Sand-gravel Materials Research Articles

Energy equation and stress–dilatancy relationship for crushable granular materials incorporating particle breakage

The ROWE’s stress–dilatancy relationship is widely employed to characterise the shear dilatancy behaviour of granular materials. However, particle breakage energy dissipation is excluded from the ROWE’s energy balance equation. In this study, three crushable granular soils with significantly different strengths were subjected to triaxial testing, and the dissipation of energy during the tests was explored. For all three materials, the incremental particle breakage energy dissipation increases and then decreases. It was assumed that at the critical state, particle breakage ended and only frictional energy dissipation occurred. To more accurately characterise the energy dissipation process, an exponential expression of particle breakage energy dissipation is added to the ROWE’s stress–dilatancy relationship. The proposed stress–dilatancy relationship is consistent with the shear dilatancy behaviour of crushable granular materials, and the modified energy equation can more precisely describe the energy dissipation process. The hypothesised stress–dilatancy relationship is applicable to three distinct types of crushable granular materials with varying strengths, including sand-gravel material, landslide dam material and calcareous sand.

Hybrid 1D-CNN and attention-based Bi-GRU neural networks for predicting moisture content of sand gravel using NIR spectroscopy

A non-destructive and rapid moisture content detection method of sand gravel material is required in loose material dams. The near-infrared (NIR) spectrum of sand materials is closely related to its moisture content. Recently, there is a growing need for fully using spectral information when establishing calibration models for sand gravel moisture content detection. To address these issues, a hybrid one dimensional-convolutional neural network (1D-CNN) and attention-based bidirectional gated recurrent unit (Bi-GRU) neural network was proposed to detect sand gravel moisture content with NIR spectrum. Two learners, namely, 1D-CNN and Bi-GRU, were constructed to extract local abstract information and sequence position information from the spectrum, respectively. In the 1D-CNN learner, multiple kernels CNN layers and one dimensional-separable convolution layers were conjunct to improve model accuracy and reduce network parameters. In the Bi-GRU learner, a multi-head self-attention mechanism was appended to evaluate the weights of the output features extracted by Bi-GRU layers. The proposed model achieved the best prediction results in LUCAS dataset (R2 greater than 0.75, RPD greater than 2.0) and our sand gravel spectral dataset (R2 = 0.96, RPD = 5.06) compared to other deep learning and conventional spectroscopy analysis methods. In addition, the top ten characteristic wavelength points of sand gravel were identified. These can be used to choose a discrete spectrum measuring instrument, which has a relatively low cost.

Compaction Density Evaluation Model of Sand-Gravel Dam Based on Elman Neural Network With Modified Particle Swarm Optimization

The compaction density of sand-gravel materials has a strong gradation correlation, mainly affected by some material source parameters such as P5 content (material proportion with particle size greater than 5 mm), maximum particle size and curvature coefficient. When evaluating the compaction density of sand-gravel materials, the existing compaction density evaluation models have poor robustness and adaptability because they do not take into full consideration the impact of material source parameters. To overcome the shortcomings of existing compaction density models, this study comprehensively considers the impact of material source parameters and compaction parameters on compaction density. Firstly, asymmetric data were fused and a multi-source heterogeneous dataset was established for compaction density analysis. Then, the Elman neural network optimized by the adaptive simulated annealing particle swarm optimization algorithm was proposed to establish the compaction density evaluation model. Finally, a case study of the Dashimen water conservancy project in China is employed to demonstrate the effectiveness and feasibility of the proposed method. The results show that this model performs high-precision evaluation of the compaction density at any position of the entire working area which can timely correct the weak area of compaction density on the spot, and reduce the number of test pit tests.

Soil cover of areas of mining sand and sand-gravel material in the Leningrad region

The article considers the component composition of soil cover in the areas of mining sand and sand-gravel material in the Leningrad region. The sites under study are anthropogenically transformed soil that have a direct and indirect impact on the natural soil cover. Direct impact should include the burial of natural soils under dumps, the complete removal of soil profile as a result of quarrying and changes in the relief. The process of rock removal can lead to a change in the parent rock. Indirect influences include stratification of soil surface by dust, soil over-consolidation, and the formation of recreational zones, dumps and bonfires. At all the studied sites, the same type of soil cover organization was detected. Nonsoils formations were found where soils had been completely destroyed. These were found at places including access roads, dumps, rock outcrops and pits filled with water. Slopes, roadsides and cavaliers of the network of protective ditches typically feature turbocharged and stratified natural soils. Ditch bottoms are formed by Nudiargic Luvisols and Nudialbic Podzols. Soil combinations of slightly altered and fully natural soils are identified in the areas adjacent to quarries.

Study on Gradation Improvement of Gravel and Sand for Surface Layer of Railway Subgrade by Blending Method

As the direct foundation of the track, the surface layer of high-speed railway subgrade bed is one of the important parts of the subgrade. Its main function is to transmit and spread the vertical load of the upper ballast bed and the vehicle dynamic load to maintain the long-term stability of the subgrade bed surface. So, the material for the surface layer of subgrade bed should have high strength, elastic modulus, wear resistance and invented filtration. The graded sand gravel, which is used as the filler for the surface layer of railway subgrade bed, has such features as high mechanical strength, high water stability, easy obtaining, convenient construction, low cost and so forth. The purpose of this study is to physically blend local sand gravel materials to solve the defect of excessive fine particle content, so that it can meet the grading requirements of the specification and design standards and also to provide a general calculation method and solution for the mix ratio design of natural sand gravel. In combination with a foreign project, the dissertation expatiated on the calculation method for improving the gradation defects of natural sand gravel by the blending method. Then, according to local conditions, the author successfully solved the gradation defects of natural sand gravel mixture with the said method and achieved good economic and social benefits.

Effects of gravel content and particle size on abrasivity of sandy gravel mixtures

During soft ground tunnel construction, the presence of sandy gravel stratum often causes serious wear and tear of cutting tools. In this paper, an experimental study to assess abrasivity of sand-gravel materials with different gravel content (GC) and gravel size (GS) was carried out with a horizontally oriented mechanical mixing device. The abrasive characteristics of testing materials were quantitatively assessed through the measurement of weight loss on the testing steel cube, with a focus on the influence of GC and GS of the mixtures. Experimental testing results indicate that GC and GS have significant impact on soil abrasion and tool wear, through affecting the packing density of the sand-gravel mixtures, breakage resistance of particles, and the soil-tool wear mechanisms. The torque required to drive the propeller in the sand-gravel mixtures during the abrasivity test was measured and provided more insights into the abrasivity of mixtures and the associated soil-tool wear mechanisms. In addition, potential relationships between coefficient of uniformity (Cu) and coefficient of curvature (Cc) of the sand-gravel mixtures and the tool wear were sought.

MINERAL POTENTIAL OF ARCTIC KARELIA

Hard useful minerals of the Louhi, Kem and Belomorian provinces are reviewed. The high demand for geological data echoes the significance of the mineral potential of this territory for the social and economic development of Arctic Russia (RF Presidential Decree of June 27, 2017). The commencement of targeted geological studies was directly connected with the construction of the Murmansk Railway. Archean granitoids occupy a large part of Arctic Karelia. One of the features of the region’ geological structure is a system of Neoarchean greenstone belts. Aunique complexly folded structure ofpolymetamorphic rocks, which evolved in polychronous manner, was formed. The Early Paleoproterozoic rift-induced system, tens of kilemetres in width, extending along the boundary between the Karelian and the Belomorian provinces, has a common source of mantle magma formation. The mineral resources of the territory mainly consist of metallic (Mo, Cu, U, Au, Ag, PGM, rare metals and REE) and nonmetallic useful minerals (diamond, apatite, granite, graphite, diatomites, ilmenite, calcareous rocks, quartz, quartzites, feldspar (ceramic pegmatite and uncommon types), kyanite, muscovite, olivinite (olivine), dunite and gemstones. Lithogeodynamic (structural and compositional) complexes with their geochemical resources are the ore-forming basis for Arctic Karelia’s mineralogenic potential. Widespread useful minerals (dimension stone, crushed stone, clay, peat, sand-gravel materials), which are abundant in Arctic Karelia, are not discussed in this paper. The authors have concluded that our knowledge of Arctic Karelia’s mineralogenic potential is still incomplete. Further scientific research, prospecting and appraisal are needed to work out a Programme for the development of Arctic Karelia’s mining industry and to facilitate its implementation with the participation of private investors and state-run corporations.

Designing the Alluvial Riverbeds in Curved Paths

The paper presents the method of determining the shape of the riverbed in curves of the watercourse, which is based on the method of Ikeda (1975) developed for a slightly curved path in sandy riverbed. Regulated rivers have essentially slightly and smoothly curved paths; therefore, this methodology provides the appropriate basis for river restoration. Based on the research in the experimental reach of the Holeška Brook and several alluvial mountain streams the methodology was adjusted. The method also takes into account other important characteristics of bottom material - the shape and orientation of the particles, settling velocity and drag coefficients. Thus, the method is mainly meant for the natural sand-gravel material, which is heterogeneous and the particle shape of the bottom material is very different from spherical. The calculation of the river channel in the curved path provides the basis for the design of optimal habitat, but also for the design of foundations of armouring of the bankside of the channel. The input data is adapted to the conditions of design practice.

Application of Composite Waterproofing and Drainage Board in Low Embankment Highway

This paper introduces the composite waterproofing and drainage board, to solve issues such as the drainage problem and lack of sand gravel material in low filled embankment of plain area highway. Through the research of its application performance, design method and drainage effect. Studies show that the materials with perfect performance on tensile and compression strength are contribute to construction property of soil which under the board, it also can effective prevent water from seeping through the underground, and expel surplus water, to make sure the long-term stability of subgrade and subsoil. It is one perfect waterproofing and drainage materials used in low embankment highway.

Geotextile Recharge Well with Filter Layer

Recharge well with filter layer is a sort of valid recharge facility in groundwater reservoirs, which is constituted by recharge well and recharge pool. The main problems of existing recharge well with filter layer are analyzed in this paper; the main reason of these problems is concluded as the defective design of the wellhead structure; the optimal outer design method of recharge pool is studied. In order to increase single-well recharge volume, improve anti-silt and anti-rush capability of recharge well and save sand-gravel materials, geotextile material and hard wall material are adopted; a new sort of geotextile recharge well with filter layer is developed. The theoretical formula of single-well recharge volume is deduced.

Mechanical Properties of Interface between Coarse-Grained Soil and Concrete

Comparative tests on interfaces between different materials are performed by means of the self-developed NHRI-4000 high-performance large interface shear apparatus. Change of mechanical properties of interfaces between different coarse-grained soils and concrete is investigated owing to the differences of materials. The influences of the existence of slurry on the strength indices of the interfaces are analyzed. The test results show that shear failures all occur in the contact zone of specimens. The properties of materials and the differences of particle shapes have great influences on the strength and deformation characteristics of interfaces as well as the residual shape of shear plane after shearing. The specific exhibition is as follows: (1) the strength and deformation indices of rock-fill materials with distinct edges are significantly superior to those of sand-gravel materials with good roundness; (2) the existence of slurry leads to obvious decrease of mechanical indices of the interfaces.

Operational experience with submersible mud pumps

The indisputable advantages of submersible mud pumps and the achieved reliability of their drives, urgently dictate the necessity of widely introducing this progressive and economic trend into practice, in the intensification of various mud-pumping operations and, in particular, for the handling of sand-gravel materials and for the removal of soils at considerable depths.

Hydromechanized extraction of sand-gravel materials

Hydromechanized extraction of sand-gravel materials