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Title: Soil-geosynthetics interaction in geosynthetics reinforced soil wall
Keywords: field and laboratory pullout tests, residual soil, geotextile, geogrid, interface friction angle, bearing resistance, twisted transverse members
Issue Date: 15-Feb-2006
Citation: LIM HENG THONG (2006-02-15). Soil-geosynthetics interaction in geosynthetics reinforced soil wall. ScholarBank@NUS Repository.
Abstract: Research for the past few years at NUS was concentrating on laboratory pullout tests and on the investigation of the drainage capability of geotextile. Only limited numbers of field pullout test on geotextile was conducted at Bukit Panjang, Singapore. Present research focus on the field and laboratory pullout tests in conjunction with the actual construction of a three-tier geosynthetics reinforced soil (GRS) slope at Bukit Batok, Singapore. This research involves the study of the interface properties between geotextile or geogrid and residual soil, aiming to arrive at an effective use of residual soil as backfill material. This research also studies the pullout mechanism of geogrid, in particular the bearing resistance component that is contributed by the transverse members. The field pullout tests were conducted on geotextile and geogrid in two different soil conditions: a??drya?? state (soil at in-situ moisture content) and a??weta?? state (soil was ponded with water). There are a total of four field pullout tests conducted in this study, two on geotextile and two on geogrid. In all these four tests, loading pattern consists of loading stage till a peak pullout force is achieved, followed by unloading stage to zero tension. It is then followed by reloading stage. For comparison purposes, a total of six laboratory pullout tests were performed to evaluate the interface properties. These were all performed using NUS large-scale pullout apparatus with the same residual soil and geosynthetics materials as used in the field pullout tests.The pullout force of geogrid is contributed by shearing resistance on the surface of the members and bearing resistance of the transverse members. This study shows that some transverse members were twisted, as seen in the exhumed sample of geogrid, during the pullout process. This twisted transverse members resulted in larger area for bearing resistance. It was shown that other published literature which obtained an unreasonable high interface friction angle, ignored this factor. The percentage of pullout force for a??weta?? soil condition with respective to the a??drya?? soil condition for both the geotextile and geogrid cases were found to be more than 70%. Both composite geotextile and this particular type of geogrid which has gaps in between yarns could dissipate excess pore water pressure, thus resulting in a relatively high pullout force in a??weta?? condition. The present research shows that the prediction of the soil-geosynthetics interface friction angle from large-scale laboratory pullout tests is within about 12% of that from the field pullout tests. It was also concluded that I'/?? of 0.45 and 0.50 can be used as a conservative design value for this type of residual soil, with this category of geotextile and geogrid respectively; if the pullout test results were not available.
Appears in Collections:Master's Theses (Open)

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