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.