Effect of grass on soil reinforcement and shear strength

ABSTRACT Natural sisal fiber is an environment-friendly and efficient material for soil reinforcement. Many studies have reported that the shear strength of soil has been improved by the addition of fiber. However, the mechanical properties of sand can be more effectively improved by the incorporation of water-based polymer and sisal fiber. An extensive laboratory testing program was conducted to determine the effect of water-based polyurethane and sisal fiber reinforcement on sand. Laboratory tests included sieve analysis, X-ray diffraction, conventional triaxial compression, and scanning electron microscopy (SEM) tests. The effects of polymer content (PC), fiber content (FC), fiber length (FL), and sample dry density (ρ) are thoroughly investigated. The results indicate that the increases of PC, FC, and ρ all improve the mechanical properties of sand. For FL, this improvement in shear strength was maintained to FLs of up to 18 mm. Beyond 18 mm, the shear strength decreased with further increase in FL. The mixing of polymer and fiber changes the failure mode from shear faulting to ductile flow. This indicates that the ductility of sand is improved. From the SEM images we found that sisal fibers, binding with colloidal materials formed by polymer, fill the sand voids and join the sand particles. This demonstrates that mixing of fiber and polymer can enhance the bonding of sand particles.

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Mechanical Behaviour of Reinforced Sand with Natural Curauá Fibers through Full Scale Direct Shear Tests

E3S Web of Conferences ◽

10.1051/e3sconf/20199212003 ◽

2019 ◽

Vol 92 ◽

pp. 12003

Author(s):

Leila Maria Coelho de Carvalho ◽

Michelé Dal Toé Casagrande

Keyword(s):

Shear Strength ◽

Sandy Soil ◽

Soil Reinforcement ◽

Direct Shear ◽

Shear Strength Parameters ◽

Shear Tests ◽

Strength Parameters ◽

Direct Shear Tests ◽

Soil Shear Strength ◽

Curaua Fibers

Inclusion of natural fibers (sisal, curauá, coco fiber and others) for soil improvement has been the study object in diverse geotechnical areas and it is a topic of growing interest, within the research area of new geotechnical materials. The state of the art in this subject highlights excellent results as soil strength parameters improve and post-cracking strength (toughness) increase. Soil reinforcement technique with fibers is established in the technology of composite materials, this being a combination of two or more materials presenting properties that the component materials do not possess on their own. The aim of this paper is to study the mechanical behaviour of sand-fiber composite by inserting natural curauá fibers into a sandy matrix, with different fiber contents. The fibers were randomly distributed in the soil mass. The experimental program included physical and mechanical characterization of the composites, using full-scale direct shear tests, with samples measuring 30 x 30 cm and 15 cm high. Direct shear tests were carried out using fibers with 25 mm length and 0.5 and 0.75% fiber content (relative to the soil dry weight). The specimens also presented a relative density of 50% and moisture content of 10%. It was sought to establish a pattern behaviour so that the addition of curauá fiber influence can be explained, thus, comparing with the sandy soil shear strength parameters. Inclusion of natural curauá fibers as soil reinforcement presented satisfactory results, as an increase in the soil shear strength parameters was observed when compared with sandy soil results.

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In situ shear tests of soil blocks with roots

Canadian Geotechnical Journal ◽

10.1139/t98-027 ◽

1998 ◽

Vol 35 (4) ◽

pp. 579-590 ◽

Cited By ~ 64

Author(s):

Tien H Wu ◽

Alex Watson

Keyword(s):

Shear Strength ◽

Root System ◽

Tensile Force ◽

Failure Surface ◽

Soil Reinforcement ◽

Shear Tests ◽

Maximum Displacement ◽

Shearing Resistance ◽

Simplified Procedures

In situ shear tests were performed on soil blocks that contained roots to study the contribution of roots to the shear strength in a case where the shear deformation is not constrained to a thin zone. The shearing resistance of the soil-root system, the tensile force in selected roots, and the deformation of the soil block were measured. The roots were exposed after the test and their positions were determined and used to estimate the initial positions. The root force and the shearing resistance of the soil-root system were estimated with known solutions and compared with measured root force and shearing resistance. None of the roots that passed through the shear zone failed in tension at the maximum displacement. As a consequence, the root resistance is much less than that found in a case where the failure surface is restricted to the boundary between a weak soil and a firm base and where roots are anchored in the firm base and fail in tension. Simplified procedures for estimating root forces are suggested for the case of a thick shear zone.Key words: in situ test, roots, shear strength, slope stability, soil reinforcement, soilroot interaction.

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An approximate method for estimating the stability of geotextile-reinforced embankments

Canadian Geotechnical Journal ◽

10.1139/t85-050 ◽

1985 ◽

Vol 22 (3) ◽

pp. 392-398 ◽

Cited By ~ 43

Author(s):

R. K. Rowe ◽

K. L. Soderman

Keyword(s):

Finite Element ◽

Shear Strength ◽

Limit Equilibrium ◽

Soft Clay ◽

Soil Reinforcement ◽

Short Term ◽

Critical Height ◽

Reinforced Embankments ◽

The Stability ◽

Conventional Limit

A method of estimating the short-term stability of reinforced embankments constructed on a deposit that can be idealized as being uniform and purely cohesive is described. This approach maintains the simplicity of conventional limit equilibrium techniques while incorporating the effect of soil–geotextile interaction in terms of an allowable compatible strain for the geotextile. This allowable compatible strain may be deduced from a design chart and depends on the foundation stiffness, the embankment geometry, the depth of the deposit, and the critical height of an unreinforced embankment. The procedure is checked against finite element results and against one published case history. Key words: embankment, geotextile, analysis, limit equilibrium, finite element, soft clay, shear strength, soil reinforcement.

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Model Tests of Soil Reinforcement Inside the Bucket Foundation with Vacuum Electroosmosis Method

Applied Sciences ◽

10.3390/app9183778 ◽

2019 ◽

Vol 9 (18) ◽

pp. 3778 ◽

Cited By ~ 1

Author(s):

Hanbo Zhai ◽

Hongyan Ding ◽

Puyang Zhang ◽

Conghuan Le

Keyword(s):

Shear Strength ◽

Moisture Content ◽

Bearing Capacity ◽

Soil Moisture Content ◽

Soil Reinforcement ◽

Vacuum Preloading ◽

Bucket Foundation ◽

Capacity Model ◽

Vertical Bearing ◽

Vertical Bearing Capacity

Offshore wind turbine foundations are commonly subjected to large horizontal, vertical, and bending moment loads. Marine soils have high moisture content, high compressibility, high sensitivity, and low strength, resulting in insufficient foundation bearing capacity. In order to improve the bearing capacity of wind turbine foundations and reduce foundation settlement, an internal vacuum preloading method combined with electroosmosis reinforcement is used to reinforce the soil within bucket foundations. The pore water pressure, vertical settlement, pumping quality of the soil during the reinforcement process, soil moisture content before and after the reinforcement, and undrained shear strength were analyzed. Horizontal and vertical bearing capacity model tests were carried out on the reinforced and nonreinforced soil inside the bucket foundation. Results show that vacuum preloading combined with electroosmosis reinforcement reduces soil moisture content inside the bucket foundation by approximately 20%, and the undrained shear strength of the internal soil increases by approximately 20 times. Soil reinforcement has high spatial uniformity. Results of the bucket foundation bearing capacity model show that when the soil inside the bucket foundation is strengthened, horizontal bearing capacity increased by 2.9 times and vertical bearing capacity increased by 2.1 times. Vacuum preloading combined with electroosmosis reinforcement can effectively improve the shear strength of soft soil and enhance the bearing capacity and stability of bucket foundations.

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The Reinforcement of Sand by Fibres with a Non-Uniform Shape

Slovak Journal of Civil Engineering ◽

10.2478/sjce-2021-0013 ◽

2021 ◽

Vol 29 (2) ◽

pp. 49-54

Author(s):

Pavel Koudela ◽

Juraj Chalmovský ◽

Lumír Miča

Keyword(s):

Shear Strength ◽

Fibre Composite ◽

Coarse Sand ◽

Theoretical Background ◽

Soil Reinforcement ◽

Triaxial Tests ◽

Fused Deposition Modelling ◽

Peak Shear Strength ◽

Fused Deposition ◽

Variable Shape

Abstract The reinforcement of soil is used to improve its strength and stiffness. The standard method of soil reinforcement is an application of geosynthetics. Soil reinforcement by distributed discrete fibres represents an alternative to those techniques. Currently used fibres have a straight shape, uniform cross-section, and smooth surface, which is not optimal in terms of the fibre-soil interaction. In this study, fibres with a variable shape were utilized. The fibres were fabricated using a fused deposition modelling technology. Firstly, a brief theoretical background is presented. Then, the proposed shapes of the fibres and their manufacturing process are described. The mechanical properties of the soil-fibre composite were investigated through consolidated drained triaxial tests. Well-graded coarse sand and poorly-graded fine sand were used. A higher peak shear strength was observed in the case of fibres with a variable shape. The effect of the variable shape of the fibres on the peak shear strength was higher in the case of the coarse sand.

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COMPARISON OF THE BEHAVIOR OF FIBER AND MESH REINFORCED SOILS

Journal of Civil Engineering Science and Technology ◽

10.33736/jcest.441.2017 ◽

2017 ◽

Vol 8 (2) ◽

pp. 82-88

Author(s):

Y. C. Fung ◽

Shenbaga. R. Kaniraj

Keyword(s):

Compressive Strength ◽

Shear Strength ◽

Unconfined Compressive Strength ◽

Failure Strain ◽

Soft Soil ◽

Soil Samples ◽

Soil Reinforcement ◽

High Plasticity ◽

Soil Matrix ◽

Treated Soil

Soft soil does not have good soil properties and is not suitable for constructing pavement structures as shear strength is required to resist the shear stress developed by traffic loading. To increase shear strength in this study, lime is used as the soil stabilizing agent and fiber and mesh are used as the soil reinforcement materials. The proper amount of lime added to soil will increase the shear strength as the lime-treated soil will decrease moisture susceptibility and migration. Shear strength of the lime-treated soil can be further improved by adding reinforcement materials such as fiber and mesh. The reinforcement materials will interlock with groups of particles and provide tensile strength to the soil matrix. The type of soil used in this study is high plasticity elastic silt with sand which is classified using the Unified Soil Classification System (USCS). Quicklime (calcium oxide) is used in this study at the minimum amount required for stabilizing the soil, which is 9%. The amount of fiber and mesh added to the soil sample is 0.5% of the dry weight of the soil used. Cylindrical samples were prepared with a moisture content of 22% (OMC) for untreated soil and 21% (OMC) for lime-treated soil samples. The lime-treated soil samples were cured for 7, 14, 28, 56, 90 and 120 days. Unconfined compression tests were conducted to determine unconfined compressive strength (UCS) and stress-strain characteristics. The unconfined compressive strength of the lime-treated samples increased as curing period increased but the failure strain decreased. The UCS and failure strain for reinforced lime-treated soil samples are higher than the unreinforced lime-treated soil samples.

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Experimental Research on the Change of Soft Soil’s Strength and Deformation Characteristics Caused by Dewatering

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.170-173.679 ◽

2012 ◽

Vol 170-173 ◽

pp. 679-682

Author(s):

Hua Yuan ◽

Jian Wei Zhang ◽

Zhi Liang Zhao

Keyword(s):

Shear Strength ◽

Compression Modulus ◽

Strengthening Mechanism ◽

Soil Reinforcement ◽

Reinforcement Effect ◽

Support Design ◽

Deformation Properties ◽

Strength And Deformation ◽

Excavation Support ◽

The Relationship

Present research results have verified the significant soil reinforcement effect of dewatering. But the reinforcement effect of dewatering suffers ignorance in current excavation design process due to lack of systematic experimental study on the strengthening mechanism, causing a certain amount of waste. This paper first theoretically describes the relationship between the increase of soil shear strength and that of compression modulus owing to pumping, then investigates the influence of well-point pumping on Shanghai soil’s shear strength and deformation properties through indoor test. The results may provide useful suggestions for future excavation support design.

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Reinforcement Pullout Capacity in Mechanically Stabilized Earth Walls with Marginal-Quality Soils

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2363-08 ◽

2013 ◽

Vol 2363 (1) ◽

pp. 66-74 ◽

Cited By ~ 12

Author(s):

Kianoosh Hatami ◽

Jaime E. Granados ◽

Danial Esmaili ◽

Gerald A. Miller

Keyword(s):

Shear Strength ◽

Matric Suction ◽

Reduction Factor ◽

Reinforced Soil ◽

Soil Reinforcement ◽

Water Infiltration ◽

Pullout Capacity ◽

Interface Shear ◽

Mechanically Stabilized Earth Walls ◽

Marginal Soil

Pullout capacity of geotextile reinforcement is an important consideration in the analysis of internal stability of reinforced soil structures, especially those constructed with marginal soils. Precipitation, ground water infiltration, and seasonal variations of water content during the construction process or service life of the structure could result in significant reductions in the matric suction and lead to a reduction in the strength of the soil–geotextile interface. Consequently, the reinforced soil structure may experience unacceptable deformations or even failure during its construction or postconstruction periods. The loss of matric suction in the soil influences both the shear strength of the soil and the soil–reinforcement interface. However, the focus of this study was merely on the latter. Nine pullout tests and 18 interface shear tests were performed to measure the pullout resistance of a reinforcement geotextile in a marginal soil that was compacted at different gravimetric water contents (GWCs). The marginal soil was selected to meet the limiting requirements of the National Concrete Masonry Association guidelines for segmental retaining walls with respect to fines content, gradation, and plasticity. The range of GWC values investigated varied from the dry to the wet side of the optimum moisture content of the soil. The matric suction in the soil was measured to evaluate its influence on the soil–reinforcement interface shear strength. A moisture reduction factor is proposed to account for the reduction in the soil–geotextile interface strength as a result of the loss in matric suction.

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The mechanism of the plant roots’ soil-reinforcement based on generalized equivalent confining pressure

PeerJ ◽

10.7717/peerj.10064 ◽

2020 ◽

Vol 8 ◽

pp. e10064

Author(s):

Ping Guo ◽

Zhenyao Xia ◽

Qi Liu ◽

Hai Xiao ◽

Feng Gao ◽

...

Keyword(s):

Shear Strength ◽

Root Distribution ◽

Plant Root ◽

Friction Angle ◽

Confining Pressure ◽

Distribution Patterns ◽

Reinforced Soil ◽

Soil Reinforcement ◽

Plant Roots ◽

Root Content

Background To quantitatively evaluate the contribution of plant roots to soil shear strength, the generalized equivalent confining pressure (GECP), which is the difference in confining pressure between the reinforced and un-reinforced soil specimens at the same shear strength, was proposed and considered in terms of the function of plant roots in soil reinforcement. Methods In this paper, silt loam soil was selected as the test soil, and the roots of Indigofera amblyantha were chosen as the reinforcing material. Different drainage conditions (consolidation drained (CD), consolidation undrained (CU), and unconsolidated undrained (UU)) were used to analyse the influences of different root distribution patterns (horizontal root (HR), vertical root (VR), and complex root (CR)) and root contents (0.25%, 0.50%, and 0.75%) on the shear strength of soil-root composites. Results The cohesion (c) values of the soil-root composites varied under different drainage conditions and root contents, while the internal friction angle (φ ) values remain basically stable under different drainage conditions. Under the same root content and drainage conditions, the shear strength indexes ranked in order of lower to higher were HR, VR and CR. The GECP of the soil-root composites with a 0.75% root content was 1.5–2.0 times that with a 0.50% root content and more than 5 times that with a 0.25% root content under the CD and CU conditions. The GECP in reinforced soil followed the sequence of CD > CU > UU. The GECP of the plant roots increased as confining pressure increased under CD and CU conditions while showed a complex change to the confining pressure under the UU condition. Conclusion It was concluded that the evaluation of plant root reinforcing soil based on GECP can be used to measure effectively the influences of roots on soil under different drainage conditions and root distribution patterns.

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