This document examines a case history of a pile raft, constructed in Gdansk, Poland. A liquid gas terminal was constructed over 2 rectangular pile caps (71 m x 61.2 m x 0.9 m thick), each one of them supported by 180 reinforced concrete bored piles (diameter: 1 m and 0.62 m, pile depth: 26.5 m).
A model of the pile raft was created with our DeepFND software program. This document presents the software input and calculation results, as well as, a comparison with the measured displacements and estimations of different methods. Some information and data that were not included in the case history, had to be assumed.
A. SOIL PROPERTIES AND STRATIGRAPHY
The piles were embedded in sand and alluvium soil layers. The following Table summarizes the estimated soil properties for all soil types.
Table 1: Soil Properties and Soil Layers (Stratigraphy)
Soil Layer Top Elev. (m) | Soil (-) | Soil Type (-) | Friction Angle (deg) | Cohesion (c’ or Su) (kPa) | Total Unit Weight (KN/m3) | Young’s Modulus (kPa) | Poisson’s Ratio (-) | |
5 | 1 | Sand (Fill) | 30 | 0 | 18 | 32000 | 0.35 | |
2.9 | 2 | Silty Sand | 26 | 2.4 | 16 | 52000 | 0.45 | |
-2.5 | 3 | Soft Sand | 28 | 0 | 17 | 9000 | 0.35 | |
-7 | 4 | Medium Sand | 34 | 0 | 18 | 35000 | 0.35 | |
-9.7 and -18 | 5 | Medium Silt | 28 | 14.5 | 19.6 | 32000 | 0.45 | |
-11.9 And -23.6 | 6 | Dense Clay (Undrained) | - | 15 | 15 | 1300 | 0.45 | |
-24 | 7 | Sandy Clay (Undrained) | - | 150 | 20 | 36000 | 0.32 | |
B. PILE SECTION PROPERTIES AND PILE POSITIONS (LAYOUT)
In the original project, two types of piles where used:
- 1 m diameter reinforced concrete piles, distributed on the whole pile raft
- 0.62 m diameter reinforced concrete piles, used along the 3 raft sides
C: GENERATED MODEL - RESULT GRAPHS (DEEPFND)
D: DEEPFND PILE RAFT SETTLEMENTS VS MEASURED AND PREDICTED WITH OTHER METHODS
Pile raft settlements were measured during the project construction. DeepFND software predicted a maximum of 17 mm settlements at the last pile row location (closest to the pile raft edge), matching the measured settlement values. Table 2 below, presents the predicted settlements at the middle of the pile raft, in comparison to values predicted from other methods and sources.
Table 2: Maximum Settlement Predictions with DeepFND and Other Methods
Method | Settlement (mm) |
DeepFND – Pile Rafts Module (Non-Linear Soil Springs Method) | 33 |
Equivalent Foundation According to Polish Code (PN-69) | 32.7 |
Equivalent Foundation According to Tomlinson | 30.9 |
Equivalent Foundation According to Poulos (Randolph Formula) | 34 |
Equivalent Foundation According to Van Impe | 33.4 |
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