Why Micro-Tunneling

New Austrian Tunneling Method (NATM) 

Building better

Though known across the world, being the most famous and cost effective tunneling method, the New Austrian Tunneling Method has widely been put into practice in our day to day Tunneling activities as we seek to ensure that we give the best services and at the same time remain to be the best option on cost.

Why tunnels?

To alleviate traffic, transportation corridors, like the buildings that feed into them, must at least meet these three qualities; Cost Effective, efficient and reliable. Thus, they should expand into three dimensions. 

Requirements for tunnels

They’re two types of tunnels (Civil Eng. Tunnels and Mining tunnel) Minex mainly ventures in the former method of tunneling which are generally driven at relatively shallow depths by comparison to those situations involving mining tunnels.

Civil engineering tunnels require higher tolerances in terms of the final tunnel profile and its ensuing stability.

Many civil engineering tunnels relate to public usage and high density traffic with projected working lives in excess of 100 years.

As a result, long term stability is desired coupled with an appropriately high factor of quality and safety. Other factors which are critical to the design and use of civil engineering tunnels include line, grade, special surface finishes and prevention of water inflow or outflow in respect of the tunnel structure.

The form and function of the support will vary according to a wide range of factors apart from just geotechnical deliberations and it would seem that for every different tunnel there is a different lining solution for our wide-ranging clients.

Minex has extensive expertise in works involving the primary support of not only tunneling but excavations which require additional strengthening depending on the type of soil profile exhibited.

Tunnel linings: main types. Grouping them into three main forms, these methods can be used individually or coupled together to achieve a desirable results in the construction of a tunnel:

  • Temporary ground support
  • Primary lining
  • Secondary lining

Temporary ground support. In tunnels where the ground has insufficient stand-up time to allow the construction of the primary lining some distance behind the face, then some form of temporary ground support applied at the- tunnel face is required e.g. rock bolts, Shot-Crete and steel sets.

Such support is not required in soft ground in conjunction with a shield driven tunnel as temporary ground support is provided by the body of the shield itself.

Primary lining. A primary lining is the main structural component of the tunnel support system which is required to sustain the loads and deformations that the ground may induce during the tunnel's intended working life.

Most commonly used process that Minex implements includes;

  • Installation of anchors, BRC mesh and shot Crete
  • Installation of precast segment sets
  • Installation of steel sets and shot-crete application

A further function performed by the primary lining is the control of water egress (exit) and ingress (entrance).

Secondary lining. Various tunnels require smooth bore profiles for their intended use, e.g. sewer and water tunnels or aesthetic finishes for public usage, e.g. highway and pedestrian tunnels. Erosion and corrosion protection for the primary lining and further waterproofing may also be required, all of which are provided by secondary linings.

Phone: 0722 999 615

Email: info@minexmt.com

Email: skarl@minexmt.com


P.O BOX 5279 - 00100,

Nairobi, Kenya.