It's all a matter of total thrust
A pipe-thruster that allows accurate monitoring on project sites is becoming a force to be reckoned with. Herrenknecht's chairman, Martin Herrenknecht, and vice-chairman, Werner Suhn, explain how it worksThe trend in the underground construction industry is to lay pipes faster, more safely and more cheaply. For probably the best part of the past decade, however, underground construction contractors and client companies in the field of utility tunnelling have been looking to install larger-diameter, longer-drive lengths for tunnels and pipelines.
They've wanted to achieve this without the major project constraints of using large-diameter TBM systems.
These installations are designed to meet the demands of expanding populations - in terms of increased utility and similar infrastructure - in many countries around the world. In general, while the equipment to achieve these installations has been available, the equipment was limited in its capabilities for diameter or length demands.
While contractors and manufacturers have tried to push the limits of these capabilities, longer, multiple-pipe installations have had to be completed with horizontal directional drilling (HDD), or larger-diameter, but shorter-drive, installations have been completed with microtunnelling to meet project requirements. Both methods could have significant cost implications.
Herrenknecht has, over the past two years, extended equipment capabilities in this area. The firm has developed two products that are designed to meet just these sorts of demanding circumstances. The two systems are known as direct pipe and online load control (OLC).
Direct pipe could be viewed as more directly akin to HDD, but in a way that uses the advantages of the line-and-grade navigational capability of microtunnelling. To achieve a direct-pipe system installation, Herrenknecht has developed an auxiliary device, known as the Herrenknecht Pipe Thruster, which is positioned in the launch shaft of the proposed bore.
The Pipe Thruster has the capacity to thrust a continuously welded-steel pipeline, which is welded on site, into the bore, behind the microtunnelling shield, with sufficient force so that it acts as the jacking pipe to advance the microtunneller shield.
Using on-board microtunnelling navigational systems, the shield advances along the line, grade and length of the required bore path whether it is a straight or curved bore.
Given the overall length of the bore is known before the project starts, the necessary feed lines and pipe for the microtunneller shield are installed within the jacking pipe prior to commencement of the drive.
After being launched the microtunneller is maintained on path, in the normal manner of microtunnelling, until it reaches the reception-shaft position.
Once at the reception shaft, the microtunneller shield is removed and the feed lines are taken out of the pipeline, leaving in place the required pipeline. The direct-pipe system is suited
- Larger-diameter installations are required over longer distances for projects on which it is not possible to achieve the installation using standard microtunnelling or HDD machines
- An HDD installation with the length or diameter capability does not have the required accuracy on line and level required for the pipeline
Herrenknecht has developed the OLC system to monitor and control jacking loads in pipe jacking, to minimise the potential of overstressing of jacked pipes, which could cause failure during installation. It has long been understood that special attention should be paid to the continuous documentation of parameters, such as angular deflections on a pipe, pipe loads and jacking forces, during pipe-jacking process.
This is particularly the case when projects are carried out along challenging alignments and in difficult geological conditions. For contractors and clients, such precautionary measures enable continuous quality-management monitoring.
Where such monitoring is not sufficiently maintained during installation works, damage to the pipeline can occur.
However, this can be avoided by using a solution such as the OLC monitoring system.
In cooperation with engineering company Ingenieurgesellschaft für Innovationen in der Kanalisationstechnik Aachen (INKA), Herrenknecht AG has developed a system which allows the machine operator to monitor the maximum permitted pipe loads parallel to the pipe jacking in real time. This means countermeasures can be taken early which will minimise the potential for jacking pipe overload or failure. The OLC system will be offered as additional integral module of the existing Herrenknecht Universal Navigation System, which is available for installation on any make or type of tunnelling equipment. The system, as a stand-alone module, can also be retrofitted to existing tunnelling equipment on the construction site. It has already been deployed on various projects.
In addition to thrust monitoring on site, the construction company management could also achieve continuous remote supervision of the pipe-load levels, using a basicinternet connection, so allowing monitoring of project progress.