Documents published in Scipedia

• CPT based classification with focus on organic soils

  A. Lengkeek*

  ISC2024.

  
  

  Abstract

  Most published research on CPT based SBT classification is on mineral soils. Consequently, these classifications do not accurately capture the classification of soft organic clays and peats. Organic soft soils are frequently present within the Holocene deposits in the Netherlands and in other deltaic areas worldwide. Organic soils can be identified by a specific combination of CPT parameters such as a high friction ratio, low cone resistance and low pore pressure response. In contrast to other soft soils, the strength is not necessarily low. This paper presents an updated CPT based classification with focus on organic soils, for the non-normalized SBT chart (Robertson, 2010, Lengkeek et al, 2022) as well as a new classification based on the stress normalized SBT chart (Robertson, 2016). In the new proposed classifications, additional boundaries are set based on the CPT pore pressure measurements, as this appears to be successful to separate organic soils from mineral soils. The performance of the classifications can be quantified by metrics such as the F1 score. The F1 score of the new proposed classifications all show significant improvement.

  Abstract
  Most published research on CPT based SBT classification is on mineral soils. Consequently, these classifications do not accurately capture the classification of soft organic [...]

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• Cone Penetration Response in Carbonate Sediments

  S. Sharma*, C. Colreavy, N. Boylan

  ISC2024.

  
  

  Abstract

  Cone penetration testing (CPT) is one of the most used site characterisation tools in geotechnical engineering. In offshore areas dominated by carbonate sediments, CPT is extensively used to characterise material types and assess their strength and flow characteristics. However, unlike for non-carbonate sediments where large number of empirical relationships are available correlating the CPT response with the corresponding soil behaviour and associated engineering parameters, there is still a lack of data correlating the CPT response with engineering behaviour of carbonate sediments. This paper presents CPT responses for different types of marine carbonate sediments. First, a brief background on carbonate sediments including key terminologies used and their characteristics in comparison to their non-carbonate counterparts are discussed. This is followed by examples of CPT data from major offshore project sites representing different type of materials ranging from uncemented fine grained (Muds and Silts) and coarse grained (Sand) sediments to variably cemented carbonate materials. The CPT results are then used, in combination with laboratory test data, to evaluate the suitability of standard soil behaviour type charts and indices available in the literature. Typical zone of results for carbonates sediments as a function of normalized cone parameters are also presented for reference purposes. Some challenges on the direct use CPT based methods to engineering analyses for carbonate sediments and the key areas of research from a practical engineering perspective are also briefly discussed.

  Abstract
  Cone penetration testing (CPT) is one of the most used site characterisation tools in geotechnical engineering. In offshore areas dominated by carbonate sediments, CPT is [...]

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• Case studies for temporal variability In site characterisation

  B. Look*

  ISC2024.

  
  

  Abstract

  While site investigation data is typically focused on the spatial variability for site characterisation, those properties may change with time. Temporal variability needs to be considered in the design and construction of roads and high-level foundations. Seasonal variation occurs in the active zone and long-term changes occur 2 to 5 years after construction using expansive clay materials in adverse climate conditions. The latter may occur below the zone of seasonal variation. A case study for seasonal changes in subgrade strength at an uncovered test site when tested at 5 different times of the year. Measurement accounted for 30% of the variation, while temporal and spatial variation accounted for an additional 30% variation over the 1-year period of testing. An appropriate probability distribution function (PDF) is required for characteristic values. Constructing embankments to the equilibrium moisture content (EMC) is more important than the optimum moisture content (OMC), which is a short-term construction expedient. Time Domain Reflectometry (TDR) probes were used to monitor embankment moisture changes over a 4-year period for a new road construction on expansive clays. This included 1) an existing 30-year-old embankment during the project planning phase, 2) a trial embankment during design, and 3) the new constructed roadway embankments. All demonstrated the importance of understanding the EMC when expansive clays are being used for embankment construction. Results in other climatic environments are compared. The results show subgrade CBR tested at OMC is meaningless for such soils and in those extreme climates.

  Abstract
  While site investigation data is typically focused on the spatial variability for site characterisation, those properties may change with time. Temporal variability needs [...]

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• Investigating crushing-induced particle shape change in granular material

  S. Allaev, M. Kikumoto

  ISC2024.

  
  

  Abstract

  High-pressure uniaxial compression tests were conducted under strain-controlled conditions using spherical glass beads. The study focused on investigating the compression behavior and particle fragmentation phenomena, particularly observing changes in particle size and shape resulting from fragmentation. The examination of particle shape, specifically sphericity and roundness, was emphasized. The samples comprised glass beads with uniform particle size and shape initially. It was observed that pressures exceeding 20MPa triggered particle fragmentation, leading to significant compression behavior. Notably, a softening phenomenon characterized by rapid fluctuations in compressive stress, despite a monotonic increase in strain, was observed during fragmentation. This phenomenon indicates the particles' catastrophic failure, unable to withstand the contact forces they previously sustained. Observations of particle shape revealed trends toward asymptotic distributions in cumulative curves for particle size, sphericity, and roundness. Moreover, changes in the cumulative curve of roundness were more pronounced compared to particle size and sphericity.

  Abstract
  High-pressure uniaxial compression tests were conducted under strain-controlled conditions using spherical glass beads. The study focused on investigating the compression [...]

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• 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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