Documents published in Scipedia

• Quasi-region-specific model uncertainties of simplified liquefaction triggering analysis

  J. Wang, J. Ching*, Y. Tu

  ISC2024.

  
  

  Abstract

  In earthquake-prone regions, assessing soil liquefaction potential is indispensable for contemporary seismic design. Various procedures for liquefaction triggering analysis have emerged over the past decades. However, most of them are derived from generic liquefaction databases, such that the model uncertainties in liquefaction potential assessments applied to a specific region of concern remain unknown, which poses a challenge for engineers to evaluate the liquefaction risks of target sites. This study aims to propose a hierarchical Bayesian model (HBM) to learn the inter-region characteristics of model uncertainties of the traditional simplified liquefaction potential evaluation methods based on a database containing global case histories of liquefaction categorized into several regions where those triggering events occurred. The learning outcomes can yield the model uncertainty of the target region, and the liquefaction probability at the target site under a given ground motion condition. For an illustration of the proposed model, a case history of liquefaction from a specific region is adopted to construct a quasi-region-specific model uncertainty and evaluate the liquefaction probability in the target soil. The illustration shows that the constructed quasi-region-specific model uncertainty with liquefaction histories in the target region can improve liquefaction occurrence prediction in comparison with the prediction without any histories, which is believed to benefit the engineering practice.

  Abstract
  In earthquake-prone regions, assessing soil liquefaction potential is indispensable for contemporary seismic design. Various procedures for liquefaction triggering analysis [...]

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• Statistical Uncertainty of Cyclic Resistance of Sand under Constant Volume Direct Simple Shear

  Y. Sun*, B. Stuyts, W. Haegeman

  ISC2024.

  
  

  Abstract

  In the design work of offshore foundations, such as monopiles and gravity platforms, the cyclic resistance of soil plays a critical role in assessing the effect of cyclic loading induced by wind, waves, and rotor dynamics during the operational lifetime. However, the cyclic behaviour of soil is often derived from only a limited number of laboratory tests, which can lead to inaccurate estimates of soil behaviour. Furthermore, this imprecision can affect the parameters selection for the design process. To gain a better understanding of the limitations and uncertainties associated with laboratory experiments, a series of cyclic direct simple shear (cDSS) tests are conducted on marine sand. Four combinations of consolidation stress and void ratio are selected, and a constant volume cDSS test is repeated a substantial number of times for each combination. This dataset captures the measurement uncertainty on the cyclic soil resistance. By analysing the variability of the results, the statistical distributions for the cyclic soil resistance parameters can be determined (e.g. number of cycles to reach a certain shear strain level). The same specimen exhibits slightly different strain-stress relationships due to the inherent variability of sand. Statistical methods are used to describe the cyclic resistance of the sand.

  Abstract
  In the design work of offshore foundations, such as monopiles and gravity platforms, the cyclic resistance of soil plays a critical role in assessing the effect of cyclic [...]

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• Comparative Assessment of the Vertical Scale of Fluctuation of Undrained Shear Strength of Clays From CPT and DMT Testing: a Case Study in Central Italy

  M. Uzielli*, A. Galassi, M. Zei

  ISC2024.

  
  

  Abstract

  The quantification of the spatial variability of soil properties allows the enhanced engineering modelling, analysis, and design of geotechnical systems. Evolutionary design codes such as Eurocode 7 are awarding spatial variability an increasing central role in geotechnical design. The spatial variability of geotechnical properties is often investigated using a random field approach. Among the defining parameters of a random field is the scale of fluctuation, which describes the extent of significant spatial correlation in a specific spatial direction. The scale of fluctuation can be estimated quantitatively using a variety of methods relying on statistical approaches. The scale of fluctuation is not an inherent property of a soil. Existing studies demonstrate its dependency from numerous factors including the spatial direction, measurement interval, and user-defined modelling options. This paper illustrates the procedures and main results of the comparative estimation of the vertical scale of fluctuation of undrained shear strength of a layer of silty clay from piezocone (CPTU) and dilatometer (DMT) testing at a rural site in the region of Tuscany in central Italy. Vertical scales of fluctuation were calculated using two methods available in the geotechnical literature. Quantitative estimates are compared and analysed critically.

  Abstract
  The quantification of the spatial variability of soil properties allows the enhanced engineering modelling, analysis, and design of geotechnical systems. Evolutionary design [...]

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• Modeling and Characterizing Locally Subsiding Ground for the Analysis and Design of Mat Foundations

  D. Coduto*

  ISC2024.

  
  

  Abstract

  Mat foundations are often used as a means of protecting buildings and other structures from excessive distortion due to differential settlements in the underlying ground. Once soil bearing capacity concerns have been addressed, the analysis of these foundations becomes a soil-structure interaction problem where the bearing pressure from the mat induces settlement in the underlying ground while localized settlement distorts the mat and redistributes the bearing pressure. An accurate representation of this soil-structure interaction is necessary to facilitate computations of the shear and flexural stresses in the mat and to develop an appropriate structural design. However, modeling and characterizing this system has long been a source of confusion and contention among both geotechnical and structural engineers. The soil response is typically characterized using the modulus of subgrade reaction, ks (also known as the coefficient of subgrade reaction) which describes a certain mechanical soil-structure interaction model known as a Winkler foundation. However, ks is arguably one of the most misunderstood and misapplied parameters in geotechnical practice, and proper assessment of this parameter is more complex and nuanced than might be expected. Further complexities are introduced when locally subsiding ground is present. This is because the Winkler model assumes settlement occurs in the soil only in response to an applied bearing pressure, whereas local subsidence introduces additional settlement (with associated shear and flexural stresses in the mat) which is independent of that caused by the applied structural loads. Methods of modeling and characterizing the subsurface conditions for the purpose of developing design values of ks to be used in mat foundation analysis and design are proposed, then these methods are extended to accommodate sites with locally subsiding ground. These methods are compatible with standard geotechnical assessment techniques as well as standard structural analysis and design software packages.

  Abstract
  Mat foundations are often used as a means of protecting buildings and other structures from excessive distortion due to differential settlements in the underlying ground. [...]

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• Identification of random field for ground stiffness by data assimilation based on surface wave method and sounding tests

  S. Nishimura*, Y. Ren, T. Shibata, T. Shuku

  ISC2024.

  
  

  Abstract

  The surface wave method (SWM) and the screw weight sounding (SWS) are employed as a geophysical exploration method and a sounding test, respectively to identify the spatial distribution of the stiffness of an earth-fill dam in the present study. The ensemble Kalman filter (EnKF) is used as a data assimilation technique. It can estimate the spatial distribution of the Young’s modulus as the stiffness of an earth-fill dam by assimilating the travel time to the first arrival of the surface waves. By the ensemble data assimilation, the measured data from the SWM is applied to simultaneously estimate the Young's modulus and evaluate the uncertainties. The SWS results are employed as the prior information to generate the initial ensemble through the sequential Gaussian simulation (sGs). Proposed method has been applied to the actual data of the SWM and the SWS measured at an earth-fill dam site. Consequently, it has been clarified the proposed approach could identify the appropriate random field of Young's modulus.

  Abstract
  The surface wave method (SWM) and the screw weight sounding (SWS) are employed as a geophysical exploration method and a sounding test, respectively to identify the spatial [...]

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• Toward probabilistic ground models for time and cost estimation of tunnel projects

  J. Spross*, I. Papaioannou, J. Grasmick

  ISC2024.

  
  

  Abstract

  The construction time and cost of a rock tunnel project are highly dependent on the rock mass quality and encountered ground behaviour. In most rock tunnel projects, the knowledge about the ground conditions along the tunnel is limited, making it difficult to predict accurately the construction time and cost. The KTH model takes a probabilistic approach to address this problem; however, it does not account for the spatial variability of the ground conditions. This paper investigates an alternative probabilistic ground model to be used within the KTH model that enables accounting for the spatial variability through Markov random field theory. The new ground model employs a parametric approach to describe the properties of the Markov field, hence, enabling the simulation of the ground conditions with limited data, but does not consider the epistemic uncertainty in the model parameters. This will be the addressed in future research.

  Abstract
  The construction time and cost of a rock tunnel project are highly dependent on the rock mass quality and encountered ground behaviour. In most rock tunnel projects, the knowledge [...]

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• Data-Driven Simulation of Multivariate Cross-Correlated Geotechnical Random Fields from Sparse Measurements

  Z. Guan, Y. Wang*

  ISC2024.

  
  

  Abstract

  It is widely acknowledged that many geotechnical properties are correlated over space and/or time. Consequently, crosscorrelated random fields play a pivotal role in geotechnical reliability analysis for properly modeling both the auto- and cross-correlation structures of correlated geotechnical properties. Existing methods for simulating cross-correlated random fields typically require precise knowledge of random field parameters as input. However, in a typical site investigation program, engineering constraints such as limited time, budget, and space often lead to sparse measurements of geotechnical properties. Estimating reliable random field parameters, particularly the auto-correlation and crosscorrelation structures of a two-dimensional (2D) cross-correlated random field, from such sparse data is a notorious challenge. To address this issue, this study introduces a 2D cross-correlated random field generator that can directly simulate 2D multivariate cross-correlated geotechnical random field samples (RFSs) from sparsely measured data points. This generator leverages the method developed by Guan and Wang (2023), which employs a joint sparse representation to simultaneously exploit auto- and cross-correlation structures of various spatial/temporal quantities directly from sparse measurements. The effectiveness of the proposed generator is demonstrated using real geotechnical properties data. The results demonstrate that RFSs generated using this method from sparse measurements accurately capture the spatial auto- and cross-correlation structures of different geotechnical properties.

  Abstract
  It is widely acknowledged that many geotechnical properties are correlated over space and/or time. Consequently, crosscorrelated random fields play a pivotal role in geotechnical [...]

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• Stratification identification and prediction of missing CPT data by Mixture of Gaussian Processes

  M. Durmaz*, A. van den Eijnden, M. Hicks

  ISC2024.

  
  

  Abstract

  Stratification identification and spatial interpolation play a fundamental role in geotechnical site characterization. A unified approach is needed to perform these two tasks simultaneously to reduce overall uncertainty in site characterization. This paper explores the applicability of the Mixture of Gaussian Processes (MoGP) to address this gap, with a specific focus on characterizing and completing missing CPT data. The investigation encompasses both synthetic and real-world field CPT datasets and includes a comparison of the MoGP's interpolation accuracy with the use of a single GP for entire datasets. Additionally, the study examines the sensitivity of the model's performance with respect to the number of training data points. Although the interpolation performance of the MoGP model is promising with synthetic data, limitations appear in its application to real-site CPT data.

  Abstract
  Stratification identification and spatial interpolation play a fundamental role in geotechnical site characterization. A unified approach is needed to perform these two tasks [...]

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• SDMT VS profiles in heterogeneous granular soil deposits

  F. Totani*, V. Tomei

  ISC2024.

  
  

  Abstract

  Many urbanized areas of the Apennines, in Italy, have complex soil stratifications. A typical example is the historical center of L'Aquila and its outskirts, founded on layers of significantly heterogeneity and struck by a strong earthquake in 2009. Under these conditions, shear wave velocity profiles (VS) obtained from in-situ measurements using SDMT techniques allow reliable analyses of local seismic response. In the soil of L'Aquila, the use of SDMT tests in sand-filled boreholes, following the procedure described by Totani et al. (2009), allowed VS to be measured at considerable depths. This article presents the results of local seismic response analyses conducted to characterize the soil foundation of the hospital complex and adjacent university buildings in L’Aquila before their seismic retrofitting. The authors developed a soil model based on the Vs profiles retrieved from the SDMT tests. This approach provided a detailed understanding of the soil seismic behaviour, essential for the proper characterization of seismic action and consequently, the design of seismic interventions. The study emphasises the importance of accurate soil characterisation prior to seismic upgrades especially in deposits where there are multiple shear wave velocity inversions. The seismic demand coming from the Italian Building Code of 2018, based on the so-called soil categories from equivalent velocity of shear wave, was compared to the results of the local seismic response analysis conducted by using the real Vs profiles from SDMT, which are extended to a much greater depths than those generally required by the regulations.

  Abstract
  Many urbanized areas of the Apennines, in Italy, have complex soil stratifications. A typical example is the historical center of L'Aquila and its outskirts, founded on layers [...]

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• Compacted Landfill Quality Based on DMT

  A. Penna*, A. Macedo, G. Freitas, L. Melo

  ISC2024.

  
  

  Abstract

  For the last 25 years we have been using DMT tests to check the quality of landfill compaction. In several situations of large areas subject to earthmoving, significant pathologies were observed associated with the occurrence of settlements, determined by poor compaction of landfills. These settlements affect the internal floors of buildings, external floors, and sometimes the foundations also. With the intense use of the DMT test as an usual geotechnical investigation practice, it was possible to group the results of these tests, separating them into cases of good, average, and bad behavior. With these systematic observations, it was possible to adapt the traditional graphical representation proposed by Silvano Marchetti and David Crapps, relating the material index "Id" with the dilatometer modulus "Ed", creating regions that represent well-compacted landfills, those with medium compaction and poorly compacted landfills. This system makes it easy to predict the settlement behavior of compacted landfills and represents an appropriate method for checking the quality of compaction.

  Abstract
  For the last 25 years we have been using DMT tests to check the quality of landfill compaction. In several situations of large areas subject to earthmoving, significant pathologies [...]

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