Sinkholes at the Dead Sea have threatened tourists and forced Israeli (and perhaps Jordanian)authorities to close various facilities and cancel development plans to avoid these geologic hazards. These are not your typical Karst sinkholes. According to a recent AP article, they are caused by the erosion of salt deposits by fresh water as a result of the lowering of the water level. This is a human caused phenomenon as current size of the Dead Sea is just 1/3 of its size in 1960 since water has been diverted from the Jordan River, its main tributary to be evaporated for its phosphates. At the end of the article is an interesting note that the World Bank is currently evaluating a proposal to replenish the Dead Sea by digging a $15 Billion canal from the Red Sea, about 100 miles away. (Photo by urban_hipster)
Yesterday the Arizona Geologic Survey (AZGS) released the first two of their 1:12,000 series earth fissure maps to the general public. The mapping program, perhaps the first of its kind in the country, came about after an earth fissures opened up in 2005 near Queen Creek, AZ, southeast of metropolitan Phoenix received much media attention. As a result, the Arizona Legislature passed House Bill 2639 of the 2006 Legislative Session that tasked the AZGS with mapping earth fissures and providing the data to the State Land Department for eventual delivery to property owners in Arizona. More after the break. (At left, the Apache Junction study area map, AZGS)
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)
The site for the new Harrison County Hospital, approximately 25-miles west of Louisville, Kentucky had 15 sinkholes formed by limestone dissolution, a geomorphologic process referred to as Karst topography. There were a number of geotechnical engineering and geological engineering challenges associated with the characterization, excavation, backfilling, foundation engineering and other mitigation measures as described by Peggy Hagerty Duffy, P.E. in her article entitled “Karst and Complications” in the August 2008 issue of Civil Engineering Magazine (Duffy, 2008b).
Mitigation measures for the sinkholes included use of graded filters with geotextiles, careful inspection of rock socket foundations along with pilot holes and careful geotechnical inspection throughout the construction process. One particularly interesting aspect of the project is that several of the sinkholes were used as drainage facilities to receive surface water runoff. Read on for a summary of this interesting article. (Photo of sinkhole in Karst Topography being used as a drainage feature, from Duffy (2008b), Civil Engineering Magazine)