Large-scale Direct Shear Tests Research Articles

Study on the Interface Reinforcement Effect of Bamboo Grid in Filled Loess Embankment in a High and Steep Gully

A bamboo grid is a new type of reinforcement material, which can replace traditional geogrids in the reinforcement of embankments. In this study, the reinforcement effect of the bamboo grid that is only set at the interface between the filled and undisturbed soils of the filled loess embankment in a high and steep gully was investigated. The influence of reinforcement position and grid spacing on the reinforcement effect was studied by carrying out a large-scale direct shear test, numerical simulation, and field measurement. The results indicated that the bamboo grid could enhance the shear strength of the reinforcement interface. The interface shear strength first improved and then decreased with the decrease in grid spacing. The differential settlement was significantly reduced after the reinforcement of the bamboo grid at the interface. Compared with other reinforcement positions, setting the bamboo grid in the upper part of the embankment was the most efficient and economical. When the grid spacing became dense, the reinforcement effect was improved as the differential settlement decreased. However, the improvement in the reinforcement effect by decreasing the grid spacing was limited, which meant there was an optimal grid spacing.

A 3D DEM modeling of soil-rock mixture considering spatial distribution orientation of blocks

Spatial distribution orientations of blocks can cause significant errors in the discrete element model (DEM) calculation of soil-rock mixture (SRM). To avoid this error, spherical harmonic (SH) series whose harmonization degrees fixed at 15 were proposed for block reconstruction. This research refers to the case-history of a deep excavation rift valley spanning from the Mabian to Zhaojue section of the Leshan-Xichang Expressway, mainly containing moderately-weathered silty mudstone, in the Leshan City, Sichuan Province, China. The appropriate degree of finite-term SH series is selected by the volume, surface area. 100 blocks were scanned on site, and sphericity and angularity of the blocks were calculated. The sphericity and angularity of 50 reconstructed blocks were considered for the error analysis of SH method. Moreover, stochastic polyhedron method was considered for comparing different block reconstructions. The maximum block placement angle was defined to control the spatial distribution orientations of the blocks. Large scale direct tests were carried. Numerical simulations of large-scale direct shear tests were conducted to study the influence of the spatial distribution orientations of the blocks on the mechanical properties of the SRMs. The results revealed that the finite-term SH series fixed at 15 accurately reflected the shape characteristics and mechanical behaviors of actual blocks. The spatial distribution orientations of the blocks had a minimal impact on the friction angle and cohesion of SRM constructed through the SH method. The SRMs developed via the SH method exhibited marginal variations in contact force and anisotropy index of contact across diverse block placement strategies. The evolution of coordination number was closer when employing the SH method under varied block placement methods. Blocks reconstructed by the SH method, could mitigate errors in DEM calculation caused by the spatial distribution orientations of the blocks.

Study on the characteristics particles of coarse grain material in high bench dump

Particle shape is an important factor affecting the strength and deformation of coarse materials in dumps. However, conducting research on particle shape in current laboratory experiments, and there exists no classification standard for the particle shape of the dump. Considering the project on high-bench dump in Jiangxi Province, based on the random particle construction method, this study determined the characteristic particles of coarse grain material in the dumping site by combining field investigation results, large-scale direct shear tests, and numerical analysis. Further, the influence mechanism of coarse grain content and characteristic particles on the mechanical characteristics of the dump were analyzed. The results showed that the increase in coarse grain content enhanced the irregularity of particle shape, increased the internal friction angle between particles, and reduced the cohesion of the dump. Moreover, with increase in the normal stress, the shear strength changed from insignificant to gradually enhanced, although the increasing trend slowed down. The constructed random particle model can well solve the effects of occlusion, nesting, and friction between particles that is neglected by the standard spherical particle model, and the fitting degree is better. The particle characteristics of coarse-grain materials in the dump were primarily block, strip, and flake. The three types of shape characteristics under low normal stress did not affect the mechanical properties of the dump. Further, with the increase in normal stress, the stress-strain curve reflected the shape characteristics and content of the dominant characteristics in the dump. Specifically, the block sample exhibited the dominant characteristics and the most content under the same normal stress, followed by the strip sample, with the flake sample exerting the least influence. The research results provide a theoretical basis for long-term safe operation, disaster monitoring, and early warning of high bench dump.

Large-Scale Direct Shear Tests on Soft Clay Treated with Reinforced Lime Columns

Large-Scale Direct Shear Tests on Soft Clay Treated with Reinforced Lime Columns

The effect of relative density, granularity and size of geogrid apertures on the shear strength of the soil/geogrid interface

The increasing use of geogrid in various geotechnical projects has made the evaluation of the shear behavior of soil reinforced with geogrid become particularly important. In this article, a series of large-scale direct shear tests have been performed on sand and gravel samples reinforced with geogrid. The purpose of the experiments was to investigate the impact of the geogrid mesh size and the relative density of the samples on the shear strength coefficient of the interface between soil and geogrid. In this study, 5 geogrids with different mesh sizes and one type of geotextile were used. According to the results, the average shear strength coefficient of sand and gravel samples reinforced with geogrid for different normal stresses and different relative densities was obtained between 0.72 and 0.94. As the relative density increases, the interface shear strength coefficient decreases, this means that the denser the sand, the more the shear strength of the sand/geogrid interface decreases. Based on the results, it was found that the contribution of particle interlocking in the shear resistance of the sand/geogrid interface is particularly important, so that the shear resistance coefficient of the interface increases with the increase in the size of the geogrid mesh.

Shear strength characteristics of mixing slag-stone ballast reinforcement with tire geo-scrap using large-scale direct shear tests

AbstractUtilizing the ballast layer with more durable and stable characteristics can help avoid significant expenses due to decreased maintenance efforts. Strengthening the ballast layer with different types of reinforcements or substituting the stone aggregates with the appropriate granular materials could potentially help to achieve this goal by reducing the ballast deterioration. One of the exquisite and most effective solutions to eliminate these challenges is to use waste materials such as steel slag aggregates and useless tires. Utilizing these waste materials in the ballasted railway track will contribute to sustainable development, an eco-friendly system, and green infrastructure. So in a state-of-the-art insightful, the ballast aggregates, including a mixture of steel slag and stone aggregates, are reinforced with a novel kind of geo-grid made of waste tire strips known as geo-scraps. This laboratory research tried to explain the shear strength behavior of the introduced mixing slag-stone ballast reinforced with tire geo-scrap. To achieve this goal, a series of large-scale direct shear tests were performed on the ballast which is reinforced by tire geo-scrap and included various combinations of slag and stone aggregates. The concluded results indicate that the optimal mixing ratio is attained by a combination of 75% slag and 25% stone aggregates which is reinforced by tire geo-scrap at a placing level of 120 mm. In this case, the shear strength‌, internal friction angle, vertical displacement, and dilatancy angle of stone–slag ballast reinforced with geo-scraps exhibited average changes of + 28%, + 9%, − 28%, and − 15%, respectively.

Unveiling the reinforcement benefits of innovative textured geogrids

The smooth surface texture of the commercially available geogrids limits the shear strength mobilization at the interfaces. This study presents the design, manufacturing, and interface performance evaluation of innovative textured geogrids. Geogrids with square, triangular, and hexagonal apertures with and without inherent surface texture were manufactured through additive manufacturing (3D printing) technique, using PLA (Poly Lactic Acid) filament. The texture includes elevated pins of 3 mm height at the junctions and inherent diamond pattern of 1 mm height on the ribs. The individual and combined effects of surface texture and aperture shape on the stress–displacement relationship, dilation angle, and the thickness of shear zone are quantified using large-scale direct shear tests and Particle Image Velocimetry (PIV) analysis. Results showed that the textured geogrid with hexagonal aperture has exhibited the maximum interface coefficient of 0.96 with sand followed by the geogrids with triangular and square apertures. Irrespective of the aperture shape, provision of the surface texture resulted in an overall increase of interface shear strength by more than 13%. Further, PIV analysis revealed that the shear zone is 25% thicker for textured geogrids of different aperture shapes, suggesting higher interlocking and passive resistance offered by their textured surfaces.

Large-scale direct shear testing for assessing interfacial parameters of natural and recycled sand with geosynthetic reinforcements

The demand for infrastructure projects is being driven by urbanization, which led to scarcity of natural sand (NS), which prompts exploration of alternative sustainable construction materials due to environmental concerns. Recycled sand (RS), processed from construction and demolition waste (C&DW), is an alternative material in infrastructure applications. Investigating interfacial shear behaviour between geosynthetic reinforcements with RS as a sustainable alternative material is crucial for infrastructure projects. This study presents the comprehensive large-scale direct shear testing (LSDST) on RS, NS, and its interfaces with ten types of geosynthetic reinforcements (i.e., polypropylene geogrids (GRD1 – GRD3), polyester geogrids (GRD4 – GRD6), and geotextiles (GT1 – GT4). LSDST were carried out using self-fabricated direct shear testing equipment of size equal to 500 mm x 500 mm x 300 mm (L x B x H). The findings indicate that the RS and NS exhibit similar shear strength parameters, sand-GRD interface demonstrates greater resistance compared to the sand-GT interface. RS and NS-GRD4 - GRD6 interfaces with transverse ribs and rough texture and NS-GRD1 interface with triangular apertures, exhibit significant shear strength parameters than the unstabilized case due to the mobilization of passive thrust. Interfacial shear coefficients for NS and RS range from 0.94 – 1.27 and 0.80 – 1.15 for GRD interfaces, and 0.89 – 1.06 and 0.86 – 0.99 for GT interfaces, respectively. Therefore, the RS can be a sustainable alternative for NS.

Characterization of embankment material using sand tire mix as additive and validating the results obtained from large scale direct shear test in Abaqus software

Laboratory direct shear tests often overlook larger particles due to limitations in shear box design, resulting in an inadequate portrayal of real-world soil conditions. To address this gap, the use of large-scale direct shear apparatus capable of accommodating larger particles is essential. However, conducting such tests with varied sizes of tire shreds, mixing ratios, and loads is intricate and resource-intensive. Therefore, the utilization of numerical modeling is suggested to simulate sand-tire mixtures under diverse conditions. This study presents conclusions derived from comparing numerical results with experimental observations, demonstrating a close correspondence between the two. It offers a comprehensive examination of the impact of sand and shredded tires mixtures on shear strength, indicating a consistent pattern: increased quantities of tire shreds correspond to heightened friction angles. Furthermore, specimens containing larger shredded tire particles display elevated friction angles, implying a possible connection between particle size and frictional behavior. This investigation underscores the importance of numerical modeling as a cost-efficient and effective approach to complement experimental inquiries, enriching our comprehension of soil-tire mixture dynamics and guiding practical applications in transportation and geotechnical engineering.

Study on the mechanism of freeze-thaw cycles on the shear strength of geogrid-sand interface

The geogrid-soil interface characteristic is a critical factor influencing the behavior of reinforced soil structures. In seasonal frozen regions, the shear strength of the geogrid-soil interface fluctuates periodically with temperature, necessitating consideration of freeze-thaw cycle effects during engineering design. In this study, a series of large-scale direct shear tests were conducted to investigate the geogrid-sand interface behavior under different freeze-thaw cycles. The mechanism of the evolution and variation of the geogrid-sand interaction was discussed based on test results and the associated mesoscopic analysis. The results indicate that freezing enhances the shear strength of the geogrid-sand interface, whereas freeze-thaw cycles reduce the geogrid-sand interface shear stress. The cohesion and friction angle of the geogrid-sand interface decreased as the number of freeze-thaw cycles increased, but tended to stabilize after several freeze-thaw cycles. The influence of freeze-thaw cycles on the tensile strength and elongation of the geogrid was insignificant. Internal changes in sand during freeze-thaw cycles were considered as the key issue that led to the deterioration of the geogrid-sand interface. Furthermore, considering the interface cohesion and normal stress, the influence of freeze-thaw cycles on the interaction coefficient k between geogrid and soil was analyzed, which is referable for the design and application of reinforced soil engineering in cold regions under similar conditions.

Research on the State-Dependent Hyperbolic Model of the Interface between Spoil Mixture and Concrete

Abstract A series of large-scale direct shear tests were carried out to study the stress-strain relationship of the interface between the spoil mixture and concrete under different roughness conditions. The results showed that roughness significantly affects the shear strength properties and dilatancy characteristics of the interface. Under different roughness conditions, the shear stress ratio and the normal deformation of the interface tend to be stable after larger shear strain, and the interface presents the characteristics of a critical state. With the increase of shear strain, the void ratio of the interface shows the law of transformation from the initial void ratio to a certain stable void ratio. Based on the void ratio prediction formula of the interface, the relationship between roughness and critical state parameters was established, and the interface state parameters were introduced into the hyperbolic model. Finally, a state-dependent hyperbolic model of the interface considering the roughness was established. Importantly, the model can well reflect the shear stress-strain relationship of the interface under different roughness conditions.

Use of Geogrid for Improved Performance of Ballasted Tracks: Experimental and DEM Approaches

This paper presents a study on the enhanced performance of ballasted tracks through the implementation of geogrids. A series of large-scale direct shear tests and impact tests was conducted with three distinct types of geogrids. The behavior of ballast was evaluated in terms of shear stress–strain responses and stress concentration using stress sensing sheets. Additionally, a micromechanical analysis utilizing the discrete element method was simulated on ballast assemblies with different geogrid reinforcements. The shear stress–strain responses of ballast simulated from DEM are comparable with those measured from large-scale direct shear tests, indicating that the inclusion of geogrid can enhance the performance of ballast by increasing its shear strength, as well as reducing the vertical displacement and the load distribution with depth. Micromechanical analysis was performed to investigate the influences of geogrids on contact force distribution, coordination number and orientation of contact which could not be captured in a laboratory environment. The use of geogrids in ballasted tracks certainly shows promise for sustainable and efficient railway infrastructure, as evidenced by the experimental and DEM-based findings, offering valuable insights into optimizing track stability and longevity.

Numerical Study on Shear Behavior of Geocell-reinforced Layer Based on Large-scale Direct Shear Tests

Numerical Study on Shear Behavior of Geocell-reinforced Layer Based on Large-scale Direct Shear Tests

Study on large scale direct shear test on soil-rock mixture with multiple grain grades in high fill slope engineering

Soil-rock mixtures are multiphase natural geological materials composed of mineral particles of multiple grain sizes, and have significant natural characteristics of multiscale material groups. In order to investigate the shear strength characteristics and deformation failure characteristics of soil-rock mixtures with multiple grain sizes under in-situ conditions in fill engineering, samples of soil-rock mixtures with multiple grain sizes under in-situ conditions were prepared, and large-scale in-situ direct shear tests were conducted under natural and water-soaked conditions. The test results showed that the shear strength of soil-rock mixtures is relatively high, and after saturated by water immersion, its shear strength decreases significantly, mainly manifested in the decrease of internal friction angle while the cohesion remains basically unchanged. The cohesion of soil-rock mixtures with multiple grain sizes is mainly provided by the shear-breaking cohesion of coarse particles such as gravel in the soil-rock mixture, and its degree of exertion is controlled by the grading characteristics and particle morphology of the soil-rock mixture and affected by constraints. The reason for the significant decrease in shear strength of soil-rock mixtures with multiple grain sizes after water-soaked saturation can be explained as follows: the clay film covering the surface of coarse particles becomes soft after water immersion, resulting in a significant decrease in the sliding friction resistance between coarse particles and the clay film, as well as the occlusion friction resistance generated by the rotation transfer between coarse particles through the clay film interface.

Soil-geogrid interaction: The shear zone thickness of seafloor sediments with geogrid compared to filling materials

In geotechnical applications close to marine areas, using soil with rounded gravel that waves have left on the seafloor as fill material can help ensure the sustainable use of natural resources. However, typical fill materials have more shear strength than rounded sediments, but geogrids can solve the issue. Nevertheless, it is not well known how the grains’ shape factors will affect the soil-geogrid interlocking mechanism and how the soil-geogrid interlocking based on grain shape will vary in the soil above and below the geogrid. This study aims to address the ambiguities specified. Therefore, three soil specimens were acquired, and the grains’ shape parameters were determined using image processing. Subsequently, soil specimens were tested using large-scale direct shear (LSDS) and California Bearing Ratio (CBR) tests. Besides, LSDS tests were conducted by placing the geogrid at the shear surface, at different depths beneath the shear surface, and at varying levels above the shear surface to assess the soil-geogrid interaction distance. The findings showed that soil with seafloor gravels, using geogrid, could have the same shear strength as soil with crushed aggregates. Also, the highest shear strength was achieved when the geogrid was located below the shear surface by the maximum grain diameter.

Investigating effects of tire geo-scrap reinforcement on shear strength characteristics of railway ballast using large-scale direct shear test

ABSTRACT The utilization of geogrids used to ballast reinforcement has been widely investigated by researchers in the technical literature. This technique aims to enhance the load-bearing capacity of ballast while mitigating its degradation by minimizing breakage and settlement. This research proposes a novel approach to enhancing ballast shear behaviour in a large-scale direct shear test through the use of geogrids composed of waste tire strips, referred to as ‘geo-scraps’. In this study, the geo-scrap performance on ballast shear reinforcing was investigated to find the best laying depth in the ballast layer and the optimum aperture size of grids. To this aim, the geo-scraps were positioned at four different depths of the ballast (6, 12, 18, and 24 cm) and then the shear tests were carried out on geo-scraps with three different aperture sizes (5 cm x 5 cm, 10 cm x 10 cm, and 25 cm x 25 cm). All the large-scale shear tests were conducted under normal stresses of 50, 100, and 150 kPa. The findings of laboratory tests indicate that the 5 cm x 5 cm aperture positioned 12 cm from the bottom of the box yields the most desirable results for the ballast in terms of enhancing shear strength, augmenting the internal friction angle, and reducing the dilatancy angle. Compared to the non-reinforced (NR) state, the shear strength and internal friction angle experienced respective increases of 20% and 7%, while the dilatancy angle decreased by 30%. These outcomes show that the geo-scraps appropriately reinforced the ballast in terms of shear behaviour.

Performance evaluation of alternative drainage material for landfill cover systems in combination with geosynthetics

The pursuit of sustainable development has prompted increased utilization of alternative materials in landfill cover systems. Despite evaluating these materials for hydraulic and strength properties, their performance with geosynthetics remains inadequately explored. This study focuses on investigating the use of recycled asphalt pavement (RAP) as an alternative drainage material and determining the interface friction angle between the drainage layer and the geomembrane through large-scale direct shear tests. Further, a numerical model of a municipal solid waste landfill in Italy was developed using Finite Element Method (FEM) software. Model validation was achieved by applying analytical two-wedge theory of veneer shear failure in layered strata. The study demonstrates a superior performance of RAP aggregates as drainage layer materials as compared to natural aggregates. It also emphasizes the importance of site-specific parameter determination and precise interface property characterization. Limitations of use of commercial software in identification of weak interfaces has also been highlighted.

Shear Properties and Pore Characteristics of Soil-Rock Mixtures Under Dry-Wet Cycling

The mechanical properties of soil-rock mixture (S-RM) can deform significantly under the influence of dry-wet cycles, affecting the safety of high-fill projects. A drying device was developed to perform direct shear tests on S-RM. Large-scale direct shear tests were carried out under the action of dry-wet cycling to study the effect of dry-wet cycling on the mechanical properties of S-RM. The open-source ImageJ software was used to identify the number and area of pores in the binary image, and the pore characteristics of S-RM under dry-wet cycles were analyzed. The results show that the section of post-peak in the shear stress-strain curve softens under the natural state (no dry-wet cycles), but it plasticizes under the application of the dry-wet cycles. The cohesion of S-RM particles is affected by the dry-wet cycling. It decreases significantly under the first dry-wet cycle and then decreases gradually for each successive cycle, after which it stabilizes during the fifth dry-wet cycle. The internal friction angle is not affected to a large degree. The effect of a dry-wet cycle on pores with different areas is significantly different. The pores with initial sizes of 0.5–10 mm2 decrease, while pores with other initial sizes are hardly affected by the dry-wet cycling. This paper quantitatively analyzed the relationship between the surface two-dimensional porosity and S-RM's cohesion and peak strain.

Shear strength and modulus of mine waste rock – Large scale laboratory testing results

This paper presents the sampling and laboratory testing results of mine waste rock consisting of limestone, siltstone, and intrusive materials collected from the Ok Tedi open pit mine in Papua New Guinea. The laboratory tests included specific gravity measurements, index testing, large-scale direct shear tests using a 720 mm square direct shear apparatus, large-scale consolidation tests using a 550 mm diameter consolidation apparatus, and shear wave velocity tests conducted on compressed waste rock samples. The obtained strength values, as well as small and larger strain modulus values, were subsequently compared with existing literature data from the literature. These findings can serve as a valuable reference for mine waste materials with similar lithology, particle size distribution, and stress condition, particularly in the context of static and seismic slope stability designs.

Case History of Random Material Shear Strength Evaluation using In-situ Large Scale Direct Shear Test in the Construction of the Longest Dam in the Southeast Asian

A modern dam offers many benefits to society, including water conservation, farming sustainability, energy source, and recreational activities. In Indonesia, more than 50 dams are constructed as strategic national projects within the last decade. A zoned earth-fill dam, built using soil and rock materials, is one of the most common dam types in Indonesia. This dam allows a specific material type to be placed in a particular zone, including random material fill zone. A random material is usually obtained from dam excavation work as well as borrow area. It normally contains wide range of grain sizes and a variety of weathering degree. On one hand, this material is very economic. On the other hand, it introduces a challenge in shear strength assessment. Random material frequently contains large size grain that inhibits regular laboratory test use. A catastrophic Indonesian dam construction failure in 2021 was partly attributed to inadequacy in assessing shear strength of random material. This case history highlighted the importance of a proper random material shear strength evaluation. The other dams coincidentally under construction at that time then experienced rigorous shear strength evaluations, including Semantok Dam in Nganjuk, East Java. This dam, designed to be approximately 33-m max high and 3.1-km long, is the current longest dam in the Southeast Asian. An in-situ large scale direct shear device as large as 80 cm × 80 cm × 30 cm was developed to test random material in Semantok Dam. Eight locations in random fill zones were selected. Three series of direct shear test were conducted in each location. Testing results based on 24-large size sample showed a great variability in Mohr-Coulomb parameters. The angle of internal friction ranged from 11.4° to 36.7° with average value of 27.8°, whereas the cohesion varied from 25.3 kPa to 138.6 kPa with average value of 85.2 kPa. High variation in shear strength parameters showed that such test should be performed to verify the design parameter. This in-situ large scale direct shear test provides an appealing method to assess shear strength of random material. This large-scale test is strongly recommended for a common practice in dam construction.