When sewer pipes crack and leak, the surrounding ground becomes saturated and soil can migrate into the pipe and leave behind a void. Eventually this void can expand until it undermines the pavement or other structures forming a sinkhole. The same ground penetrating radar technology being used by geophysicists to perform subsurface characterization and by the military to detect roadside bombs in being adapted to detect these voids before they reach the surface. Researchers at Louisiana Tech University are developing a robot to traverse sewer pipes and scan around the pipe for potential voids using the GPR. The research is being performed with $3M from NIST and $3.2M from Cues, Inc. a Louisiana sewer inspection company. Additional trials are slated to take place this month. [Source: NOLA.com. Image: AP File Photo/Mark Was via dailyreporter.com]
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Video: The Pine Hills Sinkhole – Central Florida, 2002
On June 11, 2002, a 150-foot wide and 60-foot deep sinkhole opened up in Pine Hills, Florida and came within a few feet of two 3-story appartment buildings. Geotechnical and Environmental Consultants (GEC) was contacted by the owner of the site to design emergency temporary and permanent stabilization measures to protect the buildings. The sinkhole mitigation began with a chemical stabilization of the soil using an injected sodium silicate chemical grout (incidentally, that work was performed by John N. Puder, Inc., recently acquired by Moretrench) to stabilize the sands underneath the buildings and adjacent to the sinkhole. After some GPR surveys, borings and other investigations, final sinkhole repair consisted of a 200-foot long wall omprised of interlocked 36-inch diameter steel tubular piles that extended to a depth of 50 feet. They were driven by Giken America Corp. using the press-in method which helped to avoid damage to the adjacent buildings. The entire stabilization was completed within 1-month of the initial sinkhole collapse! Click through for this fascinating video. (Photo credit Giken America Corp. by way of GEC)
Johannasburg Sinkhole Opens after Tunnel Collapse
A 12m long sinkhole opened up on Oxford Road in northern Johannesburg South Africa after a partial tunnel collapse in the Gautrain rail tunnel being constructed underneath the road. Eyewitness accounts say there was a broken water pipe flooding the sinkhole, but no word on which occurred first. The road is expected to be closed for 2 weeks. Gautrain representatives said the tunneling would resume after geotechnical/geological investigations into the collapse are completed, which could take "several weeks". (Photo credit: Werner Beukes, Sapa via News24.com)
Via The Star (Zambia) and News24.com (Johannesburg?)
City of Vancouver sues over failed shoring
The City of Vancouver is suing a developer, excavation contractor and their consulting engineer for the costs of repairs, overtime for city employees and lost revenue from parking meters etc stemming from an apparent failure of a shoring system that formed a 30-meter sinkhole. No mention of the developer’s name or the engineer, but the contractor was Matcon Excavation and Shoring. The site will be the future home of high-rise condominiums…if the City lifts it’s stop work order.
The failure of the shoring caused a break inf a 20-cm water main ultimately flooding the site. It also necessitated the closure of the adjacent street. Of course this invites the whole chicken or the egg scenario. The defendants will probably argue that the water line failed first causing the failure of the shoring, but of course the City Engineer, Tom Timm was not shy about fingering the shoring as being deficient.
"It’s some kind of a failure of the shoring system . . . either a design issue or the way it was put in place."
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Using the most recent improvements, now we will see quite a few useful purposes for ground penetrating radar and these multi-purpose radar units are actually becoming made and developed by many firms worldwide.
Thanks.
Concrete xray