Design of High-Performance Rock Bolted Thin Shotcrete Linings

From Basics to Advanced Concepts

Overview

Tunnels in poor to fair-quality rock masses (i.e. Q-values between 0.4 and 10) can generally achieve global stability and ground support primarily through ground reinforcement, such as rock bolts. Such reinforcement elements not only hold unstable rock wedges and blocks but also provide local shear and tensile reinforcement where they cross rock defects or discontinuities, enhancing the rock mass’s capacity to redistribute stresses during tunnel excavation more safely. However, to keep costs down, rock bolt spacing must also be efficient; as a result, the use of a surface retention system, such as shotcrete, is still necessary to promote local stability and stress arching, thereby supporting the rock mass between the rock bolts. In these cases, a thin shotcrete lining (75-150 mm thick) is often used. It is usually designed to span the loads between the rock bolts, accounting for both flexural and punching failure mechanisms. When combined with long cables, as it is frequently used in mining, the system can also play a greater role in global stability, reducing the risk of larger failure mechanisms with volumes of the order of the excavation. It can, in principle, also be designed for dynamic loads if the bolts are designed for them. This presentation will discuss some basic concepts of this support system, including the use of fibre reinforcement, and then move on to more advanced concepts, such as compressive membrane action and non-linear concrete design.

Speaker

Dr David Oliveira

Discipline Leader, Ground, Aurecon

Dr David is a Chartered Professional with 27 years of experience in civil engineering and mining geomechanics. He is Aurecon’s Discipline Leader for Ground Engineering, including the Geotechnical, Geology, Tunnels, Underground Structures and Pavements teams. He is also currently the Vice-Chair of Working Group 12 – Sprayed Concrete of the International Tunnelling Association. Besides major recent infrastructure such as Westconnex M8, Westconnex M4-M8, Hinkley Point C Nuclear Power (UK), Sydney Metro West-Central Tunnelling Package, Western Harbour Tunnel Package 2, and Borumba Pumped Hydro, David has worked in projects for some deep underground mining projects such as Gwalia Mines (AU), Big Gossan (Indonesia), Cuiaba Mine (Brazil) and currently Oyu Tolgoi (Mongolia).

This event is run by the Australian Geomechanics Society in collaboration with Western Australian Ground Control Group and Australian Tunnelling Society.