The Indoor Experimental Study On Coarse Saline Soil Roadbed Under Freeze-thaw Condition

Qarhan-Golmud highway is the first highway built in Strong Saline Soil Area in our country’s inland. The highway passes through the largest inland salt lake-Qarhan salt lake and its foundation soil is mainly strong saline soil. Besides Qarhan salt lake has high water table and the temperature in this area varies greatly between years. During successions of the seasons, water and salt within the saline soil will migrate, accumulate, crystallize and dissolve under the influence of freeze-thaw circle, resulting in different kinds of damage in road and building, which severely influence road construction and traffic safety operations. In order to improve the road performance of Qarhan-Golmud highway, prevent and cure roadbed disease,make full use of local resources, the present study decided to use the coarse weak saline soil along the highway to fill the roadbed. Besides, in order to investigate the migration rule of water and salt, and changes in mechanical properties when the coarse saline soil is under the condition of freezing and thawing, this study sampled from the field along Qarhan-Golmud highway, making indoor soil experiment and large-scale simulation experiment. The content and results of the present study are the followings:1. The natural coarse saline soil used as roadbed filler was taken for compaction test,grain size test and soluble salts determination test. The results show that the sample’s optimum percentage of moisture is 8.5%, maximum dry density 2.13g?cm3, and percentage of soluble salt 0.542%,which makes the soil sample belongs to bad graded gravel soil and weak saline grave soil.2. After freezing and thawing cycle finishes, moisture of gravel weak saline salt roadbed presents "parabola" type distribution in a height direction. And the percentage of moisture of fillers in every layer of the roadbed increases to lesser extent as the freezing and thawing cycle increases. The volatility of the soil below 40 cm is stronger, while the soil beyond 40 cm is less affected by freeze-thaw action and its water continues migrating and increasing upward in freeze-thaw cycles; the water content of the soil between 10 cm and 70 cm, which is the water supply source, decreases with freezing and thawing cycle’s increasing.3. The formation process of salt migration channel of gravel soil roadbed is complicated and costs long time. During the first two periods of freezing and thawing cycle, salt migration occurs in the partial of the roadbed; while at the beginning of the third period, the continuing salt migration channel gradually form in the roadbed’s height direction and the salt in the overall part of the roadbed starts migrating. Salt distribution curve is a "three-stage" wavy with the soil in 40 cm and 70 cm as the boundary point.4. Undistributed soil sample and the soil layer containing maximum salinity after experienced different periods of freezing and thawing cycle were taken for Resilient modulus test and Bearing ratio test. The results show that after salt accumulation from freezing and thawing cycle, E0 and CBR of gravel soil roadbed decrease as the salinity increases, and the bearing capacity of the gravel soil roadbed decreases to certain degree.