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Study on freeze-thaw destructive tests for wellhead sand of Karezes in Xinjiang
Author(s): 
Pages: 1-6
Year: Issue:  2
Journal: Geotechnical Investigation & Surveying

Keyword:  Karezfreeze-thawsteam supplysandshaft mouth;
Abstract: Xinjiang Karezes were approved as the sixth batch of national key cultural relics protection units in 2006. The Karezes are as the cultural heritage of humanity,with quite high historical and cultural value,and the increasing demise situation is widely concerned by the community. The thawing process of Karez shaft mouth frozen soil has been accepted with the damp and hot steam supply,which is the main difference with other plateau permafrost and frozen thawing. By improving the traditional freeze-thaw cycle test machine,the samples under different pressures in the steam supply and different freezing temperature for 20 times freezing and thawing process are studied for the porosity and moisture migration variation of Karez shaft mouth sand. The test results show that the porosity of the soil samples increases firstly and then decreases with increation of freeze-thaw cycle times which are significantly higher than that before freezing and thawing. Under the condition of the same initial water content,the lower the freezing temperature and the greater the steam supply pressure,the more the porosity increases and the stronger the moisture absorption ability is after freeze-thaw. Under different initial water content,the maximum water content ofthe samples is at 3 ~ 6cm below the top face of the sample after 20 times freezing and thawing process. It is concluded that the sand of Karez shaft mouth wall is easier to be influenced by the freezing and thawing cycles than the sand away from the borehole,and the surface sand contacted with the atmosphere is easier to be influenced by the freezing and thawing cycles than that of the lower sand,but the value of the moisture content of Karez well head sand has little effect on the freezing and thawing damage.
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