Documents published in Scipedia

• Interpretation of cone pressuremeter tests to estimate the strain dependent stiffness and strength of sensitive lacustrine clay

  J. Schorr*, R. Cudmani, S. Vogt

  ISC2024.

  
  

  Abstract

  Field and laboratory testing was carried out for the construction of a 100 m long cable stayed bridge situated in the foothills of the Alps in the south of Germany, a region dominated by deep post-glacial, fine-grained sediments. Due to the sensitivity and associated challenges with retrieving undisturbed soil samples in situ tests and their evaluation proved to be essential for the geotechnical design of the bridge foundation. This contribution focuses on the analytical and numerical interpretation of Cone Pressuremeter Tests (CPM). The non-linear 𝐺-𝛾 relationship and undrained shear strength (using both the limit pressure and reverse plasticity contraction analysis) were determined analytically. Numerical investigations were carried out as verification using both the Finite Element method (FEM) using both 1D (cavity expansion) and 2D simulations (where the penetration of the probe was modelled) as well as using the Finite Difference (FD) method. 2D simulations demonstrated that the assumption of the cylindrical cavity expansion is appropriate for modelling the CPM tests. The interpreted undrained shear strength showed good agreement with other field tests, including CPTu, vane shear (FVT) and seismic cone penetration (SCPT) tests, as well as with the results of laboratory tests on disturbed samples. CPM tests with strain rate jumps were conducted during pressuremeter expansion, wherewith it was possible to quantify the viscous response of the soil. Based on the holistic interpretation of the field and laboratory results involving both numerical simulations and analytical methods the parameters for the material model Viscohypoplasticity were calibrated.

  Abstract
  Field and laboratory testing was carried out for the construction of a 100 m long cable stayed bridge situated in the foothills of the Alps in the south of Germany, a region [...]

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• Plant Root Circumnutation-Inspired Penetration in Sand and Clay

  R. Anilkumar*, A. Martínez

  ISC2024.

  
  

  Abstract

  Site investigation (SI) and subsurface exploration are vital for characterizing soil properties. However, a common challenge is the lack of sufficient reaction force to penetrate through stiff crusts or deep layers, leading to refusal. To address this issue, rigs typically have large sizes that can make mobility and accessibility challenging and increase the carbon footprint of SI activities. This paper experimentally investigates a plant root-inspired strategy called circumnutation-inspired motion (CIM) to reduce the vertical penetration forces (𝐹𝑧) in comparison to quasi-static penetration used for example for Cone Penetration Testing (CPT). The CIM probes have a bent tip end and are rotated at a constant angular velocity (𝜔) while they are advanced at a constant vertical velocity (𝑣) in uniform specimens of clay and sand. 𝐹𝑧 for both soils decay exponentially by factors as high as 10 with increasing relative velocity, defined as the ratio of the tangential to the vertical velocity of the probe tip (𝜔𝑅/𝑣). Torques for both soils increase with initial increases in 𝜔𝑅/𝑣 which stabilize at higher velocities. While the cumulative total work, calculated for both clay and sand from the measured forces and torques, increases less than 25% for initial increases in 𝜔𝑅/𝑣 between 0 and 0.3𝜋, the 𝐹𝑧 can be reduced by around 50%. Thus, CIM penetration can produce significant reductions in 𝐹𝑧 in comparison to CPTs while limiting the additional energy consumed. CIM could be implemented to perform site investigation activities, such as obtaining samples or installing sensors, using smaller-sized, light-weight rigs

  Abstract
  Site investigation (SI) and subsurface exploration are vital for characterizing soil properties. However, a common challenge is the lack of sufficient reaction force to penetrate [...]

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• G-PFEM-aided Derivation of Undrained Shear Strength of Organic Clays from CPT Data

  A. Halleux, K. Boschi*, L. Flessati, C. Jommi

  ISC2024.

  
  

  Abstract

  Accurate evaluation of undrained shear strength of soils is crucial in geotechnical design and assessment. In the practice, undrained shear strength is obtained most frequently from CPT data, dividing the net cone tip resistance by a cone factor, 𝑁 . For organic soils, values between 8.6 and 15.3 are reported, depending on the stress history. The cone factor can be conditioned to the results of laboratory tests, although uncertainties remain on the variety of stress paths followed by the soil elements around the tip of the cone, compared to the ones tested in the laboratory. Non-uniqueness in the definition of the cone factor may lead to either unsafe or over-conservative choices, partly undermining both the reliability and the sustainability of the design. This contribution analyses numerically the inversion technique used to determine the undrained shear strength of organic clays, exploiting data from an extensive in situ and laboratory investigation. The adopted constitutive model was calibrated on the results of laboratory tests. Cone penetration tests were simulated performing coupled hydro-mechanical numerical analyses via G-PFEM, developed in the last decade at CIMNE-UPC. The role played by initial stress state and previous stress history upon stress distribution at failure, cone factor and sleeve friction is discussed. The numerical results suggest how the sleeve friction could be used to condition the cone factor depending on the over-consolidation ratio and demonstrate how combining the different available CPT readings with the aid of numerical results may reduce the uncertainty in the estimation of undrained shear strength.

  Abstract
  Accurate evaluation of undrained shear strength of soils is crucial in geotechnical design and assessment. In the practice, undrained shear strength is obtained most frequently [...]

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• A numerical analysis of CPT-based tip resistance prediction during pile installation in clays

  S. zhou*, W. Zhang, A. Osman

  ISC2024.

  
  

  Abstract

  Accurately predicting the installation resistance of offshore piles is important for their design and application. The cone penetration test (CPT) is the most widely used in situ sounding tests for pile drivability analysis and capacity prediction. While there are established empirical correlation methods to connect CPT data with pile installation resistance, the underlying mechanisms behind these correlations have yet to be fully understood. This study performs a numerical analysis to reveal such mechanisms and improve the correlations. The pile installation and cone penetration processes are modelled using a large-deformation finite-element method. For all analyses, a smooth cone and a smooth pile are simulated to quantify the relationship of tip resistance between the pile and CPT. The mechanisms of the two analogous penetration processes are visualized and compared through numerical modelling. As the cone advances, it pushes the soil at the cone tip into the far field. During the pile penetration process, soil heaving can be observed with the soil surface inside the pile moving above the mudline. The soil failure is localized at a small zone around the pile tip. The penetration resistances of pile are correlated to CPT data with the aid of numerical modelling and compared to existing CPT-based design guidelines. A discussion on the pile tip resistance correlated with cone tip resistance is included, and the value of the empirical coefficient for tip resistance kp is obtained.

  Abstract
  Accurately predicting the installation resistance of offshore piles is important for their design and application. The cone penetration test (CPT) is the most widely used [...]

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• Prediction of state parameter based on CPT MPM simulations in sandy soils

  M. Martinelli*, G. Remmerswaal

  ISC2024.

  
  

  Abstract

  Cone penetration tests (CPTs) can provide quantitative information about the mechanical state of sandy soils. In the current state of the art, the soil state is derived from the cone resistance, which is estimated from the cavity expansion solution and a calibrated scaling equation. Recently, Martinelli and Pisano (2022) showed that MPM simulations of CPTs provide accurate values of the cone resistance in sandy soils when using the critical state NorSand model. This paper adopts this framework to develop a predictive equation for cone resistance as a function of the NorSand parameters and the state parameter of the soil. This formula is straightforward to implement, and it can be adopted by researchers and practitioners to assess soil state in a soil deposits.

  Abstract
  Cone penetration tests (CPTs) can provide quantitative information about the mechanical state of sandy soils. In the current state of the art, the soil state is derived from [...]

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• Numerical Study of Cone Penetration in Calcareous Sands: Investigating Cone Tip Resistance Correction Factors for Crushable Soils

  S. Hyder*, D. Moug

  ISC2024.

  
  

  Abstract

  The cone penetration test (CPT) is used to characterize the behaviour and properties of soils, including the cyclic strength against earthquake liquefaction triggering. The cone tip resistance relates to cyclic strength through relative density, where relative density is closely related to both cone tip resistance and liquefaction susceptibility. Currently, published methods of estimating liquefaction potential (i.e., cyclic resistance ratio) are based on silica sands and do not properly characterize calcareous sands. The measured cone tip resistance in calcareous sands is lower than in silica sands at the same relative density; this difference is generally attributed to the higher compressibility of calcareous sands due to particle crushing during cone penetration. Consequently, application of CPT-based liquefaction triggering evaluations in calcareous sands result in over-conservative analysis. To avoid over-conservative analysis, projects may develop site-specific correction factors to adjust the cone tip resistance in calcareous sand to the equivalent value in silica sand at the equivalent relative density. This study aims to investigate cone penetration in calcareous sands compared to silica sands by examining the roles of soil compressibility and other fundamental soil parameters. The study is performed with a direct axisymmetric penetration model and the MIT-S1 constitutive model calibrated against published mechanical behaviour for a calcareous sand; the simulated cone penetration results are compared with simulated cone penetration in Ottawa F-65 sand. Compressibility of the calibrations is adjusted to explore the role of compressibility on cone tip resistance. The numerical results show that differences in compressibility only partially account for differences in cone tip resistance between calcareous and silica sands at the same initial state. However, the results support that critical state line position does strongly relate to differences in cone tip resistance between the two soil types. The study results provide a basis to investigate differences in critical state line position as a basis for site-specific cone tip resistance correction factors for calcareous soils.

  Abstract
  The cone penetration test (CPT) is used to characterize the behaviour and properties of soils, including the cyclic strength against earthquake liquefaction triggering. The [...]

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• On the Determination of Soil Deformation Modulus by Means of a Penetrometer

  S. Volcy*, C. Dano, L. Sibille, B. Chareyre, H. Hosseini-Sadrabadi

  ISC2024.

  
  

  Abstract

  Classical Cone Penetration Test (CPT) or CPTu (when water pore pressure is also measured) can provide so far only strength parameters of soils, specifically the tip resistance and the lateral friction. This article presents the numerical simulation in a (virtual) calibration chamber, using the Discrete Element Method (DEM), of a CPT-based test proposed in the quest for possibilities to determine soil deformability parameters as well. It is a non-standard test characterized by force-controlled cycles applied to the penetrometer tip that is movable independently of the penetrometer body. Very small irreversible displacements of the tip are observed over the first cycles whose amplitudes span a region of low fractions of the tip resistance, that is subsequently assimilated to a pseudo-elastic domain within which, deformation moduli can be derived from the slopes of the force-displacement curve properly interpreted. Results also reveal a loading level beyond which, these slopes and the corresponding deformation moduli, significantly decrease while the irreversible displacements of the tip increase substantially.

  Abstract
  Classical Cone Penetration Test (CPT) or CPTu (when water pore pressure is also measured) can provide so far only strength parameters of soils, specifically the tip resistance [...]

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• Experimental and Numerical Investigations of CPT End Resistance at Variable Penetration Rates in Mixed Soils

  A. Arafianto, Y. Tian, B. Lehane, Y. Suzuki, D. Reid

  ISC2024.

  
  

  Abstract

  This paper investigated cone penetration test end resistance under various drainage conditions in mixed soils through numerical simulations and piezocone experiments in laboratory testing chambers. The soil samples used in the laboratory tests contained various proportions of kaolin, silt, and sand. The piezocone tests were performed using a 10 mm diameter cone in consolidated soil samples. The measured variations of cone resistance and pore pressure at cone velocities varying from 0.005 mm/s to 30 mm/s are presented, which covered the full range from drained to undrained conditions. The cone resistance was evaluated using the spherical cavity expansion limit pressure predicted in Finite Element (FE) analyses that employed the NorSand (NS) constitutive model. The experimental and numerical findings allow assessment of the suitability of the normalised velocity (V) term, proposed by others, to unify cone resistances measured at variable rates.

  Abstract
  This paper investigated cone penetration test end resistance under various drainage conditions in mixed soils through numerical simulations and piezocone experiments in laboratory [...]

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• Numerical Simulations of Cone Penetration Response via Accounting for State-Dependence and Full-Strain-Range Non-Linearity of Sand

  Z. Shi*, S. Tong, M. Huang, J. Yu, B. Wang, C. Sun

  ISC2024.

  
  

  Abstract

  The penetration response of CPT is not only related to the stress and density states of sand but also influenced by the nonlinear stress-strain relations of soils from very small (10-5) to relatively large (10-1) strain levels. Appropriate considerations of the above key soil behaviours can be crucial for accurate numerical simulations of CPT response. For this purpose, an intergranular strain (IGS)-based elastic model is introduced into a critical-state-based, state-dependent plasticity model to capture the state-dependence and full-strain-range non-linearity behaviour of sand. A numerical model of the CPT penetration process is then established by combining the aforementioned constitutive model and the arbitrary Lagrangian-Eulerian (ALE) large deformation finite element technique. The latter is adopted to handle the problems of large deformations of soil and mesh distortion. Then the computed response of CPT is compared against centrifuge test observations, and the numerical model is utilized to analyse the influences of the full-strain-range non-linearity behaviour of sand on the penetration response of CPT. The results indicate that the non-linear stress-strain relations at small strains can have noticeable impacts on the tip resistance of CPT, in particular for loose sand, while having a relatively small influence on the penetration depth required to reach a steady-state penetration resistance. The above influences might be attributed to a rapid decay of soil strains with the distance from the cone tip, and consequently high stiffness and strong constraints effects of far-field soils on core soils adjacent to the cone tip

  Abstract
  The penetration response of CPT is not only related to the stress and density states of sand but also influenced by the nonlinear stress-strain relations of soils from very [...]

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• Inherent and CPTu-measured Scale of Fluctuation of Undrained Geomaterials: a Numerical Perspective

  L. Monforte*, S. Collico

  ISC2024.

  
  

  Abstract

  The vertical scale of fluctuation of soil parameters is often indirectly estimated through Cone Penetration Testing (CPTu) as the test provides nearly continuous and repeatable data. However, the variability quantified from CPTu might not be representative of a soil parameter intra-site variability, but rather the effect of the variability of soil measured through its response to the cone probe. The objective of this work -of an openly prospective nature- is to examine how the vertical inherent spatial variability of clay-like insensitive geomaterials propagates to the cone tip and friction sleeve resistance by means of numerical modelling. A total stress analysis is presented, in which the undrained shear strength is described according to random field theory. Numerical results show that the scale of fluctuation of the tip resistance and friction sleeve resistance is greater than the one assumed for undrained shear strength.

  Abstract
  The vertical scale of fluctuation of soil parameters is often indirectly estimated through Cone Penetration Testing (CPTu) as the test provides nearly continuous and repeatable [...]

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