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Influence of Water

When examining the influence of ground water 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