Shear Strength Of Sand Research Articles

Evaluation of Engineering properties of problematic soils using Bacillus pasteurii

Soil improvement method using enzymatic activity from bacteria Bacillus pasteurii that able to catalyse urea and calcium chloride enabling cementation solution has become an emerging approach to increase the shear strength of sand. The production of urease enzyme of B. pasteurii will be increased using specific medium. Determination of the volume of bacteria needed is based on the soil porosity is studied and analysed. The preliminary result of B. pasteurii that use specific medium could increase the urease enzyme activity and already verified using urease measurement kit. The treatment period required for the initiation of production of cementing material (calcite) has been reduced from one month to 3 days, while using this specific medium for enzyme urease production. This leads to the rapid filling of the soil pores that result in the hardening of soil. The bonding between the soil particles also increases that leads to increase in the density of soil. The final results of shear improvement are obtained by conducting Direct shear test and Unconfined compression test on sandy and silty soils respectively. Finally the cohesion between the soil particles was identified through the permeability test.

Desaturation for Liquefaction Mitigation Using Biogas Produced by Pseudomonas stutzeri

Abstract The shear strength of sand increases with decreasing degree of saturation. This study attempts to develop a more effective biogas desaturation method to mitigate liquefaction of sand. The microbial denitrification process of Pseudomonas stutzeri, which produces nitrogen gas, was selected for inducing partially saturated sand. First, research was undertaken to verify the denitrification performance to demonstrate the feasibility of utilizing P. stutzeri. Compared to existing methods using biogas, the reducing time of nitrate and nitrite was less in the proposed denitrifying cultivation. Then, a control method for desaturation was proposed by gas generation tests. To explore the effect of mitigation liquefaction using this method, fully and partially saturated sand specimens were prepared and shaking table simulation tests were performed under a series of cyclic loadings with different acceleration amplitudes. The influence of the initial degree of saturation on excess pore water pressure, pore water pressure ratio, and surface settlement was investigated. Finally, the exponential relationship between volumetric strain and average pore water pressure ratio was established for fully and partially saturated sand specimens.

Influence of relative density on the cyclic shear strength of sands

This paper presents a laboratory study of the influence of relative density on the liquefaction potential of a soil. The study is based on undrained triaxial tests that were performed on samples with relative density Id = 0.15, 0.5 and 0.65. The article is composed of three parts. First, we present the materials and characteristics of the studied sands. the second part deals with the procedure and the device used. The third part studies the influence of the relative density on the liquefaction potential of the three sands (Hostun Rf, Chlef and Rass). This study also makes it possible to explore the influence of granulometry on the liquefaction potential. The results of the tests show that concordant results have been obtained which clearly show that the increase of the relative density leads to a significant improvement in the resistance to liquefaction of the sands. This effect is very significant when the initial relative density Id = 0.50 to Id = 0.65.

Influence of relative density on the cyclic shear strength of sands

This paper presents a laboratory study of the influence of relative density on the liquefaction potential of a soil. The study is based on undrained triaxial tests that were performed on samples with relative density Id = 0.15, 0.5 and 0.65. The article is composed of three parts. First, we present the materials and characteristics of the studied sands. the second part deals with the procedure and the device used. The third part studies the influence of the relative density on the liquefaction potential of the three sands (Hostun Rf, Chlef and Rass). This study also makes it possible to explore the influence of granulometry on the liquefaction potential. The results of the tests show that concordant results have been obtained which clearly show that the increase of the relative density leads to a significant improvement in the resistance to liquefaction of the sands. This effect is very significant when the initial relative density Id = 0.50 to Id = 0.65.

The influence of non-plastic fines on pore water pressure generation and undrained shear strength of sand-silt mixtures

An extensive experimental study was undertaken to investigate the influence of non-plastic fines on pore water pressure generation and undrained cyclic shear strength of sand–silt mixtures. For this purpose, stress-controlled undrained cyclic simple shear (CSS) tests were carried out on reconstituted specimens of Ticino silica sand under different combinations of fines content (FC) and global void ratios (e). The applicability of several models suggested in literature for predicting cyclic residual excess pore water pressure generation in non-plastic silty soils was analyzed, and revised correlations for assessing model parameters were proposed. Finally, the study confirmed that the equivalent granular void ratio (e*) is an effective and appropriate parameter for characterizing the behavior of sand with fines up to a threshold value of fines content of sand-silt mixtures, and cyclic resistance ratio (CRR) of the mixtures can be well correlated with e*, irrespective of their fines contents and void ratios.

Effect of nonplastic silt content on undrained shear strength of sand\u2013silt mixtures

To assess the behavior of sand–silt mixtures, strain-controlled monotonic triaxial tests were conducted on sand–silt mixtures of specimen size 71 mm in diameter and 142 mm in height at various relative densities but same isotropic effective confining pressure of 100 kPa. Concept of limiting fines content (LFC) was verified by these undrained monotonic triaxial tests. LFC was found to be the very important parameter to understand the behavior of sand–silt mixtures. The behavior of sand–silt mixture changes approximately at LFC. At constant relative density, increase in silt content decreases the undrained peak shear strength till LFC. After LFC the strength becomes near about same till pure silt sample. The reason of behavior could not be explained. At constant global void ratio, the peak shear strength decreases with increase in silt content till LFC and for further increment of silt content the peak shear strength increases. Sand–silt mixtures containing certain amount of silt which is near to the LFC showed flow type as well as brittle behavior. Failure of structure on this type of soil will be catastrophic during earthquake. In the case of permeability decreased with increasing silt content up to LFC. After the LFC, dry density is decreasing with increasing silt content but permeability remains constant till pure silt.

Prevention of Liquefaction of Saturated Sand Using Biogas Produced by Pseudomonas stutzeri

Shear strength of sand increases with the decrease of saturation degree. An attempt to develop a more effective biogas desaturation method is made in this study. The microbial denitrification process of pseudomonas stutzeri, which is able to produce nitrogen gas, is selected for the desaturation of liquefiable sand. Frist, to demonstrate the feasibility of induced-partial saturation using nitrogen gas bubbles produced by pseudomonas stutzeri, research on denitrification condition and efficiency are made. The suitable range of temperature is determined. Comparing with existing method using biogas, this bacteria has advantages including faster average rate of generating gas, shorter initial stagnation period and simple technology. Then, to explore the effect of mitigation using this method, full and partially saturated sand samples are prepared and serial of shaking table simulation tests are performed under applying a series of cyclic loading with different acceleration amplitude. The influences of initial samples saturation on the excess pore water pressure, pore pressure ratio and surface settlement are investigated. Finally, the exponential relationship between volumetric strain and average pore water pressure ratio is established for full and partial saturated samples.

Effect of granulated rubber on shear strength of fine-grained sand

Review of the literature related to the mixture of shredded tire and sand shows that, despite of the increase in shear strength due to addition of tire chips, granulated rubber causes reduction in shear strength of sand. In this study, the shear behavior of mixtures of fine-grained sand and 1–5 mm granulated rubber is investigated. Sixty direct shear tests were conducted on sand–granulated rubber mixtures with various rubber contents (0%, 5%, 10%, 20% and 30%) at different relative densities (50%, 70% and 90%) and different normal stresses (34.5 kPa, 54.5 kPa, 74.5 kPa and 104.5 kPa). The obtained results show that the granulated rubber improves the shear strength of fine-grained sand at medium relative density and low normal stress. The degree of improvement in shear strength is a function of rubber content, relative density and normal stress. The results show that at relative density of 50%, by adding 5% granulated rubber, the internal friction angle of sand increases from 35.1° to 39.2°. However, at relative densities of 70% and 90%, addition of granulated rubber to sand decreases its internal friction angle. The results also indicate that the behavior of sand becomes more ductile with increasing granulated rubber content. Adding granulated rubber leads to greater yielding strain and less tangent stiffness of sand. The maximum dilation angle decreases with the decrease in granulated rubber content. The stress ratio of sample at critical state (ψ = 0°) decreases with increasing granulated rubber content.

Experimental study of the shear resistance of granular material: influence of initial state

The shear strength of sand and its mechanical properties can be affected by numerous para- meters. This work presents an experimental investigation which aims to study the influence of the fines content, the depositional method and the grain size on the shear strength of Chlef sand. Tests were conducted with the shear box on two types of soil, the natural sand and the clean sand-silt mixture. Dense samples (Dr = 88%) were reconstituted through dry deposition for each type of the material. An additional series of tests was carried out on a medium dense natural sand (Dr = 52%) prepared by dry and wet (w = 3%) deposition methods. All specimens were subjected to normal stresses of 100 kPa, 200 kPa and 300 kPa and there was no immersion of water. The tests results show that the behavior of sand can be affected by three parameters, the fines content, the deposition method and the particle size. The maximum shear stress and the friction angle decrease as the fines content increases, the initial water content increases, the effective grain size diameter decreases and the uniformity coefficient increases. The cohesion intercept increases with the increasing fines content and decreasing initial water content. Overall, the samples prepared by the dry deposition me- thod show more resistance than those prepared by the wet deposition method. The results obtained are generally in agreement with the previous research on drained and undrained saturated sand in the literature.

Mechanical Behavior of Waste Tire Crumbs–Sand Mixtures Determined by Triaxial Tests

In the last three decades, the use of scrap tires in a number of forms such as whole tires, shredded, chips, ground tire or powder tire shapes has already been common in many geotechnical applications. One of the main reasons of using shredded tires is the fact that it is cost-effective and environmental concerns. While, scrap tire improves sand behavior; so, it is suitable to transform tire to shredded for using in many industrial applications. In this research, in order to investigate the behavior of the tire-sand mixtures (small tire crumbs), drained triaxial tests have been performed. Effects of parameters such as size of tires, tire content (by weight) and confining pressure on the sand’s behavior have been studied. For achieving this objective, two sets of tire (granulate and powder tire), four various tire contents (5, 10, 20 and 30%) and three confining pressures (50, 100 and 200 kPa) have been employed. The test results showed that unlike some previous studies in which tire crumbs act as reinforcement and increase shear strength of sand–tire mixtures, shear strength mixtures have been found to decrease with the increase in the amount of tire crumbs. This study concentrates on the stress–strain and volumetric strain behavior of the tire-sand mixtures. Moreover, the angle of friction, cohesion and elastic modulus for each mixture are presented.

Effect of silt on post-cyclic shear strength of sand

Adding non-plastic fines to sand can greatly change its behavior. Size difference between sand and silt particles is the main reason which causes this change. While post-cyclic and post-liquefaction behavior of clay and clean sand has been widely studied, silty sand is wrongly considered to behave like clean sand and researches usually do not focus on it. In silty sand, through low cohesion, applying cyclic load can displace particles and result in heterogeneity within the mixture. Even if liquefaction does not occur, rearrangement of soil particles can affect monotonic ultimate strength. This study, with a series of post-cyclic monotonic triaxial tests, has shown that in sand with a considerable amount of silt, cyclic loading can change the ultimate state strength. In sand with 15% silt it decreases and in sand with 30% silt it increase the ultimate state strength. Changes are negligible in clean sand or sand with 5% silt.

The Effect of Polymer-Fiber Stabilization on the Unconfined Compressive Strength and Shear Strength of Sand

The mixed soil stabilizer of polyurethane organic polymer and polypropylene fiber was used to reinforce sand. The unconfined compressive test and direct shear test were carried out to evaluate the effects of polymer-fiber reinforced sand. The different contents of polymer and fiber were selected for the tests. The test results indicated that polymer-fiber mixture can improve strongly the strength of sand. The presence of polyurethane organic polymer enhances sand structural stability and the best composition of polymer and fiber was 4% and 0.2–0.3% of dry sand, respectively. Based on the test results and images of scanning electron microscope (SEM), the reinforcement mechanism was analyzed. The research results can be considered as the reference for sand reinforced engineering.

Influence of fibers on the shear strength and dewatering performance of geotextile tubes

Geotextile tubes have been widely used for the dewatering of high water content fine sediments. Fine sediments include lake sediments, organic soils and coal combustion products, which generally have low shear strength. Several researchers have emphasized the effect of the retained sediment (filter cake) properties on dewatering performance and stability of the geotextile tubes. Maintaining retained sediment properties, in particular permeability and shear strength, allows for faster dewatering time, better retention of sediments and improved stability of the geotextile tubes during multiple filling stages and during the tube stacking process. Several studies have shown that the use of synthetic fibers can increase the shear strength of sand, silt and clays. However, the use of fibers to improve the strength of retained sediments in geotextile tubes has not been explored. In this study, three synthetic fibers varying in length and diameter were used to evaluate the effect of fibers on the dewatering performance and shear strength of the fine sediments. A cationic polyacrylamide flocculant was used as an optimum conditioner for the selected sediment. The fibers were mixed with the flocculant conditioned slurry at 0.25, 0.5, 1 and 2% fiber concentration by mass of the dry solids. The effect of fibers on the undrained shear strength of the dewatered sediments was evaluated using a lab vane test, fall cone test and undrained unconsolidated triaxial test. Jar tests and pressure filtration tests were also conducted to evaluate the effect of fiber on the required flocculant dosage and on the dewatering performance. Based on the results of this study, 0.5% of F1 fiber type was found to be the optimum fiber concentration, yielding an approximately 100% increase in undrained shear strength. It was also found that the diameter and length of the fibers play a significant role in altering the undrained shear strength of the tested sediments. The relatively short (6 mm) and thick (38 μm) fiber did not yield an increase in shear strength for all the tested fiber concentrations, whereas thin fibers (9 μm) of similar length increased the shear strength by 100%. Furthermore, it was found that the use of fibers at any concentration decreases the required optimum doses of flocculant by about 15%, and increases the dewatering rate of the effluents by about 50%.

Effects of sulphuric acid pollutant on the shear behaviour and strength of sandy soil and sand mixed with bentonite clay

Mixture of sandy soil and bentonite clay can be used to seal the sanitary landfills and prevent the spread of leachate. Over time, this mixture may be subjected to different landfill contaminants, including acidic pollutants and shear strength variations. The objective of this research was to study the effects of sulphuric acid pollutant with pH values of 7, 3 and 1 on the shear behaviour and strength of clean sand and sand mixed with bentonite clay using common consolidated undrained triaxial tests. The tests results showed that the presence of acid in the soil pore water changes the shear behaviour pattern of the soil. Acid pollutant decreases the clean sand shear strength. In sand–bentonite mixture, the presence of sulphuric acid with a pH of 3 results in an increase in the shear strength, and with a pH of 1, it results in a decrease. Acid pollutant decreases the elastic modulus of the soil and increases the negative pore water pressure generated during shear.

Specimen size effects on direct shear test of silty sands

The main objective of this study is to investigate the effect of the scale factor on the shear strength of sands with different silt contents. For this purpose, the samples of Firouzkooh sand with 0, 10, 20 and 30% silts percentages are prepared at their maximum dry densities with corresponding optimum moisture content (Silt percentages are by weight). Direct shear tests are performed with three different shear box sizes (60 × 60, 100 × 100 and 300 × 300 mm). Results indicate that the peak shear strength and the peak friction angle decreases with increasing the shear box size while residual shear strength is constant. Also increasing the silt percentages caused a decrease in the peak shear strength. The results show that the reduction rate in friction angle decreases with increasing the box sizes and increasing the silt content.

DETERMINING CHARACTERISTIC SAND SHEAR PARAMETERS OF STRENGTH VIA A DIRECT SHEAR TEST

The article considers the peculiarities of determining quartz sand shear strength according to the Mohr-Coulomb strength criterion, via a direct shear test and that of factors influencing the characteristic angle of internal friction and cohesion values of the obtained strength parameters. The air-dry sand of the Baltic Sea region from Lithuanian coastal area near Klaipėda city has been analyzed. The solid density of the investigated sand grains was ρs = 2.65 g/cm3. The initial density of the tested samples made ~1.48–1.50 g/cm3. Processing data on the shear test yielded that the quantity of 18 tests was sufficient for the relevant accuracy of determining characteristic sand shear parameters of strength. This quantity of tests allow avoiding the influence of statistical coefficient tα that depends on a degree of freedom (K = n – 2). The paper presents additionally analyzed three different approaches to determining the characteristic shear parameters of strength and that of a comparative analysis of the applied approaches.

Influence of fines content on the undrained cyclic shear strength of sand–clay mixtures

A series of undrained cyclic triaxial tests were performed on sand–clay mixtures with various sand–clay mixing ratios. Prior to the primary tests, the threshold fines content was examined by consistency tests, which was found to be approximately 20%. For sand–clay mixtures with a sand-matrix (fines content less than the threshold fines content), the cyclic shear strength of low-density mixtures increases and that of high-density mixtures decreases with increasing fines content. However, for sand–clay mixtures with a fines-matrix (fines content greater than the threshold fines content), there exists a unique correlation between the cyclic shear strength and global void ratio for different fines content. The equivalent granular void ratio is introduced in this paper to account for the contribution ratio of the fines to soil skeleton. As a result, a unique relationship between cyclic shear strength and equivalent granular void ratio was observed for pure sand and sand–clay mixtures with a sand-matrix.

Fiber-reinforced sand strength and dilation characteristics

Abstract Randomly distributed fiber reinforcement is used to provide an isotropic increase in the sand shear strength. The previous studies were not consistent regarding the fibers effect on the volumetric change behavior of fiber-reinforced sand. In this paper, direct shear tests are conducted on 108 specimens to investigate the effects of the fibers content, relative density, normal stress and moisture content on the shear strength and volumetric change behaviors of fiber-reinforced sand. The study investigates also the possibility of using dry fiber-reinforced sand as an alternative to heavily compacted unreinforced moist sand. The results indicate that the fibers inclusion increases the shear strength and dilation of sand. Moisture suppresses the fibers effect on the peak and post-peak shear strengths, and dilation. Dry loose fiber-reinforced sand achieves the same shear strength of heavily compacted unreinforced moist sand, yet at more than double the horizontal displacement.

Reply to “Discussion of ‘Experimental investigation of shear strength of sands with inherent fabric anisotropy’ by Tong et al. (DOI 10.1007/s11440-014-0303-6)” by Gao (DOI 10.1007/s11440-015-0383-y)

The authors read with interest the discussion of their paper by Dr. Zhiwei Gao. The discusser correctly points out that a general failure criterion without a priori knowledge of the failure plane can be used in general analysis, while a criterion addressing failure at a specific plane is more restricted. However, the latter criterion is more practical for problems where the failure plane is known, and its parameters can be directly determined by the direct shear test which is relatively easy to perform. It must be pointed out that our paper does not propose such a criterion explicitly, but it lays down the experimental evidence and foundation for such a possible proposition. Having said that, we pleasantly notice that the simulations of the model of the discusser agree with, in every aspect examined, our experimental data, both the ones obtained earlier by DEM [1] and the ones on real sand samples of the paper under discussion. It should be mentioned that the model used by the discusser is based on the recently developed Anisotropic Critical State Theory (ACST) by Li and Dafalias [2] that brings into the picture the role of fabric on the response of granular media, and enhances the classical Critical State Theory (CST) by one more condition on the critical state value of the fabric (in fact Y. F. Dafalias is a co-author of that paper that develops the model). There are a few additions to the brief presentation that may interest the soil modeling community. We hope the discusser may consider these in the future.

Drained shear strength of compacted sand with clayey fines

The drained shear strength of silty sands and clayey sands is not well studied although sands with fines are encountered in many geological settings. There are limited studies that investigate the drained shear strength of sands with fines and their impact on the stability of geotechnical systems that are supported on these soils. The objective of this paper is to investigate the impact of replacing 10–40% of pure Ottawa sand with natural clay of intermediate plasticity on the drained shear strength of the composite. To achieve this objective, consolidated drained direct shear tests were conducted on pure sand specimens and specimens that included mixtures of sand and clay. Results indicate that the drained friction angle of Ottawa sand decreases from 36·2° to 20·2° and the drained cohesion increases from 0 to 7·7 kPa because of the replacement of 40% of the sand with clay. Examples that target the design of square footings and the stability of infinite slopes indicate that the allowable bearing capacity of footings and the factor of safety of slopes decrease significantly as the percentage of fines is increased from 0 to 40%.