Gravel Grains Research Articles

SPECIFICS OF LATE HOLOCENE SEDIMENTATION IN THE CHUKCHI SEA INFERRED FROM GRAIN SIZE AND MINERALOGICAL ANALYSES OF BOTTOM SEDIMENTS

The aim of this work is to elucidate the specifics of recent sedimentation in the Chukchi Sea, based on the study of the material composition of Late Holocene bottom sediments. Analytical methods included grain size and mineralogical analyses. The results of 210Pb and 137Cs dating were used. The sediments are clayey silt and silty clay containing sand admixture and single gravel grains and pebble. The content of coarse-grained material increases slightly in the upper parts of the studied sections. This is probably due to the greater contribution of ice rafting to the recent Chukchi Sea sedimentation as a result of climate warming. The ultrafine- and fine-grained (0.25–0.05 mm) sandy material is dominated by light-fraction minerals. Volcanic glass was discovered in the sediments sampled in the southern and central areas of the Chukchi Sea. It might have been transported from the volcanoes of Alaska, the Aleutian Islands, and the Kamchatka Peninsula through the Bering Strait by the Pacific currents directed from south to north. The sediments collected in the southern, central, and northern areas of the Chukchi Sea differ in grain size and mineral composition. This is probably due to their remoteness from the coastline and provenance areas and is also caused by different rates of sedimentation.

Simulation Study on the Prediction of Macroscale Young’s Modulus Based on the Mesoscale Characteristics of Tight Glutenite Reservoirs

To obtain the macroscale Young’s modulus of glutenite under gravel inclusions, a numerical simulation of macroscale Young’s modulus prediction based on the mesoscale characteristics of glutenite was carried out. Firstly, the micron indentation test was used to obtain the meso-mechanical parameters of gravel and matrix in glutenite to ensure the reasonableness of the numerical simulation parameter settings; secondly, a two-dimensional glutenite physical model generation method based on the secondary development of Python was put forward; and then, the macroscale Young’s modulus variation rule of glutenite under different gravel sizes, particle size ratios, and content characteristics were analyzed using the finite element method (FEM). The results show that Young’s modulus of gravel is larger than Young’s modulus of the matrix, and Young’s modulus of different gravel and matrix has some differences. The gravel content is the main controlling factor affecting the macroscale Young’s modulus of glutenite; the gravel content and Young’s modulus of glutenite show a strong positive correlation, and the gravel size and particle size ratio have less influence on the macroscale Young’s modulus of glutenite. The difference in Young’s modulus between gravel and matrix causes the formation of local stress concentrations during loading and compression of glutenite. The smaller the gravel grain size, the higher the degree of non-uniformity of the grain size, the more likely it is to form higher local stresses. The results of the study provide a new prediction method for the prediction of the macroscale Young’s modulus of a glutenite reservoir.

Experiments on Gravel‐Sand Transitions: Behavior of the Grain Size Gap Material

AbstractRiver bed sediments often lack fine gravel between 1 and 5 mm, a phenomenon referred to as the “grain size gap.” The gap corresponds to the rapid reduction in grain size associated with the gravel‐sand transition (GST), where median bed material grain size reduces from ∼10 mm gravel to ∼1 mm sand. Fine gravel grain sizes are often present in hillslope sediment, so it is not clear why they are absent on riverbed surfaces. We present a phenomenological laboratory experiment examining changes in sediment dynamics across a GST to examine the behavior of grain size gap material when included in the bed and feed grain size distributions. Our observations indicate that where sand falls out of washload, forming persistent surficial deposits at the GST, grain size gap material experiences enhanced mobility. This is due to hydraulic smoothing by sand that occurs because of a geometric effect, where medium sand bridges interstitial pockets in fine gravel bed surfaces. Our experiments show that gap gravel flux is enhanced by sand deposition, making gravel beds mobile at the threshold of motion. We are unable to maintain an immobile grain size gap gravel bed when sand is fed which explains why gravel beds composed of 1–5 mm particles are so rare on Earth. We hypothesize that in natural systems, grain size gap particles are either buried in the diffuse extension of GSTs or transported into coastal and marine environments where they are more commonly observed.

Sediment analysis and historical context of the 2018 Palu-Donggala tsunami deposit, Indonesia

On 28th September 2018, a magnitude 7.5 earthquake occurred on the Palu-Koro strike slip fault near Palu, Indonesia. Shortly after, large tsunami waves generated by the earthquake and the submarine landslides it triggered, washed into Palu Bay. Here, we describe sediment characteristics of the tsunami deposits and present wave height models to provide a modern analogue for tsunamis occurring on strike slip faults. We analyzed 51 sediment samples from 21 sampling points on two transects at Palu City and one transect at Pantaloan. At Palu City, the tsunami inundated between 250 and 270 m inland. Sediments were massive, with landward fining from coarse sands (φ 0) to fine sands (φ 3.7) and weak upward fining sequences (by up to 1 φ). At Pantaloan the tsunami inundated up to 275 m inland. Sediments were massive, with landward fining from a few grains of gravel (φ −2) and coarse sands (φ 0.5) to fine sands (φ 2.5) and weak upward fining sequences (by up to 1 φ). Based on the sediment data the TSUFLIND model predicted: at Palu city flow depths of 1 to 8 m, and flow velocities up to 3.9 m/s; and at Pantoloan flow depths of 2 to 8 m, and flow velocities up 3.8 m/s. The boulder transport model was applied to data from heavy concrete blocks (0.8 to 4.9 tons) deposited by the tsunami between 46 and 125 m inland, and predicted flow depths of 0.8 to 4.3 m and flow velocities up to 5.6 m/s. The rapid attenuation inland of the tsunami flow depth is consistent with the event being partially generated by landslides caused by the Palu-Donggala earthquake. A study of Dutch colonial archives and historical data reveals at least six tsunami events have occurred in or near Palu Bay since 1920, suggesting a very short return period for such events, and a significant tsunami hazard to the area.

Предварительные результаты исследования хронологии осадконакопления в Центральной впадине Баренцева моря

The article represents the results of the study of bottom sediment cores taken from the R/V “Dalnie Zelentsy” in the Central Depression of the Barents Sea during the 2022 expedition. The exposed stratum of bottom sediments is composed of silty-pelitic material, in some layers there is an admixture of uneven-grained sand and grains of well-rounded gravel. The chronology of sedimentation was determined by changing the specific activity of excess 210Pb, the obtained data were verified by 137Cs. The rate of sedimentation in the study area over the past 120 years has varied within 0.05–0.1 cm/year.

GraSSAMS: A new instrument designed for the determination of grain size and shape of sand-gravel-sized sediment

Natural coasts define the interface between land and ocean and constitute a natural barrier to protect humans and infrastructure from waves and storm surges. In the context of global sea level rise and coastal erosion, beaches, especially sand-gravel beaches, can achieve better marine energy reduction at the expense of a smaller spatial buffer zone (i.e., the lateral range of the coastal zone), meaning that nature-based coastal reconstruction and protection are becoming increasingly important. The need for beach replenishment and coastal protection necessitates fast, accurate, portable, and wide-range gravel grain size measurement technology to provide technical support and data for the designing and monitoring of artificial gravel beaches. However, existing grain size analysis methods for gravel-sized sediment are either inefficient (such as sieve analysis) or have a limited range of sizes (such as dynamic image analyzers, up to −3 φ), or have difficulty in eliminating errors caused by gravel overlap (e.g., remote-sensing in situ image analysis). In this study, a Gravel Grain Size and Shape Automatic Measurement System (GraSSAMS) was designed to analyze grain size and shape parameters of gravel-sized sediments. The mean diameters of three types of coins and some Zirconia balls measured using this method were compared with those measured by a vernier caliper. The results show that the GraSSAMS method has good accuracy and yields an acceptable relative error. The grain sizes of 67 field gravel samples were analyzed using both the GraSSAMS method and sieve analysis. The irreducible random error between the two methods is 1.41 φ. In addition, a Camsizer XT and GraSSAMS were used to measure samples with a grain size range of 1∼8 mm (0 φ ∼ -3 φ), respectively. The results of the two methods show good correspondence, with an irreducible random error of 0.31 φ. GraSSAMS was also tested in the field on several gravel beaches. Results revealed that GraSSAMS could complete the surface gravel measurement of a 0.5 m × 0.5 m quadrat within 8 min, and the analysis results avoided the fabric error involved in remote-sensing (photographic) measurement. Based on these various results, we propose that GraSSAMS can be used to analyze the grain size and shape of sand-gravel sediments in the size range of 1∼330 mm (0 φ ∼ -8.37 φ) in a laboratory as well as in the field. Compared with traditional methods, GraSSAM has the advantages of accuracy, high efficiency, and portability and can be used as an alternative for grain size analysis of gravel sediments, with broad application prospects to gravel beaches and fluvial deposits worldwide.

Investigation of the compaction behaviour of sand-gravel mixtures via DEM: Effect of the sand particle shape under vibration loading

In simulations of granular mixtures with real-shaped particles, fine particles are mostly simplified to spheres to improve computational efficiency. The basis for simplification is that the shape effect of fine particles is negligible when compared with coarse particles. However, existing simplifications are usually arbitrary without considering the size ratio between coarse and fine particles, causing fine shapes to be ignored unreasonably. Therefore, what size ratio can simplify the shape of fine particles? To solve this problem, the real model with real-shaped fines and the simplified model with simplified-shaped fines were established to explore the difference between the two models affected by size ratios. The real-shaped particles were constructed based on representative sand and gravel grains, and contact parameters were calibrated by a series of physical tests. The simulation results show that the permanent deformation of real models can be reproduced by simplified models with a large SR, while the resilient deformation cannot be reproduced no matter what SR is. Although there are some differences between the two models at macro- and mesoscales, the fine shapes can be simplified under the condition of SR ≥ 11, the computational efficiency of which can be greatly improved compared with real models. This study aims to provide a quantitative basis for the shape simplification of fine particles from the perspective of simulation accuracy and computational efficiency.

Reversible shifts between interstitial and epibenthic habitats in evolutionary history: Molecular phylogeny of the marine flatworm family Boniniidae (Platyhelminthes: Polycladida: Cotylea) with descriptions of two new species.

Tiny animals in various metazoan phyla inhabit the interstices between sand and/or gravel grains, and adaptive traits in their body plan, such as simplification and size reduction, have attracted research attention. Several possible explanations of how such animals colonized interstitial habitats have been proposed, but their adaptation to this environment has generally been regarded as irreversible. However, the actual evolutionary transitions are not well understood in almost all taxa. In the present study, we show reversible evolutionary shifts from interstitial to epibenthic habitats in the lineage of the polyclad flatworm genus Boninia. In addition, we establish two new species of this genus found from different microhabitats on a single beach in Okinawa Island, Japan: (i) the interstitial species Boninia uru sp. nov. from gravelly sediments and (ii) the epibenthic species Boninia yambarensis sp. nov. from rock undersurfaces. Our observations suggest that rigid microhabitat segregation exists between these two species. Molecular phylogenetic analyses based on the partial 18S and 28S rDNA sequences of the new Boninia species and four other congeners, for which molecular sequences were available in public databases [Boninia antillara (epibenthic), Boninia divae (epibenthic), Boninia neotethydis (interstitial), and an unidentified Boninia sp. (habitat indeterminate)], revealed that the two interstitial species (B. neotethydis and B. uru sp. nov.) were not monophyletic among the three epibenthic species. According to ancestral state reconstruction analysis, the last common ancestor of the analyzed Boninia species inhabited interstitial realms, and a shift to the epibenthic environment occurred at least once. Such an "interstitial to noninterstitial" evolutionary route seems to be rare among Animalia; to date, it has been reported only in acochlidian slugs in the clade Hedylopsacea. Our phylogenetic tree also showed that the sympatric B. uru sp. nov. and B. yambarensis sp. nov. were not in a sister relationship, indicating that they colonized the same beach independently rather than descended in situ from a common ancestor that migrated and settled at the beach.

Direct shear behavior of gravel-rubber mixtures: Discrete element modeling and microscopic investigations

In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% <VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses.

РЕЗУЛЬТАТИ ЕКСПЕРИМЕНТІВ ІЗ ПІДБОРУ СКЛАДУ ДРЕНУЮЧОГО АСФАЛЬТОБЕТОНУ

Abstract Introduction. It is established that draining asphalt concrete is asphalt concrete of frame type with a very large number of voids between grains of crushed stone. Unlike crushed stone-mastic asphalt concrete in draining asphalt concrete pores are not filled with bituminous sand mortar. The main feature is its porosity, which leads to a slight decrease in its compressive strength at a temperature of 50 ° C, while the shear strength of the coating is very high. It is achieved due to the strength of the crushed stone frame (high internal friction and jamming of gravel grains) and the strength of the binder that binds the grains. Problem statement. The long-term impact on the asphalt road surface of the aquatic environment is a determinant of its durability. The issue of timely removal of surface water from the pavement is a must and is solved by giving the road surface a cross slope. As practice shows, this does not sufficiently protect the road surface from the adverse effects of water. High operational safety, improved road performance is achieved by removing accumulations of water stains from the surface that reduce the adhesion of the wheels to the road surface. These qualities can be improved by the introduction of draining asphalt concrete. Unfortunately, today in Ukraine there are no normative documents that would regulate the design, manufacture and execution of works on this technology, which makes it impossible to use it in practice and limits the optimization and development of the Ukrainian road sector in this direction. Purpose. Perform an analysis of existing experience in the design of draining asphalt concrete. Theoretical and experimental substantiation of the possibility of obtaining draining asphalt concrete with a structure of interconnected open pores, which allows you to quickly drain surface water. Materials and methods. Experimental research of draining asphalt concrete. Results. An analytical review of the experience of designing draining asphalt concrete. The stages of selection of the composition of the mixture were studied and analyzed, experimental studies on the selection of the grain composition and bitumen content in the draining asphalt concrete were carried out. Conclusions. Analysis of experimental studies on the peculiarities of the selection of the composition of draining asphalt concrete found that for the production of draining asphalt concrete using crushed stone of narrow fractions, because it has a special particle size distribution, in contrast to typical dense and crushed-mastic asphalt concrete. to crushed stone materials. The granulometric composition of the mineral part of asphalt concrete mixtures for draining asphalt concrete was selected and the optimal bitumen content for mixtures with different maximum grain sizes was established. Keywords: draining asphalt concrete, asphalt mixtures, grain composition, open voids, porousity.

Do brown trout (Salmo trutta L.) move streambed substrate?—Implications for durability and maintenance of artificial spawning habitat

AbstractArtificial spawning habitat has been used to mitigate for lost habitat and to increase the abundance of salmonids, but the endurance and potential need of maintenance of these habitat improvements have not been well studied. We studied the movement of gravel, attributed to spawning activity of brown trout in a third‐order stream in northern Sweden by deploying PIT‐tagged grains of gravel on artificially constructed gravel patches. The results suggest that gravel movement was substantial and most prevalent at the central parts of the patches. As 76% of the tagged gravel was mobilized during a single spawning season, maintenance of this habitat improvement may be necessary in order to guarantee its functionality over time. This study provides a first step in guiding managers tasked with identifying factors degrading restored spawning habitat and maintenance needed.

Effects of Differential Subgrade Settlement on Slab Track Deformation Based on a DEM-FDM Coupled Approach

Slab track structures become deformed under the effects of differential subgrade settlement. According to the properties of the China Railway Track System (CRTS) II slab track on a subgrade, a three-dimensional (3D) coupled model based on both the discrete element method (DEM) and finite difference method (FDM) was developed. The slab track and subgrade were simulated using the FDM and DEM, respectively. The coupled model was verified. The deformation of the slab track and contact forces of gravel grains in the surface layer of the subgrade were studied under differential subgrade settlement. The effects of settlement wavelength, settlement amplitude, and other types of settlements were also discussed. The results demonstrate that the settlement amplitude and settlement wavelength of the subgrade have significant effects on track deformation. The deformation amplitude of the slab track increases nonlinearly with an increasing settlement amplitude of the subgrade. Increases in the settlement wavelength and amplitude of the subgrade significantly increase the maximum value of the contact force of the gravel grains in the subgrade. The maximum contact force of gravel grains near the boundaries of the settlement section can reach two to three times that of the unsettled condition, which makes it easy to accelerate the plastic settlement of the subgrade.

Investigation of the influence of gravel stuffing in an open drill on the productive characteristics of the well

The negative consequences of sand production from the formation into the wellbore during the operation of wells with unstable rocks are characterized. A highly effective method of preventing sand from entering the well from the formation is the use of gravel packs, which are used in Ukraine and abroad. The types of gravel packs, the conditions for their application, the choice of the diameter of gravel grains for creating gravel pack are given. The types of gravel pack installation are considered depending on the geological and technical conditions of the reservoir. Calculations have been performed using Schlumberger's PipeSim software to assess the effect of gravel pack size and permeability on the performance specification of a gas well. Based on the research results, graphical de-pendences of gas flow rates in the presence of gravel pack on the permeability of the gravel pack at its various thicknesses have been constructed and analyzed. It has been found that the gas flow rate increases with an increase in the thickness of the gravel pack in the considered interval of its variation up to 0.9 m. The effect of the thickness of the gravel pack on the gas flow rate increases with an increase in its permeability. Based on the results of statistical processing of the calculated data using the least-squares method, the optimal values of the gravel pack permeability for various values of its thickness have been determined. The optimal values of the thickness and permeability of the gravel pack have been determined, beyond which the value of the gas flow rate practically does not change. The calculation of the pressure distribution along the bore of a gas well in the presence of gravel pack with certain optimal values of its permeability and thickness is performed. Using the PipeSim software, the influence of the de-gree of relative formation penetration on the productivity of a gas well in the presence of gravel packing has been investigated for determining certain optimal values of permeability and thickness of gravel packing.

Evolution of the Bystrzyca River valley during Middle Pleistocene Interglacial (Sudetic Foreland, south-western Poland)

Abstract The article depicts the problem of river system development during the Middle Pleistocene Interglacial in the Bystrzyca River Valley (Sudetic Foreland, south-western Poland). Ten research sites located within the Świdnica Plain are presented, in which the structural, grain size (granulometry), petrographic, quartz grain morphoscopy, and heavy mineral analyses were carried out. The study results show the formation of piedmont fan deposits 2–8 km to the NE of the Sudetic Marginal Fault. The location of the fluvial deposits between the Sanian and Odranian tills indicates that they were deposited during the Holsteinian Interglacial (Krzczonów Formation, Mazovian; see Table 1). According toxthe lithofacies analysis, vast alluvial plains, composed of angular gravel grains in the south and of sands in the north, were deposited in the Sudetic Foreland in the environment of a very dynamic river. They are covered with a discontinuous layer of Odranian till. The petrographic spectrum shows 90–99% of local rocks, namely, Sudetic porphyry, Sowie Mts Gneiss and milky quartz, and 1–10% of Scandinavian rocks. In the proto-Bystrzyca river system, the existence of an oxbow lake in the distal part of the Krzczonów fan has been proved, which was developing at the end of the Holsteinian Interglacial. The continuity of the alluvial deposits is interrupted in the vicinity of Świdnica due to both the tectonic movements and the formation of the narrow tectonic graben of Roztoka–Mokrzeszów.

Distribution of clay‐sized sediments in streambeds and influence of fine sediment clogging on hyporheic exchange

AbstractIn this work, the deposition of clay‐sized fine particles (d50 = 0.006 mm) and its subsequent influence on the dune‐induced hyporheic exchange are investigated. Fine sand (D50 = 0.28 mm), coarse sand (D50 = 1.7 mm), and gravel (D50 = 5.5 mm) grains were used to form homogenous model streambeds; one control ‐ no clay input, and two treatments ‐ increasing clay inputs for each grain type. The results indicate that the clogging profiles of clay‐sized sediments may not be predicted accurately using the previously proposed metric based on the relative sizes of infiltrating and substrate sediments. Further, the depositional patterns vary with the initial concentration of clay particles in the surface water. The assessment of clogging profiles in coarse‐grained model streambeds also reveals a preferential infiltration of the clay particles in the hyporheic downwelling regions. The results from the dye tracer test suggest that the accumulation of clay particles altered the exchange characteristics in the treatment flumes. For each grain size, the treatment flumes exhibit lower hyporheic flux and higher median residence times compared to their respective control flumes. The dye penetration depths were lower in treatment flumes with fine and coarse sand compared to their respective control flumes. Interestingly, higher penetration depths were observed in treatment flumes with gravel compared to their respective control flume potentially due to the generation of preferential flow paths in the partially clogged gravel beds. The clogging altered the hyporheic fluxes and residence times in the coarse‐grained model beds to a greater degree in comparison to the fine sand beds. Overall, our findings indicate that the properties of both fine and substrate sediments influence the clogging patterns in streambeds, and the subsequent influence of fine sediment clogging on hyporheic exchange and associated processes may vary across stream ecosystems.

Filtration capacity of a gravel inlet system under low accumulation conditions

Filtration models were applied to a gravel inlet system to estimate attachment and/or detachment of particles onto collectors (gravel grain). Two methods were used to estimate total solidstrapping efficiency at the gravel inlet: mass concentration and particle count. The first method provided trapping estimate between 11% and 22% based on two averaging computations. The second method, particle count, showed that detachment of total solids occurred mostly with the clay size category and early duringrainfall events. Detachment reveals the quality of effluent and can be interpreted as particles being detached either from previous total solids deposit or not being retained by the collector. Based on a model by Rajagopalan and Tien, trapping ability of gravel inlet was expected to be relatively low (&lt;50%) for particles and aggregates smaller than 100 μm. Five rainfall events in 2002 were analyzed and showed that the first event had a retention capacity of 32% with a significant statistical difference between pairs of samples from “above” and “below” the gravel, based on a paired t-test. The following rainfall events had not seen any significant difference based on the same statistical test between the above and below water samples; however, the pattern of retention within pairs of samples showed that large filtration values were associated with incoming large solids concentrations, which, in turn, are related to rainfall bursts. The laser diffractometer technique allowed the particle count method to estimate number of particles retained or detached with respect to the gravel media. Particle count was obtained by direct measurement in the fine silt and clay size region and by extrapolation of measured data for large size in the silt-sand region including small particles and aggregates. Two rainfall events (August 3 and 21) showed important detachment based on particle counting method.

Beach Gravels as a Potential Lithostatistical Indicator of Marine Coastal Dynamics: The Pogorzelica–Dziwnów (Western Pomerania, Baltic Sea, Poland) Case Study

The petrographic composition and grain shape variability of beach gravels in the Pogorzelica–Dziwnów coast section (363.0 to 391.4 km of coastline), southern Baltic Sea, Poland were analyzed herein to characterize the lithodynamics and trends of seashore development. Gravels were sampled at 0.25 km intervals, in the midpart of the berm, following an early-autumn wave storm and before beach nourishment. Individual variations in petrographic groups along the shore were investigated. Gravel data were compared and related to coastal morpholithodynamics, seashore infrastructure, and geology of the study area. The contribution of crystalline rock gravels (igneous and metamorphic) was observed to increase along all coast sections, whereas the amount of less resistant components (limestones, sandstones, and shales) usually declined. This effect is explained by the greater wave crushing resistance of igneous and metamorphic components, compared with sedimentary components. Similarly, the gravel grain shape (mainly elongation or flattening) was observed to change, depending on resistance to mechanical destruction, or due to the increased chemical weathering in mainly the limestones, marbles, and sandstones. Observed increase in contribution of discoid and ellipsoid grains is a potential indicator of depositional trends along the coast sections investigated. On the other hand, increased contents of spheroidal and spindle-shaped grains may be related to erosional trends, where intensive redeposition and mechanical reworking of gravels occurs. However, due to the great number of coastal embankments, the petrographic composition and shape parameters of beach gravels do not always clearly indicate the dominant direction of longshore bedload transport. Increased amount of eroded limestone located east of Pogorzelica indicate increased erosion of glacial tills. These sediments are deposited, building the shallow foreshore, with additional redeposition of morainic material towards the shore.

Infrared image-based identification method for the gradation of rock grains using heating characteristics

In earth-rock dam engineering, the gradation characteristics of filling materials have an important influence on the compactability, impermeability, and stress–strain characteristics of dams. A sound gradation is the key to guaranteeing dam safety and stability. Based on the principles of the heat conduction and heating characteristic tests on rocks, the power function equation between volume and temperature increase for pebble and gravel grains in a heating environment is established with correlation coefficients of 0.98. Aiming at the low span of gray-scale change of digital infrared images, the linear gray-scale transformation method with a Gamma factor of 1 to enhancing the digital infrared images, and the maximum between-cluster variance method (OSTU method) is adopted to perform binary grain target-context segmentation on enhanced images. With regard to the phenomenon of grain adhesion, it subjects flattened images after binary segmentation to peak processing using Dis operation, and introduces an improved watershed algorithm (i.e., local minimum with threshold) for image reconstruction, effectively segmenting adhesive grains while avoiding over-segmentation. According to maximum stability theory, the shortest side of the minimum enclosing rectangle (MER) of the grains in images is proposed as the judgment index for grain sieving. Five gradation detections were carried out on pebbles and gravels, respectively. For grain mass fraction identification results for various grain size intervals, the maximum absolute errors for pebbles and gravels do not exceed 6% and 7%, and the average absolute errors do not exceed 4% and 5%, respectively. Thus, the identified gradation curve fits well with the mechanical sieving gradation curve, and can meet engineering application requirements. This new method overcomes several deficiencies of traditional methods for gradation image detection, such as the susceptibility of image sampling to various interfering factors and difficulties in controlling errors in calculating grain mass, and therefore, provides a novel conceptual technology for particle grading image recognition.

EXPERIMENTAL STUDIES OF PILE FOUNDATION GROUND BASE REINFORCED WITH HARD INCLUSIONS

Often in construction practice there is a need to strengthen the pile foundation of buildings and structures. The traditional methods include the implementation of additional, as a rule, bored piles with the subsequent erection of a grillage incorporating them into operation. Often, this work has to be done in the conditions of dense urban development, in cramped rooms of the basement, etc., which leads to significant technological difficulties. One of the alternative ways to strengthen pile foundations is the method of high-pressure group injection, which consists in injecting a movable cement-sand mortar into the soil under pressure that exceeds its structural strength. As a result, after its hardening, solid injection bodies are formed at the base, reinforcing the soil base. The article describes the results of experiments to assess the impact of the layout of hard inclusions on the deformability of the soil foundation of the pile foundation model. The experiments were carried out in a small soil tray, which was filled with medium-grained loose sand. The piles were modeled with metal rods, the pile grillage with a metal square stamp. The pile foundation model included 9 piles arranged in a square grid. As injection bodies, gravel grains of various sizes and shapes were used. The studies included 10 series of experiments (each experiment was repeated at least 3 times): the volume of the inclusions used, their sizes, the positioning step in the plan and in depth varied. As a result of the analysis of the performed experiments, conclusions were formulated regarding the purpose of the optimal layout of hard inclusions when strengthening the soil foundation of pile foundations by high-pressure injection of mobile cement-sand mixtures.

On the uniaxial compression strength of frozen gravelly soils

Frozen gravelly soils are often encountered in both cold regions engineering and urban underground constructions by artificial freezing method. This work takes a gravelly sand in Beijing as the basic material. Gravel grains of 10–20 mm in size are obtained and mixed with sand grains at certain ratios and then saturated frozen samples are prepared. Uniaxial compression test is used to study the uniaxial compression strength (UCS) of the material under 3 temperatures and 3 strain rates. Together with 4 gravel contents, 36 combinations are investigated. Test results show that stress-strain curves generally demonstrate strain-softening manner, with different strain energy dependent upon temperature and strain rate on the one hand, and on gravel content upon the other hand. An inclination of approximately 55° to 58° is found for the failure surface. UCS is obtained from all tests for analysis. It is found that the UCS of frozen gravelly soil increases with the decrease of temperature and the increase of strain rate. Generally accepted empirical relationships for fined-grained frozen soils are still applicable with the correlation coefficient of very close to 1. Gravel content plays another important role in the UCS of frozen gravel soil. UCS is found to decrease significantly with the increase of gravel content at high strain rate. At relatively low strain rates however, influence of gravel content on UCS turns out to be complicated. Mechanism of the mechanical performance of the sand-gravel-ice system is proposed in terms of gravel contents, ice contents as well as strain rate.