ABSTRACT: Hydraulic transmissivity is the most important design parameter of geocomposites used for in-plane drainage applications. This paper presents an in-depth investigation of the hydraulic behaviour of drain-tube planar geocomposites (DTPGs) and characterises the locations and causes of head losses based on a multiscale experimental approach using three different apparatus. In particular, a transmissivity rig that accommodates specimens up to 1 m² was developed to define the minimum representative surface area required to characterise DTPGs. The experimental data acquired in this study support a theoretical relationship linking head losses that occur within DPTGs to flow rate. This relationship is used to analyse the results obtained with other transmissivity rigs and to identify the key locations where head losses develop. In addition, evidence that Colebrook's equation can be applied to corrugated tubes is presented. Based on this study, it is concluded that the measured DTPG transmissivity is significantly affected by specimen length and by the experimental device used to make the measurement. For example, the DTPG transmissivity measured in accordance with ASTM D4716-08 was found to be 14% lower than the actual DTPG transmissivity.

ABSTRACT: This paper describes the reinforcing effects of multiple layers of geocell in combination with rubber–soil mixture layers in sand, and compares their behaviour with that of the multilayered geocell reinforcement alone, using plate loading at a diameter of 300 mm. The plate load tests were performed in an outdoor test pit, dug in natural ground measuring 2000 × 2000 mm in plan and 700 mm in depth. The geocell used in the tests was non-perforated with pocket size 110 × 110 mm² and height 100 mm, fabricated from continuous polypropylene filaments as a nonwoven geotextile. The optimum embedded depth of the first layer of geocell and the vertical spacing of geocell layers were found to be approximately 0.2 times the footing diameter, and the optimum percentage of rubber replacement was found to be around 8% by weight of the soil mixture. Both bearing capacity increase and settlement reduction were highest when multiple layers of geocell and rubber reinforcement were used. Results show that the reinforcements' efficiency decreased as the number of reinforcement layers increased, particularly at low settlement ratios. Higher bearing capacity and lower settlement were achieved by replacing the layers beneath the geocell layers with the rubber–soil mixture. At a ratio of settlement to plate diameter of 2%, the values of bearing pressure were in the ratio 1:2.3:3 for, respectively, the unreinforced installation, the installation with three layers of geocell, and the installation with three layers of geocell and rubber–soil between the layers. The inclusion of the geocell layers reduces the vertical stress transferred down through the foundation bed by distributing the load over a wider area. For example, at the pressure of 550 kPa applied on the soil surface, the transferred pressure at the depth of 510 mm is about 48%, 34% and 27% for the reinforced bed with one, two and three layers of geocell, respectively, compared with the stress in the unreinforced bed. Furthermore, use of the combination of geocell and rubber–soil mixture layers is more effective than use of geocell layers only in reducing the stress transferred downwards. For example, 350 mm beneath a soil surface that carries a stress of 830 kPa, the vertical stress is 15% less when two geocell layers are combined with two rubber–soil mixture layers than when there are only two geocell layers.

ABSTRACT: This paper reports an investigation into the deformation response of geosynthetic-reinforced soil layers to evaluate the level of strain required to mobilize reinforcement mechanisms during surface loading. Specifically, an assessment of data from previous studies reporting surface settlements of reinforced and unreinforced soil layers during monotonic or cyclic loading to failure is complemented with new dynamic tests performed at small- and medium-strain magnitudes. A series of test sections with and without geosynthetic reinforcement were characterized using a Vibroseis shaker truck as a dynamic loading source. The behavior of uniform sand layers under relatively small strain magnitudes (shear strain magnitudes less than 0.2%) were characterized using embedded geophones. Shear and normal strain distributions within the test sections were measured as a function of depth during application of surface shear loading. The presence of geosynthetic reinforcement (either geogrid or geotextile) at a depth of 254 mm below the surface of the sand layer does not significantly alter the distributions of shear strain or vertical normal strain relative to an unreinforced control section for the magnitudes of shear and compressive strains applied to the soil surface. The behavior of aggregate base layers overlying sand layers under medium strain magnitudes (surface deflections up to 25 mm) were characterized using an array of LVDTs on the soil surface. Surface deflection basins were measured during application of several thousand cycles of compressive loading. The presence of a geogrid within the aggregate base layer or a woven geotextile beneath the aggregate base layer were observed not to lead to a change in the surface deflection basins up to a maximum deflection of 25 mm. These observations, together with results from the literature, indicate that reinforcement mechanisms such as lateral restraint and the tensioned-membrane effect may not be mobilized until reaching relatively large displacements in some soil layers.

ABSTRACT: Laboratory triaxial compression tests were conducted to investigate the stress–strain–volumetric responses of geotextile-reinforced sand and the mobilization and distribution of reinforcement strain/loads and soil–geotextile interface shear stress within reinforced soil. Geotextile-reinforced sand specimens were tested while varying the confining pressures and number of geotextile reinforcement layers. A digital image-processing technique was applied to determine residual tensile strain of the reinforcements after tests and to estimate reinforcement tensile loads. Experimental results indicate that the geotextile reinforcement enhanced peak shear strength and axial strain at failure, and reduced loss of post-peak shear strength. The reinforced specimen had higher shear strength when compared with that of unreinforced soil after deforming by 1–3% of axial strain, which indicates that the geotextile requires a sufficient deformation to mobilize its tensile force to improve the shear strength of reinforced soil. For each reinforcement layer, mobilized tensile strain peaked at the center of the reinforcement and decreased along the radial direction, while the interface shear stress was zero at the center and peaked at a distance of 0.5–07 reinforcement radius from the center. The mobilized tensile strain of reinforcement increases as confining pressure and number of reinforcement layers increase. This work also demonstrates that the strength difference between reinforced and unreinforced soil was strongly correlated with the sum of maximum mobilized tensile forces of all reinforcement layers, indicating that mobilized tensile force of reinforcements directly improved the shear strength of reinforced soil. Last, a number of analytical models to predict peak shear strength of reinforced soil are verified experimentally. This verification demonstrates that mobilized tensile force rather than ultimate tensile strength can be used in analytical models.

ABSTRACT: Heavy traffic loading can produce loss of functionality in pipeline networks, with consequential interference with economic and social impacts in the areas involved in breakage. The consequences of breakage or disconnection of pipelines are technical, economic and social. In the case of a sewer network failure, illness and epidemics might result. In this paper, to protect the buried pipe, use of a three-dimensional geosynthetic (geocell) is investigated to reinforce the trench. Two series of three-dimensional full-scale tests under repeated loadings have been performed. The first test programme compares the performance of buried pipes installed beneath soil that is unreinforced, planar reinforced, or with geocell in a trench. Compaction difficulties necessitated a change in the process of compaction so that a second installation was proposed. In this series of tests, further understanding of the behaviour of geocells with different opening areas and heights above the buried pipes under repeated loads is presented and discussed. It is observed that the effective reinforcement and improvement of the backfill system is achievable if the geocell is installed in the backfill with an appropriate compaction process. The results further indicate the importance of compaction both below and above the level of the geocell installation. As a result of the modified compaction process, the trench reinforced with geocell showed superior performance, delivering a 65% and 35% reduction in soil surface settlement and vertical diametral strain, respectively, compared with the unreinforced soil.

ABSTRACT: The reduction factors used to account for the impact of installation damage on the tensile strength of geogrids employed in mechanically stabilised earth (MSE) walls and reinforced embankments are usually obtained from field tests that simulate actual construction conditions. Although costly and time-consuming, site-specific field tests incorporate the damage mechanisms that may occur in geogrid reinforcements during installation. Several studies have developed empirical relationships for these reduction factors for use in design calculations, typically considering the effects of construction methods and the backfill soil gradation on the damage of geogrids having a given polymer type, manufacturing method, and weight per unit area. One of the issues with these relationships is how to quantify the backfill soil gradation in the empirical relationships. In this study, a series of field test sections were constructed using geogrids with two polymer types and a range of different weights per unit area to identify quantitative relationships that can be used to better estimate the impact of backfill gradation on the reduction factors for installation damage of geogrids. The results from the field test sections indicate that the reduction in tensile strength of geogrids after installation is non-linearly related to the maximum particle size in the backfill soil. Recommended upper-bound relationships for the reduction in tensile strength for different geogrid polymers are presented based on an evaluation of data sets, with a greater reduction factor observed for polyvinyl-chloride-coated woven polyethylene geogrids than for high-density uniaxially-drawn polyethylene geogrids.

ABSTRACT: The first geosynthetic retaining wall in Brazil was constructed in 1984 as an instrumented 10 m high geotextile-reinforced soil wall with a poorly draining backfill. This structure has been showing excellent performance throughout its service life, even after long periods of rainfall. In the past, the excellent performance of the wall had been attributed to the influence of soil confinement on the geotextile strength properties as well as the comparatively high interface shear strength between the fine soil and the nonwoven geotextile. Now there is also evidence of the beneficial effect of the internal drainage capacity when using nonwoven geotextiles as reinforcements. In order to clarify the understanding of the performance of the pioneer history case wall (SP-123 wall) and the effect of nonwoven geotextiles as reinforcements of fine-grained soils, full-scale laboratory models of geotextile reinforced walls were tested under wetting conditions. Results from the instrumentation have shown no significant positive water pressures and relatively small displacements even after intense periods of precipitation. The consistency between field and laboratory investigations provides strong evidence in support of the use of nonwoven geotextiles to reinforce poorly draining soils.

ABSTRACT: Being a waste material, fly ash can be used in large quantities in construction of highway and railway embankments. This paper presents a series of plane strain model tests carried out on both reinforced and unreinforced fly ash embankment slopes. Laboratory tests were conducted by varying parameters such as embedment ratio, length and number of reinforcement layers, and edge distance from slope crest. A numerical study using finite-element analysis (PLAXIS 2D, version 9.0) was also carried out to verify the model test results. The size of the numerical model was kept the same as that of the laboratory test model. The agreement between observed and computed results was found to be reasonably good. Based on numerical and experimental results, the critical values of the geogrid parameters for maximum reinforcing effects were established.

ABSTRACT: When roads are constructed on weak soils, stability and settlement considerations are critical. At locations having poor subgrade support, it is recommended to use alternative methods to reinforce the soil. The use of fibre materials in geotechnical design and application is advantageous because randomly distributed fibres offer strength isotropy and improve the soil performance. This paper presents experimental results on the improvement of the California bearing ratio (CBR) performance of sand by the addition of buffing rubbers. Two different rubbers – granulated rubber and fibre shaped buffing rubber – were used. Three factors were found to significantly affect the CBR values: rubber shape, rubber content and aspect ratio. Test results revealed that changes in properties of sand caused by reinforcement were sensitive to the aspect ratio of the rubbers. Fibre inclusions with optimum aspect ratio increase the CBR of the subgrade and hence may cause a substantial decrease in design thickness of the pavement. Fibre inclusions mixed with subgrade will provide needed tensile strength under traffic loads.