Horst G. Brandes

An automated image analysis procedure to evaluate compacted asphalt sections

A new image analysis program is presented to determine morphological and textural properties of aggregates, asphalt binder and air voids in compacted asphalt mixes. The procedure involves scanning cut sections of laboratory or field specimens and estimating volumetric properties based on a pseudo 3D algorithm. Properties that are calculated include gradation, asphalt content, air void content, amount of flat/elongated particles, distribution of particle orientations, air void profiles, and various particle shape and textural measures. Validation of the code for specimens for which reference values were available indicates generally good predictions, particularly with regard to gradation and asphalt content. The objective of the study has been to develop a robust procedure that is easy to use, cost efficient, environmentally friendly and that can be used as a means to determine asphalt characteristics for quality control and quality assurance purposes. The new analysis technique may also find application in the study of SEM resin-impregnated soil thin sections and concrete cross sections.

Geo-acoustic characterization of calcareous seabed in the Florida Keys

Abstract Geotechnical and acoustic measurements on a set of 35 gravity cores and 11 box cores from two calcareous seabed locations in the lower Florida Keys that are characterized by contrasting environmental settings show significant differences in terms of vertical profiles of physical, acoustic, and geotechnical properties. The lower energy study site of the two is sheltered by the adjacent Dry Tortugas platform complex and reveals a higher porosity surface interval with significant changes in water content, density, and compressional wave velocity within the upper 25 cm. Sediment cores from open-water locations, such as those collected in the study area north of the Marquesas Keys, exhibit higher, less variable densities and lower velocities within the top 25 cm. This is attributed to consolidation associated with cyclic pressure variations from surface swells and strong tidal currents. Acoustic subbottom profiles display good correlation with shell-lag deposits observed in the gravity cores, although acoustic records lack the vertical resolution to detect variations in physical and acoustic properties on the order of those measured in this study. Calculated impedances at depths below 25 cm are significantly higher in the Dry Tortugas area and hence penetration of 4- and 15-kHz acoustic signals is less than at the Marquesas study site. From a geotechnical point of view, the sediments at both sites can be considered to behave like granular materials with little or no plasticity, no significant cementation, low compressibility, permeability highly dependent on void ratio, and moderate to high friction angles. A comparison with deep-sea sediments of mixed mineralogy shows that the effect of increasing calcium carbonate with decreasing clay content is to decrease plasticity and compressibility, and to increase friction angles. In other words, sediments shift from a cohesive to a granular nature as the carbonate content increases.

Physical and acoustic measurements on cohesionless sediments from the northwest Florida Sand Sheet

The effects of grain size and density on compressional wave speed and attenuation are investigated for a clastic silica sand from a seabed study site south of Panama City, Florida, using an automated core logging device that allows for highly accurate, non-destructive, fine-scale measurements to be taken on unopened core sections. Measurements were conducted on relatively undisturbed cores obtained using a large-diameter gravity corer, as well as on reconstituted sections containing sediment segregated into narrow grain size ranges. Findings indicate that whereas density is the primary physical sediment attribute controlling speed, attenuation at 500 kHz is primarily a function of grain size and grain structure. Sandy sediments, particularly those with narrow sorting, are susceptible to liquefaction, which can reduce attenuation dramatically.

Modeling of Seabed Liquefaction and Other Processes Responsible for Mine Burial

A new Office of Naval Research Program is focusing on developing new mine burial prediction models for a number of processes that have been identified for shallow water environments. These processes are briefly reviewed and preliminary modeling aspects and numerical computations for seabed liquefaction due to surface water waves are presented. Both a deterministic and a possible empirical approach are discussed.Copyright

Properties of North Atlantic Abyssal Plain Sediments From High-Quality Long Piston Cores

Two abyssal plain sites on either side of the North Atlantic Ocean are characterized by sequences of distal turbidites and pelagic clays. At the Great Meteor East location, turbidites are quite thick and geotechnical properties such as water content and shear strength can be correlated to the observed stratigraphy. At the Southern Nares Abyssal Plain site, turbidites are much thinner, harder to identify, and less distinct from the pelagic clays. Geotechnical properties there can not easily be correlated to the type of sediment.Copyright

Failure and Post-Failure Mechanics of Submarine Landslides

Theoretical contexts for each of the stages associated with underwater landsliding can be postulated with reasonable confidence, although specific constitutive models require additional work. Also still missing is a comprehensive numerical framework for predicting displacement fields from small pre-failure and post-depositional sediment volume changes and distortions to large-scale inertial sediment wasting. A particular promising modeling approach is outlined herein.Copyright

Effectiveness of Geophysical Methods in Calcareous Harbor Fills

The effectiveness of electromagnetic (EM), ground penetrating radar (GPR) and seismic refraction (SR) were evaluated by surveying a shallow trench in which a number of objects of varying composition and size were buried. The trench was excavated in granular calcareous fill material. An experienced geophysical contractor was asked to provide blind predictions of object locations using each of the techniques in turn. GPR with a 400 MHz antenna was the most successful, followed by SR and EM surveying. GPR and SR were also carried out at the port of Hilo to investigate complex subsurface conditions.Copyright

Permeability of Marine Sediments and Tropical Volcanic Soils

Permeability values for a range of fine-grained deep-sea sediments are presented and evaluated in terms of index properties such as plasticity, grain size and carbonate content. It is found that whereas clay-rich sediments have similar permeabilities to those of equivalent land-based fine-grained soils, the presence of volcanic, carbonate and other non-clay fractions tends to increase permeability somewhat. Volcanic silty-clayey soils from Hawaii have comparable permeability values, although they can be slightly more permeable.Copyright

Engineering Properties of Carbonate Marine Sediments

Geotechnical properties of deep-sea sediments are examined in terms of their plasticity, compressibility and frictional strength characteristics, especially in terms of the relative abundance of carbonate and clay fractions. The effect of carbonate content in excess of 40% is to reduce Atterberg limits and compressibility, and to increase peak friction angles, compared to sediments from the deep ocean that have lower carbonate amounts. The presence of carbonate also tends to reduce flocculation and in situ water content.Copyright

Effect of Volcanic Fines and Gradation on the Deformation and Strength Properties of Detrital Marine Sediments in Hawaii

The compressibility and triaxial response of mixed sediments, consisting of volcanic and marine calcareous fractions, are investigated for a series of samples taken in the nearshore shallow waters of Kaneohe Bay in Hawaii. The results suggest that the presence of coarse detrital calcareous sands dominates the overall behavior if present in sufficiently large quantities, resulting in low compressibilities similar to that of silica sands and friction angles larger than that for most terrigenous sands at comparable densities. Larger than expected frictional resistance is attributed to the volume change tendencies of the non-uniform grains. On the other hand, when significant fines are present, whether of a volcanic nature or consisting of silty carbonate residue, compressibility tends to increase and frictional strength tends to decrease.Copyright