laggings

The forward ends of the laggings were then supported by a timber rib and sill.

Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 The New York Tunnel Extension of the Pennsylvania Railroad. The East River Tunnels. Paper No. 1159 James H. Brace

For all exposed surfaces a 6-in. facing of 1-3 mortar was placed by setting 2×12-in. planks 4 ins. from the laggings, being kept to distance by 2×4-in. spacers, placing and ramming the concrete behind them, then withdrawing them, filling the 6-in. space with mortar and tamping it to bond with the concrete.

Concrete Construction Methods and Costs Halbert Powers Gillette