Interface Shear Behavior Research Articles

Towards concrete-rock interface shear containing similar triangular asperities

The properties of socket wall significantly affect the loading capacity of a rock socketed pile, and the shear mobilization relies heavily on the roughness of the socket surface and the boundary condition in reality. In this study, laboratory tests have been conducted to investigate the performance of concrete-rock interface shear under constant normal stiffness (CNS) condition and, in particular, an alternative profile to characterize the interface roughness is assembled as series of similar triangular asperities. The profiles of rock samples differing in the dimension of asperities have been divided into five categories (including one kind of regular triangular asperities for comparison). Direct shear tests on the samples are carried out under CNS conditions, with different initial normal loads and normal stiffnesses. The observations indicate that the shear behavior of concrete-rock interface is highly dependent on the uniformity of asperity geometry; compared with the roughness of similar triangular asperities, the one of regular asperities behaves more brittleness and shows a higher peak strength as well as a lower residual strength. In addition to the general tendency, it is found that the local lift-off of some asperities is pronounced relied heavily on their heights, and the redistribution of local stresses can further affect the global shear behavior. The size-dependent sequence of asperity failure can be also observed, confirming the earlier theoretical anticipation reported by the authors. Careful observations during this testing made it possible to develop a micromechanics-based model published elsewhere, and the comparison between them are presented.

Effects of Relative Roughness and Particle Size on the Interface Behavior of Concrete Suction Caisson Foundation for Offshore Wind Turbines

The interface behavior between a caisson and the surrounding soil plays an important role in the installation of suction caissons as foundations for offshore wind turbines. A series of shear tests were carried out using a modified direct shear apparatus to study the interface shear behavior between sand and concrete. Sand samples with three particle size ranges (0.63–1.25 mm, 1.25–2.5 mm, 2.5–5.0 mm) and concrete plates with different relative roughness were used to explore the influence of the relative roughness parameter (Rn) and mean particle size (D50) on shear behavior. The responses from the pure sand shear test are also discussed for comparison. Test results show that the higher the relative roughness (Rn), the greater the maximum shear stress (τmax) appeared. The interface shear stress was weaker than that of the pure sand test. Furthermore, the interface friction angle (φ) of sand–concrete was closely related to the relative roughness of the concrete surface. Under the same conditions, the interface friction angle (φ) increased with relative roughness due to the effect of sand particles breakage and redistribution. By contrast, the effect of the mean particle size (D50) on the interface friction angle (φ) was less significant. However, for the pure sand shear test, the friction angle (φ′) obtained from the traditional shear test apparently increased with D50, indicating that the friction angle was more affected by D50 in the pure sand test than in the interface shear test.

Effect of cyclic jacking on sand-pile interface shear behaviour

Pile jacking is a kind of competitive method for pile installation due to its less noise and vibration pollution. In this paper, the pile jacking process has been numerically simulated by considering the friction fatigue, and the characteristics of sand-pile interface shear paths at different depths were thoroughly investigated. It is found that during the cyclic jacking process, the interface shear path at a specified depth tends to transform from one-way shear to two-way shear, especially for the shallow to middle depth. But for the deep soil layer, one-way cyclic shear is still the dominated loading mode. Focusing the effects of different paths on the sand-pile interface shear behaviours, a series of cyclic interface shear tests have been conducted, in which two types of sands and four typical shear paths were adopted. It has been revealed that during continuous jacking process, the sample volume response changes significantly with different interface shear paths. The previous shear path also plays a key role in the cyclic degradation of interface strength with CNS (constant normal stiffness) condition. If the sample contraction is small during jacking process, the cyclic degradation of interface strength is obvious. But, when the sample contraction during jacking process is significant, the interface strength degradation is largely suppressed. This is mainly because the abundant broken fine particles along the pile shaft will fill into the voids and make the sand sample near the interface much denser. It is shown that the changes of pile-soil interface characteristics will affect the pile responses.

Shear Behaviour of Rock–Tailings Backfill Interface: Effect of Cementation, Rock Type, and Rock Surface Roughness

Determination of interface shear behaviour is critical for the design of many geotechnical structures, including cemented paste backfill structures. However, the shear characteristics of the CPB–rock interface is not fully understood. No studies have been conducted to assess the impact of the characteristics of rock (e.g., type of rock, rock surface roughness), cementation and the coupled effects of surface roughness and degree of cementation on the shear characteristics of the interface between rock and tailings backfill. This paper presents new findings of research conducted to investigate the effect of different types of rock, rock surface roughness and degree of cementation as well as the coupled effects of these factors on the shear properties and behaviour of the interface between cemented paste backfill (CPB) and rock. The results show that roughness and the interaction between roughness and degree of cement hydration have a significant effect on the shear characteristics of a CPB–rock interface. For a certain degree of cementation, the roughness can increase the shear strength due to the increased size of the interlocking structure. The interface samples with roughness, especially those sheared at high normal stress, tend to experience two peak shear stresses during the shear test. Moreover, the shear strength, shear dilation, and adhesion of the interface also increase with degree of cementation. However, according to the revised Barton’s equation, the effective friction angle of interface with roughness experiences a decreasing tendency with degree of cementation, despite the increasing tendency of the friction angle of the smooth interface. In other words, the interface asperity contributes more to the evolution of adhesion, and the contribution of friction angle to the shear strength is partially offset. It is also found that the rock type (considered in this study) has limited effects on the interface shear properties. The failure of the interface between CPB and rock is because of the existence of the interfacial transition zone, which is characterized by high porosity. These new findings have practical importance to the design of the underground CPB structures.

Testing and modeling of frozen clay–concrete interface behavior based on large-scale shear tests

The shear behavior of the frozen soil−structure interface is important for accurately predicting the interface responses of structures adopted in the cold regions. The purpose of this study is to experimentally and theoretically investigate the shear behavior of frozen clay–concrete interface under engineering conditions. A large-scale direct shear apparatus with a temperature-controlled shear box is used to test the interface behavior. Test specimens consisting of a cement concrete block and frozen soil with initial water content ranging between 14.6% and 24.6% were prepared at different conditions of temperatures (15.4 to −9.8 °C), shear rates (0.03–0.9 mm min−1), and normal stresses (50–200 kPa). It is found that the peak shear strength is linear developing with increasing of normal stress, initial water content, and temperature. It increased from 67.7 to 133.3 kPa as the initial water content increased from 14.9% to 24.6% at temperature of −6.8 to −6.6 °C, and it increased from 51.2 to 80.6 kPa with temperature decreasing from 15.4 to −9.8 °C at initial water content of 14.6%–14.9%, furthermore it has a power law relationship with shear rate. The final vertical displacement increases with the decreasing temperature, and increasing initial water content. While, it is slight or could be ignored at lower shear rates (e.g. 0.03 mm min−1 and 0.15 mm min−1) and it is −0.25 mm and −0.28 mm at shear rate of 0.3 mm min−1 and 0.9 mm min−1, respectively. In addition, the evolution of vertical displacement also varies with test condition, the growth rate at beginning increases with increasing initial water content and decreasing temperature or ice content, which is because of the ice film effects the particle size. Moreover, a disturbed state concept model combined with linear and nonlinear characteristics is developed to describe the interface shear behavior. The disturbance D reflects the interface mechanical response and responds differently trend for different test conditions, increasing faster with increasing temperature and decreasing initial water content or shear rate. The testing results, including the test and model results, can be used to simulate the performance of engineered geotechnical assets such as earth dams or irrigation channels with concrete linings in cold regions.

Laboratory investigation into effect of bolt profiles on shear behaviors of bolt-grout interface under constant normal stiffness (CNS) conditions

Abstract Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering. It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system. Previous studies have proposed some optimal rib parameters (e.g. rib spacing); unfortunately, the interface shear behaviors are generally ignored. Therefore, determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible. The load-bearing capacity and deformation capacity vary as bolt profiles differ, suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles. The aim of this study is to investigate the effects of bolt profiles (with/without ribs, rib spacing, and rib height) on the shear behaviors between the rock bolt and grout material using direct shear tests. Thereby, systematic interfacial shear tests with different bolt profiles were performed under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does, in particular at the post-yield stage. The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions, and optimize selection of rock bolts under in situ rock conditions.

Investigation into effect of the graphene oxide addition on the mechanical properties of the fiber metal laminates

Fiber Metal Laminates (FMLs) is developing very fast with the both features of resin-based composite and metal and its property can be improved by mixing nano-scale particles as FMLs-Nano. Based on the different mixing volume fractions, this paper investigated the effect of Graphene Oxide (GO) on the mechanical properties of the FMLs with carbon fiber used, including tensile, flexural and interface shear behaviors. The interface strengthening mechanism of GO as significant filler for enhancing the carbon woven fabric based FMLs' was explored. To encourage the application range of FMLs-Nano in the fields of aircraft, aerospace and automotive etc. to form the complicated components. It was observed that the FMLs with GO (FMLs-GO) has the better tensile performance than the FMLs without GO and the Young's modulus and tensile strength of the FMLs-GO are increased by 13.5% and 11.7%, respectively. Especially, the flexural and interface shear strength can be increased up to 134.0% and 150.4% compared to the pure FMLs and the improvement mechanism was investigated mechanically and observed with scanned micrograph. This paper also provides a fundamental reference for improving the interfacial performance of different layers of FMLs-GO by using the normal preparation condition.

Effect of particle size of sand and surface properties of reinforcement on sand-geosynthetics and sand–carbon fiber polymer interface shear behavior

Soil-reinforcement interface friction is an important geotechnical engineering parameter that needs to be assessed in achieving a safe and cost-effective design. In this study, the effect of mean particle size (D50), type, and surface properties of reinforcements on shear behavior of soil-reinforcement interface were evaluated using direct shear test. Three types of sands with different D50 and similar properties, and six types of reinforcing materials with different surface features; three conventional types (GTX, GGB, and GC) and three novel types (CFRP, SPSCFRP, and GeoFRP), were used for this purpose. The direct shear test (DST) device was modified and proposed to determine the shear strength and friction angle between soil and reinforcements at different normal stresses. Test results revealed that interface shear strength between soil and reinforcements depends on both particle size of the sand and type of reinforcement. The influence of particle size was more significant when coarser size was used since the interlocking behavior occurred between the sand particles and the asperities of reinforcing material. However, the surface roughness of reinforcement affected the shear strength to an extent.

Modelling of Shear Behaviour of Interfaces Involving Smooth Geomembrane and Nonwoven Geotextile Under Static and Dynamic Loading Conditions

The constitutive modelling of geosynthetic–geosynthetic interfaces is essential to predict the performance of the engineering structures such as landfills, flood control dykes and geotextile encapsulated-sand systems for the protection of shore. This article presents a mathematical model to simulate the shear stress/force–displacement behaviour of the interfaces involving smooth geomembrane and nonwoven geotextile under static and dynamic loading conditions. The model is the extension of an existing technique developed for predicting the soil-structure interface shear behaviour under static loading conditions. The proposed model can predict the non-linear pre-peak and the post-peak strain softening/hardening behaviour of the interfaces observed during the laboratory testing. The shear stress/force–displacement response of the interfaces has been modelled by dividing it into three parts: pre-peak, peak and post-peak behaviour. Subsequently, the modelling parameters are obtained using the results from the laboratory direct shear tests and fixed–block type shake table tests conducted on these interfaces. Finally, the shear stress/force–displacement response of the interfaces is evaluated and compared with the experimental results. The predicted shear stress/force–displacement response of the interfaces is found to be in good agreement with the experimental data for both static and dynamic loading conditions.

Effects of isothermal aging on interfacial microstructure evolution and shear behavior of Au-12Ge/Ni(P)/Kovar Solder Joints

Au-12Ge(wt.%) eutectic solder is widely used in electronic packaging thanks to its good electrical conductivity, solderability, and chemical stability. To investigate the stability of Au-12Ge solder during high-temperature service, the effects of different isothermal aging conditions on the microstructure and performance of Au/Ni(P)/Kovar substrate after soldering were investigated. Solder joints produced at 400 °C for 1 min showed excellent wetting behavior with NiGe/Ni5Ge3/Ni3(P,Ge) intermetallic layers formed at the interface. The thickness of generated interfacial intermetallic compounds was estimated to only 1.56 μm due to the amorphous nature of Ni-P coating that hindered the diffusion of Ni atoms. As aging increased with time and temperature, the interfacial intermetallic compounds grow further, leading to deterioration and failure of solder joints. The growth mechanism of interfacial intermetallic compounds was then examined, and activation energy was estimated to 95.4 kJ/mol. In turn, shear strength of solder joints declined and fracture mode became brittle as aging time and temperature increased. Meanwhile, fracture position evolved from IMC layer to Ni-P layer. At aging temperatures above 290 °C, Ni-P layer showed crystallization transition to porous Ni3P, leading to formation of holes and cracks, and resulting in exfoliation of coating with Kovar substrate.

Cyclic behavior of interface shear between carbonate sand and steel

The shear properties of carbonate sand and structure interface are of significance for the engineering construction. The parallel paper (Rui et al. in Acta Geotech, 2020) focuses on the monotonic behavior of the interface between carbonate sand and steel. In this paper, by a series of shear tests on the interface between carbonate sand and steel, the evolutions of interface strength during cyclic interface shear were investigated. Further, the influences of cyclic amplitude, particle size, surface roughness and normal stress on the sand–steel interface shear behavior were discussed. Using a kind of transparent ring, the particle movements near the interface were observed to explain the mechanism during cyclic interface shear. The experimental results show that the shear zone appears near the interface, and is mainly composed of crushed fine particles and original particles. With lower steel roughness condition, the volume contraction is dominant in cyclic interface shear, while the dilation and contraction occur alternatively for higher roughness, which leads to higher interface shear strength. Compared with monotonic shear, the thickness of shear zone after cyclic shear is relatively small. Cyclic interface shear can lead to more fine particles, but less is embedded into the interface. It is found that under cyclic shearing, the interaction between particles and steel is enhanced, which is the main factor for promoting the interface strength, so interface strength in cyclic shear is higher than that in monotonic shear.

A coupled chemo-elastic cohesive zone model for backfill-rock interface

Abstract To date, only a very few number of models are available to study the shear characteristics of the backfill-rock interface, and none of them have incorporated the effect of the interactions between sulphate ions and cement hydration on the interface shear behaviour. Therefore, a coupled chemo-elastic cohesive zone model (CZM) has been developed to simulate the shear characteristics of the cemented paste backfill (CPB)-rock interface that contains sulphate ions at the early ages. To quantitatively address the influence of sulphate on binder hydration at the early ages, the concept of equivalent chemical age is proposed and integrated into a binder hydration model. Besides, the interface shear properties, fracture toughness as well as shear stiffness are expressed as a function of the equivalent chemical age. By implementing the developed model in COMSOL Multiphysics, the results of the numerical simulation are found to agree with the experimental results. The validated results confirm the capability of the developed model to describe the shear characteristics of the interface that contains sulphate ions. The developed model will contribute to improving the assessment of the shear behaviour of the CPB-rock interface in the field, thus leading to a more economical design of safe CPB structures.

The behavior of polymer-bentonite interface under shear stress

As new building materials, polymers have gradually been used in infrastructure engineering applications such as civil engineering, water conservancy, and highway repair engineering. The shear behavior of the interface between polymer and bentonite plays an important role in the analysis of the interactions at the interface. This paper investigated the direct shear behavior of polymer-bentonite interface under various conditions. The shear stress, horizontal displacement, and failure mode were observed under four initial normal stresses, four values of the moisture content of bentonite, and three polymer densities by utilizing a large-scale multi-functional direct shear apparatus and a digital image correlation (DIC) system. The results show that the shear strength of polymer-bentonite interface is higher than that of the pure bentonite. An increase in either initial normal stress or polymer density improves the shear strength of polymer-bentonite interface, while a higher moisture content of bentonite reduces it. Moreover, the polymer-bentonite composite fails in the bentonite phase or at the interface between polymer and bentonite. Finally, the concepts of the equivalent angle of internal friction and the equivalent cohesion of the polymer-bentonite interface are proposed and applied to the analysis of the interaction between the polymer and bentonite.

Freeze-thaw cycling impact on the shear behavior of frozen soil-concrete interface

The shear behavior of a frozen soil-structure interface plays a vital role in analyzing the performance of engineered structures in cold regions. This study investigates the freeze-thaw cycling impact on the shear behavior of a frozen soil-concrete interface by direct shear tests. Test specimens consisting of a Portland cement concrete disk and frozen loess with an initial moisture content ranging between 9.2% and 20.8% were prepared and conditioned at various sub-zero temperatures (i.e., −1 °C, −3 °C, and − 5 °C) and freeze-thaw (F-T) cycles (i.e., 0, 5, 10, and 20). Experimental results, including shear stress - horizontal displacement curves, the displacements and shear strengths at both peak and residual status, are presented and analyzed. In particular, the influence of F-T cycling on shear behavior is examined. The peak displacement is found to increase linearly with increasing initial moisture content, but their correlation weakens as the number of F-T cycling increases. However, the residual displacement is found to be insensitive to the initial moisture content, temperature, normal stress, and F-T cycling. While the residual friction angle is slightly larger than the peak one before F-T cycling, both gradually increase with an increasing number of F-T cycling. Large cohesion in the peak strength, especially at lower temperatures, completely diminishes in the residual strength due to damage of ice bondage, resulting in a significant shear strength loss between the peak and residual status. The impact of F-T cycling on the interface shear behavior can be attributed to moisture migration toward, formation and accumulation of ice films at the interface. The findings from this study including the shear strength parameters and the displacements at both peak and residual status, can be used to simulate the performance of engineered geotechnical assets such as pile foundations, retaining walls, and earth dams or irrigation channels with concrete linings in cold regions.

Soil-solid interface shear strength review and its possibility on interlayer slope stability analysis

A landslide has been one of the many problems in geotechnical engineering, whereas, from one of the cases, a failure happened at the interface layer between the overburden and its underlying soil. As interface shear strength has become one of the growing topics in research, this paper summarizes and discusses the research development of interface shear strength and its possibility to explain the interface shear behavior at a slope. The discussion was limited to cohesive soils and experiment-based behavior of the interface shear. Some research has been selected in order to understand the development of interface shear strength through time and two examples of slope interlayer shear behavior were selected. It was known that there are three common tests of interface shear behavior used: simple shear, direct shear, and ring shear test. The development of interface shear strength started at 1960s between soil and construction materials where the four major components were defined. As the research grows, many other types of soils, interfaces, and the effect of the tests became the topic of the research. In the end, the examples given from modeling the interface shear behavior from a slope gives a new perspective of cases for interface shear strength in slope analysis.

Effects of bolt profile and grout mixture on shearing behaviors of bolt-grout interface

Abstract Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system. In this paper, direct shear tests on bolt-grout interfaces under constant normal load (CNL) conditions were conducted to investigate the effects of bolt profile (i.e. rib spacing and rib height) and grout mixture on the bolt-grout interface in terms of mechanical behaviors and failure modes. Test results showed that the peak shear strength and the deformation capacity of the bolt-grout interface are highly dependent on the bolt profile and grout mixture, suggesting that bolt performances can be optimized, which were unfortunately ignored in the previous studies. A new interface failure mode, i.e. ‘sheared-crush’ mode, was proposed, which was characterized by progressive crush failure of the grout asperities between steel ribs during shearing. It was shown that the interface failure mode mainly depends on the normal stress level and rib spacing, compared with the rib height and grout mixture for the range of tested parameters in this study.

Shear behavior at interface between compacted clay liner–geomembrane under freeze-thaw cycles

Bentonite sand mixtures (BSMs) are commonly used in compacted clay liners (CCLs) in waste disposal facilities when the local soil is not suitable for use in the liners. Given that the temperature tends to vary drastically in many cold regions, it is important to have a good understanding of the interface shear behavior of composite liners that are affected by freeze-thaw (F-T) cycles. However, no studies on the shear behaviour at the interface between a compacted clay liner and high-density polyethylene (HDPE) geomembrane that are subjected to F-T cycles have been conducted in the literature. Therefore, an experimental investigation on the influence of F-T cycles on the shear behaviour at the interface between a BSM and smooth HDPE geomembrane is conducted in this study. The obtained results show that the shear strength at the interface is lower than that of the BSM itself. In addition, the shear strength decreases with increasing numbers of F-T cycles, and the total reduction in the interface shear strength of the samples without undergoing any F-T cycles is 23%, 15.2% and 11.4% under normal stresses of 150 kPa, 250 and 350 kPa, respectively (in comparison to the samples that are subjected to 10 F-T cycles).

Factors Influencing the Mechanical Characteristics of a Pile–Soil Interface in Clay Soil

A series of direct shear tests using a large-scale constant-normal-stiffness direct-shear testing system was conducted to study the factors that influence the mechanical characteristics of a pile–soil interface in clay soil. Interfaces of different roughness (R = 0, 2, 4, and 6 mm) were tested in clay soil with four different water contents with four normal stresses under different shear rates during shearing. Results for the interfacial shear behavior are presented as shear-stress–shear-strain curves, shear strength, and parameters. The results show that (i) the higher the roughness, the higher the shear strength of the pile–soil interface.The larger the normal stress, the smaller the roughness effect on the shear strength and parameters of the pile-soil interface; and (ii) the higher the water content of the clay soil, the lower the shear strength of the pile–soil interface, with maximum cohesion at a water content of 25%. The main influence that increasing the water content has on the shear strength of the pile–soil interface is changing the coherence, while the shear rate in this test range has less effect on the shear strength of the pile–soil interface. Overall, the mechanical characteristics of the pile–soil interface are influenced by roughness, water content, and shear rate, and close attention should be paid to those three factors when analyzing test results.

Interface creep behavior of grouted anchors in clayey soils: effect of soil moisture condition

This study aims at investigating the influence of moisture conditions on interface shear behavior of element-grouted anchor specimens embedded in clayey soils. The tests involved comparatively short embedment lengths and a device that was specially designed to facilitate moisture conditioning. Rapidly loaded pullout tests as well as pullout tests under sustained (creep) loading were conducted to characterize both the short-term and long-term ultimate shear strength of anchor–soil interfaces. Both values of the interface shear strength were found to decrease exponentially with increasing moisture content values, although their ratio was found to show a linearly decreasing trend with increasing moisture content. The interface shear creep response under pullout conditions was characterized by a rheological hybrid model that could be calibrated using experimental measurements obtained under increasing stress levels. The accuracy of the hybrid model was examined by evaluating the stress-dependent prediction model as well as its governing parameters. This investigation uncovers the coupled impact of soil moisture condition and external stress state on the time-dependent performance of grouted anchors embedded in clayey soils by correlating the interface shear strength with soil moisture content and associating the creep model with stress levels applied to the grout–soil interface.

Experimental study on the monotonic shear strength of GM/CCL composite liner interface

The interface shear strength between a geomembrane (GM) and a compacted clay liner (CCL) or a geosynthetic clay liner (GCL) is of great importance for landfill stability analysis. An experimental study of the interface shear behaviour between a smooth GM (GMS) or a textured GM (GMX) and a CCL is presented in this paper. A series of monotonic shear tests was conducted using a large direct-shear apparatus. Peak and residual shear strength parameters were obtained by linear fitting of the experimental data. The shear strength of both GMS/CCL and GMX/CCL interfaces was mainly driven by the normal stress level, while the displacement rate had very little influence on the interface shear strength. The residual shear strength of the GMX/CCL interface was even higher than the peak shear strength of the GMS/CCL interface at all normal stress levels. The GM/CCL interface showed considerably higher shear strength over the GM/GCL interface; the residual strength of the GM/CCL interface was even higher than the peak strength of the GM/GCL interface at all normal stress levels. The results presented in this paper are useful for the preliminary design of landfill composite liner systems.