Producing aggregates from tunnel excavations

RockRoadRecycle staff writer

Despite being a highly valuable resource, rock from tunnel excavations has generally not been used to its full potential. However, recent developments in crushing and screening technology, along with growing commercial pressures, has seen tunneling contractors use excavated rock as part of the tunneling process itself.

The uses for excavated rock resulting from tunnel excavations have traditionally been limited to ballast for railways, rock for flood defenses, roads (especially in hard to reach areas) and landscaping.  Much of the excavated rock — even when used — is not processed, just removed and dumped. For many in the quarrying and construction industry, the use of the excavated rock as aggregate for construction purposes has always seemed to be the most obvious way of maximizing this highly valuable resource.

However, a lack of expertise concerning the attributes of equipment and regulatory guidance from government, as well as limited knowledge concerning specialist equipment, have held back the use of the excavated rock. Increasingly this is changing, with companies across the world showing how state of the art crushing equipment together with “out of the box” thinking, has seen rock from tunnel excavation being reused as part of the tunneling process in order to produce aggregates.

Tunnels, highways and viaducts

One interesting use of crushing technology has been on the Liantang/Heung Yuen Wai Boundary Control Point (BCP for short) project in Hong Kong. This is a series of infrastructure projects that will see the construction of the seventh land crossing between Shenzhen in China and Hong Kong involving the construction of highways and tunnels, as well as other significant infrastructure programs. The works are scheduled for completion by the end of 2018 with a budgeted cost in the region of HK 6 billion dollars. Termed Contract 6, when finished 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.

Contract 6 is seen as a project requiring a multifaceted approach to construction, requiring the use of many different techniques in order to deliver the project on time and on budget.

The first part of Contract 6 required an investment in three Sandvik Ranger DX800 surface drill rigs. These were used for the open cut of the hills by drill and break. Drill and blast was not possible as blasting was not permitted on the type of hill cut along the highway.

Refilling the tunnel base

Sandvik equipment was not limited to the excavation of the tunnel. Two QJ241 tracked jaw crushers were also put to work crushing the excavated granite in order to provide an aggregate base for the road construction in the tunnel. Although granite is a hard and notoriously difficult rock to crush, the QJ241 has dealt with the 600mm feed-size in order to produce a -250mm product. This is further fed into the second QJ241 in order to produce a -40mm product for the tunnel refilling.

The QJ241 is the smallest compact tracked jaw crusher from the Sandvik tracked crusher range. This highly productive, self-propelled machine brings the features of the Sandvik jaw crusher range to places where operating room is limited yet high performance demanded. Compact and mobile, the QJ241 is fitted with a hydraulic raise and lower facility on the main conveyor making it an ideal solution for hard rock applications such as Contract 6 tunnel rock.

Where the Sandvik crushing technology has come into its own is through marrying tracked mobility (essential where the crusher has to go to the material for immediate reuse) with a high performance jaw crusher.  When dealing with a hard rock such as granite, the latter is essential. Furthermore, as the rock will be turned into tunnel road fill on site, the jaw crusher must also operate at a reasonably high production rate, yet at the same time produce the -40mm final product for tunnel refilling.    

Norwegian road tunnels

If the Hong Kong case outlines the “traditional” use of excavated rock resulting from tunneling, then Norwegian cement and concrete manufacturer Ølen Betong AS has moved to another level. Established in 1974, it is now one of the biggest manufacturers of Ready-Mix concrete, precast elements and concrete products in Norway. The company, through its subsidiary Nor Aggregates, is also a major producer of aggregates in the country, both for its own use in concrete and cement manufacturing and for supply to the Norwegian construction industry.  A major source of material is now comes from excavated tunnels, which is being reused for a variety of applications — including on the tunnels themselves.

Investment in tunneling

In recent years Norway has seen a large amount of road and tunnel construction in order to improve links between communities, effectively straightening major highways. One of the most ambitious projects to date was the Ryfast project, which included driving the new 14.3km Ryfylke or Solbakk twin road tunnels. The estimated cost of the project is NOK 6 billion (€700 million), which will also involve construction of 53km of new roads, many of which require further tunneling. The twin road tunnel will — when completed — be the world’s longest and deepest undersea road tunnel, with Ølen Betong having supplied a staggering 340,000m3 of concrete for the tunnel linings.

An even more ambitious program of tunneling is due to extend the E39 main road north of Stavanger via several other islands heading towards Bergen, Norway’s second largest city. This will include an even longer undersea tunnel section — the Rogfast tunnel — begun in 2015, aiming to be completed by 2022. The Rogfast tunnel conception is a 25km connection below Boknafjord and Kvitsøfjord, which will upon completion set another world record for a subsea tunnel system with respect to length and maximum depth (380m below sea level).  The cost of the project was estimated in 2010 to be €500–600 million and will see 17.7km of new highways, including 14.7 km of tunnels.

Reusing the rock

Ølen Betong has played an important role in ensuring the success of the tunneling operations by providing the shotcrete for the linings, as well as increasingly providing aggregates for the highways. What is unique has been the source of the material used. Although a great deal has come from traditional sources (including Ølen Betong’s own granite quarries), much has resulted from the new crushing and screening techniques developed by Ølen Betong in partnership with contractors in order to reuse the excavated tunnel rock. This has seen the company manufacture artificial sand from rock, with the company having adapted screening and crushing equipment to deliver economical and environmentally friendly solutions for a variety of applications.

The Ølen Betong site at Fana, Bergen, utilizes tunnel-excavated rock from the Ryfast project in order to manufacture aggregates and artificial sand. The excavated tunnel rock initially has its shape improved followed by processing through a washing plant to remove the surplus fines. The granite/gneiss 0-16mm feed material is processed to produce 0-4mm, 4-8mm and 8-16mm products which are then used to replace 75-100 percent of naturally occurring sand in order to manufacture shotcrete for use on the E39 highway tunnel project in Bergen. Ølen Betong, to date, has supplied 120,000m³ of ready-mixed concrete, 160,000m² of tunnel lining elements and for the new Ulriken railroad tunnel, 80,000m³ of Ready-Mixed concrete as well as 3,892 invert sleepers.

The equipment used to process the aggregate is an Oresizer OM80 200Kw VSI, a Powerscreen Chieftain 2100 wash plant, 2 x 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, as well as reusing the material resulting from tunneling construction.

Manufactured sand

By using the excavated tunnel material, Ølen Betong has been able to reduce its reliance on naturally occurring sand. The manufactured material, in many ways, is an improvement over the naturally occurring sand because it possesses significant benefits. These include containing fewer (if any) contaminants since it is derived from quality virgin rock.

There are also significant advantages gained from the cubical shape of the end product — such as needing little alteration of the amount of water or cement required during specific stages. This makes the process far more cost effective. Additionally, the cubical shape of the manufactured sand gives greater strength to the final concrete product.

This improved manufactured sand is produced with the 0-200mm source aggregate being initially fed into a Powerscreen Maxtrack 1500 cone crusher. The resulting material is then fed into a VSI before being screened by a McCloskey mobile plant into 0-8mm and 8-16mm products.

More uses for excavated tunnel material

Through its involvement in high profile infrastructure projects such as Ryfast Stavanger, the E18 and E39 highway projects and the Ulriken TBM tunnel in Bergen, Ølen Betong is now seen as one of Norway’s leading concrete and cement suppliers. What has made the company’s offering unique is the way it has used material from tunnel excavations, as well as freshly quarried material, to provide a readily available economical and environmentally friendly resource for the projects.

A crusher purpose built for tunneling

The above cases have featured existing crushing and screening equipment, but one company has gone a step further and purpose-built a crusher specifically for crushing aggregates in tunnels. SBM’s STE 100.65 TV PB is a mobile track mounted jaw crusher tailored for the unique conditions experienced in tunnel construction, being put through its paces initially on the Albula Tunnel in Switzerland.

The construction of the 5,860 meter-long Albula Tunnel was carried out by drilling and blasting, with the removal of the excavated material being undertaken by conveyor belts. In order for this to be effective, the excavated granite and dolomite rock were pre-crushed to 0-150 mm. This challenging task was performed directly in the tunnel by the two SBM crushers, before the crushed rock was removed from the tunnel for further processing on the 3km of belting.

Features for tunneling

The specifically developed crusher possesses a material feed opening of 1,000 x 650mm, and is also equipped with an integrated hydraulic gap adjustment system to prevent unbreakable parts damaging the crusher. An apron feeder along with a special pre-screen increases the performance of the machine by 30 percent, while a fully electric drive and dust reduction system are both essential for use underground. Finally, the crusher possesses compact dimensions (19m length, 2.65m width, 4.2m height and a weight of 57.5t). The especially low feed height of 2m allows simple and easy material feed by wheel loader in the tunnel.

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