Documents published in Scipedia

• Effect of clay activity and interface surface material on residual undrained interface strength: implications on pipeline-seabed interaction analysis

  R. Das*, Z. Westgate, A. Sephoori, S. Garmon

  ISC2024.

  
  

  Abstract

  Characterization of the geomechanical behavior of the seabed along a high-pressure high-temperature (HPHT) pipeline route is important for understanding risks from geohazards and thermally induced displacements such as axial walking. Axial resistance to pipeline displacement, from the friction between seabed and the contact surface of the pipe, can be estimated through laboratory tests using interface shear box (ISB) and tilt table. Tests performed by NGI in several developements in Gulf of Mexico, South America, and West Africa revealed significant variation in shear resistance, potentially associated with the type of interface material and surface roughness characteristics. This paper illustrates the effect of clay activity and interface surface material on the residual undrained interface strength estimated from interface shear box tests. Two cohesive soil batch samples with varying activity were tested using two different interface plates (steel and silicon carbide sandpaper) of comparable surface roughness. Each soil batch-interface combination was tested under three different initial effective normal stresses and two different over consolidation ratios (OCRs). Undrained residual interface strength envelopes were developed for each soil batch-interface combination. The results from tests performed on steel interface showed an increase in residual undrained interface strength with plasticy and clay activity whereas a reverse trend was observed in the results of the tests performed using the sandpaper interface. This reinforces the importance of the choice of interface plate material (in addition to surface roughness) for PSI testing program to accurately capture the resistances offered by the seabed to pipe displacement.

  Abstract
  Characterization of the geomechanical behavior of the seabed along a high-pressure high-temperature (HPHT) pipeline route is important for understanding risks from geohazards [...]

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• Uncertainty Estimation on Active Surface-Waves Based Tests

  E. Saez*, F. Hernandez, R. Vega, J. Tiznado, R. Gallardo, F. Leyton, G. Montalva, C. Pasten

  ISC2024.

  
  

  Abstract

  Geophysical methods based on surface waves have become very popular in recent decades due to their versatility and reduced cost of execution compared to other invasive techniques. Due to space constraints in urban environments, measurements with linear arrays using active and passive techniques are usually combined to reach the exploration depth required by seismic site classification regulations. Although several good practice guidelines have been developed for performing this type of geophysical explorations, one of the remaining major challenges is to relate the results of these explorations to uncertainty metrics. In the case of active tests, there are effects associated with the filtering method used to eliminate the near and far-field effects, as well as other difficulties related to higher Rayleigh-modes or heterogeneities of the site. In this paper, we study the effect of body waves unavoidably induced in active tests on the proper determination of the dispersion curve of a site. For this purpose, active tests are carried out using triaxial geophones to extract from the records the motion effectively corresponding to Rayleigh waves by means of the Normalized Inner Product (NIP) technique. The results show that the effects of body waves are negligible for frequencies above about 8 Hz, but below this value, in the transition zone with ESPAC passive tests, the differences can be more significant. These results are used to introduce uncertainty indicators in this type of explorations

  Abstract
  Geophysical methods based on surface waves have become very popular in recent decades due to their versatility and reduced cost of execution compared to other invasive techniques. [...]

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• Record of long-term field observation of large-scale cutting slope

  S. Hijikata*, R. Kuwano, H. Nakamura

  ISC2024.

  
  

  Abstract

  This paper describes the interpretation of landslide behavior and verification of the effectiveness of countermeasure works based on the results of long-term field observations at a large-scale cutting site. The site has been subjected to various deformations since its construction due to its unique geological conditions, and has been monitored extensively by GPS surface displacement gauges, borehole inclinometers, anchor load cells, and water level gauges as an important monitoring site even after it was put into service. In the sixth year after the site was opened to public use, we assumed underground slip surfaces based on an interpretation of the observed data, constructed additional countermeasures, and verified the effectiveness of the countermeasures through continuous field observation of intermittent landslide behavior observed in several areas of the slope. As a result, it was confirmed that the displacement had not been settled even five years after the construction of the additional countermeasures and that a new slip surface had emerged, indicating the necessity of improving field observation techniques and data interpretation as well as continuous monitoring of this site

  Abstract
  This paper describes the interpretation of landslide behavior and verification of the effectiveness of countermeasure works based on the results of long-term field observations [...]

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• 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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