Documents published in Scipedia

• Reliability-based Assessment of Deep Cement Mixing Column Based on Core Strength

  T. Namikawa*

  ISC2024.

  
  

  Abstract

  In the quality assurance procedure of the deep cement mixing method, the statistical parameters of the unconfined compressive strength of core samples, core strength, are adopted to assess the quality of the cement-treated soil ground. Since the statistical parameters of the core strength are the sample statistical parameters, the statistical uncertainty emerges when estimating the population parameters. Moreover, the spatial correlation of the core strength should be considered on the evaluation of the overall strength of cement-treated soil ground. The paper presents a reliability-based assessment for the deep cement mixing soil column based on the core strength. The analysis method in which the statistical uncertainty included in the core strength and the spatial variability of the strength are considered simultaneously is adopted to calculate the overall failure probability of the cement-treated soil column. The statistical uncertainty is estimated using a Bayesian inference method and the random fields of the strength are generated with the statistical parameters involving the statistical uncertainty. The random finite element method with the generated random fields is performed to simulate the compression failure behaviour of a cement-treated soil column. The analysis result provides the cumulative distribution function of the overall strength of the cement-treated soil column. The reliability-based assessment is performed on the basis of the cumulative distribution function of the overall strength.

  Abstract
  In the quality assurance procedure of the deep cement mixing method, the statistical parameters of the unconfined compressive strength of core samples, core strength, are [...]

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• Towards the development of a standard for the PS suspension logger

  R. Hen-Jones, G. Comber, P. Worthington, S. Garantini, R. Buckley*, I. Jones

  ISC2024.

  
  

  Abstract

  The PS logger is a well-established seismic tool for measuring P and S wave velocities in a single borehole, using low frequency indirect excitation originating from a dipole source. Because of its low operating frequency, it is capable of generating seismic waves in slow, unconsolidated materials such as those found in offshore environments where S wave velocity is often used to estimate the small strain stiffness, Gmax (of particular interest to offshore construction). Despite its widespread use, there is no current standard for the use of the PS logger, even though other methods operating on similar principles have well-established reference methodologies and guidelines. As such, PS logger methodology is largely dictated by user manuals written by manufacturers, which likely introduces inconsistencies in operation guidelines, and may impede consistency in data obtained by different users. In this paper, the authors conduct a literature review of existing standards for relevant methods including CPT, SPT, SCPT and downhole and crosshole seismic testing, as well as relevant ground investigation standards, identifying the need for standardisation of the PS logging method. Examination of the current state of standardisation concludes that although existing seismic testing standards could possibly be expanded to include the PS logging method, the differing constraints and operational requirements are such that the development of a specific PS logger testing standard is highly recommended. An initial framework is presented for a PS logger standard, identifying the required components, in terms of borehole requirements, testing procedure, data interpretation and best practice.

  Abstract
  The PS logger is a well-established seismic tool for measuring P and S wave velocities in a single borehole, using low frequency indirect excitation originating from a dipole [...]

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• Development of international standard on the use of geotechnical instrumentation under the ISO umbrella

  J. Raventos*

  ISC2024.

  
  

  Abstract

  International standards for monitoring under ISO have been under development since 2010 and the intentions were presented during the 8th International Symposium on Field Monitoring in Geomechanics (FMGM 2011) in Berlin. Progress on this project was reported at FMGM 2015 in Sydney and ISFMG 2022 in London. The base standard on general rules was published in 2015, part 2, the standard on extensometers, in 2016 and in 2017 the third part on inclinometers. Part 4 on piezometers was published in 2020, Part 5 on pressure cells in 2019 and Part 8 on load cells in 2023. These standards have been published as ISO Standards in English and French worldwide. In Europe the standards have been published under EN ISO 18674 member countries of CEN have to publish these standards in their country. The standards on settlement measurements by hydraulic systems (part 6), geodetic measurements (part 9) and strain measurement (part 7) are under development and will be submitted to enquiry in the next few months.

  Abstract
  International standards for monitoring under ISO have been under development since 2010 and the intentions were presented during the 8th International Symposium on Field Monitoring [...]

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• Impact of Damping Boundaries on the Quality of the Output Signal in Bender Element Experiments

  M. Roshan, D. Bendea, I. Moldovan*, M. Martins, M. Pultorak, A. Gomes Correia, M. Azenha

  ISC2024.

  
  

  Abstract

  Bender elements are a popular experimental device for the measurement of the small strain shear modulus of geomaterials. Bender elements are easy to use, can be easily installed in most geotechnical devices (e.g., triaxial apparatus, oedometers, and Rowe cells), and yield shear modulus readings that compare well with those obtained from resonant column tests. Typically, bender element tests involve inducing a shear wave at one end of a sample (the input signal) and reading its arrival at the other end (the output signal). However, the wave propagation induced by bender elements is complex, hindering the interpretation of the output signal and inducing considerable uncertainty in the shear modulus readings. Indeed, besides the desirable shear wave, the vibration of the transmitter also generates laterally propagating compression waves, which reflect from the lateral envelope back into the sample and pollute the output signal. This study analyses the effect of lateral boundaries especially conceived to dampen the incoming compression waves on the quality of the output signal. In this context, damping moulds are designed based on computational simulations of the transient dynamics of the wave propagation, to promote an output signal that presents a clearly identifiable arrival of the shear wave, without it being concealed by compression wave pollution. Prototypes of a few promising designs are produced using 3D printing and tested in the laboratory using a benchmark material (Toyoura sand) and a range of input frequencies. The results are compared with those obtained in a conventional setup with no damping moulds.

  Abstract
  Bender elements are a popular experimental device for the measurement of the small strain shear modulus of geomaterials. Bender elements are easy to use, can be easily installed [...]

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• Use of Elastic Full Waveform Inversion for Monitoring of Dams and Levees

  J. Montgomery*, J. Coe, P. Alidoust

  ISC2024.

  
  

  Abstract

  Understanding subsurface conditions is critical to creating and maintaining resilient infrastructure systems, such as dams and levees. Seismic geophysical tools can be very effective for site characterization of these structures as they directly measure the elastic moduli and can provide insight into both the soil properties and groundwater conditions. Full waveform inversion (FWI) is one processing option for seismic geophysics that seeks to overcome some of the limitations in the traditional approaches by using the full time-domain recording of the wavefield to develop 2D or 3D profiles of shear wave velocity. In addition to providing characterization data, FWI can also potentially be used as a monitoring tool for dams and levees to assess how elastic moduli are changing with time and to infer how these changes might relate to changes in the hydromechanical properties of the soil. This study seeks to explore the use of seismic FWI as both a characterization and monitoring tool through numerical simulations of seismic surveys on a hypothetical levee with a low velocity anomaly in the foundation. The simulations are used to assess both the spatial resolution and the ability of the simulations to detect changes in properties that might be related to softening of the foundation or development of internal erosion failure modes. The findings from the study will be used to highlight potential benefits and challenges to using seismic FWI for characterization and monitoring of dams and levees.

  Abstract
  Understanding subsurface conditions is critical to creating and maintaining resilient infrastructure systems, such as dams and levees. Seismic geophysical tools can be very [...]

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• Impoundment characterisation for hydraulic mining of tailings

  C. Morales*, A. Sfriso

  ISC2024.

  
  

  Abstract

  Reprocessing old tailings storage facilities (TSFs) has become increasingly common in the past ten years because of economic, environmental, and social reasons. Tailings deposited by spigots experience segregation and layering, creating deposits that are difficult to excavate due to the highly erratic geotechnical behaviour of the exposed faces. Both in-situ and laboratory testing are necessary to understand how steep, temporary tailings slopes might behave, ensuring stability through engineering analysis. This paper describes a detailed geotechnical characterization of an old TSF impoundment by in situ and laboratory testing, including sonic drilling, SCPTu soundings, geophysical field testing, and oedometric, monotonic and cyclic triaxial lab testing. Two different areas were surveyed: tailings near the dam, where coarser material is expected, and in the centre of the impoundment for the characterization of finer materials. We focused on the critical state behaviour of tailings and estimations of the state parameter, required to calibrate the numerical models employed in the analyses.

  Abstract
  Reprocessing old tailings storage facilities (TSFs) has become increasingly common in the past ten years because of economic, environmental, and social reasons. Tailings deposited [...]

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• Determination of the S-wave propagation velocity of ballast by Spectral Analysis of Surface Waves

  R. Ruiz Bravo, J. Estaire Gepp, Á. Tijera Carrión*, M. Santana Ruiz de Arbulo

  ISC2024.

  
  

  Abstract

  The Laboratorio de Geotecnia-CEDEX uses some software and tools for studying different phenomena and performance of track sections. For this purpose, it is usually necessary to determine the S-wave (shear elastic wave) velocity of the different layers in the track section which typically are, from bottom to top: natural ground, embankment, form layer, subballast and ballast. The Laboratorio de Geotecnia-CEDEX has experimental S-wave propagation velocity (Vs) values of embankments, form layers and sub-ballast layers, obtained from several campaigns where the Spectral Analysis of Surface Waves (SASW) was applied on the different layers during the construction of several track sections. To complete the studies and to obtain Vs values for the ballast layer, two campaigns were carried out in the CEDEX Track Box (CTB), a railway testing facility where it is possible to test complete railway sections on a 1:1 scale; and a field measurement campaign on an in-service railway track. Due to the discontinuous nature of the ballast layer carrying out tests to obtain Vs presents serious problems. To avoid these problems, a new procedure was developed to obtain these values using the SASW method by installing sensors on top of the sleepers. Through the interpretation of measurements taken with the SASW technique on the ballast, the dispersion curve is obtained, and from it, the values of Vs are calculated. The results are presented in this article and are also compared with values found through a literature review obtained or estimated by other authors.

  Abstract
  The Laboratorio de Geotecnia-CEDEX uses some software and tools for studying different phenomena and performance of track sections. For this purpose, it is usually necessary [...]

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• Dynamic Response of Marginal Soil using SPT, DCPT & Cyclic Simple Shear Tests

  S. Dutta*, A. Sachan

  ISC2024.

  
  

  Abstract

  Coarse-grained soils are preferably used in geotechnical infrastructure projects such as retaining walls and highway embankments due to their superior drainage and frictional properties. However, such materials are not always available on or near the construction site. Given the limited availability, high cost, and transportation issues associated with coarsegrained fill, using the locally available marginal soil for the various infrastructure projects becomes essential. Marginal soils are soils with a high percentage of fines that can be cohesive or non-cohesive. The primary concern with marginal soil is its low permeability, which causes excess positive-pore water pressure evolution during load application. As a consequence, the soil loses shear strength over time. Previous researchers have provided some information on the dynamic behaviour of marginal soils in terms of cyclic strength and pore pressure development. However, more research is needed to understand the dynamic response of compacted marginal soils in terms of cyclic resistance ratio (CRR) using field and lab data. Therefore, an attempt has been made in this study to evaluate the cyclic resistance of compacted marginal soil (clayey sand) by performing stress-controlled cyclic simple shear (CSS) tests in the laboratory and Standard Penetration Test (SPT) and Dynamic Cone Penetration Test (DCPT) in the field. The cyclic strength of marginal soil has been determined as Cyclic Resistance Ratio (CRR) by using laboratory (CSS) and field (SPT, DCPT) test data.

  Abstract
  Coarse-grained soils are preferably used in geotechnical infrastructure projects such as retaining walls and highway embankments due to their superior drainage and frictional [...]

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• Improved Modeling and Inversion of Surface Wave Method

  T. Wu*, C. Lin, Q. Tran, E. Pan

  ISC2024.

  
  

  Abstract

  The multi-channel analysis of surface waves (MASW) is a widely employed surface wave method. The fundamental mode inversion is the usual scheme in MASW, because separating the fundamental mode from other high modes is feasible with an adequately long array. However, the extracted fundamental mode represents only part of the dynamic characteristics, it may deviate from the theoretical fundamental mode due to truncation effect, and part of it may correspond to another higher mode or leaky mode, resulting in mode misidentification. Conversely, the spectral analysis of surface waves (SASW) method features a more rigorous inversion scheme by matching the effective mode, but it may suffer from the tricky phase-unwrapping in the dispersion data reduction. This study introduces an improved dynamic response solution for elastic-layered media subjected to vertical loads. The proposed dynamic response solution is fast and accurate, facilitating the full wavefield inversion in terms of the frequency-velocity spectrum. The MASW frequencyvelocity spectrum inversion considers testing configuration and comprehensively models all wave phenomena, including near-field effect, truncation effect, and leaky waves. The MASW frequency-velocity spectrum inversion merges the convenience of MASW dispersion analysis with the rigorous inversion scheme adopted by SASW. The new MASW frequency-velocity spectrum inversion is compared with the SASW effective mode inversion and MASW fundamental mode inversion. The results show that both SASW effective mode inversion and MASW frequency-velocity spectrum inversion produce better inverted results than the MASW fundamental mode inversion, while the process of MASW frequency-velocity spectrum inversion is more convenient and robust. Finally, a field example is used to demonstrate the applicability of frequency-velocity spectrum inversion.

  Abstract
  The multi-channel analysis of surface waves (MASW) is a widely employed surface wave method. The fundamental mode inversion is the usual scheme in MASW, because separating [...]

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• The Next Generation of Testing with LWD to Assess the In-Situ Permanent Deformation of Geomaterials under Repeated Loading

  D. Kuttah*

  ISC2024.

  
  

  Abstract

  This study focuses on evaluating in-situ permanent deformation in fine-grained soils through the application of a specially designed Repeated Light Weight Deflectometer (LWD) test. The primary objective is to investigate how water content and applied stress levels influence permanent deformations in the field. Additionally, the study aims to assess the utility of LWD-derived data in predicting permanent strains. Results indicate a significant correlation between permanent deformations and key parameters, such as the number of load cycles, applied stress levels, and water content. It is observed that permanent deformations increase proportionally with these variables, particularly in cases of elevated water content and higher stress levels. The soil demonstrates an increased susceptibility to accumulating permanent deformations, persisting even after numerous LWD load applications. In response to these findings, a predictive model is presented to estimate accumulated permanent strain, exhibiting a commendable fit to data for moisture contents up to 22%, corresponding to an average water content of 19%. Ultimately, this research underscores the pivotal role of water content and applied stress levels in determining permanent deformation characteristics in fine-grained subgrade soils. The study also provides a valuable predictive model derived from repeated in-situ LWD measurements, offering critical insights into the field permanent deformation behaviour of subgrade soil. This simple and time-saving test enhances engineering practices for pavement design and construction.

  Abstract
  This study focuses on evaluating in-situ permanent deformation in fine-grained soils through the application of a specially designed Repeated Light Weight Deflectometer (LWD) [...]

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