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
This study compared soil physical, chemical, and biological characteristics between natural grassland and recently abandoned rice fields in order to identify those variables that might explain the observed increase of Camponotus punctulatus anthills in abandoned rice paddy fields from Northern Argentina. Mainly due to a reduction of macropores and mesopores, overall porosity decreased by around 6% and bulk density was about 7% greater, in the 0- to 10- and 10- to 20-cm layers of the abandoned rice fields. Carbon and nitrogen content from organic matter increased (29% and 41% respectively for the 0- to 20-cm horizon) during cultivation but decreased (38% and 24%) 2 years after the last rice harvest. Forty percent of natural grassland-organic matter and 30% of abandoned rice-organic matter mineralized in less than 2 years. There was a different community structure between the abandoned rice fields and the undisturbed natural grassland and only a 20.6% (i.e. only 19 species from a total of 92) overlap in species composition. The abundance of macrofauna was greater in abandoned rice fields (2,208 individuals m–2) in comparison to natural grasslands (288 ind m–2) due to higher densities of small earthworms and Camponotus punctulatus ants; however, the Shannon index showed lower values in comparison to natural grasslands. Earthworms and C. punctulatus in the abandoned rice fields showed a change in their 13C signature indicating a switch in diet from natural grassland organic matter (C4) to organic matter from rice (C3). Our results indicate that the effects of rice cultivation practices did not seem to produce any physical or trophic limitations to recolonization by the macrofauna. It seems that changes in overall soil conditions have favored a change in the construction behavior of C. punctulatus which, in combination with population increases, could explain the explosion in number of anthills. 相似文献