A series of constant head permeability test was performed by putting in a geotextile between a geomaterial layer and a gravel layer in order to evaluate an effect of geomaterial on the cross-plane flow performance of geotextile filter. As the geomaterials for this study, Ataka loam, Kanto loam, Rokunohe sand with fine-grained and Muroran sand with fine-grained were prepared. Based on test results, it was found that the cross-plane flow performance of geotextile depended on the relationship between an amount of clogging per unit volume on each geotextile and a percentage passing by mass of soil particle size less than an opening size of geotextile. It is expected that a clogging mass and an amount of clogging per unit volume are affected by a fiber structure of geotextile.

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A series of large-size plane strain compression (L-PSC) tests were performed on dense air-dried Toyoura sand reinforced by six layers of: a) two types (stronger and weaker) of geocomposite (GC); and b) one type of woven geotextile sandwiched by two non-woven sheets (SW-GT). The GCs basically consist of yarns for a reinforcing function and a non-woven geotextile (N-GT) sheet for drainage and/or separation functions. The two GC types have similar shapes of tensile load-strain relation whereas the ultimate strength and stiffness are largely different. On the other hand, the rupture strength of SW-GT is about 75% of the average of the values of the two types of GCs. In this study, the degree of unification between the yarns and the N-GT sheet of the weaker type of GC was improved by the following two treating methods: a) the yarns were very partially fixed to the N-GT sheet (lightly treated); and b) the full-length (23cm) of the yarns was fixed by gluing to the N-GT sheet (fully treated). The compressive strength of reinforced sand in L-PSC drastically increased when compared to the unreinforced sand and the strength increase was particularly large when the GC was fully treated. When fully treated, the tensile force mobilised in the N-GT sheet is fully transferred to the yarns, allowing the GC to effectively work as reinforcement having a mobilised covering ratio (CR) of 100%. When not treated, the mobilised CR of the GC reduced to a lower value. The sand specimen reinforced with the SW-GT, having an effective value of CR equal to 100% because of a nearly perfect fixation between the woven and non-woven sheets, showed the highest compressive strength, despite that the strength of the SW-GT was noticeably smaller than that of the untreated stronger type of GC. These tests results indicate that sufficient unification between the yarns and the N-GT for a GC is very important for the GC to effectively function as reinforcement at least in the scale of the present PSC tests. Further study will be necessary to examine whether this conclusion derived from laboratory test results can be applied to full-scale field cases.

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