In recent years, agricultural land in Switzerland has been increasingly used as temporary access ways for heavy machinery in road and pipeline construction operations. The Swiss soil protection law requires that measures are taken to prevent soil compaction in such operations, but gives no criteria to determine tolerable loads. We studied the compaction sensitivity of a loess soil (Haplic Luvisol) at different soil moisture conditions in a field traffic experiment and by a numerical model on the computer using finite element analysis. Two plots, one wetted by sprinkling and one left dry (no sprinkling), were traversed by heavy caterpillar vehicles during construction of a large overland gas pipeline. Compaction effects were determined by comparing precompression stresses of samples taken from trafficked and non-trafficked soil. A finite element model with a constitutive relation, based on the concept of critical state soil mechanics, was used to interpret the outcome of the field trials.
We found significantly higher precompression stresses in the trafficked (median 97 kPa) compared with the non-trafficked (median 41 kPa) topsoil of the wet plot. No effect was evident in the topsoil of the dry plot as well as in the subsoils of the wet and the dry plot. The observed compaction effects were in agreement with the model predictions if the soil was assumed to be partially drained, but disagreed for the wet subsoil if fully drained conditions were assumed. Agreement between model and experimental results also required that the moisture dependence of the precompression stress was taken into account. 相似文献
Heavy sugarbeet harvesters may compact subsoil. But it is very difficult to study this by field experiments that resemble agricultural practice. Therefore, an analysis was made by a finite element method (FEM) for a relevant calcaric fluvial soil profile, the mechanical properties of which were largely known. Measuring data of this Lobith loam soil includes preconsolidation stress, compression index and swelling index, all as a function of depth. Using these three types of soil parameters calculations have been done for tyre sizes, inflation pressures and wheel loads that occur with heaviest sugarbeet harvesters available on the European market in 1999. Because no values on soil cohesion were available, the calculations were done for several cohesion levels. The results include the detection of regions with Mohr–Coulomb plasticity and regions with cap plasticity (compaction hardening). For the soil studied—a typical soil strength profile for arable land with ploughpan in the Netherlands in the autumn of 1977—all studied combinations of wheel load and inflation pressure did not induce compaction in and below the ploughpan. The size of the region with Mohr–Coulomb plasticity decreased with increasing cohesion. It appeared from a sensitivity analysis that, although soil modelling may use a great number of soil parameters, the most important parameters seem to be: preconsolidation stress and cohesion. There is an urgent need for data of these parameters that are measured on a great range of subsoils and subsoil conditions. 相似文献
In the 1970s unexpected forest damages, called “new type of forest damage” or “forest decline”, were observed in Germany and
other European countries. The Federal Republic of Germany and the German Federal States implemented a forest monitoring system
in the early 1980s, in order to monitor and assess the forest condition. Due to the growing public awareness of possible adverse
effects of air pollution on forests, in 1985 the ICP Forests was launched under the convention on long-range transboundary
air pollution (CLRTAP) of the United Nations Economic Commission for Europe (UN-ECE). The German experience in forest monitoring
was a base for the implementation of the European monitoring system. In 2001 the interdisciplinary case study “concept and
feasibility study for the integrated evaluation of environmental monitoring data in forests”, funded by the German Federal
Ministry of Education and Research, concentrated on in-depths evaluations of the German data of forest monitoring. The objectives
of the study were: (a) a reliable assessment of the vitality and functioning of forest ecosystems, (b) the identification
and quantification of factors influencing forest vitality, and (c) the clarification of cause-effect-relationships leading
to leaf/needle loss. For these purposes additional data from external sources were acquired: climate and deposition, for selected
level I plots tree growth data, as well as data on groundwater quality. The results show that in particular time series analysis
(crown condition, tree growth, and tree ring analysis), in combination with climate and deposition are valuable and informative,
as well as integrated evaluation of soil, tree nutrition and crown condition data. Methods to combine information from the
extensive and the intensive monitoring, and to transfer process information to the large scale should be elaborated in future.