Passive earth pressures examples

Passive lateral earth pressures example

Passive lateral earth pressures represent a limit state condition when in theory the retained soil has reached a failure limit. This passive pressure failure limit is usually justifiable for design because the lateral displacements required to mobilize the passive conditions are very small. Conservatism in soil strength is another reason that typically justifies the use of active (Ka) conditions. An important limitation of passive lateral earth pressures is that they should not be used with braced excavations where lateral stress redistribution takes place. As such, passive lateral earth pressures should be applied for cantilever walls.

With this in mind, we will construct a cantilever wall with passive earth pressures. We will model a 4m cantilever excavation with the following information:

a) Soil has a unit weight of 20kN/m3, effective friction angle 30 degrees, cohesion 2 kPa, loading modulus of elasticity E= 10000 kPa, and reloading modulus Eur= 30000 kPa.

b) The water table is at 4m depth.

c) The walls will be reinforced concrete soldier piles (berlin type wall) with 60cm diameter piles spaced at 2m apart.

d) A construction surcharge of 15 kPa should be applied from 1m behind the wall for a length of 10m.

The analysis should be performed with the limit equilibrium method with EC7 standards.

Limit eqilibrium passive pressures braced excavation model

Wall Moment and Shear diagrams

Horizontal pressures diagram

Initial soldier pile wall section with Rebars: 17 D28 and shear reinforcement D10/12 cm

Insert and modify surcharge data.

Use passive pressures for resisting side.

User can choose among Passive pressures, At-rest Ko, Ko x Multiplier, Passive pressures divided by a safety factor, and choose to include a maximum resisting pressure limit.