Water Influence according to Chinese Standards
Seismic water influence can be dived into two parts - influence on seismic earth pressure and dynamic water pressure. Similar to water influence according to Mononobe-Okabe or Arrango theory, water influence according to Chinese standards also has two types water influence - confined water and unconfined water. The main difference between Monobe-Okabe theory and Chinese standards is that Chinese standards reduce the water influence using comprehensive influence factor Cz.
Confined water
This type is used in soils with lower permeability - app. below the value of k = 1*10-3 cm/s. When confined water is chosen, dynamic water pressure is not considered. The only difference from soils without water is that seismic angle used in calculation of seismic earth pressure is replaced by seismic angle below water θ’.
Value of seismic angle below water θ’ is determined by the following two options:
1. By seismic fortification intensity - value of θ’ is provided by the following tables:
For JTJ 004-89 (Tbl. 3.1.6 from JTJ 004-89)
Seismic fortification intensity | 7 degree | 8 degree | 9 degree | ||
Coefficient of horizontal seismic acceleration Kh | 0.10g | 0.15g | 0.20g | 0.30g | 0.40g |
Seismic angel θ | 2.5° | 4.5° | 5.0° | 9.0° | 10.0° |
For JTS 146-2012 (Tbl. 5.3.1 from JTS 146-2012)
Seismic fortification intensity | 7 degree | 8 degree | 9 degree | ||
Coefficient of horizontal seismic acceleration Kh | 0.10g | 0.15g | 0.20g | 0.30g | 0.40g |
Seismic angel θ’ | 3.0° | 4.5° | 6.0° | 9.0° | 12.0° |
2. Input seismic angle - value of θ’ is input by users. When this option is chosen, the default value of θ’ is provided by:
If you have no idea about how to calculate the value of θ’, you can use the default.
Note: For SL 203-97, there are no additional options for confined water. θ’ is calculated automatically according to the above formula.
Unconfined water
This type is used in soils with higher permeability - app. above the value of k > 1*10-1 cm/s. When unconfined water is chosen, both influence on earth pressure and dynamic water pressure is considered.
Value of seismic angle below water θ’ is determined by the following three options:
- By seismic fortification intensity - same to confined water.
- Input seismic angle - same to confined water.
- Input specific gravity of soil particles - value of θ’ is provided by:
where:
Note: For SL 203-97, there are no additional options for unconfined water. θ’ is calculated automatically according to the above formula.
Dynamic water pressure is calculated according to the standard chosen.
For JTJ 004-89 (Art. 4.2.11 from JTJ 004-89):
where: | Ew | - | over all dynamic water pressure acting on the structure [kN] |
Ci | - | ||
γw | - | unit weight of water [kN/m3] | |
d | - | depth of water above the heel of the structure [m] |
Distribution of dynamic water pressure is constant along the structure.
For JTS 146-2012 (Art. 5.4.1 from JTS 146-2012):
where:
where: | pz | - | dynamic water pressure at depth Z [kPa] |
η | - | reduction factor, for walls, it equals to 1.0 | |
Z | - | distance between calculation point and water table [m] | |
d | - | depth of water above the heel of the structure [m] | |
b | - | width of water table [m] |
For SL 203-97 (Art. 6.1.9 from SL 203-97):
where: | pz | - | dynamic water pressure at depth Z [kPa] |
d | - | depth of water above the heel of the structure [m] | |
ψ(Z) | - | distribution coefficient of dynamic water pressure at depth Z |
Value of ψ(Z) is provide by the following table (Tbl. 6.1.9 from SL 203-97):