The Influences of Sand Content and Particle Size on the Desiccation Cracks of Compacted Expansive Soil

The desiccation cracks in expansive soil, which are a common natural phenomenon, have a significant negative impact on the engineering properties of the soil and are the direct cause of many engineering problems and geological disasters. This study aims to investigate the influences of sand content and particle size on desiccation cracks of the compacted expansive soil. First, samples of compacted expansive soil with five sand contents and four sand size groups were prepared. Then, a series of drying tests were performed. The dynamic variation of geometric parameters of the surface crack network during evaporation was quantitatively analyzed by using digital image processing technology and fractal theory. The results demonstrated that the increase of the surface-cracking areas in the early and later stages was manifested by the increase of the crack length and crack width, respectively. In the same size of sand particle group (0.15, 0.3 mm), as the sand content (dry weight ratio of soil sample) increased from 0% to 40%, the surface-cracking ratio (the ratio of the crack area to the total surface area of the soil sample) showed a decreasing trend (13.20%, 11.42%, 10.50%, 8.98%, and 7.71%, respectively). When the sand content (40%) was the same, as the sand size groups increased from [0.15 mm, 0.3 mm) to [1.18 mm, 2.36 mm), the surface-cracking ratio also presented a decreasing trend (7.71%, 7.69%, 4.35%, and 3.73%, respectively). The changing law of the fractal dimension of cracks was the same as that of the surface crack ratio. During the drying process, the deformation of the sample was characterized by centripetal shrinkage or cracking, which were mainly affected by the boundary conditions of the sample. This research’s results verify the effectiveness of sand to improve the dry-shrinkage characteristics of expansive soil, providing a reference for the improvement of roadbeds and the treatment of soil slopes in expansive soil areas.

Error on the Estimation of Sand Size Parameters When Using Small Diameter Sieves and a Solution

Analyses were carried out to determine the main sand size parameters (median grain size D50 and sorting σ) for beach nourishment purposes using the sieving method aboard a dredger. Due to a lack of space and the need to carry and use the material with ease, the sieves are commonly small (10 cm diameter), and the shaking procedure is usually performed by hand. However, the influence of shaking, either mechanically or manually, has not yet been studied with 10 cm diameter sieves. Therefore, 20 samples were taken from inside the hopper of a trailing suction dredger and sieved both manually and mechanically for 10 min. The results showed that manual sieving yielded higher D50 values than the mechanical procedure. The average error arising from using the manual method was 14%, but it can reach 36.5%. The granulometric analysis carried out for different shaking times has shown that this error is < 5% when at least 20 min of shaking is performed. The mechanical procedure gave always finer sand results. In addition, the overfill ratio calculated for both mechanical and manual results reached differences of up to 48%.

Sand Production of the Shale Gas Well in Different Production Periods: Structure and Component

Complex geology and fracturing operations have led to frequent sand production problem in the shale gas well. Sand production brings huge engineering risks and seriously affects the normal production of the shale gas well. In order to study the property and source of the yielded sand, sand samples in three production periods of flowback, production test and gas production are collected from Sichuan Basin of China. Combining the methods of particle size analysis, microscope observation, scanning electron microscope, CT scanning, infrared spectroscopy and energy dispersive spectrum analysis, the multi-scale structure and composition characteristics of the yielded sand from different production periods were investigated. Results show that the sand size is the largest in the production test period and the smallest in the gas production period. The large-size sand is blocky in the flowback period, while it is flaky in the period of production test and gas production. The roundness of sand becomes worse as the sand size decreasing. Sand composition has the characteristics of fracturing proppant and shale mineral. Cementing material between large-size sands has the network structure and the higher content of aluminum and iron. Organic chemicals are found to be adhered to the sand surface in all three periods. Both shale fracture and proppant failure can generate particles that provide the material source for sand production. This research provides the source of the yielded sand and a theoretical guidance for the sand production mechanism.

On Local Scouring at Single Piers

The paper mostly summarizes disperse contributions of the authors published during the last fifteen years on the scour depth at single piers. These contributions rely on unique experiments in the sense that they are systematically longer than most of those found in the literature. The characterization of the effects of flow intensity, relative sand size, flow shallowness, time and pier shape and alignment is significantly improved as compared with existing literature. Our contributions consist on refinements of the model suggested by the school of Auckland, initiated by Raudkivi and boosted by Melville and his students. A considerable number of empirical equations and charts expresses those contributions.

Performance of Waterborne Epoxy Emulsion Sand Fog Seal as a Preventive Pavement Maintenance Method: From Laboratory to Field

To preserve the existing asphalt pavement and extend its service life, various preventive maintenance methods, such as chip seal, slurry seal, fog seal, and microsurfacing, have been commonly applied. Sand fog seal is one of such maintenance methods, which is based on the application of bitumen emulsion and sand. Thus, its performance is largely dependent on the properties of the bitumen emulsion and sand. This study aims to develop an improved sand fog seal method by using waterborne epoxy resin as an emulsion modifier. To this end, both laboratory tests and field trials were conducted. In the laboratory, the wet track abrasion and British pendulum test were performed to determine the optimum sand size for the sand fog seal, and the rubbing test was carried out to evaluate the wearing resistance of the sealing material. In the field, pavement surface regularity before and after the sand fog seal application was measured using the 3 m straightedge method, and the surface macrotexture and skid resistance were evaluated with the sand patch method and British pendulum test, respectively. The laboratory test results indicated that the optimum sand size range is 0.45–0.9 mm, and the sand fog seal with waterborne epoxy resin showed good wearing resistance and skid resistance. The field test results verified that both the pavement texture and skid resistance were substantially improved after sand fog sealing.

Erosion Wear Behavior of Natural and Industrial Material for Polymer Matrix Composite by Using Taguchi Analysis

The behavior of the erosion wear for samples manufactured by hand layup method of epoxy-supported fiberglass, eggshells and calcium carbonate particles were investigated. The test was performed in accordance with the experimental designs Taguchi (L 9) MINITAB (19) to select samples that have the resistance to erosion under the influence of factors. The erosion rate was assessed under the influence of three factors: weight fraction (2% to 8% eggshells and CaCO3 particles), sand size (450, 650, 850 µm) and angles (30º, 60º, 90º) with a fixed face distance of 30 cm, 10 hours and a flow rate of 45 L/min. The results revealed that the rate of erosion is lower for samples consisting of enhanced epoxy resins (eggshell molecules and CaCO3) with chopped fiber glass compared to unfilled samples. Also from these results, it should be noted that the maximum erosion rate was when the weight fraction (2%), the sand size of 850 µm and the angle of 90º, while the minimum rate of erosion was when weight fraction (8%), sand size 650 µm and 30º angle. In this work, the sample of composite materials behaves in a semi- ductile manner.

Influencing factors of various combinations of abrasion, cavitation, and corrosion caused by multiphase flow impact

The surface of ships and other marine transportation equipment is abraded by sandy seawater when under operation. And with a change in speed, cavitation erosion will occur. Seawater has a corrosive effect on metal materials, and the form of damage to the surface materials of ships is the combined erosion of abrasion, cavitation, and corrosion. To study the influencing factors of various forms of erosion, an experimental device for combined erosion was developed. The effects of sand concentration, sand size, salt concentration, and impact speed on the various combinations of abrasion, cavitation, and corrosion of 0.45% C steel specimens are studied experimentally. The results showed that the degree of wear of the combined erosion of abrasion, cavitation, and corrosion was stronger than the combined erosion of abrasion and cavitation or single corrosion erosion. Abrasion, cavitation, and corrosion promote each other, which aggravates the wear of materials and accelerates the loss of material. Under the conditions of low sand concentration and low salt concentration, the mass loss of metal materials for various combinations of abrasion, cavitation, and corrosion was proportional to the sand concentration, sand size, salt concentration, and impact speed. The greatest factor of metal degradation was impact speed.