Austrotherm geoBLOCK® Motorway - Connector Road Project Acıbadem - Istanbul

Austrotherm geoBLOCK® is a lightweight, closed-cell expanded polystyrene (EPS) block produced through pre-expansion and molding of granular polystyrene beads for use in geotechnical engineering applications. It is used in the construction of highway and bridge approach embankments built on soils with high settlement potential. As an alternative to traditional compacted soil embankments for addressing settlement issues, Austrotherm geoBLOCK® embankments and bridge approach ramps offer both cost savings in initial investment and faster construction when ground improvement is not required. Beyond this conventional application, embankments built over buried infrastructure require special solutions. Additional stresses applied to the ground from traditional compacted soil embankments built over buried utility systems can cause structural damage to the infrastructure facilities. Relocating these utility facilities within cities is difficult and costly. Rather than traditional compacted soil embankment, filling infrastructure corridors with Austrotherm geoBLOCK® not only protects buried utilities from structural damage but also prevents relocation costs. As part of the Istanbul Ring Road Uzunçayır Junction project to redirect part of traffic from the Harem direction exit toward Acıbadem District, a road embankment composed of Austrotherm geoBLOCK® units was constructed and opened to traffic in April 2017. To prevent structural damage that could result from traditional compacted soil embankment construction on 2.2 m diameter main water transmission lines passing approximately 3-5 m below the road alignment, Austrotherm geoBLOCK® was selected for road embankment construction. Austrotherm geoBLOCK® not only prevented relocation costs of the transmission lines but also enabled project completion without structural damage to the transmission lines.

For the project, a road embankment 37 metres long, 6.6 metres wide and 3 metres high was constructed using EPS blocks with dimensions of 1.2 m x 2.5 m x 1 m and 1.2 m x 1.25 m x 1 m, with a density of 22 kg/m³.

To ensure uniform distribution of motorized vehicle axle loads across the geofoam embankment surface, the road superstructure was constructed following the method recommended by the United States National Cooperative Highway Research Program (NCHRP). The road surface layer, recommended to have a minimum thickness of 61 cm, was designed from bottom to top as follows: (1) a 10 cm thick reinforced concrete load distribution platform, (2) a 43 cm thick stabilized subgrade-base layer, and (3) an 8 cm asphalt wearing course. To observe deformations that would occur during and after construction under service loads in this country's first geofoam road embankment, an instrumentation program using magnetic settlement plates was implemented. In a road embankment constructed using EPS blocks, post-construction cumulative deformation should remain below the elastic limit (1% of total embankment height). In this project, post-construction deformation in the geofoam embankment was measured at 0.5% (1.5 cm) of total embankment height. After eight months of the road opening to traffic, cumulative deformation (post-construction deformation plus creep deformation) reached 0.8% (2.4 cm) of total embankment height. In other words, creep deformation from road opening to present occurred at a level of 0.3%. Using measurements taken monthly since road opening, the projection of cumulative deformation in the geofoam embankment at the end of its 50-year design life was estimated at 1.7% (5.2 cm) of total embankment height. This value is below the total allowable limit of 2.0% deformation. Through this innovative engineering solution, in an area with dense urban infrastructure facilities, the relocation costs of both expensive and logistically problematic transmission lines were prevented and the completion of embankment construction was achieved.   Tolga Celayer Deputy General Manager Austrotherm Türkiye    

Emre Akınay, Construction Engineering Applications Manager