What Does Horizontal Auger Boring (HAB) Mean?
Horizontal auger boring (HAB) is a trenchless excavation method used to excavate boreholes under the earth’s surface. It uses a rotating helical shaft within a casing to extract soil while advancing. The spiral edges of the auger, similar to a large helical screw, removes the excavated soil as the operation progresses.
The auger machine is placed securely in a launching pit excavated to the required installation depth. It uses both torque and thrust to move the auger with its casing forward along a horizontal path. The pipe casing is laid in sections, one after another, as forward sections progress through the borehole. With horizontal auger boring, the creation of the hole and the installation of the pipe are accomplished simultaneously.
The method requires two pits – the launching pit and the reception or exit pit. Excavation is started from the launching pit and sufficient space is provided for workers and machinery to operate safely. The dimensions of the pits depend on the size and length of the casing being installed and on the depth of boring. The pit bottoms are over excavated and backfilled with crushed stone to provide sufficient support to the equipment.
Auger boring is widely used for the installation of oil, gas, water, and sewer pipelines. The method is well-established and widely used for installing steel pipes and casings and is also known to be cost-effective and efficient.
It can be used in different ground conditions though best suited for soft soil; the method is environmentally sound. Trenchless methods of installation prevent traffic disruptions, damage to pavements, landscaping, and roads as they do not require ground surface excavation for the length of the installation.
HAB is also known as jack and bore method or simply as auger boring.
Trenchlesspedia Explains Horizontal Auger Boring (HAB)
HAB machines are available in different sizes and capacities and soil conditions dictate the power of the machine needed. The launching pit has to be well designed and precisely constructed to ensure that the machine does not deviate while boring. Even a slight misalignment at the start can cause a major deviation from the originally designed path.
Installing Pits and Aligning Machine
The process begins by installing bore pits at the start and endpoint of a project. The size of the pit varies between 26 to 40 feet in length and 8 to 12 feet in width. The auger machine is mounted on tracks along which it slides to move the casing pipe forward.
The track is set to the precise line and grade in which the pipes have to be installed. Technological innovation has allowed for the auger machine to be steered and minor adjustments to be made but it is still critical to align the machine precisely.
Making the Bore
A suitable cutter head for the soil type is installed at the front of the aligned auger machine. The first section of the casing pipe with a steel band welded at the top is installed ahead of the first auger section. Thrust is applied to the boring machine against the back of the boring pit using hydraulic rams to advance the casing forward. The first casing is carefully installed to the precise line and grade and the machine is withdrawn.
The next casing or pipe section is placed in position and attached to the first casing. Thrust is applied to advance the bore forward while simultaneously rotating the augers inside the casing to remove the spoil. When the bore is completed, the cutting head is removed at the reception or exit pit and the augers are pulled back to the launching pit. If a carrier pipe is to be installed, it is pushed into the casing pipe using the auger machine or pulled in with a winch.