Influence of Water
When examining the influence of groundwater on the magnitudes of earth pressure the program differentiates between confined and unconfined water. Hydrodynamic pressure acting on the front face of the wall is calculated, if the wall is flooded at the front face side.
Confined water
This type is used in soils with lower permeability - app. below the value of k = 1x10-3 cm/s. In such soils the water flow is influenced, e.g. by actual grains (by their shape and roughness) or by resistance of fraction of adhesive water. General formulas proposed by Mononobe-Okabe or Arrango are used to analyze seismic effects. The only difference appears in substituting the value of the seismic angle ψ by ψ*:
where: | γsat | - | unit weight of fully saturated soil |
γsu | - | unit weight of submerged soil | |
kh | - | seismic coefficient of horizontal acceleration | |
kv | - | seismic coefficient of vertical acceleration |
Unconfined water
This type is used in soils with higher permeability - app. above the value of k > 1x10-1cm/s. In such soils it is assumed that water flow in pores is more or less independent of soil grains (e.g. turbulent flow in coarse grain soils). General formulas proposed by Mononobe-Okabe or Arrango are used to analyze seismic effects. The only difference appears in substituting the value of the seismic angle ψe by ψe+:
where: | γd | - | unit weight of dry soil |
γsu | - | unit weight of submerged soil | |
kh | - | seismic coefficient of horizontal acceleration | |
kv | - | seismic coefficient of vertical acceleration | |
GS | - | specific gravity of soil particles |
where: | ρS | - | density of the soil solids |
ρw | - | density of water |
Apart from dynamic pressure the structure is also loaded by hydrodynamic pressure caused by free water manifested by dynamic pressure applied to the structures. The actual parabolic distribution is in the program approximated by the trapezoidal distribution.
The resultant of hydrodynamic pressure behind the structure Pwd is distant by ywd from the heel of structure:
where: | H | - | height of the structure |
and its magnitude follows from:
where: | γw | - | unit weight of water |
kh | - | seismic coefficient of horizontal acceleration | |
H | - | height of the structure |
Hydrodynamic pressure acting on the front face of the wall
The resultant of hydrodynamic pressure on the front face of the wall Pwd is distant by ywd from the heel of structure:
where: | H | - | height of the structure |
and its magnitude follows from:
where: | γw | - | unit weight of water |
kh | - | seismic coefficient of horizontal acceleration | |
H | - | height of the structure |