# Experimental Study of Scour Hole Depth around Bridge Pile Using Efficient Cross-Section
## 5 Conclusions  
This study experimentally investigates the scour around pile groups of various cross-sections, namely rectangular, square and lenticular. A focus is placed on comprehending the scouring process around a rectangular array of eight pile-cap. The depth of a local scour around piles is predicted using empirical models based on piers exposed to steady water currents. The following conclusions can be drawn from this experimental study:  
* The scour at a pile group is more extreme relative to that around a single pile, mainly due to the increase in the flow velocity of closely spaced piles resulting in a compressed horseshoe vortex.
* The very first pile at the upstream side of the pile group experiences the maximum scour. This is mainly due to the weakening of the downflow at the pile upstream and the weakening of the horseshoe vortex, which results in a reduced scour around rare piles.
* The influence of geometry of piles has a particularly large effect on the scouring. The effect of scouring is more pronounced in the square piles, followed by the circular piles and minimal in the lenticular piles.
* The existing engineering practice of employing pier scour empirical models is not accurate enough in predicting the scour depth of piles. For example, the current study suggests that the popular Neill and Hanco models underestimate the scour depth by more than 50%.
* Given the inconsistencies between the pier scour predicting models and the experimental scour around the piles, new empirical models based only on piles scouring are needed. Furthermore, the preceding conclusions are valid for the pile groups that are aligned to the flow. For a skewed pile group, the variables influencing the local scour depth are different, thus requiring additional research.  
M.T.: Conceptualization, Methodology, Investigation, Software, Formal Analysis. Writing--original draft, Validation, Experimental Procedure. A.K.: Resources, Writing--review and editing, Supervision. M.K.: Supervision. All authors have read and agreed to the published version of the manuscript.  
The research work is self funded.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
Figure 9: Comparison scouring depth at Position A with Neill and Hanco Model.  
**Acknowledgments:** The experimental work is carried out in the hydraulic laboratory of UET Peshawar (Pakistan). Special thanks are extended to Hamna (Local Government, Govt. of Khyber Pakhtunkhwa), for providing Electronic Velocity meter to carry out laboratory experimental test work with high accuracy. I also thank [PERSON] (NESPAK-Peshawar) for his guidance, supervision in the selection of the bridge. His assistance and discussions for the selection of Pakhtun Gari Bridge which was suffering from a unique type of bridge piles scouring are highly acknowledged.  
**Conflicts of Interest:** The authors whose names are listed certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.