Rock-encased-backfill(RB)structures are common in underground mining,for example in the cut-andfill and stoping methods.To understand the effects of cyclic excavation and blasting activities on the damage of these RB ...Rock-encased-backfill(RB)structures are common in underground mining,for example in the cut-andfill and stoping methods.To understand the effects of cyclic excavation and blasting activities on the damage of these RB structures,a series of triaxial stepwise-increasing-amplitude cyclic loading experiments was conducted with cylindrical RB specimens(rock on outside,backfill on inside)with different volume fractions of rock(VF=0.48,0.61,0.73,and 0.84),confining pressures(0,6,9,and 12 MPa),and cyclic loading rates(200,300,400,and 500 N/s).The damage evolution and meso-crack formation during the cyclic tests were analyzed with results from stress-strain hysteresis loops,acoustic emission events,and post-failure X-ray 3D fracture morphology.The results showed significant differences between cyclic and monotonic loadings of RB specimens,particularly with regard to the generation of shear microcracks,the development of stress memory and strain hardening,and the contact forces and associated friction that develops along the rock-backfill interface.One important finding is that as a function of the number of cycles,the elastic strain increases linearly and the dissipated energy increases exponentially.Also,compared with monotonic loading,the cyclic strain hardening characteristics are more sensitive to rising confining pressures during the initial compaction stage.Another finding is that compared with monotonic loading,more shear microcracks are generated during every reloading stage,but these microcracks tend to be dispersed and lessen the likelihood of large shear fracture formation.The transition from elastic to plastic behavior varies depending on the parameters of each test(confinement,volume fraction,and cyclic rate),and an interesting finding was that the transformation to plastic behavior is significantly lower under the conditions of 0.73 rock volume fraction,400 N/s cyclic loading rate,and 9 MPa confinement.All the findings have important practical implications on the ability of backfill to support underground excavations.展开更多
Cyclic triaxial tests are conducted to analyze the evolution of strength parameters and energy dissipation of thawing silty clay under different stress paths.The effects of freezing temperature,thawing temperature and...Cyclic triaxial tests are conducted to analyze the evolution of strength parameters and energy dissipation of thawing silty clay under different stress paths.The effects of freezing temperature,thawing temperature and confining pressures on the stress-strain and strength characteristics of soil samples are studied through monotonic loading and cyclic loading tests by using high-and low-temperature triaxial apparatus.The variation of the total work,elastic deformation energy,dissipated energy,energy dissipation rate,residual strain,and damage variable during loading and unloading are discussed.The experimental results show that the samples have higher strain tolerance under high confining pressure,low freezing temperature,and low thawing temperature,and the same other conditions.The soil sample state and failure pattern can be judged by using the energy parameters measured in the experiment.展开更多
Fatigue tests were conducted on tapered plain concrete prism specimens under tri axial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2f c and the upper st...Fatigue tests were conducted on tapered plain concrete prism specimens under tri axial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2f c and the upper stress ranged from 0. 20f t to 0.65f t. Three constant lateral pressures were 0.1f c, 0.2f c and 0.3f c respec tively. Based on the results, the th ree-stage evolution rule of the fatigue stiffness, maximum(minimum) longitudina l strain and damage were analyzed, and a unified S-N curve to calculate fati gue strength factors was worked out. The results show that the fatigue strength and fa tigue life under triaxial constant-amplitude tension-compression cyclic loadin g are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing thei r relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures.展开更多
An experimental study on performance of plain concrete under triaxial constant-amplitude and variable amplitude tension- compression cyclic loadings was carded out. The low level of the cyclic stress is 0. 2f and the ...An experimental study on performance of plain concrete under triaxial constant-amplitude and variable amplitude tension- compression cyclic loadings was carded out. The low level of the cyclic stress is 0. 2f and the upper level ranges between 0. 20f and 0. 55f., while the constant lateral pressure is 0. 3 f . The specimen failure mode, the three-stage evolution rule of the longitudinal strains and the damage evolution law under cyclic loading were analyzed. Furthermore, Miner's rule is proved not to be applicable to the cyclic loading conditions, hereby, a nonlinear cumulative damage model was established. Based on the model the remaining fatigue life was evaluated. The comparison whh the experiment resuhs shaws that the model is of better precision and applicability.展开更多
Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock und...Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock under different stress paths,a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed,and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied,including the deformation modulus,elastic deformation increment ratios,fracture degree,cohesion and internal friction angle.Additionally,stress path coefficient was defined to characterize different stress paths,and the functional relationships among the stress path coefficient,rock fracture degree difference coefficient,cohesion and internal friction angle were obtained.The results show that during the true triaxial cyclic loading and unloading process,the deformation modulus and cohesion gradually decrease,while the internal friction angle gradually increases with increasing equivalent crack strain.The stress path coefficient is exponentially related to the rock fracture degree difference coefficient.As the stress path coefficient increases,the degrees of cohesion weakening and internal friction angle strengthening decrease linearly.During cyclic loading and unloading under true triaxial principal stress direction interchange,the direction of crack development changes,and the deformation modulus increases,while the cohesion and internal friction angle decrease slightly,indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks.Finally,the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.展开更多
T<span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">his research was carried out to determine the rheological parameters of later...T<span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">his research was carried out to determine the rheological parameters of lateritic soils in order to contribute to the improvement of the technical documents used for pavement design in tropical Africa. The study is based on the loading repeated of cyclic triaxial tests (LRT) performed at </span><span style="font-family:Verdana;">University Gustave Eiffel (formerly Institut Fran<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ç</span>ais des Sciences et Technologies des Transports de l’Aménagement et des Réseaux (IFSTTAR))</span></span></span></span><span><span><span><span style="font-family:;" "=""> </span></span></span></span><span></span><span><span><span style="font-family:Verdana;">in Nantes with the application of the European standard EN 13286-7: 2004</span><span style="font-family:Verdana;"> [<a href="#ref1">1</a>]</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. The tests were performed at constant confinement stress and using the stepwise method to determine the resilient axial (<img src="Edit_9d1c29ae-1a5f-434a-9fe3-00ef5aeb5d24.png" alt="" /></span></span></span><span><span><span style="font-family:;" "=""><span><span style="font-family:Verdana;">) and radial (<img src="Edit_42548459-8f50-4ea1-832d-25e9cfdad034.png" alt="" /></span><span style="font-family:Verdana;">) deformation as a function of the axial and radial stresses. Four gravel lateritic soil</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> from different sites selected in Burkina Faso and Senegal were the subject of this research for the triaxial tests. These materials have a maximum diameter of 20 mm and a percentage of fines less than 20%. The LRT tests were carried out on samples compacted at three moisture contents (</span><i><span style="font-family:Verdana;">w</span><sub><span style="font-family:Verdana;">opm</span></sub></i> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 2%, </span><i><span style="font-family:Verdana;">w</span><sub><span style="font-family:Verdana;">opm</span></sub></i><span style="font-family:Verdana;"> and </span><i><span style="font-family:Verdana;">w</span><sub><span style="font-family:Verdana;">opm</span></sub> </i><span style="font-family:Verdana;">+ 2%) and at 95% and 100% of optimal dry density (</span></span></span></span><span><span><i><span style="font-family:;" "=""><span style="font-family:Verdana;">γ</span><sub><span style="font-family:Verdana;">dopm</span></sub></span></i></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">). Test results showed that the characteristic resilient Young’s modulus (</span><i><span style="font-family:Verdana;">E</span><sub><span style="font-family:Verdana;">c</span></sub></i><span style="font-family:Verdana;">) of gravelly laterites soils depends on the compacted water content and the variation of the grains size distribution (sand (</span><i><span style="font-family:Verdana;"><span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ø</span></span></i><span style="font-family:Verdana;"> < 2 mm), motor (</span><i><span style="font-family:Verdana;"><span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ø</span></span></i><span style="font-family:Verdana;"> < 0.5 mm) and fines content (</span><i><span style="font-family:Verdana;"><span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ø</span></span></i><span style="font-family:Verdana;"> < 0.063 mm) obtained after (LRT). Materials with a high percent of fines (>20%), mortar and sand (Sindia and Lam-Lam) are more sensitive to variations in water content. The presence of water combined with the excess of fines leads to a decrease in modulus around 25% for Lam-Lam and 20.2% for Sindia. Materials containing a low percent of fines, mortar and sand (Badnogo and Dedougou) behave differently. </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">And </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">the resilient modulus increases about 225</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">67% for Badnogo and 312.24% for Dedougou with the rise of the water content for approximately unchanged the percentage of fines, mortar and sand. Granularity therefore has an indirect influence on the resilient modulus of the lateritic soils by controlling the effects of water on the entire system. </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Results of statistical analysis and coefficients of correlation (0.659 to 0.865) showed that the anisotropic Boyce’s model </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">is suitable to predict</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the volumetric </span><span style="font-family:Verdana;">(<img src="Edit_1a36888c-cad0-4f1c-9c68-b5da0ddc323f.png" alt="" /></span><span style="font-family:Verdana;">)</span><span style="font-family:Verdana;"> and deviatoric strain (<img src="Edit_993added-0ec4-49db-ae12-3e540fa49f9c.png" alt="" /></span><span style="font-family:Verdana;">)</span><span style="font-family:Verdana;"> with stress path (Δ</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><i><span style="font-family:Verdana;">q</span></i></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">/Δ</span><i><span style="font-family:Verdana;">p</span></i><span style="font-family:Verdana;">) of the lateritic soils. </span><span><span style="font-family:Verdana;">The predicted </span><i><span style="font-family:Verdana;">E</span><sub><span style="font-family:Verdana;">r</span></sub></i><span style="font-family:Verdana;"> resilient Young’s modulus from anisotropic Boyce’s model varies according to the evolution of </span></span><span style="font-family:Verdana;">the bulk stress (<img src="Edit_ab550c56-8bab-4806-9ec7-fab794d785eb.png" alt="" /></span><span style="font-family:Verdana;">). A correlation around 0.9 is obtained from the power law model.</span></span></span></span></span>展开更多
基金We acknowledge the funding support from the National Natural Science Foundation of China Youth Fund(Grant No.52004019)the National Natural Science Foundation of China(Grant No.41825018)China Postdoctoral Science Foundation(Grant No.2023M733481).
文摘Rock-encased-backfill(RB)structures are common in underground mining,for example in the cut-andfill and stoping methods.To understand the effects of cyclic excavation and blasting activities on the damage of these RB structures,a series of triaxial stepwise-increasing-amplitude cyclic loading experiments was conducted with cylindrical RB specimens(rock on outside,backfill on inside)with different volume fractions of rock(VF=0.48,0.61,0.73,and 0.84),confining pressures(0,6,9,and 12 MPa),and cyclic loading rates(200,300,400,and 500 N/s).The damage evolution and meso-crack formation during the cyclic tests were analyzed with results from stress-strain hysteresis loops,acoustic emission events,and post-failure X-ray 3D fracture morphology.The results showed significant differences between cyclic and monotonic loadings of RB specimens,particularly with regard to the generation of shear microcracks,the development of stress memory and strain hardening,and the contact forces and associated friction that develops along the rock-backfill interface.One important finding is that as a function of the number of cycles,the elastic strain increases linearly and the dissipated energy increases exponentially.Also,compared with monotonic loading,the cyclic strain hardening characteristics are more sensitive to rising confining pressures during the initial compaction stage.Another finding is that compared with monotonic loading,more shear microcracks are generated during every reloading stage,but these microcracks tend to be dispersed and lessen the likelihood of large shear fracture formation.The transition from elastic to plastic behavior varies depending on the parameters of each test(confinement,volume fraction,and cyclic rate),and an interesting finding was that the transformation to plastic behavior is significantly lower under the conditions of 0.73 rock volume fraction,400 N/s cyclic loading rate,and 9 MPa confinement.All the findings have important practical implications on the ability of backfill to support underground excavations.
文摘Cyclic triaxial tests are conducted to analyze the evolution of strength parameters and energy dissipation of thawing silty clay under different stress paths.The effects of freezing temperature,thawing temperature and confining pressures on the stress-strain and strength characteristics of soil samples are studied through monotonic loading and cyclic loading tests by using high-and low-temperature triaxial apparatus.The variation of the total work,elastic deformation energy,dissipated energy,energy dissipation rate,residual strain,and damage variable during loading and unloading are discussed.The experimental results show that the samples have higher strain tolerance under high confining pressure,low freezing temperature,and low thawing temperature,and the same other conditions.The soil sample state and failure pattern can be judged by using the energy parameters measured in the experiment.
基金Project supported by the National Natural Science Foundation of China(Grant No.50078010)
文摘Fatigue tests were conducted on tapered plain concrete prism specimens under tri axial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2f c and the upper stress ranged from 0. 20f t to 0.65f t. Three constant lateral pressures were 0.1f c, 0.2f c and 0.3f c respec tively. Based on the results, the th ree-stage evolution rule of the fatigue stiffness, maximum(minimum) longitudina l strain and damage were analyzed, and a unified S-N curve to calculate fati gue strength factors was worked out. The results show that the fatigue strength and fa tigue life under triaxial constant-amplitude tension-compression cyclic loadin g are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing thei r relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures.
文摘An experimental study on performance of plain concrete under triaxial constant-amplitude and variable amplitude tension- compression cyclic loadings was carded out. The low level of the cyclic stress is 0. 2f and the upper level ranges between 0. 20f and 0. 55f., while the constant lateral pressure is 0. 3 f . The specimen failure mode, the three-stage evolution rule of the longitudinal strains and the damage evolution law under cyclic loading were analyzed. Furthermore, Miner's rule is proved not to be applicable to the cyclic loading conditions, hereby, a nonlinear cumulative damage model was established. Based on the model the remaining fatigue life was evaluated. The comparison whh the experiment resuhs shaws that the model is of better precision and applicability.
基金the financial support from the National Natural Science Foundation of China(Grant Nos.51839003 and 42207221).
文摘Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock under different stress paths,a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed,and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied,including the deformation modulus,elastic deformation increment ratios,fracture degree,cohesion and internal friction angle.Additionally,stress path coefficient was defined to characterize different stress paths,and the functional relationships among the stress path coefficient,rock fracture degree difference coefficient,cohesion and internal friction angle were obtained.The results show that during the true triaxial cyclic loading and unloading process,the deformation modulus and cohesion gradually decrease,while the internal friction angle gradually increases with increasing equivalent crack strain.The stress path coefficient is exponentially related to the rock fracture degree difference coefficient.As the stress path coefficient increases,the degrees of cohesion weakening and internal friction angle strengthening decrease linearly.During cyclic loading and unloading under true triaxial principal stress direction interchange,the direction of crack development changes,and the deformation modulus increases,while the cohesion and internal friction angle decrease slightly,indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks.Finally,the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.
文摘T<span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">his research was carried out to determine the rheological parameters of lateritic soils in order to contribute to the improvement of the technical documents used for pavement design in tropical Africa. The study is based on the loading repeated of cyclic triaxial tests (LRT) performed at </span><span style="font-family:Verdana;">University Gustave Eiffel (formerly Institut Fran<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ç</span>ais des Sciences et Technologies des Transports de l’Aménagement et des Réseaux (IFSTTAR))</span></span></span></span><span><span><span><span style="font-family:;" "=""> </span></span></span></span><span></span><span><span><span style="font-family:Verdana;">in Nantes with the application of the European standard EN 13286-7: 2004</span><span style="font-family:Verdana;"> [<a href="#ref1">1</a>]</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. The tests were performed at constant confinement stress and using the stepwise method to determine the resilient axial (<img src="Edit_9d1c29ae-1a5f-434a-9fe3-00ef5aeb5d24.png" alt="" /></span></span></span><span><span><span style="font-family:;" "=""><span><span style="font-family:Verdana;">) and radial (<img src="Edit_42548459-8f50-4ea1-832d-25e9cfdad034.png" alt="" /></span><span style="font-family:Verdana;">) deformation as a function of the axial and radial stresses. Four gravel lateritic soil</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> from different sites selected in Burkina Faso and Senegal were the subject of this research for the triaxial tests. These materials have a maximum diameter of 20 mm and a percentage of fines less than 20%. The LRT tests were carried out on samples compacted at three moisture contents (</span><i><span style="font-family:Verdana;">w</span><sub><span style="font-family:Verdana;">opm</span></sub></i> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 2%, </span><i><span style="font-family:Verdana;">w</span><sub><span style="font-family:Verdana;">opm</span></sub></i><span style="font-family:Verdana;"> and </span><i><span style="font-family:Verdana;">w</span><sub><span style="font-family:Verdana;">opm</span></sub> </i><span style="font-family:Verdana;">+ 2%) and at 95% and 100% of optimal dry density (</span></span></span></span><span><span><i><span style="font-family:;" "=""><span style="font-family:Verdana;">γ</span><sub><span style="font-family:Verdana;">dopm</span></sub></span></i></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">). Test results showed that the characteristic resilient Young’s modulus (</span><i><span style="font-family:Verdana;">E</span><sub><span style="font-family:Verdana;">c</span></sub></i><span style="font-family:Verdana;">) of gravelly laterites soils depends on the compacted water content and the variation of the grains size distribution (sand (</span><i><span style="font-family:Verdana;"><span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ø</span></span></i><span style="font-family:Verdana;"> < 2 mm), motor (</span><i><span style="font-family:Verdana;"><span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ø</span></span></i><span style="font-family:Verdana;"> < 0.5 mm) and fines content (</span><i><span style="font-family:Verdana;"><span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">ø</span></span></i><span style="font-family:Verdana;"> < 0.063 mm) obtained after (LRT). Materials with a high percent of fines (>20%), mortar and sand (Sindia and Lam-Lam) are more sensitive to variations in water content. The presence of water combined with the excess of fines leads to a decrease in modulus around 25% for Lam-Lam and 20.2% for Sindia. Materials containing a low percent of fines, mortar and sand (Badnogo and Dedougou) behave differently. </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">And </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">the resilient modulus increases about 225</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">67% for Badnogo and 312.24% for Dedougou with the rise of the water content for approximately unchanged the percentage of fines, mortar and sand. Granularity therefore has an indirect influence on the resilient modulus of the lateritic soils by controlling the effects of water on the entire system. </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Results of statistical analysis and coefficients of correlation (0.659 to 0.865) showed that the anisotropic Boyce’s model </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">is suitable to predict</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> the volumetric </span><span style="font-family:Verdana;">(<img src="Edit_1a36888c-cad0-4f1c-9c68-b5da0ddc323f.png" alt="" /></span><span style="font-family:Verdana;">)</span><span style="font-family:Verdana;"> and deviatoric strain (<img src="Edit_993added-0ec4-49db-ae12-3e540fa49f9c.png" alt="" /></span><span style="font-family:Verdana;">)</span><span style="font-family:Verdana;"> with stress path (Δ</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><i><span style="font-family:Verdana;">q</span></i></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">/Δ</span><i><span style="font-family:Verdana;">p</span></i><span style="font-family:Verdana;">) of the lateritic soils. </span><span><span style="font-family:Verdana;">The predicted </span><i><span style="font-family:Verdana;">E</span><sub><span style="font-family:Verdana;">r</span></sub></i><span style="font-family:Verdana;"> resilient Young’s modulus from anisotropic Boyce’s model varies according to the evolution of </span></span><span style="font-family:Verdana;">the bulk stress (<img src="Edit_ab550c56-8bab-4806-9ec7-fab794d785eb.png" alt="" /></span><span style="font-family:Verdana;">). A correlation around 0.9 is obtained from the power law model.</span></span></span></span></span>