open joints could potentially form wedges not captured by the pattern bolts. Support of Construction Prior to constructing the support of exca- vation, we had to replace numerous critical utilities. These were either re-routed outside of the excavation limits or supported across the excavation. The utility replacement consisted of electric distribu- tion feeders, secondary electric, communi- cation networks, as well as natural gas, combined sewer and water trunk mains. Records show that these trunk mains were originally installed in the late 1800s. close coordination between MTACC, utility owners and the NYC Department of Transportation, completed the utility replacement while meeting the seasonal restrictions and the tight schedule. Once the utility work was complete, we installed the excavation support and street decking in over half the width of the avenue in stage 1. This, in turn, allowed the soil adjacent to the subsequent construction stage to be sloped back eliminating the need for a retaining structure between construction stages. The team drilled the soldier piles and placed critical deck beams within the middle third area with minimal or no impact to traffic during off-peak hours with temporary lane closure. The soldier piles were installed in cased Completed shaft The existing section of 48 in (1.2 m) cast iron trunk water main was in excellent condition considering that it was field cast circa 1894. It was replaced with US Pipe, 48 in (1.2 m) HP LOK Restrained Joint DIP. Natural gas cast iron trunk mains, which dated back to 1880, were replaced with welded 30 in (0.8 m) PRITEK coated steel pipe placed inside a 42 in (1.06 m) diameter vented steel casing within the shaft limits. One of the challenges for this project was coordinating MPT stages with access to existing/proposed utility lanes. Providing access for pulling and splicing of the electric cables in new vacant electrical and communication network duct banks required complex scheduling. JDSI, with 40 • DEEP FOUNDATIONS • MAR/APR 2012 drilled holes. This procedure minimized vibration and noise, extended the soldier piles to top of competent rock through the weathered rock, maintained pile plumbness and minimized the impact on traffic when soldier piles were installed within the middle third area. Once the soldier piles were installed, we filled the annulus with low strength flowable fill and removed the casing. Following the installation of the soldier piles, we drilled vertical toe pins from grade through a sleeve that was attached to each soldier pile. After installing the soldier pile and toe pin, workers excavated the street to approximately 4 ft (1.2 m) below grade and installed the capping beams over the soldier piles. Next they placed the deck beams that spanned the cap beams and hung the utilities from them. With the deck beams providing the top support, we completed the excavation to top of rock. Prior to the excavation, we installed wales and toe anchors for the final bottom support of the soldier piles. As rock excavation progressed, we mapped the rock face and installed rock dowels to stabilize the rock face. On the other side of the avenue, we line-drilled at close intervals from the top of rock to the final subgrade to control rock over-break and to maintain a minimum rock ledge adjacent to the soldier pile and lagging excavation support. Next to existing structures, we used channel drilling to minimize the impact of vibrations on the surrounding structures. In addition, several holes were drilled within the rock mass and to facilitate removal with hoe rams. Once we reached the final subgrade, we installed precast concrete planks spanning between the deck beams. Then the completed portion of the excavation opened for traffic, allowing construction to progress in a similar fashion on the other side of the avenue. Prior to any construction activity, we prepared building impact assessment repor ts for adjacent st ructures. Instrumentation was procured, installed and baselined prior to construction. We also provided a continuous automated monitoring and instrumentation program throughout the construction period as stipulated in the contract documents. The monitoring program included continuous monitoring of two automated motorized total stations (AMTS) reading more than 50 reflective prisms mounted on facades of adjacent structures, 14 seismo- graphs continuously recording vibrations and three piezometers to track groundwater levels. The program also included an in- place inclinometer to document lateral wall deflection during excavation, two sound level meters for noise monitoring and dozens of crack gages on pre-existing cracks installed following pre-construction building condition surveys. Conclusion The design and construction of this support of excavation demanded considerable attention devoted to the nature and condition of the surrounding existing structures and utilities, MPT plans, and the various construction activities. Proper instrumentation and monitoring of adjacent structures was an integral part of the project in this congested urban environment. This portion of the work was completed in November 2011. The project would not have been a success without the human factor: spirit of cooperation and positive mental attitude. Although the construction posed several challenges, each of the challenges was met and the problems solved because all parties involved cooperated and focused on developing a quick and economic solution.
