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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


Rock mass, poor quality rock, mechanical excavation with minimal disturbance


Rock mass, poor rock, mechanical excavation, significant floor heave, temporary invert or horizontal geometry of excavation sequence


Rock mass, very poor rock often very altered,  local damage of surrounding rock (app.  3 m )


Rock slope or rock outcrop, modification with  controlled blasting


Rock slope or rock outcrop, modification with blasting results to the  some disturbance


Open-pit mines, excavation with blasting


Open-pit mines, mechanical excavation


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


Unit weight of rock

γ [kN/m3]

Extremely hard rock

Very hard, intact rock strong and solid quartzite, basalt and other extremely hard rock



28.00 - 30.00

Very hard rock

Very hard granite, quartz porphyry, quartz slate, very hard sandstones and limestones

100 - 150


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


25.00 - 26.00

Fairly hard rock

Normal sandstone, medium-hard iron ore, sandy shale, flagstone

50 - 80



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

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