Piles supporting marine structures such as jetties, relieving platforms, quay walls and fixed offshore structures are subjected to lateral loads due to berthing and mooring forces, wind, waves, storm surges and current forces. This paper presents some factors that affect the design of pile groups supporting marine structures founded in cohesionless soils. Some main aspects that should be considered in the pile group design are addressed such as pile batter angle, pile group arrangement, pile spacing, pile slenderness ratio and magnitude of lateral static loading. Numerical analyses were conducted to investigate these design aspects with and without impact of scour. Different scour depths were considered to cover the possible root causes of scour around pile groups such as waves, current and ship propeller jets. The study revealed that scour has greater impact on lateral loading of pile groups compared to its impact on single piles. Pile groups with side-by-side arrangement exposed to scour are more critical than single piles and piles groups with tandem arrangement due to the combined effect of scour and pile-soil-pile interaction. It is also concluded that scour protection is not always required. More attention and considerations should be given to scour protection around piles especially if the piles are closely spaced, arranged side-by-side and if slenderness ratio is less than 12.5.
Marine structures such as jetties, seawalls, relieving platforms, quay walls and fixed offshore (jacket type) structures are often supported on pile groups. The foundation piles usually comprise a large portion of the marine structure cost. These piles are usually subjected to large lateral loads induced from waves, currents, vessel berthing and mooring forces. Also, these piles are subjected to scour due to waves, current and ship propeller jets.
Marine structures and bridge piers supported on pile groups can fail due to severe scour. Numerous publications are found in the literature for investigating the scour around piles for bridge piers and a smaller number of publications investigating the scour around marine structures. Moreover, a very limited number of publications regarding the effect of scour on the behavior of pile groups is found in the literature. Vertical pile capacity is composed of friction along pile length and end bearing at pile toe while pile lateral capacity highly depends on the soil conditions surrounding the top one third of pile length. Therefore, scour impact on lateral pile capacity is more significant than the scour impact on vertical pile capacity.
Global scour refers to a general lowering of the ground surface over a wide area.
Scour around piles varies due to the root cause. For single piles, scour depth in sandy soils (ds) is 1.3 times pile diameter (d) with a mean of 0.7 [
luate the effects of scour on the behavior of pile groups. Among this limited research, recent research focused on piles supporting bridge piers such as Lin et al. [
Effect of scour on lateral loading of single piles has been investigated in a few recent publications such as Kishore et al. [
As piles are usually installed in groups, it becomes necessary to study the effect of scour on the behavior of pile group not just single piles. The combination of scour and pile-soil-pile interaction (i.e., group effect) can lead to a significant reduction in lateral pile capacity and consequently may lead to the failure of marine structures.
This paper presents the impact of global scour around batter and vertical pile groups installed in medium dense sand. The software program GROUP V.7.0 [
Different design parameters were investigated in this paper such as pile batter angle, pile group arrangement, pile spacing and pile slenderness ratio. The impact of scour depth on all these parameters was investigated. Only global scour was considered in this study as it has more significant impacts compared to local scour.
Based on the results of the numerical analyses, this paper also provides general recommendations and guidelines on the necessity of using scour protection. Scour protection using riprap or geotextile may be necessary sometimes and may be a waste of money in other cases. The decision to protect the piles from scour depends on the maximum anticipated scour depth based on the root cause of scour and also depends on the pile, soil and loading conditions.
In this paper, numerical analyses were conducted to investigate several parameters affecting the design of pile groups supporting marine structures subjected to scour. The software program Group [
A comparison between the results from the computer program Group [