How to Compare Excavation Quotations

Start with what each quote assumes about the ground

Every excavation price rests on assumptions about soil, rock, groundwater and contamination. Some contractors include an allowance for rock; some exclude it; some carry it as a provisional sum to be adjusted later. Before comparing prices, write down for each quote how it treats each ground risk. Whatever site investigation you have should be in front of every tenderer.

Provisional sums are not fixed prices

A provisional sum is a placeholder. In the worked example below, Supplier A carries rock excavation as a $5,000 provisional sum while Supplier B prices it at a fixed $4,000:

A: $6,800 bulk excavation + $5,000 rock (provisional) = $11,800.00 ex GST
B: $7,400 bulk excavation + $4,000 rock (fixed)       = $11,400.00 ex GST
Quoted difference = $11,800.00 − $11,400.00 = $400.00 in B’s favour

A’s final cost moves with actual rock cost:
  rock costs $3,000 → A = $6,800 + $3,000 = $9,800.00 (A cheaper by $1,600.00)
  rock costs $6,500 → A = $6,800 + $6,500 = $13,300.00 (B cheaper by $1,900.00)
Break-even rock cost for A = $11,400.00 − $6,800.00 = $4,600.00

The question is not “which is cheaper?” but “how likely is rock to cost more than $4,600, and who carries that risk?” Under B’s fixed price, the contractor carries it (subject to the quote’s terms). Under A’s provisional sum, you probably do. How that allocation works under your contract is an issue for professional review.

Check the volume basis for cart-away

Soil increases in volume when excavated (bulking). A quote priced on bank (in-ground) volume and one priced on loose volume are not comparable without a stated bulking factor:

Bank volume 120 m³ × bulking factor 1.3 (assumed) = 156 m³ loose
156 m³ ÷ 10 m³ per truck (assumed) = 15.6 → 16 loads

Also confirm whether tipping fees are included, what happens if material is classified as contaminated, and whether the price covers the tip site distance actually available.

Machine size, rates and lump sums

• Machine size is a specification, not a detail. A 5 t and a 13 t excavator are not equivalent; confirm the size suits access and the work.
• Hourly or daily rates need an estimated duration to compare with a lump sum. Ask each contractor for theirs, and compare a range rather than a single number.
• Mobilisation (floating machines in and out) may be separate, included, or per visit. If the job needs two visits, check whether the price covers both.

Items commonly excluded

• Rock, dewatering and groundwater management
• Tipping fees, contaminated or acid sulfate soil
• Service locating and damage to unmarked services
• Traffic control, permits and road occupancy
• Shoring, batter stabilisation and compaction testing

Using QuantDoc for excavation quotes

QuantDoc flags provisional sums and allowances as items whose final cost can change, matches line items between quotes with a stated classification, keeps TBA and not-mentioned items as unknown, and drafts questions for each contractor. Conversions such as bank to loose volume or m³ to tonnes are only made with an assumption you enter. The example below is calculated by its engine.