Mechanical behavior of sandy soil reinforced with naturals and synthetics fibers: A laboratory study

Introduction: This paper presents an experimental investigation that aims to study the influence of silt content, glass fiber content, and their combined effect on the shear behavior of silty sand. For this purpose, a series of tests using direct shear apparatus (as methods) were carried out on sand mixed with various silt and fiber contents. Samples were prepared with a relative density of 50 %, and each mixture was tested at three different normal stresses. The experimental results indicated an increase in shear strength at 10 % silt content, followed by a decrease in shear strength with increasing silt content from 10 % to 30 %. It was also found that 0.5 % is the optimal content that can be added to sand-silt mixtures to enhance their shear strength and friction angle, although the mixtures become more contractive.

Direct shear box tests were carried out in order to evaluate the effect of different types of randomly distributed fibres; two synthetic fibres (Polypropylene and Glass fibre) and one natural fibre (Sisal fibre) on the improvement of Chlef sandy soil shear strength. All of the inclusions were randomly distributed in the soil mass with a length of 12 mm and fibre contents of (0, 0.25, 0.5, 0.75 and 1% by dry soil mass). Samples were prepared at a relative density of 50% representing medium dense state and performed at normal stresses of 50, 100 and 200 kPa. The present work is conducted in order to study the effect of material properties and fibre content on the shear strength of sand. The experimental results show that all types of fibre greatly improved the shear strength, cohesive intercept and friction angle of Chlef sand. However, samples reinforced with sisal fibres have shown a more pronounced increase in strength parameters than those reinforced with glass or polypropylene fibres. The effect of the soil initial state was also discussed.

Soil reinforcement is an efficacious technique for improvement of soil behavior against applied loads and deformations. In recent years, synthetic fibers have been introduced as a novel material for soil reinforcement. Therefore, it is essential to thoroughly investigate the behavior of fiber-reinforced soils. In this research, the behavior of synthetic fiber-reinforced sand was experimentally investigated. Consolidated undrained monotonic triaxial experiments were conducted on specimens reinforced with glass and polypropylene fibers at different effective confining pressures and relative densities. The tested soil specimens were stabilized using different fiber contents and were then subjected to compression loading. The results suggested that the shear strength of the fiber-reinforced sand specimens was increased by increasing the effective confining pressure and the relative density. The specimens reinforced with 1% of fibers exhibited the highest shear strength. Moreover, it was revealed that under the identical conditions, the polypropylene fiber-reinforced specimens illustrated higher shear strength compared to the glass fiber-reinforced specimens.

Combined Influences of Cement, Rice Husk Ash and Fibre on the Mechanical Characteristics of a Calcareous Sand

The addition of cementitious admixtures and/or inclusion of fibers are frequently used in practice to stabilize soils and to improve their mechanical properties. In this study, ring shear tests were conducted to investigate mechanical properties such as shear strength, angle of friction and cohesion values of randomly distributed discrete fiber-reinforced sand mixtures. The length and aspect ratio of the fibers used in the current study were 12 mm and 120, respectively. Specimens were prepared at four different fiber ratios (0.1, 0.3, 0.6, and 0.9 % by weight of sand). A series of ring shear tests were carried out on sand alone and fiber-reinforced sand mixtures at different normal stresses. The test results indicated that the addition of fiber had a significant effect on the shear strength of the sand. Shear stress of the unreinforced sand increases 1.29–2.32, 1.16–1.39, and 1.07–1.5 times at a normal stress of 50, 150, and 250 kPa, respectively with fiber inclusion. Fiber content had positive effects on improving the shear strength parameters (angle of internal friction and cohesion) of the mixtures. The cohesion and angle of internal friction of fiber-reinforced sand prepared at different ratios of fiber increased by 5.3–27.4 kPa and 2.0°–7.3° respectively. The inclusion of fibers improves the ductility of the soil by preventing the loss of post-peak strength.

<p>Expansive clay soils are classified as a problematic soil type, which is very sensitive to changes in moisture content. This sensitivity causes volume fluctuations and a decrease in soil strength parameters over time. The phenomenon has implications for the degradation of soil shear strength, which is often overlooked in long-term stability analysis. A real case happened in Bekasi Regency, where a slope retaining sheet pile experiencing a slant that was not predicted in the initial design. At the design and construction stage, the structure did not experience movement. However, over the time, the structure experienced a slow movement causing it to become lopsided and severely damaged, affecting the road below. This condition is suspected to be due to a decrease in soil strength over time. To investigate this issue, this thesis undertakes a numerical modeling approach with the Finite Element Method (PLAXIS 2D). It allows the simulation of gradual deterioration of soil parameters including cohesion (c), internal shear angle (ϕ) and modulus of elasticity (E) until results are obtained that match the current field conditions. The analysis revealed that the main cause of the sheet pile slope was a 35% decrease in soil shear strength after 13 years due to expansive soil characteristics. The cohesion of the top layer was reduced to 8.48 kN/m², the internal friction angle to 2.75°, and the elastic modulus to 1914.67 kN/m². In the second layer, the cohesion value was 25.14 kN/m², while the internal friction angle was 11.47° and the elastic modulus was 7218.71 kN/m². The cohesion in the third layer reached 36.28 kN/m², an internal friction angle of 12.71°, with an elastic modulus of 10466.96 kN/m², while in the fourth layer the cohesion reached 42.66 kN/m² and an internal friction angle of 13.42° with an elastic modulus of 12329.57 kN/m². Accompanied by a bending moment generated of 88.6 tons.m so it is recommended to use corrugated concrete sheet pile (CCSP) type W600 Type B for this condition. The study revealed that the stepwise decrease in the shear strength of the soil, caused by its expansive nature, was a major factor in the instability of the sheet pile structure.</p>

In this investigation, the shear strength and specimen deformation behaviour of glass fibre-reinforced clayey and sandy soils have been compared based on the results of consolidated undrained and consolidated drained triaxial tests, respectively under varying moulded states. The clayey soil specimens were moulded with varying dry unit weight, whereas sandy soil specimens were moulded at relative densities ranging from 35 to 85%. For any moulded state, no peak is noted in the stress–strain curves of reinforced clayey soil up to 20% axial strain. In case of the reinforced sandy soil, clear peak is observed well before 20% axial strain with post-peak stress reduction at all relative densities. Reinforced clayey soil shows bulging at all dry unit weights. For the reinforced sandy soil, bulging failure is noted at 35% relative density, whereas shear failure occurs at relative densities of 65% and 85%. At all dry unit weights, under undrained condition, the reinforced clayey soil exhibits only positive pore water pressure indicating contractive behaviour at all axial strains. Under drained condition, the reinforced sandy soil of 35% relative density shows contractive behaviour, while the specimens of 65% and 85% relative densities indicate contractive response at smaller axial strain followed by dilative behaviour at higher strain. The increase of shear strength is up to 0.75% and 3% fibre content in the clayey and sandy soils, respectively irrespective of moulded states. At respective optimum fibre reinforcements, the benefit of glass fibre reinforcement is greater for the sandy soil. The possible environmental impact and field application of glass fibre-reinforced soil have also been discussed.

This study presents results from a series of large-scale simple shear tests performed on sandy soil reinforced with randomly distributed fibers. The soil was mixed with polypropylene, glass and basalt fiber, respectively, with fiber content varying from 0% to 2% and sheared under a normal stress ranging from 100 kPa to 300 kPa. The effects of fiber type, content and normal stress on shear strength and the dilatancy behavior were examined. The friction state theory was employed to interpret the influence of fiber reinforcement on the dilatancy behavior. The results indicate that the additions of polypropylene and basalt fibers are beneficial to enhancing ultimate shear strength, whereas the glass fiber makes little contribution. It is shown that the fiber inclusion hinders the close packing and interlocking of soil particles and hence produces relatively looser soil fabric in the as-compacted state, leading to increased volume contraction accompanied by a negligible improvement or even reduction in shearing stiffness over a small to moderate strain range. The most obvious increase in shear strength generally occurs at a shear strain exceeding 10%, where the fibers and particles are in tight contact with each other, allowing full interface interaction and the mobilization of fiber tensile strength.

Previous studies have confirmed that for cemented tailings backfill, mechanical properties are improved through the addition of fiber. However, for fiber-reinforced cemented sulfur tailings backfill (FRCSTB), physical and flow properties are still unknown. In this paper, the changes in fluidity, splitting tensile strength (STS) and uniaxial compressive strength (UCS) of cemented sulfur tailings backfill (CSTB) are analyzed in detail. Secondly, regarding the addition of glass fiber and polypropylene fiber, the changes in the fluidity, STS and UCS of the CSTB, resulting from the fiber length, fiber content and method of fiber addition used, were analyzed. Moreover, the relationship between the UCS and fiber content is established. Finally, the mechanism behind the influence of fiber and sulfur content on the mechanical properties of CSTB is revealed. The results indicate that with the increase in sulfur content, the fluidity of the tailings slurry exhibits exponential growth. During the process of increasing sulfur content, the UCS and STS of CSTB initially increase and then decrease, reaching maximum values at 12% sulfur content. Similarly, at a fiber content of 0.6%, the UCS and 28d STS of CSTB reach their maximum values. In terms of enhancing the mechanical properties of CSTB, the effectiveness of glass fibers surpasses that of polypropylene fibers. In addition, regarding the improvement of the UCS of CSTB, the mixed addition of fibers is obviously worse than that of fiber alone. However, in terms of enhancing the STS of CSTB, the mixed addition of fibers outperforms the single addition of polypropylene fiber. From a microscopic perspective, polypropylene and glass fiber are able to form strong cohesion with the cement–tailings matrix and effectively prevent the formation and expansion of pores and cracks.

To study the mechanical properties and microscopic morphology of salt-affected soil after being improved by fiber types and contents, the article analyzes the unconfined compressive strength and shear strength of the sulfate-affected soil in Kashi, Xinjiang, China, which four different fiber contents have improved. Some samples are tested by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) microanalysis. The article selects the sample with the highest improved unconfined compressive strength for dry-wet cycling and dissolution test. The results show that polypropylene, polyester, and glass fiber can increase the maximum dry density of salt-affected soil. The unconfined compressive strength of the soil with 1% polyester fiber and 8% silica fume reinforcement is the highest, which is 1.98 times that of the original soil. The unconfined compressive strength of the soil with 1% polyester fiber reinforcement is the largest, 1.43 times that of the original soil. The unconfined compressive strength of the soil with 5% and 7% glass fiber reinforcement is relatively large, 1.56 and 1.57 times that of the original soil, respectively. The cohesion of the original soil is the largest. The internal friction angle of the soil with 6% glass fiber reinforcement is the largest. In addition, the addition of synthetic fibers can significantly reduce the dissolution coefficient of salt-affected soil, especially glass fibers. Through SEM and NMR analysis, it is found that fibers form a good clamping action with soil particles, and some fibers have a tight bond with the soil, reducing the porosity of the soil.

The inclusions of geosynthetic materials (fibers, geomembranes and geotextiles) is a new improvement technique that ensures uniformity in the soil during construction. The use of tension resisting discreet inclusions like polypropylene fibers has attracted a significant amount of attention these past years in the improvement of soil performance in a cost-efficient manner. A series of direct shear box tests were conducted on unreinforced and reinforced Chlef sand with different contents of fibers (0, 0.25, 0.5 and0.75%) in order to study the mechanical behavior of sand reinforced with polypropylene fibers. Samples were prepared at three different relative densities 30%, 50% and 80% representing loose, medium dense and dense states,respectively, and performed at normal stresses of 50, 100 and 200 kPa. The experimental results show that the mechanical characteristics are improved with the addition of polypropylene fibers. The inclusion of randomly distributed fibers has a significant effect on the shear strength and dilation of sandy soil. The increase in strength is a function of fiber content, where it has been shown that the mechanical characteristics improve with the increase in fiber content up to 0.75%, this improvement is more significant at a higher normal stress and relative density.

The effects of polypropylene fiber reinforcement on shear strength and unconfined compressive strength of silty soft soil in tidal flats were studied. Through shear test and unconfined compression test, Experimental study was conducted on silty soft soil of allene fiber reinforced beach with 0~0.6% different mass content and 3 ~18m different length. The failure process and mechanism of fiber reinforced soil samples were also discussed. The test results show that: Shear strength (cohesion and internal friction Angle) and unconfined compressive strength increased rapidly in the early stage with the increase of fiber content, and gradually decreased after reaching the peak at a certain content. In this test, the optimal fiber length corresponding to shear strength is 9mm. When the content is less than 0.6%, the optimal content of cohesion is about 0.2%, and the optimal content corresponding to the Angle of internal friction is between 0.2% and 0.3%. Within the range of 18mm fiber length in the experimental study, unconfined compressive strength increased with the increase of fiber length, and the optimal fiber content corresponding to unconfined compressive strength was 0.2%. The main effects of polypropylene fiber reinforcement on soil cohesion and unconfined compressive strength are not obvious.

This research aims to experimentally study the shear strength of steel fiber concrete beams without shear reinforcement (stirrups). Parameters of the study include two compressive strength (20, 50 MPa), three ratios of flexural reinforcement (0,77, 1,14, 1,54 %), two ratios of shear span to effective depth (a/d = 2,3), and two types of aggregates (Natural coarse aggregate and recycled aggregate (crushed bricks)) with and without steel fibers. Three ratios of the volume fraction of steel fiber are used in the study (0, 0,5, 1 %). All specimens were loaded to failure. Thirteen specimens of concrete beams without shear reinforcement were tested with dimensions (200 x 300 mm) for cross-section (width, depth) and length (2000 mm). The beams were examined to evaluate the effect of each of the above variables on the shear strength and behavior of the beams. All beams are designed to fail with shear stress (without shear reinforcement) under a two-point load test. After obtaining and analyzing the practical results, a set of conclusions were made clear, as the results showed that increasing the compressive strength leads to increases in the maximum shear strength by (60 %). Also, the increase in the flexural reinforcement causes increases in the maximum shear strength by (53 %). As for the ratio of shear span to effective depth, the effect is the opposite, the increasing from 2 to 3 leads to a decrease in shear strength by (30 %). As for the type of aggregate, replacing 50 % of the natural coarse aggregate with recycled aggregate (crushed bricks) leads to a decrease in the maximum shear strength by (10,5 %). The results also show the efficiency of the steel fibers by improving the behavior of the beams under loading, as the addition of steel fibers by 0,5 % increases the maximum shear strength by (18 %). Still, when the steel fibers are 1 % of the volume of concrete, the amount of improvement in shear strength ranges from (30-50 %) despite the difference in the details of the specimens

The modern construction industry is looking for new ecological materials (available, cheap, recyclable) that can successfully replace materials that are not environmentally friendly. Fibers of natural origin are materials that can improve the properties of gypsum composites. This is an important issue because synthetic fibers (hardly biodegradable-glass or polypropylene fibers) are commonly used to reinforce gypsum boards. Increasing the state of knowledge regarding the possibility of replacing synthetic fibers with natural fibers is another step towards creating more environmentally friendly building materials and determining their characteristics. This paper investigates the possibility of manufacturing fiber-gypsum composites based on natural gypsum (building gypsum) and hemp (Cannabis sativa L.) fibers grown in Poland. The effect of introducing hemp fibers of different lengths and with varying proportions of mass (mass of gypsum to mass of fibers) into the gypsum matrix was investigated. The experimental data obtained indicate that adding hemp fibers to the gypsum matrix increases the static bending strength of the composites manufactured. The highest mechanical strength, at 4.19 N/mm2, was observed in fiber-gypsum composites with 4% hemp fiber content at 50 mm in length. A similar trend of increased strength was observed in longitudinal tension. Again, the composite variant with 4% fiber content within the gypsum matrix had the highest mechanical strength. Manufacturing fibers-gypsum composites with more than 4% hemp fiber content negatively affected the composites' strength. Mixing long (50 mm) hemp fibers with the gypsum matrix is technologically problematic, but tests have shown a positive effect on the mechanical properties of the refined composites. The article indicates the length and quantity limitations of hemp fibers on the basis of which fiber-gypsum composites were produced.

The areas near Chlef Valley (Algeria) and the Constructions built on show many phenomena during the last earthquake (El Asnam 1980). A significant decrease in shear strength of Chlef sandy soil, especially in the presence of water, has been reported in numerous researches. Several methods and techniques of soil stability and capacity are available. However, including geosynthetic material, the use of fibres as reinforcement showed some efficiency due to friction between the synthetic material and the soil particles, which increases the bonding between the grains. In this paper, the influence of the glass-fibres content for medium and high densities on the shear strength behaviour of Chlef sandy soil was studied, highlighting the percentage of fibre content (0.1, 0.3 and 0.5 % as a fibre volumetric content), and this will be investigated by a series of direct shear tests. The results will be compared with those of unreinforced sand. Before this work, a further set of direct shear tests will be performed to study the effect of water content on shear strength behaviour (water content of 0, 1.5, 2.3 and 3 %). The experimental results show that the mechanical characteristics are improved with the addition of glass-fibres, especially for wet specimens. It has been showed also that 0.3 % of fibre content is a critical value for fibre contribution to improve the mechanical characteristics. The addition of fibres not only improves the shear strength of soil, but also provides diversity in the resistance against the deformations imposed load, which can be established by a decrease in the soil dilatancy observed by a minimization of the vertical displacement. For the dry case, the reinforcement with fibre has a negative effect on the residual strength especially for average dense samples which may explain probably by the low specific weight of geosynthetics materials.