Search

With the increasing application and study of lightweight and high strength fiber reinforced polymer composites in ocean industry, the structural failure problem of composite pressure hulls has attracted great attention from many researchers in China and globally. Analysis of the structural failure mechanisms is foundational to the design of deep-sea composite pressure hulls, since nowadays the design rules of pressurized vessels is mostly formulated according to their failure modes. Hence, this paper aims to review the research on the structural failure of composite pressure hulls in deep sea settings. First of all, the applied research status on composite material in marine equipment is analyzed, including inspection modalities for composite pressure hulls. The review then focuses on the three main failure modes, namely overall buckling, material failure and snap buckling of the deep-sea composite pressure hulls. The study identifies further problems of composite pressure hulls to be solved through the application of the deep sea equipment research, aiming to provide a reference for the study of mechanical behavior, ultimate strength computation, and design of thick composite pressure hulls for deep sea equipment. [ABSTRACT FROM AUTHOR]

Sandstone is a common sedimentary rock that is easily carved due to its weakly cemented fine grains and relatively low strength. Therefore, numerous large-scale grottoes in China are made of sandstone. However, these sandstone cultural heritage structures are often seriously damaged due to temperature and humidity changes, air pollution, biodeterioration, and repeated dissolution and crystallization of soluble salts. In general, it is imperative that a consolidant capable of providing cohesion by infilling pores between the stone grains is synthesized. In recent years, it has been reported that using organic consolidation materials for sandstone protection comes with various negative effects, such as a short lifetime, poor compatibility, and preservation damage. Using inorganic consolidation materials to protect sandstone seems to be one of the research trends for the future. Herein, this paper introduces a permeable, inorganic magnesium-based material (MMH solution) for silica sand consolidation. To assess this consolidant, the paper investigates the influence of varying molar ratios of MgO:MgCl2·6H2O:H2O on properties such as penetration depth, consolidation weight, colour variation, and compressive strength. The results demonstrate that the molar ratios of MgO:MgCl2·6H2O:H2O can significantly affect the consolidation performance. Additionally, it is believed that the MMH solution of MgO:MgCl2·6H2O:H2O = 5:1:16 can be successfully used for the consolidation of silica sand, as the cubic specimens' surface micrographs show good compatibility between the consolidation product and sand grains. Experiments (i.e. weight loss rate and mineralogical compositions analysis) are performed to evaluate the cubic specimens' water resistance properties after being immersed in water. Furthermore, the consolidation material's failure mechanism as a self-sacrificing material is preliminarily analyzed. Results indicate that MMH solution is a promising conservation material that shows great potential for consolidating severely weathered sandstone. [ABSTRACT FROM AUTHOR]

This paper presents a study on the stability of a mine entry of an innovative approach to non-pillar coal mining—gob-side entry retaining using cantilever beam theory (GERMC). This method is on the rise in China and it has shown to increase the coal seam rate of recycling and mining productivity. The method utilizes the caved-in material resulting from the mining activities to fill the gob area and ensure the stability of the roof of the already mined area. The caved-in material will form the gob-side wall of the retained entry. This characteristic is unique to this method. Thus, there are not many studies that analyze the stability of the filling material and of the gob-side entry wall under these circumstances, which is a vital element for the safety of the mining operations. This paper studies the stability of the gob-side retained entry of the Hongjingta underground coal mine in China. The authors perform the analysis using a discrete fracture network (DFN) model developed by the Massachusetts Institute of Technology (MIT), GEOFRAC, in combination with the discrete-element method (DEM) software UDEC. GEOFRAC estimates the rock blocks (fracture networks) in the filling body, from fracture traces measured along the gob-side wall of the entry. Statistical methods are used to estimate the fracture intensity and the mean fracture areas, which are inputs to the DFN. The generated fracture networks are then inputted into the DEM code, UDEC, to evaluate the stability of the mine-retained entry. For this study, we developed two types of models in UDEC, one considering the fractures generated by the DFN model and another considering the gob-filling material as a continuum. This methodology—combined DFN–DEM—is unique and provides a more realistic representation of the gob-filling material by considering the fractures in the filling body and by estimating those fractures (interfaces between rock blocks) using field data. In addition to this, we also considered the effects of uncertainties that are associated with estimating three-dimensional (3-D) fractures' networks/rock blocks from two-dimensional (2-D) field data. Finally, the results of the simulations were compared with the measurements from the mine and are in good agreement. [ABSTRACT FROM AUTHOR]

With the continuous in-depth development of oil and gas resources, unconventional oil and gas resources show great potential. In recent years, 70% of the proven oil and gas resources in China are unconventional oil and gas resources. Therefore, the development of unconventional oil and gas resources has a huge impact on the increase in the production capacity of the oil and gas resources in China. Staged fracturing of horizontal wells is the main technical measure to improve unconventional oil and gas production stimulation. In the fracturing process, the soluble bridge plug technology can not only effectively solve the problems of large investment in drilling and grinding of composite bridge plugs, high risks, self-locking of oil, casing deformation, etc., causing the bridge plug to be unable to be drilled and remove and affect subsequent production but also can successfully make up for the problems of subsequent production. The large-diameter bridge plug cannot achieve the full diameter of the wellbore and cannot carry out operations such as postproduction logging and refracturing, which can ensure the integrity of the wellbore to the greatest extent. In this paper, HNBR was used to modify MPU to prepare HNBR/MPU soluble rubber, and the effect of blending ratio on the vulcanization characteristics, mechanical properties, compatibility, thermal stability, and degradation behavior of composites was studied. The results showed that with the increase in the amount of HNBR, the degree of cross-linking of the composite material decreased gradually, and the mechanical properties decreased slightly. With the increase in the amount of HNBR, the thermal stability of the material decreases. The use of HNBR greatly reduced the degradation rate of MPU. When the amount of HNBR was changed from 20 phr to 40 phr, the tensile strength retention rate of the composite after soaking increased from 14.73% to 39.72%. [ABSTRACT FROM AUTHOR]

Bridge weathering steel produced in China has been used in bridges worldwide. Bridge weathering steel Q345qNH is the most common steel grade used in China and for export, the fatigue crack growth thresholds and fatigue crack growth rate (FCGR) parameters of Q345qDNH are investigated in this paper. The FCGR tests are conducted on 9 compact tension (CT) specimens of base metal and butt welds respectively, the fatigue crack growth threshold tests are conducted on 3 CT specimens of base metal. The fatigue crack growth threshold decreases as stress ratio increases, Q345qDNH has considerably higher fatigue crack growth thresholds than Q345qD and universal thresholds given in BS7910. Two data processing methods are employed to calculate characteristic FCGR parameters. The FCGR parameters determined by small sample method are more conservative than those obtained by group sample method. The FCGR of butt weld increases faster than that of base metal as stress intensity range increases, therefore butt weld is more brittle than base metal. Q345qDNH has slower FCGR than Q345qD and the universal parameters given in BS7910, hence Q345qDNH has better fatigue resistance. The fatigue crack growth was numerically simulated, the largest difference between predicted fatigue life and tested fatigue life is 11.3%, therefore fatigue life can be predicted reasonably accurately by numerical simulation on the basis of measured FCGR parameters, which illustrates the potential and effectiveness of numerical simulation for fatigue assessment of complex bridge structural details based on fracture mechanics and the significance to obtain accurate FCGR parameters. • Fatigue thresholds and FCGR parameters of Q345qDNH have been measured. • Bridge weathering steel Q345qDNH has proved to have excellent fatigue resistance. • This paper provides essential data for fatigue assessment of bridges using Q345qDNH. • Fatigue life of CT specimens are accurately predicted by numerical simulation. [ABSTRACT FROM AUTHOR]

Rock burst is a catastrophic dynamic disaster caused by sudden failure and instability of coal, loading paths play an important role in the failure of coal, the coal failure process is associated with charge exception information. Hence, violent coal failure mechanics and time-frequency domain distribution of charge signal such as rock burst under different loading paths should be studied in-depth. In this paper, grade and cyclic loading test were carried out for coal with impact tendency samples produced by blocks cored from 800 depth in Xiaoqing coal mine of the Tiefa coal group in northeast China. Theory discussion was carried out for the result of stress and strain, frequency-spectra analysis was conducted for the wavelet charge data, figures showing the evolution mechanism of mechanical properties and the relationship of time-frequency domain amplitude of charge signals in coal with different loading paths and stage were obtained. The failure process and characteristics of coal under different loading paths were summarized. It found that the loading path changed the manner of energy accelerate-release, there were more plastic strain generation in coal under cyclic loading than that under grade loading, the former was more likely to cause greater damage and failure, then the strength of coal under cyclic loading is generally lower than that under grade loading, an energy conversion mechanical model of stress, damage and deformation was developed and explained the effect of the loading path. Charge signal was primarily distributed in the strengthening and peak stages, where there was a high amplitude pulse at each stress drop. The charge pulse was a type of low frequency signal with a primary frequency distribution range of 1 -100 Hz. Discussion on the charge generating mechanism from the perspective of friction slip, it demonstrated that the charge obtained during the coal failure process directly to stress loaded on and damage, the result verified it better. We propose that the research results in this study could be efficiently applied to daily mining activities, to provide an early warning and effectively avoid rock burst disaster. [ABSTRACT FROM AUTHOR]

This paper predicts the possibility of water inrush from a confined aquifer under the action of mining activities and water pressure. The study uses numerical analyses to evaluate stress redistribution and crack growth which result from coal extraction operations. Two models are presented in this study. By simplifying the distribution of the disturbed vertical stress on the coal seam and floor around a working face, a model is established to analyze the additional stresses in the floor strata induced by mining activities. And some distribution features of all the additional stress components are described. By using the superposition principle in fracture mechanics, another model is developed to analyze the crack growth in the floor strata under the action of disturbed stresses and water pressure. And the stress intensity factors at the crack tip are presented and the process of crack growth is obtained in the advancement of a working face. Because of discretizing only loading areas and crack surfaces, the present methods can obtain the accurate numerical results. Finally, some suggestions are made for preventing the water inrush from a confined aquifer. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract  Whilst the Yingxiu-Beichuan fracture is considered to be the primary seismic fracture of the Wenchuan earthquake, surface ruptures, geohazards, abnormal hydrological phenomena and aftershocks occurred not only along this central fracture but also along the so-called “secondary seismic fractures” parallel to it. The paper reports some of the geohazards associated with these secondary seismic fractures and concludes that the contribution of these is important in the overall scale of the effect of the Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

The cracking damage of the high-speed railway slab track seriously affects its durability and service life. The cracking condition index (CCI) for the China railway track system (CRTS) III prefabricated slab track and the corresponding calculation methods were proposed to realize the scientific management and guide the maintenance more reasonably. In order to ensure the objectivity and rationality of each parameter's weight, first, the finite-element (FE) model of CRTS III prefabricated slab track with surface cracks was established to analyze the crack growth behavior, based on the fracture mechanics theory. The results show that the crack growth rate of transverse cracks at the same depth is greater than that of longitudinal cracks and significantly greater than that of through cracks. Then 437 valid questionnaires were obtained through expert consultation. Combining the subjective factors of expert evaluation with the objective factors of numerical simulation, the Delphi method and interval analytic hierarchy process (AHP) were used to establish the structural hierarchy, which could determine the weight of each parameter. After that, it was applied to an engineering example. The results show that the weights obtained by the comprehensive method combining the Delphi method and the interval AHP are more objective. Furthermore, the evaluation method was applied to the engineering example, obtaining the slab track CCI within [70.91, 72.83] points, which verified the rationality of the evaluation method. In short, the index evaluation method can quantitatively analyze the cracking severity of the track slab, which has important reference and practical value for line maintenance. [ABSTRACT FROM AUTHOR]

Prior studies have indicated that mining-induced surface dynamic cracks in eastern China only undergo one 'expanding-closure' development cycle. However, field measurements from the Bulianta mines of northwestern China demonstrated that ground dynamic cracks in the Ordos region went through two 'expanding-closure' cycle. Using in situ measurement data and theoretical analysis, we find that the strata control theory cannot reasonably explain this special phenomenon. In this paper, we propose a novel explanation from the perspective of soil mechanics. A comparison of two field examples in eastern and northwestern China demonstrates that our theoretical explanation is in agreement with in situ observations and therefore is a reasonable interpretation for the secondary development of ground dynamic cracks in the Bulianta mines. This study provides a theoretical basis for the mechanism of mining-induced ground dynamic cracks. [ABSTRACT FROM AUTHOR]

The Guanyinyan Yangtze River Bridge is the key structure on the second ring highway of Chongqing City, southwest of China. The bridge is a cable-stayed bridge with a main span of 436 m. The main girder is a steel-concrete composite girder with a total width of 36ṡ2 m. The final design solution was based on an extensive comparison of proposals. The main bridge was constructed using the balanced cantilever method. This paper presents the challenges in design and static analysis of the bridge, including the detailed design, global static analysis, local finite element model analysis, the determination of the allowable maximum thickness of steel plate against fatigue and brittle fracture induced by low temperature. [ABSTRACT FROM AUTHOR]

Effective migration system of coalbed methane (CBM) reservoir, which was controlled by development degree and opening-closing degree of fractures, determines the permeability of coal reservoir and can be characterized by the pore-fracture system in the extrinsic form. In this paper, based on coal matrix elastic self-regulating effect theory and coal reservoir combined elastic energy theory, the fracture opening-closing degree parameter Δ and the fracture development degree parameter ξ are suggested for the quantitative study of the effective migration system of CBM reservoir in southern Qinshui Basin. Further, the control functions of ξ and Δ to CBM enrichment and high production are discussed. The results show that in present stage the area with high ξ value is located in Anze and Qinyuan, and then Zhengzhuang and Fangzhuang, where fracture development degree is high. The area with high Δ value is located in Zhengzhuang and Fanzhuang, and then Anze and Qinyuan, indicating where coal matrix elastic self-regulating positive effect dominates and fractures tend to be open. Through the comprehensive analysis on ξ and Δ, it can be found that their best match area is located in Zhengzhuang and Fanzhuang, with high values for fracture development degree and opening-closing degree probably bringing about high fluid pressure and good permeability of reservoirs, which are advantageous to an abundant CBM production. [ABSTRACT FROM AUTHOR]

Splitting failure, which is recognized as a special engineering geology phenomenon, occurs continually in the brittle rock mass of caverns during underground excavation. In this paper, a splitting model of linear slippage crack groups is built with fracture mechanics, energy analysis, and crack extension theories. Considering intrinsic cracks in rock mass and change of outer stress, intrinsic cracks propagate into macroscopical splitting cracks that are approximately parallel to the side wall of caverns. The splitting criterion of cavern rock mass and the method for predicting displacement in view of splitting opening displacement are proposed. In the end, the forecasting method is applied to the Jinping-I Hydropower Station, underground caverns engineering in China, the splitting failure zone and forecasting displacement are accordant with the monitoring data. The new forecasting displacement method is proven to contribute to the construction of similar underground caverns. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Civil Engineering is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As a kind of existing and potential geological disaster at the source of avalanche on cliffs or steep slopes, perilous rock has developed in the western area of China widely, and it has posed a serious threat to highways, railways, pipelines, cities, and mining for a long time. More than ten years of engineering experience have shown the necessity and importance to pay our attention to the avalanche sources in active collapse mitigation. The support–anchor combined technique is devoted to the active hazard mitigation measures of perilous rock. This paper introduces fracture mechanics to investigate the design procedure of the support–anchor combined technique. To obtain reasonable design parameters of the technique, both stability assessment criterion and three safety classes of protection engineering for perilous rock is proposed, further, stable analysis methods for various types of perilous rock are established by using fracture mechanics. Abiding by the idea that to improve stability coefficient to a higher level, the support force of structure and the anchorage force of anchorbolt from the support–anchor combined technique are introduced into stability analysis methods established above, which can estimate the section dimension of support subunit and the amount of anchorbolt of the technique. Engineering applications of the technique in thousands of protection engineering have identified the remarkable effectiveness [ABSTRACT FROM AUTHOR]

• The crack propagations and patterns are described. • Presence of reinforcement bars has a significant influence on cracking behavior. • Influences of primary design parameters on cracking behavior are discussed. • Equations for estimating the reinforcement stress are developed. • Analytical model for predicting crack width is proposed. This paper aims to clarify flexural cracking behaviors (e.g., crack width and crack spacing) of a lightweight deck system composed of steel orthotropic deck and thin ultra-high performance concrete (UHPC) layer. Forty steel-UHPC composite plates and eight steel-UHPC composite beams were tested to explore their cracking characteristics in transverse and longitudinal directions, respectively. The influences of reinforcement ratios, the thickness of the UHPC cover, the spacing of stud shear connectors, and the depth of the UHPC layers on cracking behaviors were examined. According to the bridges with composite deck systems recently constructed in China, the same spacing of reinforcing bars were employed in longitudinal and transverse directions, which ranged from 30 and 75 mm. The test results show that the occurrence and growth of cracks in UHPC layers could be effectively restricted by increasing reinforcement ratios, reducing the thickness of UHPC cover and the spacing of stud shear connectors, as well as thickening the UHPC layer. For the average crack spacing, the most significant factor was the reinforcement ratio. For the longitudinal behavior of the lightweight deck system, the steel-UHPC composite beams would fail due to the yield of steel U-ribs and the crack width in the UHPC layer would be small (e.g., 0.09–0.14 mm) when the reinforcement ratio and the thickness of UHPC cover are design appropriately. Based on the experimental observations, the formulas were developed to estimate the stress in reinforcements for the composite (steel + UHPC) lightweight deck system. The reinforcement stresses predicted by these formulas were in agreement with the experimental data. A new formulation for predicting the maximum crack width in composite (steel + UHPC) lightweight deck system was also proposed. Good agreements were achieved between the test results and the predicted values of the flexural crack width. [ABSTRACT FROM AUTHOR]

Abstract Casing failures have been systematically encountered during multi-stage hydraulic fracturing of horizontal wells in some unconventional reservoirs of China. Such failures usually manifest themselves as excessive localized radial deformation of the casing after some fracturing stages, which prevent the bridge plugs of subsequent stages from being installed to the design depths, or even result in abandonment of all remaining fracturing stages. In this paper, aiming at clarifying the casing failure mechanism during hydraulic fracturing, we performed an integrated investigation of tight-oil wells in northwest China, by analyzing the field-gained data and modeling possible mechanisms responsible for the casing failure. The investigation results show that, radial deformation of the casing due to alteration of in-situ stresses, even jointly with poor cement sheath, is far smaller than that observed in the field which could reach the order of magnitude of 1–3 cm. In contrast, we find that shear slips of pre-existing fractures/faults crossing the casing can deform the casing to the observed magnitude, justifying a conclusion that casing failure is due to the shear of pre-existing fractures/faults. This modeling-derived conclusion is supported by the records of micro-seismic events. In addition, lead impression blocks have also run for determining the deformed shape of the casing, and the results match the modeling results for the casing sheared by activated fractures/faults. Effect of fracturing pressure, in-situ stresses, length and orientation of pre-existing fractures/faults on the slippage of the fractures/faults and thus the deformation of the casing are demonstrated by a series of sensitivity studies. Additionally, some insights are derived for mitigating the casing failure in future fracturing jobs in similar unconventional reservoirs. Highlights • A statistical analysis of casing failure during multi-stage hydraulic fracturing was performed. • The reduction of casing diameter was adopted as the casing-failure criterion. • The reactivation of pre-existing fracture/faults may be the primary reason for casing failure during hydraulic fracturing. [ABSTRACT FROM AUTHOR]

In most thermal coalbed methane production practices, the average single well production is low and the economic benefit is low. In order to improve the production of thermal coalbed methane (CBM), this paper presents a dual diagnosis method for fracture morphology of thermal CBM reservoir to improve hydraulic fracturing effect. The study is carried out as follows: Firstly, improved log-log curve method to adapt to coal seam fracturing construction. Secondly, establish the inclined stress calculation model of coal seam to obtain the critical depth value. Finally, combine the improved log-log method and critical depth method to form a dual diagnosis approach. Take Baiyang River in Xinjiang as an example, obtain the traffic, rock mechanics and other parameters suitable for the Baiyang River block, the fracture morphology is verified by fracturing data. The experimental results show that the approach can diagnose fracture morphology accurately. [ABSTRACT FROM AUTHOR]

Abstract In Tarim oilfield of China, the true vertical depth (TVD) is >6000 m, non-API 140 casings are often used as the intermediate and production casing. No industry standard has been established for such high grade casing, although there are some obvious shortcomings, such as sensitivity to defects and service environment, so that the fracture failure accidents of non-API 140 casing in Tarim oilfield happens frequently. Hence, this paper presents a discussion on the technical specifications of non-API 140 casing. Firstly, the system test and analysis of physical and chemical performance of non-API 140 casing material from various manufacturers have been conducted, including chemical composition, tensile properties, impact toughness, hardness, metallographic structure. Secondly, the analysis method of required minimum transverse impact toughness (CVN min) to resist cracking for pipe body and coupling of non-API casing has been presented, by which the effects of effective thickness and non-destructive examination level (defect depth) on CVN min to resist cracking of pipe body and coupling under diffenrent internal pressure have been analyzed.Thirdly, the full-scale ductile burst test of non-API 140 casing has been performed based on API 5CT standard. Finally, based on experimental data and analysis, the technical specifications for non-API 140 casing are proposed. Cases Analysis of Tarim field shows no fracture failure occurs during the subsequent service after adopting those technical specifications. Highlights • Physical/chemical performance of non-API 140 casing from three manufacturers is obtained. • Analysis method of required impact toughness to resist cracking has been presented. • Full-scale ductile burst test of non-API 140 casing has been performed. • Technical specifications for application of non-API 140 casing are proposed. [ABSTRACT FROM AUTHOR]

The model and shape equation of compression and shear fracture nucleus of rock of earthquakes are briefly recounted in this paper. Recently rock breaking areas with two special shapes have been discovered on palisade of foundation pit excavated for dam in Hunan Province, PR China. The on-the-spot investigation indicates that all two broken areas once had the stress concentration point, and the broken area was initiated and expanded from this point. Both internal crack propagation and the outline shape are consistent separately with the rock compression and shear fracture nucleus with leaf shape of KI, KII mode and the rock compression and torsion fracture nucleus with bud shape of KI, KIII mode given by the shape equations. The further research on the forming process of rock compression and shear fracture nucleus is helpful for impending earthquake prediction. [ABSTRACT FROM AUTHOR]

Steel structures with thick‐walled section tend to have local fracture before the occurrence of instability under strong earthquakes, which is termed as ultra‐low cycle fatigue (ULCF). In this study, a series of specimens made with structural steel Q345qC for bridge in China were firstly tested to investigate the ULCF fracture behaviour in material level. Based on the test data, three models for ULCF fracture were calibrated. Subsequently, the fracture behaviour of thick‐walled square section steel bridge piers were also investigated in component level. Moreover, the finite element global and submodels of steel bridge piers were established, and ULCF fracture initiation life was predicted by calibrated models and validated against test results. The research results showed that the crack firstly occurred at the bottom of piers under cyclic oblique loading, which was at the junction between base plate and bottom weld, and then, cracks propagated along the bottom weld metal which did not cause a decrease in strength capacity. Finally, the strength capacity of steel bridge piers began to rapidly declined as cracks propagated into base metal. The presented finite element global model can accurately simulate the cyclic behaviour of steel bridge piers, and the submodel has the ability of capturing the local stress and plastic strain. The fracture models accurately predicted ULCF fracture initiation life of steel bridge piers with the average discrepancy of 7.14%. The developed finite element analysis method considering ULCF fracture provides a solution for the further parametric analysis on ULCF fracture performance of steel bridge piers. [ABSTRACT FROM AUTHOR]

This paper presents a case history of geological hazards and treatment measures during the shield tunneling of Metro Line No. 7, in water-rich mylonitic faults in Guangzhou, China. The site selection of Metro Line No. 7 is introduced based on the land use and the geology in Guangzhou. Metro Line No. 7 passes through a number of dead faults, which are unavoidable due to the presence of urban residences and geological formations. The mylonitic rock faults feature rock fractures, high rock permeability, complex formation structure, susceptibility to collapse, and rich groundwater. Geohazards during tunneling in groundwater-rich mylonitic faults include ground collapse, groundwater in-flows, land subsidence, and long-term instability of tunnel. These types of hazards would delay the construction of tunnels and potentially cause significant damage to the tunnels. Preventions and treatments for these hazards aforementioned are analyzed based on the tail grouting material optimization, advanced ground monitor, grouting treatment and shield machine modification, with monitoring the feedback data. The mechanism of ground collapse is discussed according to the cavity expansion principle. [ABSTRACT FROM AUTHOR]

The non-negligible fissures, cracks or pore structures, which are contained in rocks, have significant influences on their mechanical properties. In this paper, a novel method is developed to reconstruct a three-dimensional multiple phase rock model from the limited morphological information of Chongqing sandstone. Firstly, X-ray micro-CT experimental tests are applied to Chongqing sandstone to obtain the raw CT images and the mechanical parameters. Then, the two-point correlation function, lineal-path function and fractal function are combined to generate the reconstructed model. Next, the reconstructed model subjected to compressive loads is simulated by Finite Element-Smoothed Particle Hydrodynamics (FE-SPH) coupling method with a brittle model formulation. Finally, the initiation, propagation and coalescence of cracks are investigated during the numerical simulation. The topological and mechanical properties of the reconstructed model are carefully analyzed and compared with that of the reference model. The comparison of the numerical modeling results and the experimental data shows a good consistency. This indicates that the proposed method has the ability to predict macroscopic behaviors of rocks from limited experimental information. [ABSTRACT FROM AUTHOR]

The Bianmachong Formation above the Niutitang Formation in the Lower Cambrian of South China, which was mainly deposited in a marine and transitional environment, has highly brittle characteristics and is an important shale layer for shale gas exploration, but the current level of exploration is low. This paper discusses in depth the development characteristics and dominant factors of fractures and their significance for the shale reservoir in Є 1 b 2 (middle member of the Bianmachong Formation of lower Cambrian) of the Cen'gong block in Guizhou Province based on the observations of outcrops, cores, polished thin sections and scanning electron microscope chips, as well as statistics on the fracture characteristic parameters and a test data analysis of corresponding samples. The results show that overlaps of organic-rich shale and tight sandstone vertically have created favorable generation conditions for shale gas and tight sandstone gas in Є 1 b 2 shale. Є 1 b 2 shale has similar sedimentary environment, mineral composition and organic type as American marine shale but exhibits differences in terms of the abundance of organic matter and degree of thermal evolution. The TOC content of Є 1 b 2 shale is mainly 1–2% and over-maturation. Multiple types and periods of fractures are abundant in Є 1 b 2 shale. They are mainly structural fractures, such as high dip-angle shear, bedding, tension-shear, interlayer and slip fractures. The micro fractures are mainly interlayer fractures, grain boundary fractures and organic matter contraction fractures. Structure is one of dominant factors for the fractures development, but others also have a strong correlativity, such as the lithology, abundance of organic matter, formation thickness, mechanical properties and mineral content. Under the same structural background, the content of brittle minerals such as feldspar, pyrite and quartz is higher. The brittleness is higher in shale, and more fractures are generated, which contributes to reservoir heterogeneity. The TOC content of Є 1 b 2 shale has positive correlations with the content of quartz and the total gas content, which is also positively correlated with fracture development in the cores, and the source of organic matter is siliceous organisms. For over-maturation and organic-rich shale, a high TOC content and a high silica content are beneficial for micro pores and fractures to be preserved. In addition, the fracture development is positively correlated with the total and free gas contents in Є 1 b 2 shale. Micro pores and fractures exist in internal minerals, such as calcite, quartz, and pyrite, as well as in their intervals with fracture surfaces, which reduce the capacity of fractures to resist tension and shear. The fractures are prone to rupture again. In addition, filled fractures make a greater contribution to the reservoir space of Є 1 b 2 shale through dissolution. [ABSTRACT FROM AUTHOR]

Goaf-side entry with small coal pillars (GESCPs) has an intrinsic advantage of improving the coal recovery ratio by implementing drifts with a small pillar size next to previous goafs. This technology is increasingly gaining popularity in the longwall mining of underground coal mines in China. This study focuses on understanding the critical condition of the main roof failure above the solid coal side of the goaf-side entry and investigating the key parameters that affect the structural stability of the surrounding rocks for GESCP. Mechanical models of the main roof and multi-layer cracking structures of the side wall of GESCP were established and the limiting equilibrium equation for the structural stability of the surrounding rock was proposed. The characteristics affecting the main parameters of the structural stability of the surrounding rock were analyzed. The research findings suggest that the integrity of the coal side walls plays a major role in maintaining the structural stability of the surrounding rock for GESCP under the given cross-sectional dimensions. Other factors, including the uniform load of overburden, the width of the coal pillar, the length of the roof hanging along the goaf side, and the fracture length in the main roof of the entry side wall, are less important. The key to achieving structural stability of the surrounding rocks for GESCP is to enhance the strength of the supporting coal side walls and, especially, to ensure the integrity of the small coal pillars. These conclusions were verified by engineering practice at the 1252(1) haulage gateway in a Coal Mine in China. [ABSTRACT FROM AUTHOR]

Groundwater and mud inrush during tunneling may cause severe security risk, great economic loss and unrecoverable damage to environment. However, the prediction and prevention still remain as a challenging problem. According to geological survey, Lingjiao tunnel was judged to be safe from danger of large-scale water and mud inrush. Unfortunately, a large (the largest one in China) mud outburst accident happened with bursting mud of more than 40,000 m 3 , leaving a huge collapse pit on the upper surface of the crossed mountain. Moreover, another mud inrush took place right in the paralleling tunnel nearby one year after the first accident, which triggered another follow-up collapse in the same site as the first time, though it has been reinforced with concrete cover. The two mud inrushes accidents were induced by and through the similar geological structure, which was not recognized. In this paper, the mud-inrush processes are expatiated. It is found that geological identification of water-bearing and mud-filling structures is crucial for subsequential effective geophysical or drilling probing, misunderstanding and unable to recognize these crucial geostructures accounts for a lot of hazards. The failure to predict the more than once mud inrushes in Lingjiao tunnel is due to misunderstanding of hazard-inducing geostructure. The water-bearing and mud-filling structure is fracture-induced karstified zone (Epi-Fracture-Karst-Zone, EFKZ) which is formed from the karstification enhanced by fracture zone rather than originally suspected main fault zone. The favorable conditions for EFKZ development and mud filling which include dissoluble rocks, hot, humid climate and dense vegetation, tensile fracture zone, thick soil and abundant rainfall and the mechanism of mud inrush have been identified: The adjacent water-bearing fillings with high pressure in EFKZ surrounding the working face flow into the tunnel when EFKZ is disturbed by blasting, which induced the heavy mud-inrush accident in Lingjiao tunnel. [ABSTRACT FROM AUTHOR]

In the present study, a total of 20 fatigue tests on notched plates of Q460C steel were carried out, where the effects of relative stress amplitude, Δσ/fy, and relative nominal maximum stress, σmax/fy, on the fatigue life of these notched plates were carefully examined. Theoretical analyses and numerical simulations were subsequently conducted, based on an ellipsoidal fracture model originally proposed by the second author, which has been validated for use as a fracture criterion of fatigue crack, to investigate the fatigue cracking in the Q460C steel notched plates. The theoretical model was further developed to estimate the fatigue life of the Q460C steel notched plates using a unified crack growth approach originally proposed by the second author. Based on the theoretical and simulated results, the accuracy of the unified crack growth approach, and the allowable stress fatigue life formula recommended in China's code GB50017-2017, were assessed. The comparisons indicate that the unified crack growth approach is able to provide a reliable fatigue life assessment for the Q460C steel notched plates. [ABSTRACT FROM AUTHOR]

Differential weathering is a primary cause of secondary toppling failures of rock slopes. Using the Taibaiyan cliff in the Three Gorges Reservoir as a case study, the evolution of an overhanging slope was numerically investigated using fracture mechanics. A displacement discontinuity method (DDM)-based computer program, which incorporated joint elements, was developed. In addition, a factor of safety was defined for the slope failure analysis. The progressive failure process was simulated by analyzing the propagation and coalescence of cracks through rock bridges. The influence of the joint geometry parameters was investigated based on the defined factor of safety and the calculated stress intensity factor (SIF). The weathering rate in the Three Gorges Reservoir was quantitatively estimated using field measurements. The relationship between the factor of safety and the undercutting depth was studied, and the critical undercutting depth associated with a factor of safety of 1 was determined. The approach for predicting the failure time of an overhanging slope subject to weathering processes was presented based on time-dependent weathering and the critical undercutting depth. The results show that the failure mechanism of an overhanging slope is tensile-shear fracturing and that the failure processes can be identified as weathering, undercutting, stress concentration, crack initiation and crack propagation, and coalescence. [ABSTRACT FROM AUTHOR]

Orthotropic steel decks (OSDs) are inevitably subjected to fatigue damage caused by cycled vehicle loads in long-span bridges. This study establishes a probabilistic analysis framework integrating the dynamic Bayesian network (DBN) and fracture mechanics to model the fatigue crack propagation considering mutual correlations among multiple fatigue details. Both the observations of fatigue crack length from field inspection and monitoring data of vehicle loads from the weight-in-motion (WIM) system are utilized. First, fracture mechanics-based uncertainty analysis is performed to determine the multiple uncertainty sources in the Paris crack propagation model, material property, and observation data of crack length. The uncertainty of monitoring data of vehicle loads is ignored because of its high accuracy; consequently, the vehicle-load-related uncertainty is spontaneously ignored, which is also demonstrated to be very small on the investigated actual bridges. Second, a hierarchical DBN model is introduced to construct mutual dependencies among various uncertainties and intra-correlations in the propagation process of multiple fatigue cracks at different components. Third, a stochastic traffic model is established based on the WIM monitoring data and multi-scale finite element analysis via substructure techniques to determine the probability distribution of vehicle-load-related parameters. After variable discretization, a refined exact inference algorithm in a forward–backward–forward manner is adopted to estimate the posterior distribution of equivalent initial crack length and update the established DBN model. Finally, the proposed method is demonstrated by a numerical case study and a typical application on an actual cable-stayed bridge with steel box girders using OSDs in China. The results show that the probability distribution of equivalent initial crack size can be spontaneously derived with a larger mean value than the results of conventional empirical analysis. Furthermore, the component-level fatigue reliability is tracked and predicted based on the established crack propagation model. [ABSTRACT FROM AUTHOR]

Using undrained triaxial shear tests, this study investigates the mechanical properties of fine-grained materials (silty clay and sand) which are extensively used for China's Qinghai–Tibet Railway (QTR) under different confining pressures (σ3) and freezing temperatures (T). The results show that a reduction in T causes an increase in the shear strength and elastic modulus of all the materials tested in the present study. In addition, the freezing of the silty clay has no significant effect on the type of soil behaviour (strain-hardening), whereas the freezing of the sand changes its strain-hardening behaviour to strain-softening. Supposing that the deviatoric stress–strain curves of the silty clay and sand can be divided into two segments due to a reverse bending point, it was assumed that the first segment follows a hyperbolic function. Meanwhile, the second segment is also a hyperbola, with the reverse bending point as the origin and the residual strength as the asymptote. Accordingly, a nonlinear relation constitutive model that considers σ3 and T is derived. All model parameters are identified. The reasonability of the new model was verified using the test results of the materials. A comparison of the predicted and test results shows that this model can well simulate the deviatoric stress–strain response in the failure process of the tested materials. In particular, it can reflect the residual deviatoric stress after the materials' failure. [ABSTRACT FROM AUTHOR]

With the development of infrastructure in China, the slope rock mass is affected by external forces such as roads. Tunnel excavation will cause a series of engineering problems, which are essentially caused by the instability caused by the propagation of internal cracks in the rock mass. At the same time, in practical engineering, the rock mass is formed through long-term geological structure, and its internal cracks have a variety of properties. Based on granite samples as the research object, two different angles of sample shapes, cylindrical and circular, are prefabricated. The uniaxial compression test is studied to analyze the law of inclined crack propagation in rock under uniaxial compression. Combined with the theory of fracture mechanics, the influence mechanism of crack inclination and sample shape on crack propagation in rock mass is discussed. The test results show that under uniaxial compression, the stress-strain curves of granite samples can be divided into four stages: compaction, elasticity, plasticity, and residual deformation. For the cylindrical sample, the crack initiation occurs at the tip. The compressive strength of the sample decreases with the increase in the prefabricated crack angle, and the crack initiation angle increases with the increase in the prefabricated crack angle. The fracture of the sample changes from shear slip failure to split shear failure of the penetrating rock mass with the increase in the crack angle. For the disk sample, the crack initiation location gradually increases from the tip to the middle with the increase in the crack angle, and the crack initiation angle increases with the increase in the crack angle. The peak load of the sample decreases first and then increases with the increase in the crack angle and is the minimum at 60°. The fracture mode of the sample is mainly tensile failure. When the crack dip angle is between 30° and 60°, the tensile and shear composite failure of the sample occurs, and the influence mechanism of crack dip angle and sample shape on the crack propagation path is analyzed. The research results have important theoretical significance for engineering design, construction, and stability maintenance. [ABSTRACT FROM AUTHOR]

The present work shows the application of a new methodology, to find out the seepage evolution law in the earth dam under its flow conditions, to a real field case: the Longyangxia Dam, in Qinghai, China. Under the influence of various loads and environmental factors, the creep property of dam foundation fault will be bound to be changes in the evolution of its seepage field. Therefore, the normal compression creep and the tangential shear creep of dam foundation faults are studied in this paper. Moreover, assuming the non-tension capacity in the normal direction, the normal compression creeping model and the tangential shear creeping model of the fault are established. On the basis, the time series evolution model on the permeability coefficient of the fault in dam foundation is built. These methods have already been applied into Longyangxia Dam and the result indicates that the seepage condition is normal when dam foundation seepage coefficient are getting smaller. [ABSTRACT FROM AUTHOR]

Abstract: Uniquely, China employs MgO already contained in cement clinker or as an expansive additive to compensate for the thermal shrinkage of mass concrete, particularly dam concrete, with almost 40years' experience in both research activities and industrial applications. Compensating shrinkage with expansion produced by MgO has been proved to effectively prevent thermal cracking of mass concrete, and reduce the cost of temperature control measures and speed up the construction process. Moreover, the expansion properties of MgO could be designed flexibly, through adjusting its microstructure by changing the calcination conditions (calcining temperature and residence time). The collective knowledge and experience of MgO expansive cement and concrete is worthy of sharing with relevant engineers and researchers globally but dissemination has been hindered as most of the relevant literature is published in Chinese. This paper reviews the history, state-of-the-art progress and future research needs in the field of MgO expansive cement and concrete. [Copyright &y& Elsevier]

The rehabilitation construction in the reservoir area of Xiangjiaba hydropower station in Southwest China has caused many landslides. A shallow progressive failure that occurred on the resettlement site of Xin'an Town of Pingshan County in Sichuan Province was selected as a case study. This landslide occurred in a long and gently inclined area by slope excavation under rainfall conditions. It is about 3.0 m deep with a total length of 35 m and is composed of some subfailures. Undisturbed samples were retrieved, on which the basic properties, shear strength, expansive potential, mineral compositions, and microstructures were tested and analyzed. The results show (1) the landsliding materials belong to medium expansive soil, consisting of the clay minerals of illite-smectite (I/S) and chlorite-smectite (C/S); (2) shear strength of the soil is sensitive to water, which greatly decreases once saturated; and (3) many fractures and relatively large pores are developed in the soils. Back analysis of the landslide shows that the shear strength at failure is less than the residual shear strength obtained from lab tests, indicating that some processes contributing to the slope failure could not be reflected by the shear box test. Based on the above analysis, the progressive process of the slope failure was interpreted, and it is inferred that the rainfall entered into the slope mainly through fractures and relatively large pores in the soil. It caused not only the great decrease in soil strength but also the swelling trend. The latter one would lead to growth, interaction, and coalescence of the fractures. Soon after, these fractures formed the shear planes (zones), which further decreased the resistance of the landslide. Under these favorable conditions, the slope excavation directly triggered the failure. [ABSTRACT FROM AUTHOR]

Abstract: In 2009, China accounted for half of the global steel production. As a waste material or by-product in the manufacture process, over 160 million tonnes of blast furnace slag is generated annually, of which only 55% is recycled. Blast furnace slag, ground to an appropriate fineness, can be used as a cementitious material in concrete. However, most ground granulated blast furnace slag (GGBFS) in China ends up in low-grade applications, including ‘low heat’ cementitious material used in low-grade bulk concrete and cementitious material in mortar. A recently started project at XJTLU aims to contribute to the application of GGBFS in long-span concrete structures in China by avoiding/reducing the use of more expensive crack control reinforcement. The use of GGBFS in long-span concrete structures in China is currently held back by the following: [(1)] Lack of awareness of the potential commercial benefits; [(2)] Concerns about the steady supply of GGBFS; [(3)] Difficulties in evaluating the mitigating effects of GGBFS on early-age “thermal loading”. This paper reports on the methodology which is adopted to carry out this project. Special considerations are paid to issues associated with concrete early-age thermal contraction. Modelling of a case study of a commercial building in Shanghai is used to compare the cost effectiveness of using conventional crack control steel reinforcement only with the mitigation of thermal crack stresses by adopting GGBFS as a partial replacement for traditional cement. The study includes the use of finite element modelling to investigate the development of heat during the early age cement hydration process and the resulting thermal stresses produced in the concrete. [Copyright &y& Elsevier]

Abstract: Almost all defects of earthen buildings such as roughening, erosion, volume reduction, cracking as well as crazing, etc., have been witnessed in the ancient city of Jiaohe, an earthen architectural heritage in northwest China. In this paper, their long-term durability and deterioration due to prolonged exposure to environmental factors were studied, based on the basis of field investigation and laboratory analysis. The results indicated that the deterioration of building materials should be attributed to their basic properties, including density, particle size distribution, soluble salts, mineral, mechanical strength, etc., and interaction with environmental factors. And then, four main deterioration modes can be identified, namely: wind-related deterioration, water-related deterioration, temperature-related deterioration and chemical related deterioration. It can be concluded that the greatest deterioration was wind-related deterioration on west-north facing façades, and chemical related deterioration on the surface of building materials. [Copyright &y& Elsevier]

Abstract: Fracture data available for one of the rock masses (limestone) in the dam site of Yujian River Reservoir were used to build and validate a stochastic 3-D fracture network model, and to perform a REV and equivalent continuum study in 3-D. A number of relations are developed in the paper between the rock mass mechanical parameters and fracture tensor components in 3-D. Based on the mechanical parameter values obtained in every 45° direction in 3-D, the principal parameter values, principal directions and tensors are developed for rock mass mechanical parameters to represent the REV block size properties. An incrementally linear elastic, orthotropic constitutive model is suggested to represent the equivalent continuum pre-failure mechanical behavior of the jointed rock mass by incorporating the effect of joint geometry network by the fracture tensor components. [Copyright &y& Elsevier]

Abstract: China''s Lop Nur is one of the world''s largest playas, and is located in the driest part of Central Asia. Scientific explorations by Chinese and foreign researchers have been continuously conducted there since the mid- to late 1800s, and much progress has been made, but many issues remain hotly debated. Particularly intense debate focuses on the formation, environmental evolution, drying date of the Lop Nur lake, and cause of the helical salt crusts recently revealed by remote-sensing images. In this paper, we review the status of this research to provide insights that can inform studies in other arid zones that resemble the Lop Nur. The Lop Nur depression is a secondary unit of the Tarim Block, controlled by faults and fractures formed by the Himalayan orogeny, but various competing explanations have been proposed for how these geological structures gave rise to the depression. The depression''s formation date also remains unclear. Several boreholes have been created to reconstruct the environmental evolution at different time scales since the Quaternary, and deposition rates of lake sediments, especially since the Late Pleistocene, have averaged less than 1mm annually. The drying date of the Lop Nur lake is also debated. The helical salt crust structures appear to have formed as the lake shrank, but how and when they formed is unclear. Huge potash reserves have been found, and large-scale potash fertilizer production has begun, but the origin of these deposits is debated. Understanding the factors causing environmental evolution in this region is a central issue that will help us to clarify these and other debated issues. [Copyright &y& Elsevier]

Abstract: To correctly simulate and predict the performance of fractured gas condensate reservoirs, based on the previous related studies, a new numerical dual porosity compositional simulation approach, suitable for fractured gas-condensate reservoirs, is proposed in this paper. Firstly, the proper pseudo-components should be correctly divided, and then single-matrix block models are built to establish the pseudo capillary pressure curve through comparing the single porosity model with the dual-porosity model. Based on the results, the dual-porosity compositional simulation method is studied. The study shows that dual-porosity compositional models can be used for fractured gas-condensate reservoirs without water drive, but not for reservoirs with strong water drive, whereas the model with pseudo capillary pressure curve can be correctly used for all kinds of fractured gas-condensate reservoirs. This new method was applied for a fractured gas-condensate reservoir of Tazhong No.1 gas field in the Tarim Basin, NW China, and the performance history of this field was well matched with the fitting error less than 5%. [ABSTRACT FROM AUTHOR]

Abstract: In carbonate reservoirs, effectiveness estimation using logging data has great challenges. According to the pore structure characteristics of the fractured and vuggy carbonate reservoir, Aguilera and Aguilera [Roberto F. Aguilera and Roberto Aguilera, 2004. A Triple Porosity Model for Petrophysical Analysis of Naturally Fractured Reservoir, Petrophysics, 45(2):157–166.] presented a triple porosity model, in which the secondary porosity was divided into connected fractured (and/or) vuggy porosity and non-connected vuggy porosity. In this paper, a new technology is presented to determine the values of the different porosity in the triple porosity model. Based on lateral logs responses, we derive analytical equations that contain connected fractured (and/or vuggy) porosity, non-connected vuggy porosity, matrix porosity and so on. Using these equations and the conventional log data, we can obtain the petrophysical parameters, such as connected fractured porosity, non-connected vuggy porosity and so on. Then the connected fractured (and/or vuggy) porosity and its percentage in the total porosity are used to indicate the effectiveness of the carbonate reservoir. This method has been applied for the well log interpretation of the 123 testing intervals from the 52 wells in Tarim oil field. Agreement ratio of the interpretation results is 91%, which verifies the validity of the presented method. [Copyright &y& Elsevier]

Abstract: Pores, cavities and fractures are well-developed in deep volcanic reservoirs. The simultaneous break and extension of multi-fractures in treatment caused early stage sand-block, low fracturing success ratios, small treatment scales, and bad stimulation results. Based on the geologic characteristics of the deep volcanic rocks, this paper establishes a fracturing break and extension model of volcanic rocks, introducing with time-relevant leaking factor, peak factor and modulus factor. The model is used to better describe the process of initiation and extension of major fractures and micro-fractures. On this basis, the evaluating method for the “three highs” of pump off pressure gradient, near well friction resistance and leakoff coefficient is studied, and through field practices, integrated processing measures are formed: use rubber plugging to deal with near-well high friction resistances, use silts to seal natural fractures, adjust prepad fluid ratios, and inject multi-section silt slugs. The success ratio of volcanic rock gas reservoir fracturing is raised to 90.0% from the past 36.0%. [Copyright &y& Elsevier]

The ecology of arid mining areas in western China is facing serious problems because underground coal mining destroys overlying aquifers, causing groundwater to shift along fracture zones and groundwater levels to drop. Therefore, it is important to construct strategically coal mine goafs as underground water reservoirs to store and utilize mining-affected water resources. During the long-term operation of underground water reservoirs, the stability of coal pillar dams is affected by the repeated rise and fall of mine water levels. To understand the repeated effects of water, nondestructive water immersion, ultrasonic velocity, uniaxial compression, and acoustic emission (AE) tests were performed to study the mechanical properties and damage mechanisms of coal samples under repeated drying–saturation conditions. The ultrasonic velocity test mainly achieved two functions: selecting consistent coal samples and providing evidence of changes after each drying and saturation process. Coal samples were grouped according to the number of drying–saturation processes (DSPs) to investigate and compare the mechanical and AE parameters. The post-peak phases of full stress–strain curves present perpendicular, L-shaped, and stepped forms, among which the latter two show obvious residual strength. The AE count, cumulative AE count, and stress can jointly determine the various stages and stress thresholds of the sample failure process (or crack development process), except the boundary between elastic stage and stable crack growth stage. Multiple immersions in water reduces the fractal dimension of broken blocks; that is, the degree of fragmentation decreases and the quantity and mass of large-size blocks increase. [ABSTRACT FROM AUTHOR]

• The evolution of cracking in graphite is examined by using a displacement field obtained through ESPI. • The consumed energy during the fracturing process of nuclear graphite is estimated by using the cohesive crack model. • The influence of tension softening curves with different shapes on the fracture behavior of graphite is discussed. • Correlation of the dissipated energy during the fracturing process and fracture mechanism in FPZ is evaluated by using a tri-linear model. General consensus in the literature is that the fracturing behavior of nuclear graphite shows a certain degree of nonlinearity due to the presence of a fracture process zone (FPZ) ahead of the crack tip. Thus, it is necessary to take the influence of the FPZ into account when investigating the fracture properties of nuclear graphite. Besides, the energy-based approach has been widely used to characterize the fracturing process in the FPZ. In consideration of all these factors, this paper examines the dissipated energy during the entire fracturing process of local graphite (NG-CT-01) found in China based on the cohesive crack model. The calculation process for estimating the average dissipated energy of the crack growth is obtained through three-point bending tests, which are performed on center-notched graphite beams. Electronic speckle pattern interferometry (ESPI) is used to obtain the full-field deformation of the beams. The experimental and analytical results are then compared, and a satisfactory agreement between the two results are found, which validates the reliability and accuracy of the formulas. The tension softening curves of graphite are plotted and different cohesive laws (bilinear, tri-linear and exponential) are used to determine the average amount of energy consumed during crack extension. The tri-linear softening model is used to evaluate the relationship between the energy dissipation of the fracturing process and the fracture mechanism in the FPZ of the graphite. Furthermore, the energy dissipated during the entire fracturing process of the graphite beam is examined based on three stages: initiation of cracking, propagation of stable cracking and unstable fracturing. [ABSTRACT FROM AUTHOR]

The low temperature fracture toughness of SA738Gr.B steel is as important as its strength, but the low temperature fracture toughness tends to be more complicated due to some deterministic and random inhomogeneity, such as sampling locations. In this paper, the fracture toughness of the 60 mm thick SA738Gr.B sheet in DBT region from the surface to the center was characterized by MC method and BMC method. Considering the sampling position, a distinct trend is found that the toughness of the surface is significantly higher than that of the center and T 0 is lower from center to the surface due to the faster quenching rate. Special attention was paid on the discussion of the applicability of China-produced SA738Gr.B steel to the master curve (MC) method. It was found that the inhomogeneity caused the actual distribution of the experimental data to deviate from the three-parameter weibull distribution, and the weibull slope was lower than the theoretical value of 4. Characterizing the fracture toughness of materials containing heterogeneous components by the MC method can overestimate the fracture toughness and may pose a potential hazard. The BMC method can effectively solve the problem of material inhomogeneity. It is an evaluation method based on the actual toughness distribution of materials. The BMC method takes into account the influence of material inhomogeneity on the toughness estimation, and more accurate assessment of material scatter than the standard MC method yields a slightly conservative but more appropriate prediction. • The effect of heterogeneity on the standard master curve method is mainly to destroy the Weibull distribution. • BMC method is used to predict the fracture toughness of the transition zone of heterogeneous materials. • The MC method produces non-conservative estimates for heterogeneous materials, but the BMC method provide a suitable estimation. [ABSTRACT FROM AUTHOR]

Fracture fields in coal rocks are the main channels for gas seepage, migration, and extraction. The development, evolution, and spatial distribution of fractures in coal rocks directly affect the permeability of the coal rock as well as gas migration and flow. In this work, the Ji-15-14120 mining face at the No. 8 Coal Mine of Pingdingshan Tian'an Coal Mining Co. Ltd., Pingdingshan, China, was selected as the test site to develop a full-parameter fracture observation instrument and a dynamic fracture observation technique. The acquired video information of fractures in the walls of the boreholes was vectorized and converted to planarly expanded images on a computer-aided design platform. Based on the relative spatial distances between the openings of the boreholes, simultaneous planar images of isolated fractures in the walls of the boreholes along the mining direction were obtained from the boreholes located at various distances from the mining face. Using this information, a 3-D fracture network under mining conditions was established. The gas migration pattern was calculated using a COMSOL computation platform. The results showed that between 10 hours and 1 day the fracture network controlled the gas-flow, rather than the coal seam itself. After one day, the migration of gas was completely controlled by the fractures. The presence of fractures in the overlying rock enables the gas in coal seam to migrate more easily to the surrounding rocks or extraction tunnels situated relatively far away from the coal rock. These conclusions provide an important theoretical basis for gas extraction. [ABSTRACT FROM AUTHOR]

During the construction of the concrete cut-off wall at Huangbizhuang reservior, five big collapses had occurred. In order to study the horizontal stress distribution of the foundation, the foundation was simplified to infinite elastic foundation with rectangular hole. Using conformal mapping function, infinite elastic foundation with rectangular hole was made conformal mapping to the circle, and stress function expression was derived. Combination with boundary conditions of the cut-off wall of Huangbizhuang reservior, stress distribution of the foundation was derived at any depth. The result showed that stress concentration occurred at the corner. Firstly the destruction of the soil occurred at the most concentrated stress areas, and then gradually expanded. [ABSTRACT FROM AUTHOR]

The impacts of temperature on the surface thermal damage of rock salt, gypsum and mudstone from the Yingcheng salt mine, China were investigated by the surface crack growth and propagation tests at different temperatures. We found that: (a) high temperature could strengthen the rock salt molecular thermal motion and weaken the cohesion among the rock salt grains, so that the grain boundaries were more prone to slip and thus develop into cracks; (b) high temperature could make the water molecules evaporate from rock specimens, which should change the physical properties of gypsum and mudstone; and (c) high temperature had a significant effect on the interface between rock salt and gypsum and mudstone, therefore it should be easy to produce cracks with white or light yellow cumulate powder here. The surface crack growth and propagation of the rock salt, gypsum and mudstone have a positive correlation with the temperature by stereo microscope and the method of binary images, which could observe the surface thermal damage properties. Finally, the fractal dimension of the rock salt surface cracks was calculated based on fractal theory, and the evolution of the surface thermal damage was found from 50 to 260 °C. [ABSTRACT FROM AUTHOR]

By taking into account the rheological behavior of the rock mass, the creep failure of a roof stratum seated on pillars in mined-out area is analyzed through a newly developed visco-elastic model. The time-dependent deflection of the roof stratum is obtained by numerical inversion of Laplace transform. The study shows that when creep properties of both the pillars and roof stratum are considered, the expected deflection in the roof stratum increases with time. Consequently, the roof would fail when the critical tensile stress is reached as the result of the increased deflection. To demonstrate the present analytical procedure, the failure time of roof stratum of the Xingtai Gypsum Mine in China was estimated, and the results obtained agreed with the observation. The case study indicates that the analytic approach provides a new way to assess the potential impact of the time-dependence of the roof stratum deformation and is useful in predicting its stability above a mined-out area. [ABSTRACT FROM AUTHOR]

Limited entry fracturing is rarely applied in horizontal wells in China. Compared with other horizontal fracturing methods, limited entry fracturing requires fewer down-hole tools, stimulates multiple intervals simultaneously to reduce completion costs, and is an effective treatment for horizontal wells. Some innovations are introduced for enhancing the applicability of limited entry fracturing in long cemented casing completions. Successful field experiments are presented for the thin interbedded reservoir completions. Known problems are discussed based on the analysis of a refracturing of a horizontal well applied limited entry fracturing. Recommendations on the design and operational for the successful treatments are presented. [ABSTRACT FROM AUTHOR]