Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas ...Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and|V_(Hp100)|<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.展开更多
The mechanical properties of colluvium strongly govern the stability of colluvial slopes, and they arc essential for the related analysis and design. Nevertheless, their measurement is not easy on account of heterogen...The mechanical properties of colluvium strongly govern the stability of colluvial slopes, and they arc essential for the related analysis and design. Nevertheless, their measurement is not easy on account of heterogeneity in property and difficulty of sampling. This study attempted to evaluate the shear strength of remolded colluvium by means of a simple direct shear test in the field. A portable direct shear tester was designed to overcome the inconvenience and expensiveness of the conventional large-scale in-situ direct shear test. It can be easily assembled and applied for the silnplc field direct shear test. For calibration, the results of the portable direct shear tester were compared with the results of the laboratory direct shear tester for four different types of soil samples, i.e. standard sand, slate debris, arenaceous shale debris and mixture of gravel and sand. Correlation formulas were established based on the calibration, enabling the portable direct shear tester to measure and estimate the shear strength of remoldcd colluvium in field. This study primarily focuses on the colluvium in Central Taiwan, including the lateritic Dadu Terrace and the arcnaceous shale of Taiping-Wufcng mounts. The portable direct shear tester was applied to sites selected in these areas, and the results were furthcr analyzed and discussed.展开更多
The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. Acco...The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.展开更多
The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of tal...The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.展开更多
The tests on the shear property of geocell reinforced soils were carried out by using large-scale direct shear equipment with shear-box-dimensions of 500 mm×500 mm×400 mm (length×width×height). Thr...The tests on the shear property of geocell reinforced soils were carried out by using large-scale direct shear equipment with shear-box-dimensions of 500 mm×500 mm×400 mm (length×width×height). Three types of specimens, silty gravel soil, geocell reinforced silty gravel soil and geocell reinforced cement stabilizing silty gravel soil were used to investigate the shear stress-displacement behavior, the shear strength and the strengthening mechanism of geocell reinforced soils. The comparisons of large-scale shear test with triaxial compression test for the same type of soil were conducted to evaluate the influences of testing method on the shear strength as well. The test results show that the unreinforced soil and geocell reinforced soil give similar nonlinear features on the behavior of shear stress and displacement. The geocell reinforced cement stabilizing soil has a quasi-elastic characteristic in the case of normal stress coming up to 1.0 GPa. The tests with the reinforcement of geocell result in an increase of 244% in cohesion, and the tests with the geocell and the cement stabilization result in an increase of 10 times in cohesion compared with the unreinforced soil. The friction angle does not change markedly. The geocell reinforcement develops a large amount of cohesion on the shear strength of soils.展开更多
For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous stud...For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions,as well as the water effects on compressive and tensile strengths.In this study,andesite was subjected to direct shear tests under five water saturation conditions,which were controlled by varying the wetting and drying time.The tests were conducted at alternating displacement rates under three vertical stresses.The results reveal that the shear strength decreases exponentially as water saturation increases,and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses.Based on the findings of the shear tests in this study and the compression and tension tests in previous studies,the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined.These results indicate that the brittleness index of the andesite,which is defined as the ratio of uniaxial compressive strength to tensile strength,is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.展开更多
This paper focuses on the development of the mathematical model of shear stress by direct shear test for compressible soil of the littoral region, which will be a great tool in the hand of geotechnical engineers. The ...This paper focuses on the development of the mathematical model of shear stress by direct shear test for compressible soil of the littoral region, which will be a great tool in the hand of geotechnical engineers. The most common use of a shear test is to determine the shear strength which is the maximum shear stress that a material can withstand before the failure occurs. This parameter is useful in many engineering designs such as foundations, roads and retaining walls. We carried out an experimental laboratory test of ten samples of undisturbed soil taken at different points of the border of Wouri river of Cameroon. The samples were collected at different depths and a direct shear test was conducted. The investigations have been performed under constant vertical stresses and constant sample volume with the aim to determine the frictional angle and the cohesion of the compressible soil which are so important to establish the conditions of buildings stability. Special care was taken to derive loading conditions actually existing in the ground and to duplicate them in the laboratory. Given that the buildings constructed in this area are subjected to settlement, landslide, and punch break or shear failure, the cohesion and the frictional angle are determined through the rupture line after assessed the mean values of the shear stress for the considered ten samples. The bearing capacity of the soil, which is the fundamental soil parameter, was calculated. From the laboratory experimental results, the least squared method was used to derive an approximated mathematical model of the shearing stress. Many optimizations methods were then considered to reach the best adjustment.展开更多
The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single s...The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.展开更多
Presentation of empirical equations for estimating engineering properties of soils is a simple, low cost and widely-used method. One of the major concerns in using these equations is evaluating their accuracy in diffe...Presentation of empirical equations for estimating engineering properties of soils is a simple, low cost and widely-used method. One of the major concerns in using these equations is evaluating their accuracy in different conditions and regions which often lead to doubts about obtained results. Most of these equations were derived in special laboratories, different climate conditions and in soils with different geotechnical and geological engineering properties and were generalized to other conditions. The main question is that whether these methods are also applicable to other conditions. Using local equations and narrowing the usage range of various methods based on each region’s properties are appropriate methods to solve these problems. This leads to simplified and faster analysis and high reliability in the obtained results. In this paper, empirical equations were derived to estimate internal friction angle, based on SPT numbers of Mashhad City’s soils in Iran, using SPT and direct shear tests results from 50 samples (25 GW and 25 GC soil samples). The results showed similar values for predicted?φ?values by SPT test and?φ?values determined by direct shear tests.展开更多
In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway,large scale direct shear tests were conducted with different normal pressures,wa...In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway,large scale direct shear tests were conducted with different normal pressures,water contents and temperatures.The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures,in both unfrozen and frozen states.This phenomenon was mainly due to the shear dilatation deformation effect.The shear displacement-shear stress curves show similar stages.Besides,the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state.In both the unfrozen or frozen states at the same water contents,the shear strength increased with increasing normal pressure.展开更多
In rock engineering,the shear strength of the basalt-concrete bonding interface is a key factor affecting the shear performance of hydroelectric dam foundations,embedded rock piles and rock bolts.In this study,30 sets...In rock engineering,the shear strength of the basalt-concrete bonding interface is a key factor affecting the shear performance of hydroelectric dam foundations,embedded rock piles and rock bolts.In this study,30 sets of in-situ direct shear tests were conducted on the basalt-concrete bond interface in the Baihetan dam area to investigate the shear strength characteristics of the basalt-concrete bonding interface.The bonding interface contains two states,i.e.,the bonding interface is not sheared,termed as se(symbolic meaning see Table 1);the bonding interface is sheared with rupture surface,termed as si.The effects of lithology,Joints structure,rock type grade and concrete compressive strength on the shear strength of the concrete-basalt contact surface were investigated.The test results show that the shear strength of the bonding interface(s_(e)&s_(i))of columnar jointed basalt with concrete is greater than that of the bonding interface(s_(e)&s_(i))of non-columnar jointed one with the same rock type grade.When the rock type grade isⅢ_(2),fcol is 1.22 times higher than fncol and ccol is 1.13 times greater than cncol.The shear strength parameters of the basalt-concrete bonding interface differ significantly for different lithologies.The cohesion of the bonding interface(s_(i))of cryptocrystalline basalt with concrete is 2.05 times higher than that of the bonding interface(s_(i))of breccia lava with concrete under the same rock type grade condition.Rock type grade has a large influence on the shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i)).cnol increases by 33%when the grade of rock type rises fromⅢ_(1)toⅡ_(1).the rock type grade has a greater effect on bonding interface(s_(i))cohesion than the coefficient of friction.When the rock type grade is reduced fromⅢ_(2)toⅢ_(1),f_(ncol)′increases by 2%and c_(ncol)′improves by 44%.The shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i))increases with the increase of the compressive strength of concrete.When concrete compressive strength rises from 22.2 to 27.6 MPa,the cohesion increases by 94%.展开更多
Columnar jointed basalt(CJB) widely distributes in the dam site of the Baihetan Hydropower Station.The columnar joint structure and fracture development of CJB have significant influence on the mechanical properties o...Columnar jointed basalt(CJB) widely distributes in the dam site of the Baihetan Hydropower Station.The columnar joint structure and fracture development of CJB have significant influence on the mechanical properties of rock mass,and the mechanical properties of CJB are of great significance to the Baihetan Hydropower Project.Therefore,in-situ direct shear tests were carried out on ten test adit at different locations in the dam site area to study the shear behavior of CJB.In this study,21 sets of in-situ direct shear tests were conducted for rock types of type Ⅱ_(2),type Ⅲ_(1)and type Ⅲ_(2),with horizontal and vertical shear planes and two different specimen sizes of CJB.Shear strength parameters of CJB were obtained by linear fitting of in-situ direct shear test results based on the Mohr-Coulomb strength criterion.The results indicate that the shear strength parameters of CJB with horizontal shear plane increase as the increase of rock type grade.The shear strength parameters of CJB show obvious anisotropy and the friction coefficient of the horizontal shear plane is greater than the vertical shear plane.The friction coefficient in the horizontal direction of the shear plane is 1.27 times that in the vertical direction of the shear plane.With the increase of rock type grade,the difference of friction coefficient becomes larger.However,the cohesion changes little whether the shear plane is horizontal or vertical.In addition,the size effect of CJB in this area is significant.The shear strength parameters of large size(100 cm × 100 cm) specimens are lower than those of regular size(50 cm × 50 cm) specimens.The reduction of cohesion is greater than that of the friction coefficient.For rock type Ⅲ_(2),the cohesion of large-size specimens is 0.637 of the regular-size specimens.The reduction percentage of the friction coefficient for type Ⅲ_(2)is 1.66 times that of type Ⅲ_(1).The reduction percentage of the cohesion for type Ⅲ_(2)is 1.27 times that of type Ⅲ_(1).The size effect decreases with the increase of rock type grade.The research results of this study can provide an important basis for the selection of rock mechanics parameters in the dam site area of Baihetan Hydropower Station and the stability analysis of the dam foundation and rocky slopes.展开更多
The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence o...The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method （DEM）. Experimental tests on such soil specimens were based on using the techniques designated as ＂parallel＂ and ＂scalping＂ to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.展开更多
In order to study the reliability of the empirical estimation of joint shear strength by the JRC（joint roughness coefficient）-JCS（joint compressive strength） model,natural rock joints of dif-ferent lithologic char...In order to study the reliability of the empirical estimation of joint shear strength by the JRC（joint roughness coefficient）-JCS（joint compressive strength） model,natural rock joints of dif-ferent lithologic characteristics and different sizes were selected as samples,and their shear strengths under dry and saturated conditions were measured by direct shear test and compared to those esti-mated by the JRC-JCS model.Comparison results show that for natural rock joints with joint surfaces closely matched,the average relative error of joint shear strength between empirical estimation and direct shear test is 9.9%;the reliability of the empirical estimation of joint shear strength by the JRC-JCS model is good under both dry and saturated conditions if the JRC is determined accounting for directional statistical measurements,scale effect and surface smoothing during shearing.However,for natural rock joints with joint surfaces mismatched,the average relative error of joint shear strength between empirical estimation and direct shear test is 39.9%;the reliability of empirical estimation of joint shear strength by the JRC-JCS model is questionable under both dry and saturated conditions.展开更多
Serious riverbank erosion,caused by scouring and soil siltation on the bank slope in the lower reaches of the Tarim River,Northwest China urgently requires a solution.Plant roots play an important role in enhancing so...Serious riverbank erosion,caused by scouring and soil siltation on the bank slope in the lower reaches of the Tarim River,Northwest China urgently requires a solution.Plant roots play an important role in enhancing soil shear strength on the slopes to maintain slope soils,but the extent of enhancement of soil shear strength by different root distribution patterns is unclear.The study used a combination of indoor experiments and numerical simulation to investigate the effects of varying plant root morphologies on the shear strength of the sandy soil in the Tarim River.The results showed that:(1)by counting the root morphology of dominant vegetation on the bank slope,we summarized the root morphology of dominant vegetation along the coast as vertical,horizontal,and claw type;(2)the shear strength of root-soil composites(RSCs)was significantly higher than that of remolded soil,and the presence of root system made the strain-softening of soil body significantly weakened so that RSCs had better mechanical properties;and(3)compared with the lateral roots,the average particle contact degree of vertical root system was higher,and the transition zone of shear strength was more prominent.Hence,vegetation with vertical root system had the best effect on soil protection and slope fixation.The results of this study have important guiding significance for prevention and control of soil erosion in the Tarim River basin,the restoration of riparian ecosystems,and the planning of water conservancy projects.展开更多
Some rock joints exhibit significant brittleness,characterized by a sharp decrease in shear stress upon reaching the peak strength.However,existing models often fail to accurately represent this behavior and are encum...Some rock joints exhibit significant brittleness,characterized by a sharp decrease in shear stress upon reaching the peak strength.However,existing models often fail to accurately represent this behavior and are encumbered by numerous parameters lacking clear mechanical significance.This study presents a new statistical damage constitutive model rooted in both damage mechanics and statistics,containing only three model parameters.The proposed model encompasses all stages of joint shearing,including the compaction stage,linear stage,plastic yielding stage,drop stage,strain softening stage,and residual strength stage.To derive the analytical expression of the constitutive model,three boundary conditions are introduced.Experimental data from both natural and artificial rock joints is utilized to validate the model,resulting in average absolute relative errors ranging from 3%to 8%.Moreover,a comparative analysis with established models illustrates that the proposed model captures stress drop and post-peak strain softening more effectively,with model parameters possessing clearer mechanical interpretations.Furthermore,parameter analysis is conducted to investigate the impacts of model parameters on the curves and unveil the relationship between these parameters and the mechanical properties of rock joints.Importantly,the proposed model is straightforward in form,and all model parameters can be obtained from direct shear tests,thus facilitating the utilization in numerical simulations.展开更多
Direct shear test has been widely used to measure the shear strength of soils and other particulate materials in industry because of its simplicity. However, the results can be dependent on the specimen size. The ASTM...Direct shear test has been widely used to measure the shear strength of soils and other particulate materials in industry because of its simplicity. However, the results can be dependent on the specimen size. The ASTM (American Society for Testing and Materials) publications suggest that for testing soils the shear box should be at least ten times the diameter of the largest particle and the height of the box should be no more than half of its diameter. These guidelines are empirically based. A series of two-dimensional numerical direct shear tests are performed to investigate this scaling effect. By analyzing the bulk friction, particle translation and rotation, percentage of sliding, average volume (area) and shear strain and the evolution of the shear band, we find that the traditional guidelines for direct shear tests are questionable. Scaling dependency of bulk friction on the property of granular materials is clearly present. Our current analysis points out that the scaling effects can vary significantly depending on the particle properties other than their sizes. Of all the parameters we observed, particle rotation appears to have a decisive correlation with the bulk friction. Formation of a shear band is universal. As the shearing progresses, particle rotation begins to concentrate near the shear plane. By defining the width of a shear band as the standard deviation of the distribution of translational gradient or the standard deviation of the distribution of particle rotation, quantitative evolutions of shear band are presented. Both measures of the shear band width dropped rapidly during pre-failure stage. After peak stress both measures begin to approach steady state as the bulk friction stabilizes to the residual stage. These observations suggest that structure formation inside the shear band controls the scaling effect.展开更多
Liquefaction assessment based on strain energy is significantly superior to conventional stress-based methods.The main purpose of the present study is to investigate the correlation between shear wave velocity and str...Liquefaction assessment based on strain energy is significantly superior to conventional stress-based methods.The main purpose of the present study is to investigate the correlation between shear wave velocity and strain energy capacity of silty sands.The dissipated energy until liquefaction occurs was calculated by analyzing the results of three series of comprehensive cyclic direct simple shear and triaxial tests on Ottawa F65,Nevada,and Firoozkuh sands with varying silt content by weight and relative densities.Additionally,the shear wave velocity of each series was obtained using bender element or resonant column tests.Consequently,for the first time,a liquefaction triggering criterion,relating to effective overburden normalized liquefaction capacity energy(WL=s’c)to effective overburden stresscorrected shear wave velocity(eVs1)has been introduced.The accuracy of the proposed criteria was evaluated using in situ data.The results confirm the ability of shear wave velocity as a distinguishing parameter for separating liquefied and non-liquefied soils when it is calculated against liquefaction capacity energy(WL=s’c).However,the proposed WL=s’c-Vs1 curve,similar to previously proposed cyclic resistance ratio(CRR)-Vs1 relationships,should be used conservatively for fields vulnerable to liquefaction-induced lateral spreading.展开更多
The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China.The shear behavior of t...The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China.The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software.Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing,and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity.The macroscopic properties and damage patterns were obtained for six numerical configurations;namely,loess-weathered mudstone with 0°,10°,and-10°joints and weathered mudstone with 0°,10°,and-10°weak intercalated layers.The numerical test results revealed that,in the direct shear tests,the shear stress and shear displacement of the samples increased with the normal stress.In the cyclic shear tests with a total cycle number N=20,the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop.The numerical tests also revealed that,under cyclic shear,the normal stress and shear velocity affected the shear strength.The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations.Compared with the damage pattern of the direct shear tests,the damage of the cyclic shear tests mainly comprised shear cracks and fractures,some shaking consolidation settlement and fewer shear strain occurred around the joints.In the direct shear tests,more compression cracks and fractures occurred in the samples.The damage mainly developed along the joints,and shearing-off damage occurred.The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.展开更多
A simplified in situ direct shear test （DST） was developed for measuring the shear strength of soils in fields. In this test, a latticed sheafing frame replaces the upper half of the shear box used in the convention...A simplified in situ direct shear test （DST） was developed for measuring the shear strength of soils in fields. In this test, a latticed sheafing frame replaces the upper half of the shear box used in the conventional direct shear box test. The latticed shearing frame is directly embedded in the ground to be tested after a construction process and is pulled with a flexible chain while a constant dead load is applied to the sample in the sheafing frame. This simplified in situ DST has been validated by comparing its results with those of triaxial tests on samples with parallel gradations under normal stresses less than 100 kPa. In this study, the DST was further validated by carrying out tests on samples with the same gradations, rather than on samples with parallel gradations, under normal stresses up to 880 kPa. In addition, the DST was performed inside fills in two applications.展开更多
文摘Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and|V_(Hp100)|<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.
基金support of the National Science Counci(NSC94-2211-E-005-022),Taiwan,China
文摘The mechanical properties of colluvium strongly govern the stability of colluvial slopes, and they arc essential for the related analysis and design. Nevertheless, their measurement is not easy on account of heterogeneity in property and difficulty of sampling. This study attempted to evaluate the shear strength of remolded colluvium by means of a simple direct shear test in the field. A portable direct shear tester was designed to overcome the inconvenience and expensiveness of the conventional large-scale in-situ direct shear test. It can be easily assembled and applied for the silnplc field direct shear test. For calibration, the results of the portable direct shear tester were compared with the results of the laboratory direct shear tester for four different types of soil samples, i.e. standard sand, slate debris, arenaceous shale debris and mixture of gravel and sand. Correlation formulas were established based on the calibration, enabling the portable direct shear tester to measure and estimate the shear strength of remoldcd colluvium in field. This study primarily focuses on the colluvium in Central Taiwan, including the lateritic Dadu Terrace and the arcnaceous shale of Taiping-Wufcng mounts. The portable direct shear tester was applied to sites selected in these areas, and the results were furthcr analyzed and discussed.
基金Project(2011CB013504) supported by the National Basic Research Program of ChinaProjects(50911130366, 11172090) supported by the National Natural Science Foundation of ChinaProject supported by Central University Basic Research Special Fund, China
文摘The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.
基金Project(2013BAB06B00) supported by the National Key Technology R&D Programof ChinaProject(2011CB013504) supported by the National Basic Research Program of ChinaProject(50911130366) supported by the National Natural Science Foundation of China
文摘The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.
基金Project(40672178) supported by the National Natural Science Foundation of ChinaProject(2004844009) supported by the Chinese Scholarship Council
文摘The tests on the shear property of geocell reinforced soils were carried out by using large-scale direct shear equipment with shear-box-dimensions of 500 mm×500 mm×400 mm (length×width×height). Three types of specimens, silty gravel soil, geocell reinforced silty gravel soil and geocell reinforced cement stabilizing silty gravel soil were used to investigate the shear stress-displacement behavior, the shear strength and the strengthening mechanism of geocell reinforced soils. The comparisons of large-scale shear test with triaxial compression test for the same type of soil were conducted to evaluate the influences of testing method on the shear strength as well. The test results show that the unreinforced soil and geocell reinforced soil give similar nonlinear features on the behavior of shear stress and displacement. The geocell reinforced cement stabilizing soil has a quasi-elastic characteristic in the case of normal stress coming up to 1.0 GPa. The tests with the reinforcement of geocell result in an increase of 244% in cohesion, and the tests with the geocell and the cement stabilization result in an increase of 10 times in cohesion compared with the unreinforced soil. The friction angle does not change markedly. The geocell reinforcement develops a large amount of cohesion on the shear strength of soils.
文摘For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions,as well as the water effects on compressive and tensile strengths.In this study,andesite was subjected to direct shear tests under five water saturation conditions,which were controlled by varying the wetting and drying time.The tests were conducted at alternating displacement rates under three vertical stresses.The results reveal that the shear strength decreases exponentially as water saturation increases,and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses.Based on the findings of the shear tests in this study and the compression and tension tests in previous studies,the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined.These results indicate that the brittleness index of the andesite,which is defined as the ratio of uniaxial compressive strength to tensile strength,is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.
文摘This paper focuses on the development of the mathematical model of shear stress by direct shear test for compressible soil of the littoral region, which will be a great tool in the hand of geotechnical engineers. The most common use of a shear test is to determine the shear strength which is the maximum shear stress that a material can withstand before the failure occurs. This parameter is useful in many engineering designs such as foundations, roads and retaining walls. We carried out an experimental laboratory test of ten samples of undisturbed soil taken at different points of the border of Wouri river of Cameroon. The samples were collected at different depths and a direct shear test was conducted. The investigations have been performed under constant vertical stresses and constant sample volume with the aim to determine the frictional angle and the cohesion of the compressible soil which are so important to establish the conditions of buildings stability. Special care was taken to derive loading conditions actually existing in the ground and to duplicate them in the laboratory. Given that the buildings constructed in this area are subjected to settlement, landslide, and punch break or shear failure, the cohesion and the frictional angle are determined through the rupture line after assessed the mean values of the shear stress for the considered ten samples. The bearing capacity of the soil, which is the fundamental soil parameter, was calculated. From the laboratory experimental results, the least squared method was used to derive an approximated mathematical model of the shearing stress. Many optimizations methods were then considered to reach the best adjustment.
基金Supported by the National Natural Science Foundation of China(50309004)。
文摘The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.
文摘Presentation of empirical equations for estimating engineering properties of soils is a simple, low cost and widely-used method. One of the major concerns in using these equations is evaluating their accuracy in different conditions and regions which often lead to doubts about obtained results. Most of these equations were derived in special laboratories, different climate conditions and in soils with different geotechnical and geological engineering properties and were generalized to other conditions. The main question is that whether these methods are also applicable to other conditions. Using local equations and narrowing the usage range of various methods based on each region’s properties are appropriate methods to solve these problems. This leads to simplified and faster analysis and high reliability in the obtained results. In this paper, empirical equations were derived to estimate internal friction angle, based on SPT numbers of Mashhad City’s soils in Iran, using SPT and direct shear tests results from 50 samples (25 GW and 25 GC soil samples). The results showed similar values for predicted?φ?values by SPT test and?φ?values determined by direct shear tests.
基金supported by the National Natural Science Foundation of China (No. 51378057)
文摘In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway,large scale direct shear tests were conducted with different normal pressures,water contents and temperatures.The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures,in both unfrozen and frozen states.This phenomenon was mainly due to the shear dilatation deformation effect.The shear displacement-shear stress curves show similar stages.Besides,the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state.In both the unfrozen or frozen states at the same water contents,the shear strength increased with increasing normal pressure.
基金supported by the National Natural Science Foundation of China Key Projects of International Cooperation and Exchanges(No.42020104006)the National Natural Science Foundation of China(No.41630643)+1 种基金the Fundamental Research Funds for the Central Universities(No.CUGCJ1701)the Scientific Research Project of China Three Gorges Corporation LTD.
文摘In rock engineering,the shear strength of the basalt-concrete bonding interface is a key factor affecting the shear performance of hydroelectric dam foundations,embedded rock piles and rock bolts.In this study,30 sets of in-situ direct shear tests were conducted on the basalt-concrete bond interface in the Baihetan dam area to investigate the shear strength characteristics of the basalt-concrete bonding interface.The bonding interface contains two states,i.e.,the bonding interface is not sheared,termed as se(symbolic meaning see Table 1);the bonding interface is sheared with rupture surface,termed as si.The effects of lithology,Joints structure,rock type grade and concrete compressive strength on the shear strength of the concrete-basalt contact surface were investigated.The test results show that the shear strength of the bonding interface(s_(e)&s_(i))of columnar jointed basalt with concrete is greater than that of the bonding interface(s_(e)&s_(i))of non-columnar jointed one with the same rock type grade.When the rock type grade isⅢ_(2),fcol is 1.22 times higher than fncol and ccol is 1.13 times greater than cncol.The shear strength parameters of the basalt-concrete bonding interface differ significantly for different lithologies.The cohesion of the bonding interface(s_(i))of cryptocrystalline basalt with concrete is 2.05 times higher than that of the bonding interface(s_(i))of breccia lava with concrete under the same rock type grade condition.Rock type grade has a large influence on the shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i)).cnol increases by 33%when the grade of rock type rises fromⅢ_(1)toⅡ_(1).the rock type grade has a greater effect on bonding interface(s_(i))cohesion than the coefficient of friction.When the rock type grade is reduced fromⅢ_(2)toⅢ_(1),f_(ncol)′increases by 2%and c_(ncol)′improves by 44%.The shear strength of the non-columnar jointed basalt-concrete bonding interface(s_(e)&s_(i))increases with the increase of the compressive strength of concrete.When concrete compressive strength rises from 22.2 to 27.6 MPa,the cohesion increases by 94%.
基金supported by the National Key Research and Development Program of China (No.2017YFC1501302)the National Natural Science Foundation of China (No.41630643)+1 种基金the Fundamental Research Funds for the Central Universities (No.CUGCJ1701)the Scientific research project of China Three Gorges Corporation Ltd。
文摘Columnar jointed basalt(CJB) widely distributes in the dam site of the Baihetan Hydropower Station.The columnar joint structure and fracture development of CJB have significant influence on the mechanical properties of rock mass,and the mechanical properties of CJB are of great significance to the Baihetan Hydropower Project.Therefore,in-situ direct shear tests were carried out on ten test adit at different locations in the dam site area to study the shear behavior of CJB.In this study,21 sets of in-situ direct shear tests were conducted for rock types of type Ⅱ_(2),type Ⅲ_(1)and type Ⅲ_(2),with horizontal and vertical shear planes and two different specimen sizes of CJB.Shear strength parameters of CJB were obtained by linear fitting of in-situ direct shear test results based on the Mohr-Coulomb strength criterion.The results indicate that the shear strength parameters of CJB with horizontal shear plane increase as the increase of rock type grade.The shear strength parameters of CJB show obvious anisotropy and the friction coefficient of the horizontal shear plane is greater than the vertical shear plane.The friction coefficient in the horizontal direction of the shear plane is 1.27 times that in the vertical direction of the shear plane.With the increase of rock type grade,the difference of friction coefficient becomes larger.However,the cohesion changes little whether the shear plane is horizontal or vertical.In addition,the size effect of CJB in this area is significant.The shear strength parameters of large size(100 cm × 100 cm) specimens are lower than those of regular size(50 cm × 50 cm) specimens.The reduction of cohesion is greater than that of the friction coefficient.For rock type Ⅲ_(2),the cohesion of large-size specimens is 0.637 of the regular-size specimens.The reduction percentage of the friction coefficient for type Ⅲ_(2)is 1.66 times that of type Ⅲ_(1).The reduction percentage of the cohesion for type Ⅲ_(2)is 1.27 times that of type Ⅲ_(1).The size effect decreases with the increase of rock type grade.The research results of this study can provide an important basis for the selection of rock mechanics parameters in the dam site area of Baihetan Hydropower Station and the stability analysis of the dam foundation and rocky slopes.
文摘The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method （DEM）. Experimental tests on such soil specimens were based on using the techniques designated as ＂parallel＂ and ＂scalping＂ to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.
基金supported by the National Natural Science Foundation of China (Nos. 40672186, 50809059)the Natural Science Foundation of Zhejiang Province (No. Y505008), China
文摘In order to study the reliability of the empirical estimation of joint shear strength by the JRC（joint roughness coefficient）-JCS（joint compressive strength） model,natural rock joints of dif-ferent lithologic characteristics and different sizes were selected as samples,and their shear strengths under dry and saturated conditions were measured by direct shear test and compared to those esti-mated by the JRC-JCS model.Comparison results show that for natural rock joints with joint surfaces closely matched,the average relative error of joint shear strength between empirical estimation and direct shear test is 9.9%;the reliability of the empirical estimation of joint shear strength by the JRC-JCS model is good under both dry and saturated conditions if the JRC is determined accounting for directional statistical measurements,scale effect and surface smoothing during shearing.However,for natural rock joints with joint surfaces mismatched,the average relative error of joint shear strength between empirical estimation and direct shear test is 39.9%;the reliability of empirical estimation of joint shear strength by the JRC-JCS model is questionable under both dry and saturated conditions.
基金funded by the Key Research and Development Task of Xinjiang Uygur Autonomous Region, China (2022B03024-3)
文摘Serious riverbank erosion,caused by scouring and soil siltation on the bank slope in the lower reaches of the Tarim River,Northwest China urgently requires a solution.Plant roots play an important role in enhancing soil shear strength on the slopes to maintain slope soils,but the extent of enhancement of soil shear strength by different root distribution patterns is unclear.The study used a combination of indoor experiments and numerical simulation to investigate the effects of varying plant root morphologies on the shear strength of the sandy soil in the Tarim River.The results showed that:(1)by counting the root morphology of dominant vegetation on the bank slope,we summarized the root morphology of dominant vegetation along the coast as vertical,horizontal,and claw type;(2)the shear strength of root-soil composites(RSCs)was significantly higher than that of remolded soil,and the presence of root system made the strain-softening of soil body significantly weakened so that RSCs had better mechanical properties;and(3)compared with the lateral roots,the average particle contact degree of vertical root system was higher,and the transition zone of shear strength was more prominent.Hence,vegetation with vertical root system had the best effect on soil protection and slope fixation.The results of this study have important guiding significance for prevention and control of soil erosion in the Tarim River basin,the restoration of riparian ecosystems,and the planning of water conservancy projects.
基金funded by the National Natural Science Foundation of China(No.41972266)Chongqing Natural Science Foundation(No.CSTB2024NSCQ-MSX0006).
文摘Some rock joints exhibit significant brittleness,characterized by a sharp decrease in shear stress upon reaching the peak strength.However,existing models often fail to accurately represent this behavior and are encumbered by numerous parameters lacking clear mechanical significance.This study presents a new statistical damage constitutive model rooted in both damage mechanics and statistics,containing only three model parameters.The proposed model encompasses all stages of joint shearing,including the compaction stage,linear stage,plastic yielding stage,drop stage,strain softening stage,and residual strength stage.To derive the analytical expression of the constitutive model,three boundary conditions are introduced.Experimental data from both natural and artificial rock joints is utilized to validate the model,resulting in average absolute relative errors ranging from 3%to 8%.Moreover,a comparative analysis with established models illustrates that the proposed model captures stress drop and post-peak strain softening more effectively,with model parameters possessing clearer mechanical interpretations.Furthermore,parameter analysis is conducted to investigate the impacts of model parameters on the curves and unveil the relationship between these parameters and the mechanical properties of rock joints.Importantly,the proposed model is straightforward in form,and all model parameters can be obtained from direct shear tests,thus facilitating the utilization in numerical simulations.
基金Supported by the ASEE/NASA Summer Faculty Fellowship Program and Clarkson University
文摘Direct shear test has been widely used to measure the shear strength of soils and other particulate materials in industry because of its simplicity. However, the results can be dependent on the specimen size. The ASTM (American Society for Testing and Materials) publications suggest that for testing soils the shear box should be at least ten times the diameter of the largest particle and the height of the box should be no more than half of its diameter. These guidelines are empirically based. A series of two-dimensional numerical direct shear tests are performed to investigate this scaling effect. By analyzing the bulk friction, particle translation and rotation, percentage of sliding, average volume (area) and shear strain and the evolution of the shear band, we find that the traditional guidelines for direct shear tests are questionable. Scaling dependency of bulk friction on the property of granular materials is clearly present. Our current analysis points out that the scaling effects can vary significantly depending on the particle properties other than their sizes. Of all the parameters we observed, particle rotation appears to have a decisive correlation with the bulk friction. Formation of a shear band is universal. As the shearing progresses, particle rotation begins to concentrate near the shear plane. By defining the width of a shear band as the standard deviation of the distribution of translational gradient or the standard deviation of the distribution of particle rotation, quantitative evolutions of shear band are presented. Both measures of the shear band width dropped rapidly during pre-failure stage. After peak stress both measures begin to approach steady state as the bulk friction stabilizes to the residual stage. These observations suggest that structure formation inside the shear band controls the scaling effect.
文摘Liquefaction assessment based on strain energy is significantly superior to conventional stress-based methods.The main purpose of the present study is to investigate the correlation between shear wave velocity and strain energy capacity of silty sands.The dissipated energy until liquefaction occurs was calculated by analyzing the results of three series of comprehensive cyclic direct simple shear and triaxial tests on Ottawa F65,Nevada,and Firoozkuh sands with varying silt content by weight and relative densities.Additionally,the shear wave velocity of each series was obtained using bender element or resonant column tests.Consequently,for the first time,a liquefaction triggering criterion,relating to effective overburden normalized liquefaction capacity energy(WL=s’c)to effective overburden stresscorrected shear wave velocity(eVs1)has been introduced.The accuracy of the proposed criteria was evaluated using in situ data.The results confirm the ability of shear wave velocity as a distinguishing parameter for separating liquefied and non-liquefied soils when it is calculated against liquefaction capacity energy(WL=s’c).However,the proposed WL=s’c-Vs1 curve,similar to previously proposed cyclic resistance ratio(CRR)-Vs1 relationships,should be used conservatively for fields vulnerable to liquefaction-induced lateral spreading.
基金sponsored by National Natural Science Foundation of China(No.41902269)Chinese Universities Scientific Fund(2020TC095)。
文摘The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China.The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software.Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing,and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity.The macroscopic properties and damage patterns were obtained for six numerical configurations;namely,loess-weathered mudstone with 0°,10°,and-10°joints and weathered mudstone with 0°,10°,and-10°weak intercalated layers.The numerical test results revealed that,in the direct shear tests,the shear stress and shear displacement of the samples increased with the normal stress.In the cyclic shear tests with a total cycle number N=20,the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop.The numerical tests also revealed that,under cyclic shear,the normal stress and shear velocity affected the shear strength.The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations.Compared with the damage pattern of the direct shear tests,the damage of the cyclic shear tests mainly comprised shear cracks and fractures,some shaking consolidation settlement and fewer shear strain occurred around the joints.In the direct shear tests,more compression cracks and fractures occurred in the samples.The damage mainly developed along the joints,and shearing-off damage occurred.The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.
基金supported by the Special Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University (Grant No. 2009586012)
文摘A simplified in situ direct shear test （DST） was developed for measuring the shear strength of soils in fields. In this test, a latticed sheafing frame replaces the upper half of the shear box used in the conventional direct shear box test. The latticed shearing frame is directly embedded in the ground to be tested after a construction process and is pulled with a flexible chain while a constant dead load is applied to the sample in the sheafing frame. This simplified in situ DST has been validated by comparing its results with those of triaxial tests on samples with parallel gradations under normal stresses less than 100 kPa. In this study, the DST was further validated by carrying out tests on samples with the same gradations, rather than on samples with parallel gradations, under normal stresses up to 880 kPa. In addition, the DST was performed inside fills in two applications.
