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This review focuses on different mechanical methods of tunneling and covers topics like selection of a tunneling method, suppliers, consultants and publications in the area of tunneling.


Based on InfoMine's Dictionary of Mining and Mineral Terms, tunneling is the operation of excavating, driving, and lining tunnels.
A tunnel is a horizontal or inclined stone drivage for development or to connect mine workings, seams, or shafts. It may be open to the surface at one end and used for drainage, ventilation, or haulage or as a personnel egress (walking or riding) from the mine workings. In simple words, tunneling means digging tunnels where a tunnel is an enclosed underground passageway.


As high producing underground mines are becoming the first choice of global mining companies, it is reasonable to say that such mines will also require construction of significant underground developments prior to and during ore production. As a result, long underground tunnels in excess of 10 km are not uncommon to be seen in an underground mine. To suffice the requirement to dig these long tunnels in a fairly shorter period of time, there is an increasing demand to use rapid and mechanized tunneling technologies like TBMs (Tunnel Boring Machines) and roadheaders.

Out of the five main methods of tunneling (Pipe Jacking, Drill & Blast, Impact Hammer, Roadheaders and TBMs), this review will primarily focus on the technologies of Pipe Jacking, Impact Hammers, Roadheaders, and TBMs.

Tunnel of Eupalinos (Eupalinian aqueduct) in Samos, Greece


The primary use of tunnels can be easily observed in civil constructions as for foot or vehicular road traffic, for rail traffic, or for a canal. The construction of tunnels can be traced back to the ancient Greek era around 520 BC, when a tunnel aqueduct, known as the Tunnel of Eupalinos, was built in Greece in excess of 1 km (see The Tunnel of Eupalinos on Wikipedia for more details and pictures).

The Cobble Hill Tunnel (or Atlantic Avenue Tunnel) is the world's oldest subway tunnel, built in 1844 by the cut-and-cover method under Atlantic Avenue in Brooklyn, New York. The Delaware Aqueduct in New York is the longest tunnel of any type in the world, at 137 km (85 mi) in length. Wikipedia gives a detailed overview of civil tunneling technologies.

The advent of use of TBMs for tunneling in underground mines dates back to the late 1950s, but its successful and economic application started in the early 1990s. The San Manuel Mine Tunnel (Magma Copper Company) completed on December 4, 1995 was built using a Main Beam TBM. It measures 4.6 m in diameter and 10.5 km in length.

Robbins Main Beam TBM (Source: The Robbins Company)

Robbins TBM technologies can dig tunnels from diameter as small as 0.76 m (760 mm, Big Sky Tunnels) to as large as 14.4 m in The Niagara Tunnel Project. The Pinglu Tunnel is one of the longest tunnels ever excavated by a single TBM. It extends to 25.4 km in length and has a diameter of 4.8 m.


There are five different methods of tunneling. These are:

  • Pipe Jacking/Shield Machines
  • Road Headers
  • Hammer Tunneling Splitters
  • TBMs
  • Drill and Blast

The selection of a tunneling method depends on many factors, including:

  • Desired rate of advance
  • Area of tunnel cross-section
  • Available capital for investment
  • Contractors and suppliers availability
  • Intact rock properties
  • Rock mass properties
  • Desired cutting geometry
  • Operational parameters
  • Machine specification

The last five parameters influence the performance of a tunneling method. The figure below shows a simplistic view of selection of different tunneling methods based on rock properties.

Tunnelling Methods (Source: Malcolm Scoble, Rock Fragmentation - NBK Institute of Mining Engineering, UBC)

Tunnelling Methods (Source: Malcolm Scoble, Rock Fragmentation - NBK Institute of Mining Engineering, UBC)

The ITA/AITES - Training Course Tunnel Engineering: Performance Prediction of Mechanical Excavators in Tunnels, prepared by Bilgin et. al. provides a good overview.

Brief details on these methods are presented below:

1. Pipe Jacking:

Pipe jacking is a technique of installing pipes underground using small diameter TBMs. Usually termed as micro tunneling, this method is best deployed in cohesive soils. However with recent advances in technology, this method can now be employed either in cohesive or non-cohesive soils, in dry or watery conditions, to jacking through very hard rock and ground conditions comprised of mixed composites, such as cobbles and big boulders.

RITCHIEWiki provides an excellent review on the benefits, application and process of this method. You can also visit The Pipe Jacking Association's Introduction to Pipe Jacking presentation. For various pipe jacking photos, please visit MidwestMOLE's website.

2. Hammer Tunneling:

Impact hammers have been used in mining industries since 1960s. Though typical applications include over-sized boulders, heavily reinforced concrete structures or steel slag, it has also been successfully applied in tunneling too. It basically works on two mechanisms of breaking - Penetrative breaking and Impact breaking. Penetrative breaking relates to softer materials that are demolished by combination of stress waves and wedge effect. A chisel or moil-point tool is used for the purpose. In Impact breaking, a blunt tool is used to transfer only stress waves as wedge effect is undesired here.

The productivity depends on many factors which include: impact energy and frequency, material strength and toughness, operator skill and technique, carrier condition and jobsite logistics (Source: Malcolm Scoble, Rock Fragmentation - NBK Institute of Mining Engineering, UBC).

Hydraulic impact hammers have been applied in tunneling in Instanbul with almost 11 kms of tunnels have been excavated since 1992. Here, impact hammers have been applied to tunnels of 36 m2 cross-section and in rock with RQD ranging from 0 to 100. It has achieved a net breaking rate of 5 to 35 m3/hr (an advance rate of 2 m - 10 m per day based on 16 hour daily work schedule) (source: H. Tuncdemir, ScienceDirect)

3. Roadheaders:

A roadheader is an entry-boring machine, which bores the entire section of the entry in one operation (source: Infomine Dictionary). A roadheader is basically categorized primarily on types of cutting heads, transverse or longitudinal, and on the basis of types of loading assembly - gathering arms, spinner loaders, scraper conveyor loaders, two lateral loading beams, or one central loading beam. Brief details on them are mentioned below:

Longitudinal cutting head



Pros of Longitudinal over Transverse:

  • Can run with minimum overbreak; lesser than transverse
  • Low bit consumption primarily as a result of lower cutting speed


Transverse cutting head

Pros of Transverse over Longitudinal:

  • Faster cutting rate
  • It cuts in the direction of face and is more stable than longitudinal
  • Less affected by changing rock conditions and harder rock portions
  • Better use of parting planes especially in bedded sedimentary rock
  • Greater versatility and has a wider range of applications

Gathering Arms

  • Best suited to handle coarse, blocky, interlocked and wet muck
  • Effective loading on steep slopes
  • Well suited for tunnel operations
Gathering Arms

Spinner Loader

  • for dry, interlocked and non-sticky materials
  • Wear-resistant, Low maintenance
  • Can handle high muck volumes when used for mineral production, such as in coal mines
Spinner Loader

Two Lateral Loading Beams

  • Swinging loading beams
  • Very simple and rugged solution, but somewhat restricted loading capacity
Two Lateral Loading Beams

One Central Loading Beam

One Central Loading Beam

Scraper Conveyor Loader

  • For non-blocky and non-abrasive materials
Scraper Conveyor Loader

(Source for above figures: Rock Excavation Handbook, Chapter 6: Tunnelling)

A roadheader can also be categorized under light, medium, heavy and extra heavy classes depending on their performance. A light roadheader (<40 tonnes weight) can work on rock with UCS up to 60-80 MPA and cross-section up to 25 m2. Extra heavy roadheader (>100 tonnes of weight can work on rock with UCS up to 120-140 MPA and cross-section up to 45 m2.

A longitudinal roadheader by Mitsui Miike Machinery Co., Ltd.

A longitudinal roadheader by Mitsui Miike Machinery Co., Ltd.

Please look at the publications section below for more technical information.
For general specifications, visit Sandvik or Mitsui.

4. Tunnel Boring Machines (TBMs):

Because of its capabilities to attain high rates of advance in civil tunnel construction, the Tunnel Boring Machine (TBM) is gaining popularity and interest towards its application in underground mine development.

Robbins produces and sells four different varieties of TBMs - Main Beam, Single Shield, Double Shield and Earth Pressure Balance. All are capable of digging tunnels from 3 to 15 m in diameter, with Earth Pressure Balance TBMs especially suited for soft ground conditions containing water under pressure.

For more information on TBMs, please review the section below on publications, consultants and suppliers. For TBM applications in mining, please review the case studies mentioned below.

TBMs in Mining (Case Studies):

5. Drill & Blast:

This is the most conventional method of tunneling and is still practiced and favored for shorter tunnels, in hard rocks, and where time is not constraint. Please visit the Infomine Technology Reviews on Drilling and Blasting for more information on consultants, suppliers and other technical information.


The selection of mining method depends on geological, equipment, mining and economical parameters as described in the Tunneling Methods Section above. The following table provides a quick summary of all these methods and may be used for reference purpose.
Tunneling Methods Advance Rate (m/day) Cross-section Area (m2) / Dia (m) Rock Properties Comments
Pipe Jacking 5 - 20 12 mm (0.5") 3.6 m (12') Best suited for cohesive soil; can also be applied to non-cohesive and dry conditions and in hard rocks. Primarily for laying pipelines; small cross-section and limited capability in hard rocks show little scope of its use in underground mining
Hammer Tunneling 2 - 10 Up to 30 m2 Low to medium strength; RQD: 0 - 100 Breaking, mucking and reinforcement can go together; low investment
Roadheaders 5 - 15 Up to 45 m2 Up to 140 MPa (UCS); can adapt to changing rock mass conditions Low investment, 15% - 30% of TM investment for same cross-section; can be rented; can be delivered and ready for operation in 3-6 months; free space and accessibility; can handle a variety of subsections
TBMs 15 - 50 Up to 160 m2 From 20 to 140 MPa (UCS); can be frabricated to a variety of ground conditions Fabrication period of around 12 months; Onsite set up time 3-6 months
Drill & Blast 3.5 m - 5 m & 7 - 15 m (without rock support installation) - - -


1. Pipe Jacking:

2. Impact Hammers:

3. Roadheaders:

4. TBMs:


Major contractors and consultants in tunneling are:


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