Shear Test Apparatus Research Articles

Shear Performance of Rock Joint Reinforced by Fully Encapsulated Rock Bolt Under Cyclic Loading Condition

The shear performance of bolted rock joints under cyclic loading condition was studied through laboratory shear tests. The tests were performed on a cyclic shear testing apparatus. The fully encapsulated rock bolts were inserted in the rock joints. The upper block was fixed in the horizontal direction, and the cyclic shear load was applied laterally on the lower block. A total of 16 shear tests were conducted for two types of rough joints. The results showed that the failure mode of rock bolts in cyclic shear test was different with the case of direct shear test. When the cyclic displacement was small, the rock bolt played a very small role in the second-to-fifth cycles, the rock bolt remained unbroken during cyclic shearing. The shear resistance of the rock bolt would gradually recover after the shear displacement has exceeded the cyclic displacement in the termination cyclic after five cycles. When the cyclic displacement was large, the rock bolt broke during cyclic shearing, and the shear resistance could not be recovered in the termination cyclic. It is indicated that the rock bolt had completely lost its supporting role after cyclic shear loading. The shear strength reduction of bolted joints under the cyclic loading condition was much significant compared to the un-bolted joints. Therefore, the influence of cyclic loading on the shear resistance of the rock bolt was much larger than its counterpart of the rock joint itself. These results showed that the shear performance of a rock bolt inserted in a rock joint was strongly influenced by cyclic shear loading.

Effect of temperature on behaviour of red clay–structure interface

This study presents the results of an experimental investigation conducted to assess the temperature effects on shear stress–strain behaviour and shear strength parameters of red clay and its interface with the geostructure under different normal stresses (50, 100, 200, and 400 kPa). A modified direct shear test apparatus, capable of handling temperatures up to 50 °C, was used in this study. The experimental program includes shearing the red clay and red clay–structure interface at different temperatures (2, 15, 38 °C) and after subjecting it to different heating–cooling cycles. The test results in this study and the previous studies in the literature indicated that the temperature has insignificant effects on the friction angle of clay and clay–structure interface. However, the temperature effect on the cohesion of clay and the adhesion between the clay and structure depends on the normal stress level and history. A new conceptual understanding for the possible temperature effect on the clay–structure interface was introduced in this study and it was used to interpret the different interface test results in the literature.

Customized shear test for bond-slip characterization of EBR FRP-concrete system: Influence of substrate aggregate type

Performance assessment of the bond between FRP as externally bonded reinforcement (EBR) and concrete requires establishing bond-slip characteristics using appropriate experiments, one of which is the double shear bond test. Different versions of the said test, ranging from its traditional form to improved versions, exist. Yet, the improved versions themselves are not without shortcomings. The aim of this paper is to present a simple and improved double shear test setup, customized to ease its application in FRP-concrete bond tests in addition to satisfying other important functional requirements. Designed and fabricated as a Y-hook-cylinder system to substitute half of the traditional double shear specimen size, the simple feature of traditional approach is retained in the other half. Performance of the developed setup is, first, verified against that of the traditional approach on a number of specimens. Subsequently, the proposed system is used to conduct an exploratory study on the influence of coarse aggregate type on FRP-concrete bond behavior. Two concrete types are produced; one containing fresh aggregate and the other consisting of steel slag aggregate substituting 30% of the maximum fresh aggregate size in the first concrete type. Typical bond-slip models of the two specimen types are developed and compared with several other literature sources. The results, both in terms of the debonding load and bond-slip characteristics, show improvement in bond performance when a substrate failure occur in the specimens containing steel slag aggregate.

Fatigue performance of interface bonding between asphalt pavement layers using four-point shear test set-up

This paper aims to study the fatigue performance of interface bonding between asphalt pavement layers. To fulfill this objective, a four-point shear test (4PST) set-up was developed, and a series of fatigue tests were conducted on composite asphalt beam samples made up of stone mastic asphalt (SMA) and asphalt concrete (AC) mixtures. The combined effect of test temperature (3 levels), normal pressure (6 levels), loading frequency (5 levels), and shear stress (6 levels) with single tack coat type and application rate were considered for evaluation. Two interface failure criteria were successfully adopted in this study, and high correlation was relatively found between the fatigue test results and the corresponding fatigue life criteria. Findings of this study revealed that firstly, both the interface fatigue life and shear stiffness increased at all temperatures with increasing normal stress. Secondly, with increasing loading frequency, the interface fatigue life increased at each temperature. Thirdly, shear stiffness decreased with increasing shear stress for each temperature; the decrease was more pronounced at lower temperatures. Power laws were also proposed to characterize interface fatigue life at each temperature. Finally, the results of the analysis of variance (ANOVA) indicated that unlike the fatigue life, all factors had a significant effect on the shear stiffness. A multiple regression model was established successfully to predict the initial shear stiffness.

Design and Fabrication of a Low Cost Field Vane Shear Apparatus

The un-drained shear strength of soil is of great concern in many geotechnical engineering applications. The vane shear test is a simple, easy and popular type of in-situ shear test to the geotechnical engineers and geologists. However, it is not fairly appreciated by the academic personnel or field engineers as compared to the other shear strength test of soil. There are different types of field vane shear test apparatus existing in the market, but most of them are costly and have limited measuring capacity. The main objective of the research work was to develop a low cost field vane shear apparatus with higher measurement capacity using local materials and accessories. In this research work, a simple manually operated field vane shear apparatus was designed and fabricated. Four vane blades were welded to the vane shaft and a socket was added at the top. The most important component of the design apparatus is the torque wrench which is used to determine the torque both in clock and anti-clock wise direction. The torque value is then converted into the shear strength. The designed apparatus is suitable to determine the un-drained shear strength of soft to stiff clay soil up to 300 kPa. The performance of the device was tested directly in the crop field near Kumargaon area at Sylhet city. Average shear strength from in-situ test was found 49 kPa for medium to stiff clay. For the assessment of accuracy of the designed apparatus, undisturbed soil sample was collected from the same location of the field and then tested by laboratory vane apparatus according to ASTM D4648 and fairly similar result was observed. The instrument’s output repeatability was checked from the test data and the values were found quite satisfactory with a range of 2.68 to 5.87. The designed apparatus are about five times cheaper than the conventional apparatus available in the market.

Performance of a large-scale magnetorheological elastomer–based vibration isolator for highway bridges

This study presents an experimental investigation on the magnetorheological effect of a new magnetorheological elastomer–based adaptive bridge isolation bearing system. Two identical magnetorheological elastomer–based adaptive bridge bearings (isolators) were designed and fabricated. Electromagnets were incorporated to create a closed-loop magnetic path in the magnetorheological elastomer layers. A double-lap shear and compression test setup was utilized to characterize the mechanical properties of the system subjected to scaled structural cyclic forces and strains. Experimental results demonstrated that the effective stiffness of adaptive bridge bearings increases with increased applied magnetic field and a compressive force resulted in larger apparent shear stiffness. Also, increasing loading frequency resulted in larger apparent shear stiffness and lower magnetorheological effect and similarly, however, a compressive force resulted in smaller magnetorheological effects.

Influence of temperature on soil–pile interface shear strength

Geothermal piles are subjected to daily and seasonal cyclic temperature changes during their life spans. These temperature changes (heat cycles) induce cyclic expansion/contraction along the soil–pile interface that may affect interface properties such as shear strength. A series of direct shear tests was conducted using a temperature controlled direct shear test apparatus to evaluate the effects of heat cycles on soil–pile interface strength. The interface temperature was cycled between 24 ° C and 34 ° C to simulate the real thermal conditions that an energy pile may experience. Non-cyclic and cyclic thermal loading were applied under different stress states and histories. It was found that the shearing behavior of interface under thermal loading is described through thermally induced changes in Mohr–Coulomb’s parameters of the interface. Moreover, the thermally induced changes in interface strength are mainly controlled by the soil stress state and the soil stress history.

Laboratory Investigation of Shear Behavior of High-Density Polyethylene Geomembrane Interfaces.

As a product of polymeric materials, geomembranes (GMs) are widely used in engineered systems as impervious barriers due to their low permeability. In this study, a large-scale composite shear test apparatus was developed to investigate the shear behaviors of various GM interfaces. A series of direct shear tests were conducted on GM–soil, GM–geotextile, and GM–concrete interfaces. Two types of high-density polyethylene (HDPE) GMs, a smooth GM and a textured GM, were used to evaluate the effect of GM-texturing on the shear properties of these interfaces. Based on the experimental data, the friction angles and adhesions of GM interfaces were calculated using the Mohr–Coulomb criterion. Test results describing the behavior of GM–soil and GM–geotextile interfaces from the current study were then compared with results from previous studies. The test results are shown to verify the reliability of the new large-scale composite shear apparatus. In addition, this paper presents preliminary experimental results of the GM–concrete interface shear tests.

Shear mechanical properties of the core structure of biomimetic fully integrated honeycomb plates

In the present study, the shear failure mode and mechanical properties of the core structure of biomimetic fully integrated honeycomb plates with sealing edges were investigated experimentally and through the finite element method. The findings are as follows: (1) the failure mode of the sealing edges and honeycomb walls perpendicular to the shear direction is mainly debonding between the fiber and matrix, whereas fiber breakage, debonding between the fiber and matrix and exfoliation of the resin matrix occur in the sealing edges parallel to the shear direction. Meanwhile, the reasonableness and feasibility of the double shear testing apparatus designed in this study were verified, thus confirming the results of research are reliable and valid. (2) Shear failure of the core structure of fully integrated honeycomb plates is mainly fiber debonding appearing in the middle surface of the core structure, which is a failure of the material interface. Stripping failure in the joint interface of the core layer and upper and lower plates does not occur, which indicates that the biological structure possesses excellent integral mechanical properties. (3) The sealing edges parallel to the shear direction and the honeycomb walls that are oriented 30 degrees to the shear direction are the first to fail, followed by the sealing edges and honeycomb walls perpendicular to the shear direction, which is consistent with the microscopic failure phenomenon observed in both directions. To prevent failure at the material interface, the fully integrated honeycomb plates manufactured in this experiment require further improvements. Thus, countermeasures are proposed, such as pre-treating the fiber surface. These findings will specify future research directions to perfect fully integrated honeycomb plates and improve the shear mechanical properties of core structures.

Synergy in shear response of ultra-high-performance hybrid-fiber-reinforced concrete at high strain rates

Synergistic effects on shear resistance of ultra-high-performance hybrid-fiber-reinforced concrete (UHP-HFRCs) at high strain rates was investigated using a new shear test setup. Two UHP-HFRCs: L05S10 (containing 0.5 vol-% long and 1.0 vol-% short fiber) or L10S05; and, two ultra-high-performance mono-fiber-reinforced concretes (UHP-MFRCs): L15S00 (containing 1.5 vol-% long fiber) or L00S15, were tested. The L05S10 generated high synergy in shear resistance whereas the L10S05 did little. Synergies were significant for shear strength, shear peak toughness, but not for shear strain capacity. Moreover, the L00S15 produced the highest rate-sensitivity although the shear response of both UHP-MFRCs and UHP-HFRCs was generally sensitive to the applied strain rates. The experimental shear strengths were well-matched with the theoretical calculations.

Strain rate-dependent shear failure surfaces of ultra-high-performance fiber-reinforced concretes

Strain rate-dependent shear behavior of ultra-high-performance fiber-reinforced concretes (UHPFRCs) with confining pressure was investigated using a new shear test setup in an improved strain energy impact machine (I-SEFIM). Different confining pressures were applied to the specimens prior to shear testing at both static and high strain rates, and were maintained during testing. The shear strength of UHPFRCs was highly sensitive to the applied strain rate and confining pressure. The effect of confining pressure on the shear strength was more pronounced at a static rate rather than at high strain rates. Strain rate-dependent shear failure surfaces of UHPFRCs were proposed.

Development of Large Direct Shear Test Apparatus for Passive Bolt Reinforced Mass

Shear testing of large size rock mass in the laboratory is a tedious and challenging task. Difficulties further arise when testing is done with rock bolts. Complex interaction between intact blocks of mass, joint and bolts creates problems during shear testing. Hence, for testing of large rock mass with bolts, special technique and facilities are required. The present paper summarized the details of the development of a large sized direct shear testing facility for passive bolt—reinforced rock masses. A specially designed servo-controlled direct shear test apparatus having shear box of size 750 mm × 750 mm × 1000 mm has been fabricated in the Geotechnical engineering laboratory of IIT Roorkee. The normal loading capacity of the apparatus is 1500 kN while shear loading capacity is 2000 kN. To evaluate the performance of the apparatus, specimens of blocky mass were prepared and tested without and with bolts. The present paper discusses the details about the large direct shear apparatus and testing methodology.

Interface shear behaviours between recycled concrete aggregate and geogrids for pavement applications

ABSTRACTThe usage of recycled concrete aggregate (RCA) in pavement applications is a sustainable approach for future infrastructure development, given the significant environmental benefits. Geogrid reinforcement of RCA can also improve the tensile and flexural strengths of the pavement structure to sustain high traffic loadings. The effect of aperture size, tensile strength of geogrids, normal stress and gradation on shear interaction between geogrids and RCA was investigated in this research, with the usage of a large-scale direct shear test (LDST) apparatus. Three types of biaxial geogrids, with different aperture sizes and tensile strengths, and two RCA samples with different gradations were used in this study. The interface shear strength was found to be highly dependent upon the aperture width of the geogrids, D, as well as the RCA particles finer than the aperture width of geogrid, FD. Based on the analysis of test results, a linear relationship between interface shear strength coefficient, α, the ratio of interface shear strength of geogrid/RCA and shear strength of RCA was proposed, with respect to the D/FD ratio. The proposed relationship will be useful for a rapid assessment of the interface shear strength coefficient of geogrid-reinforced RCA based on the aperture size of geogrids and RCA gradation properties.

Shaft capacity of the pre-bored grouted planted pile in dense sand

The pre-bored grouted planted pile is a new type of composite pile foundation that consists of a precast concrete pile and the surrounding cemented soil. A series of shear tests were conducted in a specific shear test apparatus to investigate the shaft capacity of the different pile–soil interfaces. The test results show that the frictional capacity of the cemented soil–sand interface is controlled mainly by the sand properties, while the strength of the cemented soil slightly influences the interface properties by affecting the normalized roughness coefficient Rn. The frictional capacity of the concrete–sand interface is similar to the frictional capacity of the cemented soil–sand interface, and the existence of mud cake layer virtually hampers the frictional properties of the interface. The maximum skin friction of the concrete–cemented soil interface increases approximately linearly with the increasing cemented soil strength, and the value of the maximum skin friction is much larger than that of the cemented soil–sand interface of identical cemented soil strength, which demonstrates the integrity of the pre-bored grouted planted pile in the load transfer process.

Cyclic strength of sand mixed with biochar: Some preliminary results

Biochar is a recycled material obtained through the thermal degradation of any organic biomass in the manufacture of bio-fuel inside a reactor in a process known as pyrolysis. It is an organic material that can endure in soil for thousands of years. Given its aromatic nature, biochar is highly recalcitrant, and has been considered to have great potential to sequester carbon and reduce greenhouse gas emissions. This material has been commonly used in environmental and agricultural applications, as it can store plant minerals in its pore spaces and provide a large water-holding capacity. However, little research has been done on the geomechanical properties of the resulting mixture of biochar and soil. Some studies have shown that biochar can increase the shear strength of clays and desaturate soil particles, and it may be possible that it can also increase the resistance to liquefaction in loose sand. Therefore, it would be very interesting to assess whether this material is able to present a more environmentally friendly alternative for improving the properties of soil. In this study, samples of pure sand are dry-mixed with 0%, 3%, and 5% biochar by weight and tested under cyclic undrained shearing using a simple shear test apparatus. The preliminary results indicate that biochar can increase the cyclic resistance of sand.

Interface Shear Strength Properties of Gravel Bases and Subgrades with Various Reinforcements

Reinforcing pavement layers with geosynthetics improve the pavement performance significantly. In addition to the use of geosynthetics, the hexagonal–steel–wire mesh has gained popularity as a reinforcing material in pavements. The interface shear property of pavement material and reinforcement is an important input parameter in numerical modeling of the reinforced pavement system. In this study, the interface shear parameters of various pavement materials, namely poor subgrade, fair subgrade, gravel base (GB), and gravel surface (GS) with geogrid and hexagonal–wire–mesh reinforcements is obtained using large-size direct shear test apparatus. GS and GB mixes are selected from Indian rural roads specification of unpaved surface and base layers of the pavement. In addition, the effect of the size of the aperture of geogrid reinforcement on interface properties is studied by considering two types of biaxial geogrids of different aperture sizes. The interface shear strength and interaction coefficients of different reinforcement types with pavement materials are also proposed. The interaction coefficients of three reinforcement types with the pavement materials considered in the study are found to range from 0.82 to 1.45. The interface shear modulus of different interfaces considered in this study ranges from about 12165–57337 kPa/m corresponding to normal streeses in the range of 30–90 kPa.

Cyclic and Post-Cyclic Shear Behaviour of Interface between Geogrid and EPS Beads-Sand Backfill

Lightweight sand–EPS beads composite is a new artificial geo-material, which has been recently found applications in geotechnical engineering projects. A series of laboratory tests were carried out using a large-scale cyclic direct shear test apparatus to evaluate the monotonic, cyclic and post-cyclic behaviour of an interface between EPS-sand mixtures and a Polyfelt geogrid. EPS were added to sand at 0%, 0.5%, 1%, and 2% by weight. Tests were conducted under three different vertical stresses (30 kPa, 60 kPa and 90 kPa). The influences of cyclic shear semi-amplitude, number of cycles and normal stress on interface properties are investigated. The test results revealed that for a given strain level, interface shear stiffness decreases and damping ratio was shown to increase with increasing EPS content. Hardening behaviour was observed with the number of cycles under different normal stress levels and EPS contents. The EPS-sand-geogrid specimens did not develop clear peak shear stress at monotonic and post-cyclic direct shear tests. The EPS-sand-geogrid mixtures represent an overall contraction behaviour in monotonic, cyclic and post-cyclic stages. The apparent adhesion of interface was shown to increase and the friction angle of interface to decrease with EPS content.

Measurement of grass root reinforcement for copper slag mixed soil using improved shear test apparatus and calculating formulas

The root permeated copper slag mixed soil is a effective way to reinforce soft soil and dispose the copper slag. In order to better investigate the strength rule of it, firstly, a new shear test apparatus is developed for the purpose of measuring the root reinforcement for copper slag mixed soil. The utilized apparatus has a much larger measurement range compared to the traditional apparatus. Secondly, based on the developed measurement equipment, the formulas for calculating the shear strength of the mixed soil is derived by taking a full consideration on the dynamic changes of the effective shear area. Thirdly, 4 different kinds of soil samples are chosen and tested in a case study to demonstrate the use of the apparatus. The calculation of the shear strength between the traditional formula and the newly proposed method is compared in the measurement results. Finally, the reinforcement effect of Bermuda grass roots on copper slag-soil mixture is studied. The influence of weight percentage of copper slag, roots content, and moisture content on the shear strength of mixed soil are investigated. The authenticates results showed that the soft clay in combination with copper slag and root of grass has promising mechanical properties over the original soil in geotechnical engineering applications.

Effect of roughness on interface shear behavior of sand with steel and concrete surface

The present study evaluates the interface shear strength between sand and different construction materials, namely steel and concrete, using direct shear test apparatus. The influence of surface roughness, mean size of sand particles, relative density of sand and size of the direct shear box on the interface shear behavior of sand with steel and concrete has been investigated. Test results show that the surface roughness of the construction materials significantly influences the interface shear strength. The peak and residual interface friction angles increase rapidly up to a particular value of surface roughness (critical surface roughness), beyond which the effect becomes negligible. At critical surface roughness, the peak and residual friction angles of the interfaces are 85-92% of the peak and residual internal friction angles of the sand. The particle size of sand (for morphologically identical sands) significantly influences the value of critical surface roughness. For the different roughness considered in the present study, both the peak and residual interaction coefficients lie in the range of 0.3-1. Moreover, the peak and residual interaction coefficients for all the interfaces considered are nearly identical, irrespective of the size of the direct shear box. The constitutive modeling of different interfaces followed the experimental investigation and it successfully predicted the pre-peak, peak and post peak interface shear response with reasonable accuracy. Moreover, the predicted stress-displacement relationship of different interfaces is in good agreement with the experimental results. The findings of the present study may also be applicable to other non-yielding interfaces having a similar range of roughness and sand properties.

Experimental study on pull-out response of geogrid embedded in sand

Geosynthetics have been widely employed to reinforce the soils over the last two decades. Pullout resistance and interface friction resistance of the geogrids are crucial design parameters for some geotechnical applications. In this study, the effects of pull-out resistance of geogrid material embedded in sand soil was examined by using simple shear test set-up with a little modification. Thus, a series of experiments carried on sand soil with different relative densities and gradations. In the tests, poor graded sand was reinforced with geogrid. The reinforcement material has 0.85 mm thickness and 1 cm grid aperture. It can be inferenced from experiments that behavior of pull-out resistance had resemblance to classical load–displacement behavior of soil. Classically when displacement increases pull-out resistance increases until a certain displacement but after a certain pull-out resistance when displacement increases pull-out resistance decreases. The tests showed that, the increase in relative density leaded to increase in pull-out load. Due to the interlocking of soil grains with geogrid gaps, interface friction between soil and geogrid was also observed greater than internal friction of soil.