River Glan diversion complete – Klagenfurt's new hospital project can begin

Can a liner do more than just seal? It can – as river diversion works carried out for the "Glanflussverlegung LKH" project at Klagenfurt in Austria clearly show.

With the River Glan diverted, the construction of Klagenfurt's new regional hospital (LKH) can begin. The Glan now has 850 metres of new river bed, which releases an additional 6 hectares of land for the hospital. The LKH will soon have a new building with an underground car park for patients, visitors and employees on the land where the river formerly flowed.

The river diversion works had to meet two basic requirements: the first was that some of the new river channel was below ground water level – and mixing of ground water and river water was to be avoided under any circumstances, as was any rise in ground water level. The second was that the zone above the waterline must be capable of supporting trees and vegetation, so that the river bank looks natural.

To allow this, the liner has to fulfil two functions: it must provide the necessary separation of ground and river water and be self-healing when roots grow through it.

A liner with self-healing properties? Herbert Lassnig from HUESKER's Austrian subsidiary explains the problem: "When you plant a tree on a synthetic liner, then at some time in the future it will fall over as its roots cannot obtain an adequate hold in the soil on top of the liner. Roots cannot grow through synthetic liners.

For this reason, the client decided in favour of an alternative that would comply with both conditions applying to this site – a geosynthetic clay liner (GCL) – often referred to a bentonite mat. The GCL NaBento® RL-N with 4,500 g/m² of pure sodium bentonite sealing medium and rough sand-coated textured surfaces was used as the sealing element on this project. NaBento® fulfils two functions at once: it provides the required seal between river and ground water (permittivity Ψ ≤ 5 x10-9 1/s) – and it is self-healing."

NaBento® advantages: the geosynthetic clay liner has a certain ability to heal itself. Below the waterline it provides a reliable seal, above this level the roots of trees and shrubs can penetrate the liner.

Herbert Lassnig: "This HUESKER product uses bentonite powder as the sealing material." It has excellent swelling properties, when a root grows through the liner, the swelling clay surrounds the root and thus retains most of its sealing properties.

This special ability of the geosynthetic clay liner is so effective that timber piles can be driven through it and those driven piles can also be assumed to be sealed. In this way it was possible to make the whole area look natural, as the piles also serve to slow down the flow along the "new" length of Glan: eddy zones can be established to provide quiet water for waterfowl as well as spawning and breeding grounds for fish.

Finally the overlaps in the liner were made shear and tension resistant by NaBento® special adhesive: the adhesive seals the joints and prevents slippage at the overlapped areas e.g. when fill is deposited by heavy earthmoving equipment, especially at the longitudinal overlaps in the river banks.

On this project the ability of the GCL to allow roots to grow through it was specifically exploited.

On other projects, such as landfill tip seals, root penetration is undesirable. NaBento® can also be used in these circumstances. Roots are prevented from penetrating the GCL by, for example, depositing an adequate layer of soil (thickness ≥ 1.0m) and by the appropriate choice of plants (no deep rooters).

HUESKER can offer another way of blocking roots - by the incorporation of a plastic membrane into the NaBento® geosynthetic clay liner.