Mätning av ljudtrycksnivåer med hög detaljgrad

I Sveriges näst största stad Göteborg pågår tunga byggen och sprängningar i takt med att en ny tunnelbana byggs under centralstationen. Den nya järnvägen kommer att ge viktiga tidsbesparingar och effektivitetsvinster, vilket gör det möjligt för tåg att resa direkt genom staden istället för att ta omvägar runt den.

One of the many measurement projects performed in connection with the new railway is the acoustic and sound measurements inside nearby residential buildings being conducted by Ensucon. The Swedish Transportation Administration has commissioned the project and as part of the environmental control, contractors need to comply with guideline values for structural noise. Structural noise occurs when vibrations transfer through solid material, such as rock, and then into to the structural frames of houses. Despite extremely low vibration levels in the structure, below human perception, sound is produced and clearly audible. In the tunnels beneath Gothenburg, holes are drilled 15-20 meters deep and loaded for blasting excavation. The blasting takes place once a day and only lasts for a few seconds. After blasting, loose rock remains in the tunnel which needs to be scaled off for safety. The drilling and scaling activities are the main sources of structural noise.

Johan Scheuer

Johan Scheuer, a monitoring consultant at Ensucon, measures the noise levels in sensitive buildings that are located next to the drilling and blasting activities. On the project, Johan is using 35 INFRA S50 noise sensors from Sigicom. Remote monitoring systems are placed in storage rooms and other secluded areas in the buildings, rarely frequented by people. Johan keeps track of the sound levels in these common areas and in the closest apartments to the activities. This allows him to get an understanding of the noise levels as they transmit through the building. This correlation of monitoring data also indicates the source location of the noise.

– Since I can correlate the signal from several microphones at the same time, it is quite easy to determine what noise is generated from the tunnel project. I can also look at the baseline ambient noise of the building occupants for noise contamination in the data, says Johan Scheuer.

The INFRA S50 measurement data is sent autonomously to INFRA Net, Sigicom’s web-based platform for managing instruments and measurement data. INFRA sensors are remotely configured and controlled by setting parameters for recording and reporting data. Key project personnel is notified at predetermined alert/alarm thresholds. Data visualization tools allow for the required analysis and project reporting, all from a computer or mobile device without having to visit the instruments on site.

– I have found a pretty good evaluation method. I use the graphical interface in INFRA Net to get a quick idea of what has been going on. Then I export all the raw data in Excel and do advanced analysis where we filter out data influenced by the ambient noise of the building occupants, says Johan Scheuer.

A Robust and User-Friendly System

Johan Scheuer has many years of experience in the monitoring business, and for him, the Sigicom INFRA system was a complete solution for the project.

It is a very robust and easy-to-use system that performs what I need. I can remotely change settings as my reporting needs to change. I can trust that these features work well in INFRA Net, which is why I chose to use Sigicom’s products, says Johan Scheuer.

Johan started the measurements in 2019 with an estimated project duration of five years. The INFRA systems are operating without an external power source and depending on the outdoor temperature or required communication intervals, field visits for internal battery replacement take place every 2-4 weeks. This is significant for the project efficiency of continuous remote noise monitoring.

Ensucon was founded in the summer of 2018 by Rickard Sallermo and Gustav Johansson. The company has performed well and today, at the beginning of 2022, Ensucon has 45 employees in three different offices around Sweden. The company focuses on environmental and sustainability issues in polluted areas, certification issues, and permit matters. Measuring vibration, sound, and other types of environmental impact is only a small part of the wide range of services they offer.

The yellow drill bit can be seen at the start of the clearing for a 65-meter-long vertical pressure equalization shaft at Föreningsgatan. The shaft reduces the pressure differences in the train tunnel that occurs when a train passes. The structural noise from the drilling amounted to just over 35 dBA in the nearest residential buildings.

The yellow drill bit can be seen at the start of the clearing for a 65-meter-long vertical pressure equalization shaft at Föreningsgatan. The shaft reduces the pressure differences in the train tunnel that occurs when a train passes. The structural noise from the drilling amounted to just over 35 dBA in the nearest residential buildings.

The West Link stretches underground from Gullberget at Skansen Lejonet in the north, via the Central Station and Kvarnberget south past Rosenlund and Haga. At Landala, the tunnel turns off to the east and passes Korsvägen and Liseberg before turning south and coming to light just south of Kallebäcksmotet. Ensucon assists the contractors with, among other things, long-term acoustical and structural noise monitoring for Stage 04 Haga and Stage 02 Centralen.