Case Studies

Project Type
Length / Hole Diameter
914 M (3,000 FEET)/ 1.06 M (42 IN)
The HDD Company

Rehoboth Beach

Ingenuity Saves Client Millions

Project Summary

When the city of Rehoboth Beach sought bids on a 914 m (3,000 ft) ocean outfall pipeline crossing to release treated effluent into the ocean, the HDD Company proposed a two-million dollar idea. By pushing a 762 mm (30 in) Permalok casing nearly half the total distance from its shore-based rig, the HDD company would significantly reduce the time a marine contractor was required on the project (by nearly half). These savings would be passed onto the municipality.

This plan called for the HDD Group to drill and forward-ream the borehole to 1067 mm (42 in), and push the casing out approximately 365.8 m (1,200 ft). Then, the directional drill would guided through the casing to complete the crossing, emerging through the seabed. The marine contractor would be tasked with pulling the casing the remainder of the distance.

Key Challenges

The design proposal indicated the geography was entirely sand. However, at the 228.6 m (750 ft) mark, the HDD Company encountered cobble – which was unforeseen by engineers and the HDD Company. This caused the casing to bundle up on a large bolder. As a result, the initial hole had to be abandoned. The HDD Company promptly proceeded to drill a second hole, adjusting to compensate for cobble.

Despite the unanticipated setback, the HDD Group completed the project on time, while still coming near two million dollars under budget.

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