Results Of Simple Shear Tests Research Articles

Liquefaction Behavior of a Well-Graded Gravelly Soil under Initial Static Shear Stress in Cyclic Triaxial and Simple Shear Conditions

Among other reasons, studies of the liquefaction potential of gravelly soils are limited because of the difficulties involved in preparing uniform specimens, without particle segregation, especially for a well-graded gravelly soil in a dry state for simple shear testing. Errors and difficulties are also involved in compensating for membrane penetration to a gravelly soil specimen in triaxial testing to get reliable data. Thus, innovative approaches for preparing triaxial and simple shear specimens for gravelly soils are introduced and implemented in this study to overcome experimental problems in acquiring accurate test results. In addition to the aim of obtaining reliable testing data on the liquefaction of gravelly soils under initial static shear stress for simulating sloping ground conditions, a study of the effect of various stress paths on the liquefaction resistance of gravelly soils was another goal of this research. In this regard, two sets of cyclic tests using medium-size triaxial and simple shear devices are conducted on a unique soil to compare the liquefaction potential of the tested gravelly soil using these two devices. Results of simple shear tests indicate that as the value of initial static shear stress increases, the cyclic resistance of the tested gravelly soil decreases. However, the results of the triaxial tests show that the variation of cyclic resistance for the tested soil depends on the initial static shear stress level and associated stress reversal conditions. Furthermore, the observed value of the pore water pressure ratio at failure using the strain-based liquefaction criteria for the tested gravelly soil was about 0.85, regardless of the type of testing. In addition, the relationship between the liquefaction resistance of gravelly soils using cyclic triaxial and simple shear devices was obtained.

Deformation simulations of sand under Bi-directional shear loading

A well-developed sand plasticity model is further revised and validated based on bi-directional simple shear test data on medium to high relative density sands, which includes circular, oval and figure-8 type stress paths at different cyclic stress ratio (CSR) levels. The sand properties revealed from non-proportional loading tests, such as extended contractive behavior for medium to dense sands, flow rule dependency on plastic strain increment direction, stress increment direction dependency of plastic moduli, as well as the so-called non-coaxial property are incorporated into the new model development. Specifically, the recently proposed strain increment direction dependent flow rule is formulated and validated using bi-directional simple shear test results; and the relatively simple plastic moduli revised for the non-proportional loading are validated.After the model parameters are calibrated using a circular stress path, predictions are made for oval and figure-8 type stress paths at two cyclic stress levels. The modeling results show that the computed deformations up to a large strain state (i.e., 6% double amplitude strain) match fairly well with the test results; and the predicted pore-water pressure generation (or the effective stress change) followed the trend of test measurements including the repeating contractive and dilative cycles near the failure surface. A fabric dilatancy concept-based stiffness reduction approach is adopted that is active for the simulations of oval and figure-8 type stress paths.By comparing with test results, the model predictions demonstrate the capability of the present model in simulating the complex deformation magnitudes and patterns for sands under bi-directional loadings.

Application of Critical State Approach to Liquefaction Resistance of Sand–Silt Mixtures under Cyclic Simple Shear Loading

An extensive experimental program of constant-volume (undrained) cyclic simple shear tests was undertaken on Ticino, Italy, sand with different contents of nonplastic fines, ranging from 0% to 40%. The samples were reconstituted by moist tamping and tested with different initial states, including void ratios and effective vertical stresses. Test results confirmed that the concept of equivalent granular void ratio e* is appropriate for the interpretation of the undrained cyclic behavior of sand with different amounts of fines up to the limiting fines content. Because a single trend for critical state (CS) data points was observed in the e*-log(p′) plane (EG-CSL) for different amounts of fines, the cyclic simple shear test results were analyzed within a unified critical state soil mechanics (CSSM) framework in terms of an alternative state parameter, Ψ*. A unique correlation between undrained cyclic strength (CRR) and Ψ* was found, irrespective of the fines content and initial state. Although a correlation between the cyclic resistance ratio and the conventional state parameter Ψ works as well, the procedure based on Ψ* has the advantage that the cyclic behavior of a certain sand with different contents of non plastic fines is described by a single reference curve (EG-CSL). In contrast to previous investigations in the literature, which mainly used triaxial tests, the CRR-Ψ* correlation proposed in the present study is based on cyclic simple shear tests, which better represent the real ground conditions under seismic loading.

Capacity degradation method for piles under cyclic axial loads

Piles used for jacket type foundation of offshore wind turbine are subjected to highly cyclic tension and compressive loading. The pile capacity under cyclic tension loading decreases with increased number of loading cycles due to reduction of the pile shaft resistance. A numerical simulation scheme is presented, which allows the calculation of the pile capacity degradation (CDM) due to cyclic loading for driven steel piles. The volume compaction of soil near the pile surface during the cyclic loading is determined from the cyclic simple shear test results and then applied to the pile-soil system.From the limited number of tests available, interaction diagrams have been developed, which give the number of load cycles leading to failure dependent on the mean load and the amplitude of the cyclic load portion, which are both related to the static pile capacity. However, such diagrams cannot account for different soil conditions or pile geometry and pile stiffness. The calculation results for different piles in sandy soil under cyclic axial loading are presented and compared with existing interaction diagrams. Finally, recommendations regarding further investigations and improvements of the method are given.

Liquefaction potential of sands at the Krško-Brežice field, Slovenia

The Krsko-Brežice field is one of the most seismically active areas in Slovenia. The most damaging recorded earthquake with an intensity of VIII (EMS) occurred on 29th January 1917. It caused damage and claimed two lives. In the last 100 years, 9 earthquakes with intensity higher than VI (EMS) have been recorded. At the investigated area, a top layer up to 5 m thick, consisting of recent deposit of very loose silts and sands (ML, SM, SP), covers the medium dense to dense Quaternary gravel, beneath which there are over-consolidated, uncemented Miocene silts and marls. The top layer could be prone to liquefaction, as reported for the close surroundings of Brežice, where the liquefaction phenomenon was observed during the Zagreb earthquake in 1880 and during the Kupa Valley earthquake in 1909. The paper presents the results of laboratory index tests, cyclic simple shear tests and field investigations (SPT, CPT, (S)DMT, vs measurements), which were carried out to assess the liquefaction potential of the top layer at the location of the Brežice Hydroelectric Power Plant (HPP). All results show that the top layer is prone to liquefaction for an earthquake with a 475 year return period. Cyclic simple shear test results show that the liquefaction potential of horizontal ground for an earthquake with a 475 year return period can be reduced by the densification of the top layer to at least 95% of maximum Proctor density.

Mechanism of improvement of biochar on shear strength and liquefaction resistance of sand

Biochar is a biomass-derived carbonaceous solid product produced by way of pyrolysis, a process whereby thermal degradation of biomass occurs in the absence of or under a limited oxygen environment. To date, little work has been done to assess its effect on soil properties from the geotechnical point of view. A few studies have shown that biochar could increase the shear strength of clays. Results of simple shear tests indicated that although the effect of adding biochar on the drained shear resistance of sand is relatively minor, the liquefaction resistance increased considerably. In this paper, to provide an insight into the mechanism, the interaction between biochar and water was studied in more detail, through an analysis of the biochar chemical active surface, morphological observations of the particles and biochar–water suspension, as well as rheological measurements. It is believed that the mechanism of improvement is related to the active chemicals on the surface and inside the pores of the biochar particles. These volatiles interact with water by repelling it (hydrophobic) and at times by attracting it (hydrophilic), creating a complex network between water and biochar particles that helps to delay the increase in excess pore-water pressure and provides some shear resistance.

A Framework for Assessing Liquefaction Hazard for Urban Areas Based on Soil Dynamics

Soil liquefaction induced by earthquakes poses a great threat to urban areas, not only by causing direct damages to infrastructures but also by delaying rescue and relief actions. Established engineering assessment methods using indices such as factor of safety against liquefaction (FL) tend to overestimate liquefaction hazards. While the standard usage of soil dynamic analysis for liquefaction assessment is limited to a single site with detailed site information. In this paper, we propose a framework based on soil dynamics for assessing liquefaction hazard for urban areas which contain numerous sites with borehole logs only. The framework is featured by generating analysis models and by estimating material parameters automatically from available borehole information. The governing equations for soil dynamics are solved by a finite element code. Liquefaction hazard is assessed according to the solutions of excess pore water pressure for given seismic waves. As demonstrations, we show simulation results of simple shear tests and of seismic response for a target site under loadings of artificial and of actual seismic waves. The automatic model construction and parameter estimation enable this framework being applied effectively for urban-area-wide liquefaction assessment, as an alternative for the current practices based on engineering indices.

Shearing of Materials with Intermittent Joints

The strength of fractures is much lower as a rule than that of intact rock. As a result they play a controlling part in the mechanical behaviour in general and the failure in particular of rock mass. Though a large volume of experimental data is available on the shear resistance of joints, as well as on the propagation of single cracks, the same is not true for the mechanical behaviour of intermittent joints. The experimental data available in this case are limited and the strength of rock mass with intermittent joints is usually modelled using averaged values of cohesion or assuming the fractures to be continuous. In the present work, the results of simple shear tests on a series of gypsum specimens with pre-existing cracks are presented. Twelve different crack orientations and two normal stresses were tested. The hypothesis of averaged cohesion and the theory of fracture mechanics are used to reproduce the results. It is found that fracture mechanics provides a more suitable model for the experimental results, especially when crack interaction is taken into account.

THE NEXT-GENERATION CONSTITUTIVE CORRELATIONS FOR SIMULATION OF CYCLIC STRESS-STRAIN BEHAVIOUR OF SAND

This paper presents an innovate approach to simulate the stress-strain behaviour of sands subjected to large amplitude regular cyclic loading. New prediction correlations were derived for damping ratio (D) and shear modulus (G) of sand utilizing linear genetic programming (LGP) methodology. The correlations were developed using several cyclic torsional simple shear test results. In order to formulate D and G, new equations were developed to simulate hysteresis strain–stress curves and maximum shear stress (τmax) at different loading cycles. A genetic algorithm analysis was per­formed to optimize the parameters of the proposed formulation for stress-strain relationship. A total of 746 records were extracted from the simple shear test results to develop the τmax predictive model. Sensitivity and parametric analyses were conducted to verify the results. To investigate the applicability of the models, they were employed to simulate the stress-strain curves of portions of test results that were not included in the analysis. The LGP method precisely charac­terizes the complex hysteresis behaviour of sandy soils resulting in a very good prediction performance. The proposed design equations may be used by designers as efficient tools to determine D and G, specifically when laboratory testing is not possible.

폐기물 매립장 접촉면의 동적 전단거동특성

최근 늘어나고 있는 폐기물량에 따라 폐기물 매립장의 건설이 증가하고 있으며, 매립장 내 폐기물의 격리, 보호 및 환경오염방지를 위하여 토목섬유가 널리 활용되고 있다. 토목섬유는 주변의 흙과 접촉면을 형성하여 폐기물 매립장의 전단 거동에 영향을 미치게 된다. 폐기물 침출수에 포함된 화학적 요소는 이러한 접촉면 거동에 중요한 영향을 미치며, 지진과 같은 동적하중 또한 접촉면 거동에 미치는 화학적 영향을 가속화시킬 수 있다. 따라서 본 연구에서는 화학적 영향을 고려한 접촉면 전단강도 감소효과를 반영하여 수치해석을 수행하였다. 반복 단순전단시험 결과를 바탕으로 수치해석을 수행한 결과, 접촉면 전단강도 감소를 미 고려시 폐기물 매립장의 동적 안정성을 과대평가할 수 있다고 판단된다. The number of the waste landfill site increases continuously in recent years. Various types of geosynthetics have been utilized in the waste landfill site for encapsulating, isolating, protecting, and so on. Geosynthetics compose the interface with soil and affect the shear behaviors of waste landfill system. The chemical aggressors in the leachate also play a critical role in the interface and it is known that the dynamic loading is able to accelerate manifestation of the effects of chemical attack. In this research, numerical analysis was conducted considering shear stress degradation in the geosynthetic-soil interface due to dynamic load with chemical effect. Cyclic simple shear test results was reviewed and applied to the numerical modeling as well. Consequently, the stability of waste landfill site could be overestimated without considering the shear stress degradation of interface.

Modeling of the simple shear deformation of sand: effects of principal stress rotation

The paper presents a simple constitutive model for the behavior of sands during monotonic simple shear loading. The model is developed specifically to account for the effects of principal stress rotation on the simple shear response of sands. The main feature of the model is the incorporation of two important effects of principal stress on stress–strain response: anisotropy and non-coaxiality. In particular, an anisotropic failure criterion, cross-anisotropic elasticity, and a plastic flow rule and a stress–dilatancy relationship that incorporate the effects of non-coaxiality are adopted in the model. Simulations of published experimental results from direct simple shear and hollow cylindrical torsional simple shear tests on sands show the satisfactory performance of the model. It is envisioned that the model can be valuable in modeling in situ simple shear response of sands and in interpreting simple shear test results.

Assessment of liquefaction triggering using strain energy concept and ANN model: Capacity Energy

In the present study, an artificial neural network (ANN) model was developed to establish a correlation between soils initial parameters and the strain energy required to trigger liquefaction in sands and silty sands. A relatively large set of data including 284 previously published cyclic triaxial, torsional shear and simple shear test results were employed to develop the model. A subsequent parametric study was carried out and the trends of the results have been confirmed via some previous laboratory studies. In addition, the data recorded during some real earthquakes at Wildlife, Lotung and Port Island Kobe sites plus some available centrifuge tests data have been utilized in order to validate the proposed ANN-based liquefaction energy model. The results clearly demonstrate the capability of the proposed model and the strain energy concept to assess liquefaction resistance (capacity energy) of soils.

Effects of boundary conditions and partial drainage on cyclic simple shear test results—a numerical study

AbstractOwing to imperfect boundary conditions in laboratory soil tests and the possibility of water diffusion inside the soil specimen in undrained tests, the assumption of uniform stress/strain over the sample is not valid. This study presents a qualitative assessment of the effects of non‐uniformities in stresses and strains, as well as effects of water diffusion within the soil sample on the global results of undrained cyclic simple shear tests. The possible implications of those phenomena on the results of liquefaction strength assessment are also discussed. A state‐of‐the‐art finite element code for transient analysis of multi‐phase systems is used to compare results of the so‐called ‘element tests’ (numerical constitutive experiments assuming uniform stress/strain/pore pressure distribution throughout the sample) with results of actual simulations of undrained cyclic simple shear tests using a finite element mesh and realistic boundary conditions. The finite element simulations are performed under various conditions, covering the entire range of practical situations: (1) perfectly drained soil specimen with constant volume, (2) perfectly undrained specimen, and (3) undrained test with possibility of water diffusion within the sample. The results presented here are restricted to strain‐driven tests performed for a loose uniform fine sand with relative density Dr=40%. Effects of system compliance in undrained laboratory simple shear tests are not investigated here. Copyright © 2004 John Wiley & Sons, Ltd.

A MICROSCOPIC CONSIDERATION ON SHEARING CHARACTERISTIC OF DECOMPOSED GRANITE SOIL

A new preparation method of undisturbed specimen of decomposed granite soil by freezing a block sample is developed. Triaxial and simple shear tests were carried out for undisturbed and compacted specimens. The following results are obtained.1) The simple shear test results can give the strength parameters of the unsaturated and the saturated specimens at the low pressure. These parameters are valid for the analysis of a slope stability.2) The relationships between stress, strain and volumetric strain on the undisturbed and compacted specimens are different. This fact, especially concerning the dilatancy characteristics of these samples, is explained by the distribution of pore size and crushing of the particles.3) The suction in unsaturated specimen is important for the strength.

Statistical Analysis of Sand Liquefaction

A consistent set of stochastic models is developed for the liquefaction resistance of a homogeneous mass of sand, such as a laboratory sample or small element of in situ material. A probabilistic model for liquefaction in the laboratory for undrained simple shear tests is developed first. This model gives the probability distribution of the number of cycles to liquefaction as a function of uniform shear stress amplitude, mean initial effective stress, and relative density. Corrections are quantified and incorporated into the model. Parameters are estimated from a large number of simple shear test results obtained by eight different groups of researchers using several sands and testing techniques. The laboratory liquefaction model is converted into one applicable in the field. Finally, the model is generalized to load cycles with nonuniform shear stress amplitude.

Consolidation and Strength Properties of a Clay

An embankment was constructed over a lake deposit, and sand drains were used to accelerate consolidation. The investigation included measurement of vertical and radial coefficients of consolidation in laboratory and in-situ tests. It was found that the ratio of horizontal to vertical coefficients of consolidation obtained from laboratory consolidation tests is larger than those obtained from in-situ permeability tests and in-situ consolidation. The shear strengths before and after consolidation were measured by unconfined compression tests and also computed from results of triaxial and simple shear tests. The strengths obtained from the results of triaxial tests are greater than those obtained from the results of simple shear tests, which are in turn greater than those measured by unconfined compression tests. /ASCE/

Recent observations on the motion of small angle dislocation boundaries

The motion of small angle dislocation boundaries in zinc crystals was investigated in the temperature range −196°C to 400°C. Boundaries were made to move by the application of a shear stress acting in the direction of the Burgers vector of the edge dislocations comprising the boundary. The character of this motion was found to vary markedly with temperature. Motion proceeded at a constant rate under a constant stress at elevated temperatures. At + 20°C movement was discontinuous, the boundary advancing through an appreciable distance during each jump. At −196°C, motion appeared to be steady. However, at both 20° and −196° a continuously increasing stress was required for continued movement. The boundary angle remained constant during motion at high temperature. At lower temperatures, the magnitude of the angle decreased, and the boundary assumed a more complex shape through interaction with structural defects. Small-angle boundaries of like sign in proximity to one another coalesced during short time annealing treatments at 400°C to form a single boundary. Closely spaced boundaries of like sign could be made to unite at any temperature by the application of a stress, thus establishing a mechanism for the formation of a substructure in the absence of appreciable thermal energy. Boundaries of unlike sign were united through their stress-induced motion and the angle of the resultant boundary equalled the algebraic sum of the angles of the constituent boundaries. The results of boundary motion experiments were compared with the results of simple shear tests on single crystals of zinc. The similarities suggested that motion of dislocations through the structural barriers of the crystal rather than generation of new dislocations may be the factor which determines the yield strength.