For a wind farm near Lawton, OK, many of the foundations consist of rock sockets 19 feet in diameter, 20 feet deep. The rock was blasted to presplit the holes and facilitate excavation. The bedrock in the area was so shallow that blasting was needed to construct the access roads, removing the high spots and providing material to fill in the low. In areas where the bedrock was deeper, spread footings were used. [Source: National Driller. Image: National Driller]
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Remediation begins on Center Hill Dam, Tenn.
LANCASTER — Months of explosive blasting are expected to begin at the site of Center Hill Dam next week as the U.S. Army Corps of Engineers prepares to begin construction work at the aging dam in Lancaster.
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"The blasting will be to excavate a platform for construction, about 40 feet wide and will look similar to a road cut through a hill," [Corps Project Manager Linda Adcock] said. "Just the nature of how we grout, and moving equipment back and forth on the current slopes, which are as much as 40 percent and greater, is just really difficult. So for these reasons, for safety, quality, the accuracy and the consistency of the drill holes are much better done from a platform, they proposed this road cut type of a platform."
The drilling is for grouting remediation of the dam foundation. Story from Herald-Citizen, Cookeville, Tennessee.
Cologne Tunnel Collapse: Investigations Focus on Tiebacks and Groundwater
The latest information to come out of the collapse of a subway tunnel excavation in Cologne, Germany is that investigators are evaluating the ground anchors or tiebacks that were holding open the subway tunnel excavation. There doesn’t appear to be much information available to the public yet, and the New Civil Engineer article mostly quoted academics saying an anchor failure “could” have caused the collapse. Apparently at the time of the collapse, the excavation had reached the bottom depth after the slurry walls had been constructed along with the ground anchor system. Crews were supposedly working on the base slab which would have undoubtedly stiffened up the whole system. For what its worth, an anonymous comment left at the bottom of that article indicated that after half of the debris had been excavated, the diaphragm walls were still intact and without apparent displacement. So what other theories have been floated? Read on for more info. (Image Credit: New Civil Engineer)
New FHWA Manual on Spread Footings for Highway Structures
Hot on the heals of the revised MSE Wall Manual, the FHWA has released another manual, this one on Spread Footings. Selection of Spread Footings on Soils to Support Highway Bridge Structures was authored by Naresh C. Samtani, PE, PhD, Edward A Nowatzki, PE, PhD and Dennis R. Mertz, PE, PhD. So what is this manual all about? I think the foreword by Scott Anderson, PE, PhD of the FHWA Resource Center says it best: