Carotte (échantillon) | EPFL Graph Search

Une carotte (core, ou core sample en anglais) est un échantillon cylindrique d'une substance. La plupart des carottes sont obtenues en forant avec des forets spéciaux dans la substance, par exemple dans les sédiments ou la roche, avec un tube d'acier creux appelé carottier. Il existe différents types de carottiers permettant d'échantillonner différents milieux dans différentes conditions. Lors du processus de carottage, l'échantillon est poussé plus ou moins intact dans le tube. Retiré du tube en laboratoire, il est inspecté et analysé par différentes techniques et équipements selon le type de données désiré. Les carottes sont notamment utilisé en géologie pour l'étude d'un sous-sol donné, pour étudier la glace. Les carottes peuvent être prélevées pour tester les propriétés de matériaux artificiels, tels que le béton, la céramique, certains métaux et alliages, en particulier les plus tendres, les revêtements de route etc. Des carottes peuvent également être prélevées sur des êtres v

Study of the microbial communities of core and water samples in a chloroethenes contaminated aquifer

Guillaume Laulan

Widely used in industrial activities, chloroethenes have become common groundwater contaminants. Dehalorespiration is an anaerobic bacterial respiration coupling their sequential degradation to energy production. The interactions between the dehalorespiring bacteria and the other guilds and environmental variables are presumed to influence the dehalorespiration efficiency. Here, water and core samples were extracted from the PCE-contaminated site of Lyss (BE, Switzerland). Bacterial DNA was extracted and the 16S rRNA gene amplified by PCR. Terminal restriction fragment length polymorphism (T-RFLP) was used to assess the diversity of the bacterial communities. Core and groundwater environmental variables were analyzed as well. The T-RFLP profiles and the environmental data obtained were processed using statistical multivariate analysis. Within a period of two months, the bacterial communities remained relatively specific to their respective sampling origins. Communities from the oxic layer shared a similar set of bacterial species whereas piezometers from the anoxic layer had a specific one. The T-RFLP profiles obtained from single depth and multi-level piezometers were clearly distinct, probably due to differences in the pumping flow rates and their associated transport regimes, which can have an impact on i) the sediments extracted from the aquifer, ii) the hydraulic zone reached and iii) a potential selective bacterial adsorption onto the pumping tube wall. Environmental factors related to the groundwater redox state appeared as the major variables influencing the bacterial populations. Bacterial communities from core samples clustered into two distinct sets: i) samples from the strongly reductive silt layer, and ii) samples from the coarser and less reductive layer. Grain size distribution and redox state both had a major influence on the bacterial communities of core samples. Finally, it was shown that microbial populations extracted from groundwater differed from the ones extracted from core material, and thus were not representative of the overall aquifer microbial diversity.

2009

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

Claire Guenat, Renée-Claire Le Bayon, Adrien Francis Olivier Liernur, Andreas Cedric Schomburg, Pascal Turberg

This paper presents the coupling of freeze-core sampling with X-ray CT scanning for the analysis of the soil structure of fine-grained, low-cohesive soils. We used a medical scanner to image the 3D soil structure of the frozen soil cores, providing X-ray CT data at a millimetric resolution over freeze-cores that are up to 62.5 cm long and 25 cm wide. The obtained data and the changes in gray level values could be successfully used to identify and characterize different soil units with distinctly different physical properties. Traditional measurements of soil bulk density, carbon and particle size analyses were conducted within each of the identified soil units. These observations were used to develop a 3D model of soil bulk density and organic matter distribution for five freeze-cores obtained at a restored floodplain in Switzerland. The millimetric X-ray CT scanning was applied to detect the impact of freeze-coring on the soil structural integrity. This allows identifying undisturbed zones, a critical precondition for any subsequent assessment of soil structure. The proposed coupling is thought to be applicable to a wide range of other low-cohesive soil types and has a large potential for applications in hydrogeology, biology or soil science.

Elsevier Science Bv2017

An X-ray computed tomography-based index to characterize the quality of cataclastic carbonate rock samples

Pierre Guillaume Christe, Vincent Labiouse, Reto Meuli, Aurèle Parriaux, Pascal Turberg

X-ray computed tomography (XRCT) can reconstruct, in a nondestructive way and in three-dimension, the distribution of densities within opaque materials. Consequently, it provides an effective possibility to characterize the inner content of rock core samples and, in particular their alteration products sensu lato which generally appear less dense than the intact rock matrix. In this paper, a new index, based on XRCT data, is tested for evaluating the degree of alteration of highly tectonized carbonate rock samples and is compared with visual-based classification systems. This XRCT-based analysis leads to a diagnosis of alteration which appears objective, precise and in agreement with the visual observations. Besides, this method takes into account the entire volume of the sample, is rapid to carry out and allows an intact rock core to be used for further laboratory testing.

2011

Study of the microbial communities of core and water samples in a chloroethenes contaminated aquifer

Guillaume Laulan

2009