Page 48

2015WinterShotcreteEMag

tunnel into the open portal area by providing a spacing of 4 ft-2 in. (1.27 m) center-to-center. The free-standing arch often termed as shotcrete arches were reinforced with two layers of welded canopy. Recent examples for the use of shotcrete wire reinforcement, W9 x W9 at 6 in. (152 mm) canopies can be found at the Weehawken Tunnel center-to-center spacing in both directions, as a in New Jersey and Devil’s Slide Tunnel in Cali- minimum reinforcement to control cracking from fornia. While the initial lining during tunnel shrinkage and temperature changes. excavation and support is applied against the ground, an artificial surface on the backside has Construction Sequence to be provided for a free-standing arch to allow The schematic of the construction sequence is for the buildup of the shotcrete lining. illustrated in Fig. 7 and detailed in the following The cross section in Fig. 3 illustrates a typical steps (see Fig. 4 and 7 through 10): configuration of a self-bearing shotcrete arch. Step 1: The construction started with demoli- Structurally, the arch wall is 6 in. (152 mm) thick tion of the existing ventilation arch wall. and supports itself as a free-standing, self-bearing Step 2: In the second step, lattice girders were arch, loaded by the weight of the two vertical installed along the arch periphery and along two overlying walls. These vertical walls do not have vertical wall sections. The lattice girders were any structural function and are for ventilation secured with undercut anchors at the top and purposes only. The arch walls and the vertical dowels at the bottom of the arch of the main tunnel walls have embedded lattice girders at a typical lining. The lattice girders were comprised of a Fig. 7: Typical construction sequence 46 Shotcrete • Winter 2015


2015WinterShotcreteEMag
To see the actual publication please follow the link above