Displacement-controlled Shear Tests Research Articles

Large-scale shear test of brash ice

A large-scale shear apparatus has been originally developed and built to test the mechanical properties of coarse-grained material. It was used to evaluate the shear behaviour of brash ice. The brash ice blocks were collected at Luleå harbour in two separate measuring campaigns in March 2020 and March 2021. The shear cylinder was loaded with brash ice in Luleå port in two different locations for the two test campaigns, and the displacement-controlled shear tests were conducted. A vertical actuator was used to set a constant normal load and then a horizontal actuator was used to move the shear swing. In this setup, time, forces, and displacements were recorded at the forward and return stroke of the horizontal actuator. In total 6 shear cycles on two brash ice samples with axial stress of 4.8 kPa, 2 kPa and 1 kPa were performed. The test data was analysed to determine the relationship between shear stress and shear strain. The macro-porosity and confining axial force were found to be the most influential factors in determining the strength and deformation of the brash ice. Furthermore, an attempt has been made to estimate a few parameters of a material model known as the Continuous Surface Cap Model.

Stress-controlled direct shear testing of geosynthetic clay liners II: Assessment of shear behavior

This paper is the second of a two-paper set on stress-controlled direct shear testing of geosynthetic clay liners (GCLs). Design of the apparatus, preliminary experiments, and shear deformation mechanisms in heat-treated and non-heat treated needle-punched (NP) GCLs were discussed in Part I. The objective of Part II (this paper) was to evaluate the effects of physical factors (i.e., peel strength and initial normal stress, σni), environmental factors (i.e., temperature and hydration solution), and creep on the internal shear behavior of NP GCLs. In addition, failure conditions of GCLs in the stress-controlled direct shear tests were compared to displacement-controlled direct shear tests to verify results. An increase in internal shear strength developed from increased GCL peel strength or increased normal stress. Elevated temperatures were observed to decrease internal shear strength for both non-heat treated and heat-treated NP GCLs. Specimens hydrated with a calcium-rich synthetic mining solution experienced increased internal shear strength due to cation exchange in the bentonite, whereas specimens hydrated with a highly alkaline synthetic mining solution experienced decreased internal shear strength. Creep tests revealed an increase in time-to-failure with decrease in applied shear stress. Finally, stress states at failure from stress-controlled and displacement-controlled shear tests corresponded to a unique failure envelope, which validates the efficacy of using stress-controlled direct shear tests to assess internal shear behavior and shear strength of NP GCLs.

Out-of-plane buckling of pantographic fabrics in displacement-controlled shear tests: experimental results and model validation

Due to the latest advancements in 3D printing technology and rapid prototyping techniques, the production of materials with complex geometries has become more affordable than ever. Pantographic structures, because of their attractive features, both in dynamics and statics and both in elastic and inelastic deformation regimes, deserve to be thoroughly investigated with experimental and theoretical tools. Herein, experimental results relative to displacement-controlled large deformation shear loading tests of pantographic structures are reported. In particular, five differently sized samples are analyzed up to first rupture. Results show that the deformation behavior is strongly nonlinear, and the structures are capable of undergoing large elastic deformations without reaching complete failure. Finally, a cutting edge model is validated by means of these experimental results.

Dynamic Shear Strength of a Needle-Punched GCL for Monotonic Loading

This paper presents an experimental investigation of the dynamic internal shear strength of a hydrated woven/nonwoven needle-punched geosynthetic clay liner (GCL) for monotonic (i.e., single direction) loading conditions. Displacement-controlled shear tests were conducted using a large direct shear machine for four normal stress levels ranging from 141 to 1,382 kPa and seven shear displacement rates R ranging from 0.1 to 30,000 mm/min. For each normal stress, peak shear strength first increased and then decreased with increasing displacement rate. Maximum values of peak strength occurred for R=100–10,000 mm/min and were 16–23% higher than corresponding static values measured at R=0.1 mm/min. For each normal stress, residual shear strength first decreased and then increased with increasing displacement rate, with minimum values occurring at R=1 mm/min. On a relative basis, residual strengths show greater dependence on displacement rate than peak strengths. The standard displacement rate for static shear tests of hydrated GCLs (0.1 mm/min) generally yielded conservative values of peak shear strength but unconservative values of residual shear strength, especially for higher normal stress levels. The GCL experienced large post-peak strength reduction for all test conditions.

Dynamic Shear Strength of GMX/GCL Composite Liner for Monotonic Loading

AbstractThis paper presents an experimental investigation of the dynamic shear strength of a composite liner consisting of a high-density polyethylene (HDPE) textured geomembrane (GMX) over a hydrated nonwoven/nonwoven needle-punched geosynthetic clay liner (GCL) for monotonic (i.e., single direction) loading conditions. Displacement-controlled shear tests were conducted using a large direct shear machine for five normal stress levels ranging from 13 to 2071 kPa and five shear displacement rates ranging from 0.1 to 30,000 mm/min. GCL internal failures occurred at high normal stress and low displacement rate. As normal stress decreased or displacement rate increased, failure mode transitioned to the GMX/GCL interface. Peak strength envelopes are slightly nonlinear (concave-down) and show dependence on displacement rate at higher normal stress. Large-displacement strength envelopes show greater dependence on displacement rate at higher normal stress due to the effect of changing failure mode. The standard ...

Dynamic Shear Behavior of a Needle-Punched Geosynthetic Clay Liner

An experimental investigation of the dynamic internal shear behavior of a hydrated needle-punched geosynthetic clay liner is presented. Monotonic and cyclic displacement-controlled shear tests were conducted at a single normal stress to investigate the effects of displacement rate, displacement amplitude, number of cycles, frequency, and motion waveform on material response. Monotonic shear tests indicate that peak shear strength first increased and then decreased with increasing displacement rate. Cyclic shear tests indicate that cyclic response was primarily controlled by displacement amplitude. Excitation frequency and waveform had little effect on cyclic shear behavior or postcyclic static shear strength. Number of cycles (greater than or equal to 10) also had little effect on postcyclic static shear strength. Shear stress versus shear displacement diagrams displayed hysteresis loops that are broadly similar to those for natural soils with some important differences due to the presence of needle-punched reinforcement. Secant shear stiffness displayed strong reduction with increasing displacement amplitude and degradation with continued cycling. Values of damping ratio were significantly higher than those typical of natural clays at lower shear strain levels. Finally, cyclic tests with increasing displacement amplitude yielded progressively lower postcyclic static peak strengths due to greater levels of reinforcement damage. Postcyclic static residual strengths were unaffected by prior cyclic loading.

Seismic Behavior of Post-Tensioned Gravity Dams: Shake Table Experiments and Numerical Simulations

Displacement controlled shear tests on small concrete lift joint specimens with different surface roughnesses reinforced with an unbonded post-tension cable are conducted to study a related joint constitutive model, and to determine the failure mechanisms associated to it. To investigate the applicability of the joint model, shake table tests are conducted on a 3.4-m high plain concrete post-tensioned gravity dam that has a cold lift joint about midheight. Numerical simulations using the joint constitutive model are compared with the experimental results. From the displacement controlled shear tests, it is shown that the post-tension cable provides additional strength to the joint by applying an additional normal load on the joint, and by the shear resistance that can be mobilized (cable dowel action). The tests performed on rough surface joints have demonstrated that the dilatancy phenomenon due to asperities increases the post-tension force. Shake table tests on the 3.4-m high dam model have shown that post-tensioning largely reduces residual sliding displacements of the joint. This reduction is a function of the frequency content of the base excitation. However, a single post-tension cable placed near the upstream face increases the upstream rocking response of the upper block, which is also a function of the frequency content of the excitation. Strong seismic excitations can induce cable failure at a lower value than its uniaxial tensile strength when significant shear displacements take place. To describe this brittle failure mechanism, a cable failure criterion that considers the mobilized shear and tensile strengths was proposed and was found to be adequate. Moreover, the post-tensioned joint model proposed showed good agreement with the static and dynamic tests performed to evaluate the joint shear force.

Static and Dynamic Behavior of Concrete Lift Joint Interfaces

Displacement controlled shear tests on concrete lift joint specimens with different surface preparations are conducted to compare dynamic sliding joint behavior with the static behavior. Experimental results indicate that the coefficient of friction decreases with the increase in normal load, under both static and dynamic shear. The shear strength is dependent on surface preparation. Monolithic specimens and water-blasted joints show higher shear strengths than untreated joints and plane independent joint surfaces. No strength degradation is noticeable under dynamic sliding shear tests since hysteresis loops are very stable. No dependency of shear strength on frequency content of the imposed shear displacements is observed. An empirical lift joint constitutive model is developed as a function of a basic friction coefficient and a roughness friction coefficient that is dependent upon the type of surface preparation. The proposed lift joint constitutive model is used to study the seismic sliding response of...