Impact of repeated loading on mechanical response of a reinforced sand

Abstract

Pavements constructed over loosely compacted subgrades may not possess adequate California bearing ratio (CBR) to meet the requirements of pavement design codes, which may lead to a thicker pavement design for addressing the required strength. Geosynthetics have been proven to be effective for mitigating the adverse mechanical behaviors of weak soils as integrated constituents of base and sub-base layers in road construction. This study investigated the behaviors of unreinforced and reinforced sand with nonwoven geotextile using repeated CBR loading test (followed by unloading and reloading). The depth and number of geotextile reinforcement layers, as well as the compaction ratio of the soil above and below the reinforcement layer(s) and the compaction ratio of the sand bed, were set as variables in this context. Geotextile layers were placed at upper thickness ratios of 0.3, 0.6 and 0.9 and the lower thickness ratio of 0.3. The compaction ratios of the upper layer and the sand bed varied between 85% and 97% to simulate a dense layer on a medium dense sand bed for all unreinforced and reinforced testing scenarios. Repeated CBR loading tests were conducted to the target loads of 100 kgf, 150 kgf, 200 kgf and 400 kgf, respectively (1 kgf = 9.8 N). The results indicated that placing one layer of reinforcement with an upper thickness ratio of 0.3 and compacting the soil above the reinforcement to compaction ratio of 97% significantly reduced the penetration of the CBR piston for all target repeated load levels. However, using two layers of reinforcement sandwiched between two dense soil layers with a compaction ratio of 97% with upper and lower thickness ratios of 0.3 resulted in the lowest penetration.