Sandy Silt Soil Research Articles

Behavior of Micropiles in Soft Soil under Vertical Loading

The behavior of micropiles in soft clay, under vertical compression and tension loading, was examined by field tests at a site in Shanghai. The soil profile consists of topsoil, silty clay, sandy silt, muddy clay, and clay soil. Two compression and three tension loading tests were conducted on five single micropiles. The piles were instrumented with vibrating wire force sensors, and they were monitored during the process of loading to investigate the mechanisms of load transfer. Both the ultimate vertical load capacity and the deflection at applied loads were examined. The results indicate that the pile load–displacement response under vertical compression or tension loadings was nonlinear. Both the compression and the tension load carrying capacity basically increased with a linear trend. But, the ultimate load capacities under tension were about 50-60% of those under compression. Tip resistance was about 10-15% of the applied compression load, not existing in the micropiles under tension. The average skin friction for micropiles under compression loading was about 50% higher than that for piles under tension loading.

Mapping of penetrometer resistance in relation to tractor traffic using multivariate geostatistics

The traffic of agricultural machines can cause soil compaction and high variability of soil structure, both along normal lines and along those parallel to the field plane. The aim of this work was to investigate the potential of an electronic penetrometer, a GPS, a GIS and geostatistical techniques for mapping soil compaction. In July 2003 soil cone penetrometer resistance was measured using a semi-automatic electronic penetrometer in a sandy-silt soil (Vertic Xerochrept) of inland Sicily where a three-year rotation wheat ( Triticum durum Desf.)–wheat–tomato ( Solanum lycopersicum L.) was practiced. The measurements were carried out along three parallel 3-m long transects, from the soil surface to a depth of 0.70 m. A multivariate geostatistical approach, including exploratory analysis, variography, stochastic simulation and post-processing of simulations, was applied to produce thematic maps of penetrometer resistance and probability exceeding a critical value, in correspondence of a different number of tractor passes. Penetrometer resistance variation resulted erratic at the surface but showed high spatial correlation between data measured at different depths. The probabilistic maps of compaction risk showed that the soil volume, exceeding the penetrometer resistance of 2.5 MPa, critical for root growth, at the probability level of p > 0.40 increased from 20% to 40% after five tractor passes.

Effects of Psychrometrics Conditions on the Drying of a Porous Soil

Coupled heat and water movement investigation in porous media is becoming increasingly relevant in sciences and engineering such as geophysics, where geothermal flux is a key issue, and in building technology where mathematical models are developed to provide better energy efficiency. In the top layers of the earth for instance, the great annual and diurnal air temperature and humidity amplitudes under the influence of radiation and rain result in significant fluctuation in soil temperature and volumetric water contents. Column evaporation experiments have been carried out with sandy silt soil in a constant-temperature-relative humidity chamber, and also by the window side exposed to varying psychrometric conditions. Atmospheric temperature and relative humidity data have been measured and logged with the help of a dataloger while soil temperatures and moisture contents have been measured and logged using a data acquisition system. Soil column has been mounted on a digital weighing balance and programmed into a computer with the aid of an evaluation software for continuous weight data acquisition of the column. Comparing the observed experimental data with predicted numerical values shows substantial agreement suggesting that the developed model can be used to generate reliable moisture evolution and temperature data base, given the weather condition and necessary physical properties of the soil. Average overall moisture transport coefficient ranged from 1.25 E—06 to 2.01 E—06 and was largely representative of the pattern of evaporation from the soil. The evaporation rate was also strongly influenced by the initial moisture content at the surface and the ambient relative humidity.

Enhanced performance of reinforced soil walls by the inclusion of short fiber

This paper presents the effects of the inclusion of short fiber in sandy silt (SM) soil on the performance of reinforced walls. The inclusion of short fiber in soil is expected to increase soil strength and improve stability when it is used as the backfill material. Short fiber of 60 mm length was used and the mixing ratio of the fiber was 0.2% by weight of the soil. The finite element method was used to examine the influence of the reinforced short fiber on reinforced walls. The vertical and horizontal earth pressure, displacement and settlement of the wall face were analyzed. These results were compared to the measured results from two full-scale tests. It is shown that use of short fiber reinforced soil increases the stability of the wall and decreases the earth pressures and displacements of the wall. This effect is more significant when short fiber soil is used in combination with geogrid.

Gelifluction: viscous flow or plastic creep?

AbstractThis paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw‐related gelifluction. A planar 12° prototype slope was modelled in each experiment, using the same natural fine sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous flow is 1/1. If gelifluction is a viscosity‐controlled flow process, scaling conflicts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling conflicts are observed, we may conclude that gelifluction is not controlled by viscosity, but rather by elasto‐plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process.Models were saturated, consolidated and frozen from the surface downwards on the laboratory floor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze–thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement profiles reflecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze–thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and profiles were also similar to those observed in earlier full‐scale laboratory floor experiments. It is concluded therefore that the modelled gelifluction was not a time‐dependent viscosity‐controlled flow phenomenon, but rather elasto‐plastic in nature. A first approximation ‘flow’ law is proposed, based on the ‘Cam Clay’ constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd.

Fate of Volatile Chlorinated Organic Compounds in a Laboratory Chamber with Alfalfa Plants

The fate of two volatile organo chlorinated compounds, 1,1,1-trichloroethane (TCA) and trichloroethylene (TCE), was studied in rhizosphere soil. Laboratory experiments were performed with alfalfa (Medicago sativa) growing in sandy silt soil fed continuously with groundwater contaminated with TCA and TCE at 50 and 200 μL/L, respectively. Methane generated in the groundwater provided evidence for anaerobic biodegradation. Groundwater samples indicated that the concentration of TCE decreased with axial position during the steady-state period. The flow rate of the effluent was significantly less than the inlet flow because of active evapotranspiration. Thus, a significant fraction of TCA and TCE disappeared. Headspace analysis of the gas in the enclosed chamber using a FT-IR spectrophotometer showed that small quantities of TCA and TCE migrated into the gas phase above the alfalfa plants ; no chlorinated intermediates or methane were found in this gas phase.

Distribution quantitative et qualitative des actinomycètes dans les horizons de sol de surface et profonds d'une palmeraie algérienne

Qualitative and quantitative distributions of actinomycetes were studied in surface and deeper soil horizons of a palm plantation in Algeria. The distributions were influenced directly by certain morphological and pedological factors of horizons, among which, the most important besides depth, were the quantity and quality of organic matter, clay abundance and calcareous content. Determination of 350 isolates showed that the genus Streptomyces was dominant in most of the horizons, with the exception of two of them, where Actinomadura and Nocardioides species were proliferating. However, whereas soil surface horizons contained very diversified species, each deeper horizon was characterized by the dominance of a particular species, often to a considerable extent. In a decreasing order of importance, the following species were found among the dominant: Streptomyces coerulescens in very deep reddish brown clay–silt sandy soils; Actinomadura cremea in light brown and sandy–silt soils; Nocardioides albus and Streptomyces aurantiogriseus in yellow nearly inorganic sandy soils. The influence of the above factors upon species distribution is discussed. Key words: actinomycetes, systematics, ecology. [Journal translation]

Aphid and Egyptian Alfalfa Weevil Larva Control, 1983

Abstract Thirteen treatments were evaluated for the control of aphids and Egyptian alfalfa weevil. Approximately 90% of the aphid population during the experiment were blue alfalfa aphid, the others pea aphid. The average height of stems on 19 Feb. was 10 in. This alfalfa was on sandy silt soil at the Yuma Mesa Citrus Stn. Plots of 8 ft by 50 ft were replicated four times. The applications on 19 Feb. were made with a small-plot sprayer at a rate of 20 gal/acre and 40 lb/in2 (pressurized with CO2). The number of aphids per stem on 19 Feb. averaged 10.53. Counts 2, 4, 7, 10, and 14 days following treatments are given. The applications coincided with the peak of abundance for the Egyptian alfalfa weevil larvae present.

Grain Production and Dry Matter Partition in Rice (Oryza sativa L.) in Response to Water Deficits during the Whole Grain-Filling Period

The grain growth of rice is highly tolerant to water stress throughout the grain-filling period. Despite a large reduction in dry matter production, the grain growth during both the period of active cell division and expansion, and the subsequent period of rapid starch deposition was little affected by water deficits. Reduction in dry matter production due to water stress was almost completely compensated by the increased transfer of reserved assimilates to the grain. But, the plants which experienced drought during the early stage of grain growth and were relieved from the stress thereafter yielded less than the plants which were well watered throughout the grain-filling period. Similar response was observed in wheat, and a deteriorated root function in stressed plants is suggested as a possible factor for this reduced grain yield. It is therefore probable that the yield reduction in rice associated with prolonged drought during the period of grain-filling is a result of the indirect effects of water stress through the function of roots with regard to the production of hormonal substances. However, in view of the highly tolerant nature of the short term grain growth to water deficits, it is more likely that the lack of assimilate supply to the grain is responsible for reduced grain yield in plants under prolonged stress, since there must be an upper limit to the amount of pre-anthesis reserves that can be available for grain growth. This situation has been clearly demonstrated with maize. The objective of this study was to examine the above premise, i.e., the total assimlate supply is the primary factor that controls grain yield in rice droughted during most of the grain-filling period. Rice plants (Oryza sativa L. cv. Nipponbare) were grown in wooden trays (1.05×1.20×0.15 m) containing sandy silt soil. The trays were placed in a vinyl-covered house located in a field and so arranged to form a block of miniature crops that simulates a field density of 95, 200 plants/10a. Part of the block was adequately watered throughout the whole growing period, while water application to the remaining block was restricted after ear emergence so that leaf water potential around midday was maintained at -10 to -15 bars. At intervals during the treatment period, water potential was measured on the flag leaves between 1300 and 1500 hours. During this period, areas of green leaves and grain growth were also monitored. Dry weights of grains, shoots and roots were determined both at the time of ear emergence and at maturity. Daytime water potential in the leaves of stressed plants declined rapidly after the start of treatment, reaching -12 bars 10 days after ear emergence (Fig. 2). Leaf water potentials in the control plants remained at -3 to -6 bars except at the later stage of the growth. Leaf senescence was accelerated in stressed plants, LAI reaching less than 50% of the initial value by the 20th clay after ear emergence, whereas the controls still retained the green leaves of about 60% of the initial value until the full-ripe stage (Fig. 3). Water deficits reduced the dry matter production by approximately 40% (Tables 2 and 3) through the reduction in both the leaf area duration and the average rate of dry matter production (Table 4). Despite this, the grain yield of desiccated plants was only reduce by 16% (Tables 1 and 2), due to the increased assimilate transfer from the shoots to the grain (Tables 2 and 3). Thus the apparent contribution of reserves to grain yield was 34% in the desiccated plants, about three times as high as in the controls (Table 3.). These findings are in agreement with our earlier studies; the grain growth for the first 10 to 20 days after ear emergence was only slightly affected by the water stress (Fig. 4). However, the rate of grain growth declined as the water stress was prolonged. [the rest omitted]

FLOW OF WATER INTO CERAMIC TUBES SIMULATING ROOT SYSTEMS

In model root systems constructed of porous ceramic tubing, accumulated outflow volumes of water from four inner tubes, simulating plant roots, surrounded by 12 outer tubes was reduced when spacings narrowed below 2.0 mm in both sandy loam and silt soils. Soil water contents and, simultaneously, capillary conductivity decreased faster at close tube spacings than at wider ones in the order of the decrease at 1.0 mm > at 1.5 mm > at 2.0 mm = that at 3.0 mm = that at 6.0 mm. The ratio of outflow from 12 tubes to that from four, surrounded by the 12, is 3 and constant if all tubes receive water from discrete equal-sized cylinders of soil. At less than 2.0 mm between tubes, the ratio increased with time to maximum of about 9 and 5 for sandy loam and silt loam, respectively, indicating soil cylinder overlap for the particular suction of −0.9 bar imposed on the tubes. At 2.0 mm spacing or greater, the ratio was relatively constant and reasonably close to 3. Radial flow of water may be quickly restricted at root spacings below some limiting distance that is probably dependent upon the demand potential at the soil–root interface.