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Your search keyword '"Germaine, John T."' showing total 12 results
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12 results on '"Germaine, John T."'

8. Consolidation properties and structural alteration of Old Alluvium

Author

Massachusetts Institute of Technology. Department of Civil and Environmental Engineering, Nikolinakou, Maria A., Whittle, Andrew J., Germaine, John T., Zhang, Guoping, Massachusetts Institute of Technology. Department of Civil and Environmental Engineering, Nikolinakou, Maria A., Whittle, Andrew J., Germaine, John T., and Zhang, Guoping

Abstract

We present experimental observations and a conceptual model for understanding the compression and swelling characteristics of Old Alluvium (OA) from San Juan, Puerto Rico. Prior studies have classified OA as a transported, in situ weathered tropical soil whose intact macrostructure comprises a cemented, pseudo-silt with a mixture of quartz grains and aggregated clay particles. The aggregates include mixtures of kaolinite and smectite coated by Fe-oxides. The Fe-oxides also act as cementing agents between the particles. This study describes results from a series of high-pressure (up to 63 MPa) incremental consolidation tests. Breakdown of the clay aggregates and cemented structure is observed through changes in the compression properties, significant swelling during unloading, and an extraordinary reduction (i.e., by three orders of magnitude) in the coefficient of consolidation. These experimental observations are explained by a combination of mechanical processes, comminution and breakdown of cementing bonds, and physicochemical changes linking pore fluid in the intra- and inter-aggregate pore space. These processes alter the fundamental particle size distribution and macro-porosity of the soil and activate the swelling potential of the smectites concealed by the Fe-oxides coating in the intact material. The experimental observations provide the basis for the formulation of a constitutive model to describe macroscopic compression and swelling behavior of Old Alluvium and offer a framework to understand the response of piedmont transported residual soils found elsewhere.

Published
2022

12. The impact of clay fraction on the strength and stress ratio (K0) in Gulf of Mexico mudrocks and quartz silt mixtures: implications for borehole stability and fracture gradient.

Author

Zablocki, Mark, Germaine, John T., Plumb, Richard, and Flemings, Peter B.

Subjects
CLAY, SILT, STRAINS & stresses (Mechanics), QUARTZ, PREDICTION models, MIXTURES
Abstract

Mudrock strength parameters are required to improve the prediction of fracture gradient during drilling in poorly consolidated formations. Understanding the influence that mineral composition and consolidation stress have on the mechanical properties of mudrocks aids safe well design. Small changes in the mudrock clay content are shown to have significant effects on two important engineering parameters: the lateral stress ratio at rest, K0, and the critical state effective friction angle, ϕ ′cs. A laboratory-testing programme using quartz silt and a Gulf of Mexico clay mixture investigates the effects of mudrock clay content on K0 and ϕ ′cs at two stress levels: 1 and 10 MPa. Values of K0 and ϕ ′cs were obtained by subjecting composition-controlled clay–silt specimens to a drained uniaxial vertical strain (K0 consolidation) phase, followed by an undrained compression triaxial shear phase. Triaxial tests illustrate consistent and systematic increases in K0 and decreases in ϕ ′cs, with increases in clay content at both stress levels. Stress dependence is observed through increases in K0 and decreases in ϕ ′cs with increases in stress level. Stress-dependent behaviour is shown to be more pronounced in mudrocks of high clay content. A predictive model is presented for K0 in normally consolidated mudrocks, as a function of clay content and effective stress. The model is used to calculate the fracture gradient (least horizontal stress) profile at the International Ocean Drilling Program (IODP) Expedition 308 Site 1324. The estimated fracture gradient illustrates the effects of clay content and consolidation stress on safe mud weight design. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure [ABSTRACT FROM AUTHOR]

Published
2022
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