Capillary Water Upward Law and Treatment Technique of Expansive Soil Subgrade

The method which utilized Richards soil-water transport equation and soil-water characteristic curve to calculate upward height was suggested.The numerical simulation of capillary water upward process for different cushion layers under the expansive soil subgrade was carried out by the suggested method.Influences of soil,gradation and depth of base cushion layer on capillary water upward law of expansive soil subgrade were studied.Results show that the capillary water upward height is controlled by gradation composition,cushion layer thickness and initial filling water content,comparatively speaking,gradation composition is the governing factor.Preferential order of barrier action for different cushion layer materials is uniform sand,bad gradation sand,lime-treated soil and good gradation gravel.It is suggested that cushion layer thickness adopts 20 mm for uniform sand and 30 mm for bad gradation sand or lime-treated soil respectively so that stability of subgrade can be effectively guaranteed.