With respective heights of 27 meters and 34 meters, the Strikici and Sveta Trojica projects in Croatia consist of tall Reinforced Earth® walls featuring geostrip reinforcements combined with TerraTee (T-shaped) concrete facing. The notable constructions are part of Croatia’s on-going roadway system expansion and support the country’s strong growth in tourism along its shoreline.
The MSE wall projects were designed by Terre Armée as an alternative to viaducts. One of the walls, identified as the Strikici project, is located on the Dugopolje-Bisko section of the Zagreb-Split-Dubrovnik motorway link. The other structure is known as the Sveta Trojica project, located along the D8 Sveti Kuzam – Križišće national road.
The geostrip reinforcements (GeoStrap®) consist of high tenacity polyester fibers contained in a polyethylene sheath to form a geosynthetic strip. This type of reinforcement is particularly well suited where available backfill for the reinforced soil structures have a low pH or contain high levels of chlorides or sulphates.
ADDRESSING SEISMIC CONSIDERATIONS
The Strikici project features a maximum height of 27 meters, yielding a total facing area of 8,500 m² over a length of 508 meters. The structure is built on bedrock with intermittent geologic discontinuities.
A study was carried out to ensure stability during the temporary phases. Since the project is located in a seismic area, internal and overall stability of the structure were verified at design stage under dynamic stresses with a nominal ground acceleration of 0.3g. The facing is made up of modular concrete panels connected to 90 mm wide GeoStrap® reinforcements. The structure was divided into three superimposed walls in order to mitigate the impact of the internal settlement on the facing and to provide aesthetically pleasing integration into the landscape.
HIGH PERFORMANCE EVEN WITH POOR FOUNDATION CONDITIONS
The Sveta Trojica structure is a 34-m-high and 430-m-long Reinforced Earth® wall. The project was complex because the ground at the site consists of a combination of compressible limestone and flysch. In spite of these exceptionally unfavorable geological characteristics, the reinforced soil structure could be designed as a Reinforced Earth® wall with a 5.5-m offset between the tiers using the GeoStrap® system. The facing is made of precast T-shaped reinforced concrete panels.
Because of its height and the difficult subsoil conditions, a well-conceived monitoring plan of the behavior of the structure, both during construction and after completion, was worked out. The measurements of the vertical and horizontal deformation of the walls show the good behavior and high performance of the Reinforced Earth® wall1.
Today, the Sveta Trojica project is one of the tallest walls in the world built using polyester geostrip reinforcements.
ADVANTAGES OF GEOSTRIP REINFORCEMENTS
These projects highlight the numerous advantages of using Reinforced Earth® for tall retaining structures:
- Ideal solution for seismic area due to the inherent flexibility of the wall system
- Adaptable to marginal or poor foundation conditions resulting from large settlements
- Cost-effective compared to traditional civil engineering structures; in particular in areas where full side slopes cannot be adopted or on poor soils where foundations for a conventional cast-in placebretaining wall are otherwise expensive
Furthermore, the excellent performance of GeoStrap™ reinforcements is confirmed when the chemical characteristics of the selected backfill or the environmental conditions are not suitable to the utilization of metallic reinforcements.
Last but not least, these walls also confirm that tall reinforced soil structures may be accommodated using either metallic or geosynthetic strips, although the latter requires a somewhat higher degree of care in the construction.
The projects presented in this article continue to show the Terre Armée Group’s proven track record of retaining structures higher than 25 meters.
Learn more about Terra Armée’s engineering solutions and services, including copper mine crushers, gravity retaining walls, transportation engineering, and much more at www.terre-armee.com.
1 P. Kvasnička, L. Sorić, K. Gradiški, M. Marohnić. 2014. Mechanically stabilized earth wall – a case history. XV Danube European Conference on Geotechnical Engineering, Vienna, Austria.
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