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Deformation characteristics of red pisha-sandstone during freezing-thawing cycles in Ordos |
Chen Suhang, Li Xiaoli, Zhang Qiang, Li Mingyu |
Water Conservancy and Civil Engineering College,Inner Mongolia Agricultural University, 010018, Huhehot, China |
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Abstract [Background]Pisha-sandstone is a kind of loose rock stratum. Since the rock stratum is thin and low in pressure,it is hard to form rock, poor to glue the sandstone and low in structural strength. In the spring of great change in temperature, pisha-sandstone soil is not only eroded by the wind, but also frozen and melted at the same time, thus freezing-thawing and wind erosion are the main erosive modes in the spring and winter. Therefore,to protect the ecological environment in this territory, it is of great necessity to study the mechanisms of freezing-thawing and wind erosion of pisha-sandstone soil and investigate the soil variation in pisha-sandstone territory. [Methods] We applied LDMD-A three temperature freezing-thawing cycle test instrument to study and analyze the influence of freezing-thawing cycle on pisha-sandstone stratum in Zhungeer,Inner Mongolia Autonomous Region, where the pisha-sandstone stratum is purple and covered by sparse vegetation, with low soil nutrient in the surface, droughty in spring, and cold in winter and severe soil erosion, interms of freezing-thawing frequency and moisture by simulating one-way freezing and thawing under natural environment. The samples were collecte dat the depth of 40-50 cm of pisha-sandstone and prepared to be as cylinder-shape specimen of 100 mm diameter and 100 mm height. The specimen was punched five holes with 1.5 cm apart between them for temperature test at different heights in order to investigate the changing law of temperature inside the test specimen. The specimen was frozen till the displacement did not change and then began to thaw, likewise, the specimen was thawed till the displacement did not change and then began to freeze. Then next freezing-thawing cycle follows the same. [Results] Experimental results showed that freezing-thawing process clearly reflected the thermal quantity in the transition between the solid phase and liquid phase as well as the volume change in the procedure of freezing and thawing of pisha-sandstone stratum. In the freezing process, the frozen heaving ratio factor of pisha-sandstone stratum was inclose relation to the freezing-thawing frequency and moisture content.The moisture content had more significant effecton frozen-heave factor; when the moisture contents were 8.56% and 10.27%, the frozen-heave factor increased with freezing-thawing frequency; when the moisture content was 8.56%,the frozen expansion was the least; when the moisture content was over 10.27%, frozen expansion obviously took place,and the frozen expansion increased with the freezing-thawing frequency; when the moisture content was over or equalto 11.53% and freezing-thawing frequency over six, the frozen-heave factor tended to bestable. [Conclusions] These results reveal the structural change law of pisha-sandstone stratum under different factors, which provides references for further researches on the erosive mechanisms of pisha-sandstone stratum.
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Received: 26 January 2016
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