نوع مقاله : مقاله پژوهشی
نویسندگان
گروه علوم و مهندسی آب، دانشکده کشاورزی و محیطزیست، دانشگاه اراک، اراک، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Adding clay to the sediment composition downstream of hydraulic structures in rivers generally increase the soil resistance to fluid erosive forces by increasing particle adhesion, improving soil structure, reducing uncontrolled permeability, and increasing water retention capacity. In the present study, the effect of adding clay to the sediment composition as a protective approach and reducing scour downstream of a submerged horizontal jet by reaching the maximum dry density of the sediment composition has been investigated experimentally. Experiments were conducted for two Froude numbers 4 and 6 and three types of sands with average diameters of 0.63 mm (S1), 1.81 mm (S2) with uniform grain size, and 1.74 mm (S3) with non-uniform grain size in a laboratory flume with a width and depth of 80 cm and a length of 10 m. In order to achieve maximum density, natural clay was used with percentages of 5, 10, and 15. The results showed that for the Sand S1, the scour hole dimensions with the finest grain size (S1) reach zero at a Froude number of 4, and at a Froude number of 6, the scour depth, dune height, and scour hole volume decrease by 37%, 50.8%, and 56.25%, respectively. Also, for Sands S2 and S3 with the same average diameter but different grain size distribution, it was observed that particle non-uniformity under maximum density conditions has a significant effect on scour hole dimensions. The results showed that for the S2 grain size and Froude number of 4, the scour hole dimensions reach their lowest value by adding 10% clay. While for the S3 grain size, by adding 5% clay to the mixture, the hole dimensions reach zero.
کلیدواژهها [English]
Previous studies have demonstrated that the application of clay in sediment mixtures may reduce scour downstream of hydraulic structures such as bridge piers and stilling ponds. In addition, the addition of clay to sediment mixtures increases the dry specific density of the soil, improves its compaction, and increases its mechanical strength, which is of great importance in the design of foundations, embankments, and geotechnical structures. However, unlike traditional compaction methods that examine clay and sand separately, the combined compaction approach for sand and sand-clay mixtures simultaneously increases the interpenetration and adhesion of particles, leading to improved resistance to deformation and erosion, which is particularly useful for hydraulic and geotechnical applications, but has not been addressed in any laboratory study to date. For this purpose, in this research, an attempt was first made to bring three non-cohesive sediments to the maximum dry specific gravity, then experiments were conducted by adding different clay contents to the sediment mixtures.
Experimental tests were conducted in a laboratory flume (see Fig. 1), with a rectangular cross-section, with 9 m length, 0.8 m width and a depth of 0.6 m. Walls and bottom of the flume were made from Plexy-Glass and metal, respectively, and slope was set to zero. For modeling the scour process, a sedimentation basin was built with a depth of 11.6 cm, length of 1 m and a width equal to the flume width. two uniform sands (S1 and S2) and one non-uniform sand (S3) were used. According to ASTM-D6913, sieve analysis was conducted on the samples to obtain gradation curve of the sediments. In addition, the Hydrometer Analysis was done based on ASTM-D7928 for used clays as cohesive particles.
For sand S1 and Froude number 4, the scour hole dimensions decrease with increasing clay content. So that at bed compaction of 100% and for 5% clay, the scour depth decreased by 59% compared to the control experiment. Interestingly, no measurable scour was observed in the sedimentary bed at 100% density and for 10 and 15% clay contents. Also, for experiments with Froude number 6, the scour hole dimensions decrease with increasing clay contents. So that at bed compaction of 100% and for 5% clay, the scour depth decreased by 37% compared to the control experiment. For sand S2 with Froude number 4 and with increasing clay content, the hole dimensions did not change significantly. Also, for experiments with Froude number 6, the scour hole dimensions decrease with increasing clay percentage. So that at bed compaction of 100% and 5% clay, the scour depth has decreased by 20% compared to the control experiment. For sand S3 at bed compaction of 100% and Froude number 4, no measurable scour was observed in the sedimentary bed. For experiments with Froude number 6, the scour hole dimensions decrease with increasing clay content. So that at 100% density and 5% clay, the scour depth has decreased by 57% compared to the control experiment.
Within the experimental conditions of this study (sediments with a diameter of less than about 2 mm and a maximum Froude number of 6), the optimal clay ratio in the sediment mixture is between 10 and 15 percent, and with this ratio, bed protection is appropriately achieved. Of course, each type of cohesive sediment has its own behavior that should be considered in future research.
Therefore, clay, as a low-cost, effective and environmentally friendly approach, plays a key role in increasing bed resistance and reducing the dimensions of the scour hole downstream of hydraulic structures by increasing the adhesion and stabilization of the sedimentary bed. It can be used as an alternative or complement to traditional scour control methods.
“Conceptualization, M.N. and J.M.; methodology, A.J.Z.; experiments, A.J.Z.; validation, M.N.; formal analysis, M.N.; investigation, J.M.; resources, A.J.Z.; data curation, M.N. and A.J.Z.; writing—original draft preparation, M.N.; writing—review and editing, M.N.; supervision, M.N.;
All authors have read and agreed to the published version of the manuscript.”
Not applicable
The authors would like to thank all participants of the present study.
The authors avoided data fabrication, falsification, plagiarism, and misconduc
The author declares no conflict of interest.
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