O-4/O-1 Eurasia Tunnel Link Road Geofoam Embankment

Üsküdar / Istanbul

Site Conditions

The roadway alignment was located between the piers of two closely spaced viaducts.
The subsurface profile consisted of excavation spoil accumulated over many years, forming a thick uncontrolled fill deposit.
The bedrock surface was highly irregular, with uncontrolled fill thicknesses ranging from approximately 15 to 30 m along the roadway alignment.
If the conventional alternative of a mechanically stabilized earth (MSE) wall had been adopted, ground improvement would have been required throughout the alignment to address stability concerns within the uncontrolled fill. However, the confined site conditions were unsuitable for the mobilization and operation of heavy, tall-mast ground improvement equipment.
If minipile technology using relatively lightweight, low-mast equipment had been selected, the required treatment depth would have resulted in very slender pile elements.

Construction of the roadway embankment using geofoam block technology.
Prior to construction of the geofoam embankment, the uncontrolled fill slope was excavated and benched, and soil nailing was applied to provide static and seismic stability of the slope under its self-weight.

The roadway embankment could be constructed without requiring deep ground improvement along the alignment.
Compared with the alternative of ground improvement combined with an MSE wall, the project was completed within a substantially shorter construction period, allowing O-4 Motorway traffic to be connected to the Eurasia Tunnel as quickly as possible.
The reduction in construction duration and elimination of extensive deep ground improvement also provided a more economical solution in terms of overall project cost.

A comprehensive instrumentation and monitoring program was implemented using settlement plates, survey reflectors and inclinometer boreholes.
Periodic measurements have been collected since the roadway was opened to traffic on March 18, 2024.