Understanding local variation in forest biomass allows for a better evaluation of broad-scale patterns and interpretation of forest ecosystems’role in carbon dynamics.This study focuses on patterns of aboveground tre...Understanding local variation in forest biomass allows for a better evaluation of broad-scale patterns and interpretation of forest ecosystems’role in carbon dynamics.This study focuses on patterns of aboveground tree biomass within a fully censused 20 ha forest plot in a temperate forest of northern Alabama,USA.We evaluated the relationship between biomass and topography using ridge and valley landforms along with digitally derived moisture and solar radiation indices.Every live woody stem over 1 cm diameter at breast height within this plot was mapped,measured,and identified to species in 2019-2022,and diameter data were used along with speciesspecific wood density to map the aboveground biomass at the scale of 20 m×20 m quadrats.The aboveground tree biomass was 211 Mg·ha^(-1).Other than small stream areas that experienced recent natural disturbances,the total stand biomass was not associated with landform or topographic indices.Dominant species,in contrast,had strong associations with topography.American beech(Fagus grandifolia)and yellow-poplar(Liriodendron tulipfera)dominated the valley landform,with 37% and 54% greater biomass in the valley than their plot average,respectively.Three other dominant species,white oak(Quercus alba),southern shagbark hickory(Carya carolinaeseptentrionalis),and white ash(Fraxinus americana),were more abundant on slopes and benches,thus partitioning the site.Of the six dominant species,only sugar maple(Acer saccharum)was not associated with landform.Moreover,both topographic wetness and potential radiation indices were significant predictors of dominant species biomass within each of the landforms.The study highlights the need to consider species when examining forest productivity in a range of site conditions.展开更多
Microscopic dynamic failure behaviors of rocks are significant to rock engineering,which is still insufficiently understood.This study combines split Hopkinson pressure bar(SHPB)and micro-CT(computed tomography)to exp...Microscopic dynamic failure behaviors of rocks are significant to rock engineering,which is still insufficiently understood.This study combines split Hopkinson pressure bar(SHPB)and micro-CT(computed tomography)to explore the microscopic failure characteristics of sandstone under impact loading.SHPB is responsible for the dynamic test,and micro-CT is responsible for pre-and post-test inspections.The results show that the pores and defect influence the dynamic strength but do not alter the overall trend of increased strength with a higher impact level.The dynamical crack development is then analyzed.Three types of cracks(i.e.I-,Y-,and H-type)are identified to describe the crack development.When rock is simply fractured,only I-type crack exists due to tensile failure,and it grows irregularly.As the strain rate increases,I-type crack is transformed into Y-and H-type crack due to shear failure.Crack coalesces at that moment,and the complexity increases along the impact direction.The coalescence occurs preferentially in the area with more pores,and around a third of pores are involved,where the maximum contribution area is in the middle of sample.Microcracks are formed inside the rock blocks,and rock grains and fragments fill in the cracks.The dynamic crack development is accompanied by microcracks,while rock grains and fragments result from the development of these microcracks.In addition,the influence of a semi-penetrating defect perpendicular to the impact direction is investigated.The defect can impede stress transfer and concentrate energy consumption.The findings are expected to enhance understanding of rock dynamics and support rock engineering development.展开更多
Analyzing large prehistoric rock avalanches provides significant data for evaluating the disaster posed by these relatively infrequent but destructive geological events. This paper attempts to study the characteristic...Analyzing large prehistoric rock avalanches provides significant data for evaluating the disaster posed by these relatively infrequent but destructive geological events. This paper attempts to study the characteristics and dynamics of the Ganqiuchi granitic rock avalanche, in the middle of the northern margin of Qinling Mountains, 30 km to the south of Xi’an, Shaanxi Province, China. In plane view, this rock avalanche is characterized by source area, accumulation area and dammed lake area. Based on previous studies, historical records and regional geological data, the major trigger of the Ganqiuchi rock avalanche is considered to be a strong paleo-earthquake with tremendous energy. The in situ deposit block size distributions of the intact rock mass and the debris deposits are presented and analyzed by using a simple model for estimating the number of fragmentation cycles that the blocks underwent. The results show that the primary controlling factor of the fragmentation process is the pre-existing fractures, and there is a relationship between the potential energy and the fragmentation energy: the latter is approximately 20% of the former. Based on the dynamic discrete element technique, the study proposes a four-stage model for the dynamic course of the Ganqiuchi rock avalanche:(1) failing;(2) highspeed sliding;(3) collision with obstacles;(4) decelerated sliding, which has implication for hazard assessment of the potential rock avalanches in China and other countries with similar geological setting.展开更多
The electromagnetic radiation(EMR)monitoring and early warning technology has experienced decades of successful applications for worldwide coal and rock dynamic disasters,yet a fundamental model unifying physical mech...The electromagnetic radiation(EMR)monitoring and early warning technology has experienced decades of successful applications for worldwide coal and rock dynamic disasters,yet a fundamental model unifying physical mechanism and generation process for EMR is still lacking.The effective revealing of EMR's mechanism is crucial for dynamic disaster control and management.With this motive,a multi-scale experimental study was conducted in the earlier stage.At the micro-scale,the charge's existence and non-uniform distribution on rock's micro-surface were confirmed by atomic force microscope(AFM),and deduced the relationship with load changes.At the meso-scale,the time sequence synchronization and frequency domain consistency of EMR and micro-vibration(MV)in the rock fracture under load have been confirmed.Therefore,it is inferred that the vibration of the crack surface acts as the power source of rock fracture-induced EMR,and the original charge on the crack surface and the charge generated by the new crack surface are the electrical basis of EMR.Based on the above two experimental findings,this paper proposes a new mechanism of rock fracture-induced EMR defined as the electricity-vibration coupling mechanism,stating that,the vibrating charged crack generates the EMR.Subsequently,a generation model was constructed based on vibrating charged crack clusters to elucidate this mechanism.The experimental results demonstrated that the EMR waveform calculated by the model and measured by antenna exhibited good correspondence,thereby verifying the effectiveness of the constructed EMR model.The proposal of this new mechanism and the model further clarified the EMR's mechanism induced by rock fracture.Moreover,the inter-relationship among crack propagation,vibration,and EMR was developed by this model,which could be immensely beneficial in EMR-based identification and prediction of dynamic disasters in complex mining environments worldwide.展开更多
Caverns and tunnels are constantly exposed to dynamic loads,posing a potentially significant threat to the safety of rock structures.To facilitate the understanding of dynamic fracture around openings,a series of disc...Caverns and tunnels are constantly exposed to dynamic loads,posing a potentially significant threat to the safety of rock structures.To facilitate the understanding of dynamic fracture around openings,a series of discrete element models were established to numerically examine the effect of hole shape on dynamic mechanical properties and crack evolution.The results indicate that the existence of a hole greatly reduces dynamic strength,and the reduction is closely related to hole shape.The strain variation of pre-holed specimens is more complicated and even larger than the value of intact specimens.Although crack initiation differs for varying hole shapes,the entire structural collapse of specimens is controlled by macro shear cracks along the diagonal direction of the specimen,which are effectively identified by velocity trend arrows and contact force distribution.Finally,comparative analysis between failure pattern of pre-holed specimens under static and dynamic loads were conducted.展开更多
Determining the dynamic behaviors of deep rocks is important but challenging for deep underground rock engineering.Recently,great advances have been made by researchers in dynamic tests of deep rocks considering insit...Determining the dynamic behaviors of deep rocks is important but challenging for deep underground rock engineering.Recently,great advances have been made by researchers in dynamic tests of deep rocks considering insitu mechanical and hydraulic conditions.It is thus imperative to systematically review the progress in this field.This paper focuses on the dynamic experiments of deep rocks using the modified split Hopkinson pressure bar(SHPB),including new advances in experimental apparatuses,methodologies,and results.A comprehensive introduction to the principles of the triaxial confinement SHPB,the true triaxial SHPB,and SHPB with a coupled hydraulic-mechanical device is provided.The development of these systems for conducting dynamic tests of deep rocks is briefly presented.Moreover,the experimental methods and results for quantifying dynamic compressive,tensile,flexure,and shear strengths and mode I/II fracture toughness of rocks under axial preload,hydrostatic pressure,triaxial stress state,and coupled hydraulic-mechanical condition are systematically discussed,and the rate-dependent characteristics and mechanisms of deep rocks under various geological occurrence conditions are also summarized.展开更多
In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized m...In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized measurement devices including a high-speed camera and a dynamic strain meter. The experimental results show that the specimens were in the state of good stress equilibrium during the post failure stage even when visible cracks were forming in the specimens. Rock specimens broke into strips but still could bear the external stress and keep force balance. Meanwhile, numerical tests with particle flow code （PFC） revealed that the failure process of rocks can be described by the evolution of micro-fractures. Shear cracks emerged firstly and stopped developing when the external stress was not high enough. Tensile cracks, however, emerged when the rock specimen reached its peak strength and played an important role in controlling the ultimate failure during the post failure stage.展开更多
Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed u...Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens.The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.展开更多
Rock drilling machine,INSTRON testing system,and SHPB device are updated to investigate the characteristics of rocks at great depth,with high loads from overburden,tectonic stresses and dynamic impacts due to blasting...Rock drilling machine,INSTRON testing system,and SHPB device are updated to investigate the characteristics of rocks at great depth,with high loads from overburden,tectonic stresses and dynamic impacts due to blasting and boring.It is verified that these testing systems can be used to study the mechanical properties of rock material under coupled static and dynamic loading condition and give useful guidance for the deep mining and underground cavern excavation.Various tests to determine the rock strength,fragmentation behavior,and energy absorption were conducted using the updated testing systems.It is shown that under coupled static-dynamic loads,if the axial prestress is lower than its elastic limit,the rock strength is higher than the individual static or dynamic strength.At the same axial prestress,rock strength under coupled loads rises with the increasing strain rates.Under coupled static and dynamic loads,rock is observed to fail with tensile mode.While shear failure may exist if axial prestress is high enough.In addition,it is shown that the percentage of small particles increases with the increasing axial prestress and impact load based on the analysis of the particle-size distribution of fragments.It is also suggested that the energy absorption ratio of a specimen varies with coupled loads,and the maximum energy absorption ratio for a rock can be obtained with an appropriate combination of static and dynamic loads.展开更多
In order to get the dynamic mechanical properties of deep rock mass suffered both high temperature and high pressure,impact loading experiments on granite subjected to temperature and axial pressure were carried out. ...In order to get the dynamic mechanical properties of deep rock mass suffered both high temperature and high pressure,impact loading experiments on granite subjected to temperature and axial pressure were carried out. Furthermore, the internalstructure characteristics of granite under different temperatures were observed by scanning electron microscopy (SEM). The results show that the longitudinal wave velocity assumes a downward trend which shows a rapid drop before falling slowly as the temperature increases. The uniaxial compressive strength of the specimen decreases significantly at temperatures of 25?100 °C compared to that at temperatures of 100?300 °C. The peak strain rises rapidly before the dividing point of 100 °C, but increases slowly after the dividing point. The internal structure of the rock changes substantially as the temperature increases, such as the extension and transfixion of primary and newborn cracks. In addition, the thermal damage under axial pressure is greater than that described by the longitudinal wave velocity and the phenomenon shows obviously when the temperature increases.展开更多
Accurate prediction of compressive strength of rocks relies on the rate-dependent behaviors of rocks, and correlation among the geometrical, physical, and mechanical properties of rocks. However, these properties may ...Accurate prediction of compressive strength of rocks relies on the rate-dependent behaviors of rocks, and correlation among the geometrical, physical, and mechanical properties of rocks. However, these properties may not be easy to control in laboratory experiments, particularly in dynamic compression experiments. By training three machine learning models based on the support vector machine(SVM), backpropagation neural network(BPNN), and random forest(RF) algorithms, we isolated different input parameters, such as static compressive strength, P-wave velocity, specimen dimension, grain size, bulk density, and strain rate, to identify their importance in the strength prediction. Our results demonstrated that the RF algorithm shows a better performance than the other two algorithms. The strain rate is a key input parameter influencing the performance of these models, while the others(e.g. static compressive strength and P-wave velocity) are less important as their roles can be compensated by alternative parameters. The results also revealed that the effect of specimen dimension on the rock strength can be overshadowed at high strain rates, while the effect on the dynamic increase factor(i.e. the ratio of dynamic to static compressive strength) becomes significant. The dynamic increase factors for different specimen dimensions bifurcate when the strain rate reaches a relatively high value, a clue to improve our understanding of the transitional behaviors of rocks from low to high strain rates.展开更多
Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for th...Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for those subject to strong dynamic loadings.In this paper,we investigate the deformation and fracturing of rocks,its physical origin at the microscopic scale,as well as the mechanisms of the time-dependence of rock strength.Using the thermo-activated and macro-viscous mechanisms,we explained the sensitivity of rock strength to strain rate.These mechanisms dominate the rock strength in different ranges of strain rates.It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation.A relationship between the particle sizes of fractured rocks and the strain rate is also proposed.Several time-dependent fracture criteria are discussed,and their intrinsic relations are discussed.Finally,the application of dynamic strength theories is discussed.展开更多
Introduced the coal and rock AE propagation rule,wave guide fixing technics onAE sensors,and AE forecasting coal and rock disaster on the scene and so on,The coaland rock AE propagation rule that follows the exponent ...Introduced the coal and rock AE propagation rule,wave guide fixing technics onAE sensors,and AE forecasting coal and rock disaster on the scene and so on,The coaland rock AE propagation rule that follows the exponent attenuation function on different AEfrequencies,different quality factors and different propagation distances were analyzedand deduced by theory,numerical simulation,and by actual experiment.Consequently,itwas deduced that the coal and rock AE propagation rule follows the exponent attenuationfunction.Based on the correlative theory of wave dynamics and AE sensor,the AE waveguide propagation mechanical model on the sensor fixing manner is found,and the relationsof displacement and speed and acceleration between the AE signal source and theAE signal receiving terminal are presented.The effect of the AE sensor fixing manners oncoal and rock surfaces,coal and rock bottoms and wave guides were studied by actualexperiment.For the results,the effect of the AE sensor fixing manner on wave guides isbetter than on coal and rock surfaces,and was equivalent to the fixing manner on coal androck bottoms.Based on the above study results,actual coal and rock dynamistic disasterswere successfully forecasted.展开更多
In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynami...In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.展开更多
The electromagnetic radiation （EMR） signal collected by monitoring system during coal or rock dynamic disaster may be interferred easily by electromagnetic noises in mines. The noises have a direct influence on the ...The electromagnetic radiation （EMR） signal collected by monitoring system during coal or rock dynamic disaster may be interferred easily by electromagnetic noises in mines. The noises have a direct influence on the recognition and analysis of the EMR signal features during the disaster. With the aim of removing these noises, an ensemble empirical mode decomposition （EEMD） adaptive morphological filter was proposed. From the result of the simulation and the experiment, it is shown that the method can restrain the random noise and white Gaussian noise mixed with EMR signal effectively. The filter is highly useful for improving the robustness of the coal or rock dynamic disaster monitoring system.展开更多
Numerous deep underground projects have been designed and constructed in China, which are beyond the current specifications in terms of scale and construction difficulty. The severe failure problems induced by high in...Numerous deep underground projects have been designed and constructed in China, which are beyond the current specifications in terms of scale and construction difficulty. The severe failure problems induced by high in situ stress, such as rockburst, spalling, damage of deep surrounding rocks, and timedependent damage, were observed during construction of these projects. To address these problems, the dynamic design method for deep hard rock tunnels is proposed based on the disintegration process of surrounding rocks using associated dynamic control theories and technologies. Seven steps are basically employed：（i） determination of design objective,（ii） characteristics of site, rock mass and project, and identification of constraint conditions,（iii） selection or development of global design strategy,（iv）determination of modeling method and software,（v） preliminary design,（vi） comprehensive integrated method and dynamic feedback analysis, and（vii） final design. This dynamic method was applied to the construction of the headrace tunnels at Jinping II hydropower station. The key technical issues encountered during the construction of deep hard rock tunnels, such as in situ stress distribution along the tunnels, mechanical properties and constitutive model of deep hard rocks, determination of mechanical parameters of surrounding rocks, stability evaluation of surrounding rocks, and optimization design of rock support and lining, have been adequately addressed. The proposed method and its application can provide guidance for deep underground projects characterized with similar geological conditions.展开更多
The wave velocity analysis of rock medium is the main method used to explore the internal compositions in the crust and research seismic.In this paper,a compression–shear coupled nonlinear elastic constitutive relati...The wave velocity analysis of rock medium is the main method used to explore the internal compositions in the crust and research seismic.In this paper,a compression–shear coupled nonlinear elastic constitutive relation is established,which is consistent with the mechanical properties of rock and mineral medium under high pressure.On this basis,numerical solutions of the wave equation and plane wave analytical solutions for the primary and secondary wave velocities are obtained.As is indicated by the comparison with the linear elastic constitutive theory,the results reflect the compression–shear coupling characteristics of the rock,including the stress path effect and the compression–shear coupling wave effect.With different parameter values,the velocity of the secondary wave changes from lower than that of the elastic shear wave,to higher than that of the elastic shear wave.The research results are expected to provide meaningful explanations for the physical mechanisms of the supershear wave and sub-Rayleigh wave,and guidance for the detection of rock and soil composition and the observation of seismic waves.展开更多
Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more...Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more challenging than their static counterparts. Dynamic tests are usually conducted using the split Hopkinson bar or Kolsl^j bar systems, which include both split Hopkinson pressure bar （SHPB） and split Hopkinson tension bar （SHTB） systems. Significant progress has been made on the quantification of various rock dynamic properties, owing to the advances in the experimental techniques of SHPB system. This review aims to fully describe and critically assess the detailed procedures and principles of tech- niques for dynamic rock tests using split Hopkinson bars. The history and principles of SHPB are outlined, followed by the key loading techniques that are useful for dynamic rock tests with SHPB （i.e. pulse shaping, momentum-trap and multi-axial loading techniques）. Various measurement techniques for rock tests in SHPB （i.e. X-ray micro computed tomography （CT）, laser gap gauge （LGG）, digital image corre- lation （DIC）, Moir~ method, caustics method, photoelastic coating method, dynamic infrared thermog- raphy） are then discussed. As the main objective of the review, various dynamic measurement techniques for rocks using SHPB are described, including dynamic rock strength measurements （i.e. dynamic compression, tension, bending and shear tests）, dynamic fracture measurements （i.e. dynamic imitation and propagation fracture toughness, dynamic fracture energy and fracture velocity）, and dy- namic techniques for studying the influences of temperature and pore water.展开更多
It is important to investigate the dynamic behaviors of deep rocks near explosion cavity to reveal the mechanisms of deformations and fractures. Some improvements are carried out for Grigorian model with focuses on th...It is important to investigate the dynamic behaviors of deep rocks near explosion cavity to reveal the mechanisms of deformations and fractures. Some improvements are carried out for Grigorian model with focuses on the dilation effects and the relaxation effects of deep rocks, and the high pressure equations of states with Mie-Grüneisen form are also established. Numerical calculations of free field parameters for deep underground explosions are carried out based on the user subroutines which are compiled by means of the secondary development functions of LS-DYNA9703 D software. The histories of radial stress, radial velocity and radial displacement of rock particles are obtained, and the calculation results are compared with those of U.S. Hardhat nuclear test. It is indicated that the dynamic responses of free field for deep underground explosions are well simulated based on improved Grigorian model, and the calculation results are in good agreement with the data of U.S. Hardhat nuclear test. The peak values of particle velocities are consistent with those of test, but the waveform widths and the rising times are obviously greater than those without dilation effects. The attenuation rates of particle velocities are greater than the calculation results with classic plastic model, and they are consistent with the results of Hardhat nuclear test. The attenuation behaviors and the rising times of stress waves are well shown by introducing dilation effects and relaxation effects into the calculation model. Therefore, the defects of Grigorian model are avoided. It is also indicated that the initial stress has obvious influences on the waveforms of radial stress and the radial displacements of rock particles.展开更多
Polycrystalline diamond compact(PDC)bit is one of the most widely used drill bits for improving the rate of penetration in deep oil and gas well and geothermal well.However,the dynamic rock fragmentation mechanics cha...Polycrystalline diamond compact(PDC)bit is one of the most widely used drill bits for improving the rate of penetration in deep oil and gas well and geothermal well.However,the dynamic rock fragmentation mechanics characteristics of PDC bits are still unclearly.A coupled fragmentation mechanics model of PDC cutter-rock interaction is established by combining the mixed fragmentation modes with dynamic strength.The coupling influence laws of cutter angle,cutting depth,dynamic strength ratio,breaking modes on the horizontal force coefficient(HFC),vertical force coefficient(VFC)and specific energy are analyzed.The model of this paper can optimize cutter inclination angle,cutting depth and minimum specific energy.With the increase of the cutter inclination angle,the dynamic VFC changes into two modes.The definition of the dynamic modes depends on the dynamic strength ratio.As the cutting angle increases,the cutting force increases.The cutting force increases nonlinearly with increasing cutting depth.The specific energy of rock fragmentation increases nonlinearly with increasing cutting depth.With the increase of dynamic strength,the specific energy of rock fragmentation increases nonlinearly.When the input-energy increases,the rate of penetration response is divided into three stages.The results have important guiding significance for the PDC bit design and drilling parameters optimization to increase the rate of penetration and the efficiency of exploration and development.展开更多
基金supported in part by the intramural research program of the US Department of Agriculture,National Institute of Food and Agriculture,Evans-Allen#1024525,and Capacity Building Grant#006531supported in part by the US National Science Foundation RII Track 2 FEC:Leveraging Intelligent Informatics and Smart Data for Improved Understanding of Northern Forest Ecosystem Resiliency(INSPIRES)#1920908by The Lyndhurst Foundation.
文摘Understanding local variation in forest biomass allows for a better evaluation of broad-scale patterns and interpretation of forest ecosystems’role in carbon dynamics.This study focuses on patterns of aboveground tree biomass within a fully censused 20 ha forest plot in a temperate forest of northern Alabama,USA.We evaluated the relationship between biomass and topography using ridge and valley landforms along with digitally derived moisture and solar radiation indices.Every live woody stem over 1 cm diameter at breast height within this plot was mapped,measured,and identified to species in 2019-2022,and diameter data were used along with speciesspecific wood density to map the aboveground biomass at the scale of 20 m×20 m quadrats.The aboveground tree biomass was 211 Mg·ha^(-1).Other than small stream areas that experienced recent natural disturbances,the total stand biomass was not associated with landform or topographic indices.Dominant species,in contrast,had strong associations with topography.American beech(Fagus grandifolia)and yellow-poplar(Liriodendron tulipfera)dominated the valley landform,with 37% and 54% greater biomass in the valley than their plot average,respectively.Three other dominant species,white oak(Quercus alba),southern shagbark hickory(Carya carolinaeseptentrionalis),and white ash(Fraxinus americana),were more abundant on slopes and benches,thus partitioning the site.Of the six dominant species,only sugar maple(Acer saccharum)was not associated with landform.Moreover,both topographic wetness and potential radiation indices were significant predictors of dominant species biomass within each of the landforms.The study highlights the need to consider species when examining forest productivity in a range of site conditions.
基金supported by Research Center for Industries of the Future(RCIF)Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province(No.ZJRMG-2022-03)+1 种基金Key Research and Development Program of Guangxi Province(No.Guike AB22080035)which are gratefully acknowledged.In addition,we are grateful for the valuable and constructive feedback provided by the anonymous reviewers,which has greatly improved this manuscript.
文摘Microscopic dynamic failure behaviors of rocks are significant to rock engineering,which is still insufficiently understood.This study combines split Hopkinson pressure bar(SHPB)and micro-CT(computed tomography)to explore the microscopic failure characteristics of sandstone under impact loading.SHPB is responsible for the dynamic test,and micro-CT is responsible for pre-and post-test inspections.The results show that the pores and defect influence the dynamic strength but do not alter the overall trend of increased strength with a higher impact level.The dynamical crack development is then analyzed.Three types of cracks(i.e.I-,Y-,and H-type)are identified to describe the crack development.When rock is simply fractured,only I-type crack exists due to tensile failure,and it grows irregularly.As the strain rate increases,I-type crack is transformed into Y-and H-type crack due to shear failure.Crack coalesces at that moment,and the complexity increases along the impact direction.The coalescence occurs preferentially in the area with more pores,and around a third of pores are involved,where the maximum contribution area is in the middle of sample.Microcracks are formed inside the rock blocks,and rock grains and fragments fill in the cracks.The dynamic crack development is accompanied by microcracks,while rock grains and fragments result from the development of these microcracks.In addition,the influence of a semi-penetrating defect perpendicular to the impact direction is investigated.The defect can impede stress transfer and concentrate energy consumption.The findings are expected to enhance understanding of rock dynamics and support rock engineering development.
基金financially supported by the National Natural Science Foundation of China(grant numbers 4167020392)the State Key Laboratory Foundation of Geohazard Prevention and Geoenvironment Protection(SKLGP2018K015)the Geological Investigation Project fromChina Geological Survey(DD20160336)
文摘Analyzing large prehistoric rock avalanches provides significant data for evaluating the disaster posed by these relatively infrequent but destructive geological events. This paper attempts to study the characteristics and dynamics of the Ganqiuchi granitic rock avalanche, in the middle of the northern margin of Qinling Mountains, 30 km to the south of Xi’an, Shaanxi Province, China. In plane view, this rock avalanche is characterized by source area, accumulation area and dammed lake area. Based on previous studies, historical records and regional geological data, the major trigger of the Ganqiuchi rock avalanche is considered to be a strong paleo-earthquake with tremendous energy. The in situ deposit block size distributions of the intact rock mass and the debris deposits are presented and analyzed by using a simple model for estimating the number of fragmentation cycles that the blocks underwent. The results show that the primary controlling factor of the fragmentation process is the pre-existing fractures, and there is a relationship between the potential energy and the fragmentation energy: the latter is approximately 20% of the former. Based on the dynamic discrete element technique, the study proposes a four-stage model for the dynamic course of the Ganqiuchi rock avalanche:(1) failing;(2) highspeed sliding;(3) collision with obstacles;(4) decelerated sliding, which has implication for hazard assessment of the potential rock avalanches in China and other countries with similar geological setting.
基金financially supported by the National Natural Science Foundation of China(Nos.51634001,52327804,52174162,52404256,and 52374180)the State Key Research Development Program of China(No.2016YFC0801408)the Fundamental Research Funds for the Central Universities(No.29-2023-025)。
文摘The electromagnetic radiation(EMR)monitoring and early warning technology has experienced decades of successful applications for worldwide coal and rock dynamic disasters,yet a fundamental model unifying physical mechanism and generation process for EMR is still lacking.The effective revealing of EMR's mechanism is crucial for dynamic disaster control and management.With this motive,a multi-scale experimental study was conducted in the earlier stage.At the micro-scale,the charge's existence and non-uniform distribution on rock's micro-surface were confirmed by atomic force microscope(AFM),and deduced the relationship with load changes.At the meso-scale,the time sequence synchronization and frequency domain consistency of EMR and micro-vibration(MV)in the rock fracture under load have been confirmed.Therefore,it is inferred that the vibration of the crack surface acts as the power source of rock fracture-induced EMR,and the original charge on the crack surface and the charge generated by the new crack surface are the electrical basis of EMR.Based on the above two experimental findings,this paper proposes a new mechanism of rock fracture-induced EMR defined as the electricity-vibration coupling mechanism,stating that,the vibrating charged crack generates the EMR.Subsequently,a generation model was constructed based on vibrating charged crack clusters to elucidate this mechanism.The experimental results demonstrated that the EMR waveform calculated by the model and measured by antenna exhibited good correspondence,thereby verifying the effectiveness of the constructed EMR model.The proposal of this new mechanism and the model further clarified the EMR's mechanism induced by rock fracture.Moreover,the inter-relationship among crack propagation,vibration,and EMR was developed by this model,which could be immensely beneficial in EMR-based identification and prediction of dynamic disasters in complex mining environments worldwide.
基金This research was financially supported by the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX21_0119)National Natural Science Foundation of China(52074349 and 52304113)China Scholarship Council(CSC)Scholarship(202106090203).
文摘Caverns and tunnels are constantly exposed to dynamic loads,posing a potentially significant threat to the safety of rock structures.To facilitate the understanding of dynamic fracture around openings,a series of discrete element models were established to numerically examine the effect of hole shape on dynamic mechanical properties and crack evolution.The results indicate that the existence of a hole greatly reduces dynamic strength,and the reduction is closely related to hole shape.The strain variation of pre-holed specimens is more complicated and even larger than the value of intact specimens.Although crack initiation differs for varying hole shapes,the entire structural collapse of specimens is controlled by macro shear cracks along the diagonal direction of the specimen,which are effectively identified by velocity trend arrows and contact force distribution.Finally,comparative analysis between failure pattern of pre-holed specimens under static and dynamic loads were conducted.
基金supported by the National Natural Science Foundation of China(Grant Nos.42141010,12172253,42377147,and 52079091).
文摘Determining the dynamic behaviors of deep rocks is important but challenging for deep underground rock engineering.Recently,great advances have been made by researchers in dynamic tests of deep rocks considering insitu mechanical and hydraulic conditions.It is thus imperative to systematically review the progress in this field.This paper focuses on the dynamic experiments of deep rocks using the modified split Hopkinson pressure bar(SHPB),including new advances in experimental apparatuses,methodologies,and results.A comprehensive introduction to the principles of the triaxial confinement SHPB,the true triaxial SHPB,and SHPB with a coupled hydraulic-mechanical device is provided.The development of these systems for conducting dynamic tests of deep rocks is briefly presented.Moreover,the experimental methods and results for quantifying dynamic compressive,tensile,flexure,and shear strengths and mode I/II fracture toughness of rocks under axial preload,hydrostatic pressure,triaxial stress state,and coupled hydraulic-mechanical condition are systematically discussed,and the rate-dependent characteristics and mechanisms of deep rocks under various geological occurrence conditions are also summarized.
基金Project(2015CB060200)supported by the National Basic Research and Development Program of ChinaProjects(51322403,51274254)supported by the National Natural Science Foundation of China
文摘In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized measurement devices including a high-speed camera and a dynamic strain meter. The experimental results show that the specimens were in the state of good stress equilibrium during the post failure stage even when visible cracks were forming in the specimens. Rock specimens broke into strips but still could bear the external stress and keep force balance. Meanwhile, numerical tests with particle flow code （PFC） revealed that the failure process of rocks can be described by the evolution of micro-fractures. Shear cracks emerged firstly and stopped developing when the external stress was not high enough. Tensile cracks, however, emerged when the rock specimen reached its peak strength and played an important role in controlling the ultimate failure during the post failure stage.
基金supported by the National Natural Science Foundation of China (No. 52074349)Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. KYCX21_0119)Hunan Provincial Natural Science Foundation (No. 2019JJ20028)。
文摘Filled inclusions in rock discontinuities play a key role in the mechanical characteristics of the rock and thereby influence the stability of rock engineering. In this study, a series of impact tests were performed using a split Hopkinson pressure bar system with high-speed photography to investigate the effect of interlayer strength on the wave propagation and fracturing process in composite rock-mortar specimens.The results indicate that the transmission coefficient, nominal dynamic strength, interlayer closure, and specific normal stiffness generally increase linearly with increasing interlayer stiffness. The cement mortar layer can serve as a buffer during the deformation of composite specimens. The digital images show that tensile cracks are typically initiated at the rock-mortar interface, propagate along the loading direction, and eventually result in a tensile failure regardless of the interlayer properties. However, when a relatively weaker layer is sandwiched between the rock matrix, an increasing amount of cement mortar is violently ejected and slight slabbing occurs near the rock-mortar interface.
基金Supported by the National Natural Science Foundation of China (10872218,50934006,50534030)Research Foundation for the Doctoral Program of Higher Education of China (200805331143)
文摘Rock drilling machine,INSTRON testing system,and SHPB device are updated to investigate the characteristics of rocks at great depth,with high loads from overburden,tectonic stresses and dynamic impacts due to blasting and boring.It is verified that these testing systems can be used to study the mechanical properties of rock material under coupled static and dynamic loading condition and give useful guidance for the deep mining and underground cavern excavation.Various tests to determine the rock strength,fragmentation behavior,and energy absorption were conducted using the updated testing systems.It is shown that under coupled static-dynamic loads,if the axial prestress is lower than its elastic limit,the rock strength is higher than the individual static or dynamic strength.At the same axial prestress,rock strength under coupled loads rises with the increasing strain rates.Under coupled static and dynamic loads,rock is observed to fail with tensile mode.While shear failure may exist if axial prestress is high enough.In addition,it is shown that the percentage of small particles increases with the increasing axial prestress and impact load based on the analysis of the particle-size distribution of fragments.It is also suggested that the energy absorption ratio of a specimen varies with coupled loads,and the maximum energy absorption ratio for a rock can be obtained with an appropriate combination of static and dynamic loads.
基金Project(51304241)supported by the Youth Project of National Natural Science Foundation of ChinaProject(2014M552164)supported by Chinese Postdoctoral Science FoundationProject(20130162120015)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘In order to get the dynamic mechanical properties of deep rock mass suffered both high temperature and high pressure,impact loading experiments on granite subjected to temperature and axial pressure were carried out. Furthermore, the internalstructure characteristics of granite under different temperatures were observed by scanning electron microscopy (SEM). The results show that the longitudinal wave velocity assumes a downward trend which shows a rapid drop before falling slowly as the temperature increases. The uniaxial compressive strength of the specimen decreases significantly at temperatures of 25?100 °C compared to that at temperatures of 100?300 °C. The peak strain rises rapidly before the dividing point of 100 °C, but increases slowly after the dividing point. The internal structure of the rock changes substantially as the temperature increases, such as the extension and transfixion of primary and newborn cracks. In addition, the thermal damage under axial pressure is greater than that described by the longitudinal wave velocity and the phenomenon shows obviously when the temperature increases.
基金supported by National Research Foundation,Singapore under its Virtual Singapore R&D Programme (Award No.NRF2019VSG-GMS-001)。
文摘Accurate prediction of compressive strength of rocks relies on the rate-dependent behaviors of rocks, and correlation among the geometrical, physical, and mechanical properties of rocks. However, these properties may not be easy to control in laboratory experiments, particularly in dynamic compression experiments. By training three machine learning models based on the support vector machine(SVM), backpropagation neural network(BPNN), and random forest(RF) algorithms, we isolated different input parameters, such as static compressive strength, P-wave velocity, specimen dimension, grain size, bulk density, and strain rate, to identify their importance in the strength prediction. Our results demonstrated that the RF algorithm shows a better performance than the other two algorithms. The strain rate is a key input parameter influencing the performance of these models, while the others(e.g. static compressive strength and P-wave velocity) are less important as their roles can be compensated by alternative parameters. The results also revealed that the effect of specimen dimension on the rock strength can be overshadowed at high strain rates, while the effect on the dynamic increase factor(i.e. the ratio of dynamic to static compressive strength) becomes significant. The dynamic increase factors for different specimen dimensions bifurcate when the strain rate reaches a relatively high value, a clue to improve our understanding of the transitional behaviors of rocks from low to high strain rates.
基金Supported by the National Science Foundation of China (50825403)the Beijing Natural Science Foundation of China (KZ200810016007)
文摘Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for those subject to strong dynamic loadings.In this paper,we investigate the deformation and fracturing of rocks,its physical origin at the microscopic scale,as well as the mechanisms of the time-dependence of rock strength.Using the thermo-activated and macro-viscous mechanisms,we explained the sensitivity of rock strength to strain rate.These mechanisms dominate the rock strength in different ranges of strain rates.It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation.A relationship between the particle sizes of fractured rocks and the strain rate is also proposed.Several time-dependent fracture criteria are discussed,and their intrinsic relations are discussed.Finally,the application of dynamic strength theories is discussed.
基金Supported by the Project of National Basic Research Program of China(973 Program)(2005CB221505)the Significant Project of National Natural Science Fund(50534080/E041503)the Project of Coal Mine Gas and Fire Hazard Prevention Major Lab in Henan Province(HKLGF200508)
文摘Introduced the coal and rock AE propagation rule,wave guide fixing technics onAE sensors,and AE forecasting coal and rock disaster on the scene and so on,The coaland rock AE propagation rule that follows the exponent attenuation function on different AEfrequencies,different quality factors and different propagation distances were analyzedand deduced by theory,numerical simulation,and by actual experiment.Consequently,itwas deduced that the coal and rock AE propagation rule follows the exponent attenuationfunction.Based on the correlative theory of wave dynamics and AE sensor,the AE waveguide propagation mechanical model on the sensor fixing manner is found,and the relationsof displacement and speed and acceleration between the AE signal source and theAE signal receiving terminal are presented.The effect of the AE sensor fixing manners oncoal and rock surfaces,coal and rock bottoms and wave guides were studied by actualexperiment.For the results,the effect of the AE sensor fixing manner on wave guides isbetter than on coal and rock surfaces,and was equivalent to the fixing manner on coal androck bottoms.Based on the above study results,actual coal and rock dynamistic disasterswere successfully forecasted.
基金financially supported by the Research and Innovation Team of Chengdu University of TechnologyProject of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Grant No. SKLGP2013Z002)
文摘In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.
文摘The electromagnetic radiation （EMR） signal collected by monitoring system during coal or rock dynamic disaster may be interferred easily by electromagnetic noises in mines. The noises have a direct influence on the recognition and analysis of the EMR signal features during the disaster. With the aim of removing these noises, an ensemble empirical mode decomposition （EEMD） adaptive morphological filter was proposed. From the result of the simulation and the experiment, it is shown that the method can restrain the random noise and white Gaussian noise mixed with EMR signal effectively. The filter is highly useful for improving the robustness of the coal or rock dynamic disaster monitoring system.
基金Financial supports from the National Natural Science Foundation of China(Grant Nos.51579188 and 51409198)the National Basic Research Program of China(Grant No.2011CB013503)
文摘Numerous deep underground projects have been designed and constructed in China, which are beyond the current specifications in terms of scale and construction difficulty. The severe failure problems induced by high in situ stress, such as rockburst, spalling, damage of deep surrounding rocks, and timedependent damage, were observed during construction of these projects. To address these problems, the dynamic design method for deep hard rock tunnels is proposed based on the disintegration process of surrounding rocks using associated dynamic control theories and technologies. Seven steps are basically employed：（i） determination of design objective,（ii） characteristics of site, rock mass and project, and identification of constraint conditions,（iii） selection or development of global design strategy,（iv）determination of modeling method and software,（v） preliminary design,（vi） comprehensive integrated method and dynamic feedback analysis, and（vii） final design. This dynamic method was applied to the construction of the headrace tunnels at Jinping II hydropower station. The key technical issues encountered during the construction of deep hard rock tunnels, such as in situ stress distribution along the tunnels, mechanical properties and constitutive model of deep hard rocks, determination of mechanical parameters of surrounding rocks, stability evaluation of surrounding rocks, and optimization design of rock support and lining, have been adequately addressed. The proposed method and its application can provide guidance for deep underground projects characterized with similar geological conditions.
基金National Natural Science Foundation of China,Grant/Award Numbers:11672286,11872361Opening Foundation of the United Laboratory of High-Pressure Physics and Earthquake Science,Grant/Award Number:2019HPPES01。
文摘The wave velocity analysis of rock medium is the main method used to explore the internal compositions in the crust and research seismic.In this paper,a compression–shear coupled nonlinear elastic constitutive relation is established,which is consistent with the mechanical properties of rock and mineral medium under high pressure.On this basis,numerical solutions of the wave equation and plane wave analytical solutions for the primary and secondary wave velocities are obtained.As is indicated by the comparison with the linear elastic constitutive theory,the results reflect the compression–shear coupling characteristics of the rock,including the stress path effect and the compression–shear coupling wave effect.With different parameter values,the velocity of the secondary wave changes from lower than that of the elastic shear wave,to higher than that of the elastic shear wave.The research results are expected to provide meaningful explanations for the physical mechanisms of the supershear wave and sub-Rayleigh wave,and guidance for the detection of rock and soil composition and the observation of seismic waves.
文摘Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more challenging than their static counterparts. Dynamic tests are usually conducted using the split Hopkinson bar or Kolsl^j bar systems, which include both split Hopkinson pressure bar （SHPB） and split Hopkinson tension bar （SHTB） systems. Significant progress has been made on the quantification of various rock dynamic properties, owing to the advances in the experimental techniques of SHPB system. This review aims to fully describe and critically assess the detailed procedures and principles of tech- niques for dynamic rock tests using split Hopkinson bars. The history and principles of SHPB are outlined, followed by the key loading techniques that are useful for dynamic rock tests with SHPB （i.e. pulse shaping, momentum-trap and multi-axial loading techniques）. Various measurement techniques for rock tests in SHPB （i.e. X-ray micro computed tomography （CT）, laser gap gauge （LGG）, digital image corre- lation （DIC）, Moir~ method, caustics method, photoelastic coating method, dynamic infrared thermog- raphy） are then discussed. As the main objective of the review, various dynamic measurement techniques for rocks using SHPB are described, including dynamic rock strength measurements （i.e. dynamic compression, tension, bending and shear tests）, dynamic fracture measurements （i.e. dynamic imitation and propagation fracture toughness, dynamic fracture energy and fracture velocity）, and dy- namic techniques for studying the influences of temperature and pore water.
基金Project(51378498)supported by the National Natural Science Foundation of ChinaProject(BK20141066)supported the Natural Science Foundation of Jiangsu Province,China+1 种基金Project(SKLGDUEK1208)supported by State Key Laboratory for Geo Mechanics and Deep Underground Engineering(China University of Mining & Technology),ChinaProject(DPMEIKF201301)supported by State Key Laboratory of Disaster Prevention & Mitigation of Explosion & Impact(PLA University of Science and Technology),China
文摘It is important to investigate the dynamic behaviors of deep rocks near explosion cavity to reveal the mechanisms of deformations and fractures. Some improvements are carried out for Grigorian model with focuses on the dilation effects and the relaxation effects of deep rocks, and the high pressure equations of states with Mie-Grüneisen form are also established. Numerical calculations of free field parameters for deep underground explosions are carried out based on the user subroutines which are compiled by means of the secondary development functions of LS-DYNA9703 D software. The histories of radial stress, radial velocity and radial displacement of rock particles are obtained, and the calculation results are compared with those of U.S. Hardhat nuclear test. It is indicated that the dynamic responses of free field for deep underground explosions are well simulated based on improved Grigorian model, and the calculation results are in good agreement with the data of U.S. Hardhat nuclear test. The peak values of particle velocities are consistent with those of test, but the waveform widths and the rising times are obviously greater than those without dilation effects. The attenuation rates of particle velocities are greater than the calculation results with classic plastic model, and they are consistent with the results of Hardhat nuclear test. The attenuation behaviors and the rising times of stress waves are well shown by introducing dilation effects and relaxation effects into the calculation model. Therefore, the defects of Grigorian model are avoided. It is also indicated that the initial stress has obvious influences on the waveforms of radial stress and the radial displacements of rock particles.
基金work is supported by the project funded by China Post-doctoral Science Foundation(2020M683357)Sichuan Science and Technology Program(2022NSFSC0975)+1 种基金CNPC-SWPU innovation alliance(2020CX040202)Open Fund(PLN2021-19)of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University).
文摘Polycrystalline diamond compact(PDC)bit is one of the most widely used drill bits for improving the rate of penetration in deep oil and gas well and geothermal well.However,the dynamic rock fragmentation mechanics characteristics of PDC bits are still unclearly.A coupled fragmentation mechanics model of PDC cutter-rock interaction is established by combining the mixed fragmentation modes with dynamic strength.The coupling influence laws of cutter angle,cutting depth,dynamic strength ratio,breaking modes on the horizontal force coefficient(HFC),vertical force coefficient(VFC)and specific energy are analyzed.The model of this paper can optimize cutter inclination angle,cutting depth and minimum specific energy.With the increase of the cutter inclination angle,the dynamic VFC changes into two modes.The definition of the dynamic modes depends on the dynamic strength ratio.As the cutting angle increases,the cutting force increases.The cutting force increases nonlinearly with increasing cutting depth.The specific energy of rock fragmentation increases nonlinearly with increasing cutting depth.With the increase of dynamic strength,the specific energy of rock fragmentation increases nonlinearly.When the input-energy increases,the rate of penetration response is divided into three stages.The results have important guiding significance for the PDC bit design and drilling parameters optimization to increase the rate of penetration and the efficiency of exploration and development.
