Geomechanical properties of rocks vary across different measurement scales,primarily due to heterogeneity.Micro-scale geomechanical tests,including micro-scale“scratch tests”and nano-scale nanoindentation tests,are ...Geomechanical properties of rocks vary across different measurement scales,primarily due to heterogeneity.Micro-scale geomechanical tests,including micro-scale“scratch tests”and nano-scale nanoindentation tests,are attractive at different scales.Each method requires minimal sample volume,is low cost,and includes a relatively rapid measurement turnaround time.However,recent micro-scale test results–including scratch test results and nanoindentation results–exhibit tangible variance and uncertainty,suggesting a need to correlate mineral composition mapping to elastic modulus mapping to isolate the relative impact of specific minerals.Different research labs often utilize different interpretation methods,and it is clear that future micro-mechanical tests may benefit from standardized testing and interpretation procedures.The objectives of this study are to seek options for standardized testing and interpretation procedures,through two specific objectives:(1)Quantify chemical and physical controls on micro-mechanical properties and(2)Quantify the source of uncertainties associated with nanoindentation measurements.To reach these goals,we conducted mechanical tests on three different scales:triaxial compression tests,scratch tests,and nanoindentation tests.We found that mineral phase weight percentage is highly correlated with nanoindentation elastic modulus distribution.Finally,we conclude that nanoindentation testing is a mineralogy and microstructure-based method and generally yields significant uncertainty and overestimation.The uncertainty of the testing method is largely associated with not mapping pore space a priori.Lastly,the uncertainty can be reduced by combining phase mapping and modulus mapping with substantial and random data sampling.展开更多
Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts.Nonetheless,prior investigations have oversimplified the three-dimensional stress state,primarily assuming hydrostatic st...Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts.Nonetheless,prior investigations have oversimplified the three-dimensional stress state,primarily assuming hydrostatic stress conditions.Under these conditions,it is assumed that the intermediate principal stress(σ_(2))equals the minimum principal stress(σ_(3)).This assumption overlooks the potential variations in magnitudes of in situ stress conditions along all three directions near an underground opening where a rock bolt is installed.In this study,a series of push tests was meticulously conducted under triaxial conditions.These tests involved applying non-uniform confining stresses(σ_(2)≠σ_(3))to cubic specimens,aiming to unveil the previously overlooked influence of intermediate principal stresses on the strength properties of rock bolts.The results show that as the confining stresses increase from zero to higher levels,the pre-failure behavior changes from linear to nonlinear forms,resulting in an increase in initial stiffness from 2.08 kN/mm to 32.51 kN/mm.The load-displacement curves further illuminate distinct post-failure behavior at elevated levels of confining stresses,characterized by enhanced stiffness.Notably,the peak load capacity ranged from 27.9 kN to 46.5 kN as confining stresses advanced from σ_(2)=σ_(3)=0 to σ_(2)=20 MPa and σ_(3)=10 MPa.Additionally,the outcomes highlight an influence of confining stress on the lateral deformation of samples.Lower levels of confinement prompt overall dilation in lateral deformation,while higher confinements maintain a state of shrinkage.Furthermore,diverse failure modes have been identified,intricately tied to the arrangement of confining stresses.Lower confinements tend to induce a splitting mode of failure,whereas higher loads bring about a shift towards a pure interfacial shear-off and shear-crushed failure mechanism.展开更多
In many engineering applications,it is important to determine both effective rock properties and the rock behavior which are representative for the problem’s in situ conditions.For this purpose,rock samples are usual...In many engineering applications,it is important to determine both effective rock properties and the rock behavior which are representative for the problem’s in situ conditions.For this purpose,rock samples are usually extracted from the ground and brought to the laboratory to perform laboratory experiments such as consolidated undrained(CU)triaxial tests.For low permeable geomaterials such as clay shales,core extraction,handling,storage,and specimen preparation can lead to a reduction in the degree of saturation and the effective stress state in the specimen prior to testing remains uncertain.Related changes in structure and the effect of capillary pressure can alter the properties of the specimen and affect the reliability of the test results.A careful testing procedure including back-saturation,consolidation and adequate shearing of the specimen,however,can overcome these issues.Although substantial effort has been devoted during the past decades to the establishment of a testing procedure for low permeable geomaterials,no consistent protocol can be found.With a special focus on CU tests on Opalinus Clay,this study gives a review of the theoretical concepts necessary for planning and validating the results during the individual testing stages(saturation,consolidation,and shearing).The discussed tests protocol is further applied to a series of specimens of Opalinus Clay to illustrate its applicability and highlight the key aspects.展开更多
Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric...Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress amplitudes.The samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 Hz.At each level of confining pressure,the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was observed.Analysis of the test results indicated that there existed a critical cyclic deviatoric stress amplitude(i.e.critical dynamic deviatoric stress)beyond which the jointed rock specimens yielded.The measured critical dynamic deviatoric stress was less than the corresponding static deviatoric stress.At cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress,minor cumulative residual axial strains were observed,resulting in hysteretic damping.However,for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress,the plastic strains increased promptly,and the resilient moduli degraded rapidly during the initial loading cycles.Cyclic triaxial test results showed that at higher confining pressures,the ultimate residual axial strain attained by the jointed rock specimen decreased,the steadystate dissipated energy density and steady-state damping ratio per load cycle decreased,while steadystate resilient moduli increased.展开更多
Triaxial tests,a staple in rock engineering,are labor-intensive,sample-demanding,and costly,making their optimization highly advantageous.These tests are essential for characterizing rock strength,and by adopting a fa...Triaxial tests,a staple in rock engineering,are labor-intensive,sample-demanding,and costly,making their optimization highly advantageous.These tests are essential for characterizing rock strength,and by adopting a failure criterion,they allow for the derivation of criterion parameters through regression,facilitating their integration into modeling programs.In this study,we introduce the application of an underutilized statistical technique—orthogonal regression—well-suited for analyzing triaxial test data.Additionally,we present an innovation in this technique by minimizing the Euclidean distance while incorporating orthogonality between vectors as a constraint,for the case of orthogonal linear regression.Also,we consider the Modified Least Squares method.We exemplify this approach by developing the necessary equations to apply the Mohr-Coulomb,Murrell,Hoek-Brown,andÚcar criteria,and implement these equations in both spreadsheet calculations and R scripts.Finally,we demonstrate the technique's application using five datasets of varied lithologies from specialized literature,showcasing its versatility and effectiveness.展开更多
The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compressio...The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compression tests,CT scanning,SEM,and EDS tests were conducted on cemented gangue backfill samples(CGBSs)with various carbon nanotube concentrations(P_(CNT))that satisfied fractal theory for the PSD of aggregates.The mechanical properties,energy dissipations,and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed.The results indicate that appropriate carbon nanotubes(CNTs)effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging,and the optimal effect appears at P_(CNT)of 0.08wt%.Taking PSD fractal dimension(D)of 2.500 as an example,compared to that of CGBS without CNT,the peak strength(σ_(p)),axial peak strain(ε_(1,p)),elastic strain energy(Ue),and dissipated energy(U_(d))increased by 12.76%,29.60%,19.05%,and90.39%,respectively.However,excessive CNTs can reduce the mechanical properties of CGBSs due to CNT agglomeration,manifesting a decrease inρ_(p),ε_(1,p),and the volumetric strain increment(Δε_(v))when P_(CNT)increases from 0.08wt%to 0.12wt%.Moreover,the addition of CNTs improved the integrity of CGBS after macroscopic failure,and crack extension in CGBSs appeared in two modes:detour and pass through the aggregates.Theσ_(p)and U_(d)firstly increase and then decrease with increasing D,and porosity shows the opposite trend.Theε_(1,p)andΔε_(v)are negatively correlated with D,and CGBS with D=2.150 has the maximum deformation parameters(ε_(1,p)=0.05079,Δε_(v)=0.01990)due to the frictional slip effect caused by coarse aggregates.With increasing D,the failure modes of CGBSs are sequentially manifested as oblique shear failure,"Y-shaped"shear failure,and conjugate shear failure.展开更多
Triaxial testing serves as a fundamental method for evaluating the elastic and strength properties of rocks,crucial for developing accurate 3D geomechanical models.This paper presents a novel method for determining st...Triaxial testing serves as a fundamental method for evaluating the elastic and strength properties of rocks,crucial for developing accurate 3D geomechanical models.This paper presents a novel method for determining strength parameters by incorporating the dependence of uniaxial compressive strength(UCS)on P-wave velocity into the Hoek-Brown criterion.Additionally,a new approach is introduced to process triaxial test data efficiently using Python libraries such as SciPy,NumPy,Matplotlib,and Pandas.Furthermore,the paper addresses challenges in determining elastic parameters through triaxial testing.A Python script is developed to automate the calculation of elastic modulus and Poisson's ratio,over-coming subjectivity in selecting the linear portion of stress-strain curves.The script optimally identifies the linear region by minimizing the fit error with appropriate constraints,ensuring a more objective and standardized approach.The proposed methodologies are demonstrated using limestone specimens from Central Asian gas fields.These innovations offer faster,more reliable results,reducing error and enhancing the comparability of analyses in geomechanics,with potential applications across various geological settings.展开更多
This study presents an in-depth investigation into the shear strength characteristics of unsaturated soils,focusing on the influenceof shear rate and initial water saturation(S_(r0)).Utilizing the drained-vented(DV)tr...This study presents an in-depth investigation into the shear strength characteristics of unsaturated soils,focusing on the influenceof shear rate and initial water saturation(S_(r0)).Utilizing the drained-vented(DV)triaxial test method,the present study investigated the shear strength behavior of silty clay under various shear rates and water saturation levels,and compared the outcomes with traditional suction-controlled(SC)and constant water content(CW)tests.The findingshighlight the pivotal role of excess pore water pressure dissipation during shearing,which significantlyaffects the shear strength of both saturated and unsaturated soils.Notably,for soils with high initial water saturation,a decrease in shear strength is observed with an increase in shear rate,which is attributed to the rise in pore water pressure.Conversely,for soils with low initial water saturation,the shear rate exhibits minimal impact on shear strength due to negligible water drainage.The research delineates the optimal shear rates for DV tests based on the initial water saturation:a slower rate of 0.0028 mm/min for samples with high water saturation(S_(r0)>66%)and a faster rate of 0.8 mm/min for samples with low water saturation(S_(r0)≤66%).A novel testing methodology for determining unsaturated soil shear strength under DV conditions is introduced,streamlining the measurement process and significantly reducing testing time.This method not only promises substantial cost savings but also aligns closely with natural engineering conditions,offering valuable guidance for geotechnical applications.展开更多
Microstructural heterogeneity of low-permeability sandstone roofs of deep unmineable coal seams due to diagenesis significantly affects rock mechanical behavior,greatly impacting the sealing potential of in situ CO_(2...Microstructural heterogeneity of low-permeability sandstone roofs of deep unmineable coal seams due to diagenesis significantly affects rock mechanical behavior,greatly impacting the sealing potential of in situ CO_(2) sequestration and the structural stability of the geological formation.However,little is known about how the microstructure of different mineral groups influences the multiscale mechanical behavior of deep sandstone.This study proposes a new method for quantitatively characterizing the multiscale mechanical properties of low-permeability sandstone and shows the mechanisms responsible for mechanical failure at the micro-,meso-,and macroscale.Triaxial compression tests and targeted nanoindentation tests were conducted to assess the micro-and macroscale mechanical properties of different types of sandstone.The micro-and macroscale experiments were coupled with numerical simulations of compression using a unified cohesive model based on Voronoi polygons to clarify the multiscale mechanical behavior.The results indicate that quartz,the primary mineral component of the sandstones examined,exhibits the strongest micromechanical properties,followed by feldspar,calcite,and clay minerals.Compared to polycrystalline quartz,monocrystalline quartz has a more stable microstructure and is mechanically stronger.The macro-mechanical properties of tight sandstone samples are weakened by increased microstructural inhomogeneity and larger grain size.This leads to a higher likelihood of splitting damage,characterized by a high degree of discrete and weak stress sensitivity.The major conclusion is that the positive rhythm lithofacies of medium-grained sandstone to siltstone are the most favorable for efficient CO_(2) sequestration in deep unmineable coal seams.展开更多
This paper presents a new criterion for determining the unloading points quantitatively and consistently in a multi-stage triaxial test.The radial strain gradient(RSG)is first introduced as an arc tangent function of ...This paper presents a new criterion for determining the unloading points quantitatively and consistently in a multi-stage triaxial test.The radial strain gradient(RSG)is first introduced as an arc tangent function of the rate of change of radial strain to time.RSG is observed to correlate closely with the stress state of a compressed sample,and reaches a horizontal asymptote as approaching failure.For a given rock type,RSG value at peak stress is almost the same,irrespective of the porosity and permeability.These findings lead to the development of RSG criterion:Unloading points can be precisely determined at the time when RSG reaches a pre-determined value that is a little smaller than or equal to the RSG at peak stress.The RSG criterion is validated against other criteria and the single-stage triaxial test on various types of rocks.Failure envelopes from the RSG criterion match well with those from single-stage tests.A practical procedure is recommended to use the RSG criterion:an unconfined compression or single-stage test is first conducted to determine the RSG at peak stress for one sample,the unloading point is then selected to be a value close to the RSG at peak stress,and the multi-stage test is finally performed on another sample using the pre-selected RSG unloading criterion.Generally,the RSG criterion is applicable for any type of rocks,especially brittle rocks,where other criteria are not suitable.Further,it can be practically implemented on the most available rock mechanical testing instruments.展开更多
Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology.Then,true triaxial compression loading experiments were conducted on those jointed spec...Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology.Then,true triaxial compression loading experiments were conducted on those jointed specimens.The increase in roughness leads to an increase in the axial strength and peak strain.With the increasing inclination angle,the axial strength initially decreases from 30°to 60°and then increases from 60°to 90°.While the peak strain first rises from 30°to 45°and then declines from 45°to 90°.The variation in failure mode results from differences in lateral stress on the joints under different strike directions.Specimens with joint strike parallel to the intermediate principal stress predominantly showed matrix or matrix-joint mixed shear failure,whereas those parallel to the minimum principal stress exhibited matrix shear failure.The analysis results of acoustic emission signals indicate the crack number and shear crack percentage increase with the increasing roughness and first decrease(30°to 60°),then increase(60°to 90°)with the increasing inclination angle.The research results can provide some guidance for the design and support of underground engineering with jointed surrounding rock.展开更多
The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods,and the large-size mined-out area is usually backfilled by multiple backfilling be...The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods,and the large-size mined-out area is usually backfilled by multiple backfilling before the recovery of a secondary stope,resulting in a layered structure of backfill in stope.Therefore,it is significant to investigate the deformation responses and mechanical properties of stratified cemented tailings backfill(SCTB)with different layer structures to remain self-standing as an artificial pillar in the primary stope.The current work examined the effects of enhance layer position(1/3,1/2,and 2/3)and thickness ratio(0,0.1,0.2,and 0.3)on the mechanical properties,deformation,energy evolution,microstructures,and failure modes of SCTB.The results demonstrate that the incorporation of an enhance layer significantly strengthens the deformation and strength of SCTB.Under a confining pressure of 50 kPa,the peak deviatoric stress rises from 525.6 to 560.3,597.1,and 790.5 kPa as the thickness ratio of enhance layer is increased from 0 to 0.1,0.2,and 0.3,representing a significant increase of 6.6%,13.6%,and 50.4%.As the confining pressure increases,the slopes of the curves in the elastic stage become steep,and the plastic phase is extended accordingly.Additionally,the incorporation of the enhance layer significantly improves the energy storage linit of SCTB specimen.As the thickness ratio of the enhance layer increases from 0 to 0.1,0.2,and 0.3,the elastic energy rises from 0.54 to 0.67,0.84,and 1.00 MJ·m^(-3),representing a significant increase of 24.1%,55.6%,and 85.2%.The internal friction angles and cohesions of the SCTB specimens are higher than those of the CTB specimens,however,the cohesion is more susceptible to enhance layer position and thickness ratio than the internal friction angle.The failure style of the SCTB specimen changes from shear failure to splitting bulging failure and shear bulging failure with the presence of an enhance layer.The crack propagation path is significantly blocked by the enhance layer.The findings are of great significance to the application and stability of the SCTB in subsequent stoping backfilling mines.展开更多
After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimension...After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference.However,the shear mechanical behavior,fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear.Therefore,this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-,bi-and tri-directional coupling disturbances to analyze its mechanical behavior,fracture evolution mechanism and precursor characteristics.The results show that as the disturbance direction increase,the shear strength of limestone generally decreases,while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend.The proportion of shear cracks on the structural plane increases with the increase of shear stress.The disturbance strain rate before failure shows a U-shaped trend.Near to disturbance failure,there were more high-energy and high-amplitude acoustic emission events near the structural plane,and b-value drops rapidly below 1,while lgN/b ratio increased to above 3.These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.展开更多
Both the repeated triaxial test （RTT） and the Hamburg wheel tracking test （HWTT） are adopted to evaluate the high temperature performance of the stone mastic asphalt （SMA） and the mastic asphalt （MA）. The corr...Both the repeated triaxial test （RTT） and the Hamburg wheel tracking test （HWTT） are adopted to evaluate the high temperature performance of the stone mastic asphalt （SMA） and the mastic asphalt （MA）. The correlation of the permanent deformations of the MA and the correlation of the deformation developments of the SMA between the two tests are analyzed, respectively. Results show that both the two tests can effectively identify the high temperature performance of mixtures, and the correlation between the final results of the two tests as well as that between the deformation developments of the two tests are excellent with R20.9. In order to further prove the correlation, viscoelastic parameters estimated from the RTT results is used to simulate the rutting development in the HWTT slabs by the finite element method （FEM）. Results indicate that the correlation between the two tests is significant with errors less than 10%. It is suitable to predict the rutting development with the viscoelastic parameters obtained from the RTT.展开更多
This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designe...This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter.The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force,penetration depth,characteristics of chippings and failure patterns.Several quantitative indexes were used to evaluate rock boreability in this investigation.The granite rock samples all had a chiselled pit and a crushed rock core.Under initial stress conditions,only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN.The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape.Moreover,a thrusting force prediction model was proposed in this paper.The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus.This study has a crucial importance for practical underground hard rock crushing in geoengineering.展开更多
To investigate the strength degradation characteristics and microscopic damage mechanisms of moraine soil under hydro-thermo-mechanical coupling conditions,a series of X-ray Diffraction(XRD),standard triaxial testing,...To investigate the strength degradation characteristics and microscopic damage mechanisms of moraine soil under hydro-thermo-mechanical coupling conditions,a series of X-ray Diffraction(XRD),standard triaxial testing,Scanning Electron Microscopy(SEM),and Nuclear Magnetic Resonance(NMR)experiments were conducted.The mechanical property degradation laws and evolution characteristics of the microscopic pore structure of moraine soil under Freeze-Thaw(F-T)conditions were revealed.After F-T cycles,the stress-strain curves of moraine soil showed a strain-softening trend.In the early stage of F-T cycles(0–5 cycles),the shear strength and elastic modulus exhibited damage rate of approximately 10.33%±0.8%and 16.60%±1.2%,respectively.In the later stage(10–20 cycles),the strength parameters fluctuated slightly and tended to stabilize.The number of F-T cycles was negatively exponentially correlated with cohesion,while showing only slight fluctuation in the internal friction angle,thereby extending the Mohr-Coulomb strength criterion for moraine soil under F-T cycles.The NMR experiments quantitatively characterized the evolution of the internal pore structure of moraine soil under F-T cycles.As the number of F-T cycles increased,fine and micro pores gradually expanded and merged due to the frost-heaving effect during the water-ice phase transition,forming larger pores.The proportion of large and medium pores increased to 59.55%±2.1%(N=20),while that of fine and micro pores decreased to 40.45%±2.1%(N=20).The evolution of pore structure characteristics was essentially completed in the later stage of F-T cycles(10–20 cycles).This study provides a theoretical foundation and technical support for major engineering construction and disaster prevention in the Qinghai-Xizang Plateau.展开更多
The lithology of fracture zone which was developed at the dam foundation of a hydropower station is weak sandstone with poor integrity and pore cementation contact.Its creep properties have a significant impact on the...The lithology of fracture zone which was developed at the dam foundation of a hydropower station is weak sandstone with poor integrity and pore cementation contact.Its creep properties have a significant impact on the deformation and stability of the dam.Based on the characteristics of loose organizational structure,high moisture content and poor mechanical properties,the triaxial compression tests and creep tests were carried out,respectively.The results show significant non-linear,low strength and no obvious strength peaks.Both axial and lateral strains are achieved more than 3%when the tests are failed.The weak sandstone has a significant creep property,but only transient and steady state appear under low stress.Increased stress causes creep intensified and lateral strain gradually exceeds axial strain.In the failure stage,it has characteristics of large axial plastic deformation,obvious volumetric ductility dilation and large steady creep rate.The accelerated creep appears shortly after transient loading under confining of pressures 1.0 MPa and 1.5 MPa.Therefore,an improved Burgers creep model considering the non-linear characteristics of weak sandstone is built based on hyperbolic equation and the creep parameters are identified.This model can well describe the creep properties of weak sandstone.展开更多
In order to investigate the influence of intermediate principal stress on the stress-strain and strength behaviour of a coarse-grained soil, a series of true triaxial tests were performed. The tests were conducted in ...In order to investigate the influence of intermediate principal stress on the stress-strain and strength behaviour of a coarse-grained soil, a series of true triaxial tests were performed. The tests were conducted in a recently developed true triaxial apparatus with constant minor principal stress σ3 and constant value of intermediate principal stress ratio b=（σ2-σ3）/（σ1-σ3） （al is the vertical stress, and % is the horizontal stress）. It is found that the intermediate principal strain, ε2, increases from negative to positive value with the increase of parameter b from zero to unity under a constant minor principal stress. The minor principal strain, ε3, is always negative. This implies that the specimen exhibits an evident anisotropy. The relationship between b and friction angle obtained from the tests is different from that predicted by LADE-DUNCAN and MATSUOKA-NAKAI criteria. Based on the test results, an empirical equation of g（b） that is the shape function of the failure surface on re-plane was presented. The proposed equation is verified to be reasonable by comparing the predicted results using the equation with true triaxial test results of soils, such as coarse-grained soils in this study, sands and gravels in other studies.展开更多
The mechanical behavior of plastic concrete used in the cut-off walls of earth dams has been studied. Triaxial compression tests on the specimens in various ages and mix designs under different confining pressures hav...The mechanical behavior of plastic concrete used in the cut-off walls of earth dams has been studied. Triaxial compression tests on the specimens in various ages and mix designs under different confining pressures have been done and the stress-strain behavior of such materials and their strength parameter changes have been experimentally investigated. It has been observed that increasing the confining pressures applied on the specimens causes the material behavior to be alike the more ductile materials and the compressive strength increases considerably as well. Moreover, a parametric study has been carded out to investigate the influence of essential parameters on the shear strength parameters of these materials. According to the research, increasing the coarse to fine aggregates ratio leads to the increase of compressive strength of the specimens as well as the increase of the cohesion and internal friction angle of the materials. Furthermore, the bentonite content decrease and the cement factor increase result in an increase of the cohesion parameter of plastic concretes and decrease of the internal friction angle of such materials.展开更多
The construction of a high-speed railway(HSR) in Southwest China is being hindered by a severe shortage of high-quality subgrade materials. However, red mudstone is widely distributed in the Sichuan Basin of China. Th...The construction of a high-speed railway(HSR) in Southwest China is being hindered by a severe shortage of high-quality subgrade materials. However, red mudstone is widely distributed in the Sichuan Basin of China. The ability to use weathered red mudstone(WRM) to fill subgrade beds by controlling its critical stress and cumulative strain would enable substantial savings in project investments and mitigate damage to the ecological environment. To better understand the dynamic behaviour of WRM, both monotonic and cyclic triaxial tests were performed. The evolution of the cumulative strain vs. increased loading cycles was measured. The influences of confining pressure and loading cycles on the dynamic modulus, damping ratio, critical cyclic stress ratio(CSR), and dynamic stress level(DSL) were investigated. The relationship between the CSR and loading cycles under different failure strain criteria(0.1%-1.0%) was analysed. The prediction model of cumulative strain was also evaluated. The results indicated that the shear strength of WRM sufficiently meets the static strength requirements of subgrade. The critical dynamic stress of WRM can thus satisfy the dynamic stress-bearing requirement of the HSR subgrade. The critical CSR decreases and displays a power function with increasing confining pressure. As the confining pressure increases, the DSL remains relatively stable, ranging between 0.153 and 0.163. Furthermore, the relationship between the dynamic strength and loading cycles required to cause failure was established. Finally, a newly developed model for determining cumulative strain was established. A prediction exercise showed that the model is in good agreement with the experimental data.展开更多
基金support of this project through the Southwest Regional Partnership on Carbon Sequestration(Grant No.DE-FC26-05NT42591)Improving Production in the Emerging Paradox Oil Play(Grant No.DE-FE0031775).
文摘Geomechanical properties of rocks vary across different measurement scales,primarily due to heterogeneity.Micro-scale geomechanical tests,including micro-scale“scratch tests”and nano-scale nanoindentation tests,are attractive at different scales.Each method requires minimal sample volume,is low cost,and includes a relatively rapid measurement turnaround time.However,recent micro-scale test results–including scratch test results and nanoindentation results–exhibit tangible variance and uncertainty,suggesting a need to correlate mineral composition mapping to elastic modulus mapping to isolate the relative impact of specific minerals.Different research labs often utilize different interpretation methods,and it is clear that future micro-mechanical tests may benefit from standardized testing and interpretation procedures.The objectives of this study are to seek options for standardized testing and interpretation procedures,through two specific objectives:(1)Quantify chemical and physical controls on micro-mechanical properties and(2)Quantify the source of uncertainties associated with nanoindentation measurements.To reach these goals,we conducted mechanical tests on three different scales:triaxial compression tests,scratch tests,and nanoindentation tests.We found that mineral phase weight percentage is highly correlated with nanoindentation elastic modulus distribution.Finally,we conclude that nanoindentation testing is a mineralogy and microstructure-based method and generally yields significant uncertainty and overestimation.The uncertainty of the testing method is largely associated with not mapping pore space a priori.Lastly,the uncertainty can be reduced by combining phase mapping and modulus mapping with substantial and random data sampling.
文摘Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts.Nonetheless,prior investigations have oversimplified the three-dimensional stress state,primarily assuming hydrostatic stress conditions.Under these conditions,it is assumed that the intermediate principal stress(σ_(2))equals the minimum principal stress(σ_(3)).This assumption overlooks the potential variations in magnitudes of in situ stress conditions along all three directions near an underground opening where a rock bolt is installed.In this study,a series of push tests was meticulously conducted under triaxial conditions.These tests involved applying non-uniform confining stresses(σ_(2)≠σ_(3))to cubic specimens,aiming to unveil the previously overlooked influence of intermediate principal stresses on the strength properties of rock bolts.The results show that as the confining stresses increase from zero to higher levels,the pre-failure behavior changes from linear to nonlinear forms,resulting in an increase in initial stiffness from 2.08 kN/mm to 32.51 kN/mm.The load-displacement curves further illuminate distinct post-failure behavior at elevated levels of confining stresses,characterized by enhanced stiffness.Notably,the peak load capacity ranged from 27.9 kN to 46.5 kN as confining stresses advanced from σ_(2)=σ_(3)=0 to σ_(2)=20 MPa and σ_(3)=10 MPa.Additionally,the outcomes highlight an influence of confining stress on the lateral deformation of samples.Lower levels of confinement prompt overall dilation in lateral deformation,while higher confinements maintain a state of shrinkage.Furthermore,diverse failure modes have been identified,intricately tied to the arrangement of confining stresses.Lower confinements tend to induce a splitting mode of failure,whereas higher loads bring about a shift towards a pure interfacial shear-off and shear-crushed failure mechanism.
基金funded by the Swiss Federal Nuclear Safety Inspectorate ENSI (Grant no. H-100897)
文摘In many engineering applications,it is important to determine both effective rock properties and the rock behavior which are representative for the problem’s in situ conditions.For this purpose,rock samples are usually extracted from the ground and brought to the laboratory to perform laboratory experiments such as consolidated undrained(CU)triaxial tests.For low permeable geomaterials such as clay shales,core extraction,handling,storage,and specimen preparation can lead to a reduction in the degree of saturation and the effective stress state in the specimen prior to testing remains uncertain.Related changes in structure and the effect of capillary pressure can alter the properties of the specimen and affect the reliability of the test results.A careful testing procedure including back-saturation,consolidation and adequate shearing of the specimen,however,can overcome these issues.Although substantial effort has been devoted during the past decades to the establishment of a testing procedure for low permeable geomaterials,no consistent protocol can be found.With a special focus on CU tests on Opalinus Clay,this study gives a review of the theoretical concepts necessary for planning and validating the results during the individual testing stages(saturation,consolidation,and shearing).The discussed tests protocol is further applied to a series of specimens of Opalinus Clay to illustrate its applicability and highlight the key aspects.
文摘Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60were prepared,and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress amplitudes.The samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 Hz.At each level of confining pressure,the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was observed.Analysis of the test results indicated that there existed a critical cyclic deviatoric stress amplitude(i.e.critical dynamic deviatoric stress)beyond which the jointed rock specimens yielded.The measured critical dynamic deviatoric stress was less than the corresponding static deviatoric stress.At cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress,minor cumulative residual axial strains were observed,resulting in hysteretic damping.However,for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress,the plastic strains increased promptly,and the resilient moduli degraded rapidly during the initial loading cycles.Cyclic triaxial test results showed that at higher confining pressures,the ultimate residual axial strain attained by the jointed rock specimen decreased,the steadystate dissipated energy density and steady-state damping ratio per load cycle decreased,while steadystate resilient moduli increased.
文摘Triaxial tests,a staple in rock engineering,are labor-intensive,sample-demanding,and costly,making their optimization highly advantageous.These tests are essential for characterizing rock strength,and by adopting a failure criterion,they allow for the derivation of criterion parameters through regression,facilitating their integration into modeling programs.In this study,we introduce the application of an underutilized statistical technique—orthogonal regression—well-suited for analyzing triaxial test data.Additionally,we present an innovation in this technique by minimizing the Euclidean distance while incorporating orthogonality between vectors as a constraint,for the case of orthogonal linear regression.Also,we consider the Modified Least Squares method.We exemplify this approach by developing the necessary equations to apply the Mohr-Coulomb,Murrell,Hoek-Brown,andÚcar criteria,and implement these equations in both spreadsheet calculations and R scripts.Finally,we demonstrate the technique's application using five datasets of varied lithologies from specialized literature,showcasing its versatility and effectiveness.
基金financially supported by the National Natural Science Foundation of China(Nos.52174092,51904290,and 52374147)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+2 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the National Key Research and Development Program of China(No.2023YFC3804204)the Major Program of Xinjiang Uygur Autonomous Region S cience and Technology(No.2023A01002)。
文摘The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compression tests,CT scanning,SEM,and EDS tests were conducted on cemented gangue backfill samples(CGBSs)with various carbon nanotube concentrations(P_(CNT))that satisfied fractal theory for the PSD of aggregates.The mechanical properties,energy dissipations,and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed.The results indicate that appropriate carbon nanotubes(CNTs)effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging,and the optimal effect appears at P_(CNT)of 0.08wt%.Taking PSD fractal dimension(D)of 2.500 as an example,compared to that of CGBS without CNT,the peak strength(σ_(p)),axial peak strain(ε_(1,p)),elastic strain energy(Ue),and dissipated energy(U_(d))increased by 12.76%,29.60%,19.05%,and90.39%,respectively.However,excessive CNTs can reduce the mechanical properties of CGBSs due to CNT agglomeration,manifesting a decrease inρ_(p),ε_(1,p),and the volumetric strain increment(Δε_(v))when P_(CNT)increases from 0.08wt%to 0.12wt%.Moreover,the addition of CNTs improved the integrity of CGBS after macroscopic failure,and crack extension in CGBSs appeared in two modes:detour and pass through the aggregates.Theσ_(p)and U_(d)firstly increase and then decrease with increasing D,and porosity shows the opposite trend.Theε_(1,p)andΔε_(v)are negatively correlated with D,and CGBS with D=2.150 has the maximum deformation parameters(ε_(1,p)=0.05079,Δε_(v)=0.01990)due to the frictional slip effect caused by coarse aggregates.With increasing D,the failure modes of CGBSs are sequentially manifested as oblique shear failure,"Y-shaped"shear failure,and conjugate shear failure.
文摘Triaxial testing serves as a fundamental method for evaluating the elastic and strength properties of rocks,crucial for developing accurate 3D geomechanical models.This paper presents a novel method for determining strength parameters by incorporating the dependence of uniaxial compressive strength(UCS)on P-wave velocity into the Hoek-Brown criterion.Additionally,a new approach is introduced to process triaxial test data efficiently using Python libraries such as SciPy,NumPy,Matplotlib,and Pandas.Furthermore,the paper addresses challenges in determining elastic parameters through triaxial testing.A Python script is developed to automate the calculation of elastic modulus and Poisson's ratio,over-coming subjectivity in selecting the linear portion of stress-strain curves.The script optimally identifies the linear region by minimizing the fit error with appropriate constraints,ensuring a more objective and standardized approach.The proposed methodologies are demonstrated using limestone specimens from Central Asian gas fields.These innovations offer faster,more reliable results,reducing error and enhancing the comparability of analyses in geomechanics,with potential applications across various geological settings.
基金The authors are grateful for the Beijing Natural Science Foundation(Grant No.8242017)。
文摘This study presents an in-depth investigation into the shear strength characteristics of unsaturated soils,focusing on the influenceof shear rate and initial water saturation(S_(r0)).Utilizing the drained-vented(DV)triaxial test method,the present study investigated the shear strength behavior of silty clay under various shear rates and water saturation levels,and compared the outcomes with traditional suction-controlled(SC)and constant water content(CW)tests.The findingshighlight the pivotal role of excess pore water pressure dissipation during shearing,which significantlyaffects the shear strength of both saturated and unsaturated soils.Notably,for soils with high initial water saturation,a decrease in shear strength is observed with an increase in shear rate,which is attributed to the rise in pore water pressure.Conversely,for soils with low initial water saturation,the shear rate exhibits minimal impact on shear strength due to negligible water drainage.The research delineates the optimal shear rates for DV tests based on the initial water saturation:a slower rate of 0.0028 mm/min for samples with high water saturation(S_(r0)>66%)and a faster rate of 0.8 mm/min for samples with low water saturation(S_(r0)≤66%).A novel testing methodology for determining unsaturated soil shear strength under DV conditions is introduced,streamlining the measurement process and significantly reducing testing time.This method not only promises substantial cost savings but also aligns closely with natural engineering conditions,offering valuable guidance for geotechnical applications.
基金supported by the project from the Exploration and Development Research Institute of PetroChina Daqing Oilfield Companyfinancial support from the research by the National Natural Science Foundation of China(42402148)+1 种基金Sichuan Provincial Fund(24NSFSC4997)Guizhou Outstanding Young Science and Technology Talent Program(YQK[2023]012).
文摘Microstructural heterogeneity of low-permeability sandstone roofs of deep unmineable coal seams due to diagenesis significantly affects rock mechanical behavior,greatly impacting the sealing potential of in situ CO_(2) sequestration and the structural stability of the geological formation.However,little is known about how the microstructure of different mineral groups influences the multiscale mechanical behavior of deep sandstone.This study proposes a new method for quantitatively characterizing the multiscale mechanical properties of low-permeability sandstone and shows the mechanisms responsible for mechanical failure at the micro-,meso-,and macroscale.Triaxial compression tests and targeted nanoindentation tests were conducted to assess the micro-and macroscale mechanical properties of different types of sandstone.The micro-and macroscale experiments were coupled with numerical simulations of compression using a unified cohesive model based on Voronoi polygons to clarify the multiscale mechanical behavior.The results indicate that quartz,the primary mineral component of the sandstones examined,exhibits the strongest micromechanical properties,followed by feldspar,calcite,and clay minerals.Compared to polycrystalline quartz,monocrystalline quartz has a more stable microstructure and is mechanically stronger.The macro-mechanical properties of tight sandstone samples are weakened by increased microstructural inhomogeneity and larger grain size.This leads to a higher likelihood of splitting damage,characterized by a high degree of discrete and weak stress sensitivity.The major conclusion is that the positive rhythm lithofacies of medium-grained sandstone to siltstone are the most favorable for efficient CO_(2) sequestration in deep unmineable coal seams.
文摘This paper presents a new criterion for determining the unloading points quantitatively and consistently in a multi-stage triaxial test.The radial strain gradient(RSG)is first introduced as an arc tangent function of the rate of change of radial strain to time.RSG is observed to correlate closely with the stress state of a compressed sample,and reaches a horizontal asymptote as approaching failure.For a given rock type,RSG value at peak stress is almost the same,irrespective of the porosity and permeability.These findings lead to the development of RSG criterion:Unloading points can be precisely determined at the time when RSG reaches a pre-determined value that is a little smaller than or equal to the RSG at peak stress.The RSG criterion is validated against other criteria and the single-stage triaxial test on various types of rocks.Failure envelopes from the RSG criterion match well with those from single-stage tests.A practical procedure is recommended to use the RSG criterion:an unconfined compression or single-stage test is first conducted to determine the RSG at peak stress for one sample,the unloading point is then selected to be a value close to the RSG at peak stress,and the multi-stage test is finally performed on another sample using the pre-selected RSG unloading criterion.Generally,the RSG criterion is applicable for any type of rocks,especially brittle rocks,where other criteria are not suitable.Further,it can be practically implemented on the most available rock mechanical testing instruments.
基金Projects(52074259,52204132)supported by the National Natural Science Foundation of ChinaProject(104023002)supported by the Yunlong Lake Laboratory of Deep Underground Science and Engineering Project,China+2 种基金Project(BK20220157)supported by Natural Science Foundation of Jiangsu Province of ChinaProject(2023JJ40285)supported by Hunan Provincial Natural Science Foundation of ChinaProject(22B0469)supported by Scientific Research Foundation of Hunan Provincial Education Department,China。
文摘Rock-like specimens containing a joint with different inclination angles and roughness were prepared using 3D printing technology.Then,true triaxial compression loading experiments were conducted on those jointed specimens.The increase in roughness leads to an increase in the axial strength and peak strain.With the increasing inclination angle,the axial strength initially decreases from 30°to 60°and then increases from 60°to 90°.While the peak strain first rises from 30°to 45°and then declines from 45°to 90°.The variation in failure mode results from differences in lateral stress on the joints under different strike directions.Specimens with joint strike parallel to the intermediate principal stress predominantly showed matrix or matrix-joint mixed shear failure,whereas those parallel to the minimum principal stress exhibited matrix shear failure.The analysis results of acoustic emission signals indicate the crack number and shear crack percentage increase with the increasing roughness and first decrease(30°to 60°),then increase(60°to 90°)with the increasing inclination angle.The research results can provide some guidance for the design and support of underground engineering with jointed surrounding rock.
基金financially supported by the Fundamental Research Funds for the Central Universities,China(No.2023JCCXNY01)Guangxi Key Technologies R&D Program,China(No.2022AB31022).
文摘The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods,and the large-size mined-out area is usually backfilled by multiple backfilling before the recovery of a secondary stope,resulting in a layered structure of backfill in stope.Therefore,it is significant to investigate the deformation responses and mechanical properties of stratified cemented tailings backfill(SCTB)with different layer structures to remain self-standing as an artificial pillar in the primary stope.The current work examined the effects of enhance layer position(1/3,1/2,and 2/3)and thickness ratio(0,0.1,0.2,and 0.3)on the mechanical properties,deformation,energy evolution,microstructures,and failure modes of SCTB.The results demonstrate that the incorporation of an enhance layer significantly strengthens the deformation and strength of SCTB.Under a confining pressure of 50 kPa,the peak deviatoric stress rises from 525.6 to 560.3,597.1,and 790.5 kPa as the thickness ratio of enhance layer is increased from 0 to 0.1,0.2,and 0.3,representing a significant increase of 6.6%,13.6%,and 50.4%.As the confining pressure increases,the slopes of the curves in the elastic stage become steep,and the plastic phase is extended accordingly.Additionally,the incorporation of the enhance layer significantly improves the energy storage linit of SCTB specimen.As the thickness ratio of the enhance layer increases from 0 to 0.1,0.2,and 0.3,the elastic energy rises from 0.54 to 0.67,0.84,and 1.00 MJ·m^(-3),representing a significant increase of 24.1%,55.6%,and 85.2%.The internal friction angles and cohesions of the SCTB specimens are higher than those of the CTB specimens,however,the cohesion is more susceptible to enhance layer position and thickness ratio than the internal friction angle.The failure style of the SCTB specimen changes from shear failure to splitting bulging failure and shear bulging failure with the presence of an enhance layer.The crack propagation path is significantly blocked by the enhance layer.The findings are of great significance to the application and stability of the SCTB in subsequent stoping backfilling mines.
基金support received from the National Natural Science Foundation of China(Nos.52274145,52469019,and 52109119)the Guangxi Natural Science Foundation(No.2025GXNSFAA069165)the Chinese Postdoctoral Science Fund Project(No.2022M723408).
文摘After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference.However,the shear mechanical behavior,fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear.Therefore,this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-,bi-and tri-directional coupling disturbances to analyze its mechanical behavior,fracture evolution mechanism and precursor characteristics.The results show that as the disturbance direction increase,the shear strength of limestone generally decreases,while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend.The proportion of shear cracks on the structural plane increases with the increase of shear stress.The disturbance strain rate before failure shows a U-shaped trend.Near to disturbance failure,there were more high-energy and high-amplitude acoustic emission events near the structural plane,and b-value drops rapidly below 1,while lgN/b ratio increased to above 3.These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.
基金The Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry (No.6821001005)
文摘Both the repeated triaxial test （RTT） and the Hamburg wheel tracking test （HWTT） are adopted to evaluate the high temperature performance of the stone mastic asphalt （SMA） and the mastic asphalt （MA）. The correlation of the permanent deformations of the MA and the correlation of the deformation developments of the SMA between the two tests are analyzed, respectively. Results show that both the two tests can effectively identify the high temperature performance of mixtures, and the correlation between the final results of the two tests as well as that between the deformation developments of the two tests are excellent with R20.9. In order to further prove the correlation, viscoelastic parameters estimated from the RTT results is used to simulate the rutting development in the HWTT slabs by the finite element method （FEM）. Results indicate that the correlation between the two tests is significant with errors less than 10%. It is suitable to predict the rutting development with the viscoelastic parameters obtained from the RTT.
基金The authors gratefully acknowledge the financial support from Natural Science Research Project of Universities in Anhui Province(No.KJ2021A0463)Scientific Research Startup Fund for introduced talents of Anhui University of Science and Technology,and Natural Science Foundation of Anhui Province(No.2108085QE208).
文摘This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter.The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force,penetration depth,characteristics of chippings and failure patterns.Several quantitative indexes were used to evaluate rock boreability in this investigation.The granite rock samples all had a chiselled pit and a crushed rock core.Under initial stress conditions,only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN.The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape.Moreover,a thrusting force prediction model was proposed in this paper.The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus.This study has a crucial importance for practical underground hard rock crushing in geoengineering.
基金support from the National Natural Science Foundation of China(Grant Nos.42107193,42077245)supported by the Sichuan Science and Technology Program(2025YFNH0008,2025YFNH0004)+1 种基金the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(SKLGP2023Z006)the Everest Scientific Research Program 2.0:Research on mechanism and control of glacial lake outburst chain catastrophe in Qinghai-Xizang Plateau based on man-earth coordination perspective.
文摘To investigate the strength degradation characteristics and microscopic damage mechanisms of moraine soil under hydro-thermo-mechanical coupling conditions,a series of X-ray Diffraction(XRD),standard triaxial testing,Scanning Electron Microscopy(SEM),and Nuclear Magnetic Resonance(NMR)experiments were conducted.The mechanical property degradation laws and evolution characteristics of the microscopic pore structure of moraine soil under Freeze-Thaw(F-T)conditions were revealed.After F-T cycles,the stress-strain curves of moraine soil showed a strain-softening trend.In the early stage of F-T cycles(0–5 cycles),the shear strength and elastic modulus exhibited damage rate of approximately 10.33%±0.8%and 16.60%±1.2%,respectively.In the later stage(10–20 cycles),the strength parameters fluctuated slightly and tended to stabilize.The number of F-T cycles was negatively exponentially correlated with cohesion,while showing only slight fluctuation in the internal friction angle,thereby extending the Mohr-Coulomb strength criterion for moraine soil under F-T cycles.The NMR experiments quantitatively characterized the evolution of the internal pore structure of moraine soil under F-T cycles.As the number of F-T cycles increased,fine and micro pores gradually expanded and merged due to the frost-heaving effect during the water-ice phase transition,forming larger pores.The proportion of large and medium pores increased to 59.55%±2.1%(N=20),while that of fine and micro pores decreased to 40.45%±2.1%(N=20).The evolution of pore structure characteristics was essentially completed in the later stage of F-T cycles(10–20 cycles).This study provides a theoretical foundation and technical support for major engineering construction and disaster prevention in the Qinghai-Xizang Plateau.
基金Project(2011CB013504)supported by the National Basic Research Program of ChinaProject(11172090)supported by the National Natural Science Foundation of China
文摘The lithology of fracture zone which was developed at the dam foundation of a hydropower station is weak sandstone with poor integrity and pore cementation contact.Its creep properties have a significant impact on the deformation and stability of the dam.Based on the characteristics of loose organizational structure,high moisture content and poor mechanical properties,the triaxial compression tests and creep tests were carried out,respectively.The results show significant non-linear,low strength and no obvious strength peaks.Both axial and lateral strains are achieved more than 3%when the tests are failed.The weak sandstone has a significant creep property,but only transient and steady state appear under low stress.Increased stress causes creep intensified and lateral strain gradually exceeds axial strain.In the failure stage,it has characteristics of large axial plastic deformation,obvious volumetric ductility dilation and large steady creep rate.The accelerated creep appears shortly after transient loading under confining of pressures 1.0 MPa and 1.5 MPa.Therefore,an improved Burgers creep model considering the non-linear characteristics of weak sandstone is built based on hyperbolic equation and the creep parameters are identified.This model can well describe the creep properties of weak sandstone.
基金Project(50639050) supported by the National Natural Science Foundation of China and Er-Tan Hydraulicpower Limited CompanyProject(50579014) supported by the National Natural Science Foundation of China+3 种基金Project(09KJD560003) supported by the Natural Science Foundation of Jiangsu Higher Education Institutions of ChinaProject(BK2007582) supported by Jiangsu Provincial Natural Science Foundation of ChinaProject(20070294002) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(GH200904) supported by Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,Hohai University,China
文摘In order to investigate the influence of intermediate principal stress on the stress-strain and strength behaviour of a coarse-grained soil, a series of true triaxial tests were performed. The tests were conducted in a recently developed true triaxial apparatus with constant minor principal stress σ3 and constant value of intermediate principal stress ratio b=（σ2-σ3）/（σ1-σ3） （al is the vertical stress, and % is the horizontal stress）. It is found that the intermediate principal strain, ε2, increases from negative to positive value with the increase of parameter b from zero to unity under a constant minor principal stress. The minor principal strain, ε3, is always negative. This implies that the specimen exhibits an evident anisotropy. The relationship between b and friction angle obtained from the tests is different from that predicted by LADE-DUNCAN and MATSUOKA-NAKAI criteria. Based on the test results, an empirical equation of g（b） that is the shape function of the failure surface on re-plane was presented. The proposed equation is verified to be reasonable by comparing the predicted results using the equation with true triaxial test results of soils, such as coarse-grained soils in this study, sands and gravels in other studies.
文摘The mechanical behavior of plastic concrete used in the cut-off walls of earth dams has been studied. Triaxial compression tests on the specimens in various ages and mix designs under different confining pressures have been done and the stress-strain behavior of such materials and their strength parameter changes have been experimentally investigated. It has been observed that increasing the confining pressures applied on the specimens causes the material behavior to be alike the more ductile materials and the compressive strength increases considerably as well. Moreover, a parametric study has been carded out to investigate the influence of essential parameters on the shear strength parameters of these materials. According to the research, increasing the coarse to fine aggregates ratio leads to the increase of compressive strength of the specimens as well as the increase of the cohesion and internal friction angle of the materials. Furthermore, the bentonite content decrease and the cement factor increase result in an increase of the cohesion parameter of plastic concretes and decrease of the internal friction angle of such materials.
基金financially supported by the CAS“Light of West China”Program(Grant No.Y6R2240240)the National Natural Science Foundation of China(Grant No.41761144077)the Sichuan science and technology plan project(Grant No.2017JY0251)
文摘The construction of a high-speed railway(HSR) in Southwest China is being hindered by a severe shortage of high-quality subgrade materials. However, red mudstone is widely distributed in the Sichuan Basin of China. The ability to use weathered red mudstone(WRM) to fill subgrade beds by controlling its critical stress and cumulative strain would enable substantial savings in project investments and mitigate damage to the ecological environment. To better understand the dynamic behaviour of WRM, both monotonic and cyclic triaxial tests were performed. The evolution of the cumulative strain vs. increased loading cycles was measured. The influences of confining pressure and loading cycles on the dynamic modulus, damping ratio, critical cyclic stress ratio(CSR), and dynamic stress level(DSL) were investigated. The relationship between the CSR and loading cycles under different failure strain criteria(0.1%-1.0%) was analysed. The prediction model of cumulative strain was also evaluated. The results indicated that the shear strength of WRM sufficiently meets the static strength requirements of subgrade. The critical dynamic stress of WRM can thus satisfy the dynamic stress-bearing requirement of the HSR subgrade. The critical CSR decreases and displays a power function with increasing confining pressure. As the confining pressure increases, the DSL remains relatively stable, ranging between 0.153 and 0.163. Furthermore, the relationship between the dynamic strength and loading cycles required to cause failure was established. Finally, a newly developed model for determining cumulative strain was established. A prediction exercise showed that the model is in good agreement with the experimental data.
