Tunneling & Trenchless

Microtunneling is a remote-controlled and steerable pipe jacking trenchless tunneling method that utilizes slurry to continuously support the excavation and transport cuttings to the surface. Installations can range from 16-inch to 144-inch in diameter with the most common sizes of 48-inch to 84-inch diameter. Drive lengths range from 200 feet (due to mobilization effort) to 2,000 feet. Drive lengths in excess of 3,000 feet are also becoming more frequent.

Microtunneling is a preferred method for projects beneath the groundwater table, under or near sensitive structures, and/or where accuracy and settlement requirements are critical.

Earth Pressure Balance Shield (EPB) is a type of tunnel boring machine (TBM) that is shielded and balances the pressure in the cutting head with the ground pressure to stabilize the excavation face. Installations range from 8-feet to 50-feet in diameter with larger machines also becoming more frequent. Drive lengths vary, but typically are in excess of 2,000-feet due to machine mobilization.

The balance of earth pressure at the tunnel face avoids uncontrolled inflow of material into the cutterhead and allows for rapid tunneling with minimum heave or settlement at the surface.

When tunneling in competent to slightly fractured rock with very high rock strengths, hard rock tunnel boring machines (TBM) use a rotating cutterhead with disc cutters to fracture and excavate the rock. This method may thrust off shoring installed within the tail shield of the machine, pipe being installed (pipe jacking), or the rock itself depending on the ground condition. Installation can vary from 4-feet to 50-feet in diameter with larger machines becoming used more frequently.

Hard rock TBMs are typically utilized in rock conditions exceeding 15,000 psi and often mobilized for drives exceeding 1,500 feet (depending on diameter) or where blasting is not permitted.

Sequential excavation is used for the construction of shallow mined tunnels in stable ground conditions with minimal groundwater inflow risk. The Sequential Excavation Method (SEM) and the New Austrian Tunneling Method (NATM) are similar methods used for creating space underground which could be large caverns or relatively short distances for tunnel connections, or when existing structures such as sewers or subways exist and cannot be relocated. The tunnel alignment is divided into segments which are then excavated using drill and blast, road header, or by hand mining in a sequential manner.

As the excavated material from each section is removed, support is installed using various methods such as shotcrete, rock bolts, steel beams, or trench plate lining.

Pipe ramming is a trenchless method that involves the use of a pneumatic or hydraulic hammer to install an
open-ended steel casing horizontally. Installations range from 6-inch to 144-inch diameter with lengths ranging from 50-feet to 400-feet.

Pipe ramming is a preferred method in ground conditions containing cobbles and boulders because of its ability to engulf or shear material that may obstruct other tunnel methods.