Train-induced wave propagation in layered soils using finite/infinite element simulation

In this paper, the transmissibility of soils for vibrations induced by trains moving at different speeds is studied. The 2.5 D finite/infinite element approach adopted herein allows us to consider the load-moving effect of the train in the direction normal to the two-dimensional profile of the soils considered, and, therefore, to obtain three-dimensional responses for the soils using only plane elements. The moving train is simulated by a sequence of moving wheel loads that may vibrate with certain frequency. Two train speeds are considered, one is smaller and the other is greater than the Rayleigh wave speed of the layered soils, to represent the effects of speed in the sub-critical and super-critical ranges. In order to evaluate the effect of each parameter on the ground response induced by moving trains, parametric studies are conducted for the following parameters: the shear wave speed, damping ratio and stratum depth of the supporting soils, and the moving speed and vibration frequency of the traveling trains. Conclusions concerning the mechanism of wave propagation in layered soils are drawn from the parametric studies, which should prove useful to practicing engineers.     

Spatially Located Platform and Aerial Photography for Documentation of Grazing Impacts on Wheat

Abstract

Goose populations that winter in Oregon's Lower Willamette Valley have increased from 25 000 to more than 250 000 birds in the last 25 years, resulting in heavy grazing of wheat and other crops. To map and document the extent and intensity of goose impacts on wheat fields, we combined rectified aerial photography with both globally positioned ground observations and vertical platform photographs. Aerial photos revealed areas of fields with sparse wheat cover while platform photos documented the cause. We estimated wheat cover in ground level photographs by ratioing red, green and blue digital numbers. From platform photographs we recorded occurrence of grazing (from grazed leaf tips), intensity of grazing (from residual plant cover and leaf length), and other indicators of goose use (footprints and droppings). Because the ground photographs were spatially positioned, we could use this information to verify the cause of “thin” wheat. Crop damage from grazing/trampling, water submergence, and other factors was evident. Our results illustrate practical ways to combine aerial and ground‐level image analysis, spectral observations, and global positioning systems to quantify field conditions in wheat.     

Assessment of salt affected soils in India using GIS

Salt affected soils are characterized by variable distribution and dynamic nature. Based on Landsat data from 1986/1987 supported by ground truth, salt affected soil maps were prepared at 1:250,000 scale for 14 states and a union territory (UT). A map legend was evolved that described the nature, degree and extent of salt affected soils suitable for varied physiographic and agroclimatic regions of the country. Fifteen categories of salt affected soil were identified for the entire country. These were merged to two categories – saline and sodic – for management purposes. Digitized maps were developed in a geographical information system (GIS) depicting salt affected areas of the country. An area of 6.73 million ha of salt affected soils was estimated for the entire country. State-wise estimates showed that this extensive area is distributed over the Gangetic plain of Uttar Pradesh; the arid and semiarid regions of Gujarat and the peninsular plains of Maharashtra state. A significant area is also located in the coastal region covering seven states. The salt affected soils are primarily saline in deltaic (C), coastal (D) and mud flats/mangrove swamps (G) and sodic in alluvial (A), aeofluvial/aeolian/arid (B) and peninsular (F) plains. The distribution of salt affected soils in agroclimatic zones (ACZs) showed occurrence in Gujarat plain, East Coast plains, Upper-Gangetic plain, Trans-Gangetic plain, Central Plateau, Lower-Gangetic plain and Southern Plateau of the country.     

Assessment of severity of the extreme River Tyne flood in January 2005 using gauged and historical information

Abstract

The extreme Tyne (Northumbria, UK) flood in January 2005 provided the opportunity to reassess flood risk and to link peak discharge and flooded area to probability of occurrence. However, in spite of the UK guidance on flood risk assessment given in the Flood Estimation Handbook (FEH), there is still considerable subjectivity in deriving risk estimates. A particular problem for the Tyne arises from the effects of river bed gravel extraction both on the reliability of gauged discharges and in the interpretation of historical level data. In addition, attenuation and drawdown of Kielder Water has reduced downstream flood risk since 1982. Estimates from single-site, pooled estimates and historical information are compared. It is concluded that the return period of the observed flood was around 71 years on the lower Tyne and was probably the largest flood since 1815.     

Accumulation of Copper and Zinc in Danish Agricultural Soils in Intensive Pig Production Areas

Geografisk Tidsskrift, Danish Journal of Geography 105(2):15–22, 2005

The change of Cu and Zn concentrations in Danish agricultural soils was studied in areas with intensive pig production. Cu and Zn are found in pig manure as the metals are added to pig feed as growth promoters. The changes in concentrations of total and 0.02 MEDTA extractable Cu and Zn in soils from 1986 to 1998 were determined from samples taken at two depths (0–25 cm and 25–50 cm) from 73 sites. Pig manure and mineral fertilizer was added to 60 sites whereas fertilizer only was used on 13 sites. During the survey period soil Cu concentrations increased in both depths but mostly in the sites where pig manure was added. Furthermore, the results indicated that some plant-available Cu and Zn were transported from the topsoil to the subsoil. No significant change in soil Zn concentration was found although a slight reduction was observed. Comparing soil metal concentrations observed in 1998 to the total pig manure application in a 12-year period, it was observed that application of manure caused an accumulation of Cu and of Zn in the upper 50 cm soil. The accumulation rates correspond to the Cu and Zn concentrations in the pig manure.     

Appraisal of World Reference Base for Soil Resources—from a nordic point of view

During the project “Nordic Reference Soils” 13 different soils from Denmark, Finland, Norway and Sweden were selected in order to represent i) soils covering the main areas of the Nordic area, ii) soils from the different climatic regions, and iii) environmental sensitive soils. The 13 Nordic Reference Soils provided an excellent basis for the evaluation of the WRB (World Reference Base for Soil Resources) performance under Nordic conditions. Classification according to the WRB poses considerable problems. These concern podzolized soils, cultivated soils, and the acid sulfate soils. Only three out of the seven podzolized soils are allocated in taxons reflecting that they were podzolized. Four out of the nine cultivated soils were exposed to substantial anthropogenic impact, resulting in man-made Mollic A-horizons, which is not reflected in the classification. The WRB-classification of the soils is compared with the FAO and Soil Taxonomy classification. This highlighted some of the classification problems. This paper will propose changes to the WRB in order to improve the performance of the system for Nordic soils.

Geografisk Tidsskrift, Danish Journal of Geography 100: 15–26     

Seasonal changes in the relationship between species richness and community biomass in grassland under grazing and exclosure, Horqin Sandy Land, northern China

How species diversity–productivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and aboveground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northern China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use (grazing and exclosure). These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and biomass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species richness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which further affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of temporal dynamics and land use in understanding the relationship between species richness and ecosystem function.     

Reinforcement effects of ground treatment with dynamic compaction replacement in cold and saline soil regions

The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences project construction. In order to improve foundation reinforcement effect of the Qarhan–Golmud Highway, Qinghai Province, China, dynamic compaction replacement (DCR) composite foundation was applied in saline soils. A field experiment was conducted in this area, where strength and working mechanism of pier-soil and deformation modulus of the composite foundation was analyzed after reinforcement. This paper presents methods for determining the coefficient on the bearing capacity evaluation and deformation modulus of composite foundation with DCR. Reinforcement case of DCR is highly effective in saline soils of the salt lake regions, which helps the migration of water and salt in saline soils.     

Experimental study on DX pile performance in frozen soils under lateral loading

Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen ...     

碎石桩复合地基复合模量取值分析

复合模量是计算复合地基沉降的关键参数,但求解出完全符合实际的精确解较困难。为此采用弹性理论中最小势能原理推求出复合模量上限值计算公式。此外,对影响复合模量上限值的几个主要参数如桩土压缩模量、土体泊松比、置换率等进行了分析,获得了一些定性的结论：上限值随着土体模量和置换率的增大而增大,复合模量取值应乘以1.1～1.4扩大系数。