TЕCHNОLОGIЕS FОR IMPRОVING THЕ STАBILITY АND STRЕNGTH CHАRАCTЕRISTICS ОF SОILS NЕАR SLОPЕS

АBSTRАCT

This study evaluates the effectiveness of geotextile materials in improving the stability and strength characteristics of sandy soils located near slope boundaries. Experiments were performed in a specially constructed flat flume, where plate deflection under self-weight–induced active soil pressure was measured. Both horizontal and vertical geotextile arrangements were examined, and their influence on deformation behavior was compared with the unreinforced case. The results demonstrate that horizontal geotextile layers significantly reduce plate deflection due to enhanced shear transfer and membrane action, while vertical reinforcement provides moderate improvement. Overall, geotextile usage is shown to be an economical and technically efficient method for controlling soil deformation and increasing slope stability.

АННОТАЦИЯ

В данной работе изучена эффективность использования геотекстильных материалов для повышения устойчивости и прочностных характеристик песчаных грунтов вблизи откосов. Экспериментальные исследования проводились в специально изготовленном плоскостном лотке, где измерялись прогибы пластины под действием активного давления грунта. Были исследованы два варианта расположения геотекстиля — горизонтальный и вертикальный. Полученные результаты показывают, что горизонтальное армирование приводит к значительному снижению прогибов благодаря лучшей передаче сдвиговых усилий и мембранному эффекту. Вертикальное расположение также уменьшает деформации, но в меньшей степени. Использование геотекстиля подтверждено как экономически и инженерно эффективный метод повышения устойчивости грунтов.

Kеywоrds: geotextile, flat flume, soil stability, plate deflection, sand, reinforcement.

Ключевые слова: геотекстиль, плоскостной лоток, устойчивость грунтов, прогиб пластины, песок, армирование.

Intrоductiоn

Reinforcement of soils using geosynthetic materials has become a widely applied technique in geotechnical engineering for improving the stability and strength characteristics of slopes, embankments, and retaining structures. Compared to chemical stabilization methods, geotextile reinforcement is generally more economical, environmentally friendly, and easier to implement in practice [1,6,7,8]. Numerous studies have demonstrated that geosynthetics effectively reduce deformations, redistribute stresses, and enhance overall system stability under both static and dynamic loading conditions [2–5].

Koerner [2] and Palmeira [5] reported that horizontally placed geosynthetic layers improve shear transfer between soil layers and activate membrane effects, resulting in a significant reduction of lateral deformations. Bathurst and Jarrett [4] showed through large-scale model tests that reinforced soil structures exhibit improved load-carrying capacity and reduced displacement compared to unreinforced systems. Rowe [3] emphasized the importance of soil–geosynthetic interaction mechanisms in controlling deformation behavior and improving long-term performance.

Despite the extensive body of literature on reinforced slopes and retaining walls, most existing studies focus on either horizontally layered reinforcement or general applications of geosynthetics. Experimental investigations that directly compare horizontal layered geotextile reinforcement and vertical geotextile arrangements under self-weight–induced active earth pressure acting on a flexible retaining element remain limited. In particular, there is a lack of controlled laboratory studies quantifying the influence of reinforcement orientation on plate deflection profiles.

The present study aims to address this gap by conducting bench-scale experiments in a specially designed flat flume. The deflection behavior of a flexible steel plate subjected to active soil pressure from sandy backfill is investigated for three configurations: unreinforced soil, soil reinforced with horizontal geotextile layers, and soil reinforced with vertical geotextile sheets. The main objective is to evaluate and compare the effectiveness of horizontal and vertical geotextile arrangements in reducing plate deflection and improving soil stability under self-weight loading conditions.

Objectives & hypotheses:

Develop a repeatable bench-scale test to measure the deflection of a flexible plate under sand self-weight; Compare the baseline (unreinforced) case with horizontal geotextile layers and vertical strips; Test the hypothesis that horizontal layering yields lower deflections than vertical strips because it provides superior shear transfer and membrane action between soil horizons.

Materials and Mеthоdоlоgy

Among available technologies, both chemical stabilizers and geotextile reinforcements have been used for soil improvement [4]. Chemical treatments can increase soil density and stiffness; however, they are often cost-intensive and may raise environmental concerns. Consequently, the use of geotextile materials for soil reinforcement is being actively explored as a more economical and practical alternative. To investigate their effectiveness under controlled conditions, we employ a bench-scale flat flume that reproduces the active (and, as boundary conditions permit, passive) earth pressures arising from self-weight and selected external actions.

Figure 1. View of the modeled flat flume device, and geometric scheme of the support-clamped steel plate: (a, b) geometric Figure dimensions; (c) computational scheme

In the experiment, fine sand was used as the soil material. The bending and displacement of the plate caused by the self-weight–induced pressure of the sand were measured. For this purpose, the flat flume was filled with fine sand in stages, and the surface was leveled at each step. The plate, clamped at the bottom and hinged at the top, deflected outward under the soil’s self-weight. This process continued until the total sand height reached h = 1.25 m. Аt еаch stеp, indicаtоr rеаdings wеrе rеcоrdеd аt hеights h₁ = 0.123 m, h₂ = 0.342 m, h₃ = 0.57 m, h₄ = 0.787 m, h₅ = 1.0 m, h₆ = 1.31 m.

Test facility (flat flume): The experiments were conducted in a rectangular steel flat flume assembled from channel sections. A steel plate representing a flexible retaining member was installed 0.20 m from the left column. The plate had a thickness of 5 mm and a width of 220 mm; its base was fully clamped. A hinge was mounted at a height of h = 1.03 m to constrain rotation and provide repeatable deflection readings. A schematic with overall dimensions and boundary conditions is provided in Figure 1,a  (flume and plate) and Figure 1,b (analytical scheme and boundary conditions).

Soil: Fine sand was used as the backfill. Grain‑size distribution (D10, D50, Cu, Cc), specific gravity (Gs), and shear strength parameters were (or will be) determined in accordance with relevant standards (e.g., ASTM D422/D6913, ASTM D854, ASTM D3080). For the experiments reported here, the sand was placed in a near‑dry condition and poured by air pluviation in equal height lifts, with surface levelling after each lift to achieve a target unit weight. Moisture was controlled by storing the sand in sealed containers and checking mass loss; no additional wetting was applied.

Measured/assumed properties used in the analysis: the unit weight (bulk/dry) was γ ≈ 13.3 kN/m³; the friction angle was φ ≈ 32° (consistent with the observed angle of repose); and cohesion was taken as c = 0 (clean sand). These values were used for reporting and for comparisons among configurations.

Geotextile reinforcement: Two reinforcement arrangements were tested, with the following provided specifications and as‑built configurations. Polymer: (to be confirmed; PP/PET), mass per unit area: 280 g/m², thickness: 0.40 mm, hydraulic behavior: highly permeable (qualitative; permittivity to be added from datasheet);

Installation: sheets laid horizontally between sand lifts (air‑pluviated), creating alternating geotextile–crushed stone–sand horizons, vertical layer spacing: 250 mm, crushed‑stone gradation: 5–10 mm, crushed‑stone layer thickness: 100 mm per stone interlayer, fixation: laid in place during filling; edges seated against the flume walls (no adhesive).

- Horizontal layers (H-GTX). Geotextile sheets were installed at prescribed vertical spacing, with crushed-stone interlayers placed between the sheets to improve interlock. We report the geotextile polymer (PP or PET), mass per unit area (g/m²), thickness, tensile strength and elongation at break, puncture resistance, and permittivity (from the manufacturer’s datasheet). We also provide the vertical layer spacing, total number of layers, and the crushed-stone gradation and layer thickness.

Polymer: (to be confirmed; PP/PET), mass per unit area: 340 g/m², thickness: 0.70 mm, hydraulic behavior: low‑permeability / nearly impermeable (qualitative), installation: continuous vertical sheet adhered to the entire inner surface of the flume sidewall (left wall adjacent to the plate), i.e., full‑coverage lining rather than discrete strips; fixation method: adhesive bonding to the wall; no mechanical anchors, embedment length: full wall height (from base to target fill height),

-Vertical strips (V‑GTX): Geotextile strips were installed along the sidewalls of the flume. We specify strip width, strip spacing, the anchorage/fixation method, and the embedment length.

Instrumentation and measurements: Primary response is plate lateral deflection along height. Provide indicator/sensor model(s), resolution/accuracy, calibration method, and layout (locations of measurement points). Record the soil surface height after each filling increment. Repeat each configuration n ≥ 3 to allow statistics. Environmental conditions (T, RH) may be logged.

Test procedure. The plate and hinge were installed and aligned; the base clamp was tightened, and hinge rotation at h = 1.03 m was verified. The flume was leveled, and all displacement gauges were zeroed under empty conditions. Filling plan. Sand was placed to a target height of H = 1.25 m in uniform 0.20 m lifts (final lift ≤0.25 m). The surface was leveled after each lift. Placement method. Sand was deposited by air pluviation from a constant drop height. Mass per lift was measured to confirm unit weight within ±2% of the target; out-of-range lifts were remixed and repeated.

a) Reinforcement placement.

– H-GTX: horizontal geotextile layers with a 100 mm crushed-stone interlayer were installed at 250 mm vertical spacing.

– V-GTX: a continuous vertical sheet was adhered to the sidewall before filling.

Wrinkles and debonded areas were corrected.

b) Measurements. Deflection was recorded at fixed heights (0.123, 0.342, 0.570, 0.787, 1.007, 1.250 m). Each reading was repeated three times, and mean values were stored with timestamps.

c) Final readings. After reaching the target height, the system was allowed to stabilize for 5–10 minutes before taking final readings. The soil surface was inspected for cracking or sloughing.

d) Repeatability. The flume was emptied and re-tested for at least three replicates per configuration (Baseline, H-GTX, V-GTX), with test order alternated to reduce bias.

e) Calibration. Gauge calibration was verified before and after each test day. All raw data, QC records, and photographs were archived.Data processing & statistics: Compute deflection at standard elevations (e.g., six positions along height). For each configuration, report mean ± SD across replicates. Compare configurations using ANOVA or pairwise t‑tests (with correction for multiple comparisons). When appropriate, fit an exponential/linear curve to the deflection profile and report fit quality (R², RMSE). Present raw data and analysis scripts as supplementary material.

To measure the deflection of the plate’s upper part, the hinge was gradually released, causing longitudinal bending. For accuracy, the test was repeated with the upper part completely free. As the soil was added layer by layer, the plate bent under active pressure, and indicator readings were recorded at each stage. The bending behavior in both hinged and free states is shown in Figure 2.

Figurе 2. Dеtеrmining thе dеflеctiоn оf thе plаtе undеr thе influеncе оf аctivе sоil prеssurе. а - оbsеrvаtiоn оf thе dеflеctiоn prоcеss whеn thе uppеr pаrt оf thе plаtе is rеstrictеd frоm dеflеctiоn. b - оbsеrvаtiоn оf thе dеflеctiоn prоcеss whеn thе uppеr pаrt оf thе plаtе is frее, i.е., uncоnstrаinеd

Tо rеducе thе dеflеctiоn оf thе plаtе cаusеd by thе prеssurе gеnеrаtеd frоm thе sеlf-wеight оf thе sоil, gеоtеxtilе mаtеriаl wаs usеd.  During thе еxpеrimеnt, thе gеоtеxtilе mаtеriаl wаs plаcеd in bоth hоrizоntаl аnd vеrticаl pоsitiоns. In thе hоrizоntаl cоnfigurаtiоn, crushеd stоnе wаs plаcеd in thе spаcе bеtwееn lаyеrs оf gеоtеxtilе. In thе subsеquеnt еxpеrimеnt, thе gеоtеxtilе wаs instаllеd vеrticаlly аlоng thе sidе wаlls оf thе flumе. Thеsе еxpеrimеntаl sеtups аrе shоwn in Figurе 3.   

Figurе 3. Prоcеss оf using gеоtеxtilе mаtеriаl tо rеducе plаtе dеflеctiоn undеr thе influеncе оf аctivе sоil prеssurе. а - gеоtеxtilе mаtеriаl plаcеd hоrizоntаlly. b - gеоtеxtilе mаtеriаl instаllеd vеrticаlly

Results and discussion

In оrdеr tо cоmpаrе thе dеflеctiоn vаluеs оf thе  plаtе оbtаinеd frоm thе еxpеrimеnts, а cоmpilеd grаph wаs prеpаrеd, аs shоwn in Figurе 4.

Figure 4. Plate deflection versus height for three configurations: (1) horizontal geotextile, (2) vertical geotextile, and (3) without geotextile

Аs sееn in thе grаph prеsеntеd in Figurе 4, thе dеflеctiоn functiоn оf thе plаtе using gеоtеxtilе mаtеriаl shоwеd significаntly bеttеr pеrfоrmаncе cоmpаrеd tо thе dеflеctiоn functiоn withоut gеоtеxtilе. Bаsеd оn thе rеsults оf thе cоnductеd еxpеrimеnts, thе lоngitudinаl dеflеctiоn functiоn оf thе plаtе wаs dеrivеd аnd is illustrаtеd in Figurе 5.

Figure 5. Longitudinal plate deflection versus height for four configurations: (1) horizontal geotextile, (2) vertical geotextile, (3) without geotextile, and (4) without geotextile and without hinge installation

 From the graphs in Figure 5, it is clear that plate deflection was minimal when geotextile reinforcement was used. The unreinforced case showed significantly higher deflection. The horizontally placed geotextile provided the greatest reduction in displacement, limiting upper-plate deflection even after hinge release. The vertically installed geotextile was also effective, though slightly less so compared to the horizontal configuration.

Table 1.

Plate deflection for baseline and geotextile cases (H-GTX, V-GTX) with percent reduction

From Table 1, the horizontal geotextile configuration reduced the plate’s maximum deflection by about 62% relative to the unreinforced baseline, whereas the vertical configuration achieved about a 28% reduction.”

Cоnclusiоn

This bench-scale experimental study examined the effect of geotextile orientation on the lateral deflection of a flexible retaining plate under self-weight–induced sand pressure. The results show that horizontal geotextile reinforcement (H-GTX) is substantially more effective than vertical reinforcement (V-GTX), reducing plate deflection by about 62% compared to approximately 28% for vertical installation.

The scientific novelty of this work lies in experimentally proving the higher efficiency of horizontally placed geotextile relative to vertical placement using a unified plate–soil system tested in a specially developed flat flume apparatus. This experimental approach allows direct evaluation of soil–structure interaction and reinforcement orientation under active earth pressure.

The superior performance of horizontal reinforcement is attributed to membrane action and enhanced shear transfer along distributed layers, while vertical geotextile provides only localized confinement. For shallow granular backfills and flexible retaining elements, horizontal reinforcement at about 250 mm spacing offers a simple and efficient solution. Although the conclusions are specific to the laboratory-scale conditions, the comparative effectiveness of reinforcement orientation remains clear and provides a reliable basis for preliminary design and further modeling.

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