The sewage system in Köge, a city of approximately 40,000 inhabitants, must be renewed in stages with strong (pipe) line culverts. The constructor Energiforsyningen has established that previous work of this type led to serious complaints from the inhabitants concerned and expensive damage claims from property owners due to supposed cracks in house foundations. How to avoid this? Modern information and measurement methods are combined with the help of consultant company NIRAS to reach a convincing result for all parties concerned – the constructor, the entrepreneur, inhabitants and property owners.
The new culverts are placed in deep street shafts. When the asphalt is removed the shaft is cleared by a bulldozer and equipped with a protective sheet pile box. When the pipes have been laid, the shaft is refilled, compressed and repaved. Different vibration-generating construction machinery is used in this process.
NIRAS together with the constructor produced a strategy that included elements such as:
– Photo documentation of all house foundations involved in advance
– Elimination of certain risk factors using test measurement in advance
– Continuous monitoring of vibrations with the help of the measurement system
– Immediate action when any sensor indicates a risk level, via SMS
– Follow-up and information with the help of diagrams of the measured levels of vibration.
To prevent, take action and follow-up
The INFRA-system plays a pertinent part in four of these five elements. Johan Finsteen Gjödvad, NIRAS’ project manager, explains: – We could eliminate vibrations surpassing the limit values right from the beginning, by measuring in conjunction with certain construction machinery and fixing them by exchanging the caterpillar treads for rubber wheels. In the case of asphalt removal and paving, the levels of vibration
were so low that further measurements were assessed as being unnecessary.
– Since work began in 2009 we have, during the summer months, continuously measured the levels of vibrations from other construction machinery by registering the maximum value every other minute. The
INFRA-sensors are mainly set on the foundation of the houses. They take measurements in three directions and automatically compare vibrations measured against the risk area (according to German standard DIN 4150-3), which indicate both the speed and frequency. As soon as a risk level is registered, the sensor sends a SMS-message to the constructor and the consultant. We contact each other immediately and discuss measures to eliminate the risk, continues Johan. In this way we could, for example, switch from ramming down the sheet pile boxes, to pressing them down.
– We continuously inform the inhabitants along the facility line of the disturbances they can expect and if there are any complaints during the work, we show easy-to-understand diagrams from the INFRA-system that indicate the vibrations that have been measured in relation to the recommended risk level. Two stages of three are now complete of the total area of 25 hectares. We have been able to meet the uneasiness shown from inhabitants and demonstrate that we have kept within the standard disturbance norms during the entire project. We have a technology and a strategy that satisfies everyone – the constructor, entrepreneur and third party, explains Johan with evident pride.