Coupled thermo-hydro-mechanical behaviour of a deep clay

Sau, Nuria; Romero, E.; Baelen, Hervé Van

doi:10.1051/e3sconf/20199210001

Cited by 3 publications

(10 citation statements)

References 19 publications

(27 reference statements)

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“…The Ycs are a sequence of marine sediments deposited during the Ypresian Age (spanning the time between 56 to 47.8 Ma). An exhaustive experimental study on core samples retrieved along 100 m depth (from 283 to 390 m) at Kallo (Belgium) has been reported by [5] to assess the natural variability of the mineralogy, bulk density and microstructural features. This section summarises selected results on six core samples using Mercury Intrusion Porosimetry (MIP) tests and measurements of the initial total suction using a chilled-mirror dew-point psychrometer (WP4).…”

Section: Suction and Microstructural Depth Profiles In Ypresian Claysmentioning

confidence: 99%

“…An alternative to these analyses when the degree of saturation is slightly less than one could be using Skempton's pore pressure parameters [15]. For example, the isotropic pore pressure parameter for incompressible solid can assumed B=0.91 based on an average bulk compressibility of the soil skeleton 2.0×10 -6 m 2 /kN and average porosity n=0.44 along a water undrained path to restore in situ conditions [5].…”

Section: Suction and Microstructural Depth Profiles In Ypresian Claysmentioning

confidence: 99%

“…This air induces some small swelling of the material. Typically a compression deformation of around 0.77% has been observed under oedometer conditions on restoring the in situ vertical effective stress [5]. It is important to point out that it is anticipated that the sample will not become homogeneously desaturated during preparation.…”

Section: Suction and Microstructural Depth Profiles In Ypresian Claysmentioning

confidence: 99%

“…ߪ ᇱ ൌ ͳǤͺ according to Table 2). The isochoric cell was developed by [20], updated by [12] and recently improved with total stress sensors by [5,21]. Figure 5 shows two schematic cross-sections of the isochoric cell.…”

Section: Swelling Pressure Test By Reducing the Induced Suction On Rementioning

confidence: 99%

“…This paper sheds light on these as-retrieved suctions with depth by relying on a series of tests carried out on Ycs by [5]. The objective of this study focuses on…”

Section: Introduction and Background Informationmentioning

confidence: 99%

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Restoring initial conditions in a deep argillaceous formation with induced suction on retrieval

Romero

Baelen

2020

E3S Web Conf.

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The deep and plastic Ypresian clays (Ycs) are one of the potential host rock formations in Belgium for the geological disposal of heat-emitting radioactive waste. Consequently, their thermo-hydro-mechanical behaviour has to be exhaustively studied at different depths. With this aim and considering that there is no underground research facility, deep core samples of Ycs have been retrieved between 300 and 450 m depth. The water-undrained sampling induces high matric suctions on the retrieved samples despite their nearly saturated state. Microstructural features, and particularly the larger dominant pore sizes with relatively low air-entry values, may also affect this induced suction. An experimental campaign has been launched to analyse the induced suction at different depths, which is complemented with pore size distributions carried out with mercury intrusion porosimetry. The study is accompanied by a constant volume test, in which a retrieved cylindrical sample with high initial suction is subjected to positive water pressure at the bottom boundary. The evolution of pore water pressure and total stress at different heights allows detecting the development of effective stress (swelling pressure) close to the initial suction. Finally, the paper emphasises the importance of following adequate experimental protocols on these high-suction samples to restore in situ conditions.

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Section: Suction and Microstructural Depth Profiles In Ypresian Claysmentioning

confidence: 99%

Section: Suction and Microstructural Depth Profiles In Ypresian Claysmentioning

confidence: 99%

Section: Suction and Microstructural Depth Profiles In Ypresian Claysmentioning

confidence: 99%

Section: Swelling Pressure Test By Reducing the Induced Suction On Rementioning

confidence: 99%

“…This paper sheds light on these as-retrieved suctions with depth by relying on a series of tests carried out on Ycs by [5]. The objective of this study focuses on…”

Section: Introduction and Background Informationmentioning

confidence: 99%

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Restoring initial conditions in a deep argillaceous formation with induced suction on retrieval

Romero

Baelen

2020

E3S Web Conf.

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Thermal conductivity of compacted Opalinus Clay at different degrees of saturation

Christ

Romero

et al. 2023

E3S Web of Conf.

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Tunnelling in bedded shale rocks induces damage around the excavation. Consequently, the rock mass in the excavation damaged zone (EDZ) shows different thermo-hydro-mechanical (THM) properties from the intact rock. In turn, the damaged material close to the tunnel wall is affected by seasonal fluctuations in temperature and relative humidity (RH) variations associated with tunnel ventilation, impacting the total suction and the saturation state of the EDZ. The monitoring data at the new Swiss BelchenA2 highway tunnel excavated in Opalinus Clay (OPA) captured these seasonal variations in the total stressacting on the lining associated with this temperature and RH fluctuation. Within this context, assessing the temperature field in the EDZ requires determining the thermal conductivity of the damaged rock at different degrees of saturation. However, obtaining good-quality cores of OPA from the EDZ is not straightforward, and partially desaturating them using controlled RH techniques is time-consuming. Consequently, instead of testing damaged OPA, statically compacted samples of OPA powder at different degrees of saturation have been considered to study the thermal conductivity. In addition, two natural OPA samples (with different bedding orientations) retrieved from the Belchen tunnel have been tested to cross-check the experimental procedure and results, which indicated a consistent increase in thermal conductivity with the degree of saturation.

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Thermo-hydro-mechanical behaviour of a deep plastic clay formation

Sau,

Romero,

Van Baelen

2023

SEG

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Several applications which are framed in the energy geotechnics field, particularly the design of energy geo-structures, energy geo-storage, enhanced geothermal energy systems and radioactive waste disposal, require a thorough thermo-hydro-mechanical (THM) characterisation of their host soil/rock formation. The present study comes up from the need to investigate the THM behaviour of deep Ypresian clays (Ycs, 300 to 400 m below ground) since they are one of Belgium’s potential host rock formations for deep geological disposal of heat-emitting and long-lived radioactive waste. The impact of temperature on the hydro-mechanical response of deep clays has been extensively tackled for the last four decades. Nevertheless, to the authors’ knowledge, the study of the evolution of radial stresses during drained thermal paths under oedometer conditions has never been addressed. Such information would allow for drawing a better-defined stress state while accurately measuring volume changes. To this aim, the present study used a newly designed and fully instrumented temperature-controlled oedometer cell [3] combined with well-planned test protocols. The local instrumentation consisted of a pore pressure transducer embedded in the soil 3 mm from the bottom boundary, thermocouples at various positions and radial displacement transducers with a localised thin-wall system to estimate radial stress. Two well-preserved Ycs core samples retrieved at different depths at Kallo (Belgium) and belonging to distinct lithological units were tested (see Table 1). Both slightly overconsolidated samples (Yield Stress Ratios of Ycs between 1.2 and 1.8, [1, 2, 3]) presented high initial matric suctions induced on deep water-undrained sampling. Consequently, the first stage of the well-planned test protocol consisted of loading at constant water content to bring the samples to the large in situ stresses and diminish the induced matric suction. The remaining matric suction was then reduced by soaking with synthetic water equivalent to in situ. Afterwards, drained loading and unloading paths were followed to attain different vertical effective stresses at varying overconsolidation ratios (OCRs) before performing the main research goal of drained thermal paths. The heating-cooling (H-C) cycles consisted of slowly stepwise increase/decrease in temperature (steps of 10ºC) with intermediate stabilising periods of around 15 hours controlled by the embedded pore pressure transducer. Figure 1 depicts the vertical deformation in terms of the mean effective stress (p’) beyond in situ stress. Changes in radial stresses ruled the variations in p’ during heating-cooling cycles since the vertical effective stress was kept constant during non-isothermal paths. At a slightly overconsolidated (OC) state (Core-48), the drained ‘1st H-C’ cycle showed a quasi-reversible response in volume changes and radial stresses. At OC state (OCR=2) on Core-103 (‘2nd H-C’), the response was reversible. However, the induced volume change in normally consolidated (NC) states was not reversible with a contractive response dependent on the stress level. Therefore, the nature of the thermal-induced volume changes aligned with the behaviour observed on other plastic clays. Nevertheless, the stress dependence of the contractive response at NC state differed from the observations made by [4] on NC Boom Clay -the other poorly indurated clay considered as potential host rock in Belgium. As observed in ‘2nd H-C’ (NC conditions) on Core-48, a reduction of the radial effective stress was only recorded at temperatures higher than 70°C. In contrast, the radial effective stress systematically increased on heating at values < 70°C, tending the sample to lower deviatoric stress. This phenomenon might be associated with some change in the soil structure on heating that tends to a more isotropic stress state despite the oedometer condition. A clear transition between the elastic and elastoplastic domains was detected during the subsequent loading after each H-C cycle at NC states. Finally, the study included a thermo-mechanical elastoplastic interpretation: thermal expansion coefficients dependent on temperature and mean effective stress in the elastic domain and thermal softening function on post-yield drained heating.

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Coupled thermo-hydro-mechanical behaviour of a deep clay

Cited by 3 publications

References 19 publications

Restoring initial conditions in a deep argillaceous formation with induced suction on retrieval

Restoring initial conditions in a deep argillaceous formation with induced suction on retrieval

Thermal conductivity of compacted Opalinus Clay at different degrees of saturation

Thermo-hydro-mechanical behaviour of a deep plastic clay formation

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