This class deals with construction, lining, support, and associated works of tunnels for transport, utilities, water conveyance, or other purposes. It includes all excavation, support, lining, drainage, and ancillary works required to complete tunnels.
1. Scope
Class T covers:
- Tunnel excavation by drilling, blasting, TBM (Tunnel Boring Machine), roadheader, or hand methods.
- Temporary support such as shotcrete, lattice girders, rock bolts, steel ribs, timber lagging.
- Permanent lining in concrete, brick, blockwork, or cast in-situ/precast segments.
- Tunnel waterproofing and membranes.
- Tunnel invert, drainage, and sumps.
- Ventilation shafts, cross-passages, niches, and chambers.
- Temporary works like portals, headings, benches, pilot tunnels.
- Removal/dismantling of temporary supports if not part of permanent structure.
2. Subdivision of Items
Work in Class T is subdivided as follows:
- T.1: Excavation
- Excavation of tunnel by blasting, TBM, or other methods.
- By ground type: soft ground, rock, mixed strata.
- By tunnel cross-sectional area (e.g., <10 m², 10–20 m², >20 m²).
- T.2: Temporary support
- Shotcrete, lattice girders, steel ribs, timber lagging, rock bolts.
- T.3: Permanent lining
- In-situ concrete lining (plain or reinforced).
- Precast concrete segmental lining.
- Masonry or brick lining.
- T.4: Waterproofing
- Membranes, PVC sheets, geotextiles, drainage layers.
- T.5: Ancillary tunnel works
- Niches, cross-passages, sumps, drainage channels, inverts.
- Shafts, portals, adits.
- T.6: Dismantling
- Removal of temporary supports, cutting excess rock, muck disposal.
3. Method of Measurement
- Excavation – measured in cubic metres (m³), classified by ground type and tunnel cross-sectional area.
- Temporary supports – measured in linear metres (m), square metres (m²), or tonnes (t) depending on type (shotcrete m², ribs t, rock bolts m).
- Permanent lining – measured in cubic metres (m³) for in-situ concrete, per segment for precast lining, or m³ for masonry.
- Waterproofing – measured in square metres (m²).
- Ancillary works – measured per item (e.g., shaft, sump, niche).
- Dismantling – measured in m³ (excavation removed) or tonnes (supports removed).
4. Item Coverage
Each item is deemed to include:
- Excavation, mucking, transporting spoil, temporary storage, and disposal.
- Provision of ventilation, lighting, and dewatering necessary during excavation.
- Placing, compacting, curing of concrete linings.
- Fixing and grouting of precast segments.
- Installing and welding steel ribs, mesh, lattice girders.
- Placing shotcrete with reinforcement if specified.
- Fixing waterproofing membranes, overlaps, joint sealing.
- Safety measures for working underground.
5. Notes for BOQ Preparation
- Clearly state excavation method (blasting, TBM, NATM, etc.).
- Distinguish ground classification (soft, medium, hard rock).
- Mention tunnel cross-sectional area for excavation.
- Specify temporary support system and thickness of shotcrete.
- Indicate permanent lining type (in-situ concrete grade, segmental thickness).
- Define waterproofing system (PVC membrane, geotextile, HDPE liner).
- If excavation includes portals or shafts, list separately.
- Spoil disposal location/lead should be defined.
6. Example BOQ Items
- T.1.1: Excavation in hard rock tunnel (cross-sectional area 15–20 m²), by drill and blast, muck disposal within 2 km, measured per m³.
- T.2.1: Rock bolts 25 mm dia, 4 m long, drilled, fixed and grouted, measured per metre.
- T.2.2: Steel ribs ISMB 200, erected and grouted, measured per tonne.
- T.2.3: Shotcrete 100 mm thick with wire mesh reinforcement, applied to tunnel crown, measured per m².
- T.3.1: In-situ RCC lining M30 grade, 300 mm thick, placed and cured, measured per m³.
- T.3.2: Precast segmental lining, 250 mm thick, supplied and erected, measured per ring.
- T.4.1: PVC waterproofing membrane, 2 mm thick, measured per m².
- T.5.1: Construction of tunnel drainage invert in M20 concrete, 300 mm thick, measured per m³.
- T.5.2: Excavation and lining of ventilation shaft 4 m dia, 20 m depth, measured per m depth.
- T.6.1: Dismantling of steel ribs and disposal, measured per tonne.
