NF P94-261 (PMT)
Settlement of spread footing using PMTs according to NF P94-261 method is based on the formula:
where: | s | - | overall settlement |
Ec, Ed | - | equivalent pressiometric modulus | |
α | - | rheological coefficient | |
q | - | stress in the footing bottom | |
λc, λd | - | shape coefficients | |
B | - | footing width | |
B0 | - | reference width (0,6 m) |
Approximate values of rheological coefficient α for soils:
Clay | Silt | Sand | Gravel | |
Overconsolidated | 1 | 2/3 | 1/2 | 1/3 |
Normally consolidated | 2/3 | 1/2 | 1/3 | 1/4 |
Non-consolidated | 1/2 | 1/2 | 1/3 | 1/4 |
Approximate values of rheological coefficient α for rocks:
Rocks | |
Type | α |
Almost intact | 2/3 |
Normally fractured | 1/2 |
Very fractured | 1/3 |
Very altered | 2/3 |
Shape coefficients λc, λd are interpolated according to the following table:
L/B | circle | square | 2 | 3 | 5 | 20 |
λd | 1 | 1,12 | 1,53 | 1,78 | 2,14 | 2,65 |
λc | 1 | 1,1 | 1,2 | 1,3 | 1,4 | 1,5 |
Equivalent pressiometric modulus Ec and Ed are determined according to the pressiometric modulus measured in layers of B/2 thickness below the foundation bottom.
Modul Ec is determined as an average pressiometric modulus in the first layer of B/2 thickness below the foundation bottom.
The determination of modulus Ed depends on the overall depth of PMT (dPMT).
Literature:
CSN EN 1997-2 Annex E
NF P94-261
Menard, L. (1975): "The Menard Pressuremeter: Interpretation and Application of the Pressuremeter Test Results to Foundations Design", Sols-Soils, No. 26, Paris, France.