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Analysis with active earth pressures

Active lateral earth pressures example


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


With this in mind, we will construct a cantilever wall with active 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 active pressures braced excavation model Moment Shear

Wall Moment and Shear diagrams


Limit eqilibrium active pressures braced excavation model horizontal pressures

Horizontal pressures diagram


Limit eqilibrium active pressures braced excavation

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


Limit eqilibrium active pressures braced excavation model

Insert and modify surcharge data.


Limit eqilibrium active pressures braced excavation model

Use active pressures for driving side.


Limit eqilibrium active pressures braced excavation model

Use Limit equilibrium method for calculations.


Limit eqilibrium active pressures braced excavation model Eurocode 7 load cases

Generate all Eurocode 7 load cases.


Limit eqilibrium active pressures braced excavation model

Results table for all design sections – critical checks and critical results, all of them satisfied for Eurocode 7 load cases.


 

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