Compacted Soil Samples Research Articles

The diffusion and sorption of volatile organic compounds through kaolinitic clayey soils

Laboratory experiments to estimate the effective molecular diffusion coefficient ( D e) and sorption coefficient ( K d) for volatile organic compounds through natural clayey soils were conducted using diffusion testing apparatus. The compounds tested were methyl ethyl ketone (MEK), toluene and trichloroethylene (TCE). The D e and K d values were determined by a curve fitting procedure. The compound losses, and the effects of porous disks used in the apparatus were significant. The transport of MEK was faster than that of TCE and toluene because of the lower sorption to the soils. The D e values of all the compounds were of the order of 10 −10 m 2/s and smaller than the diffusion coefficient in pure aqueous solution at infinite dilution ( D 0), due to the tortuosity of the samples. The effects of the sample thickness on the parameter determination were not significant. Comparison to the K d values estimated from batch sorption tests and from organic carbon content ( f oc)-based predictions showed that the diffusion test results were intermediate between those from the other two methods. The diffusion tests use compacted soil samples and should be more relevant to in situ conditions, but the reliability of the tests is affected by large compound losses that cause uncertainties in their interpretation. It is recommended that more than one method be used to assess K d values.

The frost penetration with the modified soil in the landfill bottom liner system

Many researchers have studied on the effect of freeze/thaw phenomena mainly on compacted soil samples of small diameter: Most of the experiments done so far were applied to study those effects on pavement design in civil engineering. The paper relates the freeze/thaw studies performed on large scale equipment to better simulate these effects under the existing field conditions in a landfill. A large scale (1.0 m×1.5m×2.0m) laboratory simulates the field depth of the bottom liner systems with the cold climate and it was also introduced many boundary conditions similar to those encountered in the landfill. As a bottom liner materials, the modified soil (mixed stabilizers, clays, cements, and clay minerals) was used instead of the natural clay. From bottom to top of this lysimeter, one can identify two layers: a) bottom liner of 30 cm; b) a stabilizer soil layer of 75cm. As results of the performed frezee/thaw simulations, it was found out that the depth of frost penetration increased a few centimeters more with 35–40 mm/hr simulated than that performed without simulated rainfall. Then, the frost heave increased a few millimeters. Also, a few cracks appeared, but they were not severe neither significantly opened. The results showed that compacted modified soil is as much as reliable the regual compacted clay liners normally used in landfill construction, submittd to strong winter conditions.

The Influence of Compaction on the Mechanical Behaviour of a Silty Sand

The paper analyses the mechanical behaviour of a silty sand, as it was measured in laboratory tests on samples prepared with different density and moisture contents. After a description of the physical characteristics of the material, the methods used to prepare compacted and slurry-consolidated soil samples are reported, followed by a description of the apparatus and experimental procedures adopted. The compressibility characteristics were analysed by isotropic tests at ordinary stress levels (p'<1 MPa) and by oedometer tests at stress levels up to 40 MPa. The shear behaviour was investigated by means of triaxial compression tests following conventional undrained or drained paths with variable directions ; also, the initial shear stiffness was measured by resonant column tests. The basic behaviour of the slurry-consolidated silty sand appeared consistent with the theoretical framework of Critical State Soil Mechanics ; this soil could therefore be used as a reference material to which the mechanical properties of the compacted samples were compared throughout the paper. Two volumetric state loci were taken as reference curves to investigate the behaviour of the compacted material : (i) the isotropic compression line of the remoulded soil, and (ii) the critical state line, which proved to be independent of the soil preparation procedure. Whatever the preparation technique, the mechanical behaviour of the silty sand under triaxial compression was found to be stress-path dependent from the very beginning of the stress-strain curve. The net effect of the compaction could be assessed by comparing the stress-strain behaviour of dynamically compacted soil to that of remoulded material brought to comparable density through a mechanical overconsolidation process. The stress-strain behaviour of the compacted silty sand proved to be more fragile and showed lower initial stiffness than the remoulded soil. It was therefore observed that, even though the compaction may be considerably beneficial to compression behaviour, it does not necessarily optimise the stress-strain response under shear loads.

The Influence of Soil Moisture and Compaction on Spillway Erosion

Submerged jet tests were conducted on a soil material compacted by dynamic and static load methods over a range of dry unit weights and moisture contents. The compacted soil samples were pre-wet prior to testing. An index parameter was used to compare changes in the erosion resistance of the soil at different compacted dry unit weights and compacted moisture contents. Moisture content at the time of compaction had a significant influence on soil erosion resistance. Additionally, at a constant moisture content, the erosion resistance increased as the dry unit weight increased. These results, along with results of two compacted spillway channel tests on the same soil, suggest that proper compaction should be considered in the repair of earthen auxiliary spillways.

Efeito da compactação artificial de dois solos limo-argilosos sôbre a penetração das raízes de arroz

Amostras de dois solos limo-argilosos foram compactadas, utilizando-se um compactador Bruce modificado. Tanto pela variação da intensidade de compactação como pela variação do teor de umidade do solo, obteve-se uma escala crescente de massas específicas aparentes dessas amostras. Nestas foram plantadas sementes de arroz, para determinar as relações entre a penetração das raízes da planta e a massa específica aparente do solo. Verificou-se que, a partir de determinadas massas específicas aparentes, artificialmente obtidas, a penetração das raízes era totalmente impedida e o desenvolvimento do sistema radicular grandemente reduzido.

A Study of a Large Compacted Clay Embankment-Fill Failure

The paper describes the failure during construction of a proposed 70 ft. high railway embankment fill. The fill was built of a uniform clay of medium plasticity which was used at an average moisture content of 3 per cent greater than had been provided for in the design. The fill failed under its own weight when it reached a height of 55 feet.In order to assist in the design of stabilizing works three test holes were drilled in the fill and soil samples recovered. Properties of field compacted and laboratory compacted soil samples are compared. The age of both types of samples is shown to have a significant effect on the test results.Both total and effective stress analyses of the embankment at failure have been performed using the laboratory values of soil strength. The total stress analysis gives a safety factor of 1.0 at failure whereas the effective stress analysis gives a safety factor of 1.2. The hazards of choosing the correct value of laboratory shear strength for the total stress analysis are discussed.