The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A ser...The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.展开更多
Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict te...Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict tensile mode(mode I)failure loads of cracked rocks.The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone(FPZ)based on the maximum normal strain(MNSN)ahead of the crack tip,and then use the effective crack to calculate the fracture toughness.We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN.In this way,the FPZ,non-singular terms and the biaxial stress state at the crack tip are simul-taneously considered.The principle of the model is explicit and easy to apply.To verify the proposed model,laboratory experiments were performed on a rock material using six groups of specimens.The model predicted the specimen geometry dependence of the measured fracture toughness well.More-over,the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature.The model was demonstrated su-perior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.展开更多
Rock mass is a fractured porous medium usually subjected to complex geostress and fluid pressure simultaneously.Moreover,the properties of rock mass change in time and space due to mining-induced fractures.Therefore,i...Rock mass is a fractured porous medium usually subjected to complex geostress and fluid pressure simultaneously.Moreover,the properties of rock mass change in time and space due to mining-induced fractures.Therefore,it is always challenging to accurately measure rock mass properties.In this study,a three-dimensional(3D)microseismic(MS)data-driven damage model for jointed rock mass under hydro-mechanical coupling conditions is proposed.It is a 3D finite element model that takes seepage,damage and stress field effects into account jointly.Multiple factors(i.e.joints,water and microseismicity)are used to optimize the rock mass mechanical parameters at different scales.The model is applied in Shirengou iron mine to study the damage evolution of rock mass and assess the crown pillar stability during the transition from open-pit to underground mining.It is found that the damage pattern is mostly controlled by the structure,water and rock mass parameters.The damage pattern is evidently different from the two-dimensional result and is more consistent with the field observations.This difference is caused by the MS-derived damage acting on the rock mass.MS data are responsible for gradually correcting the damage zone,changing the direction in which it expands,and promoting it to evolve close to reality.For the crown pillar,the proposed model yields a more trustworthy safety factor.In order to guarantee the stability of the pillar,it is suggested to take waterproof and reinforcement measures in areas with a high degree of damage.展开更多
In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(S...In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(SHPB)system.Firstly,the stress distribution of SBC specimen is comprehensively analyzed by finite element method(FEM),and the results show that the optimal notch separation ratio of SBC specimen is C/H?0.2 to achieve successful dynamic simple-shear tests.Then,dynamic shear tests are conducted on sandstone using the SBC-SHPB method.Via careful pulse shaping technique,the dynamic force balance is guaranteed for SBC specimens,and the testing results show that the dynamic shear strength of sandstone is significantly rate-dependent.Combining the results of dynamic compression and tension tests,the failure envelopes of sandstone under different loading rates are obtained in the principle stress plane.It is found that the failure envelope of sandstone constantly expands outwards with increasing loading rate.Moreover,the energy partition of SBC specimen is quantified by virtue of high-speed digital image correlation(DIC)technique.The results show that the kinetic energy portion is non-negligible,and the shear fracture energy increases with increasing loading rate.In addition,the microscopic shear cracking mechanism of SBC specimen is analyzed by the thin section observation:the intra-granular(TG)fracture of minerals dominates the dynamic shear failure of sandstone,and the portion of TG fracture increases with increasing loading rate.This study provides a convenient and reliable method to investigate the dynamic shear property and failure mechanism of rocks.展开更多
Rock engineering is highly susceptible to cyclic loads resulting from earthquakes,quarrying or rockbursts.Acquiring the fatigue properties and failure mechanism of rocks is pivotal for long-term stability assessment o...Rock engineering is highly susceptible to cyclic loads resulting from earthquakes,quarrying or rockbursts.Acquiring the fatigue properties and failure mechanism of rocks is pivotal for long-term stability assessment of rock engineering structures.So far,significant progress has been gained on the mechanical characteristics of rocks subjected to cyclic loading.For providing a global insight of typical results and main features of rocks under cyclic loading conditions,this study comprehensively reviews the state-ofthe-art of deformation and failure mechanism and fatigue constitutive relationship of rocks subjected to cyclic loading in the past 60 years.Firstly,cyclic tests on rocks are classified into different types based on loading paths,loading parameters,loading types and environment conditions.Secondly,representative results are summarized and highlighted in terms of the fatigue response of rocks,including the deformation degradation,energy dissipation,damage evolution and failure characteristics;both laboratory testing and numerical results are presented,and various measurement techniques such as X-ray microcomputed tomography(micro-CT)and digital image correlation(DIC)are considered.Thirdly,the influences of cyclic loads on the mechanical characteristics of rocks are discussed,including the cyclic stress,frequency,amplitude and waveform.Subsequently,constitutive relationships for rocks subjected to cyclic loading are outlined,in which typical fatigue constitutive models are compared and analyzed,regarding the elastoplastic model,the internal variable model,the energy-based damage model and the discrete element-based model.Finally,some ambiguous questions and prospective research are interpreted and discussed.展开更多
Objective:To compare radiofrequency ablation (RFA) or microwave ablation (MWA) and transcatheter arterial chemoembolization (TACE) with RFA or MWA monotherapy in hepatocellular carcinoma (HCC).Methods:A pros...Objective:To compare radiofrequency ablation (RFA) or microwave ablation (MWA) and transcatheter arterial chemoembolization (TACE) with RFA or MWA monotherapy in hepatocellular carcinoma (HCC).Methods:A prospective,randomized,controlled trial was conducted on 94 patients with HCC ≤7 cm at a single tertiary referral center from June 2008 to June 2010 at the Department of Hepatobiliary Surgery,the Second Affiliated Hospital of Southeast University.The patients were randomly assigned into the TACERFA or TACE-MWA (combined treatment group) and the RFA-alone or MWA-alone groups (control group).The primary end point was overall survival.The secondary end point was recurrence-free survival,and the tertiary end point was adverse effects.Results:Until the time of censor,17 patients in the TACE-RFA or TACE-MWA group had died.The median follow-up time of the patients who were still alive for the TACE-RFA or TACE-MWA group was 47.5±11.3 months (range,29 to 62 months).The 1-,3-and 5-year overall survival for the TACE-RFA or TACE-MWA group was 93.6%,68.1% and 61.7%,respectively.Twenty-five patients in the RFA or MWA group had died.The median follow-up time of the patients who were still alive for the RFA or MWA group was 47.0±12.9 months (range,28 to 62 months).The 1-,3-and 5-year overall survival for the RFA or MWA group was 85.1%,59.6% and 44.7%,respectively.The patients in the TACE-RFA or TACE-MWA group had better overall survival than the RFA or MWA group [hazard ratio (HR),0.526; 95% confidence interval (95% CO,0.334-0.823; P=0.002],and showed better recurrence-free survival than the RFA or MWA group (HR,0.582; 95% CI,0.368-0.895; P=0.008).Conclusions:RFA or MWA combined with TACE in the treatment of HCC ≤7 cm was superior to RFA or MWA alone in improving survival by reducing arterial and portal blood flow due to TACE with iodized oil before RFA.展开更多
Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal ...Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal stress,and minor principal stress,respectively)is essential to the safety of underground engineering.However,in the laboratory,it is difficult to maintain the constant true triaxial stress state of rocks during the dynamic testing process.Herein,a numerical servo triaxial Hopkinson bar(NSTHB)was developed to study the dynamic responses of rocks confronted with a true triaxial stress state,in which lateral stresses can maintain constant.The results indicate that the dynamic strength and elastic modulus of rocks increase with the rise of intermediate principal stressσ2,while the dynamic elastic modulus is independent of the dynamic strain rate.Simulated acoustic emission distributions indicate that the intermediate principal stressσ2 dramatically affects dynamic failure modes of triaxial confined rocks.Asσ2 increases,the failure pattern switches from a single diagonal shear zone into two parallel shear zones with a small slant.Moreover,a recent triaxial Hopkinson bar experimental system using three bar pairs is also numerically established,and the measuring discrepancies are identified between the two numerical bar systems.The proposed NSTHB system provides a controllable tool for studying the dynamic triaxial behavior of rocks.展开更多
Microseismic(MS)event locations are vital aspect of MS monitoring technology used to delineate the damage zone inside the surrounding rock mass.However,complex geological conditions can impose significantly adverse ef...Microseismic(MS)event locations are vital aspect of MS monitoring technology used to delineate the damage zone inside the surrounding rock mass.However,complex geological conditions can impose significantly adverse effects on the final location results.To achieve a high-accuracy location in a complex cavern-containing structure,this study develops an MS location method using the fast marching method(FMM)with a second-order difference approach(FMM2).Based on the established velocity model with three-dimensional(3D)discrete grids,the realization of the MS location can be achieved by searching the minimum residual between the theoretical and actual first arrival times.Moreover,based on the calculation results of FMM2,the propagation paths from the MS sources to MS sensors can be obtained using the linear interpolation approach and the Runge–Kutta method.These methods were validated through a series of numerical experiments.In addition,our proposed method was applied to locate the recorded blasting and MS events that occurred during the excavation period of the underground caverns at the Houziyan hydropower station.The location results of the blasting activities show that our method can effectively reduce the location error compared with the results based on the uniform velocity model.Furthermore,the obtained MS location was verified through the occurrence of shotcrete fractures and spalling,and the monitoring results of the in-situ multipoint extensometer.Our proposed method can offer a more accurate rock fracture location and facilitate the delineation of damage zones inside the surrounding rock mass.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
Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is of paramount importance for underground engineering const...Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is of paramount importance for underground engineering construction.Using a modified split Hopkinson pressure bar(SHPB)system,five groups of single-flawed specimens with the axial prestress ratio from 0 to 0.8 are tested at the strain rates in the range of 65-205 s-1under a fixed radial prestress.Our results indicate that both the dynamic strength and total strength show significant positive linear correlations with the strain rate,and the dynamic strength shows more strain rate sensitivity under higher axial prestress.The dynamic strength and corresponding failure strain decrease with increasing axial prestress,while the total strength is barely affected by the axial prestress.The dynamic elastic modulus initially increases before the axial prestress ratio reaches 0.6 and then decreases.The failure pattern of tested specimens changes from single diagonal failure to an“X”shaped conjugated failure as axial prestress increases.Furthermore,the progressive cracking processes of confined single-flawed specimens under different axial prestresses are numerically visualized by the discrete element method(DEM).Based on the displacement trend lines on both sides of cracking surface,five crack types are identified and classified in our simulation.The displacement field distributions of the DEM models reveal that the macroscopic single diagonal failure under lower axial prestress is mainly controlled by mixed tensile-shear cracks,while the“X”shaped conjugated failure under higher axial prestress is shear dominated.展开更多
As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the researc...As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the research on spherical harmonic analysis and approximation. In this paper, we incompletely introduce the main achievements in this area obtained by our group and relative researchers during recent 5 years (2001-2005). The main topics are: convergence of Cesaro summability, a.e. and strong summability of Fourier-Laplace series; smoothness and K-functionals; Kolmogorov and linear widths.展开更多
Objective: To explore the clinical significance of serum sB7-H3 and IL-1 in patients with hepatitis B associated hepatocellular carcinoma. Methods: 122 cases of patients with hepatitis B related liver diseases admitte...Objective: To explore the clinical significance of serum sB7-H3 and IL-1 in patients with hepatitis B associated hepatocellular carcinoma. Methods: 122 cases of patients with hepatitis B related liver diseases admitted to our hospital from January 2015 to June 2018 were selected, including 47 cases of patients with hepatitis B related hepatocellular carcinoma, 41 cases of patients with hepatitis B related cirrhosis and 34 cases of patients with hepatitis B virus, and 45 cases of healthy persons in the same period as normal control group. The serum sB7-H3, IL-1α, IL-1β levels were compared among the four groups. The relationship between serum sB7-H3, IL-1α, IL-1β and clinicopathological characteristics was analyzed, and the correlation of sB7-H3, IL-1α and IL-1β was analyzed by Pearson method. The efficacy of serum sB7-H3, IL-1α, IL-1β in early diagnosis and prognostic evaluation for hepatitis B associated hepatocellular carcinoma were analyzed by ROC and Logistic regression analysis. Results: The serum sB7-H3, IL-1α, IL-1β levels in the four groups were in order from high to low: hepatitis B related hepatocellular carcinoma>hepatitis B related cirrhosis>hepatitis B virus>normal control group, all above had statistical difference (P<0.05). The high levels of serum sB7-H3, IL-1α, IL-1β were significantly correlated with TNM stage, alpha fetoprotein level and lymph node metastasis (P<0.05). Spearman correlation analysis results showed that the serum level of sB7-H3 was positively correlated with IL-1α and IL-1β(r=0.837, 0.756;P<0.05), the serum level of IL-1α was positively correlated with IL-1β(r=0.734, P<0.05). The ROC curve and Logistic regression analysis showed that the AUC of sB7-H3, IL-1α, IL-1β and combined detection for the diagnosis of hepatitis B associated hepatocellular carcinoma was 0.893, 0.887, 0.881, 0.961 (P<0.05), respectively;the AUC of sB7-H3, IL-1α, IL-1β and combined detection for the prognostic evaluation for hepatitis B associated hepatocellular carcinoma was 0.843, 0.837, 0.834, 0.917, respectively. Conclusion:Serum sB7-H3, IL-1α, IL-1β levels could all be used for the early diagnosis and prognostic evaluation of hepatitis B associated hepatocellular carcinoma, and the combined detection is more effective, which has important clinical significance.展开更多
We study Jackson's inequality on high-dimensional spheres with respect to the modulus of smoothness defined via the rotation group.We obtain a version of Jackson's inequality with a dimensionfree constant,exte...We study Jackson's inequality on high-dimensional spheres with respect to the modulus of smoothness defined via the rotation group.We obtain a version of Jackson's inequality with a dimensionfree constant,extending Newman and Shapiro's well-known results in 1964 from the case of r=1 and p=∞to more general cases.Our results partially overcome the curse of dimensionality.We also establish similar results on the equivalence of the K-functional and modulus of smoothness.展开更多
There is considerable potential for integrating transarterial chemoembolization(TACE),programmed death-(ligand)1(PD-[L]1)inhibitors,and molecular targeted treatments(MTT)in hepatocellular carcinoma(HCC).It is necessar...There is considerable potential for integrating transarterial chemoembolization(TACE),programmed death-(ligand)1(PD-[L]1)inhibitors,and molecular targeted treatments(MTT)in hepatocellular carcinoma(HCC).It is necessary to investigate the therapeutic efficacy and safety of TACE combined with PD-(L)1 inhibitors and MTT in real-world situations.In this nationwide,retrospective,cohort study,826 HCC patients receiving either TACE plus PD-(L)1 blockades and MTT(combination group,n=376)or TACE monotherapy(monotherapy group,n=450)were included from January 2018 to May 2021.The primary endpoint was progression-free survival(PFS)according to modified RECIST.The secondary outcomes included overall survival(OS),objective response rate(ORR),and safety.We performed propensity score matching approaches to reduce bias between two groups.After matching,228 pairs were included with a predominantly advanced disease population.Median PFS in combination group was 9.5 months(95%confidence interval[CI],8.4-11.0)versus 8.0 months(95%CI,6.6-9.5)(adjusted hazard ratio[HR],0.70,P=0.002).OS and ORR were also significantly higher in combination group(median OS,19.2[16.1-27.3]vs.15.7 months[13.0-20.2];adjusted HR,0.63,P=0.001;ORR,60.1%vs.32.0%;P<0.001).Grade 3/4 adverse events were observed at a rate of 15.8%and 7.5%in combination and monotherapy groups,respectively.Our results suggest that TACE plus PD-(L)1 blockades and MTT could significantly improve PFS,OS,and ORR versus TACE monotherapy for Chinese patients with predominantly advanced HCC in real-world practice,with an acceptable safety profile.展开更多
With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A s...With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance.The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique.The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system.Therefore,the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves.Meanwhile,it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient,or decreases in a parabolic function with the increasing trapezoid internal angle.Finally,a case study on the roof block sliding of the roadway at a gold mine was conducted,and it is concluded that the sliding of the key block resulted from the coupled effects of"shear driving"and"low friction"driven by stress wave propagation,regardless of a single or multi-layer rock block system.These results may provide technical guideline for preventing rock-falling accidents caused by blasting distur-bances in underground mining.展开更多
The volume of influence of excavation at the right bank slope of Dagangshan Hydropower Station, southwest China, is essentially determined from microseismic monitoring, numerical modeling and conventional measurements...The volume of influence of excavation at the right bank slope of Dagangshan Hydropower Station, southwest China, is essentially determined from microseismic monitoring, numerical modeling and conventional measurements as well as in situ observations. Microseismic monitoring is a new application technique for investigating microcrackings in rock slopes. A micro- seismic monitoring network has been systematically used to monitor rock masses unloading relaxation due to continuous exca- vation of rock slope and stress redistribution caused by dam impoundment later on, and to identify and delineate the potential slippage regions since May, 2010. An important database of seismic source locations is available. The analysis of microseismic events showed a particular tempo-spatial distribution. Seismic events predominantly occurred around the upstream slope of 1180 m elevation, especially focusing on the hanging wall of fault XL316-1. Such phenomenon was interpreted by numerical modeling using RFPA-SRM code (realistic failure process analysis-strength reduction method). By comparing microseismic activity and results of numerical simulation with in site observation and conventional measurements results, a strong correlation can he obtained between seismic source locations and excavation-induced stress distribution in the working areas. The volume of influence of the rock slope is thus determined. Engineering practices show microseismic monitoring can accurately diagnose magnitude, intensity and associated tempo-spatial characteristics of tectonic activities such as faults and unloading zones. The integrated technique combining seismic monitoring with numerical modeling, as well as in site observation and conventional surveying, leads to a better understanding of the internal effect and relationship between microseismic activity and stress field in the right bank slope from different perspectives.展开更多
基金This work was financially supported by National Key Research and Development Program of China(Grant No.2022YFC2903903)National Natural Science Foundation of China(Grant No.52304132)Yunnan Major Scientific and Technological Projects(Grant No.202202AG050014).These support is gratefully acknowledged.
文摘The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.
基金he authors thank the financial support fromthe Key Program of National Natural Science Foundation of China(GrantNo.52039007)the Youth Science and Technology Innovation Research Team Fund of Sichuan Province(Grant No.2020JDTD0001).
文摘Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict tensile mode(mode I)failure loads of cracked rocks.The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone(FPZ)based on the maximum normal strain(MNSN)ahead of the crack tip,and then use the effective crack to calculate the fracture toughness.We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN.In this way,the FPZ,non-singular terms and the biaxial stress state at the crack tip are simul-taneously considered.The principle of the model is explicit and easy to apply.To verify the proposed model,laboratory experiments were performed on a rock material using six groups of specimens.The model predicted the specimen geometry dependence of the measured fracture toughness well.More-over,the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature.The model was demonstrated su-perior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.
基金We acknowledge the combined support from the National Natural Science Foundation of China(Grant Nos.52039007 and 42102325)Tiandi Science and Technology Co.,Ltd.(Grant No.2022-2-TD-MS012).
文摘Rock mass is a fractured porous medium usually subjected to complex geostress and fluid pressure simultaneously.Moreover,the properties of rock mass change in time and space due to mining-induced fractures.Therefore,it is always challenging to accurately measure rock mass properties.In this study,a three-dimensional(3D)microseismic(MS)data-driven damage model for jointed rock mass under hydro-mechanical coupling conditions is proposed.It is a 3D finite element model that takes seepage,damage and stress field effects into account jointly.Multiple factors(i.e.joints,water and microseismicity)are used to optimize the rock mass mechanical parameters at different scales.The model is applied in Shirengou iron mine to study the damage evolution of rock mass and assess the crown pillar stability during the transition from open-pit to underground mining.It is found that the damage pattern is mostly controlled by the structure,water and rock mass parameters.The damage pattern is evidently different from the two-dimensional result and is more consistent with the field observations.This difference is caused by the MS-derived damage acting on the rock mass.MS data are responsible for gradually correcting the damage zone,changing the direction in which it expands,and promoting it to evolve close to reality.For the crown pillar,the proposed model yields a more trustworthy safety factor.In order to guarantee the stability of the pillar,it is suggested to take waterproof and reinforcement measures in areas with a high degree of damage.
基金The authors thank the financial support from the National Natural Science Foundation of China(Grant.Nos.52039007 and 52225904)the Youth Science and Technology Innovation Research Team Fund of Sichuan Province(Grant.No.2020JDTD0001).
文摘In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(SHPB)system.Firstly,the stress distribution of SBC specimen is comprehensively analyzed by finite element method(FEM),and the results show that the optimal notch separation ratio of SBC specimen is C/H?0.2 to achieve successful dynamic simple-shear tests.Then,dynamic shear tests are conducted on sandstone using the SBC-SHPB method.Via careful pulse shaping technique,the dynamic force balance is guaranteed for SBC specimens,and the testing results show that the dynamic shear strength of sandstone is significantly rate-dependent.Combining the results of dynamic compression and tension tests,the failure envelopes of sandstone under different loading rates are obtained in the principle stress plane.It is found that the failure envelope of sandstone constantly expands outwards with increasing loading rate.Moreover,the energy partition of SBC specimen is quantified by virtue of high-speed digital image correlation(DIC)technique.The results show that the kinetic energy portion is non-negligible,and the shear fracture energy increases with increasing loading rate.In addition,the microscopic shear cracking mechanism of SBC specimen is analyzed by the thin section observation:the intra-granular(TG)fracture of minerals dominates the dynamic shear failure of sandstone,and the portion of TG fracture increases with increasing loading rate.This study provides a convenient and reliable method to investigate the dynamic shear property and failure mechanism of rocks.
基金the financial support from the National Natural Science Foundation of China(Grant Nos.52039007 and 52009086)the Sichuan Province Youth Science and Technology Innovation Team,China(Grant No.2020JDTD0001).
文摘Rock engineering is highly susceptible to cyclic loads resulting from earthquakes,quarrying or rockbursts.Acquiring the fatigue properties and failure mechanism of rocks is pivotal for long-term stability assessment of rock engineering structures.So far,significant progress has been gained on the mechanical characteristics of rocks subjected to cyclic loading.For providing a global insight of typical results and main features of rocks under cyclic loading conditions,this study comprehensively reviews the state-ofthe-art of deformation and failure mechanism and fatigue constitutive relationship of rocks subjected to cyclic loading in the past 60 years.Firstly,cyclic tests on rocks are classified into different types based on loading paths,loading parameters,loading types and environment conditions.Secondly,representative results are summarized and highlighted in terms of the fatigue response of rocks,including the deformation degradation,energy dissipation,damage evolution and failure characteristics;both laboratory testing and numerical results are presented,and various measurement techniques such as X-ray microcomputed tomography(micro-CT)and digital image correlation(DIC)are considered.Thirdly,the influences of cyclic loads on the mechanical characteristics of rocks are discussed,including the cyclic stress,frequency,amplitude and waveform.Subsequently,constitutive relationships for rocks subjected to cyclic loading are outlined,in which typical fatigue constitutive models are compared and analyzed,regarding the elastoplastic model,the internal variable model,the energy-based damage model and the discrete element-based model.Finally,some ambiguous questions and prospective research are interpreted and discussed.
文摘Objective:To compare radiofrequency ablation (RFA) or microwave ablation (MWA) and transcatheter arterial chemoembolization (TACE) with RFA or MWA monotherapy in hepatocellular carcinoma (HCC).Methods:A prospective,randomized,controlled trial was conducted on 94 patients with HCC ≤7 cm at a single tertiary referral center from June 2008 to June 2010 at the Department of Hepatobiliary Surgery,the Second Affiliated Hospital of Southeast University.The patients were randomly assigned into the TACERFA or TACE-MWA (combined treatment group) and the RFA-alone or MWA-alone groups (control group).The primary end point was overall survival.The secondary end point was recurrence-free survival,and the tertiary end point was adverse effects.Results:Until the time of censor,17 patients in the TACE-RFA or TACE-MWA group had died.The median follow-up time of the patients who were still alive for the TACE-RFA or TACE-MWA group was 47.5±11.3 months (range,29 to 62 months).The 1-,3-and 5-year overall survival for the TACE-RFA or TACE-MWA group was 93.6%,68.1% and 61.7%,respectively.Twenty-five patients in the RFA or MWA group had died.The median follow-up time of the patients who were still alive for the RFA or MWA group was 47.0±12.9 months (range,28 to 62 months).The 1-,3-and 5-year overall survival for the RFA or MWA group was 85.1%,59.6% and 44.7%,respectively.The patients in the TACE-RFA or TACE-MWA group had better overall survival than the RFA or MWA group [hazard ratio (HR),0.526; 95% confidence interval (95% CO,0.334-0.823; P=0.002],and showed better recurrence-free survival than the RFA or MWA group (HR,0.582; 95% CI,0.368-0.895; P=0.008).Conclusions:RFA or MWA combined with TACE in the treatment of HCC ≤7 cm was superior to RFA or MWA alone in improving survival by reducing arterial and portal blood flow due to TACE with iodized oil before RFA.
基金the financial support from the National Natural Science Foundation of China(Nos.52039007 and 52009086)the Sichuan Province Youth Science and Technology Innovation Team(No.2020JDTD0001)。
文摘Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal stress,and minor principal stress,respectively)is essential to the safety of underground engineering.However,in the laboratory,it is difficult to maintain the constant true triaxial stress state of rocks during the dynamic testing process.Herein,a numerical servo triaxial Hopkinson bar(NSTHB)was developed to study the dynamic responses of rocks confronted with a true triaxial stress state,in which lateral stresses can maintain constant.The results indicate that the dynamic strength and elastic modulus of rocks increase with the rise of intermediate principal stressσ2,while the dynamic elastic modulus is independent of the dynamic strain rate.Simulated acoustic emission distributions indicate that the intermediate principal stressσ2 dramatically affects dynamic failure modes of triaxial confined rocks.Asσ2 increases,the failure pattern switches from a single diagonal shear zone into two parallel shear zones with a small slant.Moreover,a recent triaxial Hopkinson bar experimental system using three bar pairs is also numerically established,and the measuring discrepancies are identified between the two numerical bar systems.The proposed NSTHB system provides a controllable tool for studying the dynamic triaxial behavior of rocks.
基金the Key Program of National Natural Science Foundation of China(52039007)for providing financial support.
文摘Microseismic(MS)event locations are vital aspect of MS monitoring technology used to delineate the damage zone inside the surrounding rock mass.However,complex geological conditions can impose significantly adverse effects on the final location results.To achieve a high-accuracy location in a complex cavern-containing structure,this study develops an MS location method using the fast marching method(FMM)with a second-order difference approach(FMM2).Based on the established velocity model with three-dimensional(3D)discrete grids,the realization of the MS location can be achieved by searching the minimum residual between the theoretical and actual first arrival times.Moreover,based on the calculation results of FMM2,the propagation paths from the MS sources to MS sensors can be obtained using the linear interpolation approach and the Runge–Kutta method.These methods were validated through a series of numerical experiments.In addition,our proposed method was applied to locate the recorded blasting and MS events that occurred during the excavation period of the underground caverns at the Houziyan hydropower station.The location results of the blasting activities show that our method can effectively reduce the location error compared with the results based on the uniform velocity model.Furthermore,the obtained MS location was verified through the occurrence of shotcrete fractures and spalling,and the monitoring results of the in-situ multipoint extensometer.Our proposed method can offer a more accurate rock fracture location and facilitate the delineation of damage zones inside the surrounding rock mass.
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financial support from the National Natural Science Foundation of China(Grant Nos.52039007and 52009086)the Youth Science and Technology Innovation Team of Sichuan Province,China(Grant No.2020JDTD0001)。
文摘Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is of paramount importance for underground engineering construction.Using a modified split Hopkinson pressure bar(SHPB)system,five groups of single-flawed specimens with the axial prestress ratio from 0 to 0.8 are tested at the strain rates in the range of 65-205 s-1under a fixed radial prestress.Our results indicate that both the dynamic strength and total strength show significant positive linear correlations with the strain rate,and the dynamic strength shows more strain rate sensitivity under higher axial prestress.The dynamic strength and corresponding failure strain decrease with increasing axial prestress,while the total strength is barely affected by the axial prestress.The dynamic elastic modulus initially increases before the axial prestress ratio reaches 0.6 and then decreases.The failure pattern of tested specimens changes from single diagonal failure to an“X”shaped conjugated failure as axial prestress increases.Furthermore,the progressive cracking processes of confined single-flawed specimens under different axial prestresses are numerically visualized by the discrete element method(DEM).Based on the displacement trend lines on both sides of cracking surface,five crack types are identified and classified in our simulation.The displacement field distributions of the DEM models reveal that the macroscopic single diagonal failure under lower axial prestress is mainly controlled by mixed tensile-shear cracks,while the“X”shaped conjugated failure under higher axial prestress is shear dominated.
基金Supported by the NSF of China under the Grant 10471010partially by the NSERC Canada under Grant G121211001
文摘As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the research on spherical harmonic analysis and approximation. In this paper, we incompletely introduce the main achievements in this area obtained by our group and relative researchers during recent 5 years (2001-2005). The main topics are: convergence of Cesaro summability, a.e. and strong summability of Fourier-Laplace series; smoothness and K-functionals; Kolmogorov and linear widths.
基金This study was supported by Nantong City Science and Technology Program 2018 (Guidance) Project, No. MSZ18183, TACE Combined with Microwave Ablation on Immune Function of Smal and Medium-sized Hepatocel ular Carcinoma Patients and Therapeutic Observation
文摘Objective: To explore the clinical significance of serum sB7-H3 and IL-1 in patients with hepatitis B associated hepatocellular carcinoma. Methods: 122 cases of patients with hepatitis B related liver diseases admitted to our hospital from January 2015 to June 2018 were selected, including 47 cases of patients with hepatitis B related hepatocellular carcinoma, 41 cases of patients with hepatitis B related cirrhosis and 34 cases of patients with hepatitis B virus, and 45 cases of healthy persons in the same period as normal control group. The serum sB7-H3, IL-1α, IL-1β levels were compared among the four groups. The relationship between serum sB7-H3, IL-1α, IL-1β and clinicopathological characteristics was analyzed, and the correlation of sB7-H3, IL-1α and IL-1β was analyzed by Pearson method. The efficacy of serum sB7-H3, IL-1α, IL-1β in early diagnosis and prognostic evaluation for hepatitis B associated hepatocellular carcinoma were analyzed by ROC and Logistic regression analysis. Results: The serum sB7-H3, IL-1α, IL-1β levels in the four groups were in order from high to low: hepatitis B related hepatocellular carcinoma>hepatitis B related cirrhosis>hepatitis B virus>normal control group, all above had statistical difference (P<0.05). The high levels of serum sB7-H3, IL-1α, IL-1β were significantly correlated with TNM stage, alpha fetoprotein level and lymph node metastasis (P<0.05). Spearman correlation analysis results showed that the serum level of sB7-H3 was positively correlated with IL-1α and IL-1β(r=0.837, 0.756;P<0.05), the serum level of IL-1α was positively correlated with IL-1β(r=0.734, P<0.05). The ROC curve and Logistic regression analysis showed that the AUC of sB7-H3, IL-1α, IL-1β and combined detection for the diagnosis of hepatitis B associated hepatocellular carcinoma was 0.893, 0.887, 0.881, 0.961 (P<0.05), respectively;the AUC of sB7-H3, IL-1α, IL-1β and combined detection for the prognostic evaluation for hepatitis B associated hepatocellular carcinoma was 0.843, 0.837, 0.834, 0.917, respectively. Conclusion:Serum sB7-H3, IL-1α, IL-1β levels could all be used for the early diagnosis and prognostic evaluation of hepatitis B associated hepatocellular carcinoma, and the combined detection is more effective, which has important clinical significance.
基金supported by National Natural Science Foundation of China(Grant No.12201412)supported by the Natural Sciences and Engineering Research Council of Canada。
文摘We study Jackson's inequality on high-dimensional spheres with respect to the modulus of smoothness defined via the rotation group.We obtain a version of Jackson's inequality with a dimensionfree constant,extending Newman and Shapiro's well-known results in 1964 from the case of r=1 and p=∞to more general cases.Our results partially overcome the curse of dimensionality.We also establish similar results on the equivalence of the K-functional and modulus of smoothness.
基金The study was supported by National Key Research and Development Program(2018YFA0704100,2018YFA0704104)National Natural Science Foundation of China(81827805,82130060)Jiangsu Provincial Special Program of Medical Science(BE2019750).The funding sources had no role in the writing of the report,or decision to submit the paper for publication.
文摘There is considerable potential for integrating transarterial chemoembolization(TACE),programmed death-(ligand)1(PD-[L]1)inhibitors,and molecular targeted treatments(MTT)in hepatocellular carcinoma(HCC).It is necessary to investigate the therapeutic efficacy and safety of TACE combined with PD-(L)1 inhibitors and MTT in real-world situations.In this nationwide,retrospective,cohort study,826 HCC patients receiving either TACE plus PD-(L)1 blockades and MTT(combination group,n=376)or TACE monotherapy(monotherapy group,n=450)were included from January 2018 to May 2021.The primary endpoint was progression-free survival(PFS)according to modified RECIST.The secondary outcomes included overall survival(OS),objective response rate(ORR),and safety.We performed propensity score matching approaches to reduce bias between two groups.After matching,228 pairs were included with a predominantly advanced disease population.Median PFS in combination group was 9.5 months(95%confidence interval[CI],8.4-11.0)versus 8.0 months(95%CI,6.6-9.5)(adjusted hazard ratio[HR],0.70,P=0.002).OS and ORR were also significantly higher in combination group(median OS,19.2[16.1-27.3]vs.15.7 months[13.0-20.2];adjusted HR,0.63,P=0.001;ORR,60.1%vs.32.0%;P<0.001).Grade 3/4 adverse events were observed at a rate of 15.8%and 7.5%in combination and monotherapy groups,respectively.Our results suggest that TACE plus PD-(L)1 blockades and MTT could significantly improve PFS,OS,and ORR versus TACE monotherapy for Chinese patients with predominantly advanced HCC in real-world practice,with an acceptable safety profile.
基金supported by National Natural Science Foundation of China(Grant Nos.U1906208,51874069,51904056)Liaoning Revitalization Talents Program,China(Grant No.XLYC1802031)+1 种基金Fundamental Research Funds for the Central Universities,China(Grant Nos.N180115009,N2101028)China Postdoctoral Science Foundation(Grant No.2020M670782).
文摘With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance.The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique.The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system.Therefore,the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves.Meanwhile,it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient,or decreases in a parabolic function with the increasing trapezoid internal angle.Finally,a case study on the roof block sliding of the roadway at a gold mine was conducted,and it is concluded that the sliding of the key block resulted from the coupled effects of"shear driving"and"low friction"driven by stress wave propagation,regardless of a single or multi-layer rock block system.These results may provide technical guideline for preventing rock-falling accidents caused by blasting distur-bances in underground mining.
基金supported by the National Natural Science Foundation of China (Nos. 50820125405, 50909013 and 50804006)the National Basic Research Program (973) of China (No. 2007CB209404)
文摘The volume of influence of excavation at the right bank slope of Dagangshan Hydropower Station, southwest China, is essentially determined from microseismic monitoring, numerical modeling and conventional measurements as well as in situ observations. Microseismic monitoring is a new application technique for investigating microcrackings in rock slopes. A micro- seismic monitoring network has been systematically used to monitor rock masses unloading relaxation due to continuous exca- vation of rock slope and stress redistribution caused by dam impoundment later on, and to identify and delineate the potential slippage regions since May, 2010. An important database of seismic source locations is available. The analysis of microseismic events showed a particular tempo-spatial distribution. Seismic events predominantly occurred around the upstream slope of 1180 m elevation, especially focusing on the hanging wall of fault XL316-1. Such phenomenon was interpreted by numerical modeling using RFPA-SRM code (realistic failure process analysis-strength reduction method). By comparing microseismic activity and results of numerical simulation with in site observation and conventional measurements results, a strong correlation can he obtained between seismic source locations and excavation-induced stress distribution in the working areas. The volume of influence of the rock slope is thus determined. Engineering practices show microseismic monitoring can accurately diagnose magnitude, intensity and associated tempo-spatial characteristics of tectonic activities such as faults and unloading zones. The integrated technique combining seismic monitoring with numerical modeling, as well as in site observation and conventional surveying, leads to a better understanding of the internal effect and relationship between microseismic activity and stress field in the right bank slope from different perspectives.