鄂尔多斯红色砒砂岩冻融循环变形特性

Deformation characteristics of red pisha-sandstone during freezing-thawing cycles in Ordos

砒砂岩区的产沙量是以非径流的冻融风化侵蚀为主形成的,冻融循环作为一种特殊的强风化作用,其对砒砂岩进行结构性的破坏。为揭示砒砂岩冻融破坏机制,使用LDMD-A三温冻融循环试验仪,以内蒙古自治区鄂尔多斯准格尔旗红色砒砂岩为研究对象,模拟自然条件进行单向冻融,研究分析冻融次数及含水率对原状砒砂岩冻融循环的影响规律。结果表明:冻融循环过程可以很清晰地反映砒砂岩在冻结和融化过程中,其固相、液相相互转化时内部热量的变化,以及砒砂岩冻结、融化过程的体积变化;在冻结过程中,砒砂岩冻胀率与含水率、冻融次数密切相关,含水率对冻胀率影响更显著。当含水率为8.56%和10.27%时,冻胀率随冻融次数增加而增大;但含水率为8.56%时,冻胀量很小,当含水率>10.27%时,发生冻胀明显,试样冻胀量会随冻融次数增加而增大;当含水率≥11.53%时,冻融循环>6次,冻胀率趋于平缓。其结果揭示了不同因素下,砒砂岩冻融循环变形规律,为砒砂岩冻融侵蚀机理的深入研究提供参考。

[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 pishasandstone 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,in terms of freezing-thawing frequency and moisture by simulating one-way freezing and thawing under natural environment. The samples werecollected at the depth of 40- 50 cm of pisha-sandstone and prepared to be as cylinder-shape specimen of100 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 freezingthawing 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 in close relation to the freezing-thawing frequency and moisture content. The moisture content had more significant effect on 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 equal to 11. 53% and freezing-thawing frequency over six,the frozen-heave factor tended to be stable.[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.