Finite element implementation of a homogenized constitutive law for stone column-reinforced foundation soils,with application to the design of structures

Making use of the homogenization method for periodic media, developed in the context of elastoplasticity, a simplified constitutive law is proposed for a stone column-reinforced soil, regarded as a homogeneous but anisotropic medium. The closed-form expressions derived for such a constitutive law allow for its implementation into a f.e.m-based numerical procedure. The computational code so obtained is then applied to simulating the response of a foundation soil reinforced by a group of floating columns, expressed in terms of load–settlement curves drawn up to the ultimate bearing capacity.     

Development of a Darcy-Brinkman model to simulate water flow and tracer transport in a heterogeneous karstic aquifer (Val d’Orléans, France)

Darcy’s law is the equation of reference widely used to model aquifer flows. However, its use to model karstic aquifers functioning with large pores is problematic. The physics occurring within the karstic conduits requires the use of a more representative macroscopic equation. A hydrodynamic model is presented which is adapted to the karstic aquifer of the Val d’Orléans (France) using two flow equations: (1) Darcy’s law, used to describe water flow within the massive limestone, and (2) the Brinkman equation, used to model water flow within the conduits. The flow equations coupled with the transport equation allow the prediction of the karst transfer properties. The model was tested by using six dye tracer tests and compared to a model that uses Darcy’s law to describe the flow in karstic conduits. The simulations show that the conduit permeability ranges from 5?×?10^?6 to 5.5?×?10^?5?m² and the limestone permeability ranges from 8?×?10^?11 to 6?×?10^?10?m². The dispersivity coefficient ranges from 23 to 53 m in the conduits and from 1 to 5 m in the limestone. The results of the simulations carried out using Darcy’s law in the conduits show that the dispersion towards the fractures is underestimated.     

A field study (Massachusetts, USA) of the factors controlling the depth of groundwater flow systems in crystalline fractured-rock terrain

Groundwater movement and availability in crystalline and metamorphosed rocks is dominated by the secondary porosity generated through fracturing. The distributions of fractures and fracture zones determine permeable pathways and the productivity of these rocks. Controls on how these distributions vary with depth in the shallow subsurface (<300 m) and their resulting influence on groundwater flow is not well understood. The results of a subsurface study in the Nashoba and Avalon terranes of eastern Massachusetts (USA), which is a region experiencing expanded use of the fractured bedrock as a potable-supply aquifer, are presented. The study logged the distribution of fractures in 17 boreholes, identified flowing fractures, and hydraulically characterized the rock mass intersecting the boreholes. Of all fractures encountered, 2.5% are hydraulically active. Boreholes show decreasing fracture frequency up to 300 m depth, with hydraulically active fractures showing a similar trend; this restricts topographically driven flow. Borehole temperature profiles corroborate this, with minimal hydrologically altered flow observed in the profiles below 100 m. Results from this study suggest that active flow systems in these geologic settings are shallow and that fracture permeability outside of the influence of large-scale structures will follow a decreasing trend with depth.     

The response of the ‘green revolution’ to climatic variability

The purpose of this research is to assess the climatic sensitivity of high yielding variety (‘HYV’) ‘green revolution’ wheat. Improved multiple regression models were constructed for yields in India and Sonora, Mexico — the two most intensively planted regions in the world. After isolating the most important climatic predictors (which, not surprisingly, are total rainfall over the irrigation basins), the models were reduced to the pre-HYV period, and then re-run with successively more years of HYV input. This test indicated that increased adoption of the HYV package is associated with a significant increase in yield sensitivity to the most important climatic determinants of yield. To serve as a control, the U.S. Winter Wheat region was also modelled with a similar method. Overall, there is no significant increase in yield sensitivity to climate during the same period that HYV's were adopted in Mexico and India. Assuming that there is no change in overall climatic variability, this study indicates that production will nonetheless become more variable, particularly as HYV culture is expanded. Ironically, countries with rapidly expanding populations, that rely increasingly on HYV's, will experience the most significant fluctuations.     

Economic and climatic factors in ‘acreage abandonment’ over marginal cropland

Crop yield projections made at planting time or during the growing season often ignore the fact that an unknown percentage of planted acreage is not harvested. As a solution, we present a model for 'acreage abandonment, based upon both economic and weather variables. Weather is shown to be a much more important determinant of the decision not to harvest than is the expected price. The explained variance in abandonment of spring wheat acreage by future delivery price is approximately 16%, but rises to over 60% when weather variables are added. In a similarly designed model for winter wheat in the southern plains, the price contribution is less than 5%.The spring wheat model was tested on two extensive sets of withheld data: three-year successive deletions through the entire (1932–1975) data set, and a ten year block at the beginning of the modelling period that included substantial weather and price perturbations induced by the dust bowl, depression, and attendant market gyrations. Predictive capability was retained in both tests.Current weather appears to weigh more heavily in the abandonment decision than does future price.     

Secular changes in the short-term preventive,positive, and temperature checks to population growth in Europe, 1460 to 1909

Annual variations in births, marriages, deaths, grain prices, and quarterly temperature series in England, France, Prussia, and Sweden are analyzed using a distributed lag model. The results provide support for the existence of the shortterm preventive, positive and temperature checks to population growth. Decreases in fertility and nuptiality are generally associated with increases in grain prices. Increases in mortality appear to be associated with high grain prices, cold winters and hot summers. Changes in these responses over time are examined within the context of economic development.The causes of a high mortality are various; but the greater number of known causes may be referred to five heads: 1) excessive cold or heat; 2) privation of food; 3) effluvial poisons generated in marshes, foul prisons, camps, cities; and epidemic diseases, such as typhus, plague, small pox, and other zymotic diseases; 4) mechanical and chemical injuries; 5) spontaneous disorders to which the structure of the human organization renders it liable. - Farr (1846, p. 164)....a foresight of the difficulties attending the rearing of a family acts as a preventive check, and the actual distresses of some of the lower classes, by which they are disabled from giving the proper food and attention to their children, acts as a positive check to the natural increase of population. - Malthus (1798, Chapter 4).The research on which this paper is based has been funded by grants R01-HD18107 and T32-HD07275 from the U.S. National Institute of Child Health and Human Development. This paper is associated with the author's Basic Patterns in Annual Variations in Fertility, Nuptiality, Mortality, and Prices in Preindustrial Europe,Population Studies 42, 2, 1988, 275-303. I thank Ronald Lee, Ulla Larsen, and Jan de Vries for helpful comments and suggestions.     

A modified parameterization of flux-profile relationships in the surface layer using different roughness length values for heat and momentum

The surface-layer flux-profile formulae of Louis (1979), used in many atmospheric models, are modified in a simple way to allow for different values of the roughness lengths for heat and momentum. The modified set of formulae simplifies the calculation of surface-layer fluxes over most natural land surfaces, where the roughness length for momentum can be almost an order of magnitude greater than that for heat.