A series of unconfined compression tests were conducted in laboratory to investigate the compressive behavior of geogrid-reinforced granular soil. Samples, each varying either in the reinforcement spacing (S) or the relative compaction of the granular soil (K), were prepared with S of 2.5 cm, 3 cm, 3.75 cm, 5 cm or 7.5 cm and K of 88 %, 92 %, or 96 % respectively. Based on a detail analysis of the effect of S and K on the compressive stress-strain response, the following conclusions were obtained: (1) the compressive strength increased either with the increase of K or with the decrease of S, but there was an optimum match of K with S, which leading an expected reinforcement benefit (enough compressive strength at a permissible strain) economically; (2) geogrid-reinforced granular soil had a higher compressive strength but a much more lower failure strain compared to geotextile-reinforced granular soil.
In order to study the effect of pile-soil-pile interaction on the mechanism of pile base resistance in pile groups,a calculating model is proposed for the ultimate tip bearing capacity of a pile group in cohesionless soil based on the Ohde's pattern derived from the compression mechanism for a single pile.From this model an approach is derived to evaluate respectively the ultimate base resistance of an individual outside pile or an individual inside pile in a pile group.In this theoretical procedure,the influence on the ultimate pile tip resistance is taken into account by the pile spacing,pile diameter,pile embedding length and the properties of the soil below the pile tip.The pattern given by the theoretical formula that the pile base bearing capacity increases with the relative pile spacing(the ratio of pile spacing to pile diameter)decrease agrees with that measured in a model test.
In order to investigate the behavior of geosynthetic-reinforced soil (GRS), a series of laboratory experiments were conducted on GRS samples made up of granular soil and a nonwoven geotextile. The resilient deflection, resilient modulus, California Bearing Ratio (CBR) and unconfined compressive strength of the GRS mass were the parameters examined to evaluate the performance of the GRS samples. The focus of the tests was to determine the effects of the vertical spacing of the reinforcement and the relative compaction of the granular soil on the performance of the GRS mass. Based on the test results, it was concluded that the compressive strength of geotextile-reinforced soil increases significantly with the decrease in reinforcement spacing or with the increase in the degree of the relative compaction of fill. Furthermore, the well-compacted granular soil reinforced with closely spaced geotextile not only has a higher compressive strength compared to that with widely spaced reinforcement, but also exhibits both ductile and flexible failure mode making it a desirable composite material for the construction of supporting structures. In addition, it was found that the standard laboratory soil resilient modulus and CBR test methods are unsuitable for geotextile-reinforced soil because sliding occurs along the geotextile-soil interface under test loading due to the lack of adequate anchorage of the geotextile in the small sample.
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