Date of Award

Fall 11-5-2015

Level of Access

Open-Access Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

Advisor

Melissa E. Landon

Second Committee Member

Thomas C. Sandford

Third Committee Member

Edwin Nagy

Abstract

The seismic cone penetration test with pore pressure measurement (SCPTu) is a geotechnical investigation technique which involves pushing a sensitized cone into the subsurface at a constant rate while continuously measuring tip resistance, sleeve friction, and pore pressure resulting from soil shearing. Additionally, shear wave velocity measurements can be collected at discrete intervals throughout the test. Empirical and theoretical correlations have been developed between these measurements and soil engineering properties such as preconsoldiation pressure and undrained shear strength. Soil classification, location of silt/sand seams, seismic design parameters, and liquefaction potential can also be obtained from SCPTu results.

The objective of this thesis is to evaluate the SCPTu as a tool to predict engineering properties of the Presumpscot Clay. When paired with conventional borings, the SCPTu can provide a more comprehensive understanding of the subsurface, help refine geotechnical analyses (i.e. settlement, slope stability), and give engineers access to continuous stratigraphy and engineering parameters throughout an entire deposit rather than at discrete sampling depths common for conventional field vane shear tests (FVT) and boring investigations for the deposit.

Four locations where the Presumpscot Formation exist in Maine were selected for investigative and laboratory testing programs. At each location, SCPTu and conventional borings were conducted. During the conventional borings, field vane shear tests were performed and Shelby tube or Sherbrooke block samples were collected for laboratory testing at 5 foot depth intervals. High quality samples were analyzed in the laboratory to determine index properties, consolidation behavior, and undrained shear strength characteristics. With these results, published correlations of SCPTu results to engineering parameters were verified and refined for the Presumpscot Formation.

Findings from the study indicate that predicting classification of the Presumpscot clay from CPTu classification charts is best performed using Robertson (1990) and Schneider et al., (2008), both of which use the relationship between normalized tip resistance and normalized pore pressure. Applying a k-value of 0.33 to measurements of tip resistance provides a reasonable estimate of preconsolidation pressure and OCR at any depth. There appeared to be an increasing relationship between k-value and OCR which should be further investigated. CPTu cone factors N­kt­ and N­Du,­ used to estimate undrained shear strength, were higher for the Presumpscot clay than most suggested values from similar studies in clay. Furthermore, s­u­ determined from triaxial compression versus direct simple shear caused a difference in both N­kt­ and N­Du­ of at least 5.0. Site-specific correlations resulted in the best CPTu correlation to engineering properties of the Presumpscot clay.

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