Rock tunneling is a specialty that is incorporated across all of our market sectors, including transportation, roads and highways, rail and transit systems, water and wastewater conveyance, power and energy, and underground storage facilities, including petroleum and nuclear waste repositories.
Our engineers have extensive experience in all aspects of rock tunneling and mined cavern projects, from conception and feasibility studies, to detailed design and construction, as well as the operation and rehabilitation of the facilities throughout their life cycle. We have been involved in rock tunnel design in major cities the world over, including most major underground transit systems in the United States.
WSP adapts traditional design and construction techniques to specific site situations, and developing innovative techniques and approaches for projects that demand solutions beyond standard practice. We have experience across various geological settings on all six continents. We anticipate complications that could arise during construction and account for them during the preparation of design and construction documents, as well as during construction.
Drill and Blast
Drill and blast is an excavation method used frequently in hard-rock tunneling because its flexibility allows for different layout setups. WSP has used drill and blast to build tunnels with diameters up to 30m wide, mostly supported by steel bolts and fiber-reinforced shotcrete (sprayed concrete). We use controlled blasting techniques in our design to control over-break, reduce vibration and aid the stability of the remaining rock formation. When vibrations or a damage zone in the rock is not feasible, the method can be supplemented with wire sawing. In these cases, a wire is fed through drilled holes and drawn along the actual surface without causing vibrations. One major project recently completed using drill and blast technique was the Stigbergsgaraget parking garage in Stockholm, a finalist in the 2016 ITA Tunnel Awards.
Tunnel Boring Machines (TBM)
The main types of tunnel boring machines used in rock are main beam open face gripper TBMs, best for hard and competent rock, and shielded or double shielded TBMs like earth pressure balance (EPB) and slurry TBMs that are best for highly fractured rock. In San Francisco, an EPB TBM was used to construct the two tubes of the Central Subway Tunnel. In Istanbul, a mix-shield slurry TBM was used in the highly fractured Trakya formation to build the Eurasia Tunnel, which won the ITA project of the Year in 2015. For the Port of Miami Tunnel, an EPB TBM mined the tunnel in Karstic limestones, which required the significant use of grouting for ground improvement.
New Austrian Tunneling Method
The New Austrian Tunneling Method (NATM)—known in the United States as the sequential excavation method (SEM) and in the United Kingdom as a sprayed concrete liner (SCL)—is based on the understanding of how rock reacts to the creation of a tunnel. NATM offers the flexibility to build tunnels of almost any size or shape; however, curvilinear (oval) is preferred to allow smooth stress redistribution. By adjusting the construction sequence expressed mainly in round length, timing of support installation and type of support, it allows for tunneling through a variety of ground conditions. For the Eurasia Tunnel, the NATM method was used for construction over 1km of tunnel in poor rock condition and with limited cover. The Chinatown station of San Francisco's Central Subway is being constructed in poor rock conditions using the NATM method.
A roadheader is used as a mechanized method of cutting that has more precise cutting, less vibration and no overbreak. Recent developments have allowed the excavation of rock tunnels in very hard rock. The basic cutting tool is a very large milling head mounted on a boom, which is in turn mounted on tracks or within a shield. The cross section can be cut to almost any desired shape to better distribute the stresses in the rock mass. In New York City, roadheaders were used for the construction of the East Side Access Project in New York on rock with compressive strength in excess of 140 MPA (20,000 psi), as well as for sections of the Lane Cove Tunnel in Sydney.
Ground Water Control
Pre-grouting is frequently used to handle water leakage in rock tunneling. Long holes are drilled ahead of the excavation and filled with grouting paste by pressure. This grout spreads along the joints around the tunnel, which minimizes the inflow of water into the tunnel.
We are able to undertake detailed appraisal of water resources (hydrology and flood prediction) and groundwater flow (hydrogeology), through detailed computer modeling and advanced risk assessment procedures. Our hydrologists and geochemists work closely with our rock engineers, primarily on cases involving joint water tracking, hydraulic testing and 3D groundwater flow.
Services Provided by WSP
Rock tunneling requires an interweaving of knowledge of rock mechanics, engineering design and construction practice and techniques. We have experience in all rock tunnel construction techniques, including drill-and-blast, New Austrian Tunneling Method, tunnel boring machines and roadheaders. The use of various construction methods usually results in different rock stabilization techniques and different support systems. Sometimes all these methods are used on the same project. For the Follo Line in Oslo, Norway, and the #7 Subway Line Extension in New York City, both TBM and drill and blast were used.
WSP provides complete services related to rock tunnels under various surface conditions, in mountainous or urban areas, in seismic zones and for all market sectors. Some of the services we provide are:
Geotechnical investigations, analyses and reporting, including GDR and GBR
Design of rock tunnels, caverns and shafts at various depth up to several hundred meters from conceptual design through development of tender documents or detailed design documents
Design of rock tunnels in difficult ground conditions, including squeezing and swelling grounds, mixed face conditions, high hydrostatic pressure, limited cover and karstic grounds
Design of the tunnel initial support, waterproofing and final liner
Environmental services related to rock tunneling, including vibration control, ground-borne noise, impact on water regimes, and sustainability
Program management and construction engineering, including constructability analysis, construction staging and sequencing, value engineering, risk analysis and management, construction management and field inspection services, claim avoidance, project control and management.