Documents published in Scipedia

• Fatigue performance of composites

  A. Comer, A. Hejjaji, G. Bhatia, J. R. Pothnis, J. Cardoso

  Fibregy OA (2024). Vol. Public Deliverables, 17

  
  

  Abstract

  The deliverable will present the results and conclusions of the different fatigue tests to be performed. An interim report will be delivered by month M24 describing the regular fatigue tests (O° and 90° lay-ups) and results. This data is the only one required by the numerical models for material calibration. The report will be completed by M29, including the advanced fatigue characterization performed on oblique (45°) lay-ups and also the connections.

  Abstract
  The deliverable will present the results and conclusions of the different fatigue tests to be performed. An interim report will be delivered by month M24 describing the regular [...]

  • 0
  •  read

• Ongoing development of applications of the Cone Penetration Test in interpretation and design

  B. Lehane*

  ISC2024.

  
  

  Abstract

  This paper presents recent research on the application of the cone penetration test to site characterisation and foundation design. Aspects considered related to characterisation include the interpretation of relative density in granular soils, the derivation of the penetration-velocity characteristic, corrections for shallow penetration and scale effects in laboratory experiments and the influence of particle size on penetration resistance. In relation to foundation design, the paper outlines the nature of CPT-based correlations and describes the development of three types of such correlations for footings, axially loaded piles and laterally loaded piles.

  Abstract
  This paper presents recent research on the application of the cone penetration test to site characterisation and foundation design. Aspects considered related to characterisation [...]

  • 0
  •  read

• The influence of soil structure on CPTu and SDMT results

  S. Oberhollenzer*, E. Lande, S. Ritter

  ISC2024.

  
  

  Abstract

  The natural structure of clays has a significant influence on its mechanical behaviour and can be characterized using insitu and laboratory tests. It was reported by Robertson (2016) that soil structure leads to an increased tip resistance (qc) and shear wave velocity (Vs) when performing seismic cone penetration tests. However, only limited studies investigated changes in soil structure by means of in-situ tests. Sensitive, marine clays were investigated within the research project "VIBE – Sustainable Ground Improvement Solution for Oslo" at the Norwegian Geo-Test site Onsøy (Gundersen et al. 2019). Possibilities and limitations of the vibro replacement method were studied for very soft ground conditions based on a full-scale field test. The influence of soil structure on in-situ measurements of piezocone penetration tests (CPTu) and seismic flat dilatometer tests (SDMT) are further studied by intentionally disturbing the soil structure by a vibrator. Results of CPTu and Medusa SDMT, executed before and after treatment, are compared to characterize changes in soil structure. The results indicate that the vibration-induced destructuration led to a significant decrease of CPTu measurements, namely tip resistance (qc), sleeve friction (fs) and measured pore pressure (u2), within medium to high sensitive clays. As the decrease in fs is more significant compared to the decrease in qc, a significant decrease in friction ration (Rf) was observed. In analogy, SDMT resulted in a decrease in shear wave velocity (Vs), horizontal stress index (KD) and dilatometer modulus (ED) after the vibro treatment. It was further shown that the soil behaviour type chart according to Robertson (2016) leads to no sufficient characterization of soil structure in soft, marine clays.

  Abstract
  The natural structure of clays has a significant influence on its mechanical behaviour and can be characterized using insitu and laboratory tests. It was reported by Robertson [...]

  • 0
  •  read

• BRIGHT SPARK LECTURE - A Machine Learning Paradigm for Subsurface Stratigraphy from Sparse Data

  C. Shi*

  ISC2024.

  
  

  Abstract

  Subsurface stratigraphy is an indispensable component of geotechnical site characterization and primarily deals with the interpretation of geological interfaces from site-specific measurements, such as boreholes. Traditional geological profiling methods often rely on engineering judgement for manual drawing or entirely depend on parametric models for interpolation. Both approaches face challenges when dealing with limited geo-data. To effectively address the dilemma, a new machine learning paradigm is proposed in this study to combine valuable prior geological knowledge and sparse site-specific measurements for data-driven predictions of both two-dimensional geological cross-sections and threedimensional geological domains. The valuable prior knowledge is quantitatively represented as training images, which are compiled and stored in a training image database that is further enriched and augmented by employing deep generative models. Subsequently, the optimal training images that are compatible with the available site-specific data are adaptively selected for onward stochastic predictions under the framework of non-parametric Bayesian analysis. The method has been successfully applied to tackle geological profiling challenges in Hong Kong. The proposed framework is demonstrated to be capable of not only predicting the most probable geological patterns but also effectively quantifying associated stratigraphic uncertainty. The framework holds great potential of revolutionizing current engineering practices

  Abstract
  Subsurface stratigraphy is an indispensable component of geotechnical site characterization and primarily deals with the interpretation of geological interfaces from site-specific [...]

  • 0
  •  read

• Interpretation of Cone Penetration Tests in Gravelly Soil

  K. Rollins*, J. Roy, A. Walburger, S. Amoroso, R. Dhakal, L. Minarelli, L. Marenghi

  ISC2024.

  
  

  Abstract

  Although gravelly soils have been observed to liquefy in 27 earthquakes in the past 120 years, many engineers believe that gravel cannot liquefy due to its high hydraulic conductivity. Gradations from gravel liquefaction case histories have shown these deposits typically contain 25 to 40% sand, reducing the hydraulic conductivity and enabling excess pore pressures to cause liquefaction. While cone penetrometers (CPT), typically used to evaluate liquefaction resistance in sand, may show increases in penetration resistance due to their small diameter relative to gravel particles, the CPT has successfully predicted gravel liquefaction for looser sandy gravels. Case histories in Wellington, New Zealand demonstrate the successful identification of gravel liquefaction hazards using CPT. Although some layers in the profile indicated high penetration resistance, most of the profile was correctly predicted to liquefy. The Soil Behavior Type (SBT) from the CPT did not consistently indicate a sandy gravel profile but was often classified as behaving like a sand or silty sand; likely influenced by higher sand percentages between gravel particles. To evaluate the ability of the CPT to characterize gravelly soils and their liquefaction potential, additional field case histories are desirable. This paper presents test results from two case histories, one in Wellington, New Zealand, and one in Petrinja, Croatia, where gravels have liquefied. In both cases, the CPT occasionally overestimated liquefaction resistance in gravel layers. The advantages of using a 74 mm diameter Dynamic Cone Penetrometer (DPT) are also highlighted with companion testing.

  Abstract
  Although gravelly soils have been observed to liquefy in 27 earthquakes in the past 120 years, many engineers believe that gravel cannot liquefy due to its high hydraulic [...]

  • 0
  •  read

• Quantitative Assessment of Tip Saturation for High Quality Piezocone Testing

  I. Rocchi*, L. Tonni, G. Gottardi

  ISC2024.

  
  

  Abstract

  The research compares 2 CPTU profiles obtained with a same piezocone setup but having a different degree of saturation associated with the pore pressure measuring system. In the reference test, saturation was performed injecting 20cS silicon oil in the conduit connecting the porous stone to the pressure sensor and applying vacuum while submerged in oil for 15 minutes. The piezocone tip was then assembled with a saturated porous stone while submerged in oil. In the other test, the degree of saturation was purposely lowered by introducing air in the same conduct, whereas all other saturation steps were unchanged. The degree of saturation was compared quantitatively by measuring an analogue of the Skempton’s coefficient B, which is routinely used in laboratory testing to assess specimen saturation in a triaxial cell. The value associated with the saturation condition was measured employing a tool specifically designed for this purpose. The saturation procedures adopted were selected based on preliminary experimental activity in the laboratory, which provided target values of the pore pressure parameter corresponding to full or partial saturation. The CPTUs were performed at a test site presenting 10m clay unit followed by sand. The profiles measured were compared in terms of pore-pressure profiles, as well as the influence this had on corrected tip resistance, Soil Behaviour Type classification and mechanical properties. Additionally, a dissipation was performed for each test to compare consolidation parameters.

  Abstract
  The research compares 2 CPTU profiles obtained with a same piezocone setup but having a different degree of saturation associated with the pore pressure measuring system. [...]

  • 0
  •  read

• Calibration Chamber Testing on Tailings for Interpretation of Partially Drained CPT

  M. Ghafghazi, L. Qi*, H. Zhao, W. Liu, M. Etezad, J. Sharp, M. Talesnick

  ISC2024.

  
  

  Abstract

  The Cone Penetration Test (CPT) is the primary site investigation tool in silt-rich tailings. The permeability and compressibility range of tailings often puts the standard CPT penetration rate in the partial drainage range where the tip resistance, pore water pressure, and sleeve friction become functions of not only the state, but also drainage conditions. This makes interpretation of the state parameter, which represents liquefaction susceptibility and residual strength of tailings particularly challenging. It is not clear whether existing CPT interpretation frameworks are capable of accounting for effects of partial drainage. Developing field correlations for interpreting partially drained CPT data in tailings is hampered by spatial variability and sampling disturbance. CPT tests were performed in a calibration chamber and in the field on a gold tailings material. Dissipation tests were performed, and the pore water pressures on the cone at the u2 position were monitored. The degree of partial drainage was estimated based on the coefficient of consolidation inferred from these dissipation tests. Similarities and differences of the calibration chamber and field CPTs were discussed.

  Abstract
  The Cone Penetration Test (CPT) is the primary site investigation tool in silt-rich tailings. The permeability and compressibility range of tailings often puts the standard [...]

  • 0
  •  read

• Methodology for Determining Optimum Vibrating Wire Piezometer Pairing Relationships in VWP Monitoring Clusters

  C. Meyer*

  ISC2024.

  
  

  Abstract

  Current trends in the mining sector and specifically tailings storage facilities have seen a significant increase in monitoring frequency, instrumentation installed on site and field tests conducted. Monitoring methodologies are also shifting away from analog and towards digital electronic systems. These instruments are also being integrated with online dashboards. Owing to all these factors, the instrument that is now most commonly being installed to meet these requirements are VWP’s (Vibrating Wire Piezometers). However interpreting VWP results and deriving the phreatic surface from these are not as straight forward as initially assumed, it requires engineering judgement and a methodology to determine and verify optimum pairing of VWP clusters. Obtaining the correct phreatic surface from VWP’s is critical as this will have a direct impact on the trigger levels and TARP’s of the online dashboard. Inaccuracies in calculating the phreatic surface can lead to the triggering of incorrect levels, which may result in flawed assessments of stability. The primary approach relied on phreatic surface and hydraulic gradients from CPTu testing being compared to the phreatic surface and hydraulic gradient determined from various combinations of VWP’s in a cluster at the time of CPTu testing. In cases where no historical VWP data is available at the time of CPTu testing, a methodology was also investigated using standpipe piezometers only. Piezometric head was converted to pressure and linear regression used to determine the phreatic surface. Results from the primary approach showed that certain pairs of VWP’s yield phreatic surfaces and hydraulic gradients that match the CPTu findings. Standpipe interpretation provided a good starting point and correlates with primary identified pairs. This methodology provides a verification tool to provide confidence when selecting VWP combinations for dashboard reporting.

  Abstract
  Current trends in the mining sector and specifically tailings storage facilities have seen a significant increase in monitoring frequency, instrumentation installed on site [...]

  • 0
  •  read

• Restrictions of CPTu Based Interpretation Methods and Impact Thereof on Limit Equilibrium Modelling

  J. Visagie*, E. du Plessis

  ISC2024.

  
  

  Abstract

  There is a large reliance on piezometric cone penetration testing (CPTu) in the tailings industry to estimate strength parameters for assessing the stability of tailings storage facilities (TSFs). It is common practice to assess the post-liquefied stability of a TSF using a residual undrained shear strength ratio (USSR). In such an assessment the residual USSR is typically applied to all saturated tailings. The current methods available to analyse CPTu data, are largely based on correlations and assumptions, and therefore contain limitations. Due to the limitations of the methods, this could lead to either over- or un-conservative estimates of stability. In this study, three methods for determining liquefaction potential and residual undrained shear strength ratio (USSR) are compared, namely: Robertson (2022), Been and Jefferies (2016), and Olsen and Stark (2002). These methods differ in the way in which they apply cone resistance, sleeve friction, and dynamic pore pressure response to estimate residual USSR. Their limitations are highlighted and discussed. A hybrid method is proposed for applying the results to post-liquefaction stability analyses. The hybrid interpretation approach uses a combination of the methods to account for different ranges of effective overburden stress and to identify weaker and stronger layers in the tailings profile based on state parameter, residual USSR, and pore pressure response. This hybrid method was applied to a stability assessment of a decommissioned platinum tailings storage facility in South Africa. The results indicated that the hybrid interpretation resulted in a more realistic phreatic surface location and a more accurate failure plane than conventional interpretations.

  Abstract
  There is a large reliance on piezometric cone penetration testing (CPTu) in the tailings industry to estimate strength parameters for assessing the stability of tailings storage [...]

  • 0
  •  read

• Technical Note on Calibration for Cone Penetration Testing in Soft Soils

  G. Scholey*

  ISC2024.

  
  

  Abstract

  Even the most experienced geotechnical engineer is likely to assume that the results of cone penetration tests are unquestionably accurate, reliable and repeatable. There are, however, multiple factors, some that have nothing to do with the soil properties, that need to be carefully addressed prior to testing if the equipment is to return results that can be relied on for design purposes. In soils which are very soft or soft, cone penetration test results can be particularly sensitive to the method of calibration. A high degree of rigour to the calibration process is required, otherwise there is a risk that the results obtained could be inaccurate and adversely impact on the reliability of the interpretation of design soil strength profiles. In this technical note sources of error in cone calibration are discussed. Reference is made to ISO 22476-1 which was revised in 2022, with the addition of a defined approach to calibration. Examples are used to demonstrate the typical errors that could be introduced during calibration.

  Abstract
  Even the most experienced geotechnical engineer is likely to assume that the results of cone penetration tests are unquestionably accurate, reliable and repeatable. There [...]

  • 0
  •  read