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The impact of grain size on the hydromechanical behavior of mudstones
  • Julia Schneider Reece
Julia Schneider Reece
Texas A&M University

Corresponding Author:[email protected]

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Porosity and compression index systematically decrease and permeability systematically increases with decreasing clay fraction over vertical effective stresses ranging from 0 – 21 MPa in reconstituted mudstones from offshore Japan. I use six sediment mixtures composed of varying proportions of hemipelagic mudstone and silt-size silica resulting in clay fractions ranging from 56% to 32% by mass. The hemipelagic mudstone is from Site C0011 drilled seaward of the Nankai Trough, offshore Japan, during Integrated Ocean Drilling Program Expedition 322. Uniaxial resedimentation and constant rate of strain consolidation experiments on these sediment mixtures illuminate how the compression and permeability behavior vary as a function of clay fraction and stress. Backscattered electron microscope images show that as compressible clay particles with small, elongated, and crescent-shaped pores are being replaced by solid quartz grains, the matrix porosity declines and large, jagged pore throats between silt grains are preserved in compaction shadows. This results in reduced compressibilities and increased permeabilities. I compare the behavior of reconstituted samples with that of intact core and field measurements and provide empirical compression and permeability models that describe the evolution of porosity (void ratio) and permeability with vertical effective stress and as a function of grain size. Characterizing the in situ hydromechanical properties of subduction inputs is critical in order to relate input sediments to those at frontal thrust regions and understand the mechanics of accretionary prisms, plate boundary earthquakes, and fault slip behavior at subduction zones.
Aug 2021Published in Geochemistry, Geophysics, Geosystems volume 22 issue 8. 10.1029/2021GC009732