Development of a Large Scale Infiltration Tank for Determination of the Hydraulic Properties of Expansive Clays

International audienceA large-scale infiltration tank was developed to study the water transfer in compacted expansive clay. Volumetric water content sensors were buried in a soil column for water content monitoring during infiltration. In addition to water content, soil suction and temperature at various locations and the heave at the soil surface were also monitored. Emphasis was put in minimizing the effect of sensors installation on water transfer and soil deformation. The results obtained for 338-days of infiltration were presented in terms of changes of suction, volumetric water content, temperature and the soil heave. Based on the recorded data, the performance and limitation of different suction and volumetric water content sensors and the adopted test procedure were analyzed. The recorded data on soil suction and volumetric water content were finally analyzed for determining the unsaturated hydraulic properties of soil such as the water retention curve and the unsaturated hydraulic conductivity. Note also that the results constitute useful data for further physical analysis or numerical models calibration

Etude de l'interaction sol-atmosphère en chambre environnementale

An environmental chamber was developed to study the behavior of soil-atmosphere interface during both infiltration and evaporation. A volume of about one cube meter of Romainville green clay was prepared by compacting. Nearly one hundred sensors were used to monitor a large range of the parameters of soil (suction, water content, temperature, heave) and of the air (wind speed, relative humidity, temperature). Soil surface temperature and cracking due to drying were also monitored. The recorded data of the first humidification phase made possible the determination of the hydraulic conductivity as a function of soil suction and the soil water retention curve. The second phase consisted of four drying tests: two for the assessment of the potential evaporation rate PE and two others for the determination of the ratio between the actual evaporation rate AE and the potential evaporation rate PE. Based on the recorded data, a new approach allowing estimation of PE was elaborated. Furthermore, a new approach allowing calculation of AE accounting for cracking at soil surface was also developed.Une chambre environnementale a été développée pour étudier le comportement de l'interface sol-atmosphère durant l'infiltration et l'évaporation. Un volume d'environ un mètre cube d'argile verte de Romainville a été mis en place par compactage. Près de cent capteurs ont été utilisés pour assurer un suivi très large des paramètres du sol (succion, teneur en eau, température, gonflement à la surface) et de l'air (vitesse du vent, humidité relative, température). La température à la surface ainsi que la fissuration due au séchage ont été également suivies. Les mesures pendant la première phase d'humidification ont permis la détermination de la conductivité hydraulique en fonction de la succion et de la courbe de rétention d'eau du sol. La deuxième phase comporte quatre essais de séchage dont deux pour l'évaluation du taux d'évaporation potentiel PE et deux autres pour la détermination du rapport du taux d'évaporation réel AE au taux d'évaporation potentiel PE. Les résultats obtenus ont permis l'élaboration d'une nouvelle approche de calcul de PE, et le développement d'une nouvelle approche de calcul de AE en tenant compte de la fissuration en surface du sol

Fissuration de sols liée au séchage

L'image, obtenue dans une chambre environnementale, montrant la fissuration de l'argile verte de Romainville pendant une période de séchage.Cette image a été obtenue dans de cadre de la thèse de doctorat de A.N Ta (Etude de l’interaction sol-atmosphère en chambre environnementale), réalisée au Laboratoire Navier/CERMES, en collaboration avec la Fondation MAIF

Etude de l'interaction sol-atmosphère en chambre environnementale

Une chambre environnementale a été développée pour étudier le comportement de l'interface sol-atmosphère durant l'infiltration et l'évaporation. Un volume d'environ un mètre cube d'argile verte de Romainville a été mis en place par compactage. Près de cent capteurs ont été utilisés pour assurer un suivi très large des paramètres du sol (succion, teneur en eau, température, gonflement à la surface) et de l'air (vitesse du vent, humidité relative, température). La température à la surface ainsi que la fissuration due au séchage ont été également suivies. Les mesures pendant la première phase d'humidification ont permis la détermination de la conductivité hydraulique en fonction de la succion et de la courbe de rétention d'eau du sol. La deuxième phase comporte quatre essais de séchage dont deux pour l'évaluation du taux d'évaporation potentiel PE et deux autres pour la détermination du rapport du taux d'évaporation réel AE au taux d'évaporation potentiel PE. Les résultats obtenus ont permis l'élaboration d'une nouvelle approche de calcul de PE, et le développement d'une nouvelle approche de calcul de AE en tenant compte de la fissuration en surface du sol.An environmental chamber was developed to study the behavior of soil-atmosphere interface during both infiltration and evaporation. A volume of about one cube meter of Romainville green clay was prepared by compacting. Nearly one hundred sensors were used to monitor a large range of the parameters of soil (suction, water content, temperature, heave) and of the air (wind speed, relative humidity, temperature). Soil surface temperature and cracking due to drying were also monitored. The recorded data of the first humidification phase made possible the determination of the hydraulic conductivity as a function of soil suction and the soil water retention curve. The second phase consisted of four drying tests: two for the assessment of the potential evaporation rate PE and two others for the determination of the ratio between the actual evaporation rate AE and the potential evaporation rate PE. Based on the recorded data, a new approach allowing estimation of PE was elaborated. Furthermore, a new approach allowing calculation of AE accounting for cracking at soil surface was also developed.MARNE-LA-VALLEE-ENPC-BIBL. (774682303) / SudocSudocFranceF

Optimizing pile driving fatigue for offshore foundations in very dense sand : a case study

With the rapid development of offshore wind energy in Europe, a large number of piled structures are being installed. Driven pipe piles are adopted as a foundation solution for the majority of offshore wind turbine support structures. In soils consisting of very dense sand, pile driving induces large-amplitude stress cycles in pile material, which have to be accounted for in fatigue calculations. These stress cycles can be calculated using one-dimensional wave equation analysis. Different ways of reducing pile driving damage are presented. Depending on the soil surrounding the pile and the target penetration depth, an optimum driving sequence can be established which minimises pile damage. As damage depends more on induced stresses than on the number of hammer blows, reducing the hammer energy at some point during driving can be beneficial for reducing the accumulated damage. In this paper, an optimum driving sequence is developed for a generic soil profile consisting of very dense sand. The pile driving damage calculated with the optimum sequence is compared to the damage calculated when driving close to maximum hammer efficiency. Additionally, using a larger hammer can also be beneficial for reducing induced stresses when keeping the transmitted energy at a similar level. The paper also highlights the advantages of using pile driving monitoring or pile driving back-analysis for verifying the stress levels in the piles during driving. Offshore design standards allow a reduction of the damage fatigue factor for inspected members. This principle may be extended to monitored piles. The differences between data from pile driving monitoring and data from pile driving back-analysis are discussed and the potential impact on the damage fatigue factor is highlighted Finally, the potential conflict of pile driving fatigue requirements and pile capacity requirements is discussed. Both considerations should eventually lead to an optimized design which satisfies the required design equations

Investigation of the hydro-mechanical behaviour of compacted expansive clay

International audienceThe hydro-mechanical behaviour of compacted expansive Romainville clay was investigated. The soil was air-dried, crushed, and passed through a 2 mm sieve before being statically compacted to a dry density of 1.35 Mg/m3. The mechanical behaviour was investigated by tests in oedometer with controlled suction using the vapor equilibrium technique (suction s = 0, 9, 39, and 110 MPa). The vertical stress was applied in the range of 0-800 kPa. The experimental results are shown as follows: 1) wetting-induced swelling was higher at lower vertical stresses; 2) the vertical stress under which no swelling occurred during water flooding was estimated at 60 kPa, which can be considered as the swelling pressure of the soil tested; 3) the soil compressibility (changes of volume upon stress increases) was strongly influenced by the soil suction: the lower the suction, the higher the compressibility. The hydraulic behaviour was investigated using a large-scale inltration chamber (800 mm × 1000 mm in section and 1000 mm high). The large size of the soil column allowed burying the volumetric water content sensors (ThetaProbe) without signicantly affecting the water transfer and the soil swelling during inltration. The soil suction was monitored along the soil height (every 100 mm) using various relative humidity sensors and psychrometers. In the inltration test, water was kept on the soil surface and changes in suction and volumetric water content were monitored for 338 d. The wetting front has reached the bottom of the soil column at the end of the test. The data from the simultaneous monitoring of suction and water content were used to determine the water retention curve and the unsaturated hydraulic conductivity using the instantaneous prole method. It has been observed that the soil water retention curve depends on the soil depth; that is to be related to the soil depth-dependent swelling. The unsaturated hydraulic conductivity was found to be quite low, comprised between 3 × 10−11 m/s (at saturated state) and 10−14 m/s (at about 100 MPa suction)

An environmental chamber for studying the soil-atmosphere interaction

International audienc

Investigation of soil desiccation cracking using an environmental chamber

International audienceno abstrac

Experimental and numerical investigation of soil-atmosphere interaction

International audienc