Rock Roadway Research Articles

Comprehensive evaluation of shaped charge blasting effect of rock roadway based on entropy-weighted matter-element extension model

In order to accurately evaluate the cumulative blasting effect of roadway, an entropy-weighted matter-element extension model was introduced to evaluate the blasting effect. Through the analysis of blasting quality, blasting economic and technical benefits, and blasting safety, 12 indexes such as bulk rate, blasting shape, and explosive consumption were selected to build a comprehensive evaluation model. Then, in order to avoid the uncertainty of subjective weighting method in the evaluation process, the entropy weighting method was introduced to determine the weight coefficient of matter-element index. Finally, the model is applied to the blasting example of Kong Zhuang coal mine, and the grading of blasting effect is evaluated qualitatively and quantitatively. Results show that the evaluation of the model is consistent with the actual grade. In addition, compared with ordinary smooth blasting, cumulative blasting can reduce the explosive consumption by 27%, increase the blasthole utilization rate to 97.1%, and improve the forming quality of roadway.

In-situ investigation on fractured evolution law of surrounding rock in weakly cemented soft rock roadway

ABSTRACT Weakly cemented soft rock has a great influence on the deformation and stability of roadway in the process of roadway excavation. There are different requirements for the excavation and support of roadway under such geological conditions. Based on the Hongqingliang Mine geological conditions, the deformation and failure characteristics of surrounding rock such as dry blasting, spalling and over width of roadway are analyzed. Through the on-site monitoring of surrounding rock deformation, bolt (cable) stress, and roof drilling in weakly cemented soft rock roadway, the results show that the deformation and failure of roadway surrounding rock can be divided into fast deformation and slow deformation; the force of bolt increases first and then decreases, finally tends to be stable, while the force of cable increases rapidly and then tends to be stable; at the same time, through the roof borehole detection, the roof fracture concentrates in the range of 3 m of the roof, and with the excavation process proceeding, the mudstone in the deep roof also appears a certain fracture. The breakdown position is about 6 m away from the roof.

Research on Failure Process and Precursor Information of Surrounding Rock of Deep Layered Roadway Based on Digital Image Correlation Method

In order to reveal the deformation and failure mechanism of surrounding rock of deep layered roadway, the deformation field of physical model experiment of surrounding rock of roadway with 45 degree dip angle is monitored by digital image correlation (DIC) method, and the deformation and failure process is analyzed. In view of the difficulties in monitoring and early warning of surrounding rock deformation and failure disaster, based on DIC, a new method for identifying the precursor information of surrounding rock failure called image coefficient of variation (ICV) is proposed, taking the displacement change and displacement change rate in the deformation field obtained from DIC analysis as calculation individuals, the ICV is obtained by calculating the whole field coefficient of variation (CV). The research shows that the DIC method is an effective non-contact deformation monitoring method in the tunnel roadway physical model experiment. Through comparative analysis, it is found that the variation trend of ICV curve can be used as the precursor information of roadway surrounding rock failure, which provides a new early warning index for roadway surrounding rock instability disaster.

Analysis on Characteristics of Surrounding Rocks of Roadway and Bearing Structure Based on Stress Regulation

To address the prominent status of great deformation and difficult maintenance of the roadway under high stresses, this study investigated the mechanical characteristics of surrounding rocks and bearing structural stability in a roadway under adjustment and redistribution of stresses through theoretical analysis, numerical simulation, and engineering field test. Stability forms of the bearing structure of roadway surrounding rocks were analyzed by using the axis-changing theory from the perspectives of surrounding rock, mechanical properties of roadways, surrounding rock stress distribution, and mechanical mechanism of the bearing structure. It is suggested that the surrounding rock stress distribution state is improved and the bearing structure is optimized through unloading and reinforcement construction. A mechanical model of roadway excavation was constructed to analyze the influences of excavation spatial effect on the stress releasing and bearing structure of surrounding rocks. A rock postpeak strain softening and dilatation model was introduced to investigate the mechanical characteristics of the surrounding rock mass in the rupture residual zone and plastic softening zone in a roadway. Moreover, we analyzed the influences of unloading and reinforcement construction on the stress path and mechanical characteristics of the rock unit model, which disclosed the adjustment mechanism of the bearing structure of surrounding rocks by the failure development status of rocks. A numerical simulation on the distribution of surrounding rock stress fields and adjustment features of the bearing structure after roadway excavation and unloading and reinforcement construction was carried out by using the FLAC3D program. Results demonstrate that the unloading construction optimizes the axial ratio of spatial excavation in a roadway and the reinforcement zones on both sides are the supporting zones of the bearing structure. Moreover, the ratio between the distance from two side peaks to the roadway sides and the distance from the roof and floor peaks to the excavation space is equal to the coefficient of horizontal pressure. In other words, the final collapse failure mode of surrounding rock is that the long axis of the excavation unloading space points to the same direction with the maximum principal stress of the primary rock. Reinforcement forces the surrounding rocks to form a “Ω-shaped” bearing structure, which is in favor of the long-term maintenance of the roadway.

Research on Deformation Characteristics and Control Technology of Soft Rock Roadway under Dynamic Disturbance

In the mining process of an underground coal mine, the dynamic load often causes great damage to the roadway and affects the normal mining of coal mine. In this paper, the deformation of surrounding rocks under static load and different disturbance intensities is studied by numerical simulation. The results show that under the same static load condition, the greater the dynamic load strength is, the more obvious the roadway roof displacement subsidence is. With the increase in dynamic load propagation distance, the amplitude of the dynamic load waveform decreases gradually. Under the same disturbance load intensity, the variation of roadway displacement with different disturbance load frequencies is studied. According to the influence of dynamic load on the deformation of the roadway, a combined support plan of shotcrete anchor net and reinforcement anchor cable is proposed. Finally, the rationality of the optimized support scheme is verified by numerical simulation and field results. The results show that the combined support scheme can effectively increase the strength of the broken soft rock and reduce the deformation of the surrounding rock. At the same time, it releases the expansion energy generated by the mutual compression and deformation of the rock layers, effectively maintaining the long-term stability of the roadway.

Study on Monitoring Technology of Surrounding Rock in Deep Layered Roadway Based on Constant Resistance and Large Deformation Bolt

The stability monitoring of surrounding rock in layered roadway is an important method to ensure the safety of deep mining coal mine. In view of the actual situation of roadway stability monitoring, based on similarity theory, the deep roadway model is built and small-sized ordinary bolts and constant resistance and large deformation (CRLD) monitoring bolts are developed to detect the mechanical real-time information of surrounding rock in the model, the accurate measurement information of the displacement field and the force value of the bolts are obtained. According to the time series characteristics of the deformation field and the force curves of the monitoring bolts, the criterion of stability and instability pattern of surrounding rock in deep layered roadway are studied. The results show that the force monitoring method based on CRLD bolt is superior to displacement monitoring, the force monitoring curve of CRLD bolt can be divided into stable mode and instability mode, the characteristic of stable mode curve is rising slowly and the instability model with rapid rising and falling stages. The stability monitoring system of roadway with CRLD bolt is developed and applied in deep rock roadway, it has been proved by field practice that the early warning of surrounding rock instability of deep layered roadway is feasible.

Research on the Formation and Development of Plastic Zones in Surrounding Rocks of Roadways Containing Gas

Considering that the gas in the gas-containing roadway has an important influence on the deformation and failure of the surrounding rock, based on the law of gas migration in the rock mass, a mathematical model of fluid–solid coupling of gas-containing coal and rock is established. Through numerical simulation, the distribution of gas in roadway containing gas and the formation and development of plastic zone of surrounding rock are studied. Research results: (1) The shape of the plastic zone of the surrounding rock of the gas-containing roadway is determined by the in-situ stress. With the increase of the principal stress ratio, the plastic zone of the surrounding rock transforms from a circle to an ellipse, and finally into a butterfly shape. (2) With the increase of the principal stress ratio of the roadway, the plastic zone of the surrounding rock of the gas-containing roadway gradually develops into a butterfly shape. The volume of the plastic zone continues to increase, and the rate of increase continues to accelerate. (3) With the increase of the principal stress ratio of the roadway, the shape of the plastic zone in front of the excavation work of the gas-containing roadway has obvious differences. The circular or elliptical plastic zone has a small leading distance in front of the excavation face, and the section shrinkage rate of the plastic zone is slow, and the overall shape is truncated cone. The butterfly plastic zone has a large leading distance in front of the excavation face, and the section shrinkage rate of the plastic zone is fast. Therefore, when the speed of roadway excavation is relatively fast, it is easy to cause accidents such as coal and gas outburst in front of the butterfly blades in the butterfly plastic zone and the excavation work.

Study on Seepage Simulation of High Pressure Grouting in Microfractured Rock Mass

In coal mines, under high in situ stress and strong mining activity, roadway surrounding rock commonly contains large amounts of larger fractures and microfractures. Along with the large deformation and continuous rheology of the soft rock roadway, the fractures in the surrounding rock are likely to be compressed and closed, forming undeveloped microfractures, which hinder conventional grouting support methods. Based on the fluid-solid coupling between slurry seepage and microfracture deformation, a theoretical model of microfracture grouting seepage is established. A program for the analysis and calculation of microfracture grouting is developed to quantitatively describe the variation in slurry seepage distance and fracture opening. Numerical experiments are carried out to study the grouting seepage of microfractures under different grouting pressures and fracture opening conditions, and the variation rules for the spatial distribution of fracture opening and slurry seepage distance during grouting pressure are obtained. Fluid-solid coupling has a significant influence on grout seepage characteristics. The grouting pressure and the fracture opening changes are nonlinearly attenuated along the grout seepage direction.

Experimental Investigations on Rheological Properties of Mudstone in Kilometer-Deep Mine

The soft rock roadway in deep high-stress environment has the problems of strong rheology and large deformation. Based on the analysis of the stress distribution of the surrounding rock of the roadway in a kilometer-deep mine, rheological tests under different stress paths are carried out for mudstone in a kilometer-deep mine. The rheological deformation curve, damage characteristics, and change rule of the main mechanical parameters of mudstone under different stress conditions are studied. The results show the following: (1) the peak strength of the triaxial compression of mudstone is closely related to confining pressure, and, with increasing confining pressure, the confining pressure effect decreases gradually; (2) the strain increases slowly under uniaxial loading, and, with increasing axial pressure, the velocity of rheological deformation increases nonlinearly, and the amount of mudstone deformation increases with time; (3) under the condition of unloading confining pressure with constant axial pressure, with decreasing confining pressure, the instantaneous axial and radial strains of mudstone specimen increase nonlinearly, the rheological strain and velocity of mudstone increase gradually, and the lateral rheological strain is close to the axial rheological strain; and, (4) in the unloading confining pressure with axial compression triaxial test, with increasing deviating stress, the axial and radial instantaneous strain increments of mudstone decrease gradually, the lateral strain and rheological velocity of mudstone increase gradually, and the lateral strain is approximately 2.05 times the axial strain. These conclusions reveal the rheological characteristics of the mudstone under different surrounding rock conditions and provide a theoretical basis for the excavation deformation and support control of roadways.

Research on Surrounding Rock Control Technology of Dongbaowei Deep Mining Roadway

In order to explore the stability control of surrounding rock in the process of deep mining, comparative analysis of stress, deformation, and fracture characteristics of surrounding rock of deep and shallow mining roadway in dongbaotou coal mine, laboratory experiments, field measurement, numerical simulation, and field industrial experiments were adopted to put forward the control plan of the surrounding rock in deep roadway, which were verified by field industrial experiments. The results of laboratory experiments and field experiments show that the mechanical properties of deep roadway surrounding rock of Dongbaowei Coal Mine are significantly lower than those of the shadow roadway, mainly due to the development of joints and fractures of the overlying strata in the deep stope, serious impact on the disturbance of the roadway which has been made by the strong pressure of the stope, and reduced crushing strength of surrounding rock. Through comparative analysis of deep roadway support plan carried out by numerical simulation, the support scheme suitable for Dongbaowei Coal Mine is put forward, which is applied in the field. Field industrial experiments show that after the optimization of support parameters, the deformation of surrounding rock of roadway is well controlled. The displacement of surrounding rock of roadway is basically stable after 10∼15 days. The support of surrounding rock of roadway has good effect, which achieves the goal of stability control of deep roadway surrounding rock.

Impact analysis of pressure-relief blasting on roadway stability in a deep mining area under high stress

In the development of deep underground engineering operations, the surrounding rock is prone to large deformation, rockbursting, and other major engineering disasters. Pressure-relief blasting can improve the stress field in a deep rock mass and prevent the occurrence of roadway collapse. Based on the excavation of the Sandaoshan Mine, ANSYS/LS-DYNA dynamic finite element software is used to simulate the damage and fracture area in the surrounding rock of the roadway under three types of pressure-relief blasting schemes. The strength of the rock mass in the damaged area is reduced, and then the ground stress balance calculation is conducted. The stability of the surrounding rock rock a deep roadway is compared and analysed from aspects of stress and energy and it is verified by theoretical calculation of impact energy factor. The research results show that the non-penetrating fracture zone formed by pressure-relief blasting will increase the stress concentration of the surrounding rock of the roadway, which is more unfavourable to engineering safety. When a reasonable blasting scheme is designed to form a penetrating fracture zone in the surrounding rock of roadway, the concentrated high ground stress in the surrounding rock can be transferred to the deeper part of the rock mass, thereby reducing the elastic strain energy, reducing the risk of a rockburst. Pressure-relief blasting increases the rock mass quality in the failure zone formed by excavation, and reduces the impact energy factor k. When k decreases below the energy threshold, it can prevent rockbursting and ensure the stability of the surrounding rock of the roadway.

Innovation and future of mining rock mechanics

The 121 mining method of longwall mining first proposed in England has been widely used around the world. This method requires excavation of two mining roadways and reservation of one coal pillar to mine one working face. Due to considerable excavation of roadway, the mining roadway is generally destroyed during coal mining. The stress concentration in the coal pillar can cause large deformation of surrounding rocks, rockbursts and other disasters, and subsequently a large volume of coal pillar resources will be wasted. To improve the coal recovery rate and reduce excavation of the mining roadway, the 111 mining method of longwall mining was proposed in the former Soviet Union based on the 121 mining method. The 111 mining method requires excavation of one mining roadway and setting one filling body to replace the coal pillar while maintaining another mining roadway to mine one working face. However, because the stress transfer structure of roadway and working face roof has not changed, the problem of stress concentration in the surrounding rocks of roadway has not been well solved. To solve the above problems, the conventional concept utilizing high-strength support to resist the mining pressure for the 121 and 111 mining methods should be updated. The idea is to utilize mining pressure and expansion characteristics of the collapsed rock mass in the goaf to automatically form roadways, avoiding roadway excavation and waste of coal pillar. Based on the basic principles of mining rock mechanics, the “equilibrium mining” theory and the “short cantilever beam” mechanical model are proposed. Key technologies, such as roof directional presplitting technology, negative Poisson's ratio (NPR) high-prestress constant-resistance support technology, and gangue blocking support technology, are developed following the “equilibrium mining” theory. Accordingly, the 110 and N00 mining methods of an automatically formed roadway (AFR) by roof cutting and pressure releasing without pillars are proposed. The mining methods have been applied to a large number of coal mines with different overburdens, coal seam thicknesses, roof types and gases in China, realizing the integrated mode of coal mining and roadway retaining. On this basis, in view of the complex geological conditions and intelligent mining demand of coal mines, an intelligent and unmanned development direction of the “equilibrium mining” method is prospected.

Study of the Double Wedge Cut Technique in Medium-Depth Hole Blasting of Rock Roadways

A double wedge cut was used to improve the cut effects in the medium-depth hole blasting of rock roadways. First, the cavity formation mechanisms of single wedge cut and double wedge cut were analysed theoretically. The results show that the cavity formation resistance of the second-order wedge cut is reduced by the first-order wedge cut. Second, simulations of the two cut modes were conducted, which visualize the stress wave evolution and indicate that the stress wave of the first-order cut holes can cause pre-damage to the rock mass in the second-order cut cavity. A comparison of the stress field distribution shows that the first-order cut holes significantly increase the stress field intensity within 0 ~ 1.6 m to enhance the failure of the rock mass in the first-order cut cavity. Hence, the rock mass in the first-order cut cavity can easily be thrown out to create a new free face, which reduces the clamping effect of the second-order wedge cut and exacerbates the tensile failure of the rock mass in the second-order cut cavity. Thus, the difficulty of second-order wedge cut is reduced. Finally, blasting experiments were performed in a rock roadway. Using the double wedge cut, the average footage increased by 0.31 m, the average utilization rate of blastholes increased by 12.4%, and the average specific charge decreased by 0.20 kg·m−3, which proves the superiority of this cut mode.

Experimental Investigation on the Mechanical Response of Coals to Uniaxial Compression and Low-Speed Dynamic Loading

The surrounding rock of roadways in underground coal mines will lose its stability or even collapse under gas explosions, especially roadways surrounded by coals. The dynamic mechanical properties of coals were tested in order to investigate the dynamic response of coals under gas explosions. The static mechanical properties of coals were also tested as comparison. It is found that the dynamic stress-strain curves showed no obvious pore compaction stage comparing with uniaxial loading. The dynamic compression strength and the elastic modulus are obviously larger than those obtained in the static mechanical properties test, and the dynamic strain shows an obvious hysteresis phenomenon. The ultimate strain and absorbed energy increased linearly with increase of the strain rate. With the increase of dynamic loading, the fragment size of coal cores decreased obviously. The results could provide a reference for the antiexplosion design of the coal roadway.

Research on Technology of Supporting in Super‐Large Section Cut in Working Face with Large Mining Height

For the support problem of the super‐large section cut in working face with large mining height, the 1105 cut pilot chamber of Zhaogu No. 2 Mine, the roof strata structure detection and the strata movement rule research were conducted. The results prove that concentrate fracture area, gradually sparse fracture area, and rare fracture area regularly distributed from the surface to the deep area of the roof of 1105 cut, and less fracture exists in the rock stratum of roof above 3.5 m, and the stratum of roof within the range of 4–6 m is stable. Authors propose the long bolt and cable combined supporting technology and optimized the design plan applying theoretical calculation and computer numerical simulation. The scheme has been applied in the field of the 1105 super‐large section cut in Zhaogu No. 2 Mine. The monitoring results show that the scheme can effectively control surrounding rock of roadway, and the support with long bolt has good effectiveness.

Analysis of pressure relief and outburst prevention effect and mining depth effect of floor roadway in single serious outburst coal seam

In order to solve the serious problem of single serious outburst coal seam gas disaster, based on the gas geological conditions of Jiangxi Fengcheng Qujiang company, theoretical analysis, numerical simulation, field test and other comprehensive research methods were used to analyze the partition fracture law of roadway surrounding rock under different mining depth conditions. The results show that: under the conditions of high ground stress, high temperature and other environmental conditions, the radius of pressure relief loose circle of surrounding rock of roadway is significantly increased, and it is significantly larger than that of shallow part. In the deep area of - 800m elevation, the distance between floor roadway and coal seam is optimized to be 12 ~ 15m. The field test results show that the original permeability coefficient of overlying coal seam of floor roadway increases by 55.74 times, and the pressure relief effect is good.

Deformation Mechanism and Support Technology of Deep and High‐Stress Soft Rock Roadway

In this study, the analysis and control of stability of surrounding rock in deep fractured soft rock roadway located in the underground mine of Jinfeng gold mine in Guizhou Province, China, has been investigated. The surrounding rock of roadway has been analyzed to characterize its deformation and failure mechanism through field survey, testing of rock physical and mechanical properties, in situ stress measure, analysis of mineral components of rock, and investigation of rock fragmentation degree. Based on the numerical simulation technology, the influence of different factors on the stability of roadway is studied. The physical and mechanical properties of surrounding rock and the bearing capacity of surrounding rock layer are to be improved to maintain the stability of broken soft rock roadway as high ground stress, rock fragmentation, and poor lithology leading to tunnel instability. Hence, a high‐strength “cable bolt + fiber‐reinforced shotcrete + steel mesh + split sets + resin bolt + cement grouting” combined support system has been proposed to improve the effective bearing structure significantly with high integrity and bearing capacity.

Bearing Capacity of Concrete Filled Steel Tube Circular Arch under the Six‐Point Uniformly Distributed Loading and Its Engineering Application

The influence of rise‐span ratio on the bearing performance of concrete filled steel tube (CFST) circular arch was studied in this paper, three groups of CFST circular arch specimens with different rise‐span ratios (0.154, 0.207, and 0.26) were selected, the six‐point uniformly distributed loading was performed, and bearing performance experiments on CFST circular arch specimens with fixed ends were carried out. In this study, the ultimate bearing capacity and deformation failure characteristics of CFST circular arch specimens were obtained. The comparative analysis shows that the deformation evolution of CFST circular arch specimens has experienced compaction stage, elastic stage, elastic‐plastic stage, and plastic stage. In the elastic‐plastic and plastic deformation stages, the circular arch shows good ductility and bearing capacity. The bearing capacity of the circular arch is significantly affected by the rise‐span ratio. Compared with circular arch specimens with a rise‐span ratio of 0.154, the yield load of specimens with a rise‐span ratio of 0.207 and 0.26 is increased by 50.8% and 61.5%, and the ultimate bearing capacity is increased by 42.7% and 68.3%, respectively. The larger the rise‐span ratio, the greater the yield load and ultimate bearing capacity of the specimen and the stronger the deformation resistance of circular arch. The numerical simulation on the bending resistance process of circular arch was performed by ABAQUS to present the compression failure process of steel tube and core concrete. The simulation results are in good agreement with the experimental results. The experimental and simulation results show that the circular arch first yields at the inner side of the arch foot, and the curvature of different positions of the specimen is no longer consistent. When the ultimate bearing capacity is reached, the steel pipe at the arch foot obviously heaves, and the hooping effect of the steel pipe on the concrete is invalid. Based on the above research results, a closed composite support scheme of “bolt mesh shotcrete + vertical elliptical CFST support + steel fiber concrete shotcrete layer + reinforced anchor cable” was proposed for the extremely soft rock roadway and successfully applied in the Qingshuiying coal mine.

Instability Mechanism and Key Control Technology of Deep Soft Rock Roadway under Long‐Term Water Immersion

More and more attention has been paid to the supporting problem of deep soft rock roadway floor with long‐term water immersion in recent years. However, the existing soft rock roadway support technology rarely takes into account the influence of the immersion softening phenomenon of the roadway floor and the self‐supporting structure characteristics of the surrounding rock on the stability of the surrounding rock at the same time, and the influence of the creep characteristics of rock on the deformation zone of the surrounding rock requires further research on the nature and division of the self‐supporting structure of the surrounding rock. In response to the issues mentioned, based on the loading and unloading properties of the surrounding rock of the soft rock roadway, a new concept of the internal and external self‐bearing structure was proposed. The fact of water‐immersed mudstone softening in the soft rock roadway floor was revealed through the field practice, and the shape of the internal and external bearing structure was determined based on the in situ monitoring results. Then, the instability mechanism of the internal and external self‐bearing structure of the surrounding rock was analyzed, the position of the critical control point was calculated, and the key control technology based on the method of controlling floor heave by using double‐row anchor cables to control the deformation of the roadway sides was put forward. Finally, the field industrial test showed that this support technology can effectively control the deformation and failure of soft rock roadway in the case of water immersion on the floor. This work can provide a technical reference for similar roadway support designs.

Mechanical properties and constitutive analyses of basalt fiber crumb rubber mortars in soft rock roadways

Uniaxial compressive stress-strain curves of several groups of basalt fiber crumb rubber mortars (BF-CRM) with different contents are tested. By comparing with the GZH model, the improved values of the parameters of the BF-CRM constitutive model based on the GZH model are obtained. Then, taking the supporting scheme of main substation of the mine as the background, using FLAC3D to simulate the roadway support, using BF-CRM to replace the ordinary mortars in the original support, and combining with the triaxial compression test of different confining pressure, the application effect of BF-CRM in roadways support is studied and analyzed.