Undrained Direct Shear Tests Research Articles

Strength Characteristic of Lightweight Modular Block (LMB) Element using Stabilized Dredged Soil-EPS

For several decades, lightweight material applications have been extensively studied. Modifying various types of soil with EPS beads or lightweight geomaterials is an alternative construction material on site that can reduce excessive problems such as large deformation and lateral pressure. This study aims to examine the strength characteristics of lightweight geomaterials, namely lightweight modular block/LMB. LMB is composed of EPS beads, dredged soil, and cement. The cement amounts are 3%, 5%, 7%, and 9%, with EPS variations of 0.5% and 0.75% to the mixture weight. Laboratory tests were conducted to investigate the strength with unconfined compression and undrained direct shear tests. Before testing, the specimens were made using the one-layer static compaction method and were cured for 7, 14, and 28 days. This paper also presents explanations related to the specimens making and treatment by providing preliminary test results to compare the effectiveness of the three-layer and one-layer methods. Moreover, the curing treatments to avoid cracking were explained explicitly. The result shows linearity between both increasing the amount of cement and adding more curing time to the increase of the strength parameter. In contrast, adding more EPS decreased the strength, but adding cement helped increase the strength parameter with a remarkable value at C7% and C9%. Increasing the amount of EPS also reduced the density of the mixture by 18%–29%. Doi: 10.28991/CEJ-2023-09-03-014 Full Text: PDF

Mechanical Properties of Frozen Glacial Tills due to Short Periods of Thawing

Due to the warming climate, glacier retreat has left massive glacial tills in steep gullies; ice in the soil is prone to change phase resulting in the decrease of the ice strength and bonding of soil particles; collapse of thawing tills can lead to debris flows with disastrous consequences for geotechnical infrastructures. To improve our understanding of the mechanics of thawing glacial tills, we conducted unconsolidated–undrained direct shear tests on glacial tills from Tianmo gully on the southeastern Tibetan Plateau. Control specimens were not subjected to freeze–thaw action. A total of 648 specimens with three different dry densities, three initial water contents, and 18 thawing times were tested. Peak shear strength, peak stress to displacement ratio (0.857), and cohesion were the highest in frozen specimens. After a thawing time of 0.25 h, there was a marked decline in shear strength; maximum friction was 2.58, which was far below the value of cohesive strength. For thawing times of 0.25–4 h, peak strength varied little with thawing time, but cohesion decreased and internal friction angle increased with increasing thawing time. Our results indicate that thawing of the solid ice in the till during the initial phase of till thawing is the key control of peak till strength; the effect of ice on cohesion is greater during the initial phase of thawing and in loose tills. Moreover, frequent sediment recharge of gullies may be explained by the decrease of cohesion with increasing thawing time caused by short-term destruction of ice bonding.

Peak shear strength of compacted GMZ bentonites in saline solution

Knowledge of the peak shear strength of compacted bentonites is of fundamental importance to high-level nuclear waste repositories, as it forms the basis of the analysis of repository stability. The shear strength properties of GMZ bentonites are throughout investigated by undrained direct shear tests with different concentrations of NaCl solutions, and are explained in the light of the modified effective stress concept, which takes into consideration of the osmotic suction. The modified effective stress concept is expressed as p’ = p + π(p/π)Ds-2, incorporated with the normal stress (p) and osmotic suction (π) based on the bentonite surface fractal model. The peak shear strength behavior of GMZ bentonites in NaCl solutions appears to be explained satisfactorily by the modified effective stress. According to the Mohr-Coulomb criterion, the peak shear strength of bentonites saturated by distilled water and NaCl solutions is expressed by the same unique line in the τ-p’ plane. GMZ bentonite has the same values of the peak friction angle and the peak cohesion in distilled water and NaCl solutions of different concentrations.

Analysis of acoustic emissions recorded during a mine-by experiment in an underground research laboratory in clay shales

During a mine-by experiment performed at the Mont Terri Underground Research Laboratory located at the transition between the sandy and the shaly facies of the Opalinus Clay formation, excavation induced micro-acoustic events were recorded in the so-called Gallery 08 (the EZ-G experiment). A first cluster of events occurred in the vicinity of the eastern sidewall of Gallery 08, and a second cluster was observed ahead of the advancing tunnel face. For each recorded micro-acoustic event (AE), all located in the sandy facies of the Opalinus Clay formation, the total stresses associated with the onset of inelastic deformations were estimated using a three-dimensional numerical model. The numerical analysis is based on the assumption that the rock mass behavior in the vicinity of the excavation is essentially elastic before the stress redistribution causes damage evidenced by the triggered AE activity. For the cluster located at the tunnel sidewall, the source mechanism analysis reveals the predominance of extensional failure (tensile) events. The numerical analysis of each individual micro-acoustic event suggests that the differential stresses at the onset of damage range between 3 and 10 MPa. These values are in reasonable agreement with crack initiation thresholds obtained in the laboratory from samples of the various sub-facies types of the sandy facies in the Opalinus Clay formation, which range between 2 and 18 MPa. For the cluster located ahead of the tunnel face, the source mechanism analysis indicates the predominance of local shear failure events. This is consistent with observed shear dislocations on bedding planes within weak beds in the sandy facies that have similar strength properties as the shaly facies. Thus, the modelled shear and total normal stresses acting across the average bedding plane orientation at each event location were modelled and used to estimate the in situ shear strength along the bedding planes. The model suggests a friction angle of 33.4° and a cohesion of 0.43 MPa. The results are overall consistent with the bedding plane strength obtained through undrained direct shear tests on specimens of the shaly facies, suggesting that the observed weak beds with a strength similar to the shaly facies govern the behavior at the tunnel face.

Evaluation of Freezing-Thawing Cycles for Foundation Soil Stabilization

Freezing-thawing cycles in soils reduce considerably the foundation capacity of buildings and infrastructure. In recent years, development of nontraditional stabilizers has created hundreds of new products for soil stabilization. Fiber portions of biomass (such as lignin) can be considered as byproducts of the conversion process, and these byproducts are generally used to produce octane booster fuels, bio-based products, and other chemical products. The use of lignin-based biofuel co-products (BCPs) to stabilize pavement subgrade soil is an innovative idea and satisfies the needs of sustainable development in construction. A series of laboratory tests, including unconsolidated undrained direct shear test, freeze-thaw durability test, and scanning electron microscope tests, was conducted to evaluate the effect of BCP addition on shear strength performance for four different soils encountered in Iowa. The results of this study indicate that BCPs are beneficial in the soil stabilization of low-quality materials for use in road construction.

Effect of Fibercast and Fibermesh inclusion on the direct shear and linear shrinkage response of clay

Inclusion of synthetic fibers is becoming a routine task in soil reinforcement. The ability of synthetic fibers in controlling the shrinkage cracks in concrete is the main drive to consider its benefits in clay and other soil materials. The polypropylene fibers are nonbiodegradable and can perform well even in aggressive chemical exposure conditions. The direct shear testing is a popular geotechnical approach to assess the shearing strength for a range of soils. This study is aimed at investigating the effect of fiber inclusion on the direct shear response of semi-arid clay soils. This research is conducted using two different types of polypropylene fibers, viz., Fibercast and Fibermesh, having different surface properties on the shear strength envelope and parameters (angle of internal friction and cohesion). The aspect lengths were varied as 6 and 12 mm, and the dosages were varied as 0.2, 0.4, and 0.6 % by weight of the soil. The results were viewed in relation to the fiber type, size, and dose. The soil response and shear resistance measured in consolidated undrained direct shear test is presented for the targeted doses, and the results revealed useful insight compared to unreinforced. The Fibermesh material proved to be the more appropriate fiber additive to typical semi-arid clay soils. The data provides helpful guide for the design geotechnical engineers.

Shear strength of landfills

Landfills are engineering structures formed with a specific material, whose shear strength properties can be determined in a similar way, as it is done for a geotechnical material. This paper presents results from an experimental program carried out to obtain the strength parameters for Presidente landfill at Valle del Cauca (Colombia). The experimental program included unconsolidated undrained direct shear tests (UU) performed on laboratory reconstituted samples. Variation of the internal friction angle and cohesion, as a function of the specific weight, depth and decomposition time of the landfill was evaluated. Results were also compared to international values used for design purposes. Results showed a remarkable influence of the waste decomposition time in the shear strength. Some relationship with the depth was also found. Obtained strength parameters are within international ranges recommended for design purposes.

Prediction of unsaturated shear strength of an adobe soil from the soil–water characteristic curve

This paper studied the unsaturated shear strength properties of a soil with the gradation characteristics of the material typically used in adobe construction. The main goal was to predict the unsaturated shear strength of the adobe soil using the soil–water characteristic curve (SWCC) and the effective cohesion and friction angle of the material. Specimens were trimmed from adobe bricks made according to the traditional technique of the southwestern region of the United States. The SWCC of the adobe soil was constructed using data obtained with the filter paper test. The effective cohesion and friction angle were found to be 11.7kPa and 31.4°, respectively, from the results of consolidated drained direct shear tests. In addition, unconsolidated undrained direct shear tests were done on specimens at different water contents to determine the apparent shear strength parameters. The predicted shear strength was found to increase significantly with decreasing water content, and the strength increase was approximately 350kPa between near saturation condition and water content of 6.01%. The predicted failure envelopes in the shear strength–matric suction plane were nonlinear; their initial slope was close to the (saturated) effective friction angle, and the slope decreased as the suction increased.

Use of Biofuel Co-product for Pavement Geo-materials Stabilization

Lignocellulosic biomass contains abundant cellulose, hemicellulose and lignin. Ethanol production, which utilizes cellulosic and hemicellulosic fractions of the lignocellulosic biomass, is obtained from the transformation of fermentable sugar. In this case, other fiber portions of biomass like lignin can be considered as byproducts during the conversion process, and these byproducts generally are used to produce octane booster fuels, bio-based products, and chemical productions.For reduction of soil stabilization costs, utilization of lignin-based BCPs (biofuel co-products) as an alternative to stabilize pavement subgrade soil is an innovative idea, and satisfies the needs of sustainable development of construction.This study aims to investigate the utilization of biofuel co-products (BCPs) containing lignin in pavement geo-materials stabilization. Laboratory tests were conducted to evaluate the effect of BCP addition on shear strength performance for a wide range of soils encountered in Iowa. The unconsolidated undrained direct shear test (DST) was used to evaluate shear performance.The results of this study indicate that Biofuel Co-Products are beneficial in the soil stabilization of low quality materials for road construction use.

Cement and lime mixture stabilization of an expansive overconsolidated clay

Urban areas of the wilaya of M'sila in Algeria nowadays experience a considerable development because of an unceasingly increasing demography, from where its extension towards virgin zones often less favorable than those already urbanized. This wilaya is located in a zone classified as semi-arid, whose geology comprises clayey formations characterized by a high variation of volume when the conditions of their equilibrium are modified (natural climatic phenomena due to a prolonged dryness, human activity by modification of the ground water level because of excessive pumping, configuration of constructions in their environment). This paper presents and analyzes the results of a series of normal Proctor compaction tests, methylene blue tests, California bearing ratio tests and undrained direct shear tests performed on Sidi-Hadjrès expansive overconsolidated clay treated with mixture of various cement and lime contents and compacted under the optimum Proctor conditions. These test results show that the geotechnical parameters values are concordant and confirm the bearing capacity improvement of this natural clay, which is translated by a significant increase in soil strength and its durability. However, the best performances are obtained for a mixt treatment corresponding to 8% cement and 4% lime contents.

Shear strength behaviour of polypropylene fibre reinforced cohesive soils

Soil reinforcement through the inclusion of oriented or randomly distributed discrete elements such as fibres has recently attracted increasing attention in geotechnical engineering. Therefore, the purpose of this paper is to investigate the influence of certain parameters (the strength properties of the fibre, the relative size of the fibres and grains, and the rate of shear) on the shear strength of polypropylene fibre reinforced cohesive soils. A series of consolidated drained or undrained direct shear tests were conducted on unreinforced and reinforced sandy silt and silty clay specimens. Two types of polypropylene fibres with different mechanical indices were used. The fibre content was varied between 0.3% and 1.1% by weight of dry soil. The test results revealed that the inclusion of fibres in soil significantly increases the shear strength. The attainment of the high shear strength is attributed to the micromechanisms involved in the fibre/soil interactions as studied through scanning electron micrographs. The results also showed that the reinforcement effect was more pronounced under undrained shearing conditions. An important outcome from the current work is that, from the data obtained, the strength of the reinforced soil composites is not practically affected by the fibre mechanical indices.

Further study of geomembrane/cohesive soil interface shear behavior: K. L. Fishman & S. Pal, Geotextiles & Geomembranes, 13(9), 1994, pp 571–590

Abstract The results presented in this paper contribute to an existing data base on the shear strength of geomembrane/cohesive soil interfaces. Three different clay materials are studied, and the interfaces include both smooth and textured HDPE geomembranes. Consolidated drained and consolidated undrained direct shear tests were performed on samples compacted wet of optimum under both partially saturated and saturated conditions. The effect of rate of shear is studied through a range from 12·7 mm/min to 0·005 mm/min (0·5 in/min to 0·0002 in/min). The shear strength of textured geomembrane interfaces during drained shear loading was equal to or less than that of the clay alone, and the consolidated undrained shear strength was higher than for the clay alone. Deformations during shear were studied and used to explain the variation in shear strength due to the rate of shear loading for textured geomembrane/clay interfaces.

Further study of geomembrane/cohesive soil interface shear behavior

The results presented in this paper contribute to an existing data base on the shear strength of geomembrane/cohesive soil interfaces. Three different clay materials are studied, and the interfaces include both smooth and textured HDPE geomembranes. Consolidated drained and consolidated undrained direct shear tests were performed on samples compacted wet of optimum under both partially saturated and saturated conditions. The effect of rate of shear is studied through a range from 12·7 mm/min to 0·005 mm/min (0·5 in/min to 0·0002 in/min). The shear strength of textured geomembrane interfaces during drained shear loading was equal to or less than that of the clay alone, and the consolidated undrained shear strength was higher than for the clay alone. Deformations during shear were studied and used to explain the variation in shear strength due to the rate of shear loading for textured geomembrane/clay interfaces.

Behaviour of normally consolidated clay as observed in undrained direct shear tests : Wroth, C P GeotechniqueV37, N1, March 1987, P37–43

Behaviour of normally consolidated clay as observed in undrained direct shear tests : Wroth, C P GeotechniqueV37, N1, March 1987, P37–43

The behaviour of normally consolidated clay as observed in undrained direct shear tests

The direct shear test as conventionally used for measuring the strength parameters of soil for use in classical stability analyses has the major disadvantage that the stress conditions in the specimen during the test are not known. The shear stress and normal stress acting on the central (horizontal) plane of the specimen are deduced from the observations made on the boundary; the values measured at failure are assumed to lie on the Mohr-Coulomb failure envelope from which the strength parameters are derived. Two special types of apparatus that apply simple shear allow measurements to be made from which the complete stress system (assumed to be uniform) within the specimen can be deduced. The effective stress paths obtained in shear tests on two normally consolidated clays reveal complex patterns of behaviour. In particular, they show that the conventional interpretation of the direct shear test is wrong; the stress point associated with the horizontal plane at failure does not lie on the failure envelope and the maximum shear stress is not the same as the undrained shear strength. L'essai de cisaillement direct employé traditionnellement pour mesurer les paramètres de résistance du sol pour les analyses classiques de stabilité a un grave défaut: les conditions de contrainte dans l'échantillon au cours de l'essai ne sont pas connues. La contrainte de cisaillement et la contrainte normale agissant sur le plan central (horizontal) de l'échantillon sont déduites des observations effectuées à la limite et on admet que les valeurs mesurées lors de la rupture sont situées sur l'enveloppe de rupture Mohr-Coulomb, à partir de laquelle les paramètres de résistance sont calculés. Deux appareils spéciaux, qui appliquent le cisaillement simple, permettent des mesures à partir desquelles on peut déduire le système entier supposé uniforme des contraintes dans l'échantillon. Les chemins de contraintes effectives obtenus dans deux essais de cisaillement sur deux argiles normalement consolidées montrent un comportement complexe et plus particulièrement ils indiquent que l'interprétation traditionnelle de l'essai de cisaillement direct est erronée: le point de contrainte associé avec le plan horizontal lors de la rupture n'est pas situé sur l'enveloppe de rupture et la contrainte de cisaillement maximale n'est pas identique à la résistance à la rupture au cisaillement dans l'état non-drainé.

The engineering properties of rice‐hull‐ash as a soil stabilizer

Click to increase image sizeClick to decrease image size Abstract The study of an effective utilization of rice hull ash, which is produced 100,000 tons per year in Taiwan, becomes necessary. This study investigates the uses of rice hull ash with lime as a soil stabilizer admixture. The primary purposes were to study the compaction characteristics and the factors affecting the strength development of the lime‐ash stabilized sandy and clayey soils. Standard compaction test and undrained direct shear test were carried out. Results showed that adding rice hull ash into a soil increased the effectiveness of lime. Lime‐ash admixture caused the compacted dry density of a soil to decrease but the as‐compacted strength to increase. The shear strength of a lime‐ash stabilized soil increased with curing time, but reduced when soaked. The optimum lime‐ash weight ratio of soils was found to be 1:2 or 1:3. To produce equivalent strength values, the percentage of lime requirement could be reduced by adding rice hull ash.