Tunnel Waterproofing Calculator

Membrane Area is the cross-section perimeter (which depends on Shape) multiplied by Tunnel Length, plus a flat 15% waste factor for the complex geometry tunnels require. Shape changes which perimeter formula applies: circular (1) uses the full circumference, horseshoe (2) approximates a semicircular arch plus straight walls plus a flat invert, and rectangular cut-and-cover (3) uses a simple box perimeter -- at this calculator's default 20 ft diameter, horseshoe actually produces slightly LESS membrane area than circular despite having flat walls added to the arch, because its approximated arch-plus-invert shape is narrower overall than a full circle of the same diameter. System selection (1=PVC sheet, 2=spray-applied, 3=injection grouting) swings Material Cost far more than shape does: at this calculator's defaults, spray-applied membrane (2) costs roughly 60% more than PVC sheet (1), while injection grouting (3) -- priced for post-construction leak repair rather than full-tunnel waterproofing -- comes in about 20% cheaper than PVC sheet because it only treats a fraction of the joints rather than the full membrane area.

Construction Joints drives Waterstop (linear ft) directly and adds a smaller, secondary contribution to Material Cost through the per-joint waterstop material. Estimated Inflow (GPM) is a separate reference figure using a simplified radial-flow groundwater formula; it does not feed into any of the material quantities and exists only to gauge how much water the system needs to keep out.