Incoherent Sediments Research Articles

РОЗРОБЛЕННЯ ТА УДОСКОНАЛЕННЯ МЕТОДІВ РОЗРАХУНКУ ДЕФОРМАЦІЇ НЕРЕГУЛЯРНИХ РУСЛОВИХ ФОРМ ТА ОСНОВ РІЧКОВИХ СПОРУД ПІД ДІЄЮ ПОВЕНЕВИХ ТЕЧІЙ

Abstract Introduction. The article presents the results of the study of irregular bottom river forms and foundations of structures, as well as coastal forms under the action of surface channel currents. It is assumed that the development of channels occurs due to the action of natural hydromorphodynamic river processes during the long stages of rivers existence formed in accordance with topographic, geological and hydrometeorological conditions. Problem Statement. Flow velocities are determined by a system of equations for the kinematics of channel flows and sediment transport, which is built on the basis of averaging the depth of flow. Purpose. Application of the developed methods of solving problems in the spatial dimension for the study of turbulent effects in the interaction with structural elements. The development of methods for applying the spatial model will be carried out at the next stage. Methods of research. Differential equations describing a nonstationary depth-averaged flow are solved using the FST2DH numerical model, which implements the finite element method. The steps typically performed when using FST2DH to study surface water flow and sediment transportation require the general necessary geographic information systems to build a network and assign boundary conditions. The equations for calculating channel erosion and erosion of bridge piers in bound soils are also considered, where it is shown that erosion depends more on soil properties than for the case of incoherent sediments, but can reach the same erosion depths with longer multi-flood calculations hydrographs. Results. Calculations of the flow kinematics of the calculated floodplain on the example of crossing the floodplain along the highway showed that the presence of a large angle of the overpass to the flood flow leads to additional conditions for increasing local erosion of supports in the form of solid rectangular columns. Significant local erosion is observed in the area of supports near the channel part. Conclusion. Based on the calculations and analysis of the kinematics and hydromorphodynamics of flows in the area of the designed bridge, recommendations on the necessary layout and design protective measures have been developed. Keywords: channel processes, erosion of bound and unbound bottom soils, erosion of piers bases of bridge crossings and overpasses, numerical methods.

LAB-SCALE TESTS OF INCOHERENT ROCK REINFORCEMENT USING TWO-COMPONENT POLYMER BLENDS

The study addresses improvement of physical and mechanical properties of incoherent sediments by means of their chemical reinforcement using two-component resins. The lab-scale testing data on reinforcement of fine-grained quartz sand using two-component activated mineral and polyurethane resin blends are presented. Resins were injected by two ways on the tests. The first method was sequential injection of the polymer blend components in rock samples. The second method was injection of finished polymer blends. The two-component activated mineral and polyurethane resin blends ensure more effective reinforcement of incoherent sediment rocks as against foamed polyurethane blends. The uniaxial compression strength of reinforced fine-grained sand is 2.5-3 times higher in case of sequential injection of the components than in injection of finished mixtures. The elasticity modulus of the reinforced samples is 5.5-6 times higher in sequential injection than in injection of finished blends. The test results are useful for selection and optimization of injection method for two-component polymer blends in stabilization of broken rocks and in water-proofing of underground excavations.

Transformation of organic matter in the Holocene sediments of Lake Ochki (south Baikal region): Evidence from pyrolysis data

Transformation of organic matter (OM) in Holocene sediments of Lake Ochki (southern coast of Lake Baikal) at the early stages of diagenesis has been studied using pyrolytic methods of Rock Eval (RE-pyrolysis) and pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS). OM has been analyzed in lacustrine sediments and their main producers, phytoplankton and zooplankton. Data on the distribution of hydrocarbon–biomarkers in sediments indicate an uninterrupted influx of terrigenous OM and transformation of OM precipitated by microorganisms. The analysis of molecular composition of pyrolysates makes it possible to assume a sharp change of sedimentation conditions in the upper part of sedimentary sequence (0–60 cm). It is shown that the macromolecular aliphatic kerogen structure begins to form in incoherent sediment at the very early stages of diagenesis.

Development of Grout for Additional Seal Embankment Dams

The technology of sealing sand and gravel by chemical injection has been known and used for a long time. Chemical grouting is however expensive and sometimes the use of cement does not lead to the desired effect. That is why we are trying to find new materials and methods of injection. Clay and cement are added to a mixture save chemical products. Clay-cement mixes are used not only because they are better quality, but also because these mixtures have a tendency to penetrate better into incoherent sediments that would need an additional sealant of a chemical injection. In order to reduce cost in future, ordinary clay is replaces in the mixture secondary raw materials can be a suitable substitute for ordinary clay to a certain extent. This is true above all for fly ash. This paper deals with the appropriateness of using fly ash (secondary raw material), cement and lime (binders) and liquefying additives and examining their properties in the mixture. The aim of the paper is to propose the optimal injection mixture for additional sealing of earth dams.

The structure of the incoherent sediments in the Ita Mai Tai Guyot (Pacific Ocean) based on geoacoustic profiling data

The results of geoacoustic studies carried out by the acoustic MAK-1M system in the southeastern Ita Mai Tai Guyot (Magellan Seamounts, Pacific Ocean) are discussed. The obtained geoacoustic sections characterize the incoherent part of the sedimentary sequence with high resolution. The geoacoustic stratification is well correlative with the deep-sea drilling data: the acoustic units are reliably correlated with the lithostratigraphic units defined in the cores of DSDP holes 200 and 202. Three geoacoustic units are distinguished in the sedimentary section (from the top downward): unit I corresponding in age to the terminal Miocene (Messinian)-Quaternary; unit II correlated with the Late Miocene (Tortonian); unit III accumulated in the Early Eocene-Early Miocene. The acoustic basement is composed of reefogenic limestones that were formed at different stages of the guyot’s development through the Aptian-Turonian to Late Paleocene-Eocene. The sonar images allow the distribution of the incoherent carbonate sediments to be contoured along the periphery of the summit’s plateau.

Seismogenic deformations in early holocene sediments of the Pechenga River Terrace (Kola Peninsula)

The Kola Peninsula, an element of the northwestern Baltic Shield, is not a high-seismicity region at present. This has not always been the case, however, as is evident from seismic paleodeformations reflecting strong earthquakes. The latter were discovered in the course of geologic‐geomorphologic works and the analysis of air photos of mainly crystalline rocks [1]. Morphologic patterns and genetic aspects of deformations in incoherent sediments of the Kola region have yet to be sufficiently studied despite the fact that many researchers have reported such structures. Their origin is usually attributed to glaciotectonic and cryoturbation processes. Indeed, distortions of such kind are widespread in Quaternary sediments, because the region under consideration was repeatedly subjected to glacial impact. At the same time, deformations in incoherent sediments were also caused by other phenomena—those related to the strong seismic impact. Deformations in incoherent sediments provoked by modern earthquakes are known not only in seismoactive regions, but also in territories of moderate seismicity, such as Canada, Fennoscandia, and Russia [2‐5]. Recently, special studies were carried out to define different types of deformations in Quaternary sediments exposed in quarries and natural outcrops along river banks in the northwestern Kola region (Fig. 1) and to discriminate them from those related to the glacial impact.

Late Cenozoic architecture of the St. Pierre Slope

The late Cenozoic seismic stratigraphy of the continental slope south of western Newfoundland is interpreted using new seismic reflection profiles. New Miocene–Pliocene biostratigraphic (palynology) age determinations on the Hermine E-94 well on the northwestern Grand Banks of Newfoundland are correlated to the study area. The Quaternary section of St. Pierre Slope is disrupted by numerous failure scarps and mass-transport deposits, but correlation from the mid- slope to the continental rise is achieved using major mass-transport deposits as markers. On the upper slope, stacked downslope-thinning wedges of acoustically incoherent sediment are interpreted as till deposits of mid- to late Pleistocene age. Sedi mentation rates in the youngest part of the succession are estimated from a 30 ka radiocarbon date 25 m below the horizon of the youngest till tongue, which is exposed on a 60 m deep failure surface. Extrapolation of sedimentation rates and comparison with dated sections on the J-Anomaly Ridge and Bermuda Rise provides a consistent interpreted age model for the till tongues that corresponds to marine isotope stages 2, 4, 6, 8, 10, and 12.

Coupling or decoupling bed and flow dynamics: Fast and slow sediment waves at high Froude numbers

The effect of coupling or decoupling bed and flow dynamics is analyzed in the framework of a linear analysis of the stability of a uniform, rotational, two-dimensional flow in an infinitely wide channel with a bed composed by incoherent sediments. It is shown that results obtained with the coupled analysis in term of instability of slow sediment waves of the dune/antidune kind are quite similar to the results obtained making use of the “quasisteady hypothesis,” which forms the basis of most of the existing linear stability analyses of bedforms and formally justifies the decoupling procedure. Small differences can be observed, for Froude numbers of O(1), in the surroundings of the marginal curves that bound the instability regions, mainly due to the removal of the artificial resonance that is introduced in the analysis when the quasisteady hypothesis is enforced. The decoupled approach, however, completely wipes out a mode of instability associated with fast-moving sediment waves, which appear at high Froude numbers in connection with the formation of roll waves on the free surface. This mode of instability, characterized by large wavelengths, is shown to coexist with the slower, shorter antidune mode.

Late Wisconsinan deglaciation of Emerald Basin, Scotian Shelf

Seismic surveys of the glacial and proglacial sediments of Emerald Basin show a systematic succession representing one complete cycle of deglaciation. The succession consists of a thin layer of acoustically incoherent sediments overlain by a thick sequence of acoustically stratified muds, capped by ponded, acoustically transparent Holocene sediments. The incoherent sediments, interpreted as a subglacial till, extend across the basin. The stratified proglacial sediments contain five erosional or nondepositional surfaces, thought to be of chronostratigraphic significance. These five surfaces are used to divide the proglacial sediments into lithosomes, each of which is influenced to varying degrees by three depositional mechanisms: suspension rain-out, ice rafting, and turbidity currents.Radiocarbon dating indicates that deglaciation started at about 18 ka. Although the main ice sheet retreated landward, deglaciation was locally complex, and a series of ice rises likely persisted until about 12 ka, grounded on the banks of the outer and central Scotian Shelf. Retreat of ice from the Scotian Shelf is recorded as a reduction of sedimentation rates, a decrease in the amount of coarse (> 500 μm) clasts supplied to the basin, the absence of iceberg scours in the upper sediments of the basin, and the disappearance of depocentres of proglacial sediments from the southern and eastern flanks of the basin by 11 ka.