Documents published in Scipedia

• Seismic P-, SH- and SV-Wave Cross-Hole Testing Using Direct-Push Technology for the Determination of Geotechnical Parameters

  T. Fechner*, U. Koedel, S. Mackens-Siemes

  ISC2024.

  
  

  Abstract

  Seismic surveys are often carried out between two or more pre-installed boreholes to assess unknown geological situation in the subsurface with high resolution. However, the cost of installing boreholes is often a budgetary constraint. Therefore, the direct-push technology, where rods are pushed into the subsurface, seems to be a more suitable tool and by incorporating seismic sources and receivers into the push rods, geophysical methods can become more flexible and adaptable, especially for larger areas of investigation or sites in harsh environments. In this paper, we present field results using such a direct-push seismic system as a cost-effective alternative to standard borehole-based investigation techniques. For both techniques complete cross-hole datasets of P, SV and SH waves were acquired at two different test sites (1) between direct-push boreholes and (2) between PVC cased boreholes. The in-situ profiles of the paired shear wave velocity profiles (SH and SV) were used to evaluate the stress history of the soils by deriving the over-consolidation difference (OCD). Many geotechnical parameters are influenced by the soil stress history, such as deformation properties and soil stiffness, but in the calculation of geotechnical parameters, such as the lateral stress state (K0), consolidation coefficient and liquefaction response the OCR also plays an important role. The tests also showed that direct-push based techniques make even seismic methods more flexible as test positions can be easily adapted and changed according to the results, local conditions or client requirements.

  Abstract
  Seismic surveys are often carried out between two or more pre-installed boreholes to assess unknown geological situation in the subsurface with high resolution. However, the [...]

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• Development of a framework for automatic quantification of uncertainty in seismic cone penetration testing

  R. Buckley, T. Zheng*, E. Febrianto

  ISC2024.

  
  

  Abstract

  Accurate quantification of the shear wave velocity, Vs, of geo-materials is an important consideration in geotechnical design. Seismic Cone Penetration Testing (SCPT) measures shear wave travel times from a source to in situ receivers along assumed travel paths to calculate Vs. Despite complexities and uncertainties associated with obtaining Vs, results are often reported to designers as a single deterministic profile without an intuitive measure of uncertainty that can be incorporated into the design process. A rigorous workflow to rapidly obtain uncertainty-quantified profiles from SCPT using a Bayesian inversion approach is developed. While similar approaches have been documented, this inversion approach explicitly considers sources of measurement error which are generally neglected (i.e., assumed to be low) in order to deliver more realistic probability distributions of true Vs and improve robustness against imperfect data. Such errors can remain undetected when using traditional approaches, despite potentially leading to inaccuracy. Additionally, an outlier detection framework is incorporated into the workflow to improve accuracy. The workflow is demonstrated by application to a large database of SCPT data. The results show significant improvement over existing methods in terms of robustness and validity, and therefore that the workflow is a valuable tool for practical analyses. Further, they provide crucial insight into the prevalence and magnitude of key errors which are traditionally present but undetected.

  Abstract
  Accurate quantification of the shear wave velocity, Vs, of geo-materials is an important consideration in geotechnical design. Seismic Cone Penetration Testing (SCPT) measures [...]

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• Multi-method in situ geophysical testing in a high porosity chalk mass

  R. Buckley*, N. Shinde

  ISC2024.

  
  

  Abstract

  Chalk is a silt-sized soft biomicrite rock often encountered as a low to medium density, high porosity, structured material within a fractured mass. In recent years, there has been increased interest in the behaviour of chalk and the development of new design procedures for pile foundation installation design, motivated by several large-scale onshore and offshore infrastructure projects. Recent modelling has demonstrated the importance of accurately characterising the operational stiffness of the chalk mass. While several methods exist to measure the chalk’s stiffness in situ, they are often subject to significant scatter, with no guidance available to the end user on interpretation or on which method should be used as a baseline. A new programme of multi-method in situ geophysical testing in chalk at a well-characterised onshore test site in Southern England is described that forms part of a wider research project. The chalk deposit is shown to be relatively uniform with depth which provides a unique opportunity to apply multiple methods and interpretations without the influence of significant layering. The experimental programme is described and the interpretation and selected results of downhole geophysical tests at depths up to 40m are presented. The chalk’s remarkably high shear stiffnesses are shown to be highly repeatable and consistent when rigorous test execution and analysis is applied

  Abstract
  Chalk is a silt-sized soft biomicrite rock often encountered as a low to medium density, high porosity, structured material within a fractured mass. In recent years, there [...]

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• A case study addressing the development of a novel marine seismic cone penetration testing system.

  D. Donaghy*, S. Whyte, H. Christian

  ISC2024.

  
  

  Abstract

  Within the offshore wind sector, following the conclusions of the Pile Soil Analysis (PISA) Project increased emphasis has been placed on the acquisition of in-situ 𝐺𝐺𝑚𝑚𝑚𝑚𝑚𝑚 data, to corroborate laboratory-based measurements, to allow for foundation weight optimization. This requirement for higher fidelity data at all wind turbine locations is coupled with the increased requirement to acquire data in shorter periods to meet ambitious development schedules for offshore wind farms. The development of a deep push seabed SCPT which can be deployed fully autonomously is considered to address this challenge facing the offshore wind industry. Recognising that within the current standards there is a shortfall on what is considered as accurate and reliable data with regards to having confidence in the shear wave velocity (𝑣𝑣𝑠𝑠) measurements obtained offshore, there is a requirement for discussion within the industry; clients, designers and contractors, on how to provide improved set-ups, acquisition and interpretation methods in order to increase the confidence in the 𝑣𝑣𝑠𝑠 data acquired. The case study described within this paper, initiated by such dialog, presents the specification, construction, testing and utilisation of a dual array non-drilling mode seismic cone penetration test (SCPT) device and seismic source to provide demonstrable reliability and accuracy in acquisition and interpretation of in-situ 𝑣𝑣𝑠𝑠 measurements. Within this context, the paper describes; the engineering considerations and optimisation of a novel device intended for deployment from a new generation of robotic vessel; application and limitations of the set-up during trials and offshore operations; commentary on the in-situ data including challenges encountered during interpretation and comparison with existing data acquired at the same location, established correlations and site-specific correlations.

  Abstract
  Within the offshore wind sector, following the conclusions of the Pile Soil Analysis (PISA) Project increased emphasis has been placed on the acquisition of in-situ 𝐺𝐺𝑚𝑚𝑚𝑚𝑚𝑚 [...]

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• 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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