An elastoplastic model for unsaturated expansive soils based on shakedown concept

It is important to model the behaviour of unsaturated expansive soils subjected to hydromechanical loadings, because these wetting and drying cycles alter significantly their hydromechanical behaviour which may cause a huge differential settlement on the foundations of individual buildings, pavements, dams, etc. From experimental observations, these expansive soils can generally reach a final equilibrium state at the end of the suction cycles where the soil behaviour can be supposed elastic. In this context, this paper presents an analytical method based on shakedown concept for the hydromechanical behaviour of expansive soils. The required parameters of the shakedown-based model are calibrated by the experimental results obtained for bentonite/sand mixtures subjected to cyclic suction loadings in an oedometric test. The comparison between the experimental results and the modeling demonstrates the capacity of the proposed shakedown-based model to simulate the hydromechanical behaviour of unsaturated expansive soils

An elastoplastic model for unsaturated expansive soils based on shakedown concept

It is important to model the behaviour of unsaturated expansive soils subjected to hydromechanical loadings, because these wetting and drying cycles alter significantly their hydromechanical behaviour which may cause a huge differential settlement on the foundations of individual buildings, pavements, dams, etc. From experimental observations, these expansive soils can generally reach a final equilibrium state at the end of the suction cycles where the soil behaviour can be supposed elastic. In this context, this paper presents an analytical method based on shakedown concept for the hydromechanical behaviour of expansive soils. The required parameters of the shakedown-based model are calibrated by the experimental results obtained for bentonite/sand mixtures subjected to cyclic suction loadings in an oedometric test. The comparison between the experimental results and the modeling demonstrates the capacity of the proposed shakedown-based model to simulate the hydromechanical behaviour of unsaturated expansive soils

Cage occupancy and compressibility of deuterated N2-clathrate hydrate by neutron diffraction

This paper reports pressure dependent high resolution neutron diffraction work on N-2-clathrates, which for the first time provides numbers on the compressibility as well as the location and degree of filling of the guest molecules in the small and large cages. N-2-clathrates crystallize, at least at lower pressures and temperatures near 0 degrees C, in the Stackelberg type II structure. However, during the diffraction experiments we have observed the transient and partial formation of the von Stackelberg type I N-2-clathrate at pressures exceeding several hundred bar. The filling of the small cages in the type II clathrate roughly follows a Langmuir isotherm, In contrast to most previous assumptions there is strong evidence that the large cages are doubly occupied in both type I and type II N-2-clathrates. The observed filling can be fitted reasonably well by a two-constant Langmuir model

Performance Research of a New Stabilized Rubber Modified Asphalt and Sand Anti-Fracture Mix for Semi-Rigid Asphalt Pavement

International audienceThis paper presented the details of various investigations conducted for the laboratory evaluation of a sand anti-fracture mix (SAF) mixed with a newly developed stabilized rubber modified asphalt (NEW-SRMA), used for mitigating reflective cracking of semi-rigid asphalt pavement in Xinjiang. Two local asphalt binders, Karamay asphalt to Kuqa asphalt, were mixed as the base asphalt for the modification and their mixing ratio was obtained based on compositions analysis. Crumb rubber (CR) was devulcanized to improve its compatibility with asphalt phase. Continuous dense aggregate gradation for the 4.75 mm SAF was designed in the investigation. Compared to styrene-butadiene-styrene modified asphalt binder (SBS-asphalt), NEW SRMA was found to have better performance temperature range, fatigue resistance, and similar workability; corresponding mixes had improved permanent deformation, low-temperature cracking, and fatigue characteristics. Application in practical projects also proves the applicability of NEW-SRMA and corresponding SAF mix for purpose of mitigating reflective cracking in Xinjiang

Micro-Raman analysis of synthetic air clathrates

Raman spectroscopic measurements on synthetic air clathrates, prepared at different pressures and temperatures, are presented. The gas fractionation for clathrates formed at -2 and -20 degrees C is determined from the integrated vibron mode intensities of nitrogen and oxygen molecules. An increasing fractionation in favour of oxygen with increasing pressure is found. An asymmetric peak shape for the O-2 vibron mode was observed in air clathrates prepared at 300 bar and -2 degrees C. The asymmetry of the N-2 vibron mode in the same sample is much less pronounced

Chemistry and morphology of dried-up pollen suspension residues

Pollen grains are covered with lots of different biochemical compounds, like proteins, saccharides and lipids, which are only loosely attached to the pollen. Therefore, they can be separated from the pollen by suspending them in water. Since these compounds play a key role in many atmospheric processes (e.g. cloud condensation nucleation, ice nucleation, aerial allergen exposure), their separation and analyzing are of interest. The chemical composition of whole pollen grains is compared by both Raman and infrared spectroscopy with material that could be extracted from pollen with water. The dominant signals in the pollen grain Raman spectra are those from sporopollenin and carotenoids. These bands decrease in the washing water spectra, since sporopollenin is high molecular and thus is not extractable. The released material shows in turn a chemical composition that differs significantly between species, what is quite expected, since they differ even in the optical properties of their aqueous suspensions. The FTIR spectra show some additional bands to appear in comparison to the Raman spectra. Furthermore, we investigated the pollen rupturing and material release in the aqueous suspensions by drying them up and picturing the residues with a scanning electron microscope. We saw that corn pollen ejected loads of micrometer-sized organelles, which are most likely starch granules. The more the pollen disrupted, the more the measured samples were covered with an amorphous film, which consists of the extracted pollen material, like lipids, sugars, and proteins - the same substances we detected by spectroscopy. Copyright (c) 2013 John Wiley & Sons, Ltd