Search results

Filters

  • Journals
  • Authors
  • Keywords
  • Date
  • Type

Search results

Number of results: 5
items per page: 25 50 75
Sort by:
Download PDF Download RIS Download Bibtex

Abstract

River training structures; such as submerged groynes are low profile linear structures that are generally located on the outside bank to form groynes fields and prevent the erosion of stream banks by keeping a flow away from it. In the present research, the maximum scour depth was measured based on laboratory experiments where different shapes of submerged groynes (I-shape, L-shape, T-shape) were used as sort of countermeasures to investigate about most shapes that reduce the scour around them. The result of submerged groynes showed a clear decrease in scour depth ratio due to increasing sub-merged ratio and increase the scour hole geometry with increasing of flow intensity, and also Froude number. The maxi-mum scour hole in this research was observed at T-shape groyne and then followed by I-shape groyne and L-shape groyne. The maximum scour depth that cased by I-shape was more than L-shape by a percentage about 8.2%, and it was less than T-shape by a percentage about 16.4%.

Go to article

Authors and Affiliations

Budoor M. Rashak
Saleh I. Khassaf
ORCID: ORCID
Download PDF Download RIS Download Bibtex

Abstract

Bridges built across a river bend and supported by more than one pier has been experimentally studied regarding the shape and nature of erosion and deposition. For this purpose, a U-shaped laboratory channel was used with two oblong piers installed at different locations. The first one was at the mid-section of the upstream straight reach, whereas in the second site within the bend, the piers have been installed at sections of central angles 0°, 30°, 60°, 90°, 120°, 150°, 170°, and 180°, from the beginning to the end of the bend segment respectively. The studies were conducted under clear water and threshold flow conditions. The results show that the higher and lower values of local scour around the pier positioned close to the outer bank, are 1.803 and 0.623 times the pier width when the bridge was installed at an angle of 90° and 30° respectively. As for the pier close to the inner bank, the deepest local scour was 1.786 times of the pier width when the bridge was installed at 60° of the bend, while the least one was 0.516 times of the pier width when the bridge was located in the 180° sector. It is worth noting that the presence of piers within sector 150 is less affected by local scour than in the other sections.
Go to article

Authors and Affiliations

Abdulrazaq K. Abdulwahd
1
ORCID: ORCID
Jaafar S. Maatooq
1
ORCID: ORCID

  1. University of Technology, Civil Engineering Department, Al-sina’a St, P.O Box 19006, Baghdad, Iraq
Download PDF Download RIS Download Bibtex

Abstract

The article presents the results of experimental research aimed at recognizing the impact of the design of energy dissipation devices on the formation of bed local scouring below the sluice gate. The experiments were carried out on a model of a sluice gate built in a rectangular flume with a width of 0.58 m, with the outflow of the stream from under the slider to a horizontal bed 0.80 m long. Behind the dam gate valve three different constructions of energy dissipation devices were used: flat, horizontal slab, slab equipped with baffle blocks arranged in two rows and rip-rap. The experiments assumed forming a scour hole in 480 minutes downstream the sluice, where the bed was filled with sorted sand. The depths of the scour were measured in the longitudinal profile after 30, 60, 90, 120, 180, 240, 300, 360, 420 and 480 minutes. The deepest scour holes of the bed, both in terms of depth and length, occurred on the structure model with energy dissipation devices made as a flat, horizontal plate. At the same time, in this case, the hole was developing the most rapidly, and its shape and size posed the greatest threat to the stability of the structure. The use of baffle blocks arranged in two rows or a rip-rap behind the structure slide noticeably reduced the size of the scour and delayed the erosion of the bottom in time, as compared to the course of this process on a model with a flat, horizontal slab.

Go to article

Authors and Affiliations

Janusz Urbański
ORCID: ORCID
Marta Justyna Kiraga
Sławomir Bajkowski
ORCID: ORCID
Download PDF Download RIS Download Bibtex

Abstract

The bridge structure’s development causes a riverbed cross-sections contraction. This influences the flow regime, being visible during catastrophic floods. Then the flow velocity increases and water piles up upstream the bridge, where headwater afflux could be observed. These changes depend on the watercourse geometry and the bridge cross-section properties, especially on the degree of flow contraction under the bridge. Hydraulic conditions under the bridge depend on flow velocity, dimensions, and shape of abutments, the granulometric composition of bedload, which can be quantitatively characterized by hydraulic resistance coefficients. The research subject of headwater afflux is equated with the recognition of morphodynamic processes occurring along the passage route. The headwater afflux could be estimated by empirical formulas and by the energy method using Bernoulli’s law. Empirical methods are optimized by adopting various statistical criteria. This paper compares the headwater afflux values calculated using two existing empirical formulas, Rehbock and Yarnell, and compares them with the results of laboratory tests. Following the assumption that the free water surface is influenced by flow resistance, an attempt was made to include friction velocity in the empirical formulas. Based on the Authors’ database, the coefficients used were optimized using bootstrap resampling in Monte Carlo simulation. The analyses demonstrated that the formula best describing the phenomenon of headwater afflux upstream the bridge is an empirical formula built based on the historical Yarnell formula, which includes friction velocity value. The optimized equation provides an average relative error of 12.9% in relation to laboratory observations.
Go to article

Authors and Affiliations

Marta Kiraga
1
ORCID: ORCID
Sławomir Bajkowski
1
ORCID: ORCID
Janusz Urbański
1
ORCID: ORCID

  1. Warsaw University of Life Sciences, Institute of Civil Engineering, Faculty of Civil and Environmental Engineering, ul. Nowoursynowska 159, 02-776 Warsaw, Poland
Download PDF Download RIS Download Bibtex

Abstract

Although the complexities and irrevocable consequences associated with bridge scour have attracted researchers interest, their studies scarcely indicated the effect of a bridge pier proximity to an abutment. This research aims to measure maximum scour depth and exhibit the impact of pier-abutment scour interference based on laboratory experiments where vertical-wall abutment and two shapes of a pier (oblong and lenticular) were used at three different spacings (23.5, 16.0, 9.0 cm). The results showed an obvious increase in the scour depth ratio when increasing flow intensity, Froude number, and a decreasing flow depth. They also showed that reduced pier-abutment spacing was accompanied by increase in pier scour for both shapes while decrease in abutment scour. The maximum scour depth that caused by an oblong shape was more than a lenticular shape by about 10.8%. Furthermore, new empirical equations were derived using IBM SPSS Statistics 21 with determination coefficients of 0.969, 0.974, and 0.978 for oblong, lenticular and abutment, respectively. They showed the correlation between predicted and observed data.
Go to article

Authors and Affiliations

Noor A.A. Muhsen
1
ORCID: ORCID
Saleh I. Khassaf
1
ORCID: ORCID

  1. University of Basrah, College of Engineering, Department of Civil Engineering, Center of Basrah, PO Box 49, Al Basrah, Iraq

This page uses 'cookies'. Learn more