The unfrozen water content and ice content of frozen soil change continuously with varying temperatures, resulting in the temperature dependence of mechanical properties of frozen soil. Thus the dynamic behavior of embankment in permafrost regions under train loading also alters with seasons. Based on a series of strong-motion tests that were carried out on the traditional embankment of Qinghai-Tibet Railway(QTR) in permafrost regions, the acceleration waveforms recorded at the embankment shoulder and slope toes were obtained. Testing results show an obvious attenuation effect on the vertical train loading from road shoulder to slope toes. Furthermore, numerical simulations of a traditional embankment under vertical train loading in different seasons were conducted, and the dynamic behavior of the embankment was described. The results show that the vibration attenuation in the cold season is greater than that in the warm season. The maximum acceleration of vibration drops to about 5% when the train vibration load is transferred through the embankment into the permafrost, and the high-frequency components are absorbed when the vibration transmits downward. Moreover, the dynamic stress under the dynamic train loading decreases exponentially with an increasing depth in different seasons. The results can be a reference for design and maintenance of embankments in permafrost regions. 相似文献
Mining and smelting activities are the main causes for the increasing pollution of heavy metals in soil, Water body and stream sediment. An environmental geochemical investiga-tion was carried out in and around the Panzhihua mining and smelting area to determine the ex-tent of chemical contamination in soil and sediment. The main objective of this study was to in-vestigate the environmental geochemistry of Ti, V, Cr, Mn, Cu, Pb, Zn and As in soil andsediment and to assess the degree of pollution in the study area. The data of heavy metal con-centrations reveal that soils and sediments in the area have been slightly contaminated. Geo-chemical maps of Igeo of each heavy metal show that the contaminated sites are located in V-Ti-magnetite sloping and smelting, gangues dam. The pollution sources of the selected elementscome mainly from dusts resultant from mining activities and other three-waste-effluents. The areaneeds to be monitored regularly for trace metal, especially heavy metal enrichment. 相似文献
Oil or gas production from unconsolidated reservoirs could be hampered by sand migration near the wellbore. This paper presents a numerical investigation of production-induced migration of fine sands towards a wellbore drilled in a gap-graded sediment. The solid–fluid interaction is simulated by coupling the discrete element method and the dynamic fluid mesh. With the merit of DEM and a dynamic mesh, the model is capable of naturally capturing particle movements and spatiotemporal variations of hydraulic properties of the sediment at the pore scale. The results show that fine particles are mobilized by radial flow under an imposed hydraulic gradient, and the increase in the hydraulic gradient causes an increase in the fines production. The microscopic pattern of sand migration is clearly visualized through the simulation. The presence of fine particles affects the process of fines migration through two competing mechanisms. Under a low fine content, fine sands mainly serve as the fines production source, and thus, fines production is enhanced as the fine content increases up to a critical value, beyond which fines production is weakened with a further increase in the fine content since the blocking effect gradually dominates. A barrier layer is likely formed during sand migration due to settling and jamming of fine sands at the throats of pores, as fine sands migrate with the radial flow towards the wellbore. This layer is helpful to slow down sand migration, while it could impede production due to reduced permeability in the affected reservoir.
This is the second paper of a series devoted to atmospheric optical turbulence Cn2 observation using a mobile polar atmospheric parameter measurement system. We present the initial results of Cn2 measu... 相似文献