Documents published in Scipedia

• Piezoball and T-Bar Application on a Brazilian Soft Soil Deposit

  J. Sosnoski*, A. Meier, G. Dienstmann, E. Odebrecht, H. Nierwinski, F. Mantaras

  ISC2024.

  
  

  Abstract

  Research has already demonstrated advantages in performing piezoball tests when compared to piezocone in estimating the soil undrained shear strength (Su) along the stratigraphy and remolded strength (Sur) through cyclic tests, showing a shorter range of strength correction factors (N) and lower dependence on the soil stiffness index (Ir). Another possible application is estimating the remolded shear strength directly from penetration (qin) and extraction (qext) measurements without requiring cyclic tests. This research performed piezocone, vane, and piezoball tests (standard and cyclic) in a soft soil deposit in southern Brazil. Additionally, undisturbed samples were collected for characterization. The in situ investigation resulted in cone and ball factors in accordance with the international practice recommendation, resulting in similar profiles of undrained strength Su which increases with depth from 3 to 14 kPa and constant values of remolded undrained strength Sur. Regarding estimating the Sur through direct measurements of penetration and extraction of the piezoball, it was necessary to carefully evaluate the time laps between probe insertion and extraction to avoid overestimating the remolded strength.

  Abstract
  Research has already demonstrated advantages in performing piezoball tests when compared to piezocone in estimating the soil undrained shear strength (Su) along the stratigraphy [...]

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• Geotechnical Characterization of an Earthfill Constructed from Schist Residual Soils

  N. Cruz*, J. Cruz, F. Paiva, C. Rodrigues, A. Ferreira

  ISC2024.

  
  

  Abstract

  Earthfills are anthropogenic soil massifs that were originated by different processes than those observed in traditional soil mechanics, thus revealing some deviations to the behaviour of common natural soils. The common characterization of earthfills is based in discontinuous testing such as nuclear densimeter gauge used together with laboratory compaction tests and the stiffness evaluation obtained from plate load tests, which does not give answers in the context of strength evaluation (Cruz et al. 2008; Cruz et al. 2006). The case study presented herein refers to the geotechnical characterization of an earth fill composed by evolutive materials obtained from the de-structuration of schists, which has developed excessive settlements. The performed geotechnical characterization consisted in boreholes and regular SPT tests, Dynamic Probing (DPSH), Piezocone (CPTu) and Marchetti Dilatometer (DMT) tests, as well as triaxial, shear box, consolidation and identification tests. DMT and CPTu tests were selected not only to obtain strength and stiffness parameters, but also because of its ability to access stratigraphy and unit weights. The whole set of obtained results are presented, compared and discussed, revealing a clear convergence between results as well as some interesting particularities that may be useful in fill characterization.

  Abstract
  Earthfills are anthropogenic soil massifs that were originated by different processes than those observed in traditional soil mechanics, thus revealing some deviations to [...]

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• Observational Method of Evaluating Secondary Compression Settlement in Artificial Fills

  D. Coduto*

  ISC2024.

  
  

  Abstract

  Secondary compression can be an important source of settlement in artificial fills, even when these fills are well constructed. In some cases, especially when the fill thickness is greater than about 15 m, the resulting long-term settlements can adversely impact the performance of structures and infrastructure, and thus may necessitate special preventive design provisions. Yet, this source of settlement is often mistakenly overlooked. Secondary compression can be even more problematic when the fill is poorly constructed. Backfills of former open-pit mines are examples of practical projects where assessments of long-term secondary compression settlement are necessary, especially when these backfills are deep and/or not properly engineered. Laboratory assessments of secondary compression in these materials are inherently problematic and become impossible when the fill contains large particles or has other complicating characteristics. However, this problem is an excellent opportunity to apply the observational method where the coefficient of secondary compression, Cαε, is assessed in-situ using settlement monument data. This Cαε value is then used to forecast future settlements, which typically continue for decades, and thus provides essential information for the site-specific design of structures and infrastructure. However, the experimental and analytical processes for conducting these evaluations are more difficult than might be expected, and missteps can lead to significant errors in the computed future settlements. Some of these difficulties are due to limitations in our knowledge of the underlying physical processes and in the analytical models used to describe them. Methods of collecting the required field data and conducting these settlement evaluations are discussed based on experience with deep fills in California as well as published data from elsewhere.

  Abstract
  Secondary compression can be an important source of settlement in artificial fills, even when these fills are well constructed. In some cases, especially when the fill thickness [...]

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• In situ and laboratory results of a bentonite-based block/pellet seal during saturation

  A. Mesa-Alcantara*, E. Romero

  ISC2024.

  
  

  Abstract

  The in situ Engineered Barrier (EB) experiment aimed at understanding the hydromechanical behaviour of sealing materials for high-level radioactive wastes as a combination of compacted blocks and high-density pellets made of Febex bentonite. The experimental program focused on the wetting process of a heterogeneous dual-component sample consisting of pellets and blocks with technological gaps. The homogenisation tendency was investigated by determining the final (local) dry densities and pore size distributions in both zones from post-mortem analyses. Global initial dry densities between 1.36–1.44 Mg/m3 were considered for the heterogeneous mixture, wetted at constant volume and constant vertical stress (oedometer conditions). The initially high-density zone of blocks with technological gaps expanded during hydration, reaching a lower dry density at saturation than the pellets’ zone. The initially low-density pellets’ zone with a high volume of inter-pellet pores underwent compression and reached a final high dry density on saturation. The experimental results were compared with the distribution of dry density at the in situ EB experiment after dismantling, and a good agreement between the laboratory and the in situ measurements was observed.

  Abstract
  The in situ Engineered Barrier (EB) experiment aimed at understanding the hydromechanical behaviour of sealing materials for high-level radioactive wastes as a combination [...]

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• 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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