Case Studies

Project Type
Length / Hole Diameter
396 m and 549 m (1,300 ft and 1,800 ft) approximate length / 305 mm and 76 mm (12 in and 3 in) conduit
The HDD Company



Project Summary

San Francisco required a redundant electrical system to provide backup service in the event of an earthquake. Due to the city’s dense and highly populated downtown, it was determined the most efficient and least disruptive solution would be to install the lines along the bay floor, connected through a shore approach using horizontal directional drilling (HDD).

The HDD Company drilled approximately 548.6 m (1,800 ft) at one location, and approximately 396.2 m (1,300 ft) at another. Both sites involved three separate landings and the installation of 304.8 m and 76.2 m (12 in and 3 in) conduit.

Key Challenges

All horizontal directional drill paths were shore approaches, from rigs set up in downtown San Francisco. The HDDs were terminated on the San Francisco Bay floor under nearly 80 feet of water. All pipe was fused on the land and loaded onto a cable ship. The piping was laid along the seabed floor and winched up through the hole using the HDD rig. A highly specialized marine diver was required to safely connect the pipe to the winch.

Drillers faced two types of bay mud: “old bay mud” and “new bay mud”. The drilling route called for a vertical and a horizontal curve. Accuracy was required to ensure the pilot holes for the 304.8 m and 76.2 m (12 in and 3 in) lines did not converge. Throughout construction, only one road was partially closed, with one-lane left open to accommodate local traffic.

Services Provided



Tunnel Boring and Pipe Jacking Systems are used to hydraulically install underground pipelines up to 4.2 m (168 in) in OD range within strict alignment and grade tolerances. The likelihood of settling or sloughing is very low. Wheel machines are equipped with various cutter heads and sand shelves. A closed-face attachment is available for boring in unstable ground conditions. This versatile system can be easily adapted to work with any jacking pipe, in any pipe joint length. It can accommodate a wide range of pipe diameters.

Tunnel Boring Machines are used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through hard rock, sand, and almost anything in between. Tunnel diameters can range from 1 m and exceed 15 m (3 ft to 49 ft).

The Crossing Group - The Tunneling Company - Tunnel Boring - Pipe Jacking - Trenchless Construction - Tunneling - Augering, Boring & Pipe Ramming


A boring technique commonly used for installing oil & gas pipelines ranging from 51 mm to 1067 mm (2 in to 42 in) in diameter without leaving casing in the ground. Product pipe is welded to steel casings and either pushed or pulled through the ground in sections. The casing is cut off and removed, leaving just the product pipe. Maximum installation length is 150 m (492 ft).

The Crossing Group - The Tunneling Company - Slip Boring - Trenchless Construction - Tunneling - Augering, Boring & Pipe Ramming


A pneumatic hammer is attached to the inside edge of the casing. The front of the DTH breaks cobles, boulders and even solid rock into small pebbles or dust. The spoil makes its way through the hammer and into the casing, where it is removed by airway augers.

The Crossing Group - The Tunneling Company - Down The Hole Hammer - DTH - Trenchless Construction - Tunneling - Augering, Boring & Pipe Ramming


A Guided Boring Machine (GBM) is used to install 305 mm to 3.6 m diameter pipe (12 in to 144 in) with grade and alignment precision. It is commonly used for installations 50 m to 150 m in length (164 ft to 492 ft) or when line and grade accuracy is critical in displaceable soil. Our GBM is extremely versatile and our customers continually approach us with new applications.

The pipe installation involves a two-step process where launch and reception shafts are strategically located to minimize surface disruption. A pilot tube with a theodolite guidance system is then pushed through the ground at the precise grade and alignment specified in the design into the reception shaft. A reaming head is welded to the pilot tube and the casing and the pilot tube is used as a guide to install casing. The GBM can be used in conjunction with auger boring or pipe ramming methodologies.

The Crossing Group - The Tunneling Company - Guided Boring - Trenchless Construction - Tunneling - Augering, Boring & Pipe Ramming


Pipe Ramming is used in a wide variety of soil types including gravel, cobble or sand. A pneumatic hammer is attached to the back of the casing pipe and driven through the material at any angle: from horizontal to vertical. The material is cleaned out of the pipe using an auger boring machine. Pipe Ramming methods are used for pipe diameters of 305 mm to 3.6 m (12 in to 144 in).

The Crossing Group - The Tunneling Company - Pneumatic Pipe Ramming - Tunneling - Augering, Boring & Pipe Ramming