ALPHA CONSTRUCTIONS S.A.

This project includes the geotechnical investigation and the design and construction of the foundation of 4-storey residential building in extreme soft soil conditions in the area of New Artaki in Evia.

For the preliminary assessment of the soil and groundwater conditions a 5.00m investigation shaft was opened, followed by more detailed investigation that included the execution of a 10.00m rotary drilling borehole, extensive in-situ testing and collection of representative samples for laboratory testing. The main difficulty of the in-situ ground profile consisted in the presence of a 4.50m thick superficial layer of very soft and extremely compressible high plasticity N.C. clay with intermediate very thin and quite permeable sand layers. Moreover, the groundwater table was found to be only 0.70 m from the surface mainly due to the short distance of the building plot from Artaki beach.

The design consisted of the replacement of the complete soft soil layer with granular material from the depth of 4.50 m (where solid foundation conditions where found due to the presence of a medium weathered serpentinite) up to a depth of 2.00 m from the surface, where the building was decided to be founded. The granular material was thoroughly compacted while the upper 1.00 m of the material was mixed carefully with construction concrete. The whole construction work demanded thorough groundwater control and complete dewatering of the excavation area. This was achieved with the installation of large pumps at a 5.00m depth well which dewatered the excavation area through the high permeable granular material.

The excavation of the plot (of total area of 350 m2) to a depth of 4.50 m was carried out within just one day with the use of a large track-laying excavator weighing more than 50 tons and dozens of earthmoving truck. Along with the excavation, the spreading of the mix of granular material and concrete was done. and spreading of lime stones from lithodematos origin and granulated appropriate rating based on the requirements of the study until the state subgrade.