Safe Utility Tunnelling Through Tailor-Made Hard-Software
Publicerad: 16 december, 2020
The process engineering limits of pipe jacking have shifted considerably in recent years. Jacking lengths of 800 m and more are no longer a special feature. Narrow bends and S-curves appear more and more frequently in the tenders of the network operators and are usually executed without major problems. The reason for this extremely positive development lies not only in the constantly increasing wealth of experience of the mostly specialized companies in Germany, but also in the integration of customized hardware and software into the daily pipe jacking routine. Some products, which guarantee static safety in particular, will be presented in this article.
The planning and execution of pipe jacking projects is based on the regulations in the currently valid DWA worksheets A 125 "Pipe Jacking and Related Methods" of December 2008 and A 161 "Static Calculation of Jacking Pipes" of March 2014. In particular, the formulations in A 161 completely dispense with unnecessary, absolutely formulated restrictions (for example, the curve radius or the jacking force) and even provide information on the necessary static proof when using alternative pressure transfer concepts other than the conventional wooden pressure transfer ring.
Static jacking support (Monitoring of joint gap differences)
On this basis, so-called pipe joint monitoring systems have been established (e.g. CoJack from STEIN Ingenieure), which now do much more than just monitor the pipe joints. Rather, these systems serve as a continuous static control instrument during jacking to determine the current stress on the jacking pipes and even enable a constantly updated forecast of the steering movements and jacking forces that will just be permissible in the future.
CoJack's hardware includes a sensor system installed at the construction site for continuous and complete recording of the most important jacking data. In a protected area of the internet, the course of the jacking force and the course of the actually jacked route curvature (scheduled curves including steering movements) are graphically displayed. The corresponding diagrams also contain the corresponding current limit values, which are continuously confirmed or updated in the background by means of static calculations accompanying the jacking process.
Thus, the observer can always judge at first glance whether the current jacking parameters are within the permissible range. Dangerous tendencies can be detected at an early stage so that countermeasures can be taken in time. This illustration of the otherwise mostly completely invisible static stresses on the jacking pipes is not only used by the Employer and construction supervisors as a control instrument. The jacking companies carrying out the work have also come to appreciate and even learn to use the transparency of the jacking data.
They can use CoJack to prove that the permissible pipe stresses are being adhered to and, if necessary, have a statically secure basis for optimising their jacking progress. CoJack provides information as to whether higher jacking forces are permitted if necessary or with which force the jacking may be continued immediately after an excessive steering movement. The safety level prescribed in the regulations is always maintained.
The optional measurement and display of the jacking force not only at the main jacking station, but also at all installed intermediate jacking stations, contributes to this. This even works when the intermediate jacking stations are not actively used at all and are only passively pushed along. For this purpose, the jacking cylinders have to be extended just a few centimeters. Thus, the jacking force applied by the main jacking station is transmitted within the passive jacking cylinders of the intermediate jacking station via the oil cushion.
By observing the jacking force progression, it is possible to localise jacking sections with increased jacking resistance if necessary. An additional help for the interpretation of the jacking force diagrams is the representation of the jacking cylinders expansion of the intermediate jacking stations, which allows a local and temporal allocation of the intermediate jacking stations activities.