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A Numerical Study for Determining Stress History and Undrained Shear Strength of Clays from Cptu Considering Excess Pore-Water Pressure Measurements

Khodayari, Mohamad Reza | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52318 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadi, Mohammad Mehdi
  7. Abstract:
  8. This study aims to numerically study the penetration process of piezocone (CPTu) in saturated intact clayey soils with emphasis on excess pore-water pressures (EPWPs) generated around the piezocone. It is well agreed in the literature that measurements of pore-water pressure during piezocone penetration tests can play an important role in assessing engineering parameters and characteristics of clays such as undrained shear strength (su) and stress history (overconsolidation ratio, OCR) of the soil. Due to the importance of role of these two parameters in analysis, design and construction in geotechnical projects e.g. slope stability and evaluation of ground settlements induced by super-structural loads, the main objective of the present study is to concentrate on EPWPs generated along the friction sleeve of a penetrating piezocone, in order to propose new, practical and better solutions to correlate field piezocone test measurements to the two aforementioned parameters in clayey soil. High accuracy and no requirement for reference laboratory tests e.g. triaxial and/or oedometer for calibration purposes with in-situ CPTu measurements, can be regarded as the advantages of the solutions presented in this study over the similar-purposed ones existing in the literature.The Present study consists of three main sections including: (i) study of EPWPs generated around the piezocone; (ii) evaluation of undrained shear strength; and (iii) evaluation of stress history; from piezocone test measurements by focusing on aforementioned EPWPs. In the first section, different clayey soils are selected on which the penetration process is numerically analyzed at different presuming stress states and distinctive stress histories. EPWPs generated along the friction sleeve are then scrutinized and an innovative solution is presented for predicting distribution of EPWPs along the friction sleeve to correlate EPWP measured at cone shoulder (Δu2) to the one at above the sleeve (Δu3). In the second section, obtained results and proposed relationships in the first section are utilized, and a new solution is presented for predicting the undrained shear strength at any depth through a clayey soil profile. Finally, in the third section, all the achievements of two previous sections are used, and a method is introduced to predict the overconsolidation ratio of a given clayey soil at a particular depth using the measurements of piezocone test emphasizing on pore-water pressure measurements and pertinent soil parameters.
    Well predicting capability of the numerical modeling procedure are compared with laboratory calibration chamber and centrifuge test results as well as other reliable numerical-experimental studies available in the literature. At the end, the new proposed relationships for evaluation of undrained shear strength and overconsolidation ratio from piezocone test readings, are validated with calibration chamber test results as well as some other existing solutions available in the literature for a relatively large database of field CPTu measurements and also with some case studies performed at different sites worldwide. Better performance of the proposed solutions is indicated
  9. Keywords:
  10. In-Situ Piezocone Penetration (CPTu) ; Clay Soils ; Excess Pore Water Pressure ; Undrained Shear Strength ; Over Consolidation Ratio (OCR) ; Finite Element Analysis

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