Case Studies

Project Type
Length / Hole Diameter
630 m (2,067 ft) / 457 mm (18 in)
The HDD Company



Project Summary

Coconut Island is a small island off the coast of Oahu, Hawaii, which houses a university research station. All sewer, fiber, telephone and cable utilities were originally installed along the seabed floor. Over time, the conduit for the utilities began to corrode and integrity of the utilities became compromised. This time, horizontal drilling was chosen to tie the island into mainland utilities. This HDD solution involved drilling a 457 mm (18 in) subsurface borehole running under Kaneohe Bay, which would contain a bundle of two HDPE lines: a 102 mm (4 inch) telecommunications conduit and a 152 mm (6 in) force main sewer line. This project was successfully completed within a 64-day timeframe.

Key Challenges

The island is extremely small with little space for construction operations. As the exit point for the drill, it offered limited area to contain drilling fluid. The HDD Company proposed an innovative solution. The pilot hole was drilled 50 m (164 ft) shy of exit. Push ream methodology was used on the plugged pilot hole. By tripping the reamer back to entry side multiple times, debris was mechanically removed, eliminating the risk of covering the island with drill spoils and fluid. Because there was limited space for the drag section on Coconut Island, crews were required to string the product lines around a walking path prior to installation.

Ground conditions were mostly basalt, with very soft beach sand on the exit. As a result, the geometry of the bore path required a horizontal bend at the approach to exit, which demonstrated our navigational precision.

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