Experimental design for a pilot study on bedrock weathering near the permafrost table
Experimental design for a pilot study on bedrock weathering near the permafrost table
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DOI：
10.1002/1096-9837(200011)25:12
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发表时间：
2000-11-01
影响因子：
3.3
通讯作者：
Simmons, P
中科院分区：
文献类型：
--
作者：
Murton, JB;Coutard, JP;Simmons, P
一个实验设计，以测试的假设，冰离析附近的顶部的永久冻土和活动层的下部，可以角砾化易受霜冻的基岩。在活动层和永久冻土顶部的季节性温度循环进行了模拟，在一块白垩测量0.30米x0.31米宽，0.33米高，周围的两侧绝缘，以尽量减少横向热传递的第一近似值。首先通过毛细上升润湿的块，最初从表面向下冻结，模拟永久冻土层加积。此后，该块的上半部分在0摄氏度以上和以下循环（模拟活动层的季节性冻结和融化），而下半部分保持在0摄氏度以下（模拟永久冻土）。在解冻循环期间，将水供应到模拟活性层的表面和基底。试验过程中对白垩层内部温度、未冻水含量、表面冻胀和孔隙水压力进行了监测，初步结果表明：（1）模拟活动层在冻融过程中既有向下冻结又有向上冻结;（2）78%的地表冻胀（总量= 4.8mm）发生在解冻期，此时活动层接近或达到其最大深度;（3）回冻期间某些情况下记录到负孔隙水压力，表明发生了低温抽吸。解冻相关的冻胀表明，冰分离白垩发生在下降的解冻前，在模拟的活动层和最上层的冻土仍然冻结的部分，并标志着岩石角砾化的开始。版权所有（C）2000约翰威利父子有限公司
An experimental design is described to test the hypothesis that ice segregation near the top of permafrost and in the lower part of the active layer can brecciate frost-susceptible bedrock. Seasonal temperature cycles in the active layer and the top of permafrost were simulated to a first approximation within a block of chalk measuring 0.30 m x 0.31 m wide and 0.33 m high and insulated around the sides to minimize lateral heat transfer. The block, moistened first by capillary rise, was initially frozen from the surface downwards, simulating permafrost aggradation. Thereafter, the upper half of the block was cycled above and below 0 degreesC (simulating seasonal freezing and thawing of the active layer) while the lower half remained below 0 degreesC (simulating permafrost). During thaw cycles water was supplied to the surface and base of the simulated active layer. Temperature, unfrozen water content, surface frost heave and porewater pressure within the chalk were monitored during the experiment.Preliminary data from three freeze-thaw cycles indicate that: (I)both downward and upward freezing occurred during freeze-back of the simulated active layer; (2) 78 per cent of the surface frost heave (total = 4.8 mm) took place during the thaw periods, when the active layer was approaching or at its maximum depth; and (3) negative porewater pressure was recorded in some instances during freeze-back, suggesting the occurrence of cryogenic suction. The thaw-related frost heave suggests that ice segregation within the chalk occurred beneath the descending thawing front, in the still frozen part of the simulated active layer and the uppermost permafrost, and marked the commencement of rock brecciation. Copyright (C) 2000 John Wiley & Sons, Ltd.