Abstract There are many soft-rock roadway coal mines in China. The surrounding rocks of the high-stress soft-rock roadways in deep mine are especially difficult to be supported using the traditional supporting way. In...Abstract There are many soft-rock roadway coal mines in China. The surrounding rocks of the high-stress soft-rock roadways in deep mine are especially difficult to be supported using the traditional supporting way. In this study, the south wing rail roadway on the second level of Yunjialing coal mine in China was used as an example to analyze the deformation and failure characteristics and influencing factors of roadway. On this basis, this study proposed the equalized yielding support idea which employs the yielding rings to realize the pressure equalization on the bolts and cables in the section. To achieve this purpose, the first bolt-mesh-cable equalizing pressure yielding support was integrated with the second grouting reinforcement. The results proved that the yield rings of the bolts and cables on the spandrel of the arched roadway firstly developed yielding deformation; then the deformation extended to the vault of the roadway; the bolts and cables achieved a yielding extreme value of 15 and 18 tonnes, respectively. The roadway surrounding rock tended to be stable at the 26th day after the maintenance. The equalizing pressure yielding supporting technology plays a moderate pressure-releasing and actively controlling role on the surrounding rocks in the soft-rock roadway with large deformation.展开更多
Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,whic...Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,which makes it difficult to meet the requirements of ground control under complex conditions. As a new support form with high strength and rigidity, the confined concrete arch plays an important role in controlling the rock deformation under complex conditions. The section shape of the tunnel has an important impact on the mechanical properties and design of the support system. However, studies on the mechanical properties and influence mechanism of the new confined concrete arch are rarely reported. To this end, the mechanical properties of traditional U-shaped steel and new confined concrete arches are compared and comparative tests on arches of circular and straight-leg semicircular shapes in deep tunnels are conducted. A large mechanical testing system for underground engineering support structure is developed. The mechanical properties and influence mechanism of confined concrete arches with different section shapes under different loading modes and cross-section parameters are systematically studied. Test results show that the bearing capacity of the confined concrete arch is 2.10 times that of the U-shaped steel arch, and the bearing capacity of the circular confined concrete arch is 2.27 times that of the straight-leg semicircular arch. Among the various influencing factors and their engineering parameters,the lateral stress coefficient has the greatest impact on the bearing capacity of the confined concrete arch,followed by the steel pipe wall thickness, steel strength, and core concrete strength. Subsequently, the economic index of bearing capacity and cost is established, and the optimization design method for the confined concrete arch is proposed. Finally, this design method is applied to a high-stress tunnel under complex conditions, and the deformation of the surrounding rock is effectivel展开更多
To investigate the creep and instability properties of a cemented gangue backfill column under a highstress area,the uniaxial compression creep tests were conducted by single-step and multi-step loading of prismatic s...To investigate the creep and instability properties of a cemented gangue backfill column under a highstress area,the uniaxial compression creep tests were conducted by single-step and multi-step loading of prismatic samples made of cemented gangue backfill material(CGBM)under the high stressstrength ratio.The creep damage was monitored using an electrical resistivity device,ultrasonic testing device,and acoustic emission(AE)instrument.The results showed that the CGBM sample has a creep hardening property.The creep failure strength(CFS)is slightly larger than the uniaxial compressive strength(UCS),ranging in ratio from 108.9%to 116.5%.The instantaneous strain,creep strain,and creep rate increase with increasing stress-strength ratio in the single-step loading creep tests.The instantaneous strain and creep strain decrease first and then increase during the multi-step loading creep process.The axial creep strain of the CGBM column can be expressed by the viscoelastic-plastic creep model.Creep instability is caused by the accumulation of strain energy under multi-step loading and the continuous lateral expansion at the unconstrained middle position during the creep process.The creep stability of a CGBM column in a high-stress area can be monitored based on the variation of electrical resistivity,ultrasonic pulse velocity(UPV),and AE signals.展开更多
Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host fra...Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host frames and hydraulic pumps,which could lead to great investment.Low-cost testing machines clearly always have great appeal.In this study,a new approach is proposed using thermal expansion stress to load rock specimens,which may be particularly suitable for tests of deep hot dry rock with high temperatures.This is a different technical route from traditional mechanical loading through hydraulic pressure.For the rock mechanics test system of hot dry rock that already has an investment in heating systems,this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes.This paper presents the basic principle and a typical design of this technical solution.Preliminary feasibility analysis is then conducted based on numerical simulations.Although some technical details still need to be resolved,the feasibility of this loading approach has been preliminarily confirmed.展开更多
Underground mining is going to be deeper gradually because near surface resources are going to be depleted. Therefore, risk of seismic events in underground mines is escalating. Additionally, existence of the large ra...Underground mining is going to be deeper gradually because near surface resources are going to be depleted. Therefore, risk of seismic events in underground mines is escalating. Additionally, existence of the large ratio of horizontal to vertical stress, could be a potential reason for high-stress condition and occurrence of dynamic activities. Depending on various parameters such as the level of induced stress, rock properties, etc., ground demand changes and it is difficult to estimate. On the other hand,under seismic condition, energy dissipation and deformation capacity of supports is the most important factors, however, rock support performance factors in dynamic conditions are still under investigation.Expanding the knowledge of reinforcement behaviour and capacity, specifically that of the rockbolt as a primary element in seismic conditions, would help to develop a suitable, safe and economic support design. This paper contains various methods to estimate ground demand including the intact rock properties approach, failure thickness and ejection velocity estimation, and rockburst damage potential method. It also covers measurement methods of rockbolts energy dissipation capacities such as drop test,blasting simulating, back calculation and momentum transfer measurement methods. A large-scale dynamic test rig is also explained. Based on the findings, a table and a graph to show the applicable range of each type of rockbolts were presented. Suitable rockbolt types for various ground energy demand and deformation capacity range were categorised in the table and the graph. The presented support selection method facilitates the selection of a suitable reinforcement system at the preliminary stages of design and guides the designer to adjust the support reinforcement system based on observed ground and support reaction.展开更多
In an extensional shear zone in the Talea Ori, Crete, quartz veins occur in high-pressure low-temperature metamorphic sediments at sites of dilation along shear band boundaries, kink band boundaries and boudin necks. ...In an extensional shear zone in the Talea Ori, Crete, quartz veins occur in high-pressure low-temperature metamorphic sediments at sites of dilation along shear band boundaries, kink band boundaries and boudin necks. Bent elongate grains grown epitactically from the host rock with abundant fluid inclusion trails parallel to the vein wall indicate vein formation by crack-seal increments during dissolutionprecipitation creep of the host rock. The presence of sutured high-angle grain boundaries and subgrains shows that temperatures were sufficiently high for recovery and strain-induced grain boundary migration, i.e. higher than 300 -350℃, close to peak metamorphic conditions. The generally low amount of strain accumulated by dislocation creep in quartz of the host rock and most veins indicates low bulk stress conditions of a few tens of MPa on a long term. The time scale of stress-loading to cause cyclic cracking and sealing is assumed to be lower than the Maxwell relaxation time of the metasediments undergoing dissolution-precipitation creep at high strain rates(10^(-10) s^(-1) to 10^(-9) s^(-1)), which is on the order of hundred years. In contrast, some veins discordant or concordant to the foliation show heterogeneous quartz microstructures with micro-shear zones, sub-basal deformation lamellae, shortwavelength undulatory extinction and recrystallized grains restricted to high strain zones. These microstructures indicate dislocation glide-controlled crystal-plastic deformation(low-temperature plasticity) at transient high stresses of a few hundred MPa with subsequent recovery and strain-induced grain boundary migration at relaxing stresses and temperatures of at least 300 -350℃. High differential stresses in rocks at greenschist-facies conditions that relieve stress by creep on the long term, requires fast stress-loading rates, presumably by seismic activity in the overlying upper crust. The time scale for stress loading is controlled by the duration of the slip event along a fault, i.e. a few seconds to minu展开更多
True-triaxial compression tests were carried out on cubic granite samples with a circular through hole using a true-triaxial testing system to investigate the influence of saturated water content(SWC) on the failure p...True-triaxial compression tests were carried out on cubic granite samples with a circular through hole using a true-triaxial testing system to investigate the influence of saturated water content(SWC) on the failure process and characteristics of a circular tunnel of surrounding rocks. The spalling failure under SWC can be divided into four periods: calm period, buckling deformation period, period of rock fragment gradual buckling and exfoliation, and period of formation of symmetrical V-shaped notches. When the horizontal axial and vertical stresses were constant, the spalling failure severity was reduced with the increase in lateral stress. Under natural water content, a strong rockburst with dynamic failure characteristics occurred on the circular hole sidewall. Under SWC, the failure severity was reduced and the circular hole sidewall experienced spalling failure, exhibiting progressive static failure characteristics.Therefore, water can reduce the failure severity of surrounding rocks in deep underground engineering, which has a certain guiding significance for the prevention and control of rockbursts.展开更多
文摘Abstract There are many soft-rock roadway coal mines in China. The surrounding rocks of the high-stress soft-rock roadways in deep mine are especially difficult to be supported using the traditional supporting way. In this study, the south wing rail roadway on the second level of Yunjialing coal mine in China was used as an example to analyze the deformation and failure characteristics and influencing factors of roadway. On this basis, this study proposed the equalized yielding support idea which employs the yielding rings to realize the pressure equalization on the bolts and cables in the section. To achieve this purpose, the first bolt-mesh-cable equalizing pressure yielding support was integrated with the second grouting reinforcement. The results proved that the yield rings of the bolts and cables on the spandrel of the arched roadway firstly developed yielding deformation; then the deformation extended to the vault of the roadway; the bolts and cables achieved a yielding extreme value of 15 and 18 tonnes, respectively. The roadway surrounding rock tended to be stable at the 26th day after the maintenance. The equalizing pressure yielding supporting technology plays a moderate pressure-releasing and actively controlling role on the surrounding rocks in the soft-rock roadway with large deformation.
基金supported by the National Natural Science Foundation of China (Nos. 42277174, 42077267, and 52074164)the Natural Science Foundation of Shandong Province, China (No. ZR2020JQ23)+2 种基金Major Scientific and Technological Innovation Project of Shandong Province, China (No. 2019SDZY04)the Project of Shandong Province Higher Educational Youth Innovation Science and Technology Program, China (No. 2019KJG013)the opening project of State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology (No. KFJJ21-02Z)。
文摘Deep underground projects(e.g., coal mines), are often faced with complex conditions such as high stress and extremely soft rock. The strength and rigidity of the traditional support system are often insufficient,which makes it difficult to meet the requirements of ground control under complex conditions. As a new support form with high strength and rigidity, the confined concrete arch plays an important role in controlling the rock deformation under complex conditions. The section shape of the tunnel has an important impact on the mechanical properties and design of the support system. However, studies on the mechanical properties and influence mechanism of the new confined concrete arch are rarely reported. To this end, the mechanical properties of traditional U-shaped steel and new confined concrete arches are compared and comparative tests on arches of circular and straight-leg semicircular shapes in deep tunnels are conducted. A large mechanical testing system for underground engineering support structure is developed. The mechanical properties and influence mechanism of confined concrete arches with different section shapes under different loading modes and cross-section parameters are systematically studied. Test results show that the bearing capacity of the confined concrete arch is 2.10 times that of the U-shaped steel arch, and the bearing capacity of the circular confined concrete arch is 2.27 times that of the straight-leg semicircular arch. Among the various influencing factors and their engineering parameters,the lateral stress coefficient has the greatest impact on the bearing capacity of the confined concrete arch,followed by the steel pipe wall thickness, steel strength, and core concrete strength. Subsequently, the economic index of bearing capacity and cost is established, and the optimization design method for the confined concrete arch is proposed. Finally, this design method is applied to a high-stress tunnel under complex conditions, and the deformation of the surrounding rock is effectivel
基金supported by the National Natural Science Foundation of China(No.51974192)Shanxi Province Postgraduate Education Innovation Project(No.2020SY567)+2 种基金the Applied Basic Research Project of Shanxi Province(No.201801D121092)Distinguished Youth Funds of National Natural Science Foundation of China(No.51925402)Shanxi Science and Technology Major Project(No.20201102004)。
文摘To investigate the creep and instability properties of a cemented gangue backfill column under a highstress area,the uniaxial compression creep tests were conducted by single-step and multi-step loading of prismatic samples made of cemented gangue backfill material(CGBM)under the high stressstrength ratio.The creep damage was monitored using an electrical resistivity device,ultrasonic testing device,and acoustic emission(AE)instrument.The results showed that the CGBM sample has a creep hardening property.The creep failure strength(CFS)is slightly larger than the uniaxial compressive strength(UCS),ranging in ratio from 108.9%to 116.5%.The instantaneous strain,creep strain,and creep rate increase with increasing stress-strength ratio in the single-step loading creep tests.The instantaneous strain and creep strain decrease first and then increase during the multi-step loading creep process.The axial creep strain of the CGBM column can be expressed by the viscoelastic-plastic creep model.Creep instability is caused by the accumulation of strain energy under multi-step loading and the continuous lateral expansion at the unconstrained middle position during the creep process.The creep stability of a CGBM column in a high-stress area can be monitored based on the variation of electrical resistivity,ultrasonic pulse velocity(UPV),and AE signals.
基金National Natural Science Foundation of ChinaGrant/Award Number:41972316+3 种基金Sichuan Science&Technology FoundationGrant/Award Number:2022YFSY0007Joint Funds of the National Natural Science Foundation of ChinaGrant/Award Number:U2344226。
文摘Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host frames and hydraulic pumps,which could lead to great investment.Low-cost testing machines clearly always have great appeal.In this study,a new approach is proposed using thermal expansion stress to load rock specimens,which may be particularly suitable for tests of deep hot dry rock with high temperatures.This is a different technical route from traditional mechanical loading through hydraulic pressure.For the rock mechanics test system of hot dry rock that already has an investment in heating systems,this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes.This paper presents the basic principle and a typical design of this technical solution.Preliminary feasibility analysis is then conducted based on numerical simulations.Although some technical details still need to be resolved,the feasibility of this loading approach has been preliminarily confirmed.
文摘Underground mining is going to be deeper gradually because near surface resources are going to be depleted. Therefore, risk of seismic events in underground mines is escalating. Additionally, existence of the large ratio of horizontal to vertical stress, could be a potential reason for high-stress condition and occurrence of dynamic activities. Depending on various parameters such as the level of induced stress, rock properties, etc., ground demand changes and it is difficult to estimate. On the other hand,under seismic condition, energy dissipation and deformation capacity of supports is the most important factors, however, rock support performance factors in dynamic conditions are still under investigation.Expanding the knowledge of reinforcement behaviour and capacity, specifically that of the rockbolt as a primary element in seismic conditions, would help to develop a suitable, safe and economic support design. This paper contains various methods to estimate ground demand including the intact rock properties approach, failure thickness and ejection velocity estimation, and rockburst damage potential method. It also covers measurement methods of rockbolts energy dissipation capacities such as drop test,blasting simulating, back calculation and momentum transfer measurement methods. A large-scale dynamic test rig is also explained. Based on the findings, a table and a graph to show the applicable range of each type of rockbolts were presented. Suitable rockbolt types for various ground energy demand and deformation capacity range were categorised in the table and the graph. The presented support selection method facilitates the selection of a suitable reinforcement system at the preliminary stages of design and guides the designer to adjust the support reinforcement system based on observed ground and support reaction.
基金funded by the German research foundation (DFG Grant No. TR534/5-1)
文摘In an extensional shear zone in the Talea Ori, Crete, quartz veins occur in high-pressure low-temperature metamorphic sediments at sites of dilation along shear band boundaries, kink band boundaries and boudin necks. Bent elongate grains grown epitactically from the host rock with abundant fluid inclusion trails parallel to the vein wall indicate vein formation by crack-seal increments during dissolutionprecipitation creep of the host rock. The presence of sutured high-angle grain boundaries and subgrains shows that temperatures were sufficiently high for recovery and strain-induced grain boundary migration, i.e. higher than 300 -350℃, close to peak metamorphic conditions. The generally low amount of strain accumulated by dislocation creep in quartz of the host rock and most veins indicates low bulk stress conditions of a few tens of MPa on a long term. The time scale of stress-loading to cause cyclic cracking and sealing is assumed to be lower than the Maxwell relaxation time of the metasediments undergoing dissolution-precipitation creep at high strain rates(10^(-10) s^(-1) to 10^(-9) s^(-1)), which is on the order of hundred years. In contrast, some veins discordant or concordant to the foliation show heterogeneous quartz microstructures with micro-shear zones, sub-basal deformation lamellae, shortwavelength undulatory extinction and recrystallized grains restricted to high strain zones. These microstructures indicate dislocation glide-controlled crystal-plastic deformation(low-temperature plasticity) at transient high stresses of a few hundred MPa with subsequent recovery and strain-induced grain boundary migration at relaxing stresses and temperatures of at least 300 -350℃. High differential stresses in rocks at greenschist-facies conditions that relieve stress by creep on the long term, requires fast stress-loading rates, presumably by seismic activity in the overlying upper crust. The time scale for stress loading is controlled by the duration of the slip event along a fault, i.e. a few seconds to minu
基金financial support from the National Natural Science Foundation of China (Nos.51904335,41630642)。
文摘True-triaxial compression tests were carried out on cubic granite samples with a circular through hole using a true-triaxial testing system to investigate the influence of saturated water content(SWC) on the failure process and characteristics of a circular tunnel of surrounding rocks. The spalling failure under SWC can be divided into four periods: calm period, buckling deformation period, period of rock fragment gradual buckling and exfoliation, and period of formation of symmetrical V-shaped notches. When the horizontal axial and vertical stresses were constant, the spalling failure severity was reduced with the increase in lateral stress. Under natural water content, a strong rockburst with dynamic failure characteristics occurred on the circular hole sidewall. Under SWC, the failure severity was reduced and the circular hole sidewall experienced spalling failure, exhibiting progressive static failure characteristics.Therefore, water can reduce the failure severity of surrounding rocks in deep underground engineering, which has a certain guiding significance for the prevention and control of rockbursts.
