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Using aggregates from tunnel excavations 11 Oct 2018

Roger Murrow for TunnelTalk
Rock resulting from tunnel excavations has been reused for ballast for railways, flood defences, roads and landscaping. Using the rock as aggregate for construction seems obvious, but lack of expertise, governmental regulations and lack of knowledge concerning specialist equipment have limited its use. Roger Murrow describes cases in Norway and Hong Kong that show how state of the art equipment and creative thinking can make reusing rock from excavation part of the tunnelling process.

Infrastructure in Hong Kong

The Liantang/Heung Yuen Wai Boundary Control Point (BCP) is a series of projects that will result in the seventh land crossing between Shenzhen in China and Hong Kong. It is the last of four major civil engineering contracts awarded under the BCP project. When complete, people and cargo flows across the boundary should become more efficient, helping to sustain long-term economic growth in the area.

Sandvik tunnelling jumbo at the Contract 6 road tunnel
Sandvik tunnelling jumbo at the Contract 6 road tunnel

The new BCP involves construction of a highway, viaducts and a road tunnel. It is scheduled for completion by the end of 2018 with a budgeted cost of HK$6 billion (€660.3 million). Termed Contract 6, it will provide a new 4.6km-long dual two-lane trunk road (with about 0.6km of grade roads), 3.3km of viaducts and a new 0.7km tunnel. These will connect the Sha Tau Kok Road Interchange to the new BCP and will see associated environmental mitigation measures, landscaping, new drainage/sewerage, utilities and waterworks.

Contract 6 requires a multifaceted approach to construction to deliver the project on time and to budget. JV contractors decided to utilize a company who could not only provide the equipment, but also support activities in the field. Sandvik Mining and Rock Technology was chosen for equipment and vital support.

“We realized that Contract 6 would require some highly specialized equipment that will need to be supported by highly trained and effective people,” says K Y Chow, Construction Manager for the JV. “We needed surface drill rigs for open cut of the hills by drill and break, tunnelling jumbos for the excavation of the tunnel, and then vitally high-quality mobile crushers to crush the excavated rock.”

The JV invested in three Sandvik Ranger DX800 surface drill rigs for the open cut of the hills by drill and break. Blasting was not permitted on the type of hill cut along the highway. The Ranger DX800 proved to be highly suited to the application and progress was rapid.

Sandvik tracked jaw crusher at the tunnel entrance
Sandvik tracked jaw crusher at the tunnel entrance

Crushing at the source

Sandvik’s role has not been limited to the excavation of the tunnel. Two QJ241 tracked jaw crushers crushed the excavated granite to provide a base for road construction in the tunnel. Although granite is notoriously difficult to crush, the QJ241 has dealt with the 600mm feed size to produce a 250mm product. This is fed into the second QJ241 to produce a 40mm product for tunnel refilling.

Sandvik technology has married tracked mobility, essential where crushed material is immediately reused, with a high-performance jaw crusher. The QJ241 is the smallest tracked jaw crusher from the Sandvik range. This highly productive, self-propelled machine is designed for places where operating room is limited. As the rock will be turned into road fill on site, the jaw crusher must also operate at a reasonably high production rate. It is fitted with a hydraulic raise and lower facility on the main conveyor making it ideal for hard-rock applications.

Ølen Betong lorries remove excavated rock for processing
Ølen Betong lorries remove excavated rock for processing

Norwegian road tunnels

Recently Norway has seen a large amount of road and tunnel construction to improve links between communities and straighten major highways. One of the most ambitious projects to date is the NOK6 billion (€700 million) Ryfast project, which included driving of the new 14.3km Ryfylke or Solbakk twin road tunnels. Ultimately, this will be the world’s longest and deepest undersea road tunnel.

The project involves construction of 53km of new roads, many requiring further tunnelling. Norwegian cement and concrete manufacturer Ølen Betong has supplied a staggering 340,000m3 of concrete for the tunnel linings.

Ølen Betong is one of the biggest manufacturers of ready-mix concrete, precast elements and concrete products in Norway and through its subsidiary Nor Aggregates is also a major producer of aggregates.

Shotcrete derived from rock from the very tunnel it is lining
Shotcrete derived from rock from the very tunnel it is lining

Reusing the rock

Ølen Betong provides shotcrete for tunnel linings and increasingly provides aggregates for highways. Although a great deal of its material is from traditional sources including Ølen Betong’s own granite quarries, much now results from tunnel excavations, with material reused for a variety of applications on the tunnels themselves.

The company manufactures artificial sand from the rock and has adapted screening and crushing equipment to deliver economical and environmentally friendly solutions for a variety of applications. Manufactured sand possesses significant benefits as it originates directly from high-quality virgin rock, and thus contains very few, if any, contaminants.

The Ølen Betong site at Fana, Bergen, utilises excavated rock from the Ryfast project. The rock initially has its shape improved followed by processing through a washing plant to remove surplus fines. The granite/gneiss 0mm to 16mm feed material is processed to produce 0mm to 4mm, 4mm to 8mm and 8mm to 16mm products, which are then used to replace 75% to 100% of the naturally occurring sand used to manufacture shotcrete for the E39 highway tunnel project in Bergen.

Already Ølen Betong has supplied 120,000m³ of ready-mixed concrete, 160,000m² tunnel lining elements and, for the new Ulriken railroad tunnel, 80,000m³ of ready-mixed concrete and 3,892 invert sleepers.

Equipment used to process excavated tunnel rock
Equipment used to process excavated tunnel rock

The equipment used to process the aggregate is an Oresizer OM80 200Kw VSI (vertical shaft impact crusher), a Powerscreen Chieftain 2100 washing plant, two CDE Hydrocyclones, CDE Evowash 151 and 71, and an Aquacycle A400 sediment tank. The setup has led to considerable environmental savings by greatly reducing the need for shipping natural sand to the concrete plant.

Manufactured sand

There are significant advantages to the cubical shape of the sand produced during manufacture, including advantages during cement and concrete manufacture that benefit the whole construction process. Production of concrete products becomes more cost effective, since very little altering of the amount of water or cement is required during specific stages of concrete production. The sand's cubical shape also gives greater strength to the final concrete product.

Manufactured sand is produced with the 0mm to 200mm source aggregate being initially fed into a Powerscreen Maxtrack 1500 cone crusher then being fed into a VSI (in this case, a UV320 from Sandvik) before being screened by a McCloskey mobile plant into 0mm to 8mm and 8mm to 16mm products.

Artificial sand manufactured on site in Norway
Artificial sand manufactured on site in Norway

High-quality concrete

Concrete using the sand and other materials is manufactured to standard NS-EN 206, with the Norwegian Concrete Association’s standard No7 as well as additional requirements of the Norwegian Road Authorities (Statens Vegvesen) Process Code 762. It is designated B35 M45 D8.

The compression strength at 28 days is well over the minimum requirement of characteristic 45MPa, and the water/binder ratio is required to be less than 0.45 including accelerator added at the tunnel front. Energy absorption classes are normally delivered between E700 and E1000. The cement types used are Cemex Miljø and Norcem Standard FA with silica added at the mixing plant at around 4% of the cement content.

References

           

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