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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

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, siltsone shale, slate

≈ 10

Arenaceous rock with strong crystal  and poorly developed crystal cleavage

Sandstone and qurtzite

≈ 15

Fine grained polyminerallic igneous crystalline rocks

Andesite, dolerite, diabase, ryolite

≈ 17

Coarse grained polyminerallic 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, silicious iron veis, 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