| The groundwater level in the Hetao plain in Inner Mongolia is high and capillary action is intense.The interaction of moisture and salinity under the prevailing climate and environmental conditions often causes roadbed salinization and other roadbed and pavement diseases,which affects the overall strength and stability of the roadbed and pavement in the area.For this reason,the soil column test,scaled subgrade solid model and numerical simulation technology are used to analyze and study the temporal and spatial distribution characteristics of the water field and salt field inside the subgrade.Based on this,the engineering measures for the prevention and control of salinization in the Hetao Irrigation District are proposed,and the main conclusions are as follows:(1)By investigating the existing environmental conditions in the study area,and sampling and analysis from different depths(10 cm,30 cm,50 cm,70 cm,and 90 cm)of the roadbed of a typical road section,the results show that the soil samples of the road sections without disease contain The salt content is low and it is non-salted soil;the soluble salt content in the saline soil within a depth of one meter below the surface of the road section where the disease occurs is between 0.26% and 0.87%,and the composition is mainly soluble chloride salt,regardless of the base layer or The salt content of roadbed samples is generally higher than that in the range of 20 cm below the ground surface,the soluble salt content accounts for 59.04% of the total soluble salt of the soil in the measurement range.With the increase of depth,the total soluble salt is significantly reduced.It shows that there is obvious salinization in the roadbed of the diseased section,which is one of the important reasons for the road surface boiling and other diseases in the Hetao Irrigation District of Inner Mongolia.(2)Homogeneous soil column test The results of the water and salt migration test show that the salt accumulation height in the shallow area of the silty clay roadbed in the Hetao Irrigation District depends on the balance position of the capillary water replenishment intensity and the evaporation intensity;the salt migration in the deep area of the roadbed is The water gradient and salt concentration gradient between the high-quality fill and the saline foundation provide the original power for it.In the whole salinization process,factors such as the type of filler,the salt concentration of groundwater,the height of the top surface of the roadbed relative to the groundwater level,the external environment temperature,the surface evaporation conditions,and the time all have an impact on the salinization of the silty clay roadbed.(3)According to the research results of soil column test and scaled roadbed model water and salt migration test,the water inside the roadbed acts as a carrier to carry salt and migrate upwards in the form of a relay between saturated and unsaturated currents.The test results show that the influence of aeolian sand layer on capillary water rise is very different in different regions: the soil layer within the range of 0-40 cm at the bottom of the soil pillar is replaced with aeolian sand layer,and the upper boundary of the saturation zone rises to 100 cm,indicating that the aeolian sand layer in the saturation zone will increase the capillary water level;after replacing the soil layer within the range of 80-120 cm of the soil pillar with the aeolian sand layer,the water content of the upper part of the sand layer is significantly lower than the same height The water content of the homogeneous soil column indicates that the aeolian sand layer located in the unsaturated zone can effectively delay the rise of capillary water,reduce the efficiency of capillary water replenishment,and then reduce the height of capillary water level.(4)The finite element software is used to simulate the water and salt transport process of the soil.Further study the law of water and salt migration inside the roadbed in Hetao Irrigation District,and estimate the height of salinization of the silty clay roadbed(with the salt content exceeding 0.3% as the critical condition).According to the simulation results of 90 days,the salinization rate of roadbed decreases with the increase of relative height,and increases with the increase of groundwater salt concentration.(5)According to the mechanism of silty clay roadbed soil salinization,measures to prevent roadbed soil salinization in the Hetao Irrigation District of Inner Mongolia are proposed: Aiming at the roadbed water migration in the Hetao Irrigation District,the main mode of water migration is the rise of underground capillary water.Sand barrier and aeolian sand layer should not only consider surface water level and groundwater capillary rise height,but also ensure that the installation height of the barrier layer is above the maximum height of the capillary water saturation zone;the optimal thickness of the barrier layer should be close to and less than 80 cm.In addition,it should be ensured that there is enough fill height above the barrier layer to ensure that the roadbed has sufficient strength and stability. |
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