TBM Costing

Tunnel Boring Equipment Cost Estimation: What a Cutterhead Really Costs and How to Quote It

A cost block by cost block breakdown of fabricated TBM equipment, from S690 plate and weld hours to superload transport and field commissioning, with the five places quotes go wrong.

A one off fabricated TBM cutterhead in the 6 to 7 m class typically lands between $650,000 and $1.2 million, and the split is remarkably consistent: 25 to 35 percent material, 30 to 40 percent welding and fitting labor, 10 to 15 percent machining, 4 to 6 percent NDT and inspection, 5 to 8 percent transport, and the balance in engineering, commissioning, and overhead. Estimators who miss on these jobs almost never miss on material; they miss on weld hours, rework, and logistics. This guide walks through each cost block, how to assemble a quote that survives negotiation, and the five places estimates go wrong most often on single piece heavy civil work.

Material cost starts with buy weight, not drawing weight. S355 heavy plate runs roughly $950 to $1,150 per tonne delivered, S690 QT runs $1,700 to $2,100, and cast steel hubs and wear parts land at $4,000 to $7,000 per tonne finished. A 21 t net part list at 74 percent plate yield means buying 29 t, so quote the gross figure and take a scrap credit near $250 per tonne on returns. Hardfacing consumables add up fast: chromium carbide overlay wire at $9 to $14 per kg, with 250 to 400 kg per cutterhead, is a $3,000 to $5,500 line on its own. The Cutterhead Fabrication Cost calculator rolls all of these into one material block.

Weld hours drive the labor block, and they scale with deposited metal, not joint count. Submerged arc deposits 4 to 8 kg per hour, FCAW out of position deposits 1.5 to 3 kg, and a heavy cutterhead carries 800 to 1,500 kg of weld metal, so plan 300 to 600 direct weld hours before fitting and gouging. Shop rates of $85 to $140 per hour, and large machine tools like a 5 m table boring mill billing $250 to $350 per hour, make work center scheduling a genuine cost lever. Bay occupancy matters too: a 25 t crane bay carries $35,000 to $60,000 per month of fixed cost, and the Assembly Bay Utilization calculator shows what three extra weeks of dwell costs a job.

Inspection is a priced cost line, not an afterthought. Full penetration structural welds on a cutterhead usually require 100 percent UT plus MT on fracture critical joints, and UT coverage runs 0.4 to 0.8 m of weld per technician hour at $95 to $130 per hour. The Weld Inspection Load calculator converts weld length and technique into inspection hours before you commit a price. Budget rework explicitly: a typical shop repairs 3 to 6 percent of weld length, and each repair costs 6 to 10 times the first pass rate once excavation, rewelding, and reinspection stack up, so a 5 percent repair rate on 900 m of weld becomes a five figure line item.

Transport quotes blow up when the piece will not split. A 6.6 m cutterhead shipped whole is a superload in most US states: expect $40,000 to $90,000 for an 800 km move once permits, police escorts, and route surveys are included, versus $12,000 to $20,000 if the head splits into three sections under 4.9 m wide. Ocean breakbulk adds $150 to $300 per freight tonne plus lashing engineering. Splitting saves freight but adds 120 to 250 shop hours of flange machining and site bolting, so run both cases through the Transport Cost calculator and price the actual crossover point instead of assuming one answer at bid time.

Field work is the most underquoted block in the category. Site assembly and commissioning of a cutterhead and main drive takes a crew of 3 to 4 between two and six weeks, and per diem, travel, and standby add 35 to 50 percent on top of wage cost. Estimate it bottom up with the Field Commissioning Hours calculator rather than as a flat 5 percent allowance, which is how shops end up absorbing 200 unbilled hours. Quote consumables and spares as a separately priced option: a starter set of 40 to 60 disc cutters at $2,500 to $4,500 each is $120,000 to $250,000 of working capital, and the Spare Cutter Buffer logic settles who should carry it.

Build the quote in the same blocks you track actuals: material at gross weight, labor by operation, machine time by work center, NDT, transport, field hours, then overhead and margin applied visibly. Carry 8 to 12 percent contingency on single piece work and tie steel to an escalation index when delivery exceeds 90 days, because heavy plate has moved 20 percent in a single quarter before. The five recurring misses: weld metal underestimated by 30 percent, plate yield assumed at 85 percent when real nests deliver 72, transport priced before the route survey, commissioning quoted flat, and rework omitted entirely. Close those gaps and quote to actual variance drops inside 5 percent.

Published 2026-07-02.