Ali Tafarojnoruz

Flow-altering countermeasures against scour at bridge piers: a review

During the past decades, several investigations were conducted to assess the adequacy of countermeasures against local scour at bridge piers. The countermeasures can be broadly classified into two categories: (1) flow-altering and (2) bed-armouring countermeasures. Flow-altering countermeasures, as treated herein, can be classified into four main groups based on their shapes and performances. A comprehensive review of the up-to-date studies on various types of flow-altering countermeasures is presented, placing special emphasis on recently proposed methods while also revisiting studies of former methods. Experimental conditions of different studies under which the tests were performed are critically examined. A preliminary evaluation of the previously conducted experiments indicates that the results of several tests were influenced by side-wall, sediment size, flow shallowness and temporal effects. Experimental results on the combinations of different countermeasures, including their limitations and difficulties in field applications, are also discussed. Finally, suggestions are presented for further research on selected countermeasures.

Combined flow-altering countermeasures against bridge pier scour

This study presents the results of clear-water tests on the following five combined flow-altering countermeasures against bridge pier scour: (1) submerged vanes and a bed sill, (2) slot and sacrificial piles, (3) a collar and sacrificial piles, (4) a slot and a collar, and (5) a bed sill and a collar. Each countermeasure was designed on the basis of the best configuration recommended in the literature. The results clarify that an improper combination of two countermeasures may be less effective than each individual countermeasure; combinations (1), (2), and (3) do not reduce the scour depth significantly with respect to the single countermeasures; combination (3) increases the scour rate during the first few hours with respect to a single collar; combination (4) may also prevent scour intrusion beneath a collar; and combination (5) in the best configuration reduces the scour depth significantly around the collar with respect to maximum scour depth of the unprotected pier, preventing also the scour hole reaching the pier body.

Effects of Pile Cap Thickness on the Maximum Scour Depth at a Complex Pier

An experimental campaign of 21 long-duration tests on scouring at complex piers of different configurations was performed to investigate the effect of pile cap thickness on the temporal evolution of the maximum scour depth and the development of equilibrium conditions. Two test series were performed with two significantly different pile cap thicknesses over a wide range of pile cap elevations with respect to the expected scour hole and the approach flow depth. In addition, the accuracy of existing methods to calculate the maximum scour depth was evaluated and discussed. The results show that, in general, the thicker the pile cap, the deeper the corresponding scour hole. The increase in scour depth that is attributable to the pile cap thickness depends on the distance between the pile cap and the original bed level. The observed maximum scour depth was greater with the thicker pile cap (with respect to the thinner pile cap) when it was entirely immerged into the flow, partially buried, or totally buried at a small depth from the initial bed level. Depending on the distance between the pile cap and initial bed level, the pile cap thickness may also influence the temporal evolution of the maximum scour depth by increasing or reducing the scouring rate. DOI: 10.1061/(ASCE)HY.1943-7900.0000704.

Evaluation of Flow-Altering Countermeasures against Bridge Pier Scour

In this study, six different types of flow-altering countermeasures against pier scour were evaluated experimentally. The selected countermeasures were submerged vanes, bed sill, transverse sacrificial piles, collar, threading, and pier slot. Laboratory tests were performed in clear-water conditions with flow intensity slightly below the threshold of sediment motion. Tests were designed on the basis of the best configurations recommended in previous studies by different authors to obtain the maximum efficiency in terms of scour depth reduction. Results showed that some countermeasures, which were recommended as highly efficient in the literature, do not perform well under other test conditions; in particular, literature tests carried out with low flow intensity or short duration or in narrow-channel conditions are criticized. The efficiency of bed sill, submerged vanes, and threading was found to be less than 20%, whereas collar, pier slot, and transverse sacrificial piles reduced the maximum scour depth ...

Bridge pier scour mitigation under steady and unsteady flow conditions

Watercourse morphology is affected by local scouring when the flow interferes with anthropic structures. Controlling the scour hole size is of predominant importance to guarantee bridge safety as well as to limit the variations of river morphology. A combined countermeasure against bridge pier scour is proposed and tested in order to reduce the maximum scour depth and deviate it away from the bridge foundation. In the first part of the laboratory campaign, combination of two countermeasures (bed-sill and collar) was evaluated for a circular pier under clear-water and live-bed steady flow conditions. The proposed combined countermeasure exhibited an efficiency of about 64% in terms of scour depth reduction. Afterwards, it was tested in unsteady flow conditions, first for a circular pier, then in the case of a rectangular pier with round nose and tail, two circular in-line piers and two rectangular in-line piers, under a hydrograph with a peak flow velocity slightly above the threshold condition of sediment motion. Results showed that the combined countermeasure had an efficiency of about 63% for a single circular pier; however, higher efficiency (about 75%) was obtained in applications to rectangular pier and two in-line circular or rectangular piers.

Modified Einstein Sediment Transport Method to Simulate the Local Scour Evolution Downstream of a Rigid Bed

AbstractThe present study consists of a new mathematical-numerical modeling formulation to simulate the spatial and temporal scour development downstream of a rigid bed for both a noncohesive sediment bed and a cohesive sediment mixture with relatively small percentage of cohesive material. Laboratory tests were conducted in a rectangular tilting flume having a recessed box filled with the selected bed sediments and placed downstream of a rigid rough bed. The scour pattern was accurately acquired with a three-dimensional laser scanner at various time instants. The numerical code was calibrated through the scour profile data obtained under steady-state flow condition and then validated on the basis of scour patterns acquired under both steady and unsteady flow conditions (symmetric and asymmetric hydrographs). Contrary to most previous studies conducted with an issuing jet, the present study’s experiments were performed under non–strictly uniform flow conditions. The numerical model utilized information co...

Experimental and Numerical Study on the Flow Field and Friction Factor in a Pressurized Corrugated Pipe

AbstractAn experimental campaign including measurement of pressure drops and velocity profiles was conducted on the pressurized flow in a commercial corrugated pipe. The results show that the empirical graphs suggested by Morris in the fifties may produce inaccurate assessments of the friction factor, in particular, for low Reynolds numbers. The experimental data was then reproduced by means of a numerical model with the large eddy simulation (LES) technique. The friction factor behavior for low and relatively high Reynolds numbers was thus investigated. The numerical simulations were in good agreement with the experimental results, showing the LES suitability to predict the effect of the pipe wall corrugation on the mean flow in a range of Reynolds numbers typical of engineering applications. To provide a quantitative evaluation of the numerical model, the Nash–Sutcliffe model efficiency coefficient E and the root mean square error (RMSE) were calculated, demonstrating the goodness of the numerical resul...

Sills and gabions as countermeasures at bridge pier in the presence of debris accumulations

(1) Grimaldi et al. (2009) neglected the density effect in the dimensional analysis, since for natural sand and gravel ≈ 1.65. The authors had = 1.44 for the sand employed in their tests, i.e. a value below than the common, so that should be inserted in Eq. (1), even if it was kept constant in the tests. A comparison of results can also be affected by this effect. (2) The effect of the 3D approach flow field may not be negligible if b/h = 3 (Graf and Altinakar 1998, Fig. 1.6). Note the typo h/b in the paper. (3) Under debris presence, the authors define the parameter T ∗ = hUt/Aacc, where Aacc = (dd − D) · td + hD, reducing to T ∗ = Ut/D for debris absence. If zmax is close to the scour depth in front of the pier, Fig. D1 shows zmax/D versus T ∗ for Tests A0, A1 and A2 of Grimaldi et al. (2009). Table 2 states T ∗(rs max) = 3.07 × 104 for their test series A, yet it is unclear to the discussers how it was computed and what the meaning of this value is. Figure D1 clarifies that zmax/D increases for T ∗ > 3.07 × 104 until the equilibrium is achieved; however, this value corresponds to only 1.6 h, far from the final test duration of TD ∼= 100 h (Table D1). Also, the values of zmax/D and rs max stated in Table 2 are referred to at test end of A0, A1 and A2 by Grimaldi et al. (2009), so that T ∗(rs max) should be the final dimensionless time (Table D1). (4) At p. 766, the authors state that the scour hole tends to equilibrium as T ∗ > 106, quoting Franzetti et al. (1994) and Grimaldi et al. (2009). Franzetti et al. (1994) proposed T ∗ ≥ 2 × 106 to assess the equilibrium scour depth with an accuracy of ±10%, whereas Grimaldi et al. (2009) adopted that criterion to estimate a reference value for the test duration, considering mandatory that the semi-logarithmic plot of scour depth versus time has a slope change (Cardoso and Bettess 1999) and that the scour depth variation within 24 h be less than 0.05D/3. Table D1 shows that the final values of T ∗ in the tests by Grimaldi et al. (2009) are much larger than 106, as confirmed also by the new tests of Tafarojnoruz et al. (2011). However, the authors’ highest T ∗ 106 for Tests P10, P25 and P35 (Fig. 3a,e,h) and the scour hole did not reach equilibrium, so that rs max ≈ 0.3 in Table 2 appears unreliable. Figure 3 shows that in many tests, no slope change occurred. This feature was also discussed by Tafarojnoruz et al. (2010). (5) The efficiencies calculated on the basis of T ∗ = O(T ∗ 3 ), as shown in Table 2, may be misleading, since the scour phenomenon experiences a rapid scour rate increase in phase IV for debris tests, but Table 2 shows that the calculated

Vortex scouring process around bridge pier with a caisson

This study deals with the role of the primary vortex on scour at a pier with a caisson, on which information is scarce since most of the previous works focused on uniform piers, neglecting the effect of foundation. The available studies indicate that, in addition to the parameters influencing the scour depth at piers, others also affect the scour depth at a pier with a foundation. According to Melville and Raudkivi (1996), the diameter ratio D/Dc and the distance from the bed to the foundation top Y influence eliminate the scour depth. Let Y be negative when the pile cap top is above the initial bed level (Fig. D1a). This condition may occur during bed degradation, for which a higher scour depth with respect to a single pier is expected. Figure D2 shows the significant effects of D/Dc and Y /D on the dimensionless scour depth hs/D. In the discussed paper, the parameter Dc is the only geometrical factor accounting for the caisson pier and the single pier, which may not be sufficient. Further, a caisson may be founded under the initial bed level, owing to geotechnical reasons or bed aggradation. According to Breusers and Raudkivi (1991), a footing or a caisson with a top below the general bed level may reduce the scour depth by intercepting the downflow. Tafarojnoruz et al. (2010) categorized this case as a scour countermeasure since, depending on the footing depth and foundation shape, it may lead to scour reduction with respect to a pier without foundation. If the foundation is deep enough, the scour may even not reach it (Fig. D1b). Then the scour depth is independent of Dc. Thus, Eqs. (1) and (2), in which Dc is the only geometrical parameter of a single uniform pier, or pier with a circular or oblong caisson eliminate need for further explanation. Actually, both values of D and Dc are not D D