8/13/2019 Iss26 PES - 3D Pile Raft Foundation FE Model

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PLAXIS Expert Services: UpdateAuthor: Ady Lehrer, Managing Director, Blank Lehrer

Plaxis was asked by Blank-Lehrer to be assisted with an advanced consulting project requiring the construction of

a 3D pile raft foundation finite element model. In the framework of PLAXIS Expert Services, a successful modeling

partnership has enabled Blank-Lehrer to quickly achieve a reliable design.

The project deals with the design of a piled-raft foundation for a 300m high building.The project deals with the design of a piled-raft

foundation for a 300m high building. The concrete

raft is 3.5 meters thick and will be cast at a depth of

15 meters below soil level.

The high rise building will be founded on a on the

soil substratum which is made of two sand layers

(from +4m to -12m and from -12m to -30m) with

respectively Eoed = 60000 kPa and Eoed = 100000

kPa.

In order to reduce settlements 20m long piles will

be placed under the raft. Each individual pile is

expected to have a skin friction of 100 kN/m2 and an

end-bearing capacity of 4000 kN/m2.

The aim of the project is to design the piles in such

a way that:

between 60% and 70% of the load will be carried

by the piles,

under ultimate limit state, the load on each pile is

not greater than 80% of the ultimate pile bearing

capacity.

Added-ValuePLAXIS has been assigned for providing an optimizedFE model that will be used by Blank-Lehrer for further

parametrical studies (pile number, pile properties,

pile location, ..). In this context, a FE model of pile

raft foundation has been set-up using PLAXIS 3D

Foundation program.

The model has been set-up based on best FE

practices (model size, geometrical modeling of

constitutive members, material model) offering an

optimized mesh (results accuracy and computational

performance) and proper modeling of piles through

embedded pile elements.

A comprehensive memorandum has also been

delivered highlighting all model assumptions and

providing a clear description of defined calculation

phases and main recommendations regarding further

model changes to be done by the client along with

result interpretation.

Lastly, extensive user support has then be provided

to Blank-Lehrer during their final design assessment

with PLAXIS 3D Foundation.

Customer QuoteOur office uses the PLAXIS 2D and theFOUNDATION 3D softwares regularly. In spite of

that, we have decided that in complex project such

as the one we are facing, an expert advice should be

used in the model assembly stage.The embedded

piles dimensions were determined after testing the

behavior of volume pilesThe Plaxis expert advice

assisted in building a flexible model which enables

to test the sensitivity of the solution to different

engineering parameters (i.e. number of piles and

soil characteristics).There is no doubt that the

solution reached, following the expertise is the most

economical one, Ady Lehrer, Managing Director

The CompanyBlank-Lehrer specializes in soil mechanics,

foundation engineering and geotechnical risk

management analysis. They provide geotechnical

consulting services, including infrastructure

investigation, geotechnical reviews, geophysical

study coordination, foundation systems analysis,

soil structure interaction analysis, geology services,

construction guidelines and site supervision. Blank-

Lehrer is one of the leaders in Israeli engineering in

these fields with more than thirty years experience in

Israel and abroad.

There is no doubt that the solution reached, following

the expertise is the most economical one