Vermeer AXIS Guided Boring System Helps Keep British Army Base DryGerman contractor Beermann Bohrtechnik GmbH recently completed a first for the German pipeline market with the utilization of a Vermeer AXIS guided boring system to install perforated drainage pipe beneath an existing building on an Army base as part of a flood-prevention scheme.
The project, known as the Mansergh Barracks Dewatering Project, took place beneath Block 29, Mansergh Barracks, at the Gütersloh British Army base, one of the main British Army bases still remaining in Germany. The extremely high water table under the building had previously caused basement rooms to flood, so a system was needed to remove the groundwater from the site to prevent future flooding. According to calculations by the project’s client, Bau- und Liegenschaftsbetriebe Bielefeld on behalf of the British Army, and the project consulting engineer, Rolf Ostmeier of Ing.-Büro Redeker GmbH, the flow rate which the new drainage system would have to be able to handle was 32 liters per meter length of pipe per minute, a huge amount of water.
After careful consideration of the options open to the contractor for the work, it was decided that a multi-pass process would not be appropriate. This was because of site conditions — including mainly sandy soils with some clay layer inclusions, confirmed using core drilling — and the required installation depth. So in association with the contract’s main contractor, Kögel Bau GmbH & Co. KG of Bad Oeynhausen, it was decided to employ the Vermeer AXIS guided boring system. This system was chosen because the space available around the site and the capacity to directly install the new pipes in a single pass on completion of the pilot bore.
According to Mario Bruns, project manager for Beermann Bohrtechnik GmbH, “This project was a challenge for us because we had no previous experience with the Vermeer AXIS guided boring system. The cooperation of all of the companies involved on the project was very important. I can only praise all who were involved. It was only because of this level of cooperation that a smooth process was possible. The success of this project certainly leaves scope for further projects.”
Given the soil conditions and high water table, preparations for the boring work included the installation of a well-point dewatering system to lower the inherent water levels to the point where start shafts and reception pits could be installed effectively and kept open for the duration of the boring work without being flooded.
Three start pits were required for the installation work, which comprised some nine individual bores that totaled some 225 m in length. Each individual bore varied in length from 15 to 35 m and utilized a pilot cutting head on the AXIS system of 344 mm in diameter. This allowed the 250-mm diameter PP (polypropylene) perforated pipes to be installed in a single direct pullback operation, eliminating the need for a reaming stage. The pipe used for the new installations was Egeplast SL PP-B modules (Multirastermodule) in 1.95-m long sections with drainage slots.
The works were all completed using not only the Vermeer AXIS guided boring system (operating in vacuum microtunnelling mode) but also a Vermeer MX240 drilling fluid mixing system; a chain retention system; a 10-cu m vacuum truck (from Beermann) to transport used drilling fluid and spoil material to the dump site and an excavator and truck knuckleboom crane for drill casing and product pipe handling and loading.
The drilling fluid used comprised Phrikolat W plus bentonite and Baroid Penetrol. The main difference with the use of drilling fluid with the AXIS system, as compared to say an HDD operation, is that the fluid is only used to improve the spoil transport capability through the vacuum channel and to lubricate the cutter head. The drilling fluid then is removed using a vacuum system to extract the spoil from the bore into the unit vac tank, so there is no filter cake buildup in the system.
Of course another major requirement for completion of the works was security. As the project was being done on a British Army base, security for personnel and equipment to enter the premises was regulated strictly. This required the contractors to register all the required employees for base ID cards, to give access to the jobsite.
The project started on Feb. 25, 2013, and was completed by March 5. Each machine setup took between two- and three-and-a-half hours, depending on whether a move to a new start pit was required. Although the timing of each bore varied according to its length, a typical installation of a 30-m pilot bore and the pipe installation that followed took just three hours.
Rolf Ostmeier of Ing.-Büro Redeker GmbH said of the project, “During the boring operation it became clear that we had chosen the right procedure and equipment. The short setup times of the AXIS system; the precise arrangement, positioning and alignment of the individual bores; and a timely completion meant that both the client and the construction managers were fully satisfied with the project outcome.”THE AXIS
system consists of a drill rack operated from inside an underground pit/shaft and a power supply that is set up on the ground surface above the pit powered by a container-mounted 104.4 kW diesel engine.
When a pipeline is installed using the AXIS system, the process is typically completed in 90- to 120-m increments, although the Army base works were shorter than this. For each increment, a pit is dug at both the start and end points of the bore. The drill rack is set up and operated from the start pit, boring through to the second pit.
The heart of the AXIS system is a hydraulically powered thrust and pullback carriage assembly and gear box that pushes the drill casing forward and turns a cutter bit at the front end to excavate the soil. The rack is seated on a leveling frame and the total assembly is 3.5 m long, 1.1 m wide and 1.5 m high. The thrust/pullback mechanism drives a 343-mm diameter drill head mounted on a 2-m drill casing. As the head goes deeper into the soil, additional 2-m drill casings are inserted behind the lead unit to extend the bore. Different drill bits are available depending on the nature of the soils, which can vary from rock to clay.
A laser unit provides precision guidance for the system to maintain exact grade and alignment. The laser unit is securely mounted at the rear of the start pit. A camera in the drill head allows the operator to align a target with the laser to ensure a straight, steady bore.
The cylindrical drill casings include a central drive shaft that turns inside the unit, turning the drill bit at the front. An external channel accommodates cables from the camera and its lighting at the front of the drill head so that the casings maintain a smooth, cylindrical external profile without the need to disconnect the cables and hoses every time a drill casing is added during the boring process.
The casing units also include two internal channels. The upper channel is to move air forward through the shaft to the front so that debris can be vacuumed out and recovered through the lower channel back to the start pit. The air in the upper channel also keeps the system cool, which is necessary to keep the laser beam on target as heat can bend the laser off target.
For the Gütersloh British Army base project, given this was the first time Beermann had used the AXIS system, support for the equipment was given by Vermeer EMEA throughout the works. The project was also supported by specialists from Vermeer Corp., Vermeer EMEA (regional office for Europe, Middle East Africa and CIS based in the Netherlands) and Vermeer Deutschland. This support included training of the Beermann crew for this and future projects.
Benny Melse, trenchless product specialist with Vermeer EMEA said, “This has been an exciting introduction of the AXIS guided boring system onto the German market, in association with Beermann. Our AXIS guided boring system gave a solution to this project that allowed the installation of new drainage pipes with accuracy and efficiency and without detriment to the building beneath which the work took place or the immediate environment. The project took just six effective drilling/installation days to install the 225 metres (738.2 feet) of PP product pipes required. This project succeeded due mainly to the great efforts applied by all parties concerned and choosing the right equipment for the site conditions.”This article was provided by Vermeer Corp., based in Pella, Iowa.