Mechanism Of And Solution For Frost Damage Of Aeolian Sand Embankment In Cold Region

Aeolian sand,also known as desert sand,is a kind of sand that has been moved to the alluvial plain by the wind flow.It is widely distributed in the cold areas of northwest arid area,Qinghai-Tibetan Plateau and the eastern monsoon area in China.The improved soil of aeolian sand can make up the loose structure and the large porosity of nature aeolian sand,which have sufficient strength to meet the demand of embankment filling engineering of high grade line in cold area.However,there appeared a lot of transverse cracks on the surface of the embankment after a freeze-thaw cycle due to the external cold temperature and the internal brittleness of embankment soil.Based on the construction project of high-speed railway in Horqin Sandy Land in Inner Mongolia,the mechanism of and solution for freezing damage of aeolian sand embankment are studied.Two improved materials,cement and clay,with different proportions for nature aeolian sand was determined to carry out the indoor test of physical and engineering properties of improved soil of aeolian sand.Using five kinds of improved soil of aeolian sand to establish an embankment with five sections in cold region and embed sensors to monitor the temperature,humidity and strain of embankment in outdoor freeze-thaw environment.Combined with the method of numerical simulation,the law of freezethaw deformation and mechanism of temperature cracks in embankment are analyzed;The control measure for embankment of improved soil of aeolian sand against frost damage is suggested by appropriate improved proportion of aeolian sand,cement and clay.The results are as follows:(1)The frost damage of embankment of improved soil of aeolian sand is characterized by shrinkage cracking.The improved soil of aeolian sand shrinks at low temperature,the lower temperature,the greater deformation of soil volume shrinkage.The embankment soil cracking and failure when the shrinkage strain is greater than the value of allowable strain of the soil,the width of the crack varies with the thermal expansion and contraction of the soil.(2)When the cement content is constant(5%),with the increase of clay content,the unconfined compressive strength and tensile strength of improved soil increase first and then decrease.The sample of 85% sand+5% cement+10% clay has the highest unconfined compressive strength,the sample of 90% sand+5% cement+5% clay is the next.Conversely,the sample of 90% sand+5% cement+5% clay has the highest tensile strength,the sample of 85% sand+5% cement+10% clay is the next.According to the mechanism of frost damage of embankment,the improved proportion of 85% sand+5%cement+10% clay is the better proportion for embankment of improved soil of aeolian sand against frost damage.(3)The moisture in the embankment is controlled by temperature and railfall,the water content of the embankment soil decreases with the decrease of temperature,the soil shrinks;As the temperature increases,the water content increases and the embankment soil stretches.The freezing and thawing of water in the embankment soil basically has no effect on the deformation of the embankment soil due to the low content of water in embankment.(4)The influence of climate temperature on embankment is limited,the response of the embankment soil to the temperature has the hysteresis action.The farther distance from the embankmentboundary,the smaller influence of temperature,the sensitivity of the embankment soil to the change of the temperature is weaker,and the hysteresis effect is more obvious.The relationship between the five road sections affected by the temperature is: road1>road3>road4>road5>road2.(5)The relationship of deformation between the five road sections is:road5>road1>road4>road3>road2.The improved scheme of road2(90% sand+ 5%cement+5% clay)is the better aeolian sand improved proportion for quality control of embankment against frost damage.