Impact of pore fluid chemistry on fine‐grained sediment fabric and compressibility

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 5495-5514, doi:10.1029/2018JB015872.Fines, defined here as grains or particles, less than 75 μm in diameter, exist nearly ubiquitously in natural sediment, even those classified as coarse. Macroscopic sediment properties, such as compressibility, which relates applied effective stress to the resulting sediment deformation, depend on the fabric of fines. Unlike coarse grains, fines have sizes and masses small enough to be more strongly influenced by electrical interparticle forces than by gravity. These electrical forces acting through pore fluids are influenced by pore fluid chemistry changes. Macroscopic property dependence on pore fluid chemistry must be accounted for in sediment studies involving subsurface flow and sediment stability analyses, as well as in engineered flow situations such as groundwater pollutant remediation, hydrocarbon migration, or other energy resource extraction applications. This study demonstrates how the liquid limit‐based electrical sensitivity index can be used to predict sediment compressibility changes due to pore fluid chemistry changes. Laboratory tests of electrical sensitivity, sedimentation, and compressibility illustrate mechanisms linking microscale and macroscale processes for selected pure, end‐member fines. A specific application considered here is methane extraction via depressurization of gas hydrate‐bearing sediment, which causes a dramatic pore water salinity drop concurrent with sediment being compressed by the imposed effective stress increase.DOI U.S. Geological Survey (USGS); U.S. Department of Energy (DOE) Grant Numbers: DE‐FE00‐28966, DE‐FE00‐261662019-01-1

Review of In Situ Measurements as Indications of Liquefaction Potential at Numerous Sites

Current practice for assessing liquefaction potential of granular soils depends heavily on in situ indices of density, and sometimes direct measurements of density. Correlations have been developed to predict resistance to liquefaction as a function of standard penetration test (SPT) blow count, cone penetrometer (CPT) tip resistance, shear-wave velocity (VS), or other index property. Recognizing that each correlation entails its own uncertainties, and that different indices of liquefaction potential may provide conflicting conclusions, the Bureau of Reclamation reviewed in situ test results from a large number of sites where multiple tests had been used. The goals were to 1) evaluate consistency among the various indices of liquefaction potential, 2) compare indirect indices of density, such as penetration resistance, against actual density measurements, and 3) survey current practice throughout the industry. This paper will provide a summary of the results

Correlations of Seismic Velocity with Depth

Correlations of seismic velocity have been made with depth for various geotechnical classifications of soil and rock described. The seismic velocities have been found to be dependent upon geologic age, gravel content, water table depth, dry density and depth of overburden

What causes large submarine landslides on low gradient (

Submarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine mega-slides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (<0.15 m/ky), such as off north-west Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties and stratigraphic layer configurations. The simulations show that in general it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes

Geotechnical properties of carbonate soils with reference to an improved engineering classification

Includes bibliography.The engineering behaviour of carbonates differ substantially from quartz based soils. A review of the literature was undertaken in an attempt to identify relevant parameters which could provide the basis for an improved engineering classification. Carbonate content, cementation, crushability, particle size distribution and Atterberg limits were found to be relevant to engineering behaviour of carbonates, and should be included. The maximum obtainable void ratio (emax), which is related to the particle shape distribution, has been proposed as an additional index for carbonate sands. Results from direct shear tests showed that this parameter correlates well with crushability and compressibility. It is recommended that this parameter (emax) as determined in the test devised by Kolbuszewski (1948), should be adopted as an index property for classifying carbonate sands

Climate-controlled submarine landslides on the Antarctic continental margin

Antarctica’s continental margins pose an unknown submarine landslidegenerated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides

Advanced CPTu and laboratory investigation of geotechnically critical on-shore and near-shore soft sediments in Germany and New Zealand

The integrated Coastal Zone and Shelf Sea Research (INTERCOAST) organization, a cooperative German and New Zealand multidisciplinary research program, concentrates on scientific issues in social and natural science disciplines in the both countries. INTERCOAST 4 (IC4) Ph.D. program tackled geotechnically problematic soft soils such as peat, clay and clayey silts which have posed considerable challenges to geotechnical engineers in all parts of the world during design and construction process. In Germany, peat is one of the prevailing groups of soil which is present in both off-shore and on-shore areas and exhibit properties such as high compressibility and low shear strength; these properties may cause complications such as differential settlement or failure in structures built on such soils. Removal or stabilization are the most important methods used to overcome geotechnical problems related to peat soilsâ engineering characteristics. In New Zealand, many off-shore and on-shore areas of the North Island are covered by volcanic ash, and weathering of this material has resulted in formation of clay minerals. Dredging of volcanic ash layers often causes major turbidity in the water column and poses risks to wildlife and humans. Due to very low effective shear strength and high sensitivity of volcanic ash, these sediments are not considered to be appropriate for off-shore construction and installation purposes. On-shore weathered volcanic ash having low permeability acts as a barrier to fluid flow, for example infiltration of rainfall, and prevents pore pressure from dissipating. This special characteristic may lead to failure of slopes with volcanic ash materials because increases in pore pressure lowers the effective normal (vertical) stress, and therefore shear strength. The aim of this dissertation is to utilize in-situ and laboratory measurements in order to (i) present soil mechanical intervention for stabilization of peat using cost-effective and environmentally-friendly stabilization method and focus on a comparison between mechanical characteristics of undisturbed and stabilized peat, (ii) investigate geological setting, lithology and depositional history of off-shore sub-seafloor volcanic soils and determine geotechnical properties of near-surface sediments and (iii) look into the role of volcanic soils in occurrence of on-shore landslides

Compressibility, structure and leaching assessments of an alluvium stabilised with a sewage treatment sludge biochar-slag binder

Deep dry soil mixing is a ground improvement technique commonly used for treating soft soils. Portland cement is the most commonly used binder, but its long-term use is unsustainable due to the high CO2 emissions associated with its manufacture. Alkali-activated cements are a low carbon alternative, involving the use of pozzolanic industrial by-products and wastes. This study provides insights into the one-dimensional compressibility, internal cemented ‘structure’ and leaching characteristics of an alluvial soil stabilised with a new 100% waste-based cementitious binder, comprising biochar as the alkali activator and blast furnace slag as the pozzolan. The binder has recently been demonstrated by the authors to satisfy European soil stabilisation 28-day compressive strength requirements when using dosages of 7.5 and 10% by dry weight. The biochar successfully activated the pozzolanic properties of the slag; whereby the stabilised soil mixtures developed a cemented microstructure which resulted in improvements in compressibility and stiffness. Oedometer datasets for untreated, biochar-slag- and CEM-II-stabilised alluvium were successfully processed through a framework developed by the authors to quantify their artificially cemented internal structure, for use as an input parameter in advanced constitutive soil models. Leaching results indicated that the heavy and trace metal content of 1- and 28-day cured biochar-slag stabilised samples complied with UK and European waste acceptance criteria, and mean baseline heavy metal concentrations for groundwater resources in England and Wales. This study advocates the new biochar-slag binder as a suitable replacement for Portland cements in soil stabilisation, contributing to the path towards net zero carbon emissions for the ground engineering sector and improving the circular economy

Physical properties of golf and sports turf root-zones as affected by amendments, construction methods, and management practices

Inorganic soil amendments have been suggested for use in sand-based golf and sports turf root zones to alleviate soil compaction, increase water retention and hydraulic conductivity. The overall objectives of my research are to investigate the physical properties of sand-based media modified by soil amendments and to quantitatively evaluate sand particle shape and roundness for sports turf surface stability.;On a flat green study we found that porous ceramic clay (PCC) increased both Ksat and water retention. Hydraulic conductivity of the sand/inorganic mixtures decreased over two years, although some increase were observed each spring.;In a laboratory study simulating freeze/thaw effects, we found that after 20 freeze/thaw cycles, sand amended with polymer coated clay (PC) had a 7.6% decrease in bulk density from the compacted sample. The percentage weight of the finest particles increased due to freeze/thaw cycles. After 20 cycles of freeze/thaw, Ksat values of sand amended with PCC and calcined diatomaceous earth (CDE) were 25 and 33% higher than the control, respectively.;A sloped research green was topdressed with mixtures of sand and soil amendments. During most of the growing season in 1999, the preloaded fertilizer in zeolite clinoptilolite might be responsible for the better quality of this product during non-stressed period. Its low turf quality after water stress and in the spring of 2000 could have been caused by toxicity from its high Na and K contents.;In the study of sand shape and roundness evaluation, mason sand, concrete sand, silica sand, crushed brick, crushed glass, and crushed stone were used to cover a wide range of shapes and roundness. We used glass beads as the base line. A roughness index (Ir) was proposed as the ratio of the particle surface area to the area of a sphere of the same volume. Angle at repose, coefficient of uniformity (CU), coefficient of friction (CF), and two-dimensional image analysis were also included in the evaluation of the materials. Principle component analysis indicated that only three factors---angle at repose, CU, and Ir---are necessary to explain 98.5% of the variance contributing to surface stability of sand-based media