Documents published in Scipedia

• Analysis of DMT Results and Comparison with Other In Situ Tests in a Sensitive Clay of Eastern Canada

  V. Silvestri*, C. Tabib

  ISC2024.

  
  

  Abstract

  This paper presents a re-evaluation of test results obtained from an extensive series of in-situ tests carried out in a lightly overconsolidated sensitive clay of eastern Canada. The geotechnical investigation involved self-boring pressuremeter tests (SBPMTs), flat dilatometer tests (DMTs), hydraulic fracture tests (HFTs), and vane shear tests (VSTs). The first surprising result is that the in-situ coefficient of lateral pressure at rest, K0, deduced from DMTs, SBPMTs, and HFTs is much higher than expected. Second, the values of the overconsolidation ratio, OCR, computed from DMT data are also much higher than oedometer-deduced values. Third, undrained shear strengths obtained from SBPMT expansion curves are higher than both DMT- and VST- deduced values, with the latter tests yielding very similar results.

  Abstract
  This paper presents a re-evaluation of test results obtained from an extensive series of in-situ tests carried out in a lightly overconsolidated sensitive clay of eastern [...]

  • 9
  •  read

• Comparative Assessment of DMT-Based and CPT-Based Transformation Models for the Estimation of Shear Wave Velocity: a Case Study in Central Italy

  M. Uzielli*, D. Marchetti, S. Amoroso

  ISC2024.

  
  

  Abstract

  The definition of the shear wave velocity profile is a fundamental step for the seismic characterization of a site in the context of Eurocode 8 and for the conduction of earthquake geotechnical engineering efforts such as site response analysis. Shear wave velocity profiles can be obtained: (1) directly from seismic geophysical and seismic geotechnical tests; or (2) indirectly, from “static” in-situ geotechnical tests such as dilatometer tests (DMT) and cone penetration tests (CPT). In the latter approach, shear wave velocity is estimated by using transformation models which are typically derived from data collected at other sites. This paper illustrates the procedures and main results of the comparative assessment of the performance of existing DMT-based and CPT-based transformation models to estimate shear wave velocity at two adjacent spatial locations in a rural site in the region of Tuscany in central Italy. Model-predicted shear wave velocity profiles were compared with direct measurements obtained by geophysical seismic dilatometer (SDMT) testing. The comparative assessment involved the definition, calculation, and assessment of quantitative performance statistics. The paper provides a critical analysis and a discussion of the outcomes with respect to soil type.

  Abstract
  The definition of the shear wave velocity profile is a fundamental step for the seismic characterization of a site in the context of Eurocode 8 and for the conduction of earthquake [...]

  • 25
  •  read

• DMT-based liquefaction assessment accounting for the fines content effect: a case study Emilia-Romagna italy

  R. Cecchi, A. Chiaradonna, P. Monaco*

  ISC2024.

  
  

  Abstract

  Simplified methods for seismic liquefaction assessment based on the flat dilatometer test (DMT), in which the liquefaction triggering curve is defined based on the horizontal stress index (KD), have been proposed over the years. One major drawback of the existing methods, valid for clean sand, is the lack of a correction factor for the fines content. An updating of the empirical relationship CRR-KD proposed by Chiaradonna and Monaco (2022) to incorporate the effects of the fines content is currently under development and validation. This paper illustrates the results obtained from application of the new method at the site of San Carlo – Terre del Reno (Ferrara) located in the Emilia-Romagna plain (Italy), where widespread liquefaction occurred in the 2012 seismic sequence. A comprehensive site characterization from previous insitu and laboratory tests carried out by various research groups is available for the sand, silty sand and sandy silt deposits in the San Carlo area. The performance of the new CRR-KD curve accounting for the fines content effect is compared with that obtained by adopting the “clean sand” curves proposed by Chiaradonna and Monaco (2022), as well as with that obtained by using the CPT-based method by Boulanger and Idriss (2014). Even though verified only for specific Italian soils in this area and requiring further field validation, the proposed approach appears as promising to improve the DMTbased liquefaction assessment in silty sands.

  Abstract
  Simplified methods for seismic liquefaction assessment based on the flat dilatometer test (DMT), in which the liquefaction triggering curve is defined based on the horizontal [...]

  • 38
  •  read

• Deformability Parameters in the Offshore In-Situ-Test Survey for the New Breakwater Project in Genova Italy

  M. Sacchetto*, D. Marchetti

  ISC2024.

  
  

  Abstract

  The harbour of Genova is currently protected by a breakwater barrier that is 4 km long. One of the ongoing PNRR projects in Italy consists in dismissing the current breakwater and rebuilding it farther away from shore. The new breakwater will extend to a length of over 6.2 km and allow large cargo and container ships with over 400 m length to access the harbour. The new breakwater will lie in the currently open and unprotected water of the Genova Bay, with water depths up to 50 m. An extensive in situ test campaign of CPT and DMT tests was carried out for soil characterization, to provide stratigraphy, deformability and strength parameters required for the design of the new breakwater foundations. The Manta seafloor penetrometer designed by Geomil was deployed with a crane, operating from a floating pontoon anchored in turn on each of the test locations. The fully automated version of the flat dilatometer (Medusa DMT) and a CPTU tip were alternatively pushed by the Manta, with penetration depths up to over 27 m from seabed. This paper presents results of the moduli obtained from DMT tests employing the standard Marchetti’ formulas and compares them with the interpretation from the CPT using different correlation factors. Additionally, the correlations between Bq (obtained from CPTU) and Ud (obtained from DMT) are analysed.

  Abstract
  The harbour of Genova is currently protected by a breakwater barrier that is 4 km long. One of the ongoing PNRR projects in Italy consists in dismissing the current breakwater [...]

  • 6
  •  read

• (S)DMT Tests in Structured Soils. Lessons Learned from Portuguese Granitic Massifs Characterization

  N. Cruz*, C. Rodrigues

  ISC2024.

  
  

  Abstract

  Characterization of structured soils by in-situ tests cannot be interpreted with success by applying the methodologies dedicated to sedimentary soils, due to the presence of cemented structures that deeply influences its mechanical behaviour, deviating from Classical Soil Mechanics concepts. From the shear strength point of view, structured soils are represented by two parameters that must be derived simultaneously (cohesion intercept and angle of shearing resistance), which is only possible to achieve in tests that measure more than one parameter, such as DMT, CPTu or PMT tests. In its turn, deformability of structured soils is characterized by 2 yield points, one related with beginning of weak bonds yield (first yield) and another one related with the complete breakage of the bond structure (bond yield or gross yield), which are not present in de-structured soils. As consequence, moduli decay curves are more pronounced than those typically displayed in sedimentary soils. The research based in Portuguese granitic environs tested by (S)DMT has shown its usefulness in the characterization of these structured materials. The whole research frame included the characterization of several sites by means of CPTu and DMT tests, laboratorial testing, a calibration apparatus where DMTs were performed in artificially cemented soils closely controlled by triaxial and other laboratorial tests and several sets of SDMT, PMT, CPTu and triaxial tests performed in a high-quality experimental site (IPG). The accumulated experience arising from these experimental frames will be summarized and discussed in the present paper.

  Abstract
  Characterization of structured soils by in-situ tests cannot be interpreted with success by applying the methodologies dedicated to sedimentary soils, due to the presence [...]

  • 5
  •  read

• Using Dilatometer to Predict Stress Increase Component of Foundation Settlement

  R. Failmezger*

  ISC2024.

  
  

  Abstract

  Because soil resists applied stresses in the x, y, and z directions, the ratio of horizontal to vertical stresses, ko, determines the soil stress distribution. The dilatometer test predicts the unit weight of the soil and the horizontal stress ratio at rest, ko, providing the necessary input to determine the stress increase applied to the soil. The Boussinesq stress distribution assumes the soil has a linear elastic stress-strain relationship. This distribution has no input from the soil’s material properties. Harr (1977) proposed using the normal probability distribution with ko input to more accurately compute stress distribution. The authors show the Harr stress distribution for different values of ko and compares them with the Boussinesq stress and Westergaard stress distributions. The authors also present some case studies of stress distribution measurements and proposes modern instrumentation needed for additional research to determine the best prediction method.

  Abstract
  Because soil resists applied stresses in the x, y, and z directions, the ratio of horizontal to vertical stresses, ko, determines the soil stress distribution. The dilatometer [...]

  • 0
  •  read

• Comparative Liquefaction Triggering Assessment of Gravelly Reclamations using the CPT, DPT, and Shear-Wave Velocity

  R. Dhakal*, M. Cubrinovski

  ISC2024.

  
  

  Abstract

  Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration Test (CPT), in gravelly soils can be challenging, and since gravelly soils are not well-represented in existing case history databases used to develop semi-empirical methods for liquefaction assessment. This has been the primary reason for the ongoing efforts to develop methods based on other invasive tests, such as shear-wave velocity (Vs), and penetration tests with larger probes and greater energy delivered to the rod, such as the Dynamic Cone Penetration Test (DPT). While CPT-based liquefaction analyses have been comprehensively studied, limited research has been conducted comparatively evaluating the performance of the other two methods. This paper performs liquefaction triggering assessment of gravelly reclamations using data from the welldocumented case history of the port of Wellington (New Zealand) using CPT, DPT, and Vs measurements. Results show that while the Vs measurements overestimate liquefaction resistance, the DPT and CPT agreed relatively well with observations from past earthquakes due to the greater sensitivity of these test methods to soil density and stratigraphy

  Abstract
  Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration [...]

  • 16
  •  read

• On-site characterization of compacted iron ore tailings-Portland cement blends for dry stacking systems

  J. de Sousa Sailva*, H. Mansur Chaves, H. Scheuermann Filho, N. Consoli

  ISC2024.

  
  

  Abstract

  Dry stacking of filtered tailings has become feasible due to the development of novel dewatering technologies. It offers an alternative to address the safety-related issues associated with conventional slurry disposal in reservoirs confined by upstream heightened dams. The operation and maintenance of such structures are challenging because of the high degree of uncertainty inherent in this material due to its spatial variability in state and gradation. It is also susceptible to liquefaction when saturated and in a loose state. In contrast, the filtered tailings can be compacted and piled up to hundreds of meters to meet prescribed design requirements. Eventually, a cementing agent can be incorporated into the tailings before compaction to enhance the general engineering properties. Nevertheless, few dry-stack facilities operate; none use cement as a stabilising agent. Accordingly, this paper assesses the mechanical response of artificially cemented iron ore tailings compacted in the field to form an experimental pile. Plate load tests and cone penetration tests were used. The experimental pile was divided into four sections, each compacted with different combinations of roller passes (4 or 6 passes) with and without vibration frequency. The results showed that the compacted material was practically insensitive to variations in compaction parameters, as evidenced by similar results in the tested sections' stress-strain responses and cone tip strength values. This study also highlights the effectiveness of field testing in investigating the response of stacking plants and the importance of using a small amount of cement to achieve adequate mechanical performance.

  Abstract
  Dry stacking of filtered tailings has become feasible due to the development of novel dewatering technologies. It offers an alternative to address the safety-related issues [...]

  • 0
  •  read

• Drying and wetting cycles in tailings dams: effects on physical, mechanical and hydraulic properties

  R. Rodriguez-Pacheco, J. Butlanska*, A. Onel Oliva, A. Muñoz-Moreno

  ISC2024.

  
  

  Abstract

  The study examines the drying and wetting cycles of tailings dams (TDs) and their impact on physical, mechanical and hydraulic properties. TDs are divided in four zones: the dike, the discharge zone, the transition zone and the distal zone (also known as the decantation pond). The filling process of the tailings dam involves five phases: 1) dumping and wetting, (2) segregation, (3) sedimentation, (4) consolidation, and (5) drying. The occurrence of drying and wetting cycles depends on the water balance, which can be expressed as Inflow = Outflow ± Storage Coefficient. These cycles are influenced by factors such as changes in the discharge point within TD dike and reservoir, weather conditions, and other external factors. The analysis of drying and wetting cycles in TDs reveals several trends: (a) grain size, density, internal friction angle, and permeability decrease from the discharge zone toward the decantation pond and (b) porosity, fine particle content (particle less than 75 microns), plasticity, cohesion, and capillarity height increase as we move toward the decanting lagoon. Despite these findings, there is currently no established methodology for managing the filling process or controlling wetting and drying cycles of TDs.

  Abstract
  The study examines the drying and wetting cycles of tailings dams (TDs) and their impact on physical, mechanical and hydraulic properties. TDs are divided in four zones: the [...]

  • 12
  •  read

• Integrated characterisation of bentonite pellet structures for in situ test installation

  J. Torres-Serra*, A. Mesa-Alcantara, E. Romero

  ISC2024.

  
  

  Abstract

  Bentonite pellet-based mixtures are currently investigated as candidate materials in large-scale in situ sealing experiments such as the Vertical SEALing project by the Institute for Radiological protection and Nuclear Safety (IRSN, France) due to their expected gap-filling capacity in engineered barrier systems for the geological disposal of radioactive waste. In the short term, after installation, the hydro-mechanical behaviour of these pellet-based structures is governed by pellet-pellet interactions, which have been characterised experimentally by oedometer compression tests and numerically by discreteelement modelling of single-layered pellet skeleton samples. In this work, we integrate these experimental and numerical tools to characterise the compressibility of three-layered pellet-based structures with axis-oriented arrangements. We validate the simulated deformation of bentonite pellet samples against experimental data and analyse the evolution of the dry density distribution and axial stiffness along the oedometer compression curve. Our integrated approach has implications for the emplacement and monitoring in situ tests on multi-layered pellet-based barrier systems.

  Abstract
  Bentonite pellet-based mixtures are currently investigated as candidate materials in large-scale in situ sealing experiments such as the Vertical SEALing project by the Institute [...]

  • 6
  •  read