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GEO5

Geotechnical software

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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

- bulk 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 number
ν 		Unit weight of rock
γ
[kN/m3]0
Extremely hard rock Very hard, intact rock strong and solid quartzite, basalt and other extremely hard rock >150 0,1 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 0,3 – 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 - 18,0

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