Documents published in Scipedia

• Portable Pressiocone System for Carrying Out CPTU+FDP (Full Displacement Pressumeter) Tests

  M. Sacchetto*, G. Vinco

  ISC2024.

  
  

  Abstract

  Geotechnical investigations in the subsoil of existing buildings have always been challenging due to limited space and difficult access. URETEK has developed a portable integrated system for simultaneously carrying out a CPT and a pressumeter test with Full Displacement Pressuremeter (FDP). The 30 kN thrust penetrometer to be used is very small. The reaction is given by two “microanchors”. The cone is a standard 10 cm2 digital memory cone (no cable), capable of measuring qc, fs, u every centimetre. Above the cone there is the FDP equipment with a rubber sheath covered by steel plates and connected, by a tube filled with water, to a device for creating pressure to inflate the sheath and measure pressure-volume curves as in a standard pressumeter test. The pressure-volume device and the depth transducer are connected to a microcomputer that is programmed to carry out CPT+FDP tests in an easy-to-use/user-friendly way.

  Abstract
  Geotechnical investigations in the subsoil of existing buildings have always been challenging due to limited space and difficult access. URETEK has developed a portable integrated [...]

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• Finite element analysis of self-boring pressuremeter tests in clay

  Y. Dong*

  ISC2024.

  
  

  Abstract

  Self-boring pressuremeter (SBPM) tests are widely used in site investigations, due to their distinct advantage to measure the shear stress-strain-strength properties of the surounding soil with minimum disturbance. The measured pressuremeter curve can be interpreted using analytical solutions based on the long cylindrical cavity expansion theory with relatively simple constitutive models. However, SBPM tests are strongly affected by the soil behavior and details of installation procedure. In addition, the derived parameters for clays (e.g. undrained shear strength, and shear modulus) are affected by a number of state variables such as overconsolidation ratio, and stress level. In this paper, SBPM tests are investigated using finite element analysis and the MIT-S1 model, to consider complex soil behavior more realistically. SBPM tests in K0-consolidated Boston Blue Clay at different OCRs are simulated in axial symmetric and plain strain conditions, consistent with the assumptions used in analytical solutions. The derived undrained shear strength from both contraction and expansion curves are compared with theoretical values from stress-strain curves, to evaluate the reliability of the derived parameters from the SBPM tests.

  Abstract
  Self-boring pressuremeter (SBPM) tests are widely used in site investigations, due to their distinct advantage to measure the shear stress-strain-strength properties of the [...]

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• Development of a Calibration Chamber System for Testing at High Confining Pressures

  M. Haynes, D. Reid, R. Fanni, K. Smith

  ISC2024.

  
  

  Abstract

  Cone penetration testing with pore pressure measurement (CPTu) represents a state of practice tool to assess the in situ state parameter, strength, and liquefaction susceptibility of sandy soils and mine tailings. Many techniques for the interpretation of CPTu data are based on the results of calibration chamber test programs on sand and, more recently, mine tailings. While these efforts have led to the current methods to interpret CPTu data, two factors relevant to CPTu interpretation require consideration: (i) the available calibration chamber data is dominated by tests with consolidated mean effective stresses < 200 kPa; and (ii) tailings storage facilities are being constructed to heights such that in situ effective stresses are far higher than those of the available calibration chamber test database. While much of CPTu interpretation is carried out in a dimensionless framework, there is evidence that existing relationships between stressnormalised tip resistance and state parameter are dependent on effective stress. This stress-dependence has been attributed to a variation in shear rigidity with effective stress, which is not accounted for in many interpretation techniques. However, at high stresses, other factors such as the curvature of the critical state line in an e-log(p’) plane may contribute. To assess CPTu of sands at high stresses, a novel small-scale calibration chamber employing a miniature cone capable of testing soils consolidated to a mean effective stress up to 2,000 kPa is outlined. Test results are presented for tests carried out over a range of mean effective stresses up to 1,000 kPa.

  Abstract
  Cone penetration testing with pore pressure measurement (CPTu) represents a state of practice tool to assess the in situ state parameter, strength, and liquefaction susceptibility [...]

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• Does CPT Reference Value Drift Really Inform CPT Correctness?

  A. McConnell*, M. Chapman

  ISC2024.

  
  

  Abstract

  The two authors’ company (IGS) is an in situ testing and sampling contractor. Approximately 40% of the company’s business is cone penetration testing (CPT). The CPT cones they use are good quality commercial units supplied by the Dutch company Geomil, with qc capacities ranging from 3MPa to 100MPa. Both compression-type and subtraction-type cones are used. IGS undertakes their own in-house calibrations on all cones, using externally calibrated load cells, and a combination of dead weights and hydraulic load application. Calibration and adjustment is undertaken on every cone on an unusually frequent basis, explained in the paper, far more frequently than current standards or manufacturer recommendations require. At each calibration, the reference readings (sometimes known as baseline readings) of each cone’s tip qc, sleeve fs, and pore pressure U sensors are noted. And the slope of the applied-load/pressure-vs-cone-readout for each of these sensors (ie accuracy) is measured and adjusted to give as close as reasonably possible 100% accurate output. All of this is recorded for each cone. Thus the authors have a database of reference reading drift that can be compared to slope adjustments (ie calibration adjustments) that have been needed to achieve the desired cone accuracy. This paper graphically reports the data for tip and sleeve of eight typical CPT cones of the day-to-day types used by the company.

  Abstract
  The two authors’ company (IGS) is an in situ testing and sampling contractor. Approximately 40% of the company’s business is cone penetration testing (CPT). The CPT [...]

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• Importance of Calibration Laboratories in In-situ Test Methods

  N. Parasie*, G. Sinjorgo, L. Vrielink, J. Peuchen

  ISC2024.

  
  

  Abstract

  Geotechnical in-situ test methods provide valuable data for asset development, operation, and decommissioning. For confidence in test results, industry typically requires calibration and verification of in-situ test sensors to be conducted in a calibration laboratory. A calibration laboratory typically operates according to ISO/IEC 17025 (2017) ‘general requirements for the competence of testing and calibration laboratories’, or similar standard. This paper summarises observations from practice, with focus on the following challenges (1) evaluation of measurement uncertainty of key parameter values for which no standardised methods or verification materials are available, (2) validation of test methods with no backup from a formal standard published by a standardisation organisation and (3) field test site and interlaboratory comparisons within a competitive industry setting. Specific examples are presented for the (1) estimation of calibration uncertainty for sleeve friction of a subtraction-type cone penetrometer and (2) method validation for thermal conductivity of soil derived from in-situ heat flow measurements.

  Abstract
  Geotechnical in-situ test methods provide valuable data for asset development, operation, and decommissioning. For confidence in test results, industry typically requires [...]

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• Offshore shear wave velocity measurements for the assessment of soil sampling quality

  A. Deu*, A. Gens, A. Viana Da Fonseca, M. Devincenzi, D. Tarragó

  ISC2024.

  
  

  Abstract

  Shear wave velocity Vs is a critical soil parameter for several geotechnical and geophysical engineering applications including seismic site response analysis, liquefaction risk assessment and design of shallow and deep foundations. Moreover, the comparison of shear wave velocity between laboratory and in situ measurements has become a standard acceptance criterion for the assessment of sampling quality. Offshore in situ shear wave velocity testing is considerably more challenging than onshore, due to the difficulties in the correct deployment of the instrumentation as well as of the wave source, in absence of direct visibility of the ground level below water. This paper describes the methodology employed for offshore shear wave velocities (Vs) measurements in the harbour of Barcelona in September 2022. Medusa SDMT tests were performed in sea depths ranging between 15-17 m from a jackup and employing a drill rig to penetrate the probe down to 40 m below the seafloor. The paper includes examples of recorded S-wave seismograms, analyses of Vs repeatability for the same depth measurements and Vs profiles with depth. In the same test locations, carefully prepared specimens of undisturbed samples were tested after reconsolidation to the estimated in situ stress states in stress path triaxial cells with bender elements transducers. The obtained lab shear wave velocities were compared with the in situ values obtained with the Medusa SDMT tests to assess sample quality.

  Abstract
  Shear wave velocity Vs is a critical soil parameter for several geotechnical and geophysical engineering applications including seismic site response analysis, liquefaction [...]

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• Influence of hydrogeological conditions on estimation of undrained shear strength by CPTu tests: case study in a tropical soil

  I. Rigatto*, L. Ferreira

  ISC2024.

  
  

  Abstract

  CPTu tests have gained prominence in the geotechnical characterization of materials, registering a significant increase in their application in the Brazilian context, especially due to requirements to consider undrained resistance in analyses guided by more recent regulations. However, the interpretation of these tests often lacks a detailed and personalized approach, as they disregard specific nuances of each location. In this study, the foundation of a dam made up of tropical soil with a specific hydrogeological condition, characterized by bottom drainage with deep percolation, previously identified in other research campaigns, was evaluated. The interpretation of the CPTu test aimed to estimate the undrained resistance of the material through two different approaches: considering the dissipation tests carried out to model the insitu pore pressure according to the elevation versus a hypothetical hydrostatic condition, which could be misinterpreted in places where there is a predominance of SPT tests and insufficient geological knowledge. Multiple methodologies were evaluated to interpret undrained shear strength, including approaches that use Bq directly and that exclusively considers the laboratory characterization of a sample and the overconsolidation ratio at that point. In this case analyzed, it was observed that the change in pore pressure conditions resulted in a considerable variation in the undrained shear strength ratio, over 10% when pore pressures are considered in the equations. The results highlight the relevance of considering local hydrogeological conditions when interpreting field tests, especially for foundations of large structures.

  Abstract
  CPTu tests have gained prominence in the geotechnical characterization of materials, registering a significant increase in their application in the Brazilian context, especially [...]

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• Engineering characterization of lacustrine soil deposits at the inner bay of Puno around Titicaca Lake

  S. Laura-Huanca

  ISC2024.

  
  

  Abstract

  The inner bay of the city of Puno has been the subject of various investigations that seek to recover and enable floodprone areas, through strategic urban development projects (urban infrastructure) and protection works. On the other hand, the characteristics of soft soil deposits, such as those in the inner bay of Puno, represent a risk of problems with excessive settlement of the infrastructure. This study presents an engineering characterization of the lacustrine soil deposits in the inner bay of the city of Puno, around Lake Titicaca. The site lies around the Pier of Puno city at Lake Titicaca, the highest navigable lake in the world, approximately a few hundred meters in front of the National University of the Altiplano of Puno (UNAP) and a few hundred meters to the southward of the Pier of Puno city. Physical, strength, and deformation properties were determined from standard laboratory tests. The material studied corresponds to the shallow layers of the study area, corresponding to sedimentary soils of the lacustrine units and fluvial-alluvial deposits of the inner bay of Puno. These lacustrine soils are classified as highly plastic silts and organic clays (MH and OH). The results show the significant influence of the quality of soil samples, due to the sampling method and storage time, on consolidation and resistance parameters. Finally, this study provides valuable insights into the influence of sample quality on consolidation parameters and shear strength of the lacustrine soils in the inner bay of Puno city around Titicaca Lake.

  Abstract
  The inner bay of the city of Puno has been the subject of various investigations that seek to recover and enable floodprone areas, through strategic urban development projects [...]

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• Assessing shear wave velocity profile uncertainty using multiple sCPT interpretation and processing methods

  L. Wotherspoon*, A. Stolte, B. Cox

  ISC2024.

  
  

  Abstract

  This paper quantifies the influence of seismic Cone Penetration Test (sCPT) interpretation and processing methods on shear wave velocity (VS) profile uncertainty using data from 20 sites in Christchurch, New Zealand. The near-surface soil profiles varied across the sites, both in terms of the soils that were present and the profile layering characteristics, reflecting the depositional environment that is influenced by alluvial and coastal processes. The same experimental setup was used at each site, consisting of a dual receiver sCPT cone and a hammer source method at a consistent horizontal offset distance. Three commonly used shear wave arrival time picking methods and the cross-correlation method were used to define arrival times and time intervals between testing depths for each site. The pseudo-interval, true-interval and slope-based processing methods were used with these arrival times and time intervals to develop 11 VS profiles for each site. Alongside this, a ray tracing inversion method provided an additional VS profile at each site. The uncertainty in the VS profiles that were developed at each site are presented, highlighting the variability resulting from different processing and picking methods. Results across sites are combined to provide a representation of the uncertainty across all methods and the differences in the uncertainty across the various processing methods.

  Abstract
  This paper quantifies the influence of seismic Cone Penetration Test (sCPT) interpretation and processing methods on shear wave velocity (VS) profile uncertainty using data [...]

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• Uniaxial Compressive Strength versus Shear Seismic Wave Velocity

  M. Cabrera*, M. Combarros

  ISC2024.

  
  

  Abstract

  Worldwide, geotechnical engineers frequently use the Uniaxial compression test for soils and rocks as a basis for determining the strength of the materials, despite the fact that test results are subject to a wide range of uncertainties (drilling technique, care during transport and stockage, sample preparation, and sample representativity of the soil or rock layer). The process of geophysical site research uses Refraction Seismic Survey and Passive Tomography to determine the shear and compression seismic wave velocities for various rock and soil layers under the surface. The study examines the correlation between the outcomes of the Uniaxial Compression Tests and the shear seismic wave velocity measured at a 400 ha location in the Atacama Desert (Chile), which was intended to host 84 km of linear solar panels. A robust survey of the axial compression value was determined at a vast site spanning 400 hectares by integrating Uniaxial compression tests, Brazilian test, Shear, and Compression seismic wave velocity.

  Abstract
  Worldwide, geotechnical engineers frequently use the Uniaxial compression test for soils and rocks as a basis for determining the strength of the materials, despite the fact [...]

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