Research On The Capillary Water Rise And Salinity Transport In The Soil Of Subgrade And Construction Techniques In The Yellow River Flood Field

In the Yellow River alluvial plain, the groundwater with high salinity has shallow water table depth. Under the effect of capillary, water and salt are transported within the subgrade, which is built by non-saline soil, resulting in serious road distress. In this research, soil subgrade and columns were constructed in laboratory to investigate the effects of depths of groundwater table and the degree of groundwater salinity on the movement and distribution of water and salt within the subgrade. Richards’equation and the diffusive and convective solute transport equation were solved simultaneously through the software of COMSOL Multiphysics. The results of laboratory experiment and numerical analysis indicate that:(1) The movement and distribution of water and salt result from capillary tubes, movement of water, existence of salt in groundwater and the effects of evaporation. Therefore, the slope and surface of the subgrade are the main areas of salt accumulation due to the effects of evaporation. And the concentration of salt in those areas is twice to fourth as much as the concentration of salt in the inner of subgrade. Thus, the slope and surface of the subgrade are the key positions for treatment of subgrade in the saline soil areas.(2) The depths of groundwater table, degree of groundwater salinity and evaporating intensity have great effect on the movement and distribution of water and salt within the subgrade. As the depths of groundwater table increase, the water content and salt concentration decrease at the same level beneath the surface. When the degree of groundwater salinity is15g/L, the critical depth of groundwater is determined to be290cm for no salt accumulation at the surface of soil columns and the slope of subgrade. As the degree of groundwater salinity increases, the water content increases first and then keeps the same level, and the salt concentration increases throughout. There was a significantly linear correlation between the degree of groundwater salinity and the salt concentration. For the evaporating intensity, the greater the evaporation is, the greater and deeper the salt accumulates alone the slope of subgrade.(3) The result calculated by COMSOL Multiphysics for the distribution and accumulation of water and salt is similar to the result obtained from the laboratory experiment. Thus, numerical analysis is an effective method to study the water and salt movement in the subgrade And for the simulation of geotextile partition, the result indicates that semi-partition coulc effectively reduce the salt concentration of slope of subgrade. In the area of deep groundwater table and low salinity groundwater, the measurement of semi-partition could be adopted. While in the area of shallow groundwater table and high salinity groundwater, the measurement of semi-partition and whole-partition should be used in combination to ensure the stability of subgrade.Combined with the construction of Bin-De highway and based on condition of groundwater and the characteristics of water and salt transport, the scheme of geotextile partition was proposed to ensure the stability of subgrade.