Parameters to Compute Foundation Bearing Capacity
Parameters to compute vertical bearing capacity of a foundation resting on bedrock
The following parameters are used in the program to compute the foundation vertical bearing capacity:
- values of coefficient D reflecting a state of damage of a rock mass
- values of strength parameter mi
- strength of rocks in simple compression σc
- Poisson's ratio of rocks ν
- unit weight of rocks γ
Estimating disturbance coefficient D
Description of rock mass | Suggested value of D |
Rock mass, intact strong rock, excavation by blasting or by open TBM | 0 |
Rock mass, poor quality rock, mechanical excavation with minimal disturbance | 0 |
Rock mass, poor rock, mechanical excavation, significant floor heave, temporary invert or horizontal geometry of excavation sequence | 0.5 |
Rock mass, very poor rock often very altered, local damage of surrounding rock (app. 3 m ) | 0.8 |
Rock slope or rock outcrop, modification with controlled blasting | 0.7 |
Rock slope or rock outcrop, modification with blasting results to the some disturbance | 1.0 |
Open-pit mines, excavation with blasting | 1.0 |
Open-pit mines, mechanical excavation | 0.7 |
Values of strength parameter mi
Type of rock | Representative rocks | mi [-] |
Carbonate rocks with well-developed cleavage | Dolomite, limestone, and marble | ≈ 7 |
Lithified argillaceous rocks | Mudstone, siltstone shale, slate | ≈ 10 |
Arenaceous rock with strong crystal and poorly developed crystal cleavage | Sandstone and quartzite | ≈ 15 |
Fine-grained polymineralic igneous crystalline rocks | Andesite, dolerite, diabase, rhyolite | ≈ 17 |
Coarse-grained polymineralic igneous and metamorphic rocks | Amphibolite, gabbro, gneiss, granite and quartz diorite | ≈ 25 |
Uniaxial compressive strength σc, Poisson's ratio ν and Unit weight of rock γ
Strength of rocks | Types of rock (examples) | Uniaxial compr. strength σc [MPa] | Poisson's ratio ν | Unit weight of rock γ [kN/m3] |
Extremely hard rock | Very hard, intact rock strong and solid quartzite, basalt and other extremely hard rock | >150 | 0.10 | 28.00 - 30.00 |
Very hard rock | Very hard granite, quartz porphyry, quartz slate, very hard sandstones and limestones | 100 - 150 | 0.15 | 26.00 - 27.00 |
Hard rock | Solid and compact granite, very hard sandstone and limestone, siliceous iron veins, hard pudding stones, very hard iron ores hard calcite, not very hard granite, hard sandstone, marble, dolomite, pyrite | 80 - 100 | 0.20 | 25.00 - 26.00 |
Fairly hard rock | Normal sandstone, medium-hard iron ore, sandy shale, flagstone | 50 - 80 | 0.25 | 24.00 |
Medium-hard rock | Hard mudstones, not very hard sandstones and calcite, soft flagstone, not very hard shales, dense marl | 20 - 50 | 0.25 - 0.30 | 23 - 24.00 |
Fairly weak rock | Soft schist, soft limestones, chalk, rock salt, frost soils, anthracite, normal marl, disturbed sandstones, soft flagstones and soils with aggregates | 5 - 20 | 0.30 - 0.35 | 22.00 - 26.00 |
Weak rock | Compact clay, hard soil (eluvium with soil texture) | 0.5 - 5 | 0.35 - 0.40 | 22.00 - 18.00 |