Skopje is the capital and largest city of the Republic of Macedonia. It is the country’s political, cultural, economic and academic centre.
Located on the upper course of the Vardar River, it sits on a major north-south Balkan route between Belgrade and Athens.
With the planned construction of an access road to Sunny Town, designers were faced with the challenge to provide a solution to the problems of slope stabilisation and drainage.
It was determined that a 21m high structure was required to support the highway above. A number of solutions were considered. Maccaferri Balkans were approached to offer alternative solutions to this problem which would be amongst the tallest retaining walls in Macedonia.
Maccaferri, in conjunction with Technical distributor, Ergo Kom, worked closely with the contractor GD Granit AD to provide technical and environmentally friendly solutions that would combine the technical and landscaping requirements.
The Terramesh® System for soil reinforcement provided an ideal engineered solution as it has been used globally on some of the most significant infrastructure schemes, including what is believed to be the tallest reinforced soil structure in the world at 74m high. It consists of a pre-assembled fascia element with an integral geogrid soil reinforcement element all in one unit. It is fabricated from double twisted steel wire mesh (8×10 type). The facing section of the unit is formed by connecting a back panel and diaphragms to the main fascia unit, thus creating the rectangular shaped cells used for stone confinement. The geogrid reinforcement, fascia and lid are all one continuous panel of mesh.
Among the benefits of the modular Terramesh® System is that it is supplied in standard lengths, so no cutting was required on site. No jointing or connections are needed between fascia unit and tail, increasing the construction efficiency.
Terramesh® units are fabricated from heavily galvanised GalMac® and polymer coated steel wire and the fascia was filled with suitable gabion stone fill. Structural backfill was then placed upon the soil reinforcement geogrids and compacted. Subsequent Terramesh® layers are placed onto the completed layer beneath.
The geogrid reinforces the soil enabling it soil to perform better than it would in its unreinforced state, enabling it to accommodate greater loads and stand at steeper angles. It can often bring environmental benefits to the project when site-won materials can be used as structural backfill to the geogrids. Terramesh performs best with more granular based fills, but many projects use more marginal fills as structural backfill. In this case, the use of polymeric geogrids such as Paragrid, are used as primary soil reinforcement, with the Terramesh used as secondary geogrids with integral fascia element. These combined ‘hybrid’ structures can be very cost effective when compared to traditional solutions, particularly taking into consideration to carbon-footprint benefits of reusing site-won fills.
Also within the project, was a requirement for water within the slope, to be managed. Excess water within the soils weakens them and can lead to erosion and slumping of the slope. Effective drainage of this water is therefore important. For this project, drainage site problems were overcome using MacDrain® W 1081; a geocomposite for planar drainage (GCD), featuring a 3-D dimensional drainage core of extruded monofilaments (GMA), thermobonded between two filtering non-woven geotextiles. The geotextiles prevent fine soil particles within the water, clogging the drainage core and reducing the effectiveness of the drainage geocomposite.
These MacDrain geocomposites are designed to replace the traditional gravel drains typically used to remove water from highway structures. As the performance of MacDrain is lab-tested, they provide long-term reliable performance. Furthermore, they reduce the amount of gravel or other quarried materials imported into the project site.
The client, Agency for State Roads, said they are very happy with the safe, fast and cost-effective solution. The project is ongoing.