Large-scale Direct Shear Tests Research Articles

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.

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.

Experimental Study on the Interface Characteristics of Reinforced Crushed Rock Cushion Layer Based on Direct Shear Tests.

Through indoor large-scale direct shear tests, the interface characteristics of the crushed rock cushions layer reinforced with ParaLink geogrid were studied. The test results indicate that the shear strength of the crushed rock aggregate and the interface strength parameters have a non-linear relationship with the normal stress. The addition of the geogrid reduces the shear strength of the crushed rock aggregate and the interface strength parameters, which is mainly due to the relatively large size, small thickness, and high smoothness of the geogrid. The reinforced geogrid has a significant impact on the deformation and fragmentation characteristics of the crushed rock aggregate. It effectively suppresses the shear contraction and shear dilation effects of the crushed rock aggregate, reducing its peak compression and peak dilation angle. Furthermore, it inhibits the tendency of particle fragmentation in the crushed rock aggregate.

Shear Behavior of Silty Clay–Concrete Interface Based on Large-Scale Direct Shear Test

Shear Behavior of Silty Clay–Concrete Interface Based on Large-Scale Direct Shear Test

Effect of Material Composition on Geotechnical Properties—Study on Synthetic Municipal Solid Waste

The geotechnical properties of municipal solid waste (MSW) are required to design and maintain a landfill structure. Several landfill failures occurring in recent times have led to the loss of revenue and people. This study aims to investigate the impact of material composition on the geotechnical properties of fresh synthetic municipal solid waste (SMSW), which imitates the real waste produced in India. The study aims to understand the contribution of each material, such as paper, plastic, and organic matter, on the shear behavior of SMSW, which is essential for designing landfills and ensuring their safety and performance. A modified proctor test and a large-scale direct shear test were used to determine the unit weight and shear strength of SMSW, respectively. The synthetic waste’s unit weight and shear strength were found to be consistent with values that had already been published. The shear strength parameters of SMSW include cohesion, which was determined to be at the lower bound of the envelope, and friction angle within the envelope. Lower unit weight, less fine soil-like material, and dry material are thought to be the causes of the observed variation in the behavior of actual waste in synthetic waste. The findings of this experiment demonstrated that as the proportion of paper increases, the cohesion (C) increases, and the friction angle (Φ) decreases. Cohesion and friction angle both decrease as the proportion of plastic increases. Cohesion and friction angle both increase with an increase in the organic percentage. These findings demonstrate that each material contributes differently to the shear behavior of SMSW. Hence, the material composition’s effect should be considered while designing a landfill for improved safety and reliability.

Micro-macroscopic mechanical behavior of frozen sand based on a large-scale direct shear test

The mechanical properties of frozen soil are of utmost importance for infrastructure development in cold regions, and the microscopic characteristics play a vital role in revealing the mechanism of strength and deformation evolution. In this study, the mechanical behaviors of frozen sand at various negative temperatures are investigated by a self-developed temperature-controlled large-scale direct shear apparatus. The shear stress-shear displacement curve, dilation curve and shear strength characteristics at different negative temperatures and normal pressures are analyzed. According to the test results, as the cooling temperature decreases, the cohesion and internal friction angle of frozen sandy sample both increase significantly, and the shear dilatation tends to be larger. The brittle behavior of frozen sand becomes more obvious at lower temperatures. Then, a discrete element method (DEM) model is established to investigate the microscopic mechanical properties of frozen sand in the direct shear test. The particle movement, force chain evolution, and shear surface development during the shearing process are analyzed. The simulations of the DEM model can well explain the microscopic mechanism of the macroscopic strength and deformation law of frozen sandy soil. It is hoped that the research results can provide a reference for the DEM application in frozen soil mechanics.

Clayey Sand Soil Interactions with Geogrids and Geotextiles Using Large-Scale Direct Shear Tests

Clayey Sand Soil Interactions with Geogrids and Geotextiles Using Large-Scale Direct Shear Tests

Evaluation of Interface Shear Strength Coefficient of Alternative Geogrid Made from Para Rubber Sheet

In this work, elastic natural rubber compound sheet (RCS) and ribbed smoked sheet grade 3 (RSS) were studied as alternative replacements for polymer geogrid for soil reinforcement. In order to investigate the reinforcing effectiveness in three distinct environments using the interface shear strength coefficient (Rin) by the large-scale direct shear test, the RSS and RCS geogrids were installed independently in sand, lateritic soil, and clay. Using either an RSS geogrid or RCS geogrid, the average Rin is progressively smaller in reinforced sand, lateritic soil, and clay, respectively. Higher tensile strength of reinforced materials using the RCS geogrid than those using the RSS geogrid is encouraged by the better elastic characteristics of the RCS geogrid. Thus, utilizing the RCS geogrid-reinforced materials can better increase the shear strength of coarse-grained soil such as sand and gravel.

Evaluating the Shear Strength of Subbase-subgrade Interface Using Large Scale Direct Shear Test

The inclusion of geogrid in road pavements can improve pavement performance through increasing the lateral confinement, bearing capacity, and overall rigidity of the pavement, as well as reducing the vertical and lateral pavement deformations. The materials used in the present study are: subbase granular materials Type B, two types of subgrade soil; clay and sandy soil, and two nonwoven biaxial geogrids (G1 and G2) used as reinforcing materials. Direct shear testing was adopted by manufacturing a large-scale direct shear apparatus consisted of an upper, square box of size 20 cm × 20 cm × 10 cm, and a lower, rectangular box of size 200 mm × 250 mm × 100 mm is used in the present study. The results show that, for the four normal stresses equal to 25, 50, 75 and 100 kPa, the interface shear stress curves increased and followed similar trend. For clay-subbase interface, installation of geogrid decreases the apparent cohesion of the material from 16.5 kPa (without reinforcement) to be 8 kPa and 13.5 kPa for G1 and G2, respectively. At sand-subbase interface, using geogrid leads to increase the cohesion of the material from 3.5 kPa to be 15.5 and 16 kPa for G1 and G2, respectively. The friction angle increases slightly from 30o (without reinforcement) to be 35o for G1 and G2 when the interface is subbase over clay. While, it decreased from 35.8o to be 32.1o for G1 and G2 at sand-subbase interface. The interaction coefficient for G1 and G2 increased when the normal strength increased at the clay-subbase interface. Otherwise, the behavior of interaction coefficient of the sand-subbase interface appears deferent trend, where increasing normal stress leads to decrease the interaction.

The deformation evolution law and stability evaluation of the high-filled slope in the cutting hills to backfill ditches project

The cutting hills to back ditches (CHBD) project has been widely implemented since urbanization in hilly areas is steadily rising. The stability of the high-filled slope and the problem of foundation settlement deformation has become one of the vital issues for safe construction. This paper focused on the deformation evolution law and stability assessment of the high-filled deposit slope composed of the soil-rock mixture (S-RM) in the CHBD project, in Shiyan City, Hubei Province as examples. First, large-scale direct shear tests of S-RM with different rock block proportions (RBPs) under different various normal stresses were carried out, and its mechanical properties were analyzed. Next, the finite element method was used to simulate the processes of the step-by-step filling, and the deformation evolution law was analyzed. Then, the limited equilibrium method (LEM) was used to obtain the potential sliding surfaces and the corresponding safety factors of the high-filled slope, and the safety of the construction was assessed. Finally, automated monitoring of the step-by-step settlement and deep soil deformation was computerized for the typical locations, and the long-term stability of the high-filled slope was studied. The results demonstrate that the first layer of backfill in the F area contains the largest incremental settlement displacement in the y-direction, whereas the value in the G area occurs at the site of the fill layer close to the slope surface at each filling timestep. The displacement response value steadily declines with the increasing filling depth and horizontal displacement, presenting a clear spatial influence range, with the site of maximum incremental displacement as the center. After filling, the safety factors of the potential sliding surface in the F and G areas are 2.531 and 1.118, respectively, and the slope is in a stable state. The monitoring data show that the deformation mostly takes place within 10 m of the surface. The study’s findings are thought to offer technical and practical knowledge for the slope risks.

A multiscale finite element method for soil-rock mixture

Soil-rock mixture is a complex multi-phase composite geotechnical material, and its strength is determined by the physical properties of constituent multi-phase materials and their coupling mechanical response between different phases of materials. Based on the Eshelby-Mori-Tanaka equivalent inclusion average stress principle, a theoretical model of multi-scale coupled shear strength of soil-rock mixture considering the interaction effect of rock block and soil is established, and the rotational freedom reflecting the microscopic motion details of rock block is introduced. Moreover, a multi-scale coupled constitutive relationship of soil-rock mixture is derived and compiled into a multi-scale finite element program. Based on the large-scale direct shear test of soil-rock mixture, the model parameters of the multi-scale finite element method are determined, and then the multi-scale finite element program is used to simulate and predict the cross-scale deformation process of the soil-rock mixture slope. The results show that the multi-scale finite element method can effectively describe the influence of the mechanism of the micro motion characteristics of the soil-rock mixture on the macro mechanical response, and can effectively overcome the pathological mesh-dependency of the classical finite element method; the rotation displacement of the rock block is mainly concentrated within the shear zone of the slope. The maximum rotational displacement of rock blocks inside the soil-rock mixture slope is 40.7°, and the rotational displacement of rock blocks outside the shear zone is about 0°. The physical mechanism of the cross scale evolution of the shear band of the soil-rock mixture slope is that: the rotation of the rock blocks weakens the strain transmission ability between the rock block and the matrix soil, thus forming the concentration and development of the plastic strain, and finally leading to the penetration of the shear bands of the slope and the overall sliding failure.

Experimental Study on Shear Strength Parameters of Round Gravel Soils in Plateau Alluvial-Lacustrine Deposits and Its Application

The shear strength parameters of conglomerate soils are crucial to the stability analysis of foundation support when excavating and supporting ultra-deep foundation pits in the highland alluvial lacustrine layer. The difference in water content of conglomerate soils in different regions will directly affect the values of shear strength parameters. At the same time, more research on the shear strength of conglomerate soils under different water contents is required. In this study, a series of large-scale direct shear tests were carried out on the round gravel soil in the plateau alluvial-lacustrine deposit, and the round gravel soil’s shear strength curves under natural and saturated conditions and water content were obtained. The influence of different water content on the shear strength characteristics of the round gravel soil was discussed, and the shear strength parameters of the round gravel soil with different water content were used in the numerical simulation of ultra-deep foundation pit excavation and support. The stress and deformation laws of the foundation pit support were analyzed. The results show that the peak strength of the round gravel soil in the natural water content state appears between 30% and 45% of the shear displacement, while the peak strength in the saturated water content state appears around 45–55% of the shear displacement. The shear strength tends to be stable or slightly weakened with the increase of the shear displacement. The angle of internal friction and cohesion of round gravel soil in the natural water content state is greater than those in the saturated water content state. The simulation of the foundation excavation support shows that the shear strength parameter of the round gravel soil influences the force deformation of the support structure. The higher the water content of the round gravel soil, the more the shear strength parameter affects the soil displacement. The research results can provide some reference for optimizing project design parameters.

Effect of Sustained Loading on the Direct Shear Behaviour of Recycled C&D Material–Geosynthetic Interfaces

Recycled construction and demolition (C&D) wastes have been pointed out as a feasible alternative to traditional backfill materials of geosynthetic-reinforced structures, but the current knowledge about the interface behaviour between these unconventional (recycled) materials and the reinforcement is still limited, particularly as far as the time-dependent response is concerned. In this study, a series of large-scale direct shear tests was conducted using an innovative multistage method to evaluate the influence of shear creep loading on the direct shear response of the interfaces between a fine-grained C&D material and two different geosynthetic reinforcements (high-strength geotextile and geogrid). The peak and large-displacement interface shear strength parameters obtained from tests involving sustained loading were compared with those from conventional interface tests. Test results have shown that the shear creep deformation of the interfaces increased with the magnitude of sustained loading. The test specimens experienced additional vertical contraction during the creep stage, which tended to increase with the applied normal stress. For the recycled C&D material-geotextile interface, the sustained loading induced a reduction in the apparent cohesion and a slight increase in the friction angle, when compared to the values estimated from conventional tests. In turn, for the geogrid interface, the apparent cohesion values increased, whereas the friction angle did not significantly change upon shear creep loading.

Large-scale direct shear testing in coir fibers reinforced sand

The need to develop and commercialize materials incorporating vegetable fibers has risen over the last 20 years to decrease environmental impact and achieve sustainability. In geotechnical engineering, soil reinforcement with plant-based fibers has gained a lot of interest, especially in temporary earthworks. Soil reinforcement with plant-based fibers is a low-cost, environmentally friendly method with excellent reproducibility and accessibility. In this context, growing appeals for using plant-based fibers such as sisal, coir, curauá, and kenaf for manufacturing new geomaterials have been verified. This paper aims to evaluate the mechanical behavior of soil-fiber composites by insertion of natural coir fibers into a sandy soil matrix with different fiber lengths and contents, where the fibers were randomly distributed in the soil mass. Large-scale direct shear test evaluated the strength-displacement behavior in samples with dimensions of 300 x 300 mm and 200 mm in height. The tests were carried out using fibers with 25 and 50 mm lengths, in 0.50 and 0.75% of fiber contents (in relation to the dry weight of the soil), in a relative density of 50% and 10% moisture content. The overall analysis of the results showed that the coir fibers addition in the well-graded sand increased the shear strength parameters and the ductility, compared with the unreinforced sand.

Study on Large-Scale Direct Shear Test on Soil–Rock Mixture in an Immersion State under Water

Soil–rock mixture (S–RM) is a natural geomaterial with multiple grain grades. It has dramatic trans-scale and hierarchical natural characteristics, and its mechanical properties are dramatically influenced by water. Various S–RM samples with multiple grain grades in engineering in situ state were prepared for large-scale and conventional direct shear tests in a native state and an immersion state under water to investigate the shear strength and deformation characteristics of S–RMs. The experimental results show that the S–RM in the natural state has high shear strength; the cohesion c is 44.0 kPa, and the internal friction angle φ is 34.7°. The shear strength of the S–RM after water immersion drops significantly: the cohesion c is 45.7 kPa, and the internal friction angle φ is 7.7°. The research results indicate that the cohesion of S–RM is mainly provided by the shear bond strength of the coarse grains, the development of which is governed by the gradation and surface topography of mineral grain and affected by constraint conditions. The interpretation of the sharp drop in the shear strength of S–RM after water immersion is that the sliding friction resistance between coarse grains and clay membrane and the occlusion friction resistance generated by the rotation transfer of coarse grains through clay membrane decreases sharply as the clay membrane around coarse grains becomes substantially soft. The shear strength of S–RM presents a dramatic scale effect and engineering design may come across major deviation and adventure when it adopts shear strength parameters determined by small-scale testing apparatus.