scope:

An Unlined Tunnel Geotechnical Risk Assessment (UTGRA) is carried out to identify geological features or geotechnical issues which may affect the stability of an unlined Tunnel.

This module describes a generic method of evaluation of unlined Tunnels or Shafts using the rock mass risk assessment system.

This module applies to:

a) unlined Tunnel Section lengths (including unlined sidewalls);

b) unlined Shafts;

c) natural rock Portals; and

d) other unlined Tunnel components (including Adits, Headings and Cross Passages).

The terms Assessment and Examination have been used throughout the standard. Assessment refers to either UTGRA (Unlined Tunnels Geotechnical Risk

Assessment) or USGRA (Unlined Shaft Geotechnical Risk Assessment). The term Examination refers to either UTE (Unlined Tunnel Exam) or USE (Unlined Shaft Examination). This module is applicable to those specifying, carrying out or reviewing an Assessment.

Purpose

This module is to mitigate the risks of instability resulting from the condition of the unlined Tunnel or Shaft and is termed either the Unlined Tunnels Geotechnical Risk Assessment (UTGRA) or Unlined Shaft Geotechnical Risk Assessment (USGRA).