Stress-Strain State of Weak Saturated Clay Beds of Embankments

Results are presented for laboratory and field tests of weak saturated soils serving as beds for embankments in Ho Chi Min City and various regions of the Mekong River Delta (Vietnam). A method is outlined for quantitative evaluation of the stress-strain state (SSS) of the weak saturated clayey beds (plane problem). A method is described for quantitative evaluation of the deformation and stability of weak beds in the initial, intermediate, and stabilized stages of the formation and transformation of the SSS. __________ Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 2–6, September–October, 2005.     

Lead contamination in tap water of households with children in Lower Saxony, Germany

Lead has numerous acute and chronic adverse effects on human beings. This is especially true for infants and children. The main path of lead ingestion in children can be different according to housing and living situation. The intake of lead through drinking water is commonly due to metal corrosion. The users plumbing can be an important factor. In recent years, many lead pipes in Germany have been replaced by pipes made of an alternative material. The aim of this study is to assess the present state of drinking water contamination and the resulting exposure of infants to lead. For this purpose mothers of new-born babies were offered a free examination of their drinking water. After a written declaration of consent had been obtained and after the infant in question had reached an age of 3 months, a stagnation sample of cold tap-water after overnight stagnation together with a random daytime sample was obtained from the family. The collected samples were analysed by atomic absorption spectrometry for their lead concentration. In total, 1485 samples from households were collected. Of the 1434 stagnation samples, 3.1% had lead concentrations greater than 0.01 mg/l (recommended limit of the WHO) and 0.6% had concentrations above the limit of the German drinking water regulation (0.04 mg/l). The values for the 1474 random daytime samples were 2.1% above 0.01 mg/l and 0.2% greater than 0.04 mg/l, respectively. By region, the areas Bovenden, Friedland, Duderstadt, Northeim and Rosdorf were particularly affected. The highest measured concentrations of lead in the stagnation samples were 0.11 mg/l and 0.15 mg/l in the random daytime samples, respectively.     

Energy and environmental comparison of three variants of a family house during its whole life span

The aim of this study is to analyse and compare three variants of a family house in order to evaluate the total environmental impacts produced during the whole building life cycle. The first variant corresponds to the standard in force in Switzerland, the second alternative to the requirements of a quality control label for houses with low energy consumption and the third case is a very low energy consumption building. The three variants have the same architectural aspect but different insulation thicknesses and types, different energy production systems and the use of different renewable energies. The calculation of the environmental impacts is carried out by means of a life cycle analysis, which includes not only the impact related to the energy consumption during the occupancy stage, but also the materials manufacture, transport, replacement and elimination at the end of the building lifetime. The results are expressed with the Swiss and the UCTE (Union for the Co-ordination of Transmission of Electricity) electricity mix to analyse how they influence the building impact.     

Air monitoring network program in Saudi Arabia

The Kingdom of Saudi Arabia has initiated a program to install air quality network stations throughout the country in order to measure concentration of the ambient air pollutants. The site selection of these stations is an important objective to be accomplished and must be done based on scientific and rational work. To accomplish this objective, a modified version of atmospheric transport and dispersion model, known as air resources laboratories - atmospheric transport and dispersion (ARLATAD) model, is used to evaluate long range transport and diffusion of air pollutants from major pollution causing sources such as refineries, open-air burning of associated gases of oil fields and major industries.Hourly meteorological data for a period of three years (from 1977 to 1979) on wind speed, wind direction, pressure, and temperature from 20 synoptic stations in Saudi Arabia is processed and used as model input. In addition to these, meteorological data from three upper air stations is also processed in order to determine base and top of critical inversion heights.Various pollution causing sources are identified within the study area. Air trajectories are drawn with sources as the origins of the trajectories and the dispersion characteristics is studied with distance and time. Based on long term meteorological records, the adversely affected zones are statistically identified for potential station sites.     

Procedure for predicting settlements of thawing bases for engineering calculations

It was shown that in order to compute the settlement of thawing cohesive soil under a load in time it is necessary to experimentally determine the consolidation coefficient. A procedure is suggested for determining this coefficient, as well as use of the classical solution of a differential equation for seepage consolidation to describe the settlement of soil, thawing of which can occur according to any law.State All-Union Scientific Research Institute of Roads. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 5–7, July–August, 1993.     

A steady-state model for the rotating biological disc reactor

A steady-state model for substrate removal in a rotating biological disc reactor is presented. The model considers the consumption of substrate by micro-organisms in the biofilm attached to the rotating disc, and mass transfer from the attached liquid film to the biofilm. A mass balance on substrate over the liquid in the trough provides an expression for effluent substrate in terms of the microbial kinetic constants, the geometry of the system and the operating conditions. In order to simplify the solution of the equations in the model, first order kinetics are assumed for the rate of microbial growth and substrate utilization. This simplified model can be solved, for example, by using a programmable calculator. The model predicts that the fractional removal of substrate per stage is strongly dependent on the hydraulic loading rate per unit disc area but independent of feed substrate concentration. It predicts constant removal independent of disc size provided the hydraulic loading per unit area is kept constant. The rotational speed has only a slight predicted effect on the rate of substrate removal. The predictions of the model are compared with published data from the literature for both domestic wastewater and some industrial wastes. Trends observed in the field are predicted qualitatively by the model.     

Continuous monitoring of short term dissolved oxygen and algal dynamics

Dissolved oxygen (DO) in coastal bays with frequent algal blooms can undergo significant diurnal changes. Short-term DO and algal dynamics in a sub-tropical, nitrogen-limited, marine ecosystem are studied by means of a specially designed telemetry system. The high resolution data show clearly the importance of the vertical DO structure, and its relationship with environmental variables (solar radiation, water temperature, wind, tidal current) and phytoplankton dynamics. The design, instrumentation and calibration, and operational experience of the system are described. The simple and robust system has proved useful in (i) providing continuous data for full testing of water quality models, and (ii) the planning of field experiments to study algal dynamics.     

Concurrent denitrification and oxygen uptake in microbial films

Mixed microbial films were grown on the inner walls of a tubular reactor with recirculation of the reactor contents and continuous flow-through of nutrient solution. The loss of total oxidized nitrogen was correlated to the film population, the nitrite concentration and the dissolved oxygen concentration in the reactor. When film population was greater than 0.5 × 10⁹ cells cm⁻², reactor dissolved oxygen concentration greater than 1 mg l⁻¹ had little effect on the nitrate loss. Nitrate loss declined for film populations greater than 2 × 10⁹ cells cm⁻². Models based on Monod and zero-order microbial kinetics were calibrated using these data and a nonlinear least squares method. There was little difference in the residual errors with these methods.     

Tunnelling projects in Southern Africa

Until some thirty years ago tunnelling in southern Africa for civil engineering purposes had been on a relatively small scale and of a sporadic nature. The first major tunnel to be built in the region was the 82 km long Orange-Fish Tunnel. Since 1970 more than 175 tunnels with an aggregate length of just over 400 km have been built. Much of the first phase of the Lesotho Highlands Water Project, which will have more than 100 km of tunnels, is about to be completed. The last thirty years represent the busiest period of tunnelling by civil engineers that southern Africa has ever known. The paper starts by summarising the early history of tunnelling in the region, and goes onto describe recent and current tunnelling projects. It also gives an indication of the possible demand for tunnels in the future.