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Blasting is a process in which the chemical energy of explosives is rapidly released, causing strong impact on the rock mass and achieving efficient rock fragmentation. The blasting stress wave and blasting gas generated by explosive detonation are the main driving forces for rock fragmentation. The high peak value and short duration of blasting stress wave are generally referred to as “dynamic action”, the low peak value and long duration of blasting gas are generally referred to as “quasi-static action”. The coupling mechanism between the work done by explosive detonation and the energy consumption of rock fragmentation, as well as the fine control principle of explosive energy release and blast crack propagation, are two key scientific problems that need to be solved in the fundamental theories of rock blasting. The study of “dynamic−static relationship” is one of the important ways to solve key scientific problems. Because of the complexity of the blasting process, traditional blasting design often relies on empirical formulas and field tests, posing problems such as low efficiency, high cost, and uncontrollable safety risk. Traditional designs often only focus on the final crushing effect but ignore the fine control of the blasting process. However, the study of dynamic–static relations has introduced a new approach to solution. This article uses a literature review analysis method to conduct a topic search and analysis of journal papers published in CNKI (China national knowledge infrastructure) and WOS (Science citation index-expanded database) in 2000–2023. The study of the dynamic–static relationship in rock blasting is divided into three different stages: Stages I (before 2006), Ⅱ (2007–2015), and Ⅲ (2016–present). Stage I focuses on the dynamic action of blasting stress waves, revealing the propagation mechanism of blasting stress waves and providing a scientific basis for related engineering applications. Stage Ⅱ studies the crack propagation behavior under the action of blasting stress waves; many studies researched the interaction mechanism between blasting stress waves and cracks and the change in the dynamic stress field at the crack tip, helping relevant researchers to understand the crack propagation and rock fracture process under the action of blasting stress waves. Under a national strategy, Stage Ⅲ has a clear application scenario, and the effect of blasting gas has become the focus of this stage. Through the combination of experiments and numerical simulations, the mechanism of the effect of blasting gas on rock fragmentation, energy transfer, and crack propagation during blasting is deeply discussed. These studies reveal the behavioral characteristics of blasting gas under different conditions and provide theoretical support for practical engineering applications. In addition, authors and research institutions with important contributions to the study of dynamic–static relationships are identified. Keywords and their cooccurrence relationships are revealed, highlighting the focus and trends of the research. Through a systematic review of existing research, combined with the research work and achievements of the author team, the research direction of the dynamic–static relationship in the new era has been clarified, including the distribution and efficient utilization of dynamic–static energy between the blasting stress wave and blasting gas, numerical simulation algorithms considering the real physical processes of rock blasting fracture, and quantitative control of the dynamic–static rock breaking effect of blasting stress waves and blasting gas. The in-depth study of the dynamic–static relationship will promote blasting engineering, from experience-led to theoretical guidance and from extensive to fine.

Rock blasting technology is crucial for national economic development, particularly resource extraction and infrastructure construction. This paper explores the constitutive relationships in rock blasting, proposing three evolutionary stages: constitutive relationships 1.0, 2.0, and 3.0. These stages focus on contradictory relationships, energy balance, and minimum action theory, respectively. Constitutive relationship 1.0 centers on the interaction between rock and explosive impact loads, emphasizing the offense–defense dynamic. It analyzes the dynamic mechanical response of rock materials under explosive and impact loads, highlighting the conflict and balance between the explosive force and the rock resistance. This stage provides fundamental insights into the behavior of rock materials under high-stress conditions. Constitutive relationship 2.0 approaches the problem from an energy perspective. It treats rocks with significant anisotropy, joints, fractures, bedding, and cavities as complex structural materials. This stage studies the dynamic equilibrium between load input energy and the energy required to destroy the material. By understanding the relationship between structural strength, input energy, dissipated energy, and releasable strain energy, researchers can better predict the response of complex rock structures to explosive loads and improve blasting efficiency. Constitutive relationship 3.0 examines the propagation laws of stress waves under explosive loads and their relationship with medium damage effects. This stage focuses on optimizing energy propagation paths based on the minimum action theory, aiming to maximize the effectiveness of the explosive force while minimizing unwanted damage to the surrounding rock mass. These theories not only reveal the mechanical behavior of rocks under different load conditions but also provide a theoretical basis for optimizing blasting design and improving blasting outcomes. In addition to these theoretical advancements, the integration of artificial intelligence and big data technologies offers a new approach to managing and predicting rock material performance. This paper proposes the concept of rock material engineering genes, which involves establishing a rock gene library to systematically manage the physical and mechanical parameters of rocks. By constructing performance prediction models using advanced data analytics and machine learning algorithms, this approach enhances the accuracy of predicting how different rock types will respond to various engineering applications. Such a comprehensive database has significant implications for resource extraction, geological disaster prevention, and infrastructure construction. The rock material gene library is expected to play an increasingly important role in mineral resource development, geological disaster prevention, and infrastructure construction, thereby promoting the development and application of engineering technology. Its integration with traditional blasting techniques can lead to more efficient and safer methods of rock blasting, ultimately contributing to the advancement of engineering practices and economic development of regions dependent on these technologies. This holistic approach underscores the importance of continued research and technological innovation in rock blasting and material science.

In response to the challenges of high rock strength in deep underground metal mines, difficulty in slotting, and low efficiency in excavation, based on the tunneling project at Xingshan Underground Iron Mine of Shougang Corporation, and utilizing precise per-hole blasting with digital electronic detonators, we propose a phased blasting scheme for slotting areas of straight-eye barrel-shaped grooves, combining segmentation within and between holes, as well as delays within each hole. In combination with numerical simulations and field tests, it presents a trench domain gradient detonation configuration with differential detonation in the hole area, between holes and within holes on the basis of the original conventional scheme, builds a three-dimensional(3D) model of the trench domain μsing LS-DYNA numerical simulation software, sets up the original conventional scheme and three gradient schemes for modelling, and provides a comparative analysis of the evolution of the effective peak stress in the dredged-trench zone for the original conventional blasting solution and the staged solution. The results of the numerical simulations show that the μse of short-delay inter-hole blasting can change the fluctuation pattern of the peak effective stress, and compared to the original conventional scheme, the peak effective stress state of the rock in the dredged-trench zone along the direction of the shell hole is increased by 40% to 57%, while the peak effective stress state of the rock in the radiμs of 0-30 cm at the bottom of the shell hole is increased by 84% to 92%. In addition to the numerical simulation results, field experiments were carried out to verify the results. It is clear that the combination of short-delay differential detonation between holes can improve debris crowding in mine excavation, and short-delay differential detonation within holes can improve throwing capacity, improve debris throwing after blasting in the upper part of the shell hole, and avoid affecting the blasting of subsequent shell holes. Incorporating the two in hard rock blasting can significantly improve the blasting effect and increase the hollowing progress by 28%. And better results can be obtained in rock point-excavation by μsing short delay between holes and long delay within hole settings. The results of this paper could provide a reference for similar mine production.

Mechanical rock breaking represented by boring machines is the direction of future development of vertical shaft and roadway excavation technology. In order to ensure the safety of rapid mechanical and intelligent excavation of shaft and roadway, advanced geological exploration is an essential link. The development status and characteristics of conventional advanced geological exploration technology and advanced geological exploration technology during excavation were classified and summarized from the aspects of detection range, applicable conditions, and advantages and disadvantages. Conventional advanced detection techniques each have a certain scope of application and have been well applied in the construction environment of blasting excavation method. When facing the complex construction environment of boring machines, conventional advanced detection techniques are difficult to apply. And advanced geological exploration technology during excavation can synchronously achieve excavation and advanced geological exploration, real-time prediction of unfavorable geology in front of the working face, which is the focus of research on advanced geological exploration technology for mechanized and intelligent excavation of shaft and roadway. The full face excavation machine for vertical shafts is the development direction and trend of comprehensive mechanized shaft sinking. However, its construction environment is very complex, and advanced geological detection based on seismic wave of boring machines rock breaking source is an effective prediction method. The difficulty of advanced detection method for rock breaking source of full face shaft boring machines lies in the dual complexity of construction environment and seismic wave field of rock breaking source. Solutions are proposed from multiple perspectives. For the source pilot signal, adopting multiple methods for joint denoising to suppress interference waves from rock breaking sources. For seismic record signals, a seismic record reconstruction method with cross correlation as the core is adopted to restore the effective wave field. Conduct research on full space three-dimensional detection and high-precision imaging of vertical shafts, etc. In addition, conducting joint inversion with multiple excavation geophysical methods can improve the reliability and interpretation accuracy of geological identification. The development of integrated equipment for excavation and exploration of vertical shaft tunneling machines is the direction of future in-depth research.

In recent years, the mining state of mineral resources has changed from open air to underground and from shallow to deep. In the drilling and blasting construction of deep rock masses, in-situ stress has a significant impact on the blasting effect. An improved continuum-discontinuum element method (CDEM) considering energy dissipation in the crushing zone under blasting load is used to study the stress evolution process and rupture damage characteristics of ordinary straight hole cut blasting and large empty hole cut blasting under different in-situ stress conditions based on a two-dimensional plane strain model. The numerical results show that the existence of the large empty hole enhances the reflection and stretching effect of the explosion stress wave, weakens the inhibitory effect of the ground stress on the explosion crack expansion, promotes the expansion of the main explosion crack, increases the fractal damage and damage area of the trough blast, and improves the crushing degree of the rock mass of the trough blasting. The bi-directional isobaric in-situ stress has an inhibitory effect on the propagation of blast-induced cracks, especially on the propagation of radial cracks. The larger in-situ stress weakens the interaction of blasting stress waves between holes, and the guiding effect of adjacent holes on the propagation of the main crack is weakened. With the increase of in-situ stress, the fractal dimension and fractal damage of explosion crack decrease gradually on the whole, but the fissure differentiated damage and damage area of large empty hole blasting are significantly greater than the fissure differentiated damage and damage area of ordinary straight hole blasting. It shows that in the high in-situ stress environment, the large empty hole cut blasting can still significantly increase the rock crushing degree and crushing range and improve the blasting effect and crushing efficiency.

The traditional hydraulic fracturing and new thermal-expansion cracking methods employed for measuring in-situ stress require a subsequent lagging test after borehole drilling. This post-drilling often leads to deformation, cracking, and stress release. Additionally, determining whether a crack occurs during the test or naturally after drilling is challenging, posing difficulties in ensuring testing accuracy. To address these challenges for determining the borehole wall integrity of the test point and authenticity of the fracture process in the in-situ stress analysis using conventional hydraulic fracturing methods, we used an optical sonic measurement while drilling system to conduct hydrofracturing measurements of rock in-situ stress in the southwest margin of the Ordos Plateau. The stress characteristics at the margin of the plateau platform were revealed, and the variation law for estimating in-situ stress with depth was obtained. The statistical results were then compared with those obtained for the in-situ stress in a typical area of the North China Plain. The results show that the in-situ stress obtained for the southwest platform margin of the Ordos Plateau is lower than the statistical results of the crustal stress obtained for the shallow crust of mainland China. The in-situ stresses increase linearly with depth, and the growth rate of the minimum horizontal principal stress is higher than that of the maximum horizontal principal stress. The maximum and minimum horizontal principal stresses are lower than those observed in the North China Plain. Due to the influence of the regional structure and plateau platform of the Ordos, the direction of geostress is deflected to the east compared with the North China Plain. The lateral pressure coefficients reflected by the ratio of the maximum and minimum horizontal principal stress to vertical stress are lower than those in the North China Plain. However, the difference between the maximum and minimum horizontal principal stresses is higher than that in the North China Plain. This indicates that although the overall level of in-situ stress in the plateau edge zone is lower than that in the North China Plain, the larger difference between the maximum and minimum horizontal principal stresses is conducive to causing shear failure in underground space structures, which is unfavorable for the stability of underground engineering. This shows that when designing underground projects in the plateau platform area, more attention should be paid to the direction arrangement of the shaft and roadway engineering, as well as the negative effects of low horizontal stress and high-stress difference.

The combination of water-jet and disc-cutter rock breaking is a key technology to improve the rock breaking efficiency of the full-face shaft boring machine and achieve the mechanized development of deep resources. It is a crux problem of selecting reasonable parameters for pre-cutting kerfs. In this paper, firstly, it examined the working characteristics of rock breaking with a disc-cutter driven by a conical cutter-head. Then, based on the cohesive element method, a discrete-continuous coupled numerical model for rock breaking with a disc-cutter under pre-cutting kerfs conditions was established. Comparing the intact rock mass, the influence of different pre-cut kerfs distances and depths on the stress and rock fragmentation characteristics of the rock breaking was analyzed. The three stage characteristics of dense core formation, blocky rock slag formation, and Hertz crack propagation during rock cutting with a disc-cutter were elaborated. The asymmetric fragmentation characteristics of the rock mass and the formation mechanism of rock slag in different regions were presented. Finally, a comprehensive analysis was conducted from four aspects: the force acting on the disc cutter, the rock breaking area, the specific energy consumption for rock breaking, and the degree of rock slag crushing, and the optimal range of distance and depth values for pre-cutting kerfs was determined. The research results indicate that the pre-cutting kerfs can significantly reduce the penetration force and lateral force during the rock breaking process of the SBM cutters. Compared with intact rock masses, the peak penetration force decreased by 44.0%−10.3%. The peak lateral force decreased by 35.2%−6.5%. When the spacing and depth of pre-cut kerfs are small, it will limit the range of rock breaking by the disc-cutter, and at the same time make the fragmentation of the rock mass smaller, resulting in an increase in specific energy consumption for rock breaking. As the pre-cut depth increases, the rock breaking volume first increases and then tends to be stabilized, while the specific energy consumption first decreases and then remains unchanged. Finally, it was determined that the cutting distance was 70−90 mm, and the best rock breaking effect was achieved when the cutting distance was 60−80 mm. The rock breaking volume was doubled compared to the case without cutting, and the specific energy consumption for rock breaking decreased by 69.2%. This provides a reference for the parameter design and determination of the cutter head.

Abstract This study investigates the impact of different water coupling coefficients on the blasting effect of red sandstone. The analysis is based on the theories of detonation wave and elastic wave, focusing on the variation in wall pressure of the blasting holes. Using DDNP explosive as the explosive load, blasting tests were conducted on red sandstone specimens with four different water coupling coefficients: 1.20, 1.33, 1.50, and 2.00. The study examines the morphologies of the rock specimens after blasting under these different water coupling coefficients. Additionally, the fractal dimensions of the surface cracks resulting from the blasting were calculated to provide a quantitative evaluation of the extent of rock damage. CT scanning and 3D reconstruction were performed on the post-blasting specimens to visually depict the extent of damage and fractures within the rock. Additionally, the volume fractal dimension and damage degree of the post-blasting specimens are calculated. The findings are then combined with numerical simulation to facilitate auxiliary analysis. The results demonstrate that an increase in the water coupling coefficient leads to a reduction in the peak pressure on the hole wall and the crushing zone, enabling more of the explosion energy to be utilized for crack propagation following the explosion. The specimens exhibited distinct failure patterns, resulting in corresponding changes in fractal dimensions. The simulated pore wall pressure–time curve validated the derived theoretical results, whereas the stress cloud map and explosion energy-time curve demonstrated the buffering effect of the water medium. As the water coupling coefficient increases, the buffering effect of the water medium becomes increasingly prominent.

Considering that fluctuations in temperature can cause variations in both the internal structure as well as the mineral composition of rocks, their fracture characteristics must be impacted accordingly. With the exponential development of geotechnical engineering in cold regions, it is urgent to study the influence of the sub-zero temperature environment on the mechanical properties and dynamic properties of rocks. In order to investigate the influence of sub-zero temperature gradient on the dynamic fracture characteristics of rocks, red sandstone was used for the preparation of notched semi-circular bend specimens. First, a water-saturated machine and a sub-zero temperature incubator were utilized to pretreat the rock for 48 h, conducive for both satiation and freezing processes. Subsequently, the dynamic tests were carried out utilizing an improved split Hopkinson bar experimental system with a cryogenic sub-system. Concurrently, the striker velocity was modulated by setting distinctive air pressures, following which the rock was loaded at various loading rates. The test results demonstrate that the fracture toughness of the rock has an evident loading rate effect, and the fracture toughness proliferates exponentially with the increase in the loading rate. In the event that the loading rate is certain, the fracture toughness of the rock primarily increases gradually and then expeditiously over the course of advancement from room temperature to −20 ℃. Contradictorily, the rock fracture toughness diminishes abruptly with plummeting temperature. Analysis of the rock fracture process, accommodated by a high-speed camera, revealed that the fracture process of the rock at distinctive temperatures is fundamentally equivalent, and the crack propagation speed is negligibly influenced by the temperature. Furthermore, the rock fracture mode was analyzed by employing a scanning electron microscope (SEM) system. The SEM images of the rock depicted that the fracture of red sandstone at sub-zero temperature is predominantly intergranular fracture and cement tearing, accompanied by a trace of transgranular fracture. Meanwhile, the experimentation also revealed that the number of micro-cracks in the rock significantly multiplied when the temperature declined to −25 ℃, illustrating that sub-zero temperature has a deteriorating effect on the rock. Conclusively, the influence mechanism of temperature on the internal structure of the rock is discussed, and it is assumed that the change in the internal structure of the rock is the collaborative effect of thermal expansion-cold contraction and ice-water phase transition. The interpretation of this study has substantial reference significance for the further consequential analysis of frigidity on the fracture properties of the rock.

Deep buried rock is often in a non-hydrostatic initial ground stress field, and the different stress states lead to different rock response under dynamic loading. To study the dynamic behavior of rocks under coupled non-hydrostatic pressure and dynamic loading, the dynamic compression tests under different initial stress are carried out by using the split Hopkinson pressure bar (SHPB) experimental system, and the influence of different non-hydrostatic pressure on energy dissipation and failure characteristics of rock is analyzed. Based on the test results, it is found that both axial and lateral confining pressure have a significant impact on the rock dynamic strength. Taking 8 MPa as the critical point, the rock dynamic strength first increases and then decreases with the increase of axial confining pressure, but the rock dynamic strength will continue to increase with the increase of lateral confining pressure. The rock dissipative energy gradually decreases with the increase of axial confining pressure, but the trend of dissipative energy changes with confining pressure is complicated. When the axial confining pressure is low, the dissipative energy decreases with the increase of the confining pressure, and when the axial confining pressure is high, the dissipative energy shows a characteristic of increasing first and then decreasing with the increase of lateral confining pressure. According to the apparent and internal damage patterns of the specimens, combined with fractal theory and CT scanning technology, the influence of the damage pattern of rocks under different non-hydrostatic pressure conditions is analyzed. It is found that there is a significant correlation between the apparent cracks of rock and the ratio of axial-confining pressure. When the axial confining pressure ratio is low, there are fewer cracks on the side and end faces of rock. With the increase of the axial confining pressure ratio, the number of apparent cracks of rock increases. Through the analysis of the cross-sectional and vertical slices of the rock, it is found that there are circumferential and radial cracks in the rock simultaneously, and the rock failure is controlled by the penetrating shear cracks. It also can be found that the damage of rocks under non-hydrostatic pressure conditions can be divided into two parts: the central spherical rock mass and the peripheral broken rock mass, and the damage degree of rocks increases when the axial pressure increases, while the elevation of the surrounding pressure makes the damage degree of rocks decrease.

With the increase of the depth of the blast hole, the rock clamping effect at the bottom of the blast hole is enhanced, resulting in low rock breaking efficiency and blast hole utilization. The past continuous charging method can not solve the above problems. On this basis, this paper studies the rock roadway deep hole segmented charging cut blasting technology to improve the cut blasting efficiency. Using the smooth particle hydrodynamics-finite element method (SPH-FEM), a single-hole cut blasting model with different segmented charge structures was established, and the blasting speed of rock particles in the rock, the number of rock blasting and the characteristics of blasting cavity were analyzed in the blasting process under different models. The results show that different charge structures affect the damage range of the rock near the blast hole, and the damage area of the traditional continuous charge structure in the direction of the blast hole is larger than that of the segmented charge structure. In addition, the continuous charge structure makes the energy distribution of the explosive uneven because the explosive is concentrated at the bottom of the blast hole, resulting in poor blasting effect. The segmented charge structure can increase the number of rock fragments and optimize the blasting cavity, and the rock particles accelerate twice in the process of flying. The large or small proportion of the first segment charge obviously causes the unreasonable use of explosive energy and the poor effect of blasting cavity. Under the conditions of blast hole length, rock parameters and explosive performance set in the simulation, when the first stage charge ratio is 0.4, deep-hole rock tunnel excavation and blasting can make full use of explosive energy to achieve better cut blasting effect. The optimal subsection ratio obtained by numerical simulation was applied to the blasting construction of roadway excavation, and the delay initiation of two explosives in the cut hole was realized by using digital electronic detonator. The field test results show that the segmented charging can create good blasting effect and improve the utilization rate of blast holes in deep hole cut blasting.

A plane mechanical model of rock breaking process by double disc cutter at the center of the cutterhead is established based on contact mechanics to analyze the stress evolution in the rock broken by cutters with different spacings. A continuous-discontinuous coupling numerical method based on zero-thickness cohesive elements is developed to simulate rock breaking using double cutters. The process, mechanism, and characteristics of rock breaking are comprehensively analyzed from five aspects: peak force, breaking form, breaking efficiency, crack mode, and breaking degree. The results show that under the penetrating action of cutters, dense cores are formed due to shear failure under respective cutters. The tensile cracks propagate in the rock, and then rock chips form with increasing penetration depth. When the cutter spacing is increased from 10 to 80 mm, the peak force gradually increases, the rock breaking range increases first and then decreases, the specific energy decreases first and then rises, and the breaking coefficient of intermediate rock decreases from 0.955 to 0.788. The area of rock breaking is positively correlated with the length of the tensile crack. Furthermore, the length of the tensile crack accounts for 14.4%–33.6% of the total crack length.

Abstract Drilling and blasting methods have been used as a common driving technique for shallow-hole driving and blasting in rock roadways. With the advent of digital electronic detonators and the need for increased production efficiency, the traditional blasting design is no longer suitable for deep hole blasting. In this paper, a disperse charge cut blasting method was proposed to address the issues of low excavation depth and high block rate in deep hole undercut blasting. First, a blasting model was used to illustrate the mechanism of the deep hole dispersive charge cut blasting process. Then, continuous charge and dispersed charge blasting models were developed using the smooth particle hydrodynamics-finite element method (SPH-FEM). The cutting parameters were determined theoretically, and the cutting efficiency was introduced to evaluate the cutting effect. The blasting effects of the two charging models were analyzed utilizing the evolution law of rock damage, the number of rock particles thrown, and the cutting efficiency. The results show that using a dispersed charge improves the cutting efficiency by about 20% and the rock breakage for the deep hole cut blasting compared to the traditional continuous charge. In addition, important parameters such as cutting hole spacing, cutting hole depth and upper charge proportion also have a significant impact on the cutting effect. Finally, the deep hole dispersed charge cut blasting technology is combined with the digital electronic detonator through the field engineering practice. It provides a reference for the subsequent deep hole cutting blasting and the use of electronic detonators in rock roadways.

A blasting experiment was conducted on iron ore samples by considering multiple coupling charge coefficients. The resulting internal fracture and damage characteristics were quantitatively analyzed via computerized tomography (CT), scanning, and three-dimensional (3D) model reconstruction. The results show that the iron ore primarily displayed radial and circumferential cracks along the blast hole under an explosive load. When the decoupling coefficient was small, the crack surface was dominated by transgranular fractures in the form of intracrystalline fractures. As the uncoupling coefficient increased, the crack surface exhibited transgranular and intergranular coupled fracture modes. Using fractal theory to analyze crack distribution characteristics, as the decoupled coefficient increased, the body fractal dimension tended to decrease, and the degree of damage gradually decreased. The degree of damage reached a turning point when the decoupling charge coefficient was approximately 1.33. A numerical simulation suggested that the explosion energy transmitted to the iron ore and the effective stress decrease sharply when the decoupling coefficient exceeds 1.33. In some optimal uncoupling coefficient range, excessive fragmentation of the ore body is prevented, thereby allowing full use of the explosive energy.

Abstract There is great variation in the lithology and lamination thickness of composite roof in coal-measure strata; thus, the roof is prone to delamination and falling, and it is difficult to control the surrounding rock when developing roadway in such rock strata. In deep mining, the stress environment of surrounding rock is complex, and the mechanical response of the rock mass is different from that of the shallow rock mass. For composite-roof roadway excavated in deep rock mass, the key to safe and efficient production of the mine is ensuring the stability of the roadway. The present paper obtains typical failure characteristics and deformation and failure mechanisms of composite-roof roadway with a buried depth of 650 m at Zhaozhuang Coal Mine (Shanxi Province, China). On the basis of determining a reasonable cross-section shape of the roadway and according to the failure characteristics of the composite roof in different regions, the roof is divided into an unstable layer, metastable layer, and stable layer. The controlled unstable layer and metastable layer are regarded as a small structure while the stable layer is regarded as a large structure. A superimposed coupling support technology of large and small structures with a multi-level prestressed bearing arch formed by strong rebar bolts and highly prestressed cable bolts is put forward. The support technology provides good application results in the field. The study thus provides theoretical support and technical guidance for ground control under similar geological conditions.

In order to explore the propagation characteristics of explosion wave and gas in blast-hole, design a model to simulate blast-hole charge in the laboratory, adopted a high-speed schlieren experiment system used to study the evolution characteristics of explosion wave field under two kinds of charge structures. The results showed similar explosion wave velocities for the two cartridges, the explosion wave was reflected when it reaches the hole wall, and the reflected wave velocity was lower than an incident wave. The explosion gas tends to cluster and spread in a cutting direction, resulting in intensified destruction in that direction. The explosion wave first emerges in the direction of the slits, and then moves towards the blast-hole walls, which indicates that the explosion energy can be accumulated in the slit direction and cause directional destruction of the medium. To study this process in detail, establish numerical model for the propagation of explosive in the hole. The results indicated that the detonation products first come out in the direction of the slits and then go around towards other areas in a distribution that is consistent with the observations by high-speed schlieren photography.

In hard rock deep-hole blasting excavation, blastholes are rarely utilized due to the clamping effect of the lower rock, which affects excavation progress and restricts the development and application of deep-hole blasting technology. Cut blasting is a key to improving excavation speed. In this paper, a new cutting method designating the two-step cutting technology was presented. The blasthole was divided into upper and lower sections without changing the blasthole layout. The upper section was detonated first, creating sufficient free surface for the lower section, which was detonated secondly. This created a larger cavity and improved blasthole utilization. Results showed good blasting effects for two-step cutting technology through theoretical analysis and engineering applications. The blasthole utilization rate was 96.1% when the upper and lower specific charge ratio = 0.78. This paper provides a good reference for resolving the low blasthole utilization problem in deep-hole blasting of vertical shafts within a hard rock.

Defects have a significant effect on the dynamic fracture characteristics of the medium. In this paper, the dynamic fracture experiment of specimens with bias precracks is designed by utilizing the digital laser dynamic caustics system, and the effect of defect eccentricity on the dynamic fracture behavior is studied. Research shows that crack propagation can be divided into four stages: crack initiation stage, attraction stage, repulsion stage, and specimen fracture stage. The change of defect eccentricity has no obvious effect on the crack propagation behavior in the crack initiation stage and penetration stage but has a significant effect on the attraction stage and specimen fracture stage. In the process of the interaction between defect and crack, mode I stress intensity factor decreases at first and then increases. The decrease of mode I stress intensity factor reduces with the increase of defect eccentricity. The value of mode II stress intensity factor changes from negative to positive. With the increase of defect eccentricity, the symbol of mode II stress intensity factor no longer changes. The fractal dimension and the deflection angle of crack trajectory both decrease with the increase of defect eccentricity. In addition, a numerical simulation of the experiment is conducted by ABAQUS, which provides results that are in good agreement with the experimental results.

A dynamic caustics test system was used, and different moving cracks were analysed to study the interaction between the crack growth rate, stress intensity factor, and curvature of the elliptical end of a moving crack under impact loading. Based on the linear elastic fracture mechanics theory, linearly fitting of the crack tip stress intensity factor and the elliptical curvature were employed to obtain the specific functional expressions. ABAQUS software was used to numerically simulate the moving crack fracture process passing through different elliptical curvatures. The crack tip stress intensity factor was calculated by the stress extrapolation method. The stress intensity factor obtained from the numerical calculation and the caustics test was consistent. The test and numerical simulation results showed that the direction of moving cracks entering and passing through the elliptical defects shows a certain regularity. As the ellipse curvature increased, the moving crack stress intensity factor passing through the ellipse gradually decreased, and the moving crack also passed easily through oval defects.

In order to explore the stability of coal pillar and the characteristics of roof movement during the process of roadway backfill mining (RBM), the 301 backfilling test working face of Ordos Chahasu coal mine is taken as the background. Based on the expansive pressure arch theory, the evolution process of the stope expansive pressure arch in RBM is studied; by establishing a mechanical model for the stability of coal pillars, the interactions between the height, width, and the maximum number of branches are obtained. When the width and height of the branch are both 5 m, the optimal number of the branches is obtained. Then, by establishing a mechanical model for the subsidence of the immediate roof, the process of the immediate roof subsidence is divided into three stages, namely, the formation stage of the local pressure arch, the merge stage of the pressure arch, and the expansion stage of the pressure arch. In addition, using the numerical method, the alternate bearing process of coal pillars and filling bodies and the change of the maximum supporting stress are studied, and the evolution of the pressure arch bearing structure above the stope and the staged subsidence characteristics of the roof are analyzed. The on-site test showed that the coal pillar has a good stability during the mining process. The maximum stress of the coal pillar is 16.5 MPa, and the maximum stress of the filling body is 9 MPa. The maximum settlement of the immediate roof is 102 mm, indicating that the roof control effect is good. This research will play an important role on engineering practice.

Most of the roadway excavation is completed by the drilling and blasting method. With the increase of buried depth, the existence of ground stress will generate a significant impact on the rock blasting, especially on the smooth blasting. In this study, self-made homogeneous similar materials and digital image correlation methods were used to determine influence of ground stress on the smooth blasting under uniform explosive charge parameters and various in situ stress conditions. The results show that the crack outline after blasting changes from zigzag to straight in shape, and multifractal calculation results of the rupture section between blastholes show that the fracture surface becomes flatter as ground stress increases, which is conducive to roadway formation. The strain and equivalent strain rate obviously decrease as the distance between the blasthole and measuring points increases. The same trend occurs as the confining pressure goes up. Meanwhile, a postexplosion acoustic wave test indicates that confining pressure inhibits damage of the retained rock, which is consistent with strain and equivalent strain rate results. Finally, we discussed the crack propagation mechanism of rock in smooth blasting.

Geological conditions are often complex during rock engineering construction (such as blasting and drilling) and usually involve rocks of several or multiple lithologies. However, comparative studies on the dynamic mechanical response of rocks of different lithologies are relatively few. To study differences in dynamic mechanical properties and energy dissipation of rocks of different lithologies, three kinds of rock that are common in rock engineering and have large differences in wave impedance were selected: red sandstone, gray sandstone, and granite. Samples of these three rocks were subjected to impact compression tests at different impact speeds, and the rock fragments after impact compression were screened to quantify the degree of fragmentation. The characteristics of stress wave propagation, dynamic stress-strain relationships, degree of fragmentation, and energy dissipation laws of the three rock types were compared and studied. The results show the following: (1) affected by the wave impedance matching relationship, the reflected waves, strain rates, and reflected energy of the three kinds of rock showed significant differences under the same incident stress wave. (2) The dynamic mechanical characteristics and energy dissipation laws of the rocks all had obvious strain rate effects, but the dynamic uniaxial compressive strength and energy dissipation density of the three rock types had different sensitivities to the strain rate. (3) The change trend of the energy utilization efficiency of the gray sandstone with incident energy was different from that of the red sandstone and granite; there was no obvious extreme point in the incident energy range. The three kinds of rock required different incident energies to reach maximum energy utilization efficiency. (4) The equivalent average fragment size of the three rock types decreased as a function of power with increasing impact velocity and energy dissipation density. (5) Under the same incident wave, although the reflection energy, transmission energy, and degree of fragmentation of the three kinds of rock showed significant differences, the differences in dissipation energy were small.

Aiming at soft rock ground support issues under conditions of high stress and long-term water immersion, the ground failure mechanism is revealed by taking the deep-water sumps of Jiulong Mine as the engineering background and employing field investigation, tests of rock structure, mechanical properties and mineral composition. The main factors leading to the surrounding rock failure include the high and complex stress state of the water sumps, high-clay content and water-weakened rock, and the unreasonable support design. In this paper, the broken and fractured rock mass near roadway opening is considered as ground small-structure, and deep stable rock mass as ground large-structure. A support technology focusing on cutting off the water, strengthening the small structure of the rock and transferring the large structure of the rock is proposed. The proposed support technology of interconnecting the large and small structures, based on high-strength bolts, high-stiffness shotcrete layer plugging water, strengthening the small structure with deep-hole grouting and shallow-hole grouting, high-pretensioned cables tensioned twice to make the large and small structures bearing the pressure evenly, channel-steel and high-pretensioned cables are used to control floor heave. The numerical simulation and field test show that this support system can control the rock deformation of the water sumps and provide technical support to similar roadway support designs. Keywords: High stress and soft rock, Water immersion, Failure mechanism, Large and small structures, Rework control

Since the cutting seam cartridge has sound directional breaking effect, in order to explore its blasting wave mechanism, an experimental study was conducted on the blast wave of a cutting seam cartridge using a high-speed laser schlieren system and air overpressure test system. The research results show that during cartridge explosion, the cutting seam pipe can effectively control the energy release and detonation gas dynamic behaviors. Additionally, the cartridge blast wave and the detonation gas remain highly symmetrical in expansion form. The blast wave first propagates along the cutting seam direction, and the detonation gas initially expands from the seam in the direction of the cutting seam. The pressure in the cutting seam direction is higher than that in the noncutting seam direction. The blast wave change of the whole flow field of the cutting seam cartridge was numerically simulated and was basically consistent with the results of the schlieren test in distribution form. The presence of a cutting seam prolongs the blast wave effect. During expansion of the cutting seam pipe under the influence of a blast wave, the inner wall of the cutting seam pipe is mainly subject to tensile stress. When the tensile force applied to the inner wall reaches the local yield limit, the cutting seam pipe fails.

The blasting stress wave and blasting gas generated by explosive blasting are the two main motive powers of rock fragmentation. An experimental method based on water jet test is used to study the energy distribution ratio of blasting stress wave and blasting gas; the utilization efficiency of blasting energy under different borehole constraint conditions is also analyzed. It proves that the blasting stress wave does not cause the water jet, and the blasting gas is the only power of the water column jet. The results show that the energy of the blasting gas and blasting stress wave respectively account for about 64% and 36% of the total energy generated by the explosion of lead azide. The utilization efficiency of the blasting gas energy under strong, medium, and weak constraint conditions is 100%, 80%, and 52%, respectively. The borehole constraint condition is crucial for the effective utilization of blasting energy.

This study uses a dynamic caustic technique to study the crack propagation in a medium containing an unfilled joint under blasting. The results show that for the medium containing a vertical unfilled joint, the reflected dilatational wave from the joint tends to suppress both the K I d and the velocity of the opposite propagating crack. However, for the medium containing an oblique joint, the reflected wave from the joint increases K II d , and induces the opposite propagating crack deflect from its original path. Compared with the medium with a vertical joint, the wing cracks are more easy to initiate at the oblique joint where a significant stress concentration is formed under the diffraction of the blast wave. Combined with numerical results, it is found that the wing crack deflects in the clockwise direction when the shear stress was negative, and it turns to counterclockwise when the shear stress was positive.

Roadway support in swelling soft rocks in coal mines has become a critical challenge in recent years. For deformation control in swelling soft rocks, high strength sets are preferred in sites. But high strength always means high costs. Therefore, higher strength sets with not too much cost will be more welcomed in situ. Based on this, three new sets, including a floor beam set, a roof + floor beams set, and a roof + floor beams + braces set, have been developed in the present research. Strength comparisons and costs comparisons have been conducted in this research. Results illustrate that compared with the original set, in the floor beam set, the relative strength of bottom corners reaches 2.964, while the relative cost reaches 1.294; compared with the original set, in the roof + floor beams set, the relative strength of the top arch reaches 2.345, while the relative strength of bottom corners reaches 2.964, and the relative cost reaches 1.568; and compared with the original set, in the roof + floor beams + braces set, the relative strength of the top arch reaches 2.635, and the relative strength of bottom corners reaches 5.905, but the relative cost reaches 1.930. Floor beam set and roof + floor beams set illustrate higher strength and not too higher costs than the original set. Although the roof + floor beams + braces set exhibit much higher strength, they also demonstrate much higher costs than the original set. These new sets can be chosen according to different geological conditions in situ.

The depth of mineral resources like coal continuously increases due to the exhaustion of shallow resources, and the characteristic of high ground stress in deep ground inevitably affects fracture of rock blasting. Combining with high-speed photography technology, the digital image correlation method (DIC) is introduced into experimental study on explosive mechanics. And strain evolution process of blasting under high stress condition is obtained by using the model experiment method. The preliminary results show that high stress condition has no obvious effects on the propagation law of blasting stress wave or its stress peak in the medium. In addition, it is found that medium in the “elastic vibration area” by conventional blast zoning is not always “elastic,” and on this basis, the concepts of “plastic area” and “quasielastic area” are put forward. The high stress condition does not influence partition range of above “plastic area” or “quasielastic area,” but in the “plastic area,” the high stress condition decreases both plastic strain value and its decay rate of relevant gauging points.

This paper studies blast-induced wing crack behavior in a dynamic–static superimposed stress field using high-speed photography in combination with the optical method of caustics. With a static–dynamic loading setup, four PMMA plate specimens with pre-existing cracks under different static loading and the same dynamic loading were tested to observe the mechanical characteristics and the kinematic characteristics of blast-induced wing cracks during the propagation process, including crack length, crack velocity and dynamic stress intensity factor (SIF) at the crack tip. The results show that the behavior of the blast-induced wing crack is affected by the explosion stress wave and initial static stress, and the initial static stress with the direction being perpendicular to the wing crack propagation direction hinders crack propagation. Furthermore, the boundary constraint condition of the specimen plays an important role on the behavior of the crack propagation in the experiment. Keywords: Dynamic–static superimposed stress field, Blast-induced wing crack, Pre-existing crack, Caustics

There is high demand for roadway support in coal mines for the swelling soft rocks. As high strength steel sets can be taken as an effective alternative to control large deformation in this type of rocks, based on an original set, three new sets, including a floor beam set, a roof and floor beams set, and a roof and floor beams and braces set, are proposed in this research. In order to examine the strengths of new sets, four scaled sets of one original set, and three new sets, have been manufactured and tested in loading experiments. Results indicated that three new sets all exhibited higher strength than the original set. In experiments, the roof beam in set plays a significant effect on top arch strengthening, while the floor beam plays significant effect on bottom arch strengthening. The maximum bearing capacity and stiffness of the top arch with roof beam are increased to 1.63 times and 3.06 times of those in the original set, and the maximum bearing capacity and stiffness of the bottom arch with floor beam are increased to 1.44 times and 3.55 times of those in original set. Based on the roof and floor beams, two more braces in the bottom arch also play a significant effect in bottom corners strengthening, but extra braces play little role in top arch strengthening. These new sets provide more choices for roadway support in swelling soft rocks.