Reliability measures for consolidation settlement by means of CPT data

Pouya Pishgah, Reza Jamshidi Chenari

In the proceedings of: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Reliability-based Design

ABSTRACT: A methodology is introduced for reliability calculation of consolidation settlement based on cone penetration test (CPT) data. The measured data of corrected cone tip resistance () is detrended using a quadratic trend and the residuals are assumed to be lognormally distributed random field. Realizations of is generated by using statistical parameters of residuals including standard deviation and the scale of fluctuation. The quadratic trend and the generated residuals are then combined to correlate shear and bulk moduli as input consolidation properties for coupled analysis and subsequently consolidation settlement was calculated by using finite difference method adopted in Monte Carlo simulations. The results of reliability analysis are presented describing the range of possible settlements by considering characteristics of uncertainties involved at the particular site. Maximum possible settlements must be smaller than the allowable settlement to guarantee proper performance.

RÉSUMÉ: Une méthodologie est introduit pour le calcul de la fiabilité d'établissement de consolidation sur la base de données de test de pénétration de cône (CPT). Les données mesurées corrigées résistance à la pointe du cône () est redressée à l'aide d'une tendance quadratique et les résidus sont supposés être distribués lognormale champ aléatoire. Réalisations de est généré en utilisant des paramètres statistiques des résidus dont l'écart-type et l'ampleur des fluctuations. La tendance quadratique et les résidus générés sont ensuite combinées pour corréler les modules de cisaillement et en vrac en tant que propriétés de consolidation d'entrée pour l'analyse couplée puis tassement de consolidation a été calculé en utilisant la méthode des différences finies adoptée en simulations de Monte Carlo. Les résultats de l'analyse de fiabilité sont présentés pour décrire la gamme des implantations possibles en tenant compte des caractéristiques de incertitudes liées à un site particulier. Colonies maximales possibles doivent être plus petit que le règlement admissible pour garantir un bon fonctionnement. 1 Introduction The importance of variability analysis is increasingly recognized in geotechnical engineering as reliability based design (RBD) methods are assuming a prominent role for the calibration of new design codes. However, in geotechnical practice, there has been rather slow progress in employing RBD, compared to other engineering disciplines. A primary reason for this slow progress is difficulty in estimating the variability of the design properties of geo-material, which is essential for any RBD procedure. A fundamental problem is the lack of data. There is a tradition of basing conclusions in laboratory testing programs on small numbers of tests. It is quite common to encounter laboratory programs consisting of three or four consolidation tests. Therefore there are seldom enough data to support broad conclusions about the statistics of soil properties. Several studies have been published on the variability of the properties of soils (e.g., Phoon and Kulhawy 1995). Sometimes the values in these publications are simply adopted into reliability calculations without further efforts to establish the variability for the particular project at hand. Despite the excellent work that has been done on this issue, it is not a closed matter, and more work needs to be done. In particular there needs to be more work on how much effort is required to improve the estimates for a particular site. However calculating the actual variability of soil properties is one of the unresolved problems in geotechnical risk and reliability (Christian and Baecher 2011). Among in situ testing methods, cone penetration (CPT) measurements are ideal for assessing soil variability because a large volume of near continuous data can be collected in a cost-effective way, the test has good repeatability, the equipment is highly standardized, and the procedure is well-defined and almost operator-independent. Moreover, CPT has strong theoretical basis for interpretation and numerous semi-empirical correlations have been developed to estimate geotechnical parameters from the CPT for a wide range of soils (e.g, Robertson 2009). A number of researches on the application of CPT measurement in reliability analysis for different geotechnical problems have recently been published (e.g., Uzielli 2004 ; Haldar and Babu 2008 ; Doherty and Gavin 2010 ; Kenarsari et al. 2011 and 2012). In this article, a methodology is introduced for reliability calculation of consolidation settlement based on statistical review of CPT data. This general approach can be an effective technique to predict consolidation settlement using probabilistic analyses considering

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