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
Soil Layer |
Soil Type |
|
General properties |
||||||
Elev. |
φ’ |
C’ or Su |
γt |
ELOAD |
ERELOAD |
Ksub |
e50 |
||
O1 |
Soft Organic Clay |
0 |
- |
400 |
105 |
120 |
360 |
- |
0.02 |
S1 |
Medium Dense Sand |
-7 |
34 |
2 |
125 |
450 |
1350 |
50 |
- |
GT |
Glacial Till |
-20 |
36 |
200 |
130 |
700 |
2100 |
100 |
- |
Table 3: Steel Pile Section Properties
Pile Type |
Driven Pipes with Concrete Fill |
Pile Section |
PP42x1 |
Material |
Steel Fy = 50ksi, Concrete 3ksi |
Pile Depth |
36 ft |
Figure 1: Offshore Pile Cap with Helical Piles Model - DeepFND
B. DEEPFND/HELIXPILE SOFTWARE – SOIL TYPES AND BORINGS
Figure 2: General soil properties – Top Fill Layer (Soil F)
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.
Figure 4: Pile Type, Position and Dimensions
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).
Figure 6: Pile Cap Dimensions and Loads at Centroid
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.
Figure 8: Pile Locations (Local X and Y Coordinates)
Figure 9: Generated 3D Model
F. PILE GROUP – PY SPRINGS ANALYSIS RESULTS
Figure 10: Pile Check Ratios, Shear Diagrams and Axial Forces, Pile Cap Moment (Section at Y=0)
Figure 11: Pile Moment & Displacement Diagrams, Pile Cap Settlements (Section at Y=0)
G. PILE GROUP – 3D FEM ANALYSIS RESULTS
Figure 12: Pile Moment & Displacement Diagrams, Pile Cap Settlements (Section at Y=0)
Figure 13: FEM Settlements in the Soil Mass – 3D Model