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1.
Since cross-anisotropic sand behaves differently when the loading direction or the stress state changes, the influences of the loading direction and the intermediate principal stress ratio (b = (σ 2 ? σ 3)/(σ 1 ? σ 3)) on the initiation of strain localization need study. According to the loading angle (angle between the major principal stress direction and the normal of bedding plane), a 3D non-coaxial non-associated elasto-plasticity hardening model was proposed by modifying Lode angle formulation of the Mohr–Coulomb yield function and the stress–dilatancy function. By using bifurcation analysis, the model was used to predict the initiation of strain localization under plane strain and true triaxial conditions. The predictions of the plane strain tests show that the major principal strain at the bifurcation points increases with the loading angle, while the stress ratio decreases with the loading angle. According to the loading angle and the intermediate principal stress ratio, the true triaxial tests were analyzed in three sectors. The stress–strain behavior and the volumetric strain in each sector can be well captured by the proposed model. Strain localization occurs in most b value conditions in all three sectors except for those which are close to triaxial compression condition (b = 0). The difference between the peak shear strength corresponding to the strain localization and the ultimate shear strength corresponding to plastic limit becomes obvious when the b value is near 0.4. The influence of bifurcation on the shear strength becomes weak when the loading direction changes from perpendicular to the bedding plane to parallel. The bifurcation analysis based on the proposed model gives out major principal strain and peak shear strength at the initiation of strain localization; the given results are consistent with experiments.  相似文献   

2.
This paper presents an experimental investigation revisiting the anisotropic stress–strain–strength behaviour of geomaterials in drained monotonic shear using hollow cylinder apparatus. The test programme has been designed to cover the effect of material anisotropy, preshearing, material density and intermediate principal stress on the behaviour of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. This paper explains phenomenological observations based on recently acquired understanding in micromechanics, with attention focused on strength anisotropy and deformation non-coaxiality, i.e. non-coincidence between the principal stress direction and the principal strain rate direction. The test results demonstrate that the effects of initial anisotropy produced during sample preparation are significant. The stress–strain–strength behaviour of the specimen shows strong dependence on the principal stress direction. Preloading history, material density and particle shape are also found to be influential. In particular, it was found that non-coaxiality is more significant in presheared specimens. The observations on the strength anisotropy and deformation non-coaxiality were explained based on the stress–force–fabric relationship. It was observed that intermediate principal stress parameter b(b = (σ 2 ? σ 3)/(σ 1 ? σ 3)) has a significant effect on the non-coaxiality of sand. The lower the b-value, the higher the degree of non-coaxiality is induced. Visual inspection of shear band formed at the end of HCA testing has also been presented. The inclinations of the shear bands at different loading directions can be predicted well by taking account of the relative direction of the mobilized planes to the bedding plane.  相似文献   

3.
During the last earthquake that occurred in Chlef (El Asnam 1980, Algeria), a significant decrease in the shear strength has caused major damages to several civil and hydraulic structures (earth dams, embankments, bridges, slopes and buildings), especially for the saturated sandy soil of the areas near Chlef valley. This paper presents a laboratory study of drained compression triaxial tests conducted on sandy soil reinforced with horizontal layers of geotextile, in order to study the influence of geotextile layer characteristics both on shear stress–strain and on volumetric change–strain. Tests were carried out on medium and dense sand. The experimental programme includes some drained compression tests performed on reinforced sand samples, for different values of the geotextile layers number (N g), of confining pressure (\( \sigma_{\text{c}}^{\prime } \)) and relative density (D r). The test results have shown that the contribution of the geotextile at low values of the axial strain (ε 1) is negligible, for higher values of (ε 1); geotextile induces a quasi-linear increase in the deviator stress (q) and leads to an increase in the volume contractiveness within the reinforced samples. A negligible influence of geotextile layers number (N g) on the stress–strain behaviour and the volumetric change has been shown, when normalized with N g. The results indicate that the contribution of geotextile to the stress–strain mobilization increases with increasing confining pressure, while its contribution to the volume contraction decreases with the increase in the confining pressure.  相似文献   

4.
In this study, the rapid consolidation equipment (RACE) was developed as an alternative device to the conventional consolidation test using Oedometer, consuming merely a few hours for the whole precedure to determine the consolidation characteristics of cohesive soil. RACE operates based on the constant rate of strain (CRS) consolidation theory, which is a continuous loading method of testing, requiring a good estimation of the loading rate such that it is ideal for the achievement of steady state condition during testing. The steady state condition is achieved when the c v values from drained and undrained face of CRS converged with the cv from Oedometer test. A slightly modification has been made on the normal constant rate of strain (CRS) test by proposing a direct back pressure system to the specimen using a tube to saturate the soil sample. This research has produced a set of criteria for determining the suitable rate for the rapid consolidation test based on the ratio of normalized strain rate, β, and proposed a new coefficient in terms of a ratio of β to clay fraction (CF), as a part of new criteria for testing a fine soil. Four types of sample were tested with different rates of strain using the RACE and their results were compared with those conducted using the Oedometer on the same soil type, from which fairly good agreements were evident in many specimens. It was found from the study that the minimum value of normalized strain rate, β, for the CRS test is 0.005 and for the u a /σ v ratio is suggested as 0.01. Also, the maximum β/CF for soils with clay friction lower and higher than 50 % are 0.008 and 0.001, respectively. The minimum β/CF value for both conditions is 0.0001.  相似文献   

5.
Mubarak shear belt provides an opportunity to investigate quantitative finite strain (Rs), proportions of pure shear and simple shear components, sense of shear indicators, subhorizontal to steeply plunging mineral lineations, in a dextral transpressional zone. The structural style of the Mubarak shear belt is consistent with dextral transpression within the Central Eastern Desert where dextral and reverse shear have developed simultaneously with the regional foliation. The high strain zone of the Mubarak shear belt is characterized by steeply dipping foliation with sub-horizontal stretching lineation (simple shear) surrounded by thrust imbrications with slightly plunging stretching lineations. Strain estimates from the Mubarak shear belt are used to determine how pure and simple shear components of deformation are partitioned. The axial ratios in XZ sections range from 1.16 to 2.33 with the maximum stretch, S X , ranges from 1.06 to 1.48. The minimum stretch, S Z , ranges from 0.65 to 0.92 indicating a moderate variation in vertical shortening. Volcaniclastic metasediments and metagabbros were subjected to prograde low-grade regional metamorphism in the range of greenschist to lower amphibolite facies (450–650°C at 2–4 kbar). Medium pressure (6–8 kbar at 530°C) was estimated from the high strain zone within the dextral strike-slip shear zones. Retrograde metamorphism occurred at a temperature range of 250–280°C. There is a trend towards decreasing the ratio of 100Mg/(Mg + Fetot + Mn) away from the high strain zone of the Mubarak shear belt. Integrated strain and temperature estimates indicate that the simple shear (non-coaxial) components of deformation played a significant role in formation and exhumation of the Mubarak shear belt during the accumulation of finite strain and consequently during progressive transpression and thrusting.  相似文献   

6.
Delhi, the capital of India, has experienced mild seismic shaking during several earthquakes in the past. The large variations of depth to bedrock and ground water table coupled with different soil types at different locations of Delhi necessitate a seismic microzonation study. Dynamic soil properties such as shear wave velocity, modulus reduction and damping characteristics of local soils are the basic and essential input parameters for conducting even a preliminary ground response analysis which is an essential input in microzonation studies. Shear wave velocity is not measured routinely due to its high cost and lack of the required expertise. Several researchers in the past developed correlations between shear wave velocity (V s ) and routinely measured N values. In the present study, shear wave velocity profiles measured in the field at more than 80 borehole locations to a depth of about 20 to 32m using Spectral Analysis of Surface Waves (SASW) are presented and correlations between shear wave velocity and N values are also presented for use by engineers and designers. Results of strain and stress controlled cyclic triaxial tests on remoulded samples of sand-silt mixtures in the high strain range are used for generating the modulus reduction and damping curves and are compared with the well-known curves in the literature. The results presented in this article can be used for microzonation studies as well as site specific ground response analyses at Delhi.  相似文献   

7.
Pile reinforcement mechanism of soil slopes   总被引：1，自引：1，他引：0  
Stabilizing piles are widely used as an effective and economic reinforcement approach for slopes. Reasonable designs of pile reinforcement depend on the understanding of reinforcement mechanism of slopes. A series of centrifuge model tests were conducted on the pile-reinforced slopes and corresponding unreinforced slopes under self-weight and vertical loading conditions. The deformation of the slope was measured using image-based analysis and employed to investigate the pile reinforcement mechanism. The test results showed that the piles significantly reduced the deformation and changed the deformation distribution of the slope, and prevented the failure occurred in the unreinforced slope. The pile influence zone was determined according to the inflection points on the distribution curves of horizontal displacement, which comprehensively described the features of the pile–slope interaction and the characteristics of reinforced slopes. The concepts of anti-shear effect and compression effect were proposed to quantitatively describe the restriction features of the piles on the deformation of the slope, namely the reduction in the shear deformation and the increase in the compression deformation, respectively. The pile reinforcement effect mainly occurred in the pile influence zone and decreased with increasing distance from the piles. There was a dominated compression effect in the vicinities of the piles. The compression effect developed upwards in the slope with a transmission to the anti-shear effect. The anti-shear effect became significantly dominated near the slip surface and prevented the failure that occurred in the unreinforced slope.  相似文献   

8.
Cyclic triaxial test by means of the geotechnical digital system is conducted for the soil near the Guoquan Road Station of Metro Line 10 in Shanghai to analyze the strain characteristics and the variation law of saturated silty soil under subway loading. Orthogonal design method is used to arrange the experiment, considering the following factors: frequency ratio f R, cyclic stress ratio σ R, vibration time ratio N R, and the interaction function among them. Results show that the cyclic stress ratio σ R, the frequency ratio f R, the vibration time ratio N R, and the interaction between the cyclic stress ratio σ R and the vibration time ratio N R have a significant effect on the axial strain of the subway tunnel. The effect of the interaction between the cyclic stress ratio σ R and the vibration time ratio N R is also significant. From the analysis of variance and regression theory, the nonlinear regression equation of the cumulative plastic strain of silty soil under subway loading is established. Residual analysis proves that the equation is ideal and credible. The results have important value for the design of subway tunnels.  相似文献   

9.
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10.
By using the lower bound finite elements limit analysis, the pullout capacity of an inclined strip anchor plate embedded in a cohesionless soil medium has been computed with an inclusion of pseudo-static horizontal earthquake body forces. The variation of the pullout capacity factor (F γ ) with changes in horizontal earthquake acceleration co-efficient (α h ) has been computed by varying the inclination angle (β) of the anchor plate between 0° and 90°. The results clearly reveal that the pullout capacity factor (F γ ) decreases significantly with an increase in the value of α h . The reduction in the pullout resistance due to seismic forces (1) becomes much more extensive for a vertical anchor plate as compared to the horizontal anchor, (2) decreases generally with increases in the soil friction angle (?) and (3) increases with an increase in friction angle between soil and anchor plate (δ). The developments of the failure zone around the anchor plate were also examined by varying α h and β. The results obtained from the analysis compare well with the solutions reported in literature.  相似文献   

11.
Flow-like landslides in clayey soils represent serious threats for populations and infrastructures and have been the subject of numerous studies in the past decade. However, despite the rising need for landslide mitigation with growing urbanization, the transient mechanisms involved in the solid-fluid transition are still poorly understood. One way of characterizing the solid-fluid transition is to carry out rheometrical tests on clayey soil samples to assess the evolution of viscosity with the shear stress. In this study, we carried out geotechnical and rheometrical tests on clayey samples collected from six flow-like landslides in order to assess if these clayey soils exhibit similar characteristics when they fluidize (solid-fluid transition). The results show that (1) all tested soils except one exhibit a yield-stress fluid behavior that can be associated with a bifurcation in viscosity (described by the critical shear rate \( \dot{\gamma_c} \)) and in shear modulus G; (2) the larger the amplitude of the viscosity bifurcation, the larger the associated drop in G; and (3) the water content (w) deviation from the Atterberg liquid limit (LL) seem a key parameter controlling a common mechanical behavior of these soils at the solid-fluid transition. We propose exponential laws describing the evolution of the critical shear stress τc, the critical shear rate \( \dot{\gamma_c} \), and the shear modulus G as a function of the deviation w-LL.  相似文献   

12.
The small strain shear stiffness G0 of the soil is of interest and importance in both theory and practice. It is expected that for granular materials G0 would slightly increases with over-consolidation ratio (OCR). However, laboratory tests indicate that G0 may decrease with increasing OCR, especially for loose specimens, which is counterintuitive. To explore the underlying mechanism, discrete element method (DEM) is used to investigate the effect of OCR on G0. The DEM simulations successfully capture the laboratory observations. The analyses at the particulate level reveal that the decrease in small strain stiffness is mainly due to the decreases in coordination number and the uniformity of contact force distribution during unloading process.  相似文献   

13.
The rock mass failure process can be divided into several distinct deformation stages: the compaction stage, elastic stage, stable failure stage, accelerated failure stage, and post-peak stage. Although each stage has been well studied, the relationship among the stages has not been established. Here, we establish two models which are the Strain model Q and Energy density model S by using the renormalization group theory and investigate the mechanical relationship between the volume dilatant point and peak stress point on the rock stress-strain curve. Our models show that the strain ratio (ε f /ε c ) and energy ratio (E f /E c ) at the volume dilatant point and peak stress point are solely functions of the shape parameter m. To verify our models, we further studied the failure process of rock specimens through several uniaxial compression experiments and found that the relationship between ε f /ε c or E f /E c and m shares a notably similar pattern to that from our theoretical model. However, the ε f /ε c and E f /E c values in our experiments are slightly smaller than those predicted by the models. In brief, we demonstrate that our models can be used to predict the failure process of the laboratory-scale hard brittle rock samples.  相似文献   

14.
Neoproterozoic rocks, Oligocene to Neogene sediments and Tertiary Red Sea rift-related volcanics (Harrat) are three dominant major groups exposed in the Jeddah tectonic terrane in Western Arabia. The basement complex comprises amphibolites, schists, and older and younger granites unconformably overlain by a post-amalgamation volcanosedimentary sequence (Fatima Group) exhibiting post-accretionary thrusting and thrust-related structures. The older granites and/or the amphibolites and schists display mylonitization and shearing in some outcrops, and the observed kinematic indicators indicate dextral monoclinic symmetry along the impressive Wadi Fatima Shear Zone. Finite strain analysis of the mylonitized lithologies is used to interpret the deformation history of the Wadi Fatima Shear Zone. The measured finite strain data demonstrate that the amphibolites, schists, and older granites are mildly to moderately deformed, where XZ (axial ratios in XZ direction) vary from 2.76 to 4.22 and from 2.04 to 3.90 for the Rf/φ and Fry method respectively. The shortening axes (Z) have subvertical attitude and are associated with subhorizontal foliation. The data show oblate strain ellipsoids in the different rocks in the studied area and indication bulk flattening strain. We assume that the different rock types have similar deformation behavior. In the deformed granite, the strain data are identical in magnitude with those obtained in the Fatima Group volcanosedimentary sequence. Finite strain accumulated without any significant volume change contemporaneously with syn-accretionary transpressive structures. It is concluded that a simple-shear deformation with constant-volume plane strain exists, where displacement is strictly parallel to the shear plane. Furthermore, the contacts between various lithological units in the Wadi Fatima Shear Zone were formed under brittle to semi-ductile deformation conditions.  相似文献   

15.
The estimated undrained shear strength (su) is often not a unique value because it can be evaluated by various test types and/or procedures, such as different failure modes, shear strain rates, and boundary conditions. This study explores (1) the relationship between reference undrained shear strength and in situ shear wave velocity in terms of the effective overburden stress, and (2) the independent relationships to evaluate the undrained shear strength with special consideration of different directional and polarization modes (VH, HV, HH shear waves), which has not been reported. This evaluation is done via a worldwide database compiled from 43 well-documented geotechnical test sites associated with soft ground. Finally, new correlation models are proposed to estimate the undrained shear strength based on the in situ shear wave velocity as well as the plasticity index or the overconsolidation ratio. The application of the shear wave velocity–undrained shear strength relation is illustrated through two independent case studies. The proposed relationships are expected to contribute to reasonable estimates of undrained shear strength as well as offer practical guidance on even extrapolation beyond the data that is available to geotechnical engineers.  相似文献   

16.
For determination of atrazine isotherms in agricultural soils of Fars Province, composite soil samples from 0 to 5 cm depth with textures of silty clay loam, clay loam and loam were collected. In order to form the atrazine isotherms, 10, 50 and 100 µg atrazine g?1 soil was added to the soil samples. Soluble atrazine in water:soil ratios of 10:1, 50:1 and 200:1 was measured after 3-h shaking. Finally, for each cases of applied atrazine, water extractable atrazine was determined and quantified using gas chromatography instrument. The results indicated that there was a linear relationship between the logarithms of water extractable atrazine and added atrazine for different water:soil ratios. A general equation of WEA = K(WS) α (AA) β is obtained experimentally between water extractable atrazine, µg g?1(WEA), and added atrazine, µg g?1 (AA), where K, α and β are absorption constants; WS is the water:soil ratio, g g?1. For the loam, silty clay loam and clay loam soil textures, the α were 0.49, 0.23 and 0.13, respectively, the β were 0.55, 0.806 and 0.21, respectively, and the K were 1.44, 0.78 and 25.38, respectively.  相似文献   

17.
Arc fissure is one of the basic forms of defective rock, where the expansion and evolution mechanism plays an important role in the stability of engineering rock mass under the external load action. Uniaxial compression experiments of sandstone samples that contained various angles of arc fissures (sandstone sample was 80 mm?×?160 mm?×?30 mm) were performed in order to investigate the effect that arc angle α had on the mechanical properties, the failure mode, and the fracture evolution process of sandstone. The results showed that when arc angle α was increased, the peak strength and the strain of the sandstone samples initially decreased before increasing and the minimum peak strength and strain were reached when α?=?15°. The deterioration of the bearing capacity and the number of cracks that appeared during the sandstone loading process decreased as the arc angle of the fissure increased. The arc fissure destruction was primarily initiated from the fragile area of the arch tip. The tensile cracks appeared on the fissure tip and non-tip as the axial force increased. The various arc angle α played an important role in the initiation stress and the rupture evolution of the specimen.  相似文献   

18.
This paper presents the creep behaviour of intact and remoulded specimens of fibrous peat obtained from a field site near Anzac, Alberta, Canada. The creep behaviour was investigated by means of long-term drained and undrained triaxial tests. The development of volumetric, axial, and undrained axial strain and strain rate during drained and undrained creep tests under variable stress conditions is presented. The stress – strain – strain rate (p′–ε v–\(\dot{\varepsilon }_{\text{v}}\)) relationship is found to be unique for different stress and loading durations. The p′–ε v–\(\dot{\varepsilon }_{\text{v}}\) relationship is analysed and represented by creep isotaches. The applicability of different creep models developed for normally consolidated clay is discussed and applied to define the development of creep strain in fibrous peat under varying isotropic and deviator stresses. The secondary consolidation coefficient for evaluating the volumetric strain rate of peat is found to be applicable with some limits. The drained creep behaviour of remoulded peat specimens differs from the behaviour shown by Shelby tube specimens, whereas the undrained creep behaviour in remoulded and Shelby tube specimens is similar.  相似文献   

19.
Absorption of the synchrotron emission of the quasar 3C 345 in the continuum and H(93–95)α and H(78–79)α radio recombination lines is studied. The upper limit for absorption in the H(93–95)α lines is Tal/Tac < 0.7%; absorption in the H(78–79)α lines with antenna temperature Tal = 25 mK, linewidth Δf = 5.3 ± 0.08 MHz, and Tal/Tac ≥ 0.3% has been detected. A correction to the redshift Δz = 0.00135 ± 0.00008 (z = 0.59365) has been determined.  相似文献   

20.
Pore solution salinity has important bearing on engineering behavior of marine sediments as they influence electrochemical stress (A–R) and differential osmotic stress (?π) of the salt-enriched clays. The electrochemical stress (A–R) is contributed by van der Waals (A) attraction and diffuse ion layer repulsion (R), while the differential osmotic stress (?π) is governed by the differences in dissolved salt concentrations in solutions separated by osmotic membrane. The paper examines the relative influence of differential osmotic stress (Δπ) and electrochemical stress (A–R) on the consolidation behavior of slurry consolidated kaolinite specimens, which are known to be encountered in recent alluvial marine sediments. Methods are described to evaluate the magnitudes of these physico-chemical components and their incorporation in true effective stress. Results of the study demonstrate that differential osmotic stress finitely contributes to true effective stress. The contribution from differential osmotic stress enables kaolinite specimens to sustain larger void ratio during consolidation.  相似文献   

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