Determination of pre-compression stress of a variously grazed steppe soil under static and cyclic loading
Determination of pre-compression stress of a variously grazed steppe soil under static and cyclic loading
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DOI：
10.1016/j.still.2008.01.008
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发表时间：
2008-06
影响因子：
6.5
通讯作者：
J. Krümmelbein;S. Peth;R. Horn
中科院分区：
文献类型：
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作者：
J. Krümmelbein;S. Peth;R. Horn
随着土地利用强度的不断增大，土壤变形已成为世界各国土地利用系统中的一个主要问题。在可耕地上，机械运输在负载和旋转频率方面不断加强，导致（下层）土壤压实和更深的土壤退化，涉及液压或气动功能。土壤功能改变，特别是导水率降低和通气受阻，可能会降低作物生长和生产力，以及土壤的过滤和缓冲能力。由于孔隙连续性和孔隙功能降低，土壤中的气体交换受阻，缺氧持续时间延长，也影响全球变化过程。为了评估土壤不可逆变形的潜在风险，有必要量化其机械稳定性。一种常用的方法是确定预压应力，通常在静载荷条件下进行固结试验。在静态荷载下确定预压应力可能与现场遇到的情况不太相似，在现场，土壤反复加载一系列短暂的间歇性加载-卸载-再加载事件。这种动态载荷条件是会遇到的，例如在多次车轮通过或在草原土壤中由于动物踩踏。在这项研究中，我们提出了一个标准的（静态加载）和修改后的（循环/动态加载）oedometer测试的数据，从内蒙古草原钙华土壤在不同的放牧强度进行了比较。每个加载步骤的静态加载持续10 min，而动态/循环加载通过30 s加载和30 s卸载（=1个循环）进行，共20个循环。在相同的加载时间，静态和循环确定的预压应力之间的差异表明，与循环确定的预压应力值相比，静态确定的预压应力值较低。在动态确定的预压应力中，其值分别随着加载步数和加载时间的增加而减小。对于未放牧的地点来说，情况尤其如此。因此，也可以证明，放牧强度的增加导致结构变形，增加对风蚀和水蚀的敏感性，随后是草地土壤的严重退化，特别是在半干旱地区。此外，水力效应，例如，由于放牧动物引起的强烈剪切和揉捏过程而产生的正孔隙水压力，会加剧这种结构恶化。因此，动态或循环载荷导致强烈的土壤变形，这也导致生态和土壤物理性质如水力传导性或气体通量的严重变化。
In many land use systems all over the world soil deformation is a major problem due to increasing land use intensity. On arable soils machine traffic is continuously intensified with respect to load and wheeling frequency leading to (sub-)soil compaction and deeper soil degradation concerning hydraulic or pneumatic functions. Altered soil functions, in particular reduced hydraulic conductivities and impeded aeration, may decrease crop growth and productivity as well as the filtering and buffering capacity of soils. Prevented gas exchange and longer lasting anoxia in soils due to the reduced pore continuity and pore functioning also affects global change processes. In order to evaluate potential risks for irreversible soil deformation, it is necessary to quantify their mechanical stability. A commonly applied method is the determination of the pre-compression stress, commonly under static loading conditions in oedometer tests. The determination of pre-compression stresses under static loading may not quite resemble the conditions encountered in the field where soils are loaded repeatedly with a sequence of short intermittent loading–unloading–reloading events. Such dynamic loading conditions are encountered, e.g. at multiple wheel passes or in grassland soils due to animal trampling. In this study we present a comparison of a standard (static loading) and a modified (cyclic/dynamic loading) oedometer test using data of a Calcic Chernozem from the Inner Mongolian steppe under various grazing intensities. Static loading lasted for 10min per loading step, while the dynamic/cyclic loading was carried out by 30s loading and following 30s unloading (=1 cycle) for in total 20 cycles. Differences between statically and cyclically determined pre-compression stresses at an identical time of loading show lower values for the statically determined pre-compression stress values compared to those determined cyclically. Among the dynamically determined pre-compression stresses, the values decrease with increasing number of loading steps and loading time, respectively. This is particularly true for the ungrazed sites. Thus, it could also be proofed that increased grazing intensities lead to structure deformation and increased sensitivity to wind- and water erosion followed by severe land degradation of grassland soils, particularly in semi-arid areas. Furthermore, hydraulic effects, e.g. positive pore water pressure due to intense shearing and kneading processes induced by grazing animals can enhance this structural deterioration. Thus, dynamic or cyclic loading results in an intense soil deformation which also causes serious changes in ecological and soil physical properties like hydraulic conductivity or gas flux.