Built in 1940 and hailed as America’s first Superhighway, the original 160-mile stretch of the Pennsylvania Turnpike, between Irwin and Carlisle, has been undergoing a phased total reconstruction and widening since the late 1990s. Near the New Stanton interchange, where a residential area lies close to the mainline roadway, work included the construction of a sound barrier approximately 3,500 feet in length. The general contractor for this section of roadway and interchange reconstruction, Trumbull Corporation of West Mifflin, PA, awarded Moretrench the drilling sub-contract for the installation of the sound barrier foundations. A wingwall supporting mainline traffic was also retrofitted under the same contract.
Sound Barrier Foundations
The sound barrier was designed as a steel beam and precast lagging structure ranging in height from 15 to 20 feet. To counteract wind loads, the steel beams were anchored to 36-inch diameter drilled shaft foundations installed at 12 feet on center. Shaft drilling, concreting and setting of the anchorage system was a coordinated effort between Moretrench and Trumbull.
At each of the 281 shaft locations, Moretrench augered through the upper 15 feet of silty clay overburden to top of rock and then drilled out a 30- inch diameter rock socket to an average depth of 7 feet. Trumbull followed close behind to lower the dual reinforcing cage assembly, set the anchor bolts, and tremie 4000 psi concrete in place to complete the foundation.
The wingwall was located at one end of a highway that crossed beneath the Turnpike mainline. Since mainline expansion and the creation of a new shoulder would place additional weight on the wall, installation of three, double- corrosion protected, 4-and 5-strand tieback anchors was specified as a precaution against potential movement.
Specifications called for the anchors, which varied in capacity from 75 to 105 kips, to be installed on an approximate eight feet horizontal spacing, with the lower two anchors stepping down two feet. Working from an earth bench placed by Trumbull, Moretrench used duplex drilling techniques to advance each drill hole at 15° from horizontal through the predominantly silty gravel fill material and terminated in limestone bedrock. The anchor assembly was placed, and the annulus between the anchor and the drill hole was filled with Type II Portland cement grout for the full length of the hole. Following a 7-day grout curing period, the anchor head was placed and the anchor was proof-tested to 133% of design load before being locked off.
More to Moretrench
Tieback anchors and deep foundation drilling are just two of the specialty techniques that Moretrench offers. The company’s wide range of services caters to virtually all subsurface conditions and project applications, allowing Moretrench to offer the optimum solution, or solutions, to problems ranging from the straightforward to the most complex.