Documents published in Scipedia

• Evolution of fracture permeability in active clayey formations

  A. Seiphoori*, P. Marschall, U. Mok

  ISC2024.

  
  

  Abstract

  Opalinus Clay (OPA), a potential geological host formation for the disposal of high-level radioactive waste in Switzerland, is characterized by a low intrinsic permeability on the order of ~ 10-20 to 10-21 m2. Nonetheless, its effective permeability can increase significantly due to active fractures, which are influenced by factors such as fracture geometry, solid-liquid interaction, and stress conditions. The evolution of the permeability and geometry of such active fractures, particularly in rocks containing swelling clay minerals, is important for assessing the long-term safety of the repositories. Here we present the results of an experimental investigation focused on understanding the evolution of permeability in fractured OPA. We employed an advanced high-pressure triaxial system to evaluate gas permeability, followed by a phase where gas was replaced with synthetic water. We observed a three-order-of-magnitude reduction in apparent permeability as fractures evolved, primarily due to active clay minerals and the associated swelling deformations. Furthermore, we conducted a detailed analysis of the material's internal pore structure at each stage of the experiment using X-ray computed tomography. Results may be used to understand the underlying processes in the evolution of fracture permeability in clayey formations applied in hydrocarbon reservoirs, carbon sequestration, and nuclear waste containment.

  Abstract
  Opalinus Clay (OPA), a potential geological host formation for the disposal of high-level radioactive waste in Switzerland, is characterized by a low intrinsic permeability [...]

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• On The Wildfire-Induced Changes In The Properties Of A Vegetated Clayey Slope Cover

  N. Stasi*, V. Tagarelli, F. Cafaro, F. Cotecchia

  ISC2024.

  
  

  Abstract

  Wildfires are generally believed to be detrimental to slope stability, by both damaging the vegetation and altering the hydro-mechanical properties of soil cover through burning action. However, the extent to which wildfires may impact on state of the vegetation and soil state is still an open issue, as it depends on several factors such as fire intensity, on the soil and vegetation state and type. The research activity was carried out with reference to in-situ test-site, the Pisciolo hillslope, where selected vegetation has been seeded and farmed, with the aim to assess its effectiveness in reducing surface water infiltration. The test site caught fire in September 2023, during which most of the vegetation was burned down. Pre and post fire soil properties were evaluated using laboratory and in-situ methods including Loss-on-Ignition (LOI), water drop penetration time (WDPT), and in-situ seepage tests (i.e., by means of Guelph permeameter and double ring infiltrometer). Furthermore, the wildfire-induced thermal stress in the soil was monitored with a thermocouple recording soil temperature within 15 cm b.g.l.. Monitoring results showed that significant wildfire-induced temperature variations were limited to the very near-surface soil layer, up to 25 cm; the soil organic matter decreased after the fire exposure; the hydraulic behaviour was also affected but only to a minor extent, since the coefficient of saturated permeability was found to change only slightly. The logged information may be used for a better understanding of the soil and vegetation post-fire evolution states. Indeed, this research activity is expected to impact the modelling of the slope-vegetation-atmosphere interaction at the ground surface, which is the factor mainly controlling the current activity of several weather-induced landslide in both fine and coarser slopes.

  Abstract
  Wildfires are generally believed to be detrimental to slope stability, by both damaging the vegetation and altering the hydro-mechanical properties of soil cover through burning [...]

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• Influence of the Weathering Degree on the Dispersion Susceptibility of Allophanic Soils

  A. Castañeda Jaimes*, J. Colmenares Montañez, L. Viveros Rosero

  ISC2024.

  
  

  Abstract

  The behavior of allophanic soils is directly related to their fabric and structure. They are transformed according to their weathering degree through biogeochemical processes that may give rise to changes in the minerals. This paper investigated the influence of weathering degree on the susceptibility to dispersion in materials derived from volcanic ash soil in Armenia (Colombia). X-ray fluorescence (XRF) tests and scanning electron microscopy (SEM) tests were conducted to identify mineralogical composition and correlate it with the use of geochemical indices. Pinhole tests were developed on natural and compacted samples (with prior air and oven drying), to assess susceptibility to dispersion. It was found that the most weathered material exhibits lower susceptibility to internal erosion due to particle aggregation generated during the material alteration process. At similar dry density, natural materials present intermediate permeability values compared to compacted ones under both water content conditions. Samples dried in the air retain part of their structure and promote lower hydraulic conductivity values compared to samples dried in the oven, indicating that material alteration due to drying generates differences in porosity and hydraulic conductivity. The drying process at higher temperatures changes the material properties, eliminating the gel texture and hence the cementing bonds, inducing imminent changes in microporosity. The findings contribute to evaluating the application of allophanic soils for embankment construction, where the loss of cementation contributes to the degree of infiltration, reducing shear strength and affecting internal stability.

  Abstract
  The behavior of allophanic soils is directly related to their fabric and structure. They are transformed according to their weathering degree through biogeochemical processes [...]

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• Collapsible Behaviour of a Compacted Lateritic Sandy Soil

  I. Augusto Silveira*, B. Padovezi Rocha, H. Giacheti, R. Rodrigues

  ISC2024.

  
  

  Abstract

  Collapsible unsaturated soils are characterized by a low-density composition and exhibit sudden settlement after wetting while maintaining in-situ stress levels. This issue is effectively mitigated by compaction, a simple and economical technique that improves the soil properties and geotechnical behaviour. In this study, the collapsible behaviour of a compacted sandy laterite soil is analysed, focusing on the influence of relative compaction, water content, initial suction and inundation stress. The primary aim is to analyse the effect of initial compaction conditions on collapse potential. Conventional and suction-controlled oedometer tests were conducted on soils from Ilha Solteira, São Paulo, Brazil, where there is a large amount of geotechnical data available. The laboratory data reveal that collapse deformations of compacted soil depend on relative compaction, initial water content, soil suction, and inundation stress. Poorly compacted soils exhibit greater susceptibility to collapse when wetted, and the magnitude of collapse potential varies with water content. Additionally, this study shows the influence of initial suction on collapsibility of less compacted soils. The laboratory results highlighted the importance of considering suction and inundation stress in understanding the collapsible behaviour of compacted soil, whereas traditional empirical methods often emphasize low density and water content as primary factors predisposing soils to collapse.

  Abstract
  Collapsible unsaturated soils are characterized by a low-density composition and exhibit sudden settlement after wetting while maintaining in-situ stress levels. This issue [...]

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• Measurement of soil temperature with depth using multiple sensor arrays

  M. Zizzi*, G. Elia, O. Bottiglieri, F. Cotecchia

  ISC2024.

  
  

  Abstract

  Accurate measurement of soil temperature is essential for the diagnosis of various environmental processes and their impact on ecosystems. Indeed, continuous monitoring of temperature profiles with depth provides valuable understanding of the soil thermal response, which could support studies related to climate change, hydrology, agriculture, and geothermal energy. The paper describes an innovative installation procedure of temperature strings (CS225) to measure the temperature field of an undisturbed soil deposit at different depths in real time. The strings consisted of multiple temperature probes connected in series, placed at specific depths within the soil profile. The CS225 probes require little maintenance and no initial calibration, guaranteeing a high accuracy and resolution of the temperature measurements. The initial field measurements have shown a good performance of the probes, which have been able to detect the gradual decrease of soil temperature and the reduction of oscillations with depth. Further research will include the detailed analysis of the influence of ambient wind speed, solar radiation and soil moisture on the heat transfer from the ground surface to the deeper soil layers, as well as laboratory tests and numerical analysis.

  Abstract
  Accurate measurement of soil temperature is essential for the diagnosis of various environmental processes and their impact on ecosystems. Indeed, continuous monitoring of [...]

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• Monitoring Climate Induced Degradation Processes of Dutch Regional Dykes

  I. de Wolf*, C. Jommi

  ISC2024.

  
  

  Abstract

  A large part of the Dutch regional dyke network is classified as drought-susceptible given that both the dyke body and the foundation layers consist of soft organic soils. The erratic weather conditions over recent years, which included prolonged drought, new temperature records and intensified rainfall, are linked to an increased number of accidents related to dyke degradation. As global warming continues to exacerbate extreme weather, there is a growing concern on the impact of changing climatic conditions on this type of regional dykes. Poor understanding of climate induced soil degradation processes poses a serious challenge in the development of adaptation strategies. The challenges are caused by the large variety of interplaying factors, dynamic environmental actions and the complex description of coupled degradation processes with varying spatial-temporal scales. This study demonstrates the potential use of field monitoring to overcome some of these limitations. Field monitoring data on ten Dutch regional dyke sections, with varying geometry, stratigraphy and vegetation are presented. The data provide insight into changes in dyke hydraulic state as a function of atmospheric conditions and allow to infer possible climate induced soil physical degradation mechanisms depending on dyke characteristics. To fully evaluate the impact of degradation on the water protection system, ancillary monitoring data are required, able to quantify the mechanical implications of climate induced state variations. The design of dedicated monitoring set up on three selected dykes, which will serve as representative case studies for the development of geotechnical assessment methods, is eventually presented.

  Abstract
  A large part of the Dutch regional dyke network is classified as drought-susceptible given that both the dyke body and the foundation layers consist of soft organic soils. [...]

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• Multi-Sensor Core Logging of Marine Sediments for Continuous Thermal Conductivity Profiles

  S. Smith*, M. Vanneste, T. Faleide, A. Bertrand

  ISC2024.

  
  

  Abstract
  Thermal conductivity of shallow (

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• Characterization of Thermal Conductivity of Backfill Materials for UPCS by Various Methods: Lab, in Situ and Numerical Analysis

  B. Dinh, Y. Kim*, C. Nguyen, G. Kang

  ISC2024.

  
  

  Abstract

  This research evaluates the thermal properties of the proposed backfill materials (prepacked concrete (PAC)) that function as the heat release medium for the underground power cable system (UPCS). First, a hot disk sensor was used to measure the thermal conductivity of small-scale backfill materials in the laboratory. The horizontal thermal response test (TRT) was then performed with a 5 × 3 × 2 m full-scale sample for the in-situ evaluation. Afterward, the data from the TRT was utilized to couple with the infinite line source model (ILS) to predict the thermal conductivity of the full-scale sample. Finally, the thermal conductivity of the PAC was back-calculated using COMSOL Multiphysics. All these tests were also performed with natural sand (conventional backfill material) to compare with the PAC. Thermal conductivities calculated by numerical simulation and the ILS model were in good agreement (difference < 3%), demonstrating that the proposed ILS model coupled with horizontal TRT data is appropriate for estimating the thermal conductivity of full-scale backfill material in situ. The results of three testing methods indicated that the prepacked concrete has a high thermal conductivity (> 2 W/(mK)), thus satisfying the heat release ability requirement for the UPCS. The laboratory test slightly underestimated the thermal conductivity (less than 8%) compared to the estimated values from the ILS model and numerical model involving prepacked concretes; however, natural sand showed a significant difference (1.365 W/(mK) and 1.8 W/(mK), 32 %) attributed to the influence of the water content change during the TRT. Therefore, it is recommended that the in-situ testing conditions should be considered for the sand (or soils) to avoid the overestimation or underestimation of their thermal conductivity.

  Abstract
  This research evaluates the thermal properties of the proposed backfill materials (prepacked concrete (PAC)) that function as the heat release medium for the underground power [...]

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• Interpreting repeated CPT in unsaturated soils

  C. Jommi*, S. Muraro, C. Chao

  ISC2024.

  
  

  Abstract

  Cone penetration tests, CPTs, are extensively used in the Netherlands to assess the stability of fourteen thousand kilometres of dykes protecting the country from flooding. On the regional dykes, site testing is planned and executed only from spring to autumn. The data collected in the drier season of the year must be used then in safety factor calculation for dyke stability with reference to the worst expected conditions, including the highest weights and the highest water pressures over the year. Inferring reliable values of the shear strength in a different season implies understanding the unsaturated response of the dyke material and the effect of variable water content on the CPT response. In previous studies referring to CPTs in unsaturated soils, it was observed that both the cone resistance and the sleeve friction depend on suction, however, only the cone resistance was used to determine the shear strength in combination with water content or suction probes installed into the ground. In this contribution, we analyse an extensive set of data, coming from repeated CPTs performed over one year on the Maasdijk near Oijen in the Netherlands. The data are elaborated to investigate whether the entire set of data can be exploited to try to derive the water content and the constant water content shear strength at the same time, if the test is repeated in different seasons.

  Abstract
  Cone penetration tests, CPTs, are extensively used in the Netherlands to assess the stability of fourteen thousand kilometres of dykes protecting the country from flooding. [...]

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• Estimation of Pore Pressure for Unsaturated-Saturated Bentonite Sand Mixture

  T. Nishimura*

  ISC2024.

  
  

  Abstract

  To investigate thermal hydration mechanical chemical couple phenomena is an important issue of the high-level radioactive waste disposal and a key indicator of artificial barrier system. Major objectives of the thermal and mechanical site characterization include the status of the environmental. Several research reports are aimed at the barrier layers for heating from radioactive waste disposal. This study appears the occurrence of the pore pressure under heat conditions for bentonite and bentonite-sand mixture material, which are completely undrained condition and unexhausted condition. It is considered that mechanics of pore pressure in macro-micro void structure due to heating-cooling repetition. A thermal chamber is used in heating method, which have high specification with accurate controlling sensitivity. The maximum temperature is 80 degrees Celsius temperatures. The prepared specimens are unsaturated specimens and saturated specimens, and silica sand are mixture into three different bentonites that various dry densities are required. Two different solutions are prepared for saturated specimen, which are distilled water and salinity water with concentration of 3.5 %. The specimens are placed into a thermostat oven, and heating application is applied isotropic conductivity. The obtained results are significant as followings; The measured pore pressures are obviously with increment of temperature, and the sand mixture ratio is small influence factor. Also, large por fluid pressures are produced for saturated condition that indication of small pore fluid pressure is verified for unsaturated specimen comparison with saturated specimen.

  Abstract
  To investigate thermal hydration mechanical chemical couple phenomena is an important issue of the high-level radioactive waste disposal and a key indicator of artificial [...]

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