Transport infrastructure sector


From landfill to landslide stabilisation. Innovative composite of two recycling paper waste streams

Current situation/ Problematic addressed

Pulp and Paper Industry VIPAP is a producer of newsprint and coated graphic papers. The main raw material used is recycled fibre obtained from recovered paper in the deinking process. As a consequence, three main waste streams are generated: Deinking Paper Sludge (DPS), Wastepaper Fly Ash (WPFA) and Wastepaper Bottom Ash (WPBA), producing annually, 25.000 tonnes of ash. Only a small percentage of this amount is used in civil engineering for low grade applications while most of them are still disposed to landfill, incurring in considerable costs.

Partners involved

VIPAP: Pulp and Paper industry generating the waste. It will improve the handling for both materials, optimizing the process to improve waste applicability.

ZAG: Research Institute in charge of the design of the innovative composite (WPA/DPS) in a defined ratio, characterization and testing at laboratory level for the demo case site. Technical support to get the required quality of the composite. Geo-mechanical characterization of the landslide.

SZ infrastructure (SZ): Railways infrastructure operator, End User

Dušan Holešek (DH): Construction SME in charge of the implementing the developed solution in the demonstration site.

Alternative proposed:

A synergistic beneficial use of VIPAP’s waste materials can be proven in the field of renovation of the railway infrastructure. To this end, along the last years, ZAG has been researching to find alternative cost-effective materials based on PPI waste products. An innovative composite made of WPA/DPS has been developed as a result. This material develops a considerable strength (2.70 MPa at 28 curing days), it is light (< 1 t/m3) and then easy to handle especially when the available space is limited.
PAPERCHAIN will demonstrate the use of this recycled composite as a valuable material for the rehabilitation of landslides near the railway line. The batter of a gabion wall will be backfilled with the WPA/DPS composite replacing borrow material and reducing the section of the wall. The use of this recycled composite will contribute to tackle the slope stability problem in railway infrastructure lines in a sustainable manner. In addition, it will lead to a reduction of waste material diverted to landfilling with the subsequent cost savings for the Pulp and Paper company.


The demonstration will take place in a section/area of 70 metres of length of the Slovenian railway. WPA/PSD composite will be filled in layers of about 15 cm. These layers will be compacted separately and covered at the top with protective vegetation.


The gabion retaining walls will be filled will gravel material, as standard material for gabions. The WPA/DPS composite will be used as backfilling material between gabions and slope (unstable soil or rock). The composite will be mixed and installed properly, together with an adequate drainage system and the protective covering layer above the landslide. The slope stability will be calculated by numerical methods based on geotechnical properties determined in ZAG´s geo-mechanical laboratory and with onsite testing in the landslide area. The advantages of the innovative solution are:

Metres of length

cm Filled layers WPA/PSD

The advantages of the innovative solution are

Reduction of the wall section, using less gabions

Strengthening of the slope-gabions contact

Technical performance:

Geo-mechanical characterization of the landslide: in situ tests (borehole drillings and in-situ testing) and geo-mechanical laboratory tests to map and define the landslide structure and behaviour. Quality control assurance programme, laboratory tests for the composite and the landslide material (water content, density, direct shear strength, uniaxial compressive strength, etc). Field tests will be done to check both the slope and the wall stability (geometric and extensiometric measurements). Some KPIs will include: Landslide movement (mm/day) and retention wall verticality. The workability of the new composite will be evaluated. It is expected to have light density and enough workability time from the mixing at plant, to its installation. KPIs will include workability period (in minutes), bulk density (t/m3) and percentage over the maximum dry density (%).

Environmental performance:

Leachability tests will be done before the implementation to assure that the composite complies with the Slovenian Environmental Regulation. After implementation, soil and water samples from the demo site will be periodically taken and compared with previous data.

Quantification of the valorisation achieved during the project & Replication potential


of the gabions replaced

tonnes of the WPA/DPS used

During the project:
For the demo purposes, at least 50 tonnes of the WPA/DPS composite will be used as part of the retaining walls structural solutions, replacing up to 30 % of the gabions.

The project can be easily replicated in the Slovenian railway network, as every year this kind of structures are constructed for slope stabilisation and the whole value chain is involved in the demonstration action.