Modification of some soil mechanical properties (penetration resistance and consolidation pressure) induced by vehicle compaction during mechanized forest exploitation was studied in an acid and loamy leached forest soil of the loessic belt of central Belgium. In situ penetration tests and laboratory Bishop–Wesley cell tests were undertaken for the two main soil horizons of a beech high-forest, i.e. the eluvial E horizon (5–30 cm depth) and the underlying clay-enriched Bt horizon (30–60 cm depth). Both undisturbed and wheel-rutted soil areas were studied (E and Bt horizons vs. Eg and Btg horizons).
Results show that: The experimental overconsolidation pressure of the eluvial reference horizon (E) is about 50 kPa higher than the value calculated from soil overburden pressure; this probably results from suction action during dry periods. The clay-enriched reference horizon (Bt) shows the same trends. In wheel-rutted areas, seven years after logging operations, the Eg horizon memorizes only 14.5% of the wheel induced stress due to forest machinery.
In the compacted Btg horizon, the experimental overconsolidation pressure represents 96% of the exerted theoretical stresses due to harvesting actions. The good recording of the exerted stresses, after seven years, can be explained by: (1) The Btg depth which keeps it from seasonal variations i.e. from desiccation–moistening or freeze–thaw cycling; (2) amorphous and free iron accumulation inducing a “glue” effect of the Btg soil matrix, which could stabilize the soil structure and prevent recovery to initial conditions. These results provide clear evidence that on loessic materials, soil compaction due to logging operations leads to modifications in both physical (bulk density, total porosity) and mechanical (penetration resistance and consolidation pressure) soil properties. 相似文献
An interference-free, fast, and simple method is proposed for Pb determination in environmental solid samples combining slurry sampling and electrothermal atomic absorption spectrometry. Samples were ground to an adequate particle size and slurries were prepared by weighing from 0.05 g to 0.20 g of dry sediment, adding nitric acid, and a solution containing 0.1% Triton X-100. Ultrasonic agitation was employed for slurries homogenization. Analytical variables including acid pre-treatment conditions, particle size, slurry stability, temperature program of the graphite furnace, and type and concentration of the chemical modifier were studied. The undesirable effects of potential non-specific and spectral interferences on Pb signal were also taken into account. Continuum source and self-reversal methods for background correction were evaluated and compared. For calibration, synthetic acid solutions of Pb were employed. Calibration was linear within the range 1-30 μg L−1 and 5-30 μg L−1 when the 217.0 nm and 283.3 nm analytical lines were used. Correlation coefficients of 0.9992 and 0.9997 were obtained. Using optimized conditions, limits of detection (3σ) of 0.025 μg g−1 and 0.1 μg g−1 were achieved for the 217.0 nm and 283.3 nm analytical lines, respectively. The method was successfully applied to the determination of lead in soil, contaminated soil, municipal sludge, and sediment samples. The accuracy was assessed by the analysis of two certified reference materials: municipal sludge (QC MUNICIPAL SLUDGE A) and lake sediment (TRAP-LRM from IJS). 相似文献
Hydrocarbons and metabolites from biodegradation in soil have been isolated and separated using Soxhlet extraction, with n-heptane and dichloromethane, combined with solid-phase extraction on silica gel and basic aluminum oxide using n-pentane, dichloromethane, methanol, and sulfuric acid – methanol as eluents. This procedure can be used for determination of metabolites both in laboratory-prepared soil samples containing mineral oils and in actual contaminated soil. After microbiological degradation, organic acids and ketones which were not original components of the diesel fuel and lubricating oil contaminating the soil samples were identified using capillary gas chromatography – mass spectrometry in batch-soil experiments. Predominantly alicyclic and branched-chain aliphatic organic acids and diacids, and aromatic ketones, were found to be formed after a few weeks degradation. 相似文献
Electrical-mechanical and mechanical-electrical coupling phenomena have been observed in geo-materials. Underlying internal phenomena are not always clear. In this paper, we identify potential microscale processes on the bases of previously published research; fundamental physical principles and analytical models are included. Second, we notice important inconsistencies between theoretically predicted values or high-frequency laboratory data with respect to low-frequency field observations. To explore these differences, we conduct a laboratory experimental study that simulates field conditions, placing emphasis on low frequency coupling, that is, less than 10 kHz. Both, mechanical-electrical and electrical-mechanical effects are observed. Finally, hypotheses are presented in an attempt to explain observed differences. 相似文献
A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account of circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe may degenerate into those for the conventional rectangular-shaped strip footing while the pipe embedment approaches zero. Parametric studies indicate that, the pipe-soil interfacial properties have much influence on the bearing capacity for the pipe foundation on clayedy soils. 相似文献
A brief review of the literatures on the titled subject is given. A set of wave equations, taking the inertial coupling effect
between soil skeleton and pore water into account, are established for saturated soils. The preliminary analysis shows that
the nature of wave propagation is mainly influenced by permeability coefficient,k. There are three types of waves, two (P-and S-wave) propagating through soil skeleton and one(P-wave) through pore water.
For a soil with large value ofk, compression wave velocity through pore water will be greater than that through single-phased water, and ask→∞, the former could be
times as great as the latter. For a soil with extremely low permeability, the compression wave velocity could be either less
or greater than that through single-phased water, depending on the rigidity of the soil passing through. Some phenomena observed
from tests presented in the literature may be reasonably explained by the proposed theory herein, and thus more reliable parameters
of soil could be obtained from wave velocity measurements. Further studies on this subject are still needed.
This paper is a part of the dissertation of the first author for the Ph.D. degree, the second author is his advisor. 相似文献
Diffusive transport through geosynthetic clay liners and engineered compacted clay landfill liners is the primary mechanism for mass transport from well-engineered modern landfills. For this reason, accurate estimates of diffusion coefficients for clay soils are essential for the design of engineered liner systems. A long-standing theoretical problem is the role of anion exclusion on the estimation of diffusion coefficients for ionic solutes migrating through charged porous media. This paper describes the steady-state solution of a fully coupled set of transport equations modeling ion movement through a permanently charged platy-clay soil. The microscale analysis takes into account the actual diffusion coefficient for each ion species, ion-pairing (as required by electroneutrality of the solution), as well as anion exclusion and cation inclusion ,arising from the permanent charge on clay particles. To render the problem tractable, the theoretical analysis focuses on an extremely small two-dimensional unit cell in an ideal, saturated, two-phase porous medium. The analysis presented here is limited to a particular geometrical example, but this example is sufficiently general for characteristic behaviours of systems of this kind to be identified. Most importantly, new insight is gained into the mechanism of ion migration through a charged platy-clay soil. The numerical results obtained from this study show that the identification of macroscopic transport quantities such as effective diffusion coefficients and membrane potentials from diffusion cell tests using standard diffusion theory only hold for a specific system. While ion exclusion behaviours are often referred to in the literature, as far as the authors are aware there has been no previous detailed microscale analysis of their role in steady-state diffusion through a charged platy-clay soil. 相似文献