Physical and Chemical Properties of Recycled Tire Shreds for Use in Construction

The purpose of this study was to determine the physical and chemical properties of tire shreds for use in engineering construction as a replacement for aggregates in embankments or as backfill. In general, test results revealed that tire shreds can be utilized in construction applications. As the size of tire shreds increases, physical properties such as specific gravity remained constant at 1.06–1.1. Gradation of tire shreds was also tested, and the results were comparable to other researchers (i.e., ranging from 50 to 300 mm). As the tire shred size increased, the hydraulic conductivity increased from 0.2 to 0.85 cm/s. Increasing the compaction energy had little effect on the final compaction density. The angle of friction and cohesion ranged from 15 to 32° and 349 to 394?N/m2, respectively. As the particle size (from 50 to 300 mm) of the tire shreds increased, the shear strength of the scrap tire increased. Moreover, as the tire shred size increased, compressibility increased. Chemical analysis of tire shreds was conducted to illustrate how properties such as total organic carbon (TOC), pH, and turbidity change with tire size. As tire shred size increases, the results illustrated a decrease in TOC (from 22.7 to 3.1 ppm) and turbidity (from 254 to 99 NTU). Continuous flow column tests were conducted on tire shreds and showed improved water quality (TOC, turbidity, and iron) with time. However, pause flow column tests showed reduced water quality, which implies that placement of a tire embankment below the water table where ponding can occur may reduced water quality. TGA tests were also conducted to determine the thermal stability of tire shreds. In general, tire shreds are stable up to temperatures of 200°C. This indicates that other mechanisms may be attributed to the exothermic reactions, which occurred in tire fills.     

Shear Strength Parameters of Municipal Solid Waste with Leachate Recirculation

The objective of this study was to characterize relative changes in waste shear strength parameters during waste decomposition. Twelve direct shear tests (100?mm diameter by 50?mm thickness) were performed on waste specimens ranging from fresh to well-decomposed residential refuse. In addition, nine direct shear tests were performed on selected waste components including fresh paper, partially decomposed refuse, and plastics. Results indicate that the friction angle of refuse decreased with decomposition. As refuse decomposed, the plastic content increased, which contributed to a decrease in friction angle as the friction angle of plastics is 18–19° as compared to 33° for fresh shredded waste. The extent of refuse decomposition was characterized by the cellulose plus hemicellulose to lignin ratio [(C+H)/L]. The measured friction angle decreased from 32 to 24° as (C+H)/L decreased from 1.29 to 0.25. The shearing pattern for decomposed refuse showed a peak, followed by residual, which was then followed by a steady increase in shear stresses with displacement; the final rate of increase was similar to that observed in fresh paper specimens. Results from this work were comparable to data from previous reports, though it is important to characterize the extent of solids decomposition for a valid comparison with published studies.     

含水量对压实粘土抗剪强度的影响

通过室内直剪试验,研究了含水量对压实粘土的抗剪强度的影响,并从土体结构与土中基质吸力变化两个方面分析了作用机理。试验表明,随压实含水量增大,粘土的抗剪强度降低,粘聚力随压实含水量增加并非单调变化,其曲线型式类似于“”型,内摩擦角随压实含水量增加大体上是减小的;压实粘土浸水饱和后抗剪强度和粘聚力则显著降低,且压实含水量越小的土体在其它条件相同的条件下因饱和引起的抗剪强度和粘聚力损失越大,内摩擦角受浸水饱和的影响较小。     

Shear Behavior of Compacted Rubber Fiber-Clay Composite in Drained and Undrained Loading

The ductility, toughness, and resistance to tensile cracking of clays can be improved with the inclusion of short fibers. Tire buffings are derived from the tire retread process and because of their elongated shape, may be used as fiber inclusions. The objective of this study was to evaluate the drained and undrained shear strength of mixtures of clay and tire buffings. Mixtures of silty low plasticity kaolinitic clay and 10% by dry weight of tire buffings were compacted at both Standard and Modified compaction energy. Consolidated-drained and consolidated-undrained triaxial tests were run at confining stresses ranging from 50?to?300?kPa. Preshear and postshear permeability tests were conducted. Results showed that the peak strength of the composite is comparable to or greater than that of clay alone when tested at confining stresses below 200–300?kPa. Above this threshold, the presence of inclusions tends to degrade the strength of the clay. Changes in permeability were not significant.     

Immediate and Time-Dependent Compression of Tire Derived Aggregate

This paper examines immediate and time-dependent compression of tire derived aggregate (TDA) and TDA-soil composites. To accommodate large particle sizes, modified experimental devices were developed and used to test tire chips and tire shreds. Immediate compression of TDA, which results almost entirely from the reduction of pore volume, increases with TDA content and tire particle size. The secant constrained modulus (Msec) of TDA defined over the stress range of 0–50?kPa varied from a low of 255?kPa (100% tire shreds) to a high of 1,320?kPa (50% tire chips). A characteristic relationship between strain and time exists for TDA and TDA composites under one-dimensional confined compression. Time-dependent deformation is well described by the modified secondary compression index (Cαε), which ranged from 0.0010 (50% tire chips) to 0.0074 (100% tire chips). Time-dependent deformation was inversely proportional to sand content, with the most significant changes resulting from the addition of 15% sand. Both applied stress and tire particle size appear to have a negligible effect on time-dependent compression of TDA. Based on the findings of this study it is recommended that practitioners assess time-dependent settlement when designing a TDA structure and if necessary incorporate design features to accommodate these settlements.     

Compression and Shear Behavior of Mudstone Aggregates

In this paper, a staged compression–immersion–direct shear test was conducted on the compacted samples of crushed mudstone aggregates, and its compressive and shear behavior are discussed with attention to cementation effects. Compression behavior of the compacted samples was influenced significantly by the compaction degree as expected. So were the shear behavior and shear strength. Immersion caused an additional compression and a reduction in mobilized shear stress and in the dilatant nature during shear at low applied pressure levels. Moreover, immersion reduced significantly the peak shear strength parameter c with only a little change in ?. The compression lines and critical state lines of the nonimmersed and immersed specimens seem to parallel each other, and the compression line of the nonimmersed and the critical state line of the immersed form the upper and lower bounds, respectively. A gap between the shear stress–void ratio lines of the specimens with and without immersion can be considered to represent a combined effect of cementation retained in a crushed mudstone aggregate itself and an interlocking effect of aggregates.     

Shredded Tires and Rubber-Sand as Lightweight Backfill

The growing interest in utilizing waste materials in civil engineering applications has opened the possibility of constructing reinforced soil structures with unconventional backfills. Scrap tires are a high-profile waste material for which several uses have been studied, including the use of shredded tires as backfill. A triaxial testing program was conducted to investigate the stress-strain relationship and strength of tire chips and a mixture of sand and tire chips. The test results and additional information from the literature were used in the numerical modeling of wall backfills, both unreinforced and reinforced with geosynthetics. The numerical modeling results suggest tire shreds, particularly when mixed with sand, may be effectively used as backfill.     

Shear Strength of Municipal Solid Waste

A comprehensive large-scale laboratory testing program using direct shear (DS), triaxial (TX), and simple shear tests was performed on municipal solid waste (MSW) retrieved from a landfill in the San Francisco Bay area to develop insights about and a framework for interpretation of the shear strength of MSW. Stability analyses of MSW landfills require characterization of the shear strength of MSW. Although MSW is variable and a difficult material to test, its shear strength can be evaluated rationally to develop reasonable estimates. The effects of waste composition, fibrous particle orientation, confining stress, rate of loading, stress path, stress-strain compatibility, and unit weight on the shear strength of MSW were evaluated in the testing program described herein. The results of this testing program indicate that the DS test is appropriate to evaluate the shear strength of MSW along its weakest orientation (i.e., on a plane parallel to the preferred orientation of the larger fibrous particles within MSW). These laboratory results and the results of more than 100 large-scale laboratory tests from other studies indicate that the DS static shear strength of MSW is best characterized by a cohesion of 15?kPa and a friction angle of 36° at normal stress of 1?atm with the friction angle decreasing by 5° for every log cycle increase in normal stress. Other shearing modes that engage the fibrous materials within MSW (e.g., TX) produce higher friction angles. The dynamic shear strength of MSW can be estimated conservatively to be 20% greater than its static strength. These recommendations are based on tests of MSW with a moisture content below its field capacity; therefore, cyclic degradation due to pore pressure generation has not been considered in its development.     

Effects of Cross Anisotropy on Three-Dimensional Behavior of Sand. I: Stress–Strain Behavior and Shear Banding

The significance of material cross anisotropy in sands is underscored and experimentally evaluated in a series of true triaxial tests on Santa Monica beach sand in a cubical device. Failure patterns, initiation and development of shear banding, and complete stress–strain behavior are described for the entire range of the Lode angle under general three-dimensional loading conditions. Localized failure was found to govern the ultimate resistance of the sand for intermediate values of parameter b = (σ2?σ3)/(σ1?σ3) in each of the three sectors of the octahedral plane. Variations of the friction angle are fully described and show its significant dependence on the inherent cross-anisotropic material structure.     

Large and Small Strain Properties of Sands Subjected to Local Void Increase

Local strain effects are proposed as a source of shear strength reduction in cemented particulate media, shales, and heterogeneous systems. Shear strength degradation through local straining may arise from particle dissolution, double-layer shrinkage in reactive clay phases, and volume change associated with thermal processes. This study focuses on mechanical property changes produced by local straining in particulate systems made of sand–salt mixtures. Local strains were induced by the dissolution of salt particles. Large-strain properties (angle of shear resistance and dilation rate) were measured using triaxial test methods. Small-strain properties (acoustic wave velocity and attenuation) were measured with a resonant column device and piezocrystals (bender elements). Experimental data showed that large-strain properties are sensitive to changes in aggregate volume; a reduction in the angle of shearing resistance up to 26% was observed for a 90% sand–10% salt mixture after salt dislocation. Acoustic wave velocity and attenuation values changed up to 25% during particle dissolution. Fine sand–salt specimens showed smaller changes in macroscopic parameters, compared to coarse-grained specimens. Changes at the microscale assessed using small-strain measurements are clearly reflected at the macroscale as a reduction in the angle of shearing resistance. Finally, it is shown that changes in macroscale parameters produced by internal volumetric strains can be estimated by considering the change in the void ratio and assuming a random distribution of internal strains. However, small-strain parameters cannot be evaluated using the same approach because the microstructure has a stronger effect on wave propagation parameters (velocity and attenuation) than the macroscopic parameters.     

Use of State-Dependent Strength in Estimating End Bearing Capacity of Piles in Sand

The pressure and density dependence of the shear strength of sand poses a tricky problem in pile foundation design. In this study, a correlation is suggested to link the effective friction angle of sand with its initial confining pressure and relative density, and a simple approach incorporating this correlation is presented for predicting pile end bearing capacity. Assessment of the approach against pile load tests shows reasonably good agreement between predictions and measurements. It is also shown that the effect of the state-dependent strength is particularly important in cases where long piles are installed in dense sand deposits and the use of critical state friction angle will produce a conservative prediction in such cases.     

Shear Strength Behavior of Fiber-Reinforced Sand Considering Triaxial Tests under Distinct Stress Paths

The results of drained triaxial tests on fiber reinforced and nonreinforced sand (Osorio sand) specimens are presented in this work, considering effective stresses varying from 20 to 680?kPa and a variety of stress paths. The tests on nonreinforced samples yielded effective strength envelopes that were approximately linear and defined by a friction angle of 32.5° for the Osorio sand, with a cohesion intercept of zero. The failure envelope for sand when reinforced with fibers was distinctly nonlinear, with a well-defined kink point, so that it could be approximated by a bilinear envelope. The failure envelope of the fiber-reinforced sand was found to be independent of the stress path followed by the triaxial tests. The strength parameters for the lower-pressure part of the failure envelope, where failure is governed by both fiber stretching and slippage, were, respectively, a cohesion intercept of about 15?kPa and friction angle of 48.6?deg. The higher-pressure part of the failure envelope, governed by tensile yielding or stretching of the fibers, had a cohesion intercept of 124?kPa, and friction angle of 34.6?deg. No fiber breakage was measured and only fiber extension was observed. It is, therefore, believed that the fibers did not break because they are highly extensible, with a fiber strain at failure of 80%, and the necessary strain to cause fiber breakage was not reached under triaxial conditions at these stress and strain levels.     

Experimental Investigation of the Hydraulic Erosion of Noncohesive Compacted Soils

This paper presents the results of a laboratory investigation whose purpose was to evaluate the effects of compaction on the erodibility of cohesionless soils. By means of a recently developed flume experiment, sediment erosion rates and incipient motion, as a function of shear stress, average velocity, and dry density, have been determined for three compacted sand and gravel mixtures. A preliminary comparison of the incipient motion values shows that granular soils compacted at the Proctor optimum have a higher resistance to free surface flow erosion than those compacted at lower and higher densities. This leads one to infer that the Proctor optimum, generally used as a standard for construction, might also be an optimum for hydraulic resistance and stability. Additional comparison of the experimental data with two commonly used incipient motion criteria also suggests that Yang’s criterion is a better predictor of soil detachment than the Shields-Yalin criterion.     

Foundry Green Sands as Hydraulic Barriers: Laboratory Study

A laboratory testing program was conducted to assess the use of foundry sands from gray iron foundries, typically called green sands, as hydraulic barrier materials. Foundry green sands are mixtures of fine uniform sand, bentonite, and other additives. Specimens of foundry sand were compacted in the laboratory at a variety of water contents and compactive efforts and then permeated in rigid-wall and flexible-wall permeameters to define relationships between hydraulic conductivity, compaction water content, and dry unit weight. Additional tests were conducted to assess how hydraulic conductivity of compacted foundry sand is affected by environmental stresses such as desiccation, freeze-thaw, and chemical permeation. Results of the tests show that the hydraulic conductivity of foundry sand is sensitive to the same variables that affect hydraulic conductivity of compacted clays (i.e., compaction water content, and compactive effort). However, hydraulic conductivities <10?7 cm∕s can be obtained for many foundry sands using a broad range of water contents and compactive efforts, including water contents dry of optimum and at lower compactive effort. The hydraulic conductivity of foundry sand was generally unaffected by freeze-thaw, desiccation, or permeation with 0.1 N salt solution or municipal solid waste leachate, but was incompatible with acetic acid (pH = 3.5). Hydraulic conductivity of foundry sands correlates well with bentonite content and liquid limit, with hydraulic conductivity less than 10?7 cm∕s being achieved for bentonite content ≥6% and∕or liquid limit >20.     

Laboratory Evaluation of Crushed Glass–Dredged Material Blends

A comprehensive laboratory evaluation of blending 9.5?mm (3/8?in.) minus curbside-collected crushed glass (CG) with dredged material (DM) was conducted to evaluate their potential for beneficial use as fill materials for urban applications. Tests were performed on 100% CG (USCS classification SP) and 100% DM (OH) specimens and 20/80, 40/60, 50/50, 60/40, and 80/20 CG–DM blends (dry weight percent CG content reported first). The addition of 20% CG resulted in a 10–20 point (33–67%) reduction in wopt while increasing the dry density by approximately 1–3?kN/m3 for standard and modified levels of compaction, respectively. Simultaneously, the compressibility of the DM was reduced by approximately 50% and the hydraulic conductivity was reduced by ? order of magnitude. The addition of 20% CG significantly decreased the moisture content and significantly improved the workability of the 100% DM, where workability refers to the ease of handling, transport, placement, and compaction of the CG–DM blends (compared to 100% DM). CIū triaxial strength testing indicated effective friction angles of 34 and 37° for 100% DM and CG compacted to a minimum of 95% relative compaction by ASTM D1557, respectively. A peak effective friction angle of 39° occurred for the 60/40 and 80/20 CG–DM blends which were also 1 and 3 orders of magnitude more permeable than 100% DM, respectively. Related increases in cv resulted in decreased times required for consolidation. The range of properties obtainable by the CG–DM blends offers a versatility that allows for the design of fills that can be potentially optimized to meet multiple design parameters (e.g. strength, settlement, drainage, or higher CG or DM content).     

Geological and Physical Factors Affecting the Friction Angle of Compacted Sands

This study evaluated the effects of physical characteristics and geologic factors on the shear strength of compacted sands from Wisconsin that are used as granular backfill for mechanically stabilized earth walls and reinforced soil slopes. Physical properties and shear strength were determined for 30 compacted sands collected from a broad range of geological deposits. Relationships between strength/deformation behavior, geologic origin, and physical properties were used to categorize the sands into four friction angle groups. Sands with the lowest friction angle are derived from weathering of underlying sandstones, and tend to be medium-fine, well-rounded, and poorly graded sands. Sands with the highest friction angle are from recent glacial activity and tend to be coarser grained, well-graded, and/or angular sands. A multivariate regression model was developed that can be used to predict friction angle (?′) of compacted sands from comparable geological origins based on effective particle size (D10), maximum dry unit weight (γdmax), and Krumbein roundness (Rs).     

夯实高饱和度地基土的强度特性

运用改进的非饱和土三轴仪,对某地税大楼强夯后高饱和度地基土进行了控制吸力条件下的固结排水剪切实验.实验结果表明,基质吸力对非饱和土的强度特性有重要影响,抗剪强度参数有效内聚力和有效内摩擦角都与吸力呈良好的线性关系.随吸力增加,有效内聚力呈线性增加,而有效内摩擦角则相应地减小.在实验吸力的范围内,有效内聚力受吸力的影响比有效内摩擦角更明显.而实验土的破坏包线并不是平面,它随净平均应力和吸力的增高而呈收敛状,说明对这种高饱和度击实粉土,当围压加至300kPa以上时,吸力对强度的增长不再明显,此时围压将起主导作用.     

State-Dependent Strength of Sands from the Perspective of Unified Modeling

This paper discusses the state-dependent strength of sands from the perspective of unified modeling in triaxial stress space. The modeling accounts for the dependence of dilatancy on the material internal state during the deformation history and thus has the capability of describing the behavior of a sand with different densities and stress levels in a unified way. Analyses are made for the Toyoura sand whose behavior has been well documented by laboratory tests and meanwhile comparisons with experimental observations on other sands are presented. It is shown that the influence of density and stress level on the strength of sands can be combined through the state-dependent dilatancy such that both the peak friction angle and maximum dilation angle are well correlated with a so-called state parameter. A unique, linear relationship is suggested between the peak friction angle and the maximum dilation angle for a wide range of densities and stress levels. The relationship, which is found to be in good agreement with recent experimental findings on a different sand, implies that the excess angle of shearing due to dilatancy in triaxial conditions is less than 40% of that in plane strain conditions. A careful identification of the deficiency of the classical Rowe’s and Cam-clay’s stress–dilatancy relations reveals that the unique relationship between the stress ratio and dilatancy assumed in both relations does not exist and thereby obstructs unified modeling of the sand behavior over a full range of densities and stress levels.     

Modified Direct Shear Test for Anisotropic Strength of Sand

This paper presents a simple method to estimate the directional dependency of granular soil strength using a modified shear box and a special specimen preparation procedure. This method is used to investigate the strength anisotropy of granular materials with particle shapes varying from spherical to angular. The experimental results show that the friction angle of granular materials varies with the orientation of shear plane relative to the bedding plane, and the degree of anisotropy is affected by particle shape. Comparison of the data from direct shear tests in this study with those of plane strain and torsional simple shear tests in the literature shows that direct shear using the modified direct shear box can reasonably capture the directional dependency of the friction angle for cohesionless materials.