Development of a multifunctional sediment consolidometer: Capable of concurrent measuring of bidirectional electrical effects, salinity, and fluid compositions
We report here on the initial results from developing a prototype consolidometer focused on determining the anisotropic resistivity evolution in water-saturated sediments during burial. A key difference in this apparatus from comparable versions is the ability to simultaneously measure resistivity horizontally and vertically (parallel and perpendicular to σ1 respectively), which allows for anisotropic effects to be determined. Complexities arise when clay fabrics generate anisotropic resistivity, along with two forms of total pore water (dual water). Dual water exists in consolidated high surface area sediments, and is comprised of: (a) Electric Double Layer (EDL) attached to mineral surfaces, and (b) bulk pore water in the pore center. The EDL water is more saline and conductive than bulk water under pressure due to the density of counter ions required to balance the negative surface charge. Clays have comparatively large surface areas and EDL components compared to other sediments. As a result, clay-dominated sediments (a) have anomalously low resistance compared to low surface area granular sediments and (b) a net pore resistivity that should decrease during consolidation due to the preferential loss of low salinity bulk pore water and retention of the saline conductive EDL water. The EDL increased salinity (reduced pore resistivity) effects should become acute at low porosities when the few tens of nanometer-thick EDL films become compressed (Brown et al., 2017) and are expected to partially counter the expected overall increases in resistivity with general porosity reduction. The anisotropy due to clay compaction fabrics is also expected to become simultaneously acute during compaction, addressing both effects concurrently is beneficial. Given this novel approach, this is a primarily technical report on developing a prototype consolidometer capable of simultaneously measuring porosity evolution and anisotropic resistivity, along with fluid composition and salinity. Future projects will address several associated themes related to consolidation, fluid flow, nanofilm interactions, and ultrafiltration responses in active tectonics and sedimentary environments. This report also briefly describes the collection of over 270 hold-slip-hold trials on westerly granite. The data will be used in the future to build upon works like Brown et al. 2012 by incorporating a varied composition and fluid content(Mitchell et al., 2011, 2016; Brown and Fialko, 2012). The main goals of this study are to continue work on wet melt mechanisms where fluid content effects were evaluated and incorporate clays into the mixture.