Analysis According to EC 7-1 (EN 1997-1:2003)
The bearing capacity of the foundation Rd with a horizontal footing bottom is determined according to a design method for the derivation of expected bearing capacity of spread footings resting on a bedrock outlined in a supplement G (informative) EC 7-1 (EN 1997-1:2003) "Design of geotechnical structures - Part 1: General rules". For low strength or damaged rocks with closed discontinuities including chalks with low porosity less than 35% the derivation of expected bearing capacity follows from the classification of rocks into groups of rocks stored in the table below. The analysis further requires an input of discontinuity spacing Sd, unit weight of rock γ, Poisson's ratio ν and uniaxial compressive strength σc. It is assumed that the structure is able to transmit a settlement equal to 0,5 % of the foundation width. The expected values of bearing capacity for other settlements can be estimated using direct proportion. For weak and broken rocks with opened or filled discontinuities it is recommended to use lower values than the expected ones.
Rock groups
Group | Type of rock |
1 | Pure limestones and dolomites Carbonate sandstones of low porosity |
2 | Igneous Oolitic and marly limestones Well cemented sandstones Indurated carbonate mudstones Metamorphic rocks, including slates and schist (flat cleavage / foliation) |
3 | Very marly limestones Poorly cemented sandstones Slates and schist (steep cleavage / foliation) |
4 | Uncemented mudstones and shales |
Literature:
Eurocode 7:Geotechnical design - Part 1:General rules.