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Crushing and screening for sustainable excavation 01 Nov 2018

Roger Murrow for TunnelTalk
When a tunnel is constructed there is always a problem - what to do with the excavated material? Increasingly the best solution is to reuse it some way and to do that the rock needs processing. Traditionally this has been accomplished by hauling the material to an aggregate plant for a multi-stage process to produce a valuable product. Today, production of aggregate is more frequently managed directly on the tunnel project site. The challenge then for tunnelling contractors is the selection and mobilisation of the best equipment for the job. Roger Murrow reviews the best of the crushing and screening equipment currently on the international market.

Before looking at the crushing and screening equipment of various manufacturers, it is apt to explain initially the potential for using excavated tunnel rock. Broadly there are three uses:

  • First as aggregate for construction projects such as sub base material for roads;
  • Secondly for processing into high value manufactured sand; and
  • Thirdly as ballast or flood control material on dam projects.
Terex sand and gravel processing plant
Terex sand and gravel processing plant

There are, of course, other uses, but it is the first two that are of interest for this review and as a result of crushing and screening equipment developments and the realisation that the excavated tunnel rock is too valuable a commodity to discard.

In addition, many commissioning authorities of tunnels (a politically sensitive subject in many countries) are keen to stress the environmental credentials of the project. Reusing excavated material is a benefit for both the tunnellers and their political paymasters. It also goes some way to explain why manufacturers of equipment have placed an emphasis on fuel consumption and reducing harmful emissions.

To transform excavated tunnelling material into something valuable, a combined crushing and screening process is required. Further treatment may require washing plant and concrete batching facilities.

Fully mobile crushing and screening train in operation
Fully mobile crushing and screening train in operation

Aggregate production

This is the most straightforward of the processes and has been used on countless tunnelling projects worldwide. Effectively this involves reduction of excavated rock to a size suited for further processing, then sizing to the required dimensions of 0-5mm; 5-10mm; 10-40mm, 40-100m and so forth. As a rule, the smaller the processed aggregate the more specialised the application.

To accomplish this, a large jaw crusher is used in the first instance to reduce the rock into more manageable sizes, often -250mm. In many cases, the larger elements are not reduced further as they can be used for flood prevention and other applications. The second stage requires a secondary crusher to a more tightly defined parameter via an impact, roller or large cone crusher.

Following on, the precise sizing of the material is undertaken using sizer screening decks. The smaller the diameter of the screens the slower the production, but the more accurate the screening. There are many types of screening meshes available, all designed to process aggregate based on the specific properties of the material and its final use.

Metso crushing and screening installation
Metso crushing and screening installation

Artificial sand

If artificial sand is to be manufactured for shotcrete or to be used in concrete, then two more stages are required. The first involves a cone crusher to produce a 0-5mm product. This is of direct benefit to the tunnelling industry as it reduces the reliance on naturally occurring sand.

This is proving to be an increasingly accepted idea, held back in the past only by the lack of equipment up to the task. Environmental concerns have seen a total ban on the use of naturally occurring sand in many places. Manufactured material is in many ways an improvement on naturally occurring sand as it originates directly from high quality virgin rock, and thus contains very few, if any, contaminants.

There are also significant advantages to be gained from the cubical shape of the manufactured product. This is especially valuable in the production of concrete as there needs to be very little altering of the amount of water or cement required during specific stages, thereby making the process far more cost effective. The cubical shape of the manufactured sand also provides greater strength to the final concrete product.

Artificial sand from excavated tunnel rock has many benefits
Artificial sand from excavated tunnel rock has many benefits

The final stage if needed is a washing plant to wash away light particles or impurities that could contaminate the end product.

Static or mobile?

Traditionally excavated tunnel material has been hauled to specialist static processing sites, or aggregate plants. Following processing the material is then transported to the next stage such as a concrete plant or to the point of use. These aggregate plants operate as dynamic high quality, high productivity manufacturing processes. The downside is that it requires the material to come to the process, and then be transported out again. To lessen the need for transporting material back and fore, many cement companies now have specialised aggregate plants attached to their production yards.

Increasingly popular are mobile crushing and screening trains. These consist of a tracked or wheeled jaw or cone or impact crushers, along with a mobile scalper, a three- or four-way split screener and sometimes a washing plant.

Close up of a CV impactor manufacturing sand
Close up of a CV impactor manufacturing sand

The benefits are easy to see. In effect the equipment is easily transported directly to the material or to the concrete plant and is able to process the rock to the required specifications. The crushers are often smaller scale versions of those used in static plants for example. Productivity is also lower and where static plants these days operate off mains electricity, in virtually all cases, mobile plants utilise diesel engines with the resulting higher operational costs and emissions.

In tunnel processing

A recent development in the processing of excavated material has been the crushing and screening of rock actually in the tunnel using mini crushers and screens. These are in the main track mounted and were originally developed for small building companies. However, tunnelling companies soon became open to the possibilities of the equipment with a large number of crushers being used on different projects.

Who supplies what?

There is a large number of crushing and screening equipment manufacturers. As a generalisation, Scandinavia is the traditional home of manufacturers of stationary plant and the UK (Northern Ireland to be specific) the home of mobile equipment manufacturers. Today, and increasingly, mobile plant manufacturers are producing stationary plant and vice versa, with recent acquisitions and mergers blurring the geographic boundaries.

Producing concrete in Norway
Producing concrete in Norway

Sandvik Mining and Rock Technology

Sandvik is perhaps the most instantly recognisable name to tunnellers due to its leading ranges of tunnelling and drilling equipment. The company also possesses expertise in manufacturing crushing and screening equipment ideal for underground operations. All Sandvik equipment is available as static, mobile or semi mobile wheeled or skid mounted.

Amongst its large range, Sandvik supplies crushers of all types – jaw, cone, impact, roller crushers – as well as hammer mills and primary gyratory crushers, together with a wide range of scalpers, screens and feeders. The emphasis has been on supplying equipment to produce more accurate fractions of aggregate as well as solutions for any size-reduction challenge, from individual components and consumables, to complete solutions or turnkey installations.

Of particular interest to tunnellers is the company’s CV series of impact crushers. These have been purpose-designed to manufacture artificial sand and have been doing so successfully for many years across the globe.

Mobility now enhanced through tracked stockpiling systems
Mobility now enhanced through tracked stockpiling systems

Continuing a trend in the development of intelligent equipment, Sandvik has placed a great deal of emphasis on crushing and screening systems similar to its tunnelling offering. This often encompasses the entire aggregate plant, with a series of recently launched and developed systems based around Sandvik Plant Solutions. These have been developed to help operators control running hours, empty running, standstills and energy consumption, all in efforts to create more accurate production forecasts and maximise return on equipment investment. The company has also recently launched the CH800i series of connected cone crushers. These are the first to offer intelligent crushing based on actionable information via a Sandvik portal.

SBM

SBM Mineral Processing of Austria specialises in supply of mineral processing and conveying plant. The product range includes individual machines, mobile and stationary mineral processing plant and concrete mixing plants, as well as service and support. The range is similar to other manufacturers, but what the company does do is manufacture a purpose developed crusher for the tunnelling industry.

The SBM STE 100.65 TV PB is a mobile track-mounted jaw crusher designed to operate in the most difficult tunnelling conditions. Although relatively new, the crusher was put through its paces during the construction of the Albula Tunnel in Switzerland. The unit possesses the ability to work in confined spaces and possesses a low feed height of 2m alongside specific tunnelling safety aspects including electric drive and dust reduction systems.

Sandvik stationary plant manufacturing sand
Sandvik stationary plant manufacturing sand

Metso Minerals

Metso, headquartered Finland, is a leading industrial company serving the mining, aggregates, tunnelling, recycling and process industries. Its equipment portfolio ranges from mining and aggregate processing equipment and systems to industrial valves and controls. Of direct interest is its extensive range of mobile and stationary crushing and screening plant. This includes the famous Locotrak range of mobile crushers.

The Metso Nordberg C Series jaw crushers are engineered to process the toughest of materials making them a choice for the primary and secondary crushing of excavated tunnel rock. The MX, HP, GP and MP series of cone crushers feature a combination of crusher cavity design and crushing force with reliability and safety to provide higher capacity and a quality end-product for secondary, tertiary and quaternary applications.

Crushing and screening train in operation
Crushing and screening train in operation

As with the Sandvik CV series, the Metso Barmac VSI is also ideal for the manufacturing of sand from rock and uses the rock fed into the machine as the crusher. This autogenous crushing action (as with Sandvik’s CV series) offers the lowest possible cost/tonne of any impact crushing method. The high velocity impact crushing achieved in a Barmac VSI improves the soundness and shape of the material.

A comprehensive range of Metso IC intelligent automation solutions is also available for Metso crushers. Metso IC automation ensures full performance and is precisely designed to improve productivity with inbuilt systems for consistent performance, safety and easy control of crusher parameters.

Allis Saga

As a relatively new company operating in today’s market, Allis Saga equipment is familiar to the industry. After merging Construction and Mining, Sandvik disposed of what it considered redundant product lines and these formed the basis of the initial Allis Saga equipment range. The lines have since been developed further to provide a range geared more towards customer requirements. Many of the add-ons and systems found on Sandvik equipment have been removed and the trimmed down units have proved popular with high volume aggregate producers.

SBM jaw crusher purpose designed for tunnelling
SBM jaw crusher purpose designed for tunnelling

One product in the range that has proved itself is the Allis Saga cone crusher. Designed specifically for heavy-duty conditions, often found when dealing with excavated tunnel rock, the range has an installed power of up to 750kW in the new MH900 machine, and a throughput capacity of more than 2,000 tonne/hr. The product granularity is guaranteed by adjusting the eccentricity and an intelligent control system ensures the crusher operates to its optimal condition.

GIPO

The Swiss based company GIPO manufactures a highly respected range of stationary and mobile crushing and screening equipment. Its line of single toggle jaw crushers enables easy and precise setting for the desired material size using plug-in plates to adjust the hydraulic gap. This hydraulic actuation incorporates a variable speed adjustment and the constant crushing power provides the facility for full crusher start-up.

A combined crushing and screening plant ideal for processing rock
A combined crushing and screening plant ideal for processing rock

Integrated pre-screening in the feeder channel allows fines to be removed on a conveyor belt from the side of the machine. In a separate screening machine, the lower deck screen design also results in the classified material being screened out from the side of the machine. The fully diesel hydraulic actuation concept used on all GIPO machines ensures minimum susceptibility to failure from dust, humidity and vibration, making them ideal for tunnelling operations.

Terex

The Terex Group of companies provides a full range of screening and crushing solutions ideal for tunnellers, both static and mobile. This is offered through its Mineral Processing Systems (MPS) brand and marketed by its subsidiaries, Finlay and Powerscreen. The company is also able to design and build modular crushing and screening plants.

The MPS range of jaw crushers is designed with the power, reliability and performance to meet the toughest demands of primary crushing applications. The Terex MPS cone crushers have proved ideal for processing medium strength rocks. The MPS range of cone crushers provides flexibility, high rates of productivity and uniform product shape for secondary and tertiary applications.

MH900 cone crushers used to process excavated tunnel rock
MH900 cone crushers used to process excavated tunnel rock

New from Terex is its EvoQuip range. As its name suggests, this range was developed originally for the small-scale construction and recycling market but possesses attributes that make it eminently suitable for tunnelling applications. The comprehensive portfolio of products is ideal for addressing the needs of the compact crushing and screening markets and useful for material processing inside tunnels.

Wholly owned by Terex, Powerscreen is one of the original suppliers of mobile screening units, and now encompasses the former Pegson line of crushers. As well as cone, jaw and impact crushers, the Powerscreen manufactures perhaps the largest range of mobile screening equipment on the market as well as washing plant.

Terex Finlay may, arguably, claim to be the world’s first mobile screen manufacturer and like the Powerscreen range, its product line includes tracked jaw, cone and impact crushers as well as a variety of screens and scalpers.

Mobile crushing from Terex Finlay
Mobile crushing from Terex Finlay
Compact crushing has found favour with tunnellers
Compact crushing has found favour with tunnellers

Red Rhino

The range of Red Rhino mini crushers starts with the 750kg 2000 series increasing in size to the 10,000kg 7000 series. These units, together with Red Rhino screens, are ideal for processing tunnelling material underground.

Rock from road tunnels in Norway being turned into shotcrete for use on the same tunnels
Rock from road tunnels in Norway being turned into shotcrete for use on the same tunnels

CDE Global

A company that has found a particular niche in a relatively short time in supplying equipment and systems to the tunnelling industry is CDE Global. Slightly different to other companies, CDE supplies and installs equipment from other manufacturers as well as its own equipment. The common feature is that all the plant is of the washing type making the units ideal for use in the manufacture of sand from excavated tunnel material.

A huge range available

The review of these crushing and screening manufacturers is the tip of the proverbial iceberg. There are manufacturers of all shapes and sizes of crushing and screening units across all corners of the globe. What all the mentioned companies have in common is a range of equipment and the expertise and support services for customers to get the very best out of rock excavated from tunnelling operations.

References

           

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