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CONSOLIDATION OF A ROCK FILL EMBANKMENT CONSTRUCTED ON SOFT CLAYS

C. Chiotan, V. Chiotan
Thursday 11 October 2018 by Libadmin2018

ABSTRACT

For one motorway project in Romania, the alignment has to cross an artificial lake that was made for drying a former swamp. The alternatives considered were crossing the lake with a bridge or with an embankment. According to the geotechnical investigations, the soil in the area consisted of soft saturated clays of 10-18m followed by marle.
Crossing the lake with a bridge involved raising the vertical alignment of the motorway to nine meters above ground level in order to ensure the clearance for the maintenance of the lake’s dam. This would generate settlements of the embankment near the abutment of approximately one meter due to soft saturated clays. That is why the embankment solution was selected.
In order to construct the embankment, a fill of big rocks 4-6m thick was considered. In order to accelerate the settlement, an overload of 3m of fill was foreseen over the rock fill. The fill and the overload have been constructed in February. During construction, very low temperatures (-15°C) have been recorded. These very low temperatures made surface water freeze and generated a bond between the rocks on the surface. When thaw came, the bond between the rocks disappeared, thus the sudden transfer of load from the overload to the rock fill underneath generated a loss of stability in the rock fill due to the sudden increase of the water pressure in the pores of the saturated clay.
In order to consolidate the rock embankment, the following measures have been taken: the rock fill was reinstated to the original level; a grid of concrete columns was drilled in order to transfer the load of the embankment to the stiff marle underneath. A geogrid mat one meter thick filled with stones was constructed as well, to ensure a uniform distribution of the load.

Keywords: Soft clay, fill, slope stability, consolidation


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