Flux de liquides au travers des étanchéités composites d'installations de stockage de dechets. influence des caractéristiques du GSB

National audienceL'objectif de ce chapitre est de faire le point de l'état de l'art et des dernières connaissances relatives au comportement hydraulique des étanchéités composites géomembrane-GSB, en particulier en fonction de la nature de la bentonite contenue dans les GSB. On tire des préconisations pour le choix des matériaux à utiliser in situ en fonction de résultats d'essais de laboratoire

Influência da natureza da bentonita na transmissibilidade da interface entre geomembrana e GCL de barreiras compostas

National audienceLes géosynthtéiques bentonitiques (GSB) sont des matériaux géosynthétiques généralement formés par un ou deux géosynthétiques et de la bentonite qui peut être de différentes natures en fonction des cations interfoliaires majoritairement présents. On peut distinguer les calciques naturelles, les sodiques naturelles et les calciques activées. Lorsqu'elles sont confinées et hydratées les bentonites possèdent une très faible conductivité hydraulique . De plus, d'après la littérature, la conductivité hydraulique des GSB dépend justement de la nature de la bentonite qu'ils contiennent.Les GSB contenant de la bentonite sodique ont généralement une conductivité hydraulique plus faible que ceux contenant de la bentonite calcique. C'est pourquoi on a cherché à investiquer l'effet que pouvait avoir la nature de la bentonite sur le comportement hydraulique des étanchéités composites, et sur la transmissivité d'interface géomembrane - GSB en particulier. Différentes conditions de charge hydraulique et de contraintes mécaniques ont été simulées. On a pu vérifier que malgré des différences significatives de conductivité hydraulique des GSB, l'impact sur la transmissivité d'interface est faible

Influence of structural and material properties of GCLs on interface flow in composite liners due to geomembrane defects

International audienceThe flow rates along the interface between damaged geomembranes (GM) and geosynthetic clay liners (GCL) placed on top of a compacted clay liner (CCL) were measured by means of laboratory tests performed with an apparatus especially designed for this purpose. The tests performed were aimed at verifying the influence of the structural and material properties of the GCL on the transmissivity along the GM–GCL interface and flow rates through composite liners. Four types of GCLs with two different bonding processes (stitch-bonded or needle-punched) and different bentonites (natural sodium or natural calcium) were tested. The results obtained showed no significant differences among flow rate versus time in most of the tests performed, especially after the steady-state conditions of flow were reached. An analytical solution was employed to estimate the transmissivity of the GM–GCL interfaces. This solution also allowed predictions of flow rates and radius of wetted areas for typical configurations of composite liners in the field. The results obtained showed little influence of the nature of the bentonite and the predominance of the presence of preferential flow paths between the geomembrane and the GCL surface on the transmissivity of GM–GCL interfaces and flow rates through composite liners

Influence de la nature de la bentonite dans les GSB sur les transferts advectifs dans les étanchéités composites géomembrane-GSB

International audienceThe flow rates along the interface between damaged geomembranes (GM) and geosynthetic clay liners (GCL) placed on top of a compacted clay liner (CCL) were measured by means of laboratory tests performed with an apparatus especially designed for this purpose. The tests performed aimed at verifying the influence of the structural and material properties of the GCL on the transmissivity along the GM-GCL interface and flow rates through composite liners. Four types of GCLs with two different bonding processes (stitch-bonded or needle-punched) and different bentonites (natural sodium or natural calcium) were tested. The results obtained showed no significant differences among flow rate versus time in most of the tests performed, especially after the steady-state conditions of flow were reached. An analytical solution was employed to estimate the transmissivity of the GM-GCL interfaces. This solution also allowed predictions of flow rates and radius of wetted areas for typical configurations of composite liners in the field. The results obtained showed little influence of the nature of the bentonite and the predominance of the presence of preferential flow paths between the geomembrane and the GCL surface on the transmissivity of GM-GCL interfaces and flow rates through composite liners

Characterisation of permeability to gas of geosynthetic clay liners in unsaturated conditions

International audienceThis paper is a contribution to the characterisation of permeability to gas of unsaturated GCLs, with applications in cover liners of municipal solid waste landfills. Conducting such tests at low gas pressure gradient limits the risk of moisture distribution change in the bentonite, which has been observed under high pressure gradients. However, a consequence of a low pressure gradient is a small gas flow rate that is difficult to measure with good accuracy. Therefore a solution may be the use of transient state tests, such as the falling pressure test adapted to GCL permeability characterisation. This paper shows the influence of the main parameters related to the test, and to the material tested (natural or activated calcium bentonite, moisture content, presence or not of small cracks in the bentonite). The results obtained showed good repeatability for gas differential pressures up to 40 kPa for the test conditions employed in this work. The results showed that the gravimetric moisture content of the GCL necessary to attain a certain permeability value depends on the nature of the bentonite, which was not observed in terms of volumetric moisture content. However, other factors were shown to be more important than the nature of bentonite in GCL permeability to gas: the desiccation due to the gas flow can significantly increase the permeability, which compromises the GCL's performance as a gas barrier

Caractérisation de la perméabilité au gaz des GSB en conditions non saturées

International audienceThis paper is a contribution to the characterization of permeability to gas of unsaturated GCLs, with applications in cover liners of municipal solid waste landfills. Conducting such tests at low gas pressure gradient limits the risk of moisture distribution change in the bentonite, which has been observed under high pressure gradients. However, a consequence of a low pressure gradient is a small gas flow rate that is difficult to measure with good accuracy. Therefore, a solution may be the use of transient state tests, like the falling pressure test adapted to GCLs permeability characterization. This paper shows the influence of the main parameters related to the test and to the material tested (natural or activated calcium bentonite, moisture content, presence or not of small cracks in the bentonite). The results obtained showed good repeatability for gas differential pressures up to 40 kPa for the test conditions employed in this work. The results showed that the gravimetric moisture content of the GCL necessary to attain a certain permeability value depends on the bentonite nature, which was not observed in terms of volumetric moisture content. However, other factors showed to be more important than the nature of bentonite in the GCL permeability to gas: the desiccation due to the gas flow can increase significantly the permeability, which compromise the GCL performance as a gas barrier

Quantification of diffusion of phenolic compounds in virgin GCL and in GCL after contact with a synthetic leachate

International audienceTo quantify the diffusion coefficients of p-cresol, 2,4-dimethylphenol (2,4-DMP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-DCP), 2,3,5,6-tetrachlorophenol (2,3,5,6- TeCP), and pentachlorophenol (PCP), in-laboratory tests were conducted of diffusion through a needlepunched geosynthetic clay liner (GCL) containing natural sodium bentonite. The diffusion coefficient was qualified for the virgin GCL and for GCL that had undergone cation exchange after being exposed to a synthetic leachate. The goal of the experiment was to see if an increase in the hydraulic conductivity generated by cation exchange in a GCL would lead to significant increases in the diffusion coefficients of phenolic compounds. For all pollutants studied at a given bulk-GCL void ratio close to 3.0, the results reveal an increase in the diffusion coefficient for transit through the GCL exposed to the synthetic leachate. The increase in the diffusion coefficient due to synthetic-leachate permeation ranged from a maximum factor of 5.0 for 4-CP to a minimum factor of 1.3 for 2,3,5,6-TeCP and PCP. For virgin GCL specimens, the chemical properties of the compounds studied did not influence the diffusion coefficient. However, for the GCL specimens exposed to the synthetic leachate, the diffusion coefficient increased with the aqueous solubility and decreased with log Kow and the molecular weight

Safety and efficacy of non-steroidal anti-inflammatory drugs to reduce ileus after colorectal surgery

Background: Ileus is common after elective colorectal surgery, and is associated with increased adverse events and prolonged hospital stay. The aim was to assess the role of non-steroidal anti-inflammatory drugs (NSAIDs) for reducing ileus after surgery. Methods: A prospective multicentre cohort study was delivered by an international, student- and trainee-led collaborative group. Adult patients undergoing elective colorectal resection between January and April 2018 were included. The primary outcome was time to gastrointestinal recovery, measured using a composite measure of bowel function and tolerance to oral intake. The impact of NSAIDs was explored using Cox regression analyses, including the results of a centre-specific survey of compliance to enhanced recovery principles. Secondary safety outcomes included anastomotic leak rate and acute kidney injury. Results: A total of 4164 patients were included, with a median age of 68 (i.q.r. 57\u201375) years (54\ub79 per cent men). Some 1153 (27\ub77 per cent) received NSAIDs on postoperative days 1\u20133, of whom 1061 (92\ub70 per cent) received non-selective cyclo-oxygenase inhibitors. After adjustment for baseline differences, the mean time to gastrointestinal recovery did not differ significantly between patients who received NSAIDs and those who did not (4\ub76 versus 4\ub78 days; hazard ratio 1\ub704, 95 per cent c.i. 0\ub796 to 1\ub712; P = 0\ub7360). There were no significant differences in anastomotic leak rate (5\ub74 versus 4\ub76 per cent; P = 0\ub7349) or acute kidney injury (14\ub73 versus 13\ub78 per cent; P = 0\ub7666) between the groups. Significantly fewer patients receiving NSAIDs required strong opioid analgesia (35\ub73 versus 56\ub77 per cent; P < 0\ub7001). Conclusion: NSAIDs did not reduce the time for gastrointestinal recovery after colorectal surgery, but they were safe and associated with reduced postoperative opioid requirement

Safety of hospital discharge before return of bowel function after elective colorectal surgery

Background: Ileus is common after colorectal surgery and is associated with an increased risk of postoperative complications. Identifying features of normal bowel recovery and the appropriateness for hospital discharge is challenging. This study explored the safety of hospital discharge before the return of bowel function. Methods: A prospective, multicentre cohort study was undertaken across an international collaborative network. Adult patients undergoing elective colorectal resection between January and April 2018 were included. The main outcome of interest was readmission to hospital within 30 days of surgery. The impact of discharge timing according to the return of bowel function was explored using multivariable regression analysis. Other outcomes were postoperative complications within 30 days of surgery, measured using the Clavien\u2013Dindo classification system. Results: A total of 3288 patients were included in the analysis, of whom 301 (9\ub72 per cent) were discharged before the return of bowel function. The median duration of hospital stay for patients discharged before and after return of bowel function was 5 (i.q.r. 4\u20137) and 7 (6\u20138) days respectively (P < 0\ub7001). There were no significant differences in rates of readmission between these groups (6\ub76 versus 8\ub70 per cent; P = 0\ub7499), and this remained the case after multivariable adjustment for baseline differences (odds ratio 0\ub790, 95 per cent c.i. 0\ub755 to 1\ub746; P = 0\ub7659). Rates of postoperative complications were also similar in those discharged before versus after return of bowel function (minor: 34\ub77 versus 39\ub75 per cent; major 3\ub73 versus 3\ub74 per cent; P = 0\ub7110). Conclusion: Discharge before return of bowel function after elective colorectal surgery appears to be safe in appropriately selected patients