NUMERICAL MODELING OF BRANCHING FOUNDATIONS

Resumo

Piles are foundation elements whose mechanism for transferring loads occurs, in many
cases, by lateral friction. It is a fact that branched systems have large surface areas and tree roots use
this fact to increase their ability to withstand requests on the trees, such as lateral wind loads. In this
paper we present a branched structure model based on fractal geometry, used as an alternative solution
for foundations, instead of a standard pile model. With three parameters it is possible to generate an
infinity of classes of branched systems composed of elements in different quantities, lengths and
thicknesses. The aim of this paper is to compare the performance of the branched against standard
models from the point of view of support capacity, stresses and displacements. The model was
simulated using the software PLAXIS 2D, which is based on the finite element method and it was
considered elastoplastic constitutive model with Mohr-Coulomb failure criterion for the soil. The
results evidence that a branched structure compared to a standard pile with same volume presents
higher carrying capacity and lower maximum displacements. For example, for a single branching with
a form of an inverted Y, the load capacity amounts to about three times the carrying capacity of a
single pile, and can reach up to about four times in the case of two and three branching orders.
Moreover, with only one branch it was verified a reduction of the maximum vertical displacement of
the foundation, for a same load, in about 85% of the displacement of the conventional foundation,
being able to reach about 90% for two and three order branches, showing a significant reduction of the
displacement below the foundation. On the other hand, the displacements around the foundation
increase since a branched structure distributes better (because of the higher surface area) the external
solicitation to the ground, which may influence possible neighboring structures. Another characteristic
of a branched foundation is that the highest stress occurs within the structure whereas in a pile
foundation the immediately below soil deals with the highest stress. In addition, we show that the
higher the branching angles the higher the load capacity.