Documents published in Scipedia

• A Cylindrical Cavity Expansion Test on Sand

  S. Nachum*, M. Talesnick, M. Ghafghazi

  ISC2024.

  
  

  Abstract

  Cylindrical cavity expansion is one of the fundamental boundary value problems in geotechnical engineering used as a simplified analogue to the pressuremeter test, pile driving and the Cone Penetration Test. Much of the popularity of cavity expansion comes from the simplicity of modelling it numerically. All numerical models require verification and validation, but doing so for cavity expansion has been limited due the relatively small amount of physical modelling of the problem. Past cavity expansion tests in calibration chambers have often been limited in range of strains, diameter to length ratio, and the amount and type of measurements made. This paper describes a calibration chamber set up used to perform cylindrical cavity expansion tests in a dry fine sand. Instead of attempting to replicate a specific application (e.g., pressuremeter test), the goal was to create a near-perfect cylindrical cavity expansion model, with in-soil measurement of stresses and strains, to serve as baseline data for validation of numerical models. The experimental set up is described, the material properties are summarized, and results of a cavity expansion tests are presented and discussed.

  Abstract
  Cylindrical cavity expansion is one of the fundamental boundary value problems in geotechnical engineering used as a simplified analogue to the pressuremeter test, pile driving [...]

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• How much does the spatial variability of CPTu measurements affect the hydro-mechanical variables' estimation?

  G. Vessia*, D. Di Curzio, W. Pula

  ISC2024.

  
  

  Abstract

  Using CPTu profiles for subsoil characterisation, transformation equations must be used to obtain the hydro-mechanical properties for structures and infrastructure designing. Additionally, the uncertainty and the spatial variability of measured parameters must be taken into account for a reliable geotechnical design. In this work, we used a Stochastic Simulation approach to define reliable 3D models of two geotechnical designing variables for granular soils (friction angle–’ and the Darcy permeability coefficient–k) from tip resistance (qc), sleeve friction (fs), and pore pressure (u2) profiles. The selected method – the Sequential Gaussian Co-Simulation (SGCS) – provided reliable optimized 3D models of the spatial distribution of the variables of interest and allowed quantifying the propagation of the estimation uncertainty associated with the raw measurement models through the transformation equations. Overestimation (OE) and Underestimation (UE) percentages for a confidence interval of 68% were calculated throughout the 3D model: granular soils showed a larger uncertainty than fine soils concerning the measured variables (qc, fs, and u2). In granular soils, the measured variable uncertainty varies up to 100% but the derived variables show different behavior: ’ shows UE and OE less than 25% while k reaches 100%. These differences in the propagated uncertainties depend on the transformation equations and the measured variable dependence.

  Abstract
  Using CPTu profiles for subsoil characterisation, transformation equations must be used to obtain the hydro-mechanical properties for structures and infrastructure designing. [...]

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• A practical method to derive shear modulus from pressumereter tests in clay

  J. Habert*, A. Lopes

  ISC2024.

  
  

  Abstract

  Pressuremeter tests are an efficient tool to derive shear modulus of ground, and its decay with shear strain. Non-linear behaviour of ground during cavity expansion, and its consequence on shear modulus and stress with the distance to the pressuremeter cavity, have to be taken into account. For tests in fine soils, for which constant volume can be assumed during the test, retrofitting of unload-reload loops based on closed form solutions integrating the non-linear elastic behaviour can be implemented. In a first phase, this paper presents a practical straightforward method to derive shear modulus decay with shear strain based on the cylindric cavity expansion theory including non-linear elasticity under undrained conditions and hyperbolic ground behaviour. In a second phase, the method is applied step by step to a pressuremeter test in clay with unload-reload loops. Finally, on a third and last phase, this paper compares the previous results from to i) other interpretation methods integrating prior strains transformations, but also to ii) other investigation tests providing the initial shear modulus G0 associated with very small strain levels or the shear modulus decay with strain level.

  Abstract
  Pressuremeter tests are an efficient tool to derive shear modulus of ground, and its decay with shear strain. Non-linear behaviour of ground during cavity expansion, and its [...]

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• Correlations Between The Pressuremeter And The Rigid Dilatometer Parameters In Soils

  C. Jacquard*, T. Besson, M. Rispal, P. Reiffsteck, F. Szymkiewicz

  ISC2024.

  
  

  Abstract

  The Dilatometer Fondasol Test (DFT) is a unidirectional loading test in a borehole that provides an in-situ stress-strain curve. Two rigid shells are spread in the soil at a constant displacement rate by several small hydraulic jacks. First results using this probe in soils were obtained by Besson (2022) who also provided methods to compute from the stress-strain curve both a pseudo-elastic modulus and a limit stress. However, additional data were required to establish strong correlations between the dilatometer parameters and the pressuremeter parameters. This paper introduces new results obtained in various sites in France and synthetises all the results obtained so far. For each site, pressuremeter soundings and dilatometer soundings are carried out in pairs using the same drilling methods. DFT and PMT are performed at the same depths and at the same strain rate. For the computation of moduli and limit stresses, semi-automatic methods are employed to prevent subjective interpretations. Correlations are proposed between the dilatometer modulus and the pressuremeter modulus as well as between the dilatometer limit stress and the pressuremeter limit pressure. The established correlations, along with their limitations, are interpreted.

  Abstract
  The Dilatometer Fondasol Test (DFT) is a unidirectional loading test in a borehole that provides an in-situ stress-strain curve. Two rigid shells are spread in the soil at [...]

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• Comparative tests between Texam and Menard Pressuremeters

  L. Marcil*, G. Sedran

  ISC2024.

  
  

  Abstract

  Two testing programs were undertaken for comparing results of the Texam and Menard pressuremeters with regards to the deformation modulus (E) and limit pressure (Pl). Two configurations of the Texam pressuremeter were used; one with a probe fitted with metal rings, the other with a probe fitted with polymer (vulcolan) rings. The results of the first program carried out in laboratory and presented in a previous article, have been completed and are presented here. The second testing program have been undertaken in the field. A total of 41 tests were completed in three boreholes in silty and clay materials. The comparative tests produced excellent correlations in the laboratory, with regression coefficients (R2) of 0.99, and fairly good correlations in the field (R2 ranging fron 0.64 to 0.73). The main findings are that the Texam produces equivalent or conservative results. More specifically : (1) the Texam with metal-ring probe produces comparable moduli values, (2) the Texam with polymer-ring probe produces lower moduli values, and (3) the two configurations of Texam produce lower limit pressures. The observed differences range between 10 to 20 %. Equivalence factors have been proposed.

  Abstract
  Two testing programs were undertaken for comparing results of the Texam and Menard pressuremeters with regards to the deformation modulus (E) and limit pressure (Pl). Two [...]

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• Deriving Strength Parameters of Granitic Residual Soils from Menard Pressuremeter Tests

  C. Rodrigues*, N. Cruz, C. Mateus

  ISC2024.

  
  

  Abstract

  Residual soils are non-textbook materials that are hard to be modelled by traditional soil mechanics, which creates serious difficulties in the in-situ test interpretations and the consequent applications to geotechnical design. This is due to the presence of a cementation structure that is responsible for a cohesive-frictional behaviour of these soils, meaning that two strength parameters must be derived to represent the overall strength. Furthermore, cementation structure also deeply affects the stiffness behaviour, deviating from typical response of transported soils. The common interpretation of in-situ tests usually considers extreme behaviours represented by only one parameter, namely undrained cohesion for clays and angle of shearing resistance for sands, which naturally do not work in these cohesive-frictional materials. For this purpose, only tests that take two or more independent measurements can be used to solve this problem, as it is the case of SCPTu, SDMT and PMT tests, while SPT and DPSH tests cannot be effective in this determination. Portuguese research institutions have been looking over the granitic residual soil characterization through specific research works, from which resulted several publications on the subject. Following previous research works of calibration with (S)DMT (Cruz, 2010) and (S)CPTu (Cruz et al. 2018) tests performed in Polytechnic Institute of Guarda (IPG), Portugal, a new research frame was developed to settle a methodology for obtaining strength parameters of granitic residual soils from pressuremeter tests (PMT), which is presented and discussed herein.

  Abstract
  Residual soils are non-textbook materials that are hard to be modelled by traditional soil mechanics, which creates serious difficulties in the in-situ test interpretations [...]

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• Expansion test with one unload-reload loop and pore pressure measurement, first interpretation of dissipation tests, Larivot site

  V. Savatier, P. Reiffsteck*, A. Philippe, M. Peronne

  ISC2024.

  
  

  Abstract

  This paper presents an interpretation of cyclic pressuremeter tests with pore pressure measurement performed at Larivot bridge site (French Guyana). In cohesive soils, test results are in accordance with the pressuremeter theory. The times at 50% dissipation correlate closely with those obtained from dissipation tests performed using a piezocone in the immediate vicinity.

  Abstract
  This paper presents an interpretation of cyclic pressuremeter tests with pore pressure measurement performed at Larivot bridge site (French Guyana). In cohesive soils, test [...]

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• Interpretation of the undrained pressuremeter test in unsaturated condition

  J. Monnet*, L. Boutonnier

  ISC2024.

  
  

  Abstract

  The pressuremeter measures both the pressuremeter modulus and the limit pressure, which are used to estimate the bearing capacity of the foundation according to different standards. The results of the pressuremeter test include the pLM limit pressure and the EM pressuremeter modulus. These quantities cannot be directly input as data for geotechnical calculations using Finite Elements or Finite Differences in the study of civil engineering structures such as retaining walls, tunnels, embankments, and excavations. These modern calculation methods require, at a minimum, knowledge of the mechanical characteristics of the soil, including elasticity (with Young’s modulus (E) and the Poisson ratio ()) and resistance (with cohesion (c’) and the angle of friction (’)). This study is devoted to the interpretation of the pressuremeter test so that it is possible to use it for the determination of the mechanical characteristics of the soil. When the pressuremeter test is carried out into clay, it appears pore pressure during the test when only shearing is applied. In summary, understanding pore pressure and interpreting measurements to determine the effective shear modulus are crucial for geotechnical engineering and subsurface exploration. Effective shear modulus can differ significantly from the value determined solely based on total pressure. This study provides the theoretical value of the Skempton coefficient B. Additionally, it proposes an interpretation theory for the pressuremeter test in clay. Finally, the theory is validated through a comparison with tests performed in London clay at a depth of 20.6 meters

  Abstract
  The pressuremeter measures both the pressuremeter modulus and the limit pressure, which are used to estimate the bearing capacity of the foundation according to different [...]

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• CPTU Onshore Testing with Pre-Drilling and/or Re-Drilling of the Ground at the Port of Barcelona. Lessons Learned

  J. Rubio, L. Casas*

  ISC2024.

  
  

  Abstract

  SOCOTEC Spain, together with our partner GEM (Geotecnia y Exploraciones Marítimas), has been performing one of the largest geotechnical survey investigations in the development of new areas in the Port of Barcelona. This investigation includes multiple onshore and offshore tests including drilling and sampling, CPTU, and both in situ and laboratory testing. The CPTU (Cone Penetration Test with pore pressure measurement) is currently one of the most widely used in situ tests for soil characterization. Regarding the regularization of this test, all Standards specify the technical requirements of the equipment, the method of execution of the field test and the presentation of results and minimum corrections that have to be considered when performing and interpreting a CPTU. However, the current regulations do not refer to the methodology to be followed for the pre-drilling and/or re-drilling of the ground before a CPTU test, which is a common and operationally ‘standard’ procedure. In this sense, during the onsite research campaign, the results obtained in numerous onshore and offshore CPTU tests have been analyzed and, a variation in the pore pressure data recorded in the onshore CPTU tests associated with the pre-drilling and/or re-drilling operations has been identified. For this reason, the purpose of the paper is to highlight the need for a standardized procedure to execute this type of drilling operations and/or the necessary corrections to be taken into account during the interpretations of the results obtained in order to correct the anomalies associated with the injection of an artificial water flow.

  Abstract
  SOCOTEC Spain, together with our partner GEM (Geotecnia y Exploraciones Marítimas), has been performing one of the largest geotechnical survey investigations in the development [...]

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• Impact of better pressuremeter interpretation on the cost of geotechnical structures

  R. Granjon*, J. Monnet

  ISC2024.

  
  

  Abstract

  This paper deals with the contribution of the realistic evaluation of the pressuremeter probe inflation mechanism and its technical and economic consequences for the project manager. This new approach allows to, within the framework of the Caderousse PCH studies, to significantly optimize the sheet pile modulus used by reassessing the soil characteristics in a more detailed way.

  Abstract
  This paper deals with the contribution of the realistic evaluation of the pressuremeter probe inflation mechanism and its technical and economic consequences for the project [...]

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