Use of bulk density profiles from X-radiography to examine structural crust models
Use of bulk density profiles from X-radiography to examine structural crust models
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DOI：
10.2136/sssaj2004.1169
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发表时间：
2004-07-01
影响因子：
2.9
通讯作者：
Assouline, S
中科院分区：
文献类型：
--
作者：
Bresson, LM;Moran, CJ;Assouline, S
有人建议用指数函数和 S 形函数来描述地壳的堆积密度分布。目前的工作旨在使用高分辨率 X 射线照相术评估这些概念模型。由两种土壤材料重新填充的苗床，风干或通过毛细管上升预湿，经受模拟降雨，产生三种类型的结构结皮，即熟化、填充和聚结。使用来自树脂浸渍的结皮苗床的切片的高分辨率（70μm）、校准的X射线图像生成随深度的堆积密度分布。体积密度随着深度逐渐减小，这支持了地壳应被视为不均匀层的建议。对于熟化和聚结的地壳，指数函数低估了地壳和底层物质之间形态定义的过渡过程中体积密度的强烈变化； sigmoidal 函数提供了更好的描述。这些地壳模型都没有有效地描述整个苗床的堆积密度剖面的形状。在填充和熟化的地壳下方，由于塌陷，堆积密度随深度线性增加。在聚结结皮苗床中，整个苗床均匀塌陷，结皮内堆积密度的变化大部分归因于塌落(0.33 g cm(-3))，而不是结皮(0.12 g cm(-3))。最后，（i）X射线照相术似乎是生成高分辨率堆积密度剖面的独特工具，并且（ii）在结构结壳中，只要耦合坍落模型，就可以使用现有的指数和S形结壳模型对堆积密度剖面进行建模。
Exponential and sigmoidal functions have been suggested to describe the bulk density profiles of crusts. The present work aims to evaluate these conceptual models using high resolution X-radiography. Repacked seedbeds from two soil materials, air-dried or prewetted by capillary rise, were subjected to simulated rain, which resulted in three types of structural crusts, namely, slaking, infilling, and coalescing. Bulk density distributions with depth were generated using high-resolution (70 mum), calibrated X-ray images of slices from the resin-impregnated crusted seedbeds. The bulk density decreased progressively with depth, which supports the suggestion that a crust should be considered as a nonuniform layer. For the slaking and the coalescing crusts, the exponential function underestimated the strong change in bulk density across the morphologically defined transition between the crust and the underlying material; the sigmoidal function provided a better description. Neither of these crust models effectively described the shape of the bulk density profiles through the whole seedbed. Below the infilling and slaking crusts, bulk density increased linearly with depth as a result of slumping. In the coalescing crusted seedbed, the whole seedbed uniformly collapsed and most of the bulk density change within the crust could be ascribed to slumping (0.33 g cm(-3)) rather than to crusting (0.12 g cm(-3)). Finally, (i) X-radiography appears as a unique tool to generate high resolution bulk density profiles and (ii) in structural crusts, bulk density profiles could be modeled using the existing exponential and sigmoidal crusting models, provided a slumping model would be coupled.