Effect of Cyclic Suction History (Hydraulic Hysteresis) on Resilient Modulus of Unsaturated Fine-Grained Soil

Abstract

This study explored the effect of hydraulic hysteresis on the resilient modulus (Mr) of subgrade soils. For that purpose, suction-controlled Mr tests were performed on compacted specimens along the primary drying and wetting and secondary drying and wetting paths. First, Mr tests were performed continuously on the same sample at various suction values along all of the paths (drying, wetting, etc.). A relationship between Mr and matric suction was obtained and identified as the resilient modulus characteristic curve (MRCC). MRCC results indicated that Mr increased with suction along the drying curve. Results along the primary wetting curve indicated a higher Mr than along primary drying and secondary drying curves. The second series of tests, referred to as virgin tests, were performed at suction values without subjecting the sample to previous Mr testing. Results indicated that Mr values were lower compared with results from the other type of test (i.e., with continuous Mr testing), and that Mr results were influenced by the continuous stress loading. However, Mr values along the wetting curves were still higher than for the drying curves for these virgin tests and therefore indicated that results were also influenced by hydraulic hysteresis (i.e., cyclic suction stress loading). New models to predict the MRCC results during drying and wetting were proposed on the basis of the soil–water characteristic curve hysteresis. The models favorably predicted the drying and then the wetting results with the use of the soil–water characteristic curve at all stress levels.