Use of Capillary Barrier to Prevent Loess Subgrade Desiccation and Its Design Parameters
Clay subgrades are prone to desiccation cracking after long-term droughts.A capillary barrier cover(CBC)is proposed instead of traditional engineering methods,such as anti-seepage membranes and waterproof curtains,to maintain moisture stability in subgrades.Physical model tests were conducted to verify the effectiveness of the proposed approach.The working mechanism of the CBC in a drought environment was analyzed based on unsaturated soil mechanics principles.The results show that after 15 days of continuous drying(35 ℃-50 ℃),the water content of the subgrade without CBC decreases by 4.6％-7.9％,and cracks appear at the top surface and slope of the subgrade owing to shrinkage.The water content only decreases by 1.0％-2.0％in the subgrade with CBC,where no cracks develop.The temperature at the side with CBC is 5.5 ℃ lower than that at the side without CBC.This demonstrates that the CBC can effectively adjust the moisture and temperature of the subgrade and limit moisture evaporation.Corresponding numerical tests were conducted to investigate the effects of the design parameters on the CBC performance.It was found that an increase in fine-and coarse-grained particles,particularly the latter,could decrease the evaporation of subgrade moisture.A 40 mm increment in the coarse-grained layer thickness decreases the water evaporation at each observed point by 1.7％-4.5％,whereas the same increment in the fine-grained layer thickness induces a decrease of less than 1％.In addition,the numerical results show that the initial water contents of the fine-and coarse-grained soil layers minimally influence the performance of the CBC,which can be determined by the required degree of compaction in practice.
subgrade engineeringloess subgradedesiccation crackingcapillary barrierstability of moisture fielddesign parameter
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