Shallow foundations · SPT
Shallow Foundation Design using SPT Blowcounts
Corrects the SPT blow count, then estimates the allowable bearing stress from three bearing capacity methods and the stress that causes the allowable settlement, for five footing widths.
SPT corrections
Corrected blow count at the depth of interest below each footing.
| Footing width, B (m) | 0.6 | 1 | 1.5 | 2 | 3.048 |
|---|---|---|---|---|---|
| Depth of interest (m) | |||||
| Vertical effective stress, σ′v (kPa) | |||||
| Liao & Whitman depth correction factor | |||||
| N1,60 |
Bearing capacity
Terzaghi bearing capacity equation for sands, with the friction angle from two SPT correlations, and the empirical Meyerhof (1956) equation.
| Footing width, B (m) | 0.6 | 1 | 1.5 | 2 | 3.048 |
|---|---|---|---|---|---|
| Hatanaka & Uchida (1996), Mayne (2001) | |||||
| Friction angle, φ′ (°) | |||||
| Nγ (Chen) | |||||
| Nγ (Brinch-Hansen) | |||||
| Nq | |||||
| Ultimate capacity (kPa) | |||||
| Allowable stress (kPa) | |||||
| De Mello (1971), Schmertmann (1975), Mayne (2001) | |||||
| Friction angle, φ′ (°) | |||||
| Nγ (Chen) | |||||
| Nγ (Brinch-Hansen) | |||||
| Nq | |||||
| Ultimate capacity (kPa) | |||||
| Allowable stress (kPa) | |||||
| Meyerhof (1956), empirical | |||||
| Ultimate capacity (kPa) | |||||
| Allowable stress (kPa) | |||||
Deformation criterion: Burland & Burbidge (1984)
Bearing stress that induces the allowable settlement.
| Footing width, B (m) | 0.6 | 1 | 1.5 | 2 | 3.048 |
|---|---|---|---|---|---|
| Inducing stress, mean − σ (kPa) | |||||
| Inducing stress, mean (kPa) | |||||
| Inducing stress, mean + σ (kPa) |
Allowable stress
Allowable stress from each bearing capacity method against the stress that induces the allowable settlement, by footing width.