Large-scale Direct Shear Tests Research Articles

Food waste impact on municipal solid waste angle of internal friction

The impact of food waste content on the municipal solid waste (MSW) friction angle was studied. Using reconstituted fresh MSW specimens with different food waste content (0%, 40%, 58%, and 80%), 48 small-scale (100-mm-diameter) direct shear tests and 12 large-scale (430 mm × 430 mm) direct shear tests were performed. A stress-controlled large-scale direct shear test device allowing approximately 170-mm sample horizontal displacement was designed and used. At both testing scales, the mobilized internal friction angle of MSW decreased considerably as food waste content increased. As food waste content increased from 0% to 40% and from 40% to 80%, the mobilized internal friction angles (estimated using the mobilized peak (ultimate) shear strengths of the small-scale direct shear tests) decreased from 39° to 31° and from 31° to 7°, respectively, while those of large-scale tests decreased from 36° to 26° and from 26° to 15°, respectively. Most friction angle measurements produced in this study fell within the range of those previously reported for MSW.

Influence of tire fiber inclusions on shear strength of sand

ABSTRACT: Reinforcement of soils with natural and synthetic fibers is a viable technique for increasing the soil strength. The objective of this study is to reinforce sand with tire waste inclusions. In this study, two different experimental programs were performed. In the first program, sand, tire crumb and tire crumb–sand mixtures were tested in the standard direct shear test equipment to observe the optimum content for modifying the shear strength properties of the sand. In the second program, large-scale direct shear tests were performed to observe the shear strength improvement imparted by tire waste inclusions. Two different processed tire wastes were used: tire crumb (TC) and fiber-shaped tire buffings (TB). The tire buffings were divided into two parts for representing different aspect ratios (TB1 and TB2). The following factors were studied to evaluate the influence of TC, TB1 and TB2 inclusions on the shear strength: normal stress, tire waste type, aspect ratio, and tire waste content. Three factors were found to significantly affect the shear strength values: normal stress, aspect ratio, and tire waste content. Also, it is seen that increasing the aspect ratio of the fibers increases the shear strength of the mixture.

Large-scale direct shear testing of municipal solid waste

Large direct shear testing (300 mm × 300 mm box) of municipal solid waste (MSW) collected from a landfill located in the San Francisco Bay area was performed to gain insight on the shear response of MSW. The study investigated the effects of waste composition, confining stress, unit weight, and loading rate on the stress–displacement response and shear strength of MSW. The amount and orientation of the fibrous waste materials in the MSW were found to play a critical role. The fibrous material had little effect on the MSW’s strength when it was oriented parallel to the shear surface, as is typically the case when waste material is compressed vertically and then tested in a direct shear apparatus. Tests in which the fibrous material was oriented perpendicular to the horizontal shear surface produced significantly stronger MSW specimens. The test results indicate that confining stress and loading rate are also important factors. Based on 109 large-scale direct shear tests, the shear strength of MSW at low moisture contents is best characterized by cohesion = 15 kPa, friction angle = 36° at a normal stress of 1 atmosphere, and a decrease in the friction angle of 5° for every log-cycle increase in normal stress.

Influence of different processing techniques on the mechanical properties of used tires in embankment construction

Use of the processed used tires in embankment construction is becoming an accepted way of beneficially recycling scrap tires due to shortages of natural mineral resources and increasing waste disposal costs. Using these used tires in construction requires an awareness of the properties and the limitations associated with their use. The main objective of this paper is to assess the different processing techniques on the mechanical properties of used tires–sand mixtures to improve the engineering properties of the available soil. In the first part, a literature study on the mechanical properties of the processed used tires such as tire shreds, tire chips, tire buffings and their mixtures with sand are summarized. In the second part, large-scale direct shear tests are performed to evaluate shear strength of tire crumb–sand mixtures where information is not readily available in the literature. The test results with tire crumb were compared with the other processed used tire–sand mixtures. Sand–used tire mixtures have higher shear strength than that of the sand alone and the shear strength parameters depend on the processing conditions of used tires. Three factors are found to significantly affect the mechanical properties: normal stress, processing techniques, and the used tire content.

Degradation of marls; two case studies from the Iberian Peninsula

Abstract The strength degradation of two marl formations (Pamplona marls in Spain and Abadia marls in Portugal) is analysed in the paper. In the case of Pamplona marls, a number of large-scale direct shear tests on natural and saturated specimens of the undisturbed material were performed. Tests on marl–concrete interfaces were performed and are also presented. Both cases analysed show that the saturation of the marl leads to a strong reduction of friction and effective cohesion. Negative effects of suction changes on the mechanical behaviour of the marls were investigated in more detail in suction controlled tests on Abadia marls, a more plastic material. A numerical simulation of wetting effects on a marl fragment of finite size helps to identify the nature of degradation mechanisms, which are associated with the development of tensile surfaces inside the marl matrix. They, in turn, are due to the expansive behaviour of the clay fraction of the marl relative to suction changes.

Shear strength and compressibility of oyster shell–sand mixtures

This paper investigates the fundamental characteristics of shear strength and deformation of crushed oyster shell–sand mixtures to stimulate recycling of waste oyster shells. Standard penetration tests (SPT) and large-scale direct-shear tests were carried out with different kinds of dry unit weight and mixing rate of oyster shell–sand mixture. Correlations between N-value, dry unit weight, and friction angle of mixtures were observed from the results of experimental tests, making it possible to estimate the in situ strength from SPT, and the coefficient of volume compressibility from the confined direct-shear compression test. These results also make it possible to compute the settlement of oyster shell–sand mixture when used in soft ground improvement.

Interaction between geogrid reinforcement and tire chip–sand lightweight backfill

This paper deals with the interaction between the geogrid and the tire chip–sand mixture including the determination of the index properties of the backfill materials, the shear strength parameters, the interaction coefficients, and the efficiency of geogrid reinforcements in tire chip–sand backfills. Numerous experiments including index tests, compaction tests, pullout tests, and large-scale direct shear tests were conducted. Saint–Gobain (geogrid A) and Polyfelt (geogrid B) were selected as reinforcing materials. Tire chip–sand mixtures with mixing ratios of 0:100, 30:70, 40:60, and 50:50 by weight were used as fill materials. The test results revealed that the dry unit weight of tire chip–sand mixtures depended more on the sand content, and less on the water content. The mixture at the mixing ratio of 30:70 by weight or 50:50 by volume was found to be the most suitable fill material compared to other mixing ratios. The pullout resistance and the pullout interaction coefficients of geogrid A were slightly higher than those of geogrid B. In contrast, in the direct shear resistance, the direct shear interaction coefficients, and the efficiency values of geogrid B were slightly higher than those of geogrid A. Since geogrid B has the needed uniaxial reinforcement properties and its sufficient interaction characteristics with tire chip–sand mixture, the geogrid B was utilized in this study. The interaction coefficients between the tire chip–sand backfill with 30:70 mixing ratio by weight were found to be 0.71 in pullout mode and 0.92 in direct shear mode for geogrid B.

Evaluating shear mobilization in rockfill columns used for riverbank stabilization

The major rivers within the City of Winnipeg are founded in glacial Lake Agassiz clay and silt sediments that have low shear strength. As such, riverbank instabilities are a common issue along many stretches of the rivers. The use of rockfill columns has become an increasingly utilized approach for stabilizing failing banks. Recent cases in Winnipeg have shown that movements can occur following installation of rockfill columns. Uncertainty regarding the magnitude of these movements that is required to mobilize shearing resistance in the rockfill columns has resulted in situations where the stability of riverbanks following remediation has been questioned. This has provided a need to improve our understanding about how much movement a stabilized slope must undergo before sufficient shear resistance of the rockfill column will be mobilized. The results of experimental testing conducted to assess the shear mobilization of rockfill column materials using a large-scale direct shear test apparatus are presented in this paper. The testing methodology is described along with the test results. The results show that the development of material specifications, construction, and placement methods and appropriate methods of analysis requires understanding of the stress–strain properties of the in situ soil and the rockfill material.

Analysis of a Large Database of GCL-Geomembrane Interface Shear Strength Results

A database of 534 large-scale direct shear test results was assembled in this study to evaluate the interface shear strength between geosynthetic clay liners (GCLs) and geomembranes (GMs). The tests were conducted between 1992 and 2003 by a single independent laboratory using procedures consistent with current testing standards. The number of results in the database allowed quantification of the impact of GCL type, GM type, normal stress, and procedures for specimen hydration and consolidation on the shear strength of GCL-GM interfaces, as well as identification of sources of shear strength variability. The interface shear strength was found to be sensitive to the type of GCL internal reinforcement, GM polymer, and GM texturing, but not to the GM thickness or manufacturer. On average, the GCL internal shear strength was observed to be higher than the GCL-GM interface shear strength when tested using the same procedures. GCLs sheared internally show similar stress-displacement responses and friction angles to GCL-GM interfaces that incorporate a GCL with the same reinforcement type. Hydration under normal stresses below those used during shearing (followed by a consolidation period) led to higher GCL internal shear strength, but lower GCL-GM interface shear strength, than when hydration was conducted under the shearing normal stress. Such different responses are attributed to bentonite extrusion from the GCL into the interface. Good repeatability of test results was obtained using GCL and GM specimens from the same manufacturing lot, while high variability was obtained using specimens from different lots. GCL-GM interface peak shear strength variability was found to increase linearly with normal stress.

Large-scale direct shear testing of geocell reinforced soil

The tests on the shear property of geocell reinforced soils were carried out by using large-scale direct shear equipment with shear-box-dimensions of 500 mm×500 mm×400 mm (length×width×height). Three types of specimens, silty gravel soil, geocell reinforced silty gravel soil and geocell reinforced cement stabilizing silty gravel soil were used to investigate the shear stress-displacement behavior, the shear strength and the strengthening mechanism of geocell reinforced soils. The comparisons of large-scale shear test with triaxial compression test for the same type of soil were conducted to evaluate the influences of testing method on the shear strength as well. The test results show that the unreinforced soil and geocell reinforced soil give similar nonlinear features on the behavior of shear stress and displacement. The geocell reinforced cement stabilizing soil has a quasi-elastic characteristic in the case of normal stress coming up to 1.0 GPa. The tests with the reinforcement of geocell result in an increase of 244% in cohesion, and the tests with the geocell and the cement stabilization result in an increase of 10 times in cohesion compared with the unreinforced soil. The friction angle does not change markedly. The geocell reinforcement develops a large amount of cohesion on the shear strength of soils.

Comparison of shear strength of sand backfills measured in small-scale and large-scale direct shear tests

Direct shear tests were conducted on 30 sand backfill materials having gravel contents ranging from 0% to 30% in a 64 mm square small-scale direct shear (SSDS) box and a 305 mm square large-scale direct shear (LSDS) box. The objectives were to compare the shearing behavior of a broad range of natural sand backfill materials tested in SSDS and LSDS and to determine if the same friction angle (φ′) is obtained in SSDS and LSDS when the natural backfill material contains gravel. Triaxial compression (TC) tests were also conducted on four of the backfill materials for comparison with the SSDS and LSDS tests. Specimens tested in SSDS and TC included only material passing the No. 4 sieve (P4). Test specimens in LSDS included the P4 material as well as material retained on the No. 4 sieve (R4), to a maximum particle diameter of 25.4 mm. Friction angles corresponding to peak strength (φ′) measured in SSDS and LSDS differed by no more than 4° for a given sand backfill, and in most cases were within 2°. The friction angles also were unaffected by removal of the R4 material. Repeatability tests showed that statistically similar failure envelopes (p-value = 0.98) are obtained in SSDS and LSDS, and that highly repeatable friction angles (φ′) are obtained using the SSDS (φ′ ± 0.25°) and the LSDS (φ′ ± 0.45°) methods. No statistically significant difference was found among the failure envelopes measured in SSDS, LSDS, and TC, suggesting that φ′ for clean sand backfill with less than 30% gravel can be measured with similar accuracy using any of the three test methods.

Large scale direct shear tests of soil/PET-yarn geogrid interfaces

The interface shear strength of soil against geosynthetic is of great interest among the researchers in geosynthetic properties. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of different soils (sand, gravel, and laterite) against PET-yarn geogrids of various tensile strengths, percent open area, and aperture patterns. First, the appropriateness of different set-ups of a lower shearing box is examined in this study. It reveals that a lower box which is filled with the test soil and is of the same size as the upper box is more suitable for testing the soil/geogrid interface. The test results show that the soil/PET-yarn geotextile interface has significantly lower shear strength than soil strength. The ratio of shear strength soil/PET-yarn geotextile interface to internal shear strength of soil is about 0.7–0.8 for Ottawa sand and for laterite, and it is about 0.85–0.95 for gravel. On the other hand, the soil/geogrid interface has higher shear strength. The ratio of shear strength soil/PET-yarn geogrid interface to internal shear strength of soil is about 0.9–1.05. It is found that the shear strength ratio of soil/PET-yarn geogrid interface is positively correlated to the transverse tensile strength of the PET-yarn geogrid. However, it is negatively correlated with the aperture length and percent open area of the PET-yarn geogrid. The interface shear test results of PET-yarn geogrid against different soils are compared with the test results predicted by a classical model for analyzing the applicability of the classical model. Further, a simple model is proposed herein to estimate the bearing resistance provided by the transverse ribs of geogrid. It shows this component to be about 0–15% when PET-yarn geogrid is against Ottawa sand or laterite, while it is smaller when the PET-yarn geogrid is against gravel.

Study on the mesostructure and mesomechanical characteristics of the soil–rock mixture using digital image processing based finite element method

The soil–rock mixture (SRM) is a kind of inhomogeneous geomaterial, which poses difficulties of in situ sample acquisition and in laboratory geomaterial tests; hence, the study of the SRM's mechanical properties is still at an early stage. In this paper, the technique of digital image processing based on the finite element method (DIP-FEM) is introduced to study SRMs in the Leaping Tiger Gorge Reservoir Area, China. Based on the DIP, the mesostructural characteristics of the SRM are analyzed statistically. The mesostructural concept model of SRM that can actually represent the inhomogeneity of SRM is built. By using geometry vectorizaiton transformation, the mesostructural model of SRM in the binary image format has been translated into a vector format (such as DWG or DXF format) which can be imported into the finite element software. By using the finite element method, two large-scale direct shear tests of inhomogeneous SRM and homogeneous soil are simulated. The numerical results indicate that the existence of “rock” blocks in SRM will greatly influence the distribution and the failure models of the internal stress field. As a result, three kinds of failure models of the SRM are put forward.

Large-scale interface shear testing of sandbag dyke materials

This paper presents results of large-scale direct shear testing of six interfaces with materials used to construct sandbag dykes for flood protection structures. Two additional test series using intact sandbags were also conducted to examine the influence of sandbag-to-sandbag interaction in typical stacked sandbag dyke construction and sandbag-to-sod (grass) contact representing the interface condition at the dyke foundation. The interface test results are summarised using Mohr–Coulomb shear strength parameters and interface shear stiffness parameters. The data presented in this paper are necessary for stability analyses of instrumented and monitored sandbag dyke structures that are currently under way as part of the development of a new guidance document for the design of sandbag dykes for temporary flood protection works in Canada.

Large-scale Apparatus for Monotonic and Cyclic Soil-Structure Interface Test

AbstractA large-scale direct shear test apparatus was developed to investigate the monotonic and cyclic behavior of a soil-structure interface. The apparatus provides a constant sample size 50 cm in length and 36 cm in width. Three kinds of normal boundary conditions, namely, constant normal stress, constant normal stiffness, and constant normal displacement, can be directly applied on the interface with high accuracy. The apparatus is equipped with an automated loading system with capacity up to 200 kN in both directions. The stress and displacement of the interface can be automatically measured with the apparatus. In addition, the movement and crushing of soil particles near the structure can be observed and recorded. Therefore, this apparatus is suitable for monotonic and cyclic tests of the interface between structure and gravelly soil. The effectiveness of this apparatus was confirmed by tests of the interface between structure and gravel. The test results show that the steel-gravel interface exhibits significant change in the physical state and volumetric strain due to shear application.

Analysis of a Large Database of GCL Internal Shear Strength Results

A database of 414 large-scale direct shear test results was assembled to evaluate variables governing geosynthetic clay liner ~GCL! internal shear strength. The tests were conducted by a single independent laboratory over 12 years using procedures consistent with current testing standards. A wide range of GCL types, normal stresses, and shear displacement rates allowed investigation of the effect of reinforcement, pore water pressure generation, and sources of shear strength variability. Reinforced GCLs showed higher strength than unreinforced GCLs, with needle-punched GCLs performing better than stitch-bonded GCLs. Thermal locking of needle-punched GCLs was found to be effective at high normal stress, but hydration using low hydration normal stress was found to decrease the effectiveness of thermal locking. Shear-induced pore water pressures were indirectly evaluated using shear strength results from tests conducted using normal stresses above and below that corresponding to the GCL swell pressure. The peak shear strength was found to increase with decreasing shear displacement rates for high normal stresses, while the opposite trend was observed for low normal stresses. Shear strength envelopes showed a bilinear response, with a break at normal stresses consistent with the GCL swell pressure. Good repeatability of test results was obtained using the same-manufacturing-lot GCL specimens, while comparatively high variability was obtained using different-lot specimens. Peak shear strength variability was found to increase linearly with normal stress, but to be insensitive to specimen conditioning procedures. Evaluation of reinforced and unreinforced GCL test results indicates that, in addition to reinforcement variability, bentonite variability contributes to the shear strength variability of reinforced GCLs. Peel strength was found not to be a good indicator of the contribution of fibers to the GCL peak shear strength.

Determination of static and dynamic behavior of recycled materials for highways

Utilization of wastes in highway applications may be feasible with a better understanding of waste behavior under static and dynamic loading. Waste materials such as tires, plastics, glass, fly ash, etc. may be used in highway construction potentially saving waste disposal costs. Physical, mechanical, and dynamic properties of waste materials are required for a successful design, which can be determined using techniques available in geotechnical engineering. Construction of highway fills in earthquake prone regions requires knowledge of dynamic behavior of the waste materials. Due to its low unit weight, high porosity, and interlocking behavior, waste materials response to earthquake loads are different from those of natural soil. In this study, large-scale direct shear tests and dynamic triaxial tests were carried out for two potential wastes: tire buffings and manufactured fly ash pellet aggregates. Tire buffings added to sand altered the deformation behavior of the mixture by stiffening the material at low strains and softening the mixture at large strains. The shear modulus and damping values of sand–tire buffings mixtures were higher than those measured for tire buffings only. Processing fly ash to manufacture pellet aggregates resulted in high performance fill material with an internal friction angle of 46° and with unit weight of 10.5 kN/m 3. The shear modulus values of pellet aggregates were slightly lower than those of tire buffings added sand, and the damping values were as high as those for tire buffings–sand mixture.

Reliability-based stability analysis considering GCL shear strength variability

The impact of different levels of uncertainty in geosynthetic clay liner (GCL) shear strength on landfill stability is evaluated in this study. The uncertainty in shear strength of the interface governing landfill stability is defined using statistical parameters obtained from a significant database of GCL internal and GCL–geomembrane interface large-scale direct shear tests. Uncertainty in GCL shear strength arises from material variability within a single product type and between different product types. For a given product type, uncertainty arises from material differences among specimens from the same manufacturing lot as well as among specimens from different manufacturing lots. In addition, uncertainty was observed to arise from differences in test procedures such as hydration, consolidation and shear displacement rate. A framework for incorporating the observed laboratory shear strength variability into realistic field applications is presented. Reliability-based stability analyses were used to assess the impact of uncertainty in laboratory GCL shear strength test results on conventional design methodologies. Specifically, the impact of uncertainty on the relationships between the conventional safety factor and the probability of failure is assessed. Owing to the high shear strength variability observed in the database, high probability of failure values were found to correspond to safety factors typically used in geotechnical practice.

Interaction Between Hexagonal Wire Reinforcement and Rubber Tire Chips with and without Sand Mixture

Abstract The interaction between tire chips with and without sand mixtures and the hexagonal wire reinforcement, as well as the strength characteristics of mix, were investigated by in-soil pullout tests and large-scale direct shear tests. Rubber tire chips with and without sand mixtures have lower shear strengths than pure sand. Compared with the tests in sand, the hexagonal wire reinforcement in the rubber tire chips with and without sand mixtures had lower pullout resistances. However, with increasing sand content in the mixtures, the pullout resistances of hexagonal wire in mixtures increased. The proposed empirical equations successfully predicted the pullout resistances of hexagonal wire with different mixing ratios. Based on limit equilibrium method, the results of the parametric studies of a reinforced wall for the required spacing and embedment length of hexagonal wire reinforcement have been presented. For a reinforced wall, the total amount of the required hexagonal wire reinforcement in rubber tire chip fill is less than in sand and tire chip-sand fills. Furthermore, the required embedment length of the hexagonal wire reinforcement in sand and tire chip-sand fills is approximately identical, but lower than those in tire chip fill.

Load plate rigidity and scale effects on the frictional behavior of sand/geomembrane interfaces

The possible load plate rigidity and scale effects on the frictional behavior of the interface between a quartz sand and high-density polyethylene (HDPE) geomembranes was investigated. The test materials included a quartz sand against smooth and textured HDPE geomembranes. The American Society for Testing and Materials D-5321 standard test method is adopted for measuring the shear strength of the interface between the test soil and geomembranes. The dimensions of the shear boxes are 100×100, 200×200, 300×300 and 400×400 mm 2 . In addition to the use of conventional rigid load plates to transfer applied load to the test specimens, a silicon-membrane-type water bladder was also designed to attach at the bottom of the conventional rigid load plate to form a flexible load plate. Moreover, a measuring device was used to replace the lower shear box for measuring the variation of normal pressures at the shearing plane. The results of the study indicated that the use of conventional rigid load plate to perform direct shear test results in a concave pressure distribution at the shearing plane. A minimum of 5 cm thickness of soil in upper shear box is recommended in order to ensure the reproduction of normal pressures at the shearing plane when a rigid load plate is used for applying the normal load. The use of flexible load plate for large-scale direct shear test machine would provide an anticipated uniform pressure distribution at interface shearing plane. A thickness of 2– 3 cm of sand layer in the upper shear box should be enough if loading is applied using a flexible load plate. The shear resistance associated with flexible and rigid load plate is quite similar to each other under same test conditions. However, the direct shear test performed using flexible load plate showed a better reproducibility of test data than that using rigid load plate. The size of shear box has an effect on the shear strength at the interface of sand/geomembrane systems. In general, the shear strength for larger shear box is greater than that associated with smaller shear box. However, the shear strength associated with 300×300 and 400×400 mm 2 shear boxes is almost identical to one another. Thus, it is recommended that minimum dimension of 300×300 mm 2 direct shear box should be used for determining the shear strength at the interface of a sand/geomembrane system. The shearing resistance associated with textured HDPE geomembrane is greater than that associated with a smooth-surfaced geomembrane. The shear strength associated with textured HDPE geomembranes increases with increasing shear strain. No peak values were observed. Stress–strain curves with peak values only occur for sand/smooth geomembrane system under high normal stress conditions. The friction angle for sand/textured geomembrane combinations is about 12° greater than that for sand/smooth geomembrane combinations.