Arian Nazeri

This paper experimentally studies the efficiency of a multi-task geosynthetic comprised of a geogrid and a nonwoven geotextile layer in diminishing the required thickness of base course constructed over different soft subgrades in container yards pavements. In this research, a total number of 24 laboratory static plate load tests (PLT) were conducted in a large-scale steel test box. In all tests, the reinforcement was embedded at the interface of the base course and subgrade to get both reinforcing and separation functions involved simultaneously. The investigated parameter was bearing capacity coefficient K 30 obtained directly from the results of laboratory PLTs through a 305 mm-diameter circular steel plate. Results illustrated that in the case of composite-geosynthetic inclusion, the required thickness of the base course could be reduced from 17 to 23 percent depending on the strength of the underlying subgrade layer. This could be both economically and environmentally instrumental in real heavy-duty pavement design. Moreover, considering the geosynthetic end-fixation led to better functionalities of all reinforcements in fixed-end models compared to free-end ones. The results also demonstrated that the efficiency of the geocomposite is contingent on the thickness of the base course. As the thickness increases, the efficiency of the reinforcement reduces.

Loose soils normally are of weak bearing capacity due to their structural nature. Being exposed to heavy traffic loads, they would fail in most cases. To tackle the aforementioned issue, geotechnical engineers have come up with different approaches; one of which is making use of geosynthetic-reinforced soil-aggregate systems. As these polymeric reinforcements have highlighted economic and environmentally-friendly features, they have become widespread in practice during the last decades. The present research investigates the efficiency of four different types of these reinforcements in increasing the bearing capacity of two-layered soil sections using a series California Bearing Ratio (CBR) test. The studied sections are comprised of a 10 cm-thick layer of no. 161 Firouzkooh sand (weak subgrade) and a 10 cm-thick layer of compacted aggregate materials (base course) classified as SP and GW according to the United Soil Classification System (USCS), respectively. The aggregate layer was compacted to the relative density (Dr) of 95% at the optimum water content (Wopt) of 6.5%. The applied reinforcements were including two kinds of geocomposites (type A and B), a geotextile, and a geogrid that were embedded at the interface of the lower and the upper layers of the soil-aggregate system. As the standard CBR mold was not appropriate in height for this study, the mold used for soaked CBR tests were utilized. To make a comparison between the results of stress-settlement behavior in the studied specimens, CBR values pertinent to the penetrations of 2.5 mm and 5 mm were considered. The obtained results demonstrated 21% and 24.5% increments in the amount of CBR value in the presence of geocomposite type A and geogrid, respectively. On the other hand, the effect of both geotextile and geocomposite type B on CBR values was generally insignificant in this research.

The present research has been performed to investigate the effect of base course application on load-settlement characteristics of sandy subgrade using plate load test. The main parameter investigated in this study was the subgrade reaction coefficient. The model tests were conducted in a 1.35 m long, 1 m wide, and 1 m deep steel test box of Imam Khomeini International University (IKIU Calibration Chamber). The base courses used in this research were in three different thicknesses of 15 cm, 20 cm, and 30 cm. The test results indicated that in the case of using base course over loose sandy subgrade, the values of subgrade reaction coefficient can be increased from 7 N/cm^3  to 132 N/cm^3, 224 N/cm^3, and 396 N/cm^3 in presence of 15 cm, 20 cm, and 30 cm
base course, respectively.