Documents published in Scipedia

• In-situ Characterization of Strength and Small-strain Stiffness in a Weathered Mudstone Profile

  K. Briggs*, Y. Trinidad Gonzalez, G. Meijer, W. Powrie, N. Sartain, S. Butler

  ISC2024.

  
  

  Abstract

  The weathering profile in mudstone outcrops can range from weathered clay to unweathered mudstone. The strength and small-strain stiffness of these materials, and of stiff clays and weak rocks in general, is critical to the design of geotechnical structures. Monitoring data and ground investigation data were gathered during the construction of a trial embankment founded on weathered, Jurassic-aged mudstone, for the HS2 high-speed railway project (UK). These data included outputs from in-situ downhole geophysical tests and extensometers at the embankment location. These were compared to ground investigation data from the wider mudstone outcrop over an 18.2 km stretch of the route. The installation of extensometers prior to loading by the embankment construction enabled the measurement of in-situ strains for a range of small and medium strains. It was therefore possible to characterise the stress-strain behaviour of the individual layers within the ground profile. The results showed that stiff clays derived from weathered mudstone at shallow depth (300 kPa) and higher maximum stiffness than the overlying clay. Both the strength and stiffness profiles showed a transition zone between the weathered clay and the unweathered mudstone. This zone included a partially weathered mudstone that had the visual appearance and index properties of a mudstone, but the strength of a stiff clay (i.e. τu < 300 kPa).

  Abstract
  The weathering profile in mudstone outcrops can range from weathered clay to unweathered mudstone. The strength and small-strain stiffness of these materials, and of stiff [...]

  • 0
  •  read

• Installation of Load Cells in Ground Anchors

  E. Aceñero, T. Laqué*, Ó. Pérez

  ISC2024.

  
  

  Abstract

  Load cells are used to measure tension (kN, tonne-force) in ground anchors and tendons in pre- or post-tensioned structures. Before installing and commissioning, it is strictly necessary to know the characteristics of the anchors to control as well as the installation and service scenery. Although it may look a simple assignment, there are several issues before supplying and installing a load cell: geometry of the anchor head, measurement range, expected precision, type of output signal and data transmission, temperature variations in the structure, and foreseen service life. The sort of tensioning jack and load steps are additional, unavoidable points to consider. By installing a load cell on a tieback, this is transformed into a measurement element, helping to understand the performance of the anchor as well as that of the surrounding area, medium- and long-term. To ensure load cells’ values are correct, we must take extra care with installation. Otherwise, the outcome will be flawed, and it will lead to erroneous conclusions and actions, with the subsequent increase in risk and money loss. In this paper, we share our experience regarding design, installation, and follow-up of load cells as elements to monitor the behaviour of anchored and post-tensioned structures and their area of influence

  Abstract
  Load cells are used to measure tension (kN, tonne-force) in ground anchors and tendons in pre- or post-tensioned structures. Before installing and commissioning, it is strictly [...]

  • 0
  •  read

• A Soil Base Model of Adjacent Various Story Structures

  O. Samorodov, S. Tabachnikov*

  ISC2024.

  
  

  Abstract

  The paper proposes an improved soil base model in the form of a continuous layer of finite distribution capability to simulate and calculate adjacent multistory structures in the base - foundations - structures system using powerful calculation packages such as SOFiSTiK, ABAQUS, PLAXIS, SCAD, Lira and others. The improved model considers the parameters of the stress-strain properties of the soils of the bases, the geometric profile taking account of the distribution capability of the base and different boundary conditions, but differs from the existing models in that it has a stepped geometric profile at the lower boundary of the model because of different compressible layer depths under each foundation of the structures. The use of this model improves the accuracy of simulating a soil base for large-sized foundations of adjacent structures to obtain reliable results of the stress-strain state of the base - foundations - structures system. An example demonstrates how to simulate and calculate raft foundations of a two-section multistory building in the base - foundations - structures system that interacts with an improved soil base model (linear strains of soils under loads are considered here) with reference to different numbers of stories of the sections. The numerical study results show on a specific calculation example that considering different compressible layers depths in the model under differently loaded foundations results in an increase in moment forces of up to 65% as compared with simulating the whole compressible layer, which may lead to the disruption of large-sized raft foundations.

  Abstract
  The paper proposes an improved soil base model in the form of a continuous layer of finite distribution capability to simulate and calculate adjacent multistory structures [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read

• 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 [...]

  • 0
  •  read