## LSU Historical Dissertations and Theses

1993

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Civil and Environmental Engineering

Mehmet T. Tumay

#### Abstract

The electronic piezocone penetrometer is potentially a very powerful in-situ testing device used for soil profiling and in the determination of engineering soil properties. The focus of this research is on the laboratory calibration of a miniature piezocone penetrometer in cohesive soil specimens instrumented to monitor the spatial pore pressure distribution. Two automated slurry consolidometers were developed for this research that were successful in preparing homogeneous and reproducible cohesive soil specimens. The results of eight miniature piezocone penetration tests (PCPT) and three miniature quasi-static friction cone penetration tests (QCPT) performed in a flexible double wall calibration chamber system are presented. The influence of soil type, stress history, penetration boundary conditions and filter locations on PCPT data are investigated. The PCPT results are evaluated using some of the existing methods to estimate the undrained shear strength, s$\sb{\rm u};$ lateral stress coefficient, K$\sb{\rm o};$ over-consolidation ratio, OCR; and the radial coefficient of consolidation, c$\sb{\rm r}.$ The influence of lateral stress and soil type on the empirical cone factor and the pore pressure factor used to estimate s$\sb{\rm u}$ are investigated. The influence of lateral stress on penetration pore pressures is investigated and the validity of a recent method for K$\sb{\rm o}$-profiling is verified. The OCR and the K$\sb{\rm o}$ are found to influence the penetration depth required to attain a steady excess pore pressure value. An existing model to predict OCR from PCPT data is modified to include the influence of K$\sb{\rm o}.$ The method is used to evaluate the OCRs of the chamber specimens and its validity is further verified by application to well documented field sites. The need to base the interpretation of c$\sb{\rm r}$ on the initial dissipation values of the excess pore pressure instead of the penetration pore pressure and also the need to include the influence of stress history on the proposed time factors are realized. The importance of the rate of penetration and the pore pressure dissipation that occurs even during piezocone penetration while interpreting dissipation data on the piezocone shaft is recognized.

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