The experimental study of the river sand and gravel mining on the scouring pattern around pier group

Document Type : Research Article

Authors

1 Assistant Professor

2 Civil Engineering Department, Faculty of Engineering, University of Maragheh, Maragheh, Iran.

3 Student MSc Maragheh University, Iran

Abstract

Sand mining, especially from places with lower potential, impacts on the hydraulically and sedimentary properties around the bridge piers. The creation of the turbulence causes to the negative effects on the scouring depth and width around the piers. In the present study, the consequences of the mining material, the hydraulical, and sedimentary parameters on the scouring patterns of the piers group were investigated. In order to investigate the scouring of a bridge pier group, 22 experiments were carried out in a rectangular canal with a dimensions of 13 m length, 1.2 m width and 0.8 m depth. The experimental facility is housed at the Hydraulic Lab of Maragheh University. Two false glass floors were installed upstream and downstream at a distance of 4.25 m relative to each other and with a height of 22 cm in the middle of the canal. Sandy movable bed with a height of 22 cm was placed between the aprons. Two pier groups were located upstream and downstream of the bed a specified distance from the aprons. The pier groups with the same arrangement (three consecutive piers in the direction of flow and at the center of the canal's width) were located with center-to-center distances of 21 cm. To eliminate the effect of the canal wall on local scour, the ratio of the pier center-canal wall distance to the pier diameter was greater than 6.25 (Raudkivi and Ettema (1983)). Consequently, piers of diameter of 9 cm were used. To prevent the formation of a ripple, the average diameter of the bed particles should be greater than 0.7 mm and the ratio of the pier diameter to the average particle should exceed 20-25 (Raudkivi and Ettema (1983)). Therefore, the experiments were tested in two different beds, grading ꞌAꞌ with =0.78 mm and grading ꞌBꞌ with =1.7 mm. In order to investigate the effect of the mining pit hole on scouring rate, the mining was done between the upstream and downstream pier groups. The results showed that granulation with coarse particles (B) had lower scour depth than substrate with fine grain size (A). So that the maximum scour depth for B aggregate for Froud number equal to 0.5 and 0.25, was respectively, 14.14 and 47.58 percent less than A. By mining of bed from the downstream and upstream of the group piers, the scouring depth has been increased and reduces respectively. In the Froude number of 0.5 with the mining of materials from the upstream of the groups in the grain size A, the scour depth was 12 to 10.9 cm. However, taking off the bottom of the bases in the same Froude and grading number increased the maximum scour depth from 15 to 15.6 cm. Also, the maximum scour depth in a discharge of 15 liters per second was less for B, compared with A, for gravel A, in Froud number of 0.25 and 0.5 respectively, 44.87% at the fourth base and 61.86% at the first pier, less observation. Although the ratio values in the Froude number of 0.25 for grain size A in the downstream bed is approximately 4 times the grain size of B. Also, the lowest ratio in the Froude number of 0.25 is for the B model with the non-pit hole mining material, while the grain size A with the downstream bed is one of the most scouring models in this Froude number. The phenomenon of scouring in addition to depth dimension, can be studied along the transverse and longitudinal direction. Scouring area is another dimension of the scouring phenomenon that can be affected by parameters. Therefore, the extent of scour area changes in two parts of the scour pattern and bed topography were investigated. In this research, nonlinear regression method is used to predict scour depth around bridges. The relationship between experimental data and empirical of other researchers has been verified using experimental data of this study. In the present study, the scour area around the pier group, along the flow direction for two bed and pit hole was investigated. The effect of this impression on the pattern and depth of scouring showed that the mining of materials from the upstream of the pier groups led to a decrease and this withdrawal from the downstream, increased the depth and extent of scouring. Therefore, it was observed that the pier groups were more sensitive to the mining of materials from their downstream, and it would be better to take this impression upstream of the pier group. Increasing the number of Froude from 0.25 to 0.5 has increased the depth of scouring around the pier group. This increase is higher in larger discharges. Increasing the Froude number in mining of material mode will affect the downstream bed more than the no-pit. So, increasing the Froud number in the bed with the pit hole compared with the non-pit hole bed increases the scour maximum for A, 33% and for B, 73.5%.

Keywords


Tafarojnoruz, A., Gaudio, R. and Calomino F. (2012). Evaluation of flow-altering countermeasures against bridge pier scour. Journal of Hydraulic Engineering, 138, 297-305.
Daneshfraz, R., Chabokpour, J. and Dasine, M. (2018). The experimental investigation of the maximum depth and length of pit holes created by bed material removal under subcritical flow condition. Water and Soil Conservation, 26(1), 111-130 (in Persian).
Zarrati, A.R., Chamani, M.R., Shafaie, A. and Latifi, M. (2010). Scour countermeasures for cylindrical piers using riprap and combination of collar and riprap. International Journal of Sediment Research, 25, 313-22.
Graf, W. and Istiarto, I. (2002). Flow pattern in the scour hole around a cylinder. Journal of Hydraulic Research, 40, 13-20.
Ansari, S., Kothyari, U. and Ranga Raju, K. (2002). Influence of cohesion on scour around bridge piers. Journal of Hydraulic Research, 40, 717-29.
Rambabu, M., Rao, S.N. and Sundar, V. (2003). Current-induced scour around a vertical pile in cohesive soil. Ocean Engineering, 30, 893-920.
Melville, B.W. and Chiew, Y.-M. (1999). Time scale for local scour at bridge piers. Journal of Hydraulic Engineering, 125, 59-65.
Majedi ASL, M., Daneshfaraz, R. and Valizadeh, S. (2018). Experimental investigating effect of river materials mining on scouring around armed pier groups. Iranian Journal of Soil and Water Research. http://dx.doi.org /10.22059/ijswr.2019.269942.668062 (in Persian).
Vittal, N., Kothyari, U. and Haghighat, M. (1994). Clear-water scour around bridge pier group. Journal of Hydraulic Engineering, 120, 1309-18.
Valizadeh, S., Majedi Asl, M., Daneshfaraz, R. and Chabokpour, J. (2018).  Laboratory study of the effect of Froude number on scour around a cable-protected base group in the presence of mining materials. Seventh National Hydraulic Conference of Iran, University of shahrekord (in Persian).
Özalp, M.C. and Bozkuş, Z. (2013). Experimental investigation of local scour around bridge pier groups: MSc thesis, Department of Civil Engineering. The graduate School of Natural and Applied Sciences of Middle East Technical University.
Hannah, C. (1980). Scour at pile groups, University of Canterbury Library.
Hancu, S. (1971). Sur le calcus des affouillements locaus dams la zone des piles des ponts, Proc., 14th IAHR Congress, Paris, France, Vol. 3, 299-313.
Salim, M. and Jones, J.S. (1996). Scour around exposed pile foundations.  North American water and environment congress & destructive water: ASCE, 2202-11.
Rezaei, M., Daneshfraz, R. and Dasine, M. (2018). Experimental Investigation on the Effect of Adding Cationic and Polyacrylamide Caps on the Scouring of pier and Pit hole Under the Effects of River Matter. Iranian Hydraulic Association. 10.30482/jhyd.2018.81358. (in Persian)
Amini, A. (2001). Field and Laboratory Survey of Moving the Cavity of Harvesting Materials. Tarbiat Modarres University, Tehran. (in Persian)
Raudkivi, A.J. and Ettema, R. (1983). Clear-water scour at cylindrical piers. Journal of Hydraulic Engineering, 109, 338-350.
Richardson, E.V. and Davis, S.R. (2001). Evaluating scour at bridges. Publication No. FHWA NHI 01-001, Hydraulic Engineering Circular No. 18, Federal Highway Administration, U.S. Dept. of Transportation, Washington, D.C.
Jain, S. (1981). Maximum Clear-Water Scour around Cylindrical Piers, Journal of Hydraulic Engineering, 107(5), 611-625.
Julien, P.Y. (2010). Erosion and sedimentation: Cambridge University Press.
Volume 14, Issue 3 - Serial Number 143
December 2019
Pages 129-145
  • Receive Date: 09 June 2019
  • Revise Date: 28 July 2019
  • Accept Date: 05 August 2019
  • First Publish Date: 22 November 2019