This master's thesis deals with the design and analysis of the excavation support in Brdo near Ljubljana
using the Plaxis 2D programme, which applies the finite element method. This analysis is particularly
complex due to the very unfavourable geotechnical and hydrogeological conditions at the site, which
has two aquifers: the upper aquifer and the lower aquifer of Ljubljana, separated by a soft clay layer
with low permeability. The primary method of excavation support investigated was the use of steel sheet
piles anchored with geotechnical anchors. This method is cost-effective and the sheet piles can be reused
several times. In view of the difficult hydrogeological conditions and the flexibility of the sheet pile wall
construction, the excavation must be carried out in several phases. After each phase, the sheet piles are
anchored with pre-stressed anchors to further reduce possible movement.
An alternative solution is to use a reinforced concrete diaphragm wall. Whilst this method is more
difficult and costly to implement, it allows the use of a single-sided formwork and provides an extremely
effective barrier against water ingress into the pit. Due to the greater stiffness of the diaphragm wall,
one less row of anchors is required compared to sheet piling, which reduces the number of excavation
phases required and enables the work to be completed more quickly. We modelled the diaphragm wall
in two different ways and compared the results. In the first modelling method, plate elements were used
(similar to sheet piles), where the friction between the soil and the protective structure was not taken
into account. Alternatively, we modelled the diaphragm wall with 2D surface elements, taking into
account the actual thickness of the structure and thus more accurately accounting for the effect of soilstructure interface friction. Although there are differences between the calculation results for both
variants, we found that for a membrane thickness of 60 cm, friction along the soil-structure interface has
no significant influence on the extreme values of the internal forces and displacements. The verifications
for the ultimate limit state and the design of the structural elements were carried out in accordance with
the Eurocode standards.
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