Waldmannhalle closed due to asphalt subsidence

There was an unusual incident in Baar on Monday: the asphalt in the forecourt of the Waldmannhalle subsided by about one metre over an area of ​​approximately ten by ten metres. The building will therefore remain closed until at least Wednesday evening.
 

A section of the asphalt pavement near the entrance to the Waldmannhalle sports hall and the Sport-Inn restaurant in Baar has sunk by about one metre, as the municipality of Baar announced on Tuesday morning. An on-site inspection reveals that the resulting hole, roughly ten by ten metres in size, looks as if it has been punched into the ground by a giant fist; the asphalt is cracked and splintered.

Confusion reigned at the scene on Tuesday morning. The area was cordoned off extensively, schoolchildren milled around it, pedestrians were stranded behind the barrier, and access was denied to the press.

The employees of a security company stated that photography was only permitted with authorisation. An inquiry with the municipality of Baar revealed, however, that photography was allowed as long as one remains behind the security barrier.

A municipal worker noticed the damage.
A municipal worker noticed a suspicious crack in the asphalt on Monday afternoon, explained Silvan Meier, media spokesperson for the municipality of Baar, in response to an inquiry. "After the crack widened, he informed the experts at the local civil engineering office (Tiefbauamt) and asked them to take a look." They immediately inspected the damage and called in the local fire brigade. "The fire brigade cordoned off a large area around the crack so that no one was injured and monitored the process, which lasted for several hours," continued Silvan Meier.

The ground in front of the Waldmannhalle in Baar subsided by about one metre on Monday.
The area around the Waldmannhalle was cordoned off extensively.
On the left: The Wiesental school building. In the middle: The Waldmannhalle in Baar.
“Wow!”:  there was considerable interest in the large hole on Tuesday. A number of pedestrians stopped by and were quite astonished                              
Water damage is suspected as the cause. Further investigations are underway     Photos: Jakob Ineichen
 

He himself was also on site for about three hours. "It wasn't a sudden, loud crack, but a slow, dynamic process. You could simply hear and see individual pieces of asphalt breaking off now and then." Water damage is suspected as the cause, and further investigations are currently being carried out.

As the municipality later wrote in a press release, the depression filled with water during the evening. As a further precaution, the underground parking garage (Tiefgarage) and the Waldmann hall were evacuated in case the water level rose. "The Baar fire brigade installed a water barrier and distributed sandbags as a preventative measure, but these were ultimately not needed," the municipality stated.

In addition to the fire department, several members of the municipal council (Gemeinderat), and various employees of the municipal administration, a specialist from the Office for Forests and Wildlife, commissioned by the Office for the Environment of the Canton of Zug, as well as a specialist from the Fire Inspectorate (Feuerwehrinspektorat) were also on site, as the municipality reported.

"The situation was monitored throughout the night and remained stable. A security service will remain on site until further notice." Although no subsidence or cracks were visible at the Waldmannhalle, the building will remain closed at least until Wednesday evening, and the hall will be monitored until then. The underground parking garage is expected to be inaccessible for an extended period.

The buildings stand on stilts.
As a further measure, a return line will be inspected, the municipality further informed. Water drawn from a groundwater aquifer approximately 100 metres deep is returned to the groundwater via this line to heat the Waldmannhalle via a heat exchanger. "It’s highly likely that a leak in this return line has eroded the soil and triggered the subsidence," the municipality stated. The subsidence is located at the so-called ‘deep groundwater return well’, where the water is returned to the ground.

Whether a leak is indeed the cause and how this leak might have occurred is the subject of ongoing investigations. "Until the completion of this inspection and the subsequent remediation work, the entire entrance area to the Waldmann Hall, including the stairs to the hall and the red all-weather sports field, will be closed."

The neighbouring Wiesental School will remain open, and school operations can continue safely. “Like the Waldmann Hall, the school building, which opened in August, also stands on stilts that are firmly planted on solid ground,” the municipality concludes.

Construction woes on the Lorze plain
The neighbouring, brand-new Wiesental school recently made it into the headlines due to water damage and a defective gymnasium partition wall from which a metal rod had come loose. The gym had to be closed for several days for safety reasons.

The hole in front of the Waldmannhalle. A video from Jakob Ineichen can be viewed on:
https://www.zugerzeitung.ch/zentralschweiz/zug/baar-krater-vor-der-waldmannhalle-halle-geschlossen-ld.4086106