不同边界条件对多年冻土上限影响的模型试验研究

Influence of Climate Warming on Permafrost Table Studied with Different Models and Temperatures

在全球气候转暖对多年冻土影响的情景下 ,开展了在多模式下气温升高对冻土上限的影响试验研究 .针对不加抛石遮阳棚、加抛石、加抛石遮阳棚 3种情况 ,地表温度均采取基本温度加 2次不同升温冻融循环 ,每次温控指标逐级提高 0 .5℃ ,即地表温度 3次变化依次按照 - 16 .1～ 5 .8～ - 13.3℃、 - 15 .6～ 6 .3～ - 12 .8℃、 - 15 .1～ 6 .8～ - 12 .3℃进行 .结果表明 ,加抛石及遮阳棚对多年冻土上限有着明显的影响 ,冻土上限的变化与气温基本上呈正相关 。

Model tests are conducted for studying the influence of air temperature rising on permafrost table under three conditions (without riprap and awning, with riprap, with riprap and awning). All tests were warmed up twice by different freeze-thaw cycle upon a basic temperature, with a temperature step of 0.50 ℃. The scale of the model that simulates the cutting is 1∶20. The length, width and height of the model are 140 cm, 70 cm and 70 cm, respectively. Loam from the Fenghuoshang region of the Qinghai Tibetan Plateau is used in the model test, of which the initial dry unit weight is 1 500 kg·m -3 and the initial moisture content is 21%. The tests were performed in the State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS. First, the model was kept at -16.10 ℃ under the nature condition for 3 days. Afterwards, the temperature of the soil surface was warmed up and then cooled down repeatedly in the manner of -16.1～5.8～-13.30 ℃, -15.6～6.3～-12.80 ℃ and -15.1～6.8～-12.30 ℃ in turn. Then, riprap, 0.2～1.0 cm in particle diameter and 2 cm in thickness (simulating actuall thickness of the blocked stone of 40 cm), was added to protect the slopes of the cut, and kept at -16.10 ℃ for 3 days, and then the repeatedly warming and cooling mentioned above was performed. Finally, awning, 30 cm in height (simulating actuall awning height of 6.0 m), was added to the model, and then kept at -16.10 ℃ for 3 days, and then the repeatedly warming and cooling mentioned above was performed. It is found from the tests that there is an obvious influence on the permafrost table under the protection of riprap and the awning, and the change of permafrost table is positively relating to air temperature. With the climate warming up, the permafrost table will descend step by step. But at the same temperature, using the riprap and the awning can uplift obviously the permafrost table, specially at high temperature. The effect is more obvious when jointly using riprap and awning. Therefore, using riprap to protect the cut slopes must be considered more and more in the engineering constructions in cold regions, because it is cheaper. Under special condition, it is necessary to jointly use riprap and awning. In this way, it is very good to reduce the frost heaving and thaw collapse of the road and canal etc. in cold regions.