility of rock.

Model Tests on the Effect of Dip Angles on Flow Behavior of Liquefied Sand

The flow behavior of liquefied sand is reported using a self-developed testing system that enables the flow processes of liquefied sand to be studied at different slopes of the soil layers.The test device is mainly composed of a vibrating table,a transparent model box and a high-speed video monitoring camera.The tests replicated the horizontal and sloping flows of saturated sand in the model box,which can be tilted to various angles to study the flow characteristics of liquefied sand.The high-speed video monitoring camera captured and recorded the processes within the flowing sand.With increasing downslope,the strain,strain rate,duration time,and sand flow distance increased.The results of our experiment indicate that when selecting sites for engineering structures,the surface downslopes should be taken into account if liquefiable soils are present.Finally,some suggestions regarding site assessment and structural design for sites prone to liquefaction were presented.

foF2 Diurnal Variability at African Equatorial Stations:Dip Equator Secular Displacement Effect

The paper goal is to analyze the variability of foF2 at African equatorial stations and the effect of dip angle on this variability. The gap between the dip angle of Dakar and Ouagadougou is superior to that between Djibouti and Ouagadougou. The trend of the dip angle at Ouagadougou and Dakar decreases while that of Djibouti increases. The relative position of the station with respect to the equator and the trend sign explains the difference observed in foF2 variability at Dakar station and at the two other stations. At Djibouti and Ouagadougou, foF2 exhibits noon bite out profile during all solar cycle phases while at Dakar observed profile is dome or plateau during the maximum and the predominance afternoon peak for the other solar cycle phases.

Regional Finite-Fault Source Model for Development of Ground Motion Attenuation Relationship in Sichuan, China

The attenuation relationship of ground motion based on seismology has always been a front subject of engineering earthquake.Among them,the regional finite-fault source model is very important.In view of this point,the general characteristics of regional seism-tectonics,including the dip and depth of the fault plane,are emphasized.According to the statistics of regional seism-tectonics and focal mechanisms in Sichuan,China,and the sensitivity of estimated peak ground acceleration(PGA)attenuation is analyzed,and the dip angle is taken as an average of 70°.Based the statistics of the upper crustal structure and the focal depth of regional earthquakes,the bottom boundary of the sedimentary cover can be used as the upper limit for estimating the depth of upper-edge.The analysis shows that this value is sensitive to PGA.Based on the analysis of geometric relations,the corresponding calculation formula is used,and a set of concepts and steps for building the regional finite-fault source model is proposed.The estimation of source parameters takes into account the uncertainty,the geometric relationship among parameters and the total energy conservation.Meanwhile,a set of reasonable models is developed,which lay a foundation for the further study of regional ground motion attenuation based on seismology.

高地层倾角油藏高低部位油井液量配比研究

在高倾角断块油藏中,受重力作用影响,高、低部位油井开发效果差异大。运用物理模拟实验分析了地层倾角对高、低部位油井开发效果的影响,推导了考虑均衡驱替的水驱断块倾角油藏高、低部位油井产液量配比计算方法,并通过与数值模拟结果对比,验证了油井产液量配比计算方法的准确性。研究发现:随着储层倾角的增加,高部位流线变少、水驱波及区域变小、采出程度变低。随着储层倾角增加,达到均衡动用所需的油井产液量配比(高部位油井产液量与低部位油井产液量比)增加。在相同储层倾角的情况下,随着原油密度和注水强度增加,倾角对达到均衡驱替所需的油井产液量配比的影响变弱,油井产液量配比降低。该研究对高倾角断块油藏均衡开发具有指导意义。

低应变率冲击荷载下节理花岗岩的动力响应规律

岩体中节理面的存在是引起冲击应力波衰减的主要原因,会造成爆炸能量的衰减及降低爆破效果。为探讨低应变率下不同节理倾角花岗岩在冲击荷载作用下的动态力学性质、应力波传递规律和能量传递规律,利用分离式霍普金森压杆(split Hopkinson pressure bar,简称SHPB)试验装置对低应变率下3种不同冲击气压、4种不同倾角的节理花岗岩进行冲击试验。结果表明:(1)在含节理的岩样中,其峰值应力随节理倾角的增大呈下降趋势,随冲击荷载的增大呈上升趋势;(2)透射系数随节理倾角的增加先增大后减小,随冲击荷载的增大先减小后增大;(3)能量传递系数随节理倾角的增加先增高后降低,完整岩样、节理倾角θ=0º和45º的岩样,其能量传递系数都随着冲击荷载的增大而减小,而节理倾角θ=15º和30º的岩样,其能量传递系数随着冲击荷载的增大先减小后增大。