Tunnelling & Caverns

Global demand for underground civil engineering tunnel and cavern construction for rail and road networks underneath large cities is in constant and increasing demand, due to dense surface infrastructure precluding cost effective surface expansion of road and rail networks.

However, tunnelling is not confined to excavations under large cities. Globally, long road and rail tunnels are now common under mountain ranges and under the sea. There are also proposals to bring potable water to large cities by tunnels from remote dams.

Additionally, there is an increasing requirement to store liquids, such as oil, gas and ammonia, in large underground caverns instead of surface tanks. Many of these underground tanks are located at seaports so these liquids can be stored in quantities sufficient for import and export.

The transition away from fossil fluids has resulted in increased activity in the construction of hydroelectric power generating capacity. Hydroelectric power stations are often built underground in complex networks and tunnels and caverns.

Safe nuclear waste disposal also often requires underground tunnels and caverns in rock types that are suitable for very long-term storage without leakage. This is probably the most challenging underground technical issue in not only civil, but also military engineering, applications.

What has happened from a geotechnical engineering perspective is that civil engineering has now encroached into complexities which previously were only encountered in the mining and petroleum industries. Because Sigra works across the mining, petroleum and underground civil sectors of engineering, it has been at the forefront in providing technologies to civil engineering for the development of increasingly complex and demanding projects requiring tunnels and caverns.

Directional Drilling for Tunnel Investigation

Sigra has for many years been involved in directional drilling in mining and for some civil horizontal directional drilling operations for cable installation. Sigra has now focused its drilling skills on tunnel site investigations. Sigra can provide both consulting advice on what type of drilling is suitable for this and in providing tools for this purpose. These tools include stress and permeability test equipment for long holes and a developing suite of drilling equipment. Sigra aims to get the best balance between open hole drilling with geophysics and coring, and sometimes a combination of both. Sigra has adapted oilfield technologies to suit civil tunnelling purposes where possible. These technologies can change the economics of tunnel site investigation.

Road and rail tunnelling projects in Australia

Over the past 20 years, Sigra has performed large numbers of IST 2D and hydrofracture stress measurements for underground road and rail projects across Australia. Significant clients include Cross River Rail and the Brisbane Airport Link road tunnel in Brisbane, WestConnex road tunnels and Sydney Metro Rail in Sydney, and Melbourne Metro Rail.

Snowy 2.0 Pumped Hydro Project

In 2017 the Australian Federal Government made a decision to proceed with the development of Snowy 2.0. This project is to be owned and run by Snowy Hydro which is a Federal Government corporation. It is a pumped storage addition to the original Snowy Hydro project completed in the 1970s.

The new work involves the development of 27 km of headrace and tailrace tunnel between the Tatangara and Talbingo Reservoirs at depths up to 1050 m in the Snowy Mountains of New South Wales. In addition to the tunnels the design requires the development of a turbine and transformer caverns.

At the end of 2017, Sigra was asked to supply stress measurement services to the initial site investigation consultant, SMEC, using Sigra’s IST tool.

This was followed in 2018 by an expanded site investigation through the new site investigation consultant, GHD, which involved stress measurement using both the Sigra IST system (77 successful measurements) and hydrojacking to measure stress in more fractured rock. In addition, Sigra were asked to supply packer testing to measure permeability. Sigra later replaced packer testing with their drill stem test procedures that yielded meaningful values of permeability and fluid pressure. Sigra also supplied rock property testing services.

At the end of the site investigation Sigra were asked by Snowy Hydro to provide a geotechnical review of the project. This involved examining all core logs and geophysics as well as the work conducted by Sigra.

Both stress changes and changes in direction of bedding planes in the meta-sediments revealed an additional two major faults in the area of the planned caverns. As a result of this, the location of the caverns has been moved in the design now being constructed.

Kidston Pumped Hydro Project

Sigra conducted stress measurements using the Sigra IST stress test as part of Kidston pumped hydro project, located at the decommissioned Kidston gold mine at Einasleigh in North Queensland. The work was requested by GHD Pty Ltd, on behalf of Genex Power.

Underground Nuclear Waste Storage Facility, Hungary

Sigra has undertaken stress measurements using the Sigra IST stress tool as part of the nuclear waste repository investigations near Pecs in southern Hungary.