2469
Method of improvement of the subsoil under Adora facility – Ohrid, Republic Of
Macedonia
Méthode d’amélioration du sous-sol sous le bâtiment Adora – Ohrid, République de Macédoine
Dimitrievski L.
Faculty of Civil Engineering, Skopje, Republic of Macedonia
Ilievski D., Dimitrievski D., Bogoevski B., Strasheski A.
GEING Krebs und Kiefer International and others ltd. Skopje, Republic of Macedonia
ABSTRACT: Adora residential building is a 6-storey structure, built nearby Ohrid Lake (Ohrid, Republic of Macedonia). The
foundation depth of the building is approximately 1,5 m (foundation construction – foundation slab). The foundation soil consists of
soil materials which have a poor strength properties and low bearing capacity. The ground water table (GWT) on the location is on 1,0
m bellow the ground surface. On such geotechnical conditions a big settlements are expected. Therefore, a project on soil
improvement was prepared. Several preliminary solutions were considered, but most appropriated was the one which involves
geosyntetic reinforcement as subsoil improvement measure. In order to evaluate the settlements, performance of the building, axial
forces developed in the geogrids and stress-strain condition in the subsoil during static and dynamic loads, detailed analyses were
conducted. The software models developed in Plaxis 2D clearly showed the effectiveness on the applied measures for soil
improvement.
RÉSUMÉ : le bâtiment de résidence Adora est-une construction de 6 étages, bâti à coté du lac d’Ohrid (Ohrid, République de
Macédoine). La profondeur des fondations du bâtiment est d’environ 1,5 m (construction de fondation – dalle de fondation). Le sol de
fondation est composé de sols de mauvaise qualité et faible capacité portante. La nappe phréatique (NP) du site est située 1,0 m en
dessous de la surface de sol. Avec ces conditions géotechniques des tassements du sol sont attendus. Un projet d’amélioration des sols
a donc été préparé. Plusieurs solutions préliminaires ont été considérées, mais la plus appropriée est celle qui implique le
renforcement par géosynthétiques, comme mesure d’amélioration du sous-sol. Des analyses détaillées ont été menées afin d’évaluer
les tassements du sol, la construction du bâtiment, les forces axiales développées dans le géogrille et la relation contrainte-
déformation dans le sous-sol sous chargements statique et dynamique. Les modèles logiciels développés dans Plaxis 2D montrent
clairement l’efficacité des mesures appliquées pour l’amélioration des sols.
KEYWORDS:soil imporovement, geogrid, geotextile
1 INTRODUCTION
Adora residential building is foreseen to be built on a site which
hasvery poor geomechanical properties or in other words the
geotechnical conditions on the site are very unfavorable. In such
casesalways major problems are low bearing capacity of the
subsoil and large differential settlements. The city of Ohrid is
located in active seismic area which is classified in the 9
th
seismic zone according to MCS. Moreover, on the site there are
layers of loose uniform sand. Having in mind these two facts a
liquefaction becomes also a serious danger for the structure. In
order to adopt a solution for soil improvement and to check the
liquefaction potential of the soil,comprehensive analyses were
conducted.
Figure 1.Excavation pit on a site
2 GEOLOGICAL SITE PROPERTIES
According to the geological formations on the site, there are
present sediments from the Quaternary period (Pleistocene
epoch), i.e. lake and swamp sediments, represented with gravel,
sand, sandy clays, silt, different types of clay and clayey-silty
sediments, as well as occasional presence of peat. The
sediments are well sorted, so that they have heterogenic particle
size distribution and heterogenic mineralogy composition, i.e.
they are fine to medium gravels and sands; fine silty sands,
sandy clays and soft lake/swamp clays with low to medium
plasticity. The thickness of these sediments varies between 50.0
– 80.0 m. According to the hydrogeological properties, they
belong to the group of low permeability sediments with
interparticle porosity. A closed type of springs with free level is
present in the sediments, at depth to 20.0 m with GWT = 5.0 –
7.0 m, and with permeability k = nx10
-4
– nx10
-5
m/s.
Also there is a closed type of springs under pressure (artesian
springs) at depth from 20.0 – 60.0 m with discharge of Q = 1.0
– 5.0 l/sec.
From engineering geological point of view, these sediments
belong to the group of weathered rocks, well placed and sorted
with heterogenic particle size distribution, low compacted, with
smooth surfaces, fully saturated with water. In other words they
present materials with poor physical and mechanical properties
that have different strength and deformability parameters.
3 GEOMECHANICAL SITE PROPERTIES
The site for construction of the new building is located
approximately 200 m from the shore of Ohrid Lake, so, as it
was mentioned before, the soils found on the site are with
