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Abstract

In this research, loop-formed fiber is introduced as a novel reinforcement method of soil composites instead of using ordinary fibers. In order to investigate the materials' mechanical properties, the shear behavior of both fiber and looped-fiber-reinforced soil composites was analyzed by micromechanical method (finite element method) and a set of direct shear tests. The results indicate that the looped-fiber soil composite exhibits greater failure strain energy compared with fiber-reinforced soil composite at the same fiber orientation in the substrate. Furthermore, the proposed model demonstrated two major reinforcing components: “the fiber effect” and “the loop effect.” The latter effect is the key benefit and the main advantage of using looped fibers over ordinary fibers in soil reinforcement. Altogether, there is a close agreement between finite element method outputs and experimental results, suggestive of a novel technical textile material that could potentially be used in geotechnical engineering.

Keywords

Loop-formed fiber soil composite finite element method slippage theory

Introduction

A comprehensive literature review shows that using natural and/or synthetic fibers in geotechnical engineering is feasible in fields such as pavement layers (road construction), retaining walls, earthquake engineering, railway embankments, protection of slopes, and soil-foundation engineering [1].

Fiber-reinforced soil structures have been conventionally designed using composite approaches to characterize the contribution of fibers to stability. In these cases, the mixture is considered as a homogenous composite material. The contribution of the fibers has been typically quantified by an equivalent friction angle and cohesion of soil [2]. Therefore, composite models have been proposed by several investigators including mechanistic models [3 –5], a statistical model [6], and an energy-based limit analysis model [7].

Models based on a volumetric homogenization technique but limited to the description of non-linear elastic behavior have been presented by Ding and Hargrove [8] for monotonic loading and by Li and Ding [9] in cyclic loading conditions. A complete constitutive law for soils reinforced with continuous filament (Texsol) has been presented by Villard et al. [10] and Prisco and Nova [11], employing the superposition of sand and fiber effects. Villard’s model is the only one that recognizes the importance of fiber orientation as a parameter governing the effectiveness of fiber inclusion. In another work, a two-dimensional distinct element method has been developed for the micromechanical analysis of mixtures of granular materials and flexible fibers [12]. Numerical analysis with finite difference code has been performed by Babu et al. [13]. Some researchers extended the shear lag theory proposed by Cox [14] to explain the role of fiber length and fiber diameter in short fiber soil composites. Thus, it was found that the compressive strength of the composite soil improves by increasing the fiber length and deceasing fiber diameter [15]. In another work, Diambra et al. [16] presented a model based on the rule of mixtures of composite materials at conventional triaxial soil tests. The model considers that the fibers behave linear elastically and the soil, when unreinforced, obeys the simple linear elastic perfectly plastic Mohr–Coulomb model. In addition, Abtahi et al. [17] have reported using artificial neural network to predict the role of fiber parameters on shear strength of short fiber soil composites.

It is important to know that lack of scientific standards, clumping (local aggregation) and balling (folding of fibers) of fibers, and adhesion of fiber to soil are the three major executive problems involved with short-fiber soil composite production. In this manner, fiber lengths beyond 2 in. (51 mm) did not improve soil properties significantly and proved more difficult to work with both in laboratory and field experiments [1,18].

On the other hand, since composite structures with soft-material matrix do not have adequate pullout resistance with flat-type reinforcements such as fibers, there are increasing cases where reinforcements with passive resistance are used in conjunction [5,19]. Therefore, in this research, loop-formed fiber is introduced as a novel reinforcement method for soil composites instead of ordinary fibers. On the whole, this article introduces a new technical textile material that can be potentially commercially attractive in geotechnical engineering. Mainly, soils mixed with randomly distributed fibers can be used as patches in the localized repair of failed slopes, soil protection, and/or wall stabilization, and hence the shear strength of fiber-reinforced soil would be considered an important concept [20].

Materials and methods

Preparation of treatments

The soil used in this work was a silty sand type, from the Segzi Desert, Isfahan, Iran. The sample was collected by manual excavation in sufficient quantity (about 300 kg) to complete all the tests. Table 1 presents some physical and mechanical properties of the soil.

Table 1.

Physical and mechanical properties of the soil used in this study.

Property	Value
Specific gravity (g/cm³)	2.680
Liquid limit (%)	29.00
Plastic limit (%)	10.62
Plasticity index (%)	18.37
Maximum dry unit weight, γ_dmax (kN/m³)	18.05
Optimum moisture content (%)	13.82
California bearing ratio (%)	1.62
c (kPa)	19.07
ϕ (°)	35.56

Polyethylene (PE)-reinforcing elements were used to compare experimental results with the proposed micromechanical model outputs. The reinforcements consisted of both PE fibers and PE-looped fibers to evaluate separately the “fiber effect” and the “loop effect,” as well as to compare the experimental results with the model outputs. PE reinforcements were selected due to economical advantages, feasibility of using waste PE strands, and excellent alkaline resistance [1]. Therefore, three types of PE-welded geogrids were prepared (Iran Tour Company, Tehran, Iran). After that the grid samples were cut to produce discrete grids and/or looped fibers from each treatment. The reinforcements were selected to give a range of elastic modulus (E_f = 74 and 230 MPa), fiber diameter (d_f = 1 and 2 mm), loop dimension (L_f = 7 and 14 mm), and grid fraction (N_f = 8, 16 and 32). In addition, fiber-reinforcing elements were made from one type of geogrid samples (E_f = 230 MPa, L_f = 7 mm, and d_f = 1 mm) to produce fiber-reinforced soil samples at three fiber-mass fractions of 0.5%, 1%, and 2%. These fiber dosages equal with grid fractions of N_f = 8, 16, and 32, respectively. Table 2 summarizes the properties of the reinforcements (both fibers and looped fibers) at each treatment that have been obtained by the authors.

Table 2.

Physical and mechanical properties of PE-reinforcing elements.

No.	Code no.	Mass fraction (%)	Type of reinforcement	Mesh size (mm)	Fiber diameter (mm)	N_f	Elastic modulus (MPa)	Percentage of open area (%)
1	PEG/7/8	0.5	Looped fiber	7.00	1.0389	8	230	58.5
2	PEG/7/16	1	Looped fiber	7.00	1.0389	16	230	58.5
3	PEG/7/32	2	Looped fiber	7.00	1.0389	32	230	58.5
4	PEG/14/10/2	1	Looped fiber	14.00	1.8663	10	76	63.8
5	PEG/14/10/1	1	Looped fiber	14.00	1.0413	10	74	77.5
6	PEF/7/0.5%	0.5	Fiber	7.00^a	1.0389	32	230	-
7	PEF/7/1%	1	Fiber	7.00^a	1.0389	64	230	-
8	PEF/7/2%	2	Fiber	7.00^a	1.0389	128	230	-

Fiber length.

PE: polyethylene.

Primary evaluations demonstrated that the prepared welded geogrids include the same longitudinal and transverse properties, i.e. they are square technical fabrics.

The percentage of open area (POA%), an important property to describe geogrids, was calculated using equation (1)

POA % = (AW \times AL) / ([AW + 2 LRW] \times [AL + 2 TRW])

(1)

where AW and AL are aperture width and aperture length, respectively, while LRW and TRW represent longitudinal rib width and transverse rib width, respectively (Figure 1(a)). Figure 1(b) shows looped and ordinary PE fibers.

Figure 1.

(a) Schematic of a geogrid element and (b) looped (left) and ordinary (right) PE fibers used in this study.

Determination of input parameters for micromechanical analysis

Fiber diameter d_f is an important input parameter to predict shear improvement of fiber and/or looped fiber-reinforced soil composite. Therefore, microscopic method with zoom of 40 was used to measure d_f and rib widths of geogrid samples accurately. The results are shown in Table 2.

The elastic modulus of geogrid samples was measured according to ASTM D 6637 using an Instron Tensile Tester (Zwick universal testing machine 1446 60, 1994, Germany). The test was carried out in accordance with the constant rate of elongation (CRE) method using gage length of 300 mm and the strain rate of 30 mm/min.

The important input parameter for micromechanical analysis is coefficient of friction between PE fiber and soil µ, which is generated by the contact of two surfaces. A novel single fiber pull-out test method was used to assess this property. The Instron Tensile Tester was modified to provide fiber pull-out test through the soil matrix. Initially, soil was poured into a cylindrical mold made from PVC with diameter of 15 mm and height of 40 mm. A hole (D = 4 mm) was entrenched on the mold, 15 mm above the horizon. More details can be found in the study of Hejazi et al. [5]. On the base of optimum moisture content (OMC) (13.82%), the soil should be statically compacted in the mold to fill 30 mm of the mold. Second, to prevent evaporation of moisture, the specimens should be wrapped immediately with plastic membrane, prior to testing. Consequently, a single PE strand (30 mm length) was placed within the soil matrix through the hole and compacted using a small hammer. The embedded fiber length within the soil matrix was 10 mm in all specimens. The PE strand had been disparted from the original geogrid. Five parallel specimens were prepared for each treatment. The apparatus for single fiber pull-out test is shown in Figure 2. The vertical stress on all samples was 25 kPa, and the speed of the pull-out test was 20 mm/min. It was determined according to the fiber length and duration of the test performed (30–60 s). The index of interfacial shear stress between PE strand and soil matrix is called mean value and was 0.35.

Figure 2.

Sketch drawing of the pull-out test (not to scale).

Direct shear test

The shear tests were conducted using a standard, laboratory-direct shear apparatus, following the ASTM D 3080 test method. The specimens were shaped in a cylindrical mold with 20 mm height and 63 mm inner diameter by static compaction at the respective OMC of the soil. The testing was performed at 13.82% OMC, according to ASTM 698.

Three vertical normal stresses (σ_v) of 49, 98 and 196 kPa were used in order to determine the shear behavior of the soft-matrix composite at different compressive loads. The shear tests were strain controlled at the rate of 1 mm/min. A set of three experimental tests was conducted in order to achieve reproducibility of the selected test method. The results of three different tests for the neat soil were presented in a chart with peak stress on horizontal axis and normal (confining) stress on the vertical axis. A linear curve fitting was made on the test result points, and the intercept of this line with the vertical axis gives the cohesion c, whereas its slope gives the peak friction angle ϕ. Consequently, the corresponding friction angle of neat soil ϕ and cohesion c measured in direct shear was 35° and 19 MPa, respectively.

PE fibers and/or looped fibers were always carefully placed in a regular pattern at approximately equal spacing from each other and from the sides of the shear box. Reinforcing elements were placed in a perpendicular orientation to the shear plane, according to the proposed model in micromechanical analysis. Both shear stress and vertical deformation were recorded as a function of shear or horizontal displacement up to a total displacement of 9 mm. The experimental shear improvement of composite soil ΔS_exp(σ_v) was calculated for each sample at each vertical stress σ_v using the following equation

Δ S_{\exp} (σ_{_{V}}) = S_{\exp . comp} (σ_{_{V}}) - S_{\exp . neat} (σ_{_{V}})

(2)

where S_exp.comp(σ_v) and S_exp.neat(σ_v) are shear strength of composite soil and neat soil at the same vertical stress σ_v, respectively.

Micromechanical analysis

In this section, the shear strength of fiber-reinforced soil composite is analyzed by finite element method (FEM). Direct shear test (ASTM D 3080) was simulated through Abaqus 6.9 software. Micromechanical analysis demonstrated the stress distributed on the soil and reinforcing element, i.e. fiber and/or looped fiber, during the shear of the composite. To identify the deformation of reinforcing element and soil in this model, fiber and soil matrix were modeled as deformable parts, whereas rigid body was used to make displacement around the soil matrix. The contact of reinforcing element with the crossing soil was assumed to be surface-to-surface, based on fiber pull-out test results (μ = 0.35). In addition, the dynamic/explicit solution with the following boundary conditions was used:

The lower half of the soil composite volume was fully fixed in the course of shear loading.

The upper half of the soil composite volume was vertically loaded (vertical static stresses of 49, 98 and 196 kPa at different treatments).

The upper half of the soil volume was moved with a constant speed of 0.5 mm/s in one direction onto the composite, as suggested in the test specifications.

C3D8R elements were used to mesh the reinforcing element and soil bodies. Drucker Prager property was considered for the soil to describe the failure behavior of the matrix. So friction angle (ϕ = 35°) and cohesion (c = 19 MPa) of the neat soil measured in direct shear test were used for further calculations.

At each treatment, the soil composite was enclosed within a metal mold with a height of 20 mm and a diameter of 63 mm, as described in direct shear test. The results are shown in Table 2. At each vertical stress σ_v, i.e. 49, 98 and/or 196 kPa, shear strength of each composite soil S_FE.comp(σ_v) and neat soil S_FE.neat(σ_v) were calculated. Consequently, shear strength envelopment of each composite sample ΔS_FE(σ_v) with regard to the neat soil can be obtained through

Δ S_{FE} (σ_{_{V}}) = S_{FE . comp} (σ_{_{V}}) - S_{FE . neat} (σ_{_{V}})

(3)

It is important to address that the shear strength of the soil and/or composite soil is the point when the total shear resistance within the material starts to plateau.

Results and discussion

Comparison of fiber and looped-fiber performance

Figure 3(a)–(d) shows different aspects of the simulated sample PEG/7/8 (sample number 1 in Table 2) during the course of shear loading. According to the treatment description in Table 2, eight looped fibers and/or discreet grids have been vertically oriented within the soil matrix. Figure 4(a)–(d) shows the simulated sample PEF/7/0.5% (sample number 6 in Table 2) during the shear of the soil composite. In this case, 32 fibers reinforcing the soil matrix have been arranged with the same orientation similar to the grid-reinforced sample PEG/7/8. By comparing these two treatments, it is observed that the horizontal fibers in the case of fiber-reinforced sample do not withstand against shear loading of the soil composite (see Figure 4(b)–(d)). This clearly indicates that only vertical fibers deform and resist with the soil matrix against shearing of soil composite. On the other hand, in the case of fiber-reinforced soil composite, the reinforcing phenomenon is related to the performance of vertical fibers. Figure 3(b)–(d) demonstrates that both vertical and horizontal fibers forming loop elements and/or discreet grids are involved in shear resistance of loop-formed fiber-reinforced soil composite. At this stage it can be concluded that pullout resistance of loop-formed fibers has two major components: (a) the friction between soil matrix and vertical elements of looped fiber (the fiber effect) and (b) shear resistance of soil matrix within the loop (the loop effect). Therefore, the total improvement in shear strength of soil composite (ΔS_t) can be written in the following format [5]

Δ S_{t} = Δ S_{F} + Δ S_{G}

(4)

where ΔS_F and ΔS_G represent the roles of “fiber effect” and “loop effect” in shear envelopment of loop-formed fiber-reinforced soil composite, respectively. Figure 5 shows the strain energy induced within the simulated neat soil (blue line) and simulated soil composites of PEG/7/8 (red line) and PEF/7/0.5% (green line). As it can be seen, the looped-fiber sample has more failure strain energy compared with the ordinary fiber-reinforced soil composite. It seems that this phenomenon is achieved by the concept of “loop effect,” which is the main benefit and the key advantage of using loop-formed fibers over ordinary fibers in the reinforcement process. It means that the existence of matrix, i.e. soil, within the loop leads to the production of an additional resisting shear stress during shear of composite. The produced shear stress performs between “soil matrix surrounded by loop” and soil matrix mass tangential over the loop. Consequently, shear strength improvement of soil composite derived by the “loop effect” ΔS_G can be calculated through division of effective shearing force “(σ_v × tanϕ) × D²× cos(ψ)” within the loop over the total shear area of the composite A_s [5]. Furthermore, the total shear improvement ΔS_G achieved by N_f-looped fibers can be calculated through

Δ S_{G} = N_{f} \times (σ_{v} \times \tan ϕ) \times D^{2} \times \cos (ψ) / A_{s}

(5)

where σ_v and D are vertical stress (inserted on soil mass in direct shear test) and internal mesh size of the grid, respectively. ϕ represents the friction angle of the soil, while ψ is the angle between deformed looped-fiber plane and soil shear surface. It was noticed that only simulated results of treatments of PEG/7/8 and PEF/7/0.5% has been proposed herein to comply with the summary of this article.

Figure 3.

FEM results of looped fiber-reinforced soil composite under shear loading at σ_v = 98 kPa: (a) the sample after loading and (b–d) deformation of reinforcing elements during the shear of the composite.

Figure 4.

FEM results of fiber-reinforced soil composite under shear loading at σ_v = 98 kPa: (a) the sample after loading and (b, c and d) deformation of reinforcing elements during the shear of the composite.

Figure 5.

Failure strain energy (J) via time (s) of neat soil (blue line), fiber-reinforced sample (green line), and looped fiber-reinforced treatment (red line).

Shear strength envelopment of treatments

Figures 6–8 show comparison of the experimental results with the model outputs of shear improvement of different soil composite samples at vertical stresses of 50, 100 and 200 kPa, respectively. In general, both fiber and looped-fiber reinforcements increase the ultimate shear strength of composite soils. Regardless of applied vertical stress, shear envelopment of composite soil will increase as the fiber mass fraction enhances (PEF/7/0.5%, PEF/7/1% and PEF/7/2% samples). The same trend can be observed in the case of loop-formed fiber reinforcement at any vertical stress for the PEG/7/8-, PEG/7/16- and PEG/7/32-treated fibers. It is clear that the presence of more fibers extending across the shear plane creates more reinforcing effect. On the basis of the proposed model, under shearing, fiber reinforcement contributes to the increase of shear resistance by mobilizing tensile stress within fibers.

Figure 6.

Shear strength improvement of different treatments at σ_v = 49 kPa (comparison of FEM outputs and experimental tests).

Figure 7.

Shear strength improvement of different treatments at σ_v = 98 kPa (comparison of FEM outputs and experimental tests).

Figure 8.

Shear strength improvement of different treatments at σ_v = 196 kPa (comparison of FEM outputs and experimental tests).

Additionally, with the increase in vertical stress σ_v from 50 to 200 kPa, the shear strength improves (Figures 6 –8). In order to understand the results, it is necessary to give a short explanation about the stress transfer mechanism in short fiber composites. According to Shao et al. [21], the transferred stress from matrix into the fiber surface in a short-fibre composite can cause an interfacial shear stress τ between fiber and matrix and consequently induces a tensile stress σ within the fiber. It is suggested that during extension, the slippage effect occurs near both ends of the fiber and a central region along the fiber length gripped by the matrix, which is called non-slippage region. If λ is defined as the fiber slippage ratio, which is the ratio of fiber length of the slipping portion to the whole fiber length L_f, the following equation is introduced [21,22]

λ = (d_{f} E_{f} ɛ_{f}) / (2 τ L_{f})

(6)

in which d_f, E_f and ɛ_f are diameter, Young’s modulus, and induced strain of fiber, respectively. It is clear that the interfacial shear stress between fiber and soil τ can be obtained through [5]

τ = μ \times σ_{v}

(7)

Therefore, equation (6) changes to

λ = (d_{f} E_{f} ɛ_{f}) / (2 μ σ_{v} L_{f})

(8)

The above equation states that as the vertical stress σ_v increases, the stress transfer from the matrix into the fiber will be improved (λ has been decreased). In other words, the fiber slippage decreases.

A set of samples in Table 2 (PEF/7/0.5%, PEG/7/8), (PEF/7/1%, PEG/7/16), and (PEF/7/2%, PEG/7/32) were compared, and it was observed that apart from applied vertical stress σ_v, the value of ΔS in the case of looped-fiber-reinforced samples is greater than that of fiber-reinforced treatments. As was discussed previously through the presented model, this result might be due to the “loop effect.” Therefore, at the same orientation, fiber content, fiber finesse, and fiber length, looped-form fibers lead to superior reinforcement of the soil compared with ordinary fibers. For instance, the shear improvement value of PEG/7/32 is about 44,603 Pa at σ_v = 200 kPa; meanwhile, under the same conditions (fiber length, vertical stress, and fiber weight fraction), ΔS is 30,782 Pa in the case of PEF/7/2%, i.e. the loop effect causes approximately 50% increase in shear strength of soil composite.

The loop samples of PEG/1.4/10/2 (number 4) and PEG/1.4/10/1 (number 5) are only different in fiber diameter (Table 2). Figures 6 –8 show that sample PEG/1.4/10/2 gives more shear improvement compared with PEG/1.4/10/1 in all tested vertical stresses. This result can be explained through the model proposed by Waldron [23]. In Waldron’s method, the performance of plant roots in shear resistance of soil has been macromechanically modeled using force equilibrium approach. It is supposed that under shearing, plant roots contribute to the increase of soil shear resistance by mobilizing tensile stress σ_T within the roots. It is proved that σ_T can be obtained through

σ T = (τ ZE f / d f) 0.5 (sec β - 1) 0.5

(9)

where Z and β are the shearing amplitude and the angle of distortion of plant root in the course of shear loading, respectively (Figure 9). Consequently, the induced tensile strength σ_T is converted into two-force components within the fiber performing against shear loading of the soil matrix. The role played by the plant root in increasing the shear strength of the composite ΔS_F soil can be calculated by dividing the induced tensile force within the fiber over the total shear area of the composite A_s

Δ S F = (π d_{f}^{2} / 4) (τ ZE f / d f) 0.5 (sec β - 1) 0.5 \times (sin β + cos β \times tan φ) / A s

(10)

As can be observed, the higher the fiber diameter, the more induced tension force is obtained. Herein, the authors emphasize that as the fiber diameter decreases, the stress transfer from matrix to fiber will be improved due to reduction in slippage (equation (8)); however, the induced tension force resistance against inserted shear stress is minimal.

Figure 9.

The schematic of a plant root within the soil matrix under shear loading.

It seems that the main reason for the difference between simulation and experiments is that in direct shear test, the distribution of vertical stress is not uniform through the shear plane. Therefore, different fibers and/or looped fibers do not deform uniformly. In addition, it is doubtful whether the desired fiber orientation will be retained in the mold after the compaction of the composite soil. Figure 10 shows X-ray computed tomography images of three different looped fibers within the soil matrix after shear loading. The average fiber alignment angle β is about 34^o; meanwhile, according to the soil thickness (20 mm) and final shear displacement of soil sample (9 mm), β should be about 24°. One reason may be misalignment of vertical fibers during the compaction process.

Figure 10.

X-ray computed tomography images of three different looped fibers within the soil matrix after shear loading.

In this study, vertical fiber orientation was used to reinforce the soil matrix. It does not mean that in the field and/or real conditions, these elements should be aligned vertically within the soil. The loop-formed fibers can be randomly placed within the soil just like ordinary flat-type fibers. In this study, in order to compare experimental results with FEM outputs, we had to use a certain fiber orientation, i.e. vertical orientation. It is emphasized that since fiber orientation plays an important role in shear strength of soil composites, by using randomly distributed fiber orientation, we could not compare experimental results with FEM outputs (see equation (10), the angle of fiber alignment β and its influence on shear strength of soil composite).

Conclusion

The aim of this article was to investigate a novel method to reinforce soil composites by introduction of loop-formed fibers. The looped fibers were prepared by cutting different PE geogrid samples followed by a set of direct shear tests performed on neat, fiber and looped-fiber-reinforced soil composites. Furthermore, the analytical micromechanical model was introduced in order to investigate the performance of fiber and looped-fiber soil composite. The presented model demonstrates that shear resistance of loop-formed fibers has two major components including “fiber effect” and “loop effect.” It was observed that in the case of fiber-reinforced soil composite, the reinforcing phenomenon is related to the performance of vertical fibers; meanwhile, both vertical and horizontal fibers forming loop elements and/or discreet grids are involved in shear resistance of loop-formed fiber-reinforced soil composite. Further FEM analysis showed greater failure in strain energy of looped-fiber soil composite compared with the fiber-reinforced at the same fiber orientations. This concept related to the “loop effect.” “Slippage theory” and “force equilibrium” method were used to explain the experimental and micromechanical results.

Additionally, a coefficient of friction between PE fiber and soil μ, as an important input parameter for micromechanical analysis, was successfully measured through a novel single fiber pull-out test method by modifying the Instron Tensile Tester. In general, the studies open a new window to technical materials development, which might be a potential interest for geological engineering.

In this article, it was shown that in the same fiber mass fraction and fiber orientation, looped fibers provide superior reinforcement of soil compared with ordinary fibers. Therefore, the only imposed cost of producing looped fibers is economically related to grid processing compared with ordinary fibers. For future studies, the use of randomly looped fiber orientation and/or other fiber orientations is also suggested.

Footnotes

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

References

Hejazi

Sheikhzadeh

Abtahi

. A simple review of soil reinforcement by using natural and synthetic fibers. Construct Build Mater 2012; 30: 100–116.

Li C. Mechanical response of fiber-reinforced soil. PhD Thesis, Faculty of the Graduate School of the University of Texas at Austin, 2005.

Gray

Ohashi

. Mechanics of fiber-reinforcement in sand. J Geotech Eng ASCE 1983; 109: 335–353.

Maher

Gray

. Static response of sand reinforced with randomly distributed fibers. J Geotech Eng ASCE 1990; 116: 1661–1677.

Hejazi

Sheikhzadeh

Abtahi

. Using slippage theory to analyze shear behavior of loop-formed fiber reinforced soil composites. J Ind Text 2014; 44(2): 332–348.

Ranjan

Vasan

Charan

. Probabilistic analysis of randomly distributed fiber-reinforced soil. J Geotech Eng ASCE 1996; 122: 419–426.

Michalowski

Zhao

. Failure of fiber-reinforced granular soils. J Geotech Eng ASCE 1996; 122: 226–234.

Ding

Hargrove

. Nonlinear stress–strain relationship of soil reinforced with flexible geofibers. J Geotech Geoenviron Eng 2006; 132: 791–794.

Ding

. Nonlinear elastic behavior of fiber-reinforced soil under cyclic loading. Soil Dynam Earthquake Eng 2002; 22: 977–983.

10.

Villard

Jouve

Riou

. Modélisation du compertment mécanique du Texsol. Bull Liaison Labo 1990; 168: 15–27.

11.

Prisco

Nova

. A constitutive model for soil reinforced by continuous threads. Geotext Geomembrane 1993; 12: 161–178.

12.

Ibraim E and Maeda K. Numerical analysis of fiber-reinforced granular soils. In: 5th international symposium on earth reinforcement, 14–16 November 2007, Kyushu, Japan, pp. 387–393.

13.

Babu

Vasudevan

Haldar

. Numerical simulation of fiber-reinforced sand behavior. Geotext Geomembrane 2008; 26: 181–188.

14.

Cox

. The elasticity and strength of paper and other fibrous materials. Br J Appl Phys 1952; 3: 72–78.

15.

Hejazi

Sheikhzadeh

Abtahi

. Shear behavior of soft-matrix composites reinforced with polyethylene loop-formed fibers. Iranian Polym J 2013; 22: 15–24.

16.

Diambra

Ibraim

Wood

. Fiber reinforced sands: Experiments and modeling. Geotext Geomembrane 2010; 28: 238–250.

17.

Abtahi M, Okhovat N, Pourhosseini R, et al. Shear strength of composite soils reinforced with natural fibers. In: 5th national congress on civil engineering, 4–6 May 2010, Mashad, Iran, pp. 1–8.

18.

Newman K and White J. Rapid assessment of cement/fiber stabilized soil using roller-integrated compaction monitoring. In: Transportation research board, 87th annual meeting, 13–17 January 2008, Washington DC, USA, pp. 95–102.

19.

Kwon

Bae

Lee

. Pullout resistance characteristics of chain type retaining system. Int J Phys Sci 2010; 5: 1344–1359.

20.

Zornberg

Kavazanjian

. Prediction of the performance of a geogrid- reinforced slope founded on solid waste. Soil Found 2002; 42: 129–130.

21.

Shao

Qiu

Wang

. Theoretical modeling of the tensile behavior of low-twist staple yarns: Part I – theoretical model. J Tex Inst 2005; 96: 61–68.

22.

Hejazi

Abtahi

Sheikhzadeh

. Introducing two simple models for predicting fiber reinforced asphalt concrete (FRAC) behavior during longitudinal loads. Int J Appl Polym Sci 2008; 109: 2872–2881.

23.

Waldron

. Shear resistance of root-permeated homogeneous and stratified soil. Soil Sci Soc Am Proc 1977; 41: 843–849.

Micromechanical analysis of loop-formed fiber-reinforced soil composite

Abstract

Keywords

Introduction

Materials and methods

Preparation of treatments

Determination of input parameters for micromechanical analysis

Direct shear test

Micromechanical analysis

Results and discussion

Comparison of fiber and looped-fiber performance

Shear strength envelopment of treatments

Conclusion

Footnotes

Funding

References