GEOSYNTHETIC-REINFORCED SUBGRADE IMPROVEMENT UNDER CYCLIC LOADING: A GIROUD–HAN METHOD ANALYSIS

Abstract

Pavement damage is a common problem caused by a combination of environmental factors and repeated traffic loads. One of the leading causes is subgrade saturation from heavy rainfall, followed by repeated pressure from heavy vehicle wheels. This study aims to analyze the effect of cyclic loading on the soaked California Bearing Ratio (CBR) of subgrade soil and to determine the required thickness of the subgrade improvement layer using the Giroud–Han method. Two soil materials from the Gumitir area, East Java, were tested under saturated conditions with cyclic load variations of 50, 100, and 150 psi, up to 100 repetitions. The test results showed that the CBR value decreased exponentially with the number of load cycles, with a decay constant k = 0.034. The initial CBR values of 5.3% and 5% declined to 1.4 % and 2.7%, respectively, after repeated loading. The results of this study confirm that cyclic loading significantly reduces the bearing capacity of saturated soil, which affects pavement design. Without cyclic loading, the soil has a higher CBR value. However, after being subjected to traffic loads, it has a lower minimum CBR value and requires subgrade improvement. Analysis of the subgrade improvement layer thickness using the Giroud–Han method shows that geotextiles can reduce thickness by up to 38%, while geogrids can reduce it by up to 52%. The use of geosynthetics has been proven effective in enhancing subgrade performance and reliability.