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Offshore Pile Foundation Design

A. PROJECT DESCRIPTION – PILE SECTION – SOIL PROPERTIES

In this example we will design an offshore pile foundation – a 25’x25’ rectangular concrete cap over driven pipe foundation piles. Table 1 below presents the soil properties and stratigraphy that has been estimated and used within the DeepFND software. Table 2 presents the helical pile section properties. The water table is at El: +10ft.

Table 1: Soil properties & Stratigraphy

Pile Type


Driven Pipes with Concrete Fill


Pile Section


PP42x1

Material

Steel Fy = 50ksi, Concrete 3ksi


Pile Depth


36 ft


Table 2: Steel Pile Section Properties


Offshore Pile Foundation Design
Figure 1: Offshore Pile Cap with Helical Piles Model - DeepFND

B. DEEPFND/HELIXPILE SOFTWARE – SOIL TYPES AND BORINGS

Offshore Pile Foundation Design
Figure 2: General soil properties – Top Fill Layer (Soil F)

Offshore Pile Foundation Design
Figure 3: Soil Layers

C. DEEPFND SOFTWARE – PILE SECTION PROPERTIES

In this example we will use 42in diameter steel pipes (PP42x1) driven into the soil. The pipes will be filled with concrete grout. Figures 4 and 5 present the pile type and length, and the pile section properties respectively.


Offshore Pile Foundation Design
Figure 4: Pile Type, Position and Dimensions

Offshore Pile Foundation Design
Figure 5: Pile Section Properties

D. PILE GROUP – DIMENSIONS AND LOADS

In this case, we will design a 3ft thick concrete rectangular pile cap (25ft x 25ft), supported by 9 piles (PP42x1). The 8 piles at the perimeter of the cap will be battered piles (75deg inclined from horizontal & and locally rotated along the global z-z' axis to point outwards). An additional 2800 Kips vertical load and two lateral loads (250 kips along the local x and 140 kips along the local y directions) are applied on the pile cap centroid. Figure 6 presents the pile cap dimensions and the loads applied on the cap centroid. Figure 7 presents the loads are presented on the pile cap centroid (side view).

Offshore Pile Foundation Design
Figure 6: Pile Cap Dimensions and Loads at Centroid

Offshore Pile Foundation Design
Figure 7: Loads on the Pile Cap

E. PILE GROUP – PILE LOCATIONS AND GENERATED MODEL

In this case, 9 piles (PP42x1) have been distributed to the pile cap. Figures 8 and 9 present the piles layout (pile center local x and y coordinates, local rotation angle) and the generated 3D model respectively.

Offshore Pile Foundation Design
Figure 8: Pile Locations (Local X and Y Coordinates)

Offshore Pile Foundation Design
Figure 9: Generated 3D Model

F. PILE GROUP – PY SPRINGS ANALYSIS RESULTS

Offshore Pile Foundation Design
Figure 10: Pile Check Ratios, Shear Diagrams and Axial Forces, Pile Cap Moment (Section at Y=0)

Offshore Pile Foundation Design
Figure 11: Pile Moment & Displacement Diagrams, Pile Cap Settlements (Section at Y=0)

G. PILE GROUP – 3D FEM ANALYSIS RESULTS

Offshore Pile Foundation Design
Figure 12: Pile Moment & Displacement Diagrams, Pile Cap Settlements (Section at Y=0)

Offshore Pile Foundation Design
Figure 13: FEM Settlements in the Soil Mass – 3D Model


 

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