Pore Size Changes in Marine Soft Soil under Various Freezing Conditions

Artificial freezing methods can help highlight the mechanical properties of marine clay. The construction of cross passages in metro tunnels employs the freezing method. Freeze–thaw circulation, which is part of the process, affects the engineering properties of clay and produces differential settling. This paper describes the percentages of specific diameters of frozen–thawed soil under different freezing temperatures, measured with the help of nuclear magnetic resonance (NMR). In response to the experimental results, a weakening effect of freezing temperature and speed on soft soil is proposed. All sizes of undisturbed soil pores tend to increase under various freezing temperatures. Owing to differences in free water content, the water in medium pores freezes quicker than that in tiny pores. The quicker the freezing, the greater the resulting void ratio. Finally, potential reasons for changes in pore size under different freezing conditions are explained from a microcosmic perspective.

On the collision of rods in a quiescent fluid

Rods settling under gravity in a quiescent fluid can overcome the bottleneck associated with aggregation of equal-size spheres because they collide by virtue of their orientation-dependent settling velocity. We find the corresponding collision kernel Γrods=lβ1ΔρVrodg/(16Aμ), where l, A, and Vrod are the rods’ length, aspect ratio (length divided by width), and volume, respectively, Δρ is the density difference between rods and fluid, μ is the fluid’s dynamic viscosity, g is the gravitational acceleration, and β1(A) is a geometrical parameter. We apply this formula to marine snow formation following a phytoplankton bloom. Over a broad range of aspect ratios, the formula predicts a similar or higher encounter rate between rods as compared to the encounter rate between (equal volume) spheres aggregating either by differential settling or due to turbulence. Since many phytoplankton species are elongated, these results suggest that collisions induced by the orientation-dependent settling velocity can contribute significantly to marine snow formation, and that marine snow composed of elongated phytoplankton cells can form at high rates also in the absence of turbulence.

Integrity Management Program for Geo-Hazards in the OCENSA Pipeline System

Oil pipelines systems for hydrocarbons transportation are linear projects that can reach great lengths. For this reason, theirs paths may cross different geological formations, soil types, navigable or torrential waters; and they may face geotechnical and hydrological instability problems such as creeping slopes, geological faults, landslides, scour and differential settling which causes different relative movements between the soil and the pipeline. The OCENSA (Oleoducto Central S.A) 30″ and 36″ diameter system was built in 1997 to transport crude oil from the eastern foothills of the Andes to the Caribbean Coast along some 830 km of the Eastern Andes mountains range and the spurs of the central Andes mountains range of Colombia: it was a major challenge to secure the integrity of the pipeline in the face of natural events.

Repercussions of differential settling on sediment assemblages and multi-proxy palaeo-reconstructions

Microfossils preserved in marine sediments are at the centre of numerous proxies for palaeoenvironmental reconstructions. Their precision is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. In this paper, we assess the possibility of a pre-depositional bias in sediment assemblages caused by horizontal drift, due to differential settling velocities of sedimenting particles based on their shape, size and density. We calculate the lateral transport undergone by planktic foraminifera and a range of other proxy carriers in several regions with high current velocities. Lateral transport of different planktic foraminiferal species is minimal due to high settling velocities; no significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. Diatoms, radiolaria and faecal pellets can be transported up to 500 km in some areas. This transport bias suggests that sediment assemblages could contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction. For example in the Agulhas current, transport can lead to differences of up to 2 °C in temperature reconstructions between different proxies. For future palaeoenvironmental reconstructions, further sediment-trapping studies and multi-proxy analyses should attempt to quantify the margin of error associated with particle transport.

Integrity Management Program for Geo-Hazards in the OCENSA Pipeline System

Oil pipelines systems for hydrocarbons transportation are linear projects that can reach great lengths. For this reason, theirs paths may cross different geological formations, soil types, navigable or torrential waters; and they may face geotechnical and hydrological instability problems such as creeping slopes, geological faults, landslides, sudden river surges and differential settling which causes different relative movements between the soil and the pipeline. The OCENSA (Oleoducto Central S.A) 30″ and 36″ diameter system was built in 1997 to transport crude oil from the eastern foothills of the Andes to the Caribbean Coast along some 830 km of the Eastern Andes mountains range and the spurs of the central Andes mountains range of Colombia: it was a major challenge to secure the integrity of the pipeline in the face of natural events.

Palaeoenvironmental significance of clay minerals in Upper Cenomanian–Turonian sediments of the Western High Atlas Basin (Morocco)

Upper Cenomanian–Turonian clay mineral assemblages of sediments cropping out in the Western High Atlas basin are studied in four sections. Smectite and mixed-layer illite-smectite (I-S) have been identified as major constituents of the deposits. The composition of clay associations in black shales and associated sediments varies considerably according to age, but usually depends either on the general lithology, the abundance of organic matter, or the depth of burial. A distinct correlation is evident between clay mineral distribution and sea-level. Smectite and mixed-layer I-S with greater percentages of smectite layers increase in sediments deposited during transgressive periods, whereas they decrease progressively in the shallower facies deposited during regression in favour of illite and mixed-layer I-S with a greater percentage of illite. The vertical evolution and lateral distribution of clay assemblages and their relationships with sea-level as well as the palaeogeographic conditions prevailing during the Late Cenomanian–Turonian period (flattened topography and arid climate), indicate a detrital origin of the smectite minerals and a distribution pattern controlled by differential settling processes.