Documents published in Scipedia

• Evaluation of the Liquefaction Resistance of Sandy Soil for Shaking Table Tests

  F. Castelli, S. Grasso, V. Lentini, M. Sammito*

  ISC2024.

  
  

  Abstract

  Seismic liquefaction of loose saturated cohesionless soils is one of the most dangerous and catastrophic phenomena that involves a temporary loss of soil shear strength and stiffness as a consequence of increase pore pressure and reduced effective stress. Therefore, the evaluation of the excess pore pressure induced by shaking is important to predict the liquefaction behaviour of soils at a large scale. In this regard, the study provides the static and dynamic characterisation of a liquefiable sand. For this purpose, a laboratory testing programme, which included the execution of cyclic direct simple shear (CDSS) tests, was performed. The CDSS tests were carried out by means of the CDSS device at the Soil Dynamics and Geotechnical Engineering Laboratory of the University “Kore” of Enna (Italy). The device is designed to allow the soil specimen to be consolidated one-dimensionally and then sheared under constant volume conditions, which replicates the undrained shear condition of the soil specimen. The CDSS tests were conducted to evaluate the liquefaction resistance of the sand under several test conditions, i.e. initial relative density, vertical effective stress or cyclic stress ratios. Results of this study provide useful information for the geotechnical characterisation of the liquefiable sand to be used in shaking table tests at the Laboratory of Earthquake Engineering and Dynamic Analysis (L.E.D.A.) of the University “Kore” of Enna. The laboratory is equipped with a large biaxial laminar shear box for reduced-scale model tests developed to monitor liquefaction under two-dimensional shaking.

  Abstract
  Seismic liquefaction of loose saturated cohesionless soils is one of the most dangerous and catastrophic phenomena that involves a temporary loss of soil shear strength and [...]

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• Liquefaction Assessment at Gravel Sites in Croatia Based on Vs and DPT Blow count

  K. Rollins*

  ISC2024.

  
  

  Abstract

  Liquefaction of loose saturated soil poses a significant threat to civil infrastructure during major earthquake events. Although liquefaction is most common in loose saturated sands, numerous liquefaction events in gravelly soil profiles have been reported. Assessing liquefaction resistance in gravelly soils is challenging because large particle sizes can interfere with the standard penetration test (SPT) and the cone penetration test (CPT). To address this challenge, recent efforts have focused on developing liquefaction triggering curves based on a large diameter (74 mm) dynamic cone penetrometer (DPT) blow count and normalized shear wave velocity, Vs1, which are less affected by gravel-sized particles. While based on field case histories, the curves are poorly constrained in some areas; additional case histories continue to be highly desirable. This paper describes an investigation of six gravel sites that liquefied in the 2020 Mw6.4, Petrinja, Croatia earthquake. At each site, boreholes were completed to define the soil profile, accompanied by DPT soundings and shear wave velocity profiling using the Multi-channel Analysis of Surface Waves (MASW) approach. At some sites, the DPT blow count increased through a silty clay surface layer even though the CPT cone resistance remained constant in this layer. This increase was thus attributed to side friction on the drill rods during penetration. Subsequent DPT tests performed after casing through the silty clay eliminated the rod friction. The measured blow count and shear wave velocities in the critical layers at these sites correctly predicted liquefaction using recent probabilistic DPT- and Vs1-based triggering curves

  Abstract
  Liquefaction of loose saturated soil poses a significant threat to civil infrastructure during major earthquake events. Although liquefaction is most common in loose saturated [...]

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• Estimating the Small Strain Modulus G0 from DMT tests for loess subsoil as an example of the practical application of the non-seismic method

  K. Nepelski*, T. Godlewski, M. Rudko, M. Witowski

  ISC2024.

  
  

  Abstract

  Seismic tests in geotechnics are used to determine the maximum shear modulus, which is a parameter characterising the subsoil in the range of very small strains. Maximum shear modulus is employed in deformation analyses, in particular when using advanced constitutive models describing the behaviour of the subsoil. Deriving parameters indirectly is a routine procedure in geotechnics. In the absence of seismic measurements or at an early stage of analysis, knowing the correlation between the shear modulus and other parameters measured in situ makes it possible to approximately estimate these parameters. The value of the shear modulus is closely related to, among others, the density of the medium and the shear wave velocity, which is significantly influenced by the in situ vertical effective stress. Therefore, the rule is that the shear modulus increases with depth. The article presents the results of research on loess subsoil. Based on the seismic dilatometer tests (SDMT), a formula was established that allows the shear modulus to be estimated from non-seismic dilatometer tests (DMT). The results were compared to those obtained in laboratory tests such as bender element test (BET) in an advanced triaxial testing apparatus. Formulas were derived to estimate the maximum shear modulus in the loess subsoil based on the vertical geostatic stress and the value of the constrained modulus MDMT. Moreover, the results were analysed with reference to the results for other soils in Poland and validated in additional field tests.

  Abstract
  Seismic tests in geotechnics are used to determine the maximum shear modulus, which is a parameter characterising the subsoil in the range of very small strains. Maximum shear [...]

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• Upgrading a resonant column apparatus to reliably measure specimen void ratio

  C. Vulpe*

  ISC2024.

  
  

  Abstract

  The small strain shear modulus of soils is an important design geotechnical parameter for a wide range of civil infrastructure applications. The small strain shear modulus can be determined by using elastic theory as a relationship between the soil density, which is expressed as a function of void ratio, and the measured shear wave velocity. Thus, the void ratio has a fundamental impact on the accuracy of the result. Laboratory testing involving resonant column apparatus allows for determining the changes in stiffness of soils with varying void ratios. Standard of-the-shelf resonant column apparatus works well for clayey soils but presents a number of limitations for coarse soils that makes accurate and reliable void ratio measurement difficult due to both pore fluid and (often) sample loss during removal from the equipment. This paper presents the development of a modular set-up which allows for complete specimen sealing at the end of shear wave velocity testing. The modular set-up along with the specimen can be removed from the resonant column apparatus and the void ratio can be determined by means of end-of-test-freezing similar to triaxial testing. From this, reliable small strain stiffness at well-determined void ratio can be computed. The void ratio measurements using the new modular set-up were compared to those from triaxial tests performed on identically prepared specimens. The difference in void ratio at any given isotropic confining stress was between 0.001 and 0.011.

  Abstract
  The small strain shear modulus of soils is an important design geotechnical parameter for a wide range of civil infrastructure applications. The small strain shear modulus [...]

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• Engineering surveys for construction based on the concept of sustainability resource to external influences and nature-based solutions

  V. Iegupov*, G. Strizhelchik, R. Goodary

  ISC2024.

  
  

  Abstract

  The resource of resistance to external influences (or sustainability resources) is understood as the ability of natural or natural-technogenic objects and systems to withstand negative impacts and at the same time preserve and maintain their basic functional properties within acceptable or specified limits. The use of the concept of sustainability resources (SR) to assess the risk of a system leaving an acceptable state necessitates a revision of some methodological issues in surveys for construction. Traditionally, the purpose of research is to obtain initial data for design decisions and calculations for various purposes. We emphasize that the existing approach corresponds to the strategy of protection from hazardous processes, and the use of the SR concept to external influences is more consistent with the strategy to prevent negative consequences. In addition, social and environmental factors, combined with global climate change, also increase the risks of hydrometeorological hazards and associated floods, activation of landslides, erosion, and karst-suffusion processes. Reducing these risks has traditionally been achieved by implementing protective engineering controls (or gray infrastructure), but nature-based solutions (green and blue infrastructure) are increasingly being explored. This approach, in our opinion, corresponds to the goals of ensuring rational and sustainable interaction with the geological environment during construction. The methodology is discussed and examples of the use of nature-based solutions are given.

  Abstract
  The resource of resistance to external influences (or sustainability resources) is understood as the ability of natural or natural-technogenic objects and systems to withstand [...]

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• Interface direct shear tests with novel binders

  A. Boiero, E. Romero, M. Arroyo, G. Spagnoli*

  ISC2024.

  
  

  Abstract

  In the offshore/marine environment, foundation elements need to be particularly long or wide in diameter in order to reach a competent bearing stratum through weak, low-strength sediments. The seabed conditions in oil&gas and renewable energy projects can be difficult, and the skin friction produced during driving operations could be insufficient to support the service loads placed on the structures. In this study, low-pressure injections of an acrylate gel and a colloidal silica product were made into reference sand, and interface direct shear tests were conducted under constant stiffness conditions. Conventional ground improvement projects already employ these items. Oedometer tests on untreated sand were used to evaluate the stiffness properties of the sand, which provided the foundation for determining the stiffness in the DSTCNS system. At an initial low relative density (Dro) of 0.40, Holcim sand samples were generated. This value is thought to be representative of the top zone of normal sediment profiles under offshore settings. Shearing the sand over a steel plate has been done by direct shear experiments conducted under constant normal stiffness conditions. The effects of injection have been compared using pre- and post-grout interface shear tests. The new binders' activity is causing an increase in skin friction, according to the results.

  Abstract
  In the offshore/marine environment, foundation elements need to be particularly long or wide in diameter in order to reach a competent bearing stratum through weak, low-strength [...]

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• Evaluation of the challenges present in the obtaining, processing and interpreting useful data from offshore seismic cone penetration testing

  T. Masters, I. Cazarez*, N. Tejani, G. Verbeek

  ISC2024.

  
  

  Abstract

  The Seismic Cone Penetration Test (SCPT) is an essential tool for establishing in-situ shear wave velocity (𝑣𝑠), which is then used to establish profiles of Small Strain Shear Modulus (𝐺𝑚𝑎𝑥), a direct input parameter to the design of offshore wind turbine foundations. Performance of SCPT offshore presents greater challenges than on land and each offshore site investigation contractor uses their own different non-standard equipment to try to address these challenges. This contributes to the multiple areas of uncertainty in the assessment of wave arrival time and distance, which can result in less reliable data sets. Additionally, a variety of data processing and interpretation methods are used across the industry, the benefits and limitations of which must be understood if one is to specify, plan or undertake such testing. The authors provide a review of methods of acquiring data, the equipment required and the different processing and interpretation methods available, specifically comparing true interval straight ray analyses with pseudo interval true ray path analyses and the different processing steps which can be taken to increase reliability in datasets.

  Abstract
  The Seismic Cone Penetration Test (SCPT) is an essential tool for establishing in-situ shear wave velocity (𝑣𝑠), which is then used to establish profiles of [...]

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• Development of a 3D Ground Model for an Offshore Wind Farm with Complex Interlayering of Silty Soils

  X. Peng*, Y. Gao, Y. Du, D. Wang, P. Li, X. Li, Y. Zhang

  ISC2024.

  
  

  Abstract

  Three-dimensional (3D) ground models enable the visualization of complex subsurface conditions in offshore wind farms, which aid engineers in understanding the spatial morphologies and interrelations of different soil layers. Due to the large areas of offshore wind farms, 3D ground models established solely based on limited geotechnical data (e.g., boreholes and cone penetration tests) might lack the required accuracy. Geophysical data, particularly seismic profile data, is capable of revealing stratigraphic information and can be obtained at a relatively low cost. This study presents a case study in which a 3D ground model for an offshore wind farm located off the Southern China coast is developed through the integration of geotechnical and geophysical data. The wind farm features complex interlayering of silty materials below the soft Holocene marine deposits due to repeated sea level changes during the Quaternary period. This created significant challenges for developing a reliable ground model. In this paper, the challenges that were faced and solutions that were applied in this project are presented and discussed.

  Abstract
  Three-dimensional (3D) ground models enable the visualization of complex subsurface conditions in offshore wind farms, which aid engineers in understanding the spatial morphologies [...]

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• Exploration for Wave Propagation Around Ground Loosening Using Discrete Element Method

  K. Kuwashiro*, M. Otsubo, R. Kuwano

  ISC2024.

  
  

  Abstract

  Ground loosening and subsurface cavities potentially cause ground cave-ins, even if they are deep in the ground. Loosened soil and cavities, for example, formed by shield tunnel excavation or breakage of underground pipes occur frequently. Recently, ground-penetrating radar method has been utilized to detect subsurface cavities, and studies such as dynamic wave surveys have been considered. However, these methods assume that cavities several meters deep can be detected by surface-based surveys, and do not target loosened soil directly above a deep tunnel. This contribution is a fundamental study aimed at detecting loosening depth in the ground, with the goal of measuring dynamic waves from the inside of a tunnel. To understand wave propagation and particle-scale response around loosened sandy soil, this study adopts the discrete element method (DEM) using cohesionless spherical particles. A series of DEM simulations are performed to understand how dynamic waves propagate or reflect around loosened sandy soil in comparison with dense ground without loosening.

  Abstract
  Ground loosening and subsurface cavities potentially cause ground cave-ins, even if they are deep in the ground. Loosened soil and cavities, for example, formed by shield [...]

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• Statistical analysis between intensity measures at the bedrock and the seismic response of the site

  A. Avellaneda, Y. Vargas-Alzate*, J. Vaunat, A. Di Mariano, A. Zapata-Franco

  ISC2024.

  
  

  Abstract

  This research work focuses on the seismic response of sites considering uncertainties. There are two main objectives. The first consists on assessing the effectiveness of intensity measures to predict properties of the expected wave motion at the surface. According to recent studies, special attention has been paid to predicting velocity-related ground motion parameters, which are highly correlated to the nonlinear dynamic response of civil infrastructures. The second objective is to analyse the evolution of the dynamic properties of the soil because of seismic waves. The main database of acceleration records in Colombia has been analysed, as well as three soil profiles that correspond to real building projects designed and built in the same country. From this information, a series of site seismic response analyses have been carried out using the equivalent linear method. Then, using statistical regression techniques, the correlation between input variables (parameters of the seismic records) and output results (intensity measures at the surface, maximum soil deformations, damping and shear wave velocity variations) have been evaluated. The paper shows that a series of highly correlated variables can be used to incorporate, in a simplified manner, site effects in the analysis of seismic risk at a regional scale.

  Abstract
  This research work focuses on the seismic response of sites considering uncertainties. There are two main objectives. The first consists on assessing the effectiveness of [...]

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