Subaru – Wohlsen Construction Concrete Scanning Case Study

The job was to scan a slab on grade area for multiple sawcuts and trenches for a proposed bathroom installation. The problem was that this was a building addition from the original building and no prints or asbuilts existed, to show any potential sanitary tie in points for the client or existing utilities in or under the slab. The client was originally contracted to tunnel under the building footer to an outside area where a known sanitary line was located for tie in access. The room had not much, if any, surface features to investigate and no mechanical or electrical rooms nearby. There were only a couple wall panels that were seen. The wall panels were opened by an electrician but no conduit penetrations went down into the slab. There was simply an open slab on grade concrete floor with a sectional carpet on top.

Due to the setting, this scan was mostly going to rely on a passive mode locate and ground penetrating radar. The passive scans ended up not picking up anything throughout the entire scope. GPR on the other hand, had an entirely different story to tell. There were several anomalies and unknowns that were consistently seen with GPR throughout the entire scope. I was scanning on a sectional carpet and upon further GPR investigation, I ended up coming across surface features that were covered over the carpet and a bit of concrete including several buried cleanout lids, unknown utilities running just underneath the slab, an elongated disturbance in the slab, and an unknown circular lid. The plumber helped me pull back some of the carpet where some of the anomalies were found and revealed some cleanouts and access lids for walker ducts. We broke open the cleanout lids and was able to camera and duct rod the sanitary inside their work area to the outside main that they were originally contracted to tie into.

The client was able to demo the floor safely knowing where the existing utilities and anomalies existed in and under the concrete floor. With an added bonus, they were able to confirm the anomalies that looked like cleanout lids were, in fact, an abandoned sewer line right in their scope of work and would be able to be used after being inspected and cleaned. This saved time and money while avoiding tunneling under the foundation and out to a known sanitary. The client would now be able to tie into the sanitary inside the building where they were already sawcutting.

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