Measuring vibrations and noise and accounting for the measurement data afterwards is no longer sufficient for sensitive infrastructural projects. The INFRA-system allows active “live” monitoring in your web reader. This wins the trust of today’s builders and construction companies and helps far-sighted consultant companies such as the Danish Grontmij A/S to win large orders. With the help of the INFRA-system, Grontmij won all monitoring of vibrations and noise during the construction of a new 15.5 kilometer subway line being built underground in Copenhagen in 2012.
The environmental focus was put on vibrations and noise during the construction of the ring line Cityringen. 30 INFRA-geophones and 12 noise meters are being used. It is calculated that all will be on-stream at the same time and gradually be moved as the tunnel is built. The new ring line runs entirely under traditional inner-city buildings including housing, offices and shop premises. A museum and two historical churches ¬will require special vibration monitoring, due to sensitive ceiling frescos. Two building methods will alternately be used during construction of 17 stations and the four building worksites for the tunnel itself. One method involves the casting of secant piles in 15 to 28 meter deep drill holes together forming a tunnel wall. The other method involves the casting of so-called diaphragm walls. In both cases the walls are covered with a cement cover. All equipment and staff enter the tunnel through a hole in this cover and all excess soil is also removed through it.
Background measurements provide valuable information
The assignment began in October 2011 with background measurements of existing noise levels on future building sites. In most cases these measurements were made on two weekdays, as well as on a Saturday and a Sunday. Vibrations were also measured on some of these sites. The background measurements will be used in discussions concerning disruptions during the actual building process. All measurements made throughout the entire project are carried out as per the DIN4150 standard, which is programmed into the equipment. A limit value of 5mm/s applies to normal property and 3mm/s to culturally protected buildings. At a number of sensitive sites the triggering levels are set even lower than these limit values.
Advanced alarm functions for active monitoring
Active monitoring is a linchpin in this assignment. The direct SMS-alarms are received by Grontmij’s project manager Trine Maaholm Kraemer, the manager of the construction consortium’s environmental department, as well as one employee there. Little by little those responsible for construction at the different work sites will also become involved in the SMS-alarms and can thereby take immediate action at the disturbance sites. Every SMS-alarm shows the measurement point in question and the level of vibrations, as well as how big the divergence is from the limit value. Trine also receives alarms for low battery levels; however a number of measurement points will be electrically coupled in the buildings concerned. All data loggers also have the software for ”live”-reporting and can be used whenever necessary. A GSM-modem in the data logger sen¬ds data every fifth second and this is directly presented on the computer monitors of the receivers in the form of bar diagrams with the alarm levels marked in a red/yellow color. Sensors with live functionality can be remotely controlled to turn each function on or off directly or at certain set times. An audio signal from the computer can also be received on incoming alarm levels in measurement data.
Fast and easy-to-understand reporting simplifies collaboration
Flexible collaboration with CMT construction consortium is secured thanks to Grontmij having a resource person at CMT’s office three days a week. Some challenge exists since the Italian entrepreneurs are used to working with other limit values for noise and vibrations, both when it comes to the planning and the execution of the work on the building sites. Grontmij considers the alarm functions of the INFRA-equipment as a very valuable aid in the monitoring assignment, since many people can receive an alarm simultaneously. “Both the customer and I are very satisfied with the reporting options INFRA Net Manager offers”, says Trine Maaholm Kraemer. When limits are exceeded or inquiries are made, a report can be quickly and easily accessed from the system on the measurement point in question. The function that shows individual occurrences, established when the triggering levels are exceeded are especially good. Trine feels that “The graphs showing the excess amounts’ “appearance” and extent in mm/s, together with the frequency and limit values are really good when you inform the constructor about the individual occurrence.”