Microtunnelling and pipe jacking: building gravity sewers on tight grade

01 /What is pipe jacking?

Pipe jacking installs a pipeline by pushing it. The Iowa SUDAS design manual describes the set-up: pits at both ends, a guide rail or jacking frame to hold the pipe and jacks, and a thrust block, normally concrete, for the jacks to push against. A steel jacking shield leads the pipe string and gives workers a protected space to excavate the face, by hand or with machinery. Spoil goes back to the pit in small carts, augers or a conveyor. As each length of pipe is pushed in, the jacks retract, the next pipe is set in the pit, and the cycle repeats.

Steering is precise. A laser set to line and grade in the pit shines through the pipe onto a target at the face, and modern equipment adjusts automatically. Because people work at the face, SUDAS says man-entry pipe jacking and utility tunnelling are typically limited to pipes of 42 inches (about 1,067 mm) and larger, and 48 inches for extremely long drives. Length is theoretically unlimited: intermediate jacking stations spaced along the pipe let it be pushed in sections rather than all at once.

02 /How does microtunnelling work?

Microtunnelling takes the people out of the pipe. SUDAS defines it by four features: it is remote controlled from a panel usually on the surface; it is guided, normally by a laser projected onto a target in the machine; it is pipe jacked, with the machine and pipes pushed forward by a jacking system; and it is continuously supported, with pressure applied at the face to balance groundwater and earth pressure.

1. Build the shafts

   A jacking shaft is sunk at one end with a thrust wall, and a reception shaft at the other. Shaft size depends on the machine and pipe length.

2. Launch the machine

   The microtunnel boring machine is set on the jacking frame, aimed with the laser, and pushed through a seal in the shaft wall.

3. Cut and jack

   The cutting head excavates the face while the jacks push the machine and the pipes behind it forward one length at a time.

4. Remove spoil

   Soil is mixed with water into slurry and pumped to a separation plant on the surface, or removed by an auger inside a separate casing in the jacking pipe.

5. Steer

   The operator reads the laser target and adjusts the machine's steering to hold line and grade.

6. Receive

   The machine breaks into the reception shaft and is lifted out; the jacked pipe is the finished sewer or a casing for it.

03 /Why do cities choose microtunnelling for gravity sewers?

Because grade is everything in a gravity sewer and microtunnelling holds it. SUDAS describes microtunnelling, like pipe jacking, as laser-guided, steerable and highly accurate, with installations within about one inch of the proposed line and grade possible, and says it is normally used for pipelines that need high accuracy such as gravity storm and sanitary sewers. The other new-path methods are typically closer to ±1% of the bore length.

It also copes with difficult ground. SUDAS says microtunnelling can handle a wide variety of soil conditions and that boulders or rocks up to 20 to 30 percent of the pipe diameter can normally be removed by the machine. The pressurised face limits ground loss below the water table, which is where open trenches and simpler bores run into trouble.

04 /What sizes and pipes does microtunnelling use?

The name misleads: SUDAS notes that "micro" refers to the method's origin as pipe jacking for pipes too small for a person, and that the technique has since been used at very large diameters because removing people from the bore adds safety. The jacking pipe must survive the thrust, so it is a rigid pipe with a strong joint; often it is also the finished sewer.

05 /Where is microtunnelling used in Canada?

Large Canadian cities use it for trunk sewers and local sewers under built-up streets. Two examples we verified on municipal sites in September 2026:

• Calgary, TransCanada Sanitary Trunk. The City describes a new 8.5 km underground wastewater pipe for Calgary, Cochrane and nearby communities, using pipes of 1.35 m and 1.5 m diameter, with more than 85 percent built by microtunnelling to limit surface disruption, preserve the sound barrier along 16 Avenue N.W. and protect existing trees. Construction began in spring 2025 with completion expected in early 2027.
• Toronto, Fairbank-Silverthorn storm system. Toronto's basement-flooding project pairs a 4.5 m diameter, 2.4 km storm trunk tunnel built with a tunnel boring machine at depths of 15 to 40 m with new local storm sewers constructed by microtunnelling along several residential streets, supported by twenty shafts.

Both show the pattern: microtunnelling is chosen where the sewer must hold grade, the surface is valuable, and the drive is long enough to justify shafts. For how owners weigh those factors, see municipal and commercial trenchless, and for city-by-city notes, the across Canada page.

06 /What are the limits and risks?

• Short drives. SUDAS says microtunnelling tends to be costly for relatively short bores, because the shafts, machine and separation plant cost much the same whatever the length.
• Shaft space. Launch and reception shafts, a crane, a control unit and slurry separation need a work site, often a lane closure or a park corner for months.
• Obstructions. Buried timber, steel or large boulders beyond the machine's capacity can stop a drive; recovery may need a rescue shaft.
• Ground loss. Poor face-pressure control in wet ground can cause settlement above the tunnel.
• Pipe damage. Jacking forces rise with length and friction; pipe joints must be designed for them, and lubrication is used on long drives.

Microtunnelling is a municipal and major-project method, priced by tender, so this site publishes no planning range for it. For smaller crossings, compare auger boring and pipe ramming and directional drilling; for the related pipe-eating technique that replaces an old sewer with microtunnelling equipment, see bursting, splitting and reaming.

07 /How does microtunnelling compare with other crossing methods?

The choice is usually made by grade first and cost second: if the sewer's slope leaves little room for error, the laser-guided methods win, and the question becomes whether the drive is long enough to carry the cost of the shafts.

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