The Impact of Grain Size on the Hydromechanical Behavior of Mudstones

Abstract

The consolidation behavior of mudstone is controlled by the clay fraction and affects a wide range of deformation and fluid transport processes in accretionary wedge systems. I analyze the compression and permeability behavior of six sediment mixtures based on uniaxial resedimentation and constant rate of strain consolidation data. The sediment mixtures are 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. I show that porosity and compression index consistently decrease and permeability consistently increases with decreasing clay fraction over vertical effective stresses ranging from 0 to 21 MPa. Backscattered electron microscope images reveal that matrix porosity declines and large, jagged pore throats are being preserved in compaction shadows between silt grains as the clay fraction decreases. I compare the behavior of reconstituted samples with that of intact core and field measurements and interpret that increasing creep with depth and different mudstone fabrics explain differences in their compression curves. Finally, I 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 predict pore fluid pressures and compaction‐driven fluid sources within the outer part of the accretionary prism.

Hydromechanical Effects of Micro‐Organisms on Fine‐Grained Sediments During Early Burial

“…Resedimentation experiments are used to replicate natural burial processes of fine‐grained sediments (e.g., Reece, 2021; M. Santagata & Kang, 2007; Schneider et al., 2011) and follow the procedure of a traditional oedometer test as specified in ASTM Standard D2435 (ASTM International, 2020). We use this technique because it allows us to control the stress conditions acting on a mudstone, create a replicable mudstone sample (e.g., Reece, 2021; M. Santagata & Kang, 2007; M. C. Santagata et al., 2005), eliminate sample disturbance, isolate variables affecting consolidation, and perform a systematic study to address fundamental research questions.…”

“…Resedimentation experiments are used to replicate natural burial processes of fine-grained sediments (e.g., Reece, 2021;M. Santagata & Kang, 2007;Schneider et al, 2011) The first step in the resedimentation process is to mix a dry mudstone powder with a pore fluid solution (explained below) to create a stable and homogeneous slurry.…”

“…The geological and geotechnical engineering communities have extensively studied the compression and permeability behaviors of fine‐grained sediments, such as mudstones (Hart et al., 1995; Neuzil, 2019; Reece, 2021; Rubey & Hubbert, 1959; Skempton, 1970; Terzaghi, 1943; Yang & Aplin, 2004). Mudstones exhibit a dramatic decline in porosity within the first several hundred meters of burial followed by a gradual decline through deeper burial (Dzevanshir et al., 1986; Ingebritsen et al., 2006; Mondol et al., 2007).…”

“…Mudstones exhibit a dramatic decline in porosity within the first several hundred meters of burial followed by a gradual decline through deeper burial (Dzevanshir et al., 1986; Ingebritsen et al., 2006; Mondol et al., 2007). Additionally, the compressibility (rate of porosity loss with effective stress) of a mudstone is dependent on its grain size, grain shape, stress history, and clay mineralogy, with clay‐rich mudstones being more compressible (more porosity loss) than silt‐rich mudstones (Dewhurst et al., 1998; Reece, 2021). This decrease in porosity with progressive burial results in a decrease in mudstone permeability, where porosity and permeability have a log linear relationship (e.g., Neuzil, 1994, 2019; Reece et al., 2012; Schneider et al., 2011).…”

Factors affecting the oedometric modulus of till soil

“…In such cases, soil compressibility and the compression index (C c ) increase (Fig. 2), while permeability decreases (Akayuli et al 2013;Reece 2021). Under applied load, the mechanism of soil failure changes from the splitting one to the shear one with the increasing soil particle size (Wang et al 2021).…”