Direct Shear Tests Research Articles

An Experimental Investigation on Shear Strength, Deformation, and Particle Breakage of Carbonate Sand–Concrete Interface through Direct Shear Tests Subjected to Monotonic–Cyclic Thermal Loadings

An Experimental Investigation on Shear Strength, Deformation, and Particle Breakage of Carbonate Sand–Concrete Interface through Direct Shear Tests Subjected to Monotonic–Cyclic Thermal Loadings

Experimental study on synergistic treatment of dredged sludge with cement-waste concrete fine aggregate

Traditional disposal of dredged sludge with high moisture content and construction waste, causes a huge waste of resources and environmental pollution. This study used cement-waste concrete fine aggregate to synergistically treat dredged sludge (called double mixing stabilized clay, DMSC) to solve these problems. The effects of recycled fine aggregate and cement contents on the compressive, shear, and consolidation properties of DMSC were compared and analyzed through the unconfined compression test, direct shear test, and consolidation test. The consolidation mechanism of DMSC was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The test results showed that the incorporation of waste concrete fine aggregate improved the mechanical properties of cement solidified sludge, and the optimal aggregate dosage was 15%. Under the optimal fine aggregate content, the maximum increase of UCS and shear strength can reach more than 20 kPa. However, cement content was the main factor affecting the mechanical properties of DMSC. An equation was established to predict the unconfined compressive strength (UCS) of DMSC with different ratios and curing ages. Based on the correlation among UCS, cohesion, and structural yield strength, cohesion and structural yield strength of DMSC can be predicted. It was found that the waste concrete fine aggregate enhanced the mechanical properties of DMSC by improving pore structure, promoting hydration reaction, and enhancing spatial skeleton. It was proved that the synergistic treatment of DMSC improved its mechanical properties and can contribute to resource conservation and environmental protection.

Study on the interlayer bonding state of an asphalt pavement based on the stacking peak ratio method

The interlayer bonding of an asphalt pavement significantly influences the mechanical properties and long-term durability of the pavement structure. In order to develop a rapid and comprehensive evaluation method for assessing the interlayer condition of asphalt pavements using 3D GPR, we propose the stacking peak ratio (SPR) method. This method involves stacking the ratio between the amplitude peak of the interlayer and that of surface reflection to evaluate the interlayer state. Comparative analysis with direct shear tests and field measurements leads us to draw several conclusions: the optimal test parameters for the SPR method are a stacking peak ratio at 35 ns with a residence time of 1 us; the SPR method is compatible with various bonding materials and pollution layers, demonstrating its ability to effectively assess the bonding state of asphalt pavements; field tests further validate that the SPR approach can identify insufficient layer bonding and predict potential flaws in advance. Through our test findings and data analysis, it is evident that this SPR approach provides theoretical support and technological assistance for promptly evaluating the bonding status in asphalt pavements.

Geomechanical Properties of Clay Stabilised with Fly Ash-Based Geopolymer Subjected to Long-Term Sulfate Attack

Fly ash-based geopolymers have emerged as an eco-friendly alternative binder compared to conventional Portland cement for soil stabilisation. However, the gap in the current literature is the lack of a comprehensive study regarding the geomechanical behaviour of fly ash geopolymer-treated clay subjected to long-term sulfate attack, particularly in terms of potential ettringite formation and the corresponding impact on cementitious soil structure. The goal of this paper is to address this knowledge gap and provide a comprehensive study to fulfil it. In this work, sulfate attack was simulated by submerging geopolymer-treated clay specimens in two distinct sulfate-based solutions (i.e., sodium and magnesium), for one year. Subsequently, comparative analyses of the geomechanical and microstructural changes in geopolymer-treated clay under various curing conditions were conducted through unconfined compressive strength, direct shear, volume change and microscopic tests. The findings indicate that the addition of geopolymer for the stabilisation of clay soil significantly improves soil strength without affecting the soil volumetric response. Although the clay used exhibited similar qualitative stress–strain behaviour across all simulated attacks, notable quantitative differences emerged in the peak strength, stiffness and shear strength parameters. Such discrepancies can primarily be attributed to the varying buffering capacities (i.e., pH changes associated with acidification) of the sulfate solutions and the subsequent residual pH, cementitious product formation and strength enhancement within the treated clay.

Pengaruh Inklusi Karet dan Semen yang Mengandung Graphene Oxide terhadap Perilaku Sifat Fisis dan Mekanis Tanah

Improving the physical properties of problematic soil has became fundamental consideration in various constructions, especially geotechnical engineering, to avoid failures, increase stability and strength of soil. Silty sand is one of the problematic soils and often encountered in the field where the fine gradation contained in the soil allows the soil to easily deform under pressure and lateral forces. In this study, silty sand was mixed with three variations of crumb rubber content (5, 10, and 15% based on soil weight), 6% cement (based on soil weight), and 0.05% graphene oxide (based on cement weight) to measurement and analysis of physical and mechanical properties. Soil Consistency limits, compaction testing using the Proctor Apparatus, and direct shear test were carried out for each mixed variable. The test results showed that the consistency limits and dry density decreases with increasing rubber content in the soil-cement matrix containing graphene oxide. Substitution of graphene oxide into the soil-cement matrix was able to increase in the stress and shear strength of the soil at each in variation in rubber content.

Shear strength degradation of gas hydrate-bearing sediment due to partial hydrate dissociation

Extraction of methane hydrate from subseafloor reservoir may potentially trigger seabed slides and induce subsidence. To address the problems, it is crucial to properly characterize the phase equilibrium condition of pore hydrate and the shear strength of the soil. As one of the key constitutive components, the phase equilibrium condition enforces a constraint over pore gas pressure, temperature and unhydrated water content. Such a constraint, however, has been traditionally ignored in analyzing the mechanical behavior of hydrate-bearing soil. In this paper, a series of stepwise hydrate dissociation tests was performed, and the phase equilibrium condition of pore hydrate was determined, providing an effective way to evaluate the unhydrated water content during hydrate dissociation. Meanwhile, a series of direct shear tests was also conducted to explore the shear strength characteristics of the soil. It is shown that the shear strength of the hydrate-bearing soil can be significantly influenced by pore gas pressure, unhydrated water content, hydrate saturation and several other factors. In particular, the measured shear strength depends upon the initial water content of the sample, pointing to a potential problem that the shear strength could be wrongly determined if not properly interpreted. A shear strength criterion, which enforces the equilibrium condition of pore hydrate, is developed for hydrate-bearing soil, establishing a link between the equilibrium condition and the shear strength. The proposed equation describes well the shear strength characteristics of hydrate-bearing soils, remarkably unifying the effects of pore pressure, temperature, water content and hydrate saturation.

Study on the mechanical properties of embankment soil under long-term immersion conditions

During flood season, embankments are often submerged in high water levels for extended periods, leading to deterioration in their soil mechanics performance and increasing the risk of slope instability and other hazards. In order to investigate the changes in mechanical properties of embankment slopes during long-term water immersion, direct shear tests were conducted. Scanning electron microscopy, chemical composition analysis, and laser particle size analysis were conducted on samples taken at different immersion periods. Clay samples were taken from the embankments at Jiangxinzhou in Nanjing, Jiangsu Province, China. Results showed the shear strength of the soil gradually decreases with the increase of immersion time, while the cohesive force and internal friction angle gradually decrease as well. This suggests that immersion has a softening effect on the shear strength of the soil. As the immersion time increases, the colloidal particles (soluble salt) rapidly dissolves, the microstructure of the soil is destroyed, and sticky particles increases, resulting in a change in the shear strength of the soil. The research results provide a basis for flood control and prevention of embankments immersed in high water levels for long periods during the flood season.

Test and DEM study on cyclic hysteresis characteristics of stereoscopic geogrid–soil interface

The bearing resistance provided by the geogrid's transverse ribs is a non-negligible aspect of the strength mechanism in mobilizing the geogrid–soil interface. Therefore, studying its influence on the response mechanism of geosynthetic-reinforced soil structures under cyclic loading is crucial. The stereoscopic geogrids were manufactured using 3D printing technology by quantitatively thickening the transverse ribs of planar geogrids. To investigate the cyclic hysteresis relationship and stress–dilatancy phase-transformation characteristics of the stereoscopic geogrid–coarse particle interface, cyclic direct shear tests were conducted. Additionally, a discrete element method (DEM) was employed to study the evolution of shear bands and fabric anisotropy at the interface under cyclic loading. The results of the study indicate that the stress–displacement phase angle of the stereoscopic geogrid in the horizontal direction of cyclic shear is smaller compared to the planar geogrid. Furthermore, thickening the transverse ribs decreases the stress–dilatancy phase-transformation angle of the interface. The thickness of the interface shear band in the stereoscopic geogrid is greater than that of the planar geogrid. Moreover, as the transverse-rib thickness increases, the principal direction of the average normal contact force and average tangential contact force under cyclic loading also increases.

Investigating the impact of travertine powder on strength and permeability of swelling clay

Stabilization of swelling soils with high volume change potential is an important topic in geotechnical engineering because irreversible and catastrophic damages will occur if they are not appropriately managed. This study aimed to determine the effect of travertine powder on the swelling, strength, and permeability properties of weak and swellable soils. Within the scope of the study, soil improvement performance of travertine powder, which can be used as a soil improvement tool, was analyzed in detail, and the effect of travertine powder on the hydraulic and strength properties of the soil was discussed comparatively. Waste powder from travertine quarries taken from Eskipazar (Turkey) and Bentonite clay with high swelling potential taken from Tokat (Turkey) was used in the study. Samples were prepared by adding 10%, 20%, 30%, and 40% by weight of travertine powder to the Bentonite, and these mixtures were cured for 0-7-14-21-28-35 and 42-day periods. Unconfined compressive strength test, direct shear test, swelling pressure, and permeability tests were then conducted on each of the cured-stabilized samples. While the permeability coefficient, unconfined compressive strength, cohesion, and internal friction angle of bentonite samples with the additive increased over the curing time, the swelling pressure value decreased. The addition of travertine led to a substantial enhancement in the unconfined compressive strength (by 35%), internal friction angle (by 350), and cohesion (by 26%), while simultaneously reducing the swelling pressure by 58%. These findings emphasize that travertine powder enhances weak and swellable soils, offering an eco-friendly and cost-effective solution for improving engineering properties.

The Influence of Different Curing Environments on the Mechanical Properties and Reinforcement Mechanism of Dredger Fill Stabilized with Cement and Polypropylene Fibers.

An effective method widely used in geotechnical engineering to solve the shrinkage and cracking issues in cement-stabilized soil (CS) is evenly mixing randomly distributed fibers into it. Dredger fills stabilized with cement and polypropylene fibers (PFCSs) are exposed to rainwater immersion and seawater erosion in coastal areas, influencing their mechanical performance and durability. In this study, direct shear and consolidation compression tests were conducted to investigate the influence of different curing environments on the mechanical properties and compressive behavior of PFCSs. Dominance and regression analyses were used to study the impact of each factor under different curing regimes. The reinforcement mechanism of different curing environments was also explored using scanning electron microscopy (SEM) imaging. The results show that the cohesion and elastic modulus of the specimens cured in seawater were reduced compared with those cured in freshwater and standard curing environments. The best fiber content for the strength and compressive modulus of PFCSs was determined to be 0.9% of the mass of dredged fill. The results of value-added contributions and the relative importance of each factor in different curing environments show that the overall average contribution of cement content in the seawater curing environment is reduced by 6.79% compared to the freshwater environment. Multiple linear regression models were developed, effectively describing the quantitative relationships of different properties under different curing conditions. Further, the shear strength was improved by the coupling effect of soil particles, a C-S-H gel, and polypropylene fibers in the PFCSs. However, the shear strength of the PFCSs was reduced due to the structural damage of the specimens in the freshwater and seawater curing environments.

Calibration of Model Parameters for Soda Saline Soil-Subsoiling Component Interaction Based on DEM

To apply the discrete element method (DEM) to simulate the interaction process between soda saline–alkali soil and subsoiling component in Northeast China, establishing the soda saline–alkali soil particle model and selecting more accurate simulation parameters are important. In this paper, we studied the soda saline–alkali soil of the Songnen Plain in China. First, we studied the geometric shape of soda saline–alkali soil particles and proposed a modeling method for single soil particles based on the multisphere combination method. Considering the cohesion of soda saline–alkali soil particles, the Hertz–Mindlin with JKR (JKR) model was used as the contact model between soil particles. Then, the calibration method was used to obtain simulation parameters of soils that are difficult to obtain experimentally. We conducted soil angle of repose (AoR) tests, the Plackett–Burman (PB) tests, and steepest ascent (SA) tests in turn to perform a sensitivity analysis for microscopic contact parameters and select the parameters that have a significant effect on the response value (static AoR), i.e., soil surface energy, soil–soil static friction coefficient, and soil–soil rolling friction coefficient. Then, the optimal combination of simulation parameters was obtained via the Box–Behnken (BB) tests, using ANOVA to optimize the multiple regression equation. Finally, the optimal parameter combination was verified by the AoR test and the direct shear (DS) test. The results showed that the parameters had good adaptability for the AoR test. However, the simulation results of the DS test were significantly different from the experimental values. Therefore, the contact model needs to be further modified by adding Bonding bonds between soil particles based on the JKR model and further correcting for Rayleigh time step, shear modulus, and surface energy. By comparing the simulation and the experimental results, it was found that the simulation results obtained from both the DS test and AoR test had relatively small errors relative to physical tests, the two trends are the same, and the values are similar. This verified the feasibility and effectiveness of the soda saline–alkali soil particle modeling method and parameter selection proposed in this paper.

Dynamic properties of high-density polyethylene–sand by large-scale direct shear experiments

Recycling and reuse of plastic waste in civil projects is one way to reduce its negative impacts on the environment. High-density polyethylene (HDPE) is a highly abundant plastic waste found widely and in high volumes worldwide. Although sand has a relatively high frictional resistance, if its dynamic parameters are improved, it can be used in geotechnical projects that require higher dynamic parameters than those of pure sand. This study aimed to investigate the dynamic properties of sand mixed with crushed HDPE waste and its application to mitigate its negative environmental impacts. Crushed HDPE was added to sand at 0, 4 and 8% by weight. Under three vertical stresses and two shear amplitudes, the dynamic parameters of the mixture, including damping and shear stiffness, were investigated by conducting a large-scale cyclic direct shear test under ten cycles and are discussed. The results showed that with increasing HDPE percentage, the damping ratio rose and the shear stiffness decreased compared with those of pure sand due to the elasticity, deformation, tensile properties and high potential of HDPE for energy absorption. Furthermore, the rise in shear amplitude decreased the dynamic shear stiffness and raised the damping ratio of the mixtures.

Mechanical Review of Fine Sand-Clay Varians


 
 
 
 Clay in nature consist of a mixture of grains and minerals with or without the content of organic matter. The variation in the size of clay grains and the proportion of their distribution is a very useful indicator for knowing soil behavior. Testing the combination of fine sand - clay (FSC) using clay from Kulim Pekanbaru and fine sand from Teratak Buluh Riau. Variants of the percentage of FSC are carried out with the types of tests carried out are Standard Proctor Test, Unconfined Compressive strength test, Direct Shear Test and sieve analysis test and hydrometer. Increasing the percentage of clay in the FSC variant, increases the liquid limit, increasses the plastic limit and increases the plasticity index. Increases optimum moisture content, decreases maximum dry density and increases soil friction angle and decreases compressive strength
 
 
 

Synergistic Effects of Red Clay and Lime for Improving Phyllite Soil

Phyllite soil and red clay belong to the soils that negatively impact the engineering performance of railway subgrade and may cause subgrade bulges, uneven subgrade settlement, and other subgrade distresses. In order to make full use of these two soils, a collaborative improvement plan was proposed. A series of tests were conducted to analyze the synergistic effects of lime and red clay on the improvement of phyllite soil. The tests included the no loading swelling ratio, swelling pressure, consolidation, and direct shear tests. Additionally, scanning electron microscopy was used to investigate the role of lime and red clay in soil improvement. The test results show that a red clay ratio of 60% + lime content of 3% is the optimal composite improvement scheme. The scheme led to a 93% reduction in the no loading swelling ratio and an 88% reduction in swelling pressure. Additionally, cohesion, the internal friction angle, and the compression modulus increased by 345%, 73%, and 373%. Red clay and lime had weak synergistic improvement effects on the no loading swelling ratio, the swelling pressure, and the internal friction angle of phyllite soil, that is, the synergistic improvement effect of red clay and lime was less than the sum of the single improvement effect but greater than the single improvement effect. Red clay and lime had a strong synergistic improvement effect on the cohesion and the compression modulus of phyllite, that is, the synergistic improvement effect of red clay and lime was greater than the sum of the single improvement effect. The microstructure analysis test results show that red clay can fill the pores of phyllite soil and improve its immediate strength. Through hardening and cementation, lime can enhance the strength of phyllite soil as well as address the issue of the reduced engineering properties of phyllite soil and red clay when exposed to water. Red clay and lime promote each other’s reactions and have a synergistic improvement effect on phyllite soil.

Effect of nano-gypsum on mechanical properties cement admixed marginal silty soil

Even though the chemical stabilization is by far the most common ground improvement technique, very few studies have been conducted on the joint incorporation of two or more additives (cement-nanogypsum mix) to stabilise soft soil. This study investigates the effect on the mechanical properties of cement-stabilised silty soft soil (CSS) using nano-gypsum (NG). Unconfined compression strength (UCS) test trials were conducted to achieve soft soil conditions. The effect of NG and cement on soft soil was investigated by performing Atterberg limit, compaction, UCS, and Direct shear tests. The soil was treated with four percentages (10%, 15%, 20%, and 25%) of cement and with three percentages (1%, 1.5%, and 2%) of NG by its dry unit weight. The test results showed that the plasticity index of the soil was reduced significantly by the addition of stabilizers (Cement-NG mix) making the soil stiffer. The compaction tests suggested that optimum cement content was 20% for CSS and for cement-NG mix maximum strength was achieved at cement: NG proportion of 20:1. The unconfined compression strength (UCS) was increased by 9.11 times in comparison to untreated soft soil at cement: NG proportion of 20:1.5. The direct shear test (DST) suggested that there was an increase in cohesion by 4.44 times in comparison to the untreated sample at the soil–cement-NG combination of 78.5: 20: 1.5. However, the angle of internal friction remained almost unchanged. The development of cementitious substances was confirmed through XRD spectroscopy. Microstructural and chemical properties were observed using combined FESEM-EDAX analysis and Fourier transform infrared spectroscopy (FTIR). The multivariate linear regression (MLR) predictive model was developed for the unconfined compressive strength and failure strain as a function of various parameters considered in the study. The test results demonstrated that the combination of cement and NG can result in remarkable improvement in the geotechnical properties of soft soil. The use of NG may also reduce the demand for cement in deep cement mixing technique, which eventually reduces the carbon footprint and renders the ground improvement technique, ecologically beneficial.

Stability Analysis of Strongly Weathered Muddy Slate Slopes Considering Softening Conditions of Water Immersion

To understand the stability of strongly weathered muddy slate slopes under water immersion effects, we obtained shear strength parameters of the weakly layered structures within this slate through direct shear tests. Point load tests were performed on in-site slate samples with varying water immersion durations to assess the water immersion’s softening impact on slate strength. Results highlight that muddy slate strength presents pronounced random variability, declining as water immersion duration increases. Drawing from shear strength parameters and the water immersion softening observed in laboratory and in-site tests, we formulated a numerical slope model that considers layered structures and water immersion conditions to evaluate slope stability. Numerical simulations suggest that the slate slope’s sliding surface, when layered, does not consistently form a basic circular arc or straight line. The slope safety factor (FOS) drops below 3, marking a notable decrease compared to a homogeneous slope (FOS = 3.22). In the model, multiple secondary sliding surfaces can emerge, leading to a sliding band with a specific thickness after introducing the random distribution of layer strength parameters. This further reduces the slope’s FOS to below 2.9. Water immersion makes slopes inclined to slide following the layered structure. If the dip angle of the slate’s layered structure is less steep than the slope’s dip angle, water immersion notably diminishes the FOS, which can dip to a minimum of 1.12.

The Influence of Different Shear Directions on the Shear Resistance Characteristics of Rock Joints

The joint roughness coefficient JRC of rock joints is an important parameter for measuring the geometric morphology of rock joints. However, the parameter obtained from traditional calculation methods has certain limitations in reflecting the differences in shear strength of rock joints in different shear directions with the same orientation. Firstly, native joint surface test blocks were cast using three-dimensional reverse reconstruction technology. Subsequently, direct shear tests were conducted under different normal stress and shear direction conditions, followed by numerical simulations using the finite difference software Flac3d. The JRC coefficient calculation method proposed by Yuan was modified and extended by considering the percentage of climbing sections and the effective contact area during the ramping process. This study indicates that the numerical simulation results are in good agreement with the shear test results. The introduction of the shear climbing rate SCR and the curvature coefficient of profile CCP is used to reflect the geometric differences of the joint surfaces in different shear directions. These two parameters are nonlinearly fitted with the experimental results, leading to a calculation formula that characterizes the shear strength characteristics of the joint surfaces in different shear directions. This novel formula is an extension of the JRC–JCS model.

The Shear Strength of Root–Soil Composites in Different Growth Periods and Their Effects on Slope Stability

Vegetation slope protection plays an important role in improving the slope stability and protecting the environment. In this study, the mechanical properties of root–soil composites in different growth periods and their effects on slope stability were investigated. First, the shear strength of undisturbed root–soil composites associated with Cynodon dactylon (C.d), Magnolia multiflora (M.m) and grass and shrub mixture (G.s) were measured by large direct shear tests. Then, the effects of plant reinforcement in different growth periods on slope stability were analyzed using ABAQUS. The results show that the shear strength of the root–soil composites were significantly higher than that of the unreinforced soil. The root–soil composites met the Mohr–Coulomb criterion. The shear strength of the three root–soil composites increased first and then decreased during the vegetation growth period. The calculation results show that the factor of safety (FS) of the bare slope was 1.482. The FS values of the C.d, M.m, and G.s slopes were 1.601, 1.658 and 1.715, which increased by 8%, 11.9% and 15.7% compared to the bare soil slopes. Therefore, vegetation could significantly improve slope stability, especially the grass–shrub mixture model. This could provide a rational basis for designing and constructing plant slope protection.

The Shear Strength of Clay Stabilized with Palm Bunch Ash and Cement

Roads with soft subgrade have low bearing capacity. The result is non-uniform soil settlement. One way to overcome this is with soil stabilization. Stabilization of clay soil is done chemically with palm bunch ash and cement. The purpose of this study was to determine the bearing capacity of soil for the shear strength value of clay soil with variations in mixing 5%, 10%, 15%, 20% oil palm bunch ash, and 10% cement with a 7-day curing period, and then the samples were tested using a direct shear test tool SNI 3420: 2016. The results showed that in the addition of a mixture of oil palm bunch ash and cement with levels of 5%, 10%, 15%, 20%, and 10% cement, the cohesion value increased at a percentage of 20% oil palm bunch ash and 10% cement, namely 0.5448 kg/cm2 compared to the cohesion value in the original soil of 0.0081 kg/cm2, an increase of 98.51%, and a shear angle value of 53.12° while the value of the original soil shear angle was 16.93°. This research concludes that the shear strength value of clay soil stabilized with oil palm bunch ash and cement increases.

Roadway fracture mechanism investigation subjected to static and blast loading under different lateral pressure coefficients

Blasting disturbance generated by the drilling and blasting is a significant factor in inducing damage to the rock mass surrounding a nearby roadway. Understanding the roadway fracture mechanism triggered by blasting disturbance is crucial for improving support efficiency. This study conducted the Brazilian disk splitting and direct shear tests on cement mortar to determine the classification for distinguishing between tensile and shear cracks based on acoustic emission (AE) parameters, i.e., rising time/amplitude and the average frequency (RA-AF). In the study context, various roadway failure experiments were conducted under the combined effects of static stress loading and repeated blasting disturbances. The temporal-spatial evolution characteristics of AE activities and identifying crack types were investigated to reveal roadway failure mechanisms in response to blasting disturbances under different lateral pressure coefficients. The results show that as the increases of blast disturbance numbers and stress level, the damage within the surrounding rock around the roadway increases and peaks at the moment of roadway destruction. Roadway failure involves a transition from tensile to shear fractures. When the stress level within the rock is low, blasting disturbance leads to compressive deformation and mainly causes tensile fractures, while it promotes dislocation formation and primarily results in shear cracks at a high-stress level. Different proportions of tensile and shear cracks were counted quantitatively around the roadway, and tensile cracks are more likely to cluster on the sides of facing blasting as the lateral pressure coefficient rises.