Excavation and shoring BOQ: piles, ground anchors and subbase
The items of an excavation and shoring BOQ (bill of quantities) are usually among the largest in the bill, and they are almost never in the architectural model. The excavation, piles, ground anchors and subbase are measured from several sources, and these are checked against each other before the quantities go into the construction BOQ.
Four sources for an excavation and shoring BOQ, and what to take from each
- Survey map. The natural ground level, from which the excavation depth is measured.
- Soil report. The layers, the groundwater, the pile type, and the recommendations for foundations and excavation.
- Shoring plan. The shoring line, the pile diameter and the spacing between piles, and the rows of anchors or struts.
- Structural drawings. The basement slab, the rafts, the ground beams and the subbase details.
Whatever is missing from the sources is not filled in by guesswork. The line is flagged, with a note of what is missing.
For illustration only. The numbers on this page come from a synthetic example. Any question about the ground, the foundations or the shoring must be checked against the project's soil report and with the geotechnical consultant and the structural engineer.
Excavation and shoring: by the shoring line and the levels
General excavation is usually measured by the shoring line, not by the area of the rooms in the basement. The depth is the difference between the natural ground level and the level of the bottom of the excavation. In the example: 1,240 m² inside the shoring line, natural ground at level -0.30 and the bottom at level -6.80, which gives a depth of 6.50 m and 8,060 m³. The exact method, including local excavation for foundations and pits, should be checked against the methods of measurement and the shoring plan of the project.
When there is no natural ground level from a survey map, the depth is not guessed. The map is requested, and until then the line stays flagged.
Shoring piles: count, length and concrete
The number of piles is taken from the shoring plan and checked against the geometry: the perimeter of the shoring line divided by the spacing. In the example, 142 m divided by 2.10 m is 67.62, which means 68 piles, the same as the count on the plan. In the example the length is measured without the capping beam, so 68 piles 16 m deep come to 1,088 linear metres. Where the measurement starts and ends is set in the specification and the detail, and it should be checked on every project.
In some bills the pile item includes the concrete, and in others the concrete is a separate item. Both ways are accepted, as long as the concrete is not counted twice. A simple check: the theoretical volume, π times the radius squared times the length, should appear in one place in the bill only. In the example it is 307.62 m³.
Shoring piles and foundation piles, for example under the lift shaft, are usually different groups in diameter and depth. Check that each group is counted once, in its own item.
Ground anchors: by the shoring plan, row by row
Ground anchors are counted for each row separately, according to the shoring plan and the sections. When a row runs continuously along the whole perimeter, the perimeter divided by the spacing gives a reasonableness check. In the example there are two rows at a spacing of 3.40 m, 42 anchors in each row and 84 in total. The design is done by the project's designers, according to the soil report and the applicable standards, for example Israeli Standard SI 940 Part 4.2, which deals with grouted ground anchors. The bill shows the number, the length and the tests required by the design.
Anchors and steel struts are two ways of supporting the shoring, and usually one replaces the other. When the plan shows struts at the corners, check that anchors were not counted there as well, unless the combination appears in the sections.
Subbase and blinding: only under what bears on the ground
In the example, a 20 cm compacted subbase is measured only under the slab that bears on the ground, and it is entered in m³. Under the suspended slab, which sits on void formers, there is no subbase; there is an item for void formers instead. The bottom in the example is 1,120 m², of which 140 m² is raft and 260 m² is suspended slab, so the subbase is 720 m² times 0.20 m, which is 144 m³.
Blinding, a thin layer of lean concrete, is measured in the example under the raft and under the ground-bearing slab: 860 m². The actual layers come from the detail and the soil report, so the quantity is taken from the detail, not from habit.
Example: a basement section, eight lines
Clicking a row in the table highlights in the section what was measured in it and shows the formula. The section is schematic and shows half of the basement, up to the axis of symmetry.
| Item | Description | Unit | Quantity | Source |
|---|---|---|---|---|
| 01.010 | General excavation inside the shoring line down to level -6.80, including removal of surplus soil | m³ | 8,060.00 | Shoring line and survey map |
| 23.010 | Bored shoring piles cast in place, diameter 60 cm, depth 16 m (68 nr) | m | 1,088.00 | Shoring plan |
| 02.030 | Concrete in a capping beam 80/60 cm along the shoring line | m³ | 68.16 | Shoring plan |
| 23.020 | Temporary grouted ground anchors, two rows, 15 and 14 m long, including testing | nr | 84 | Shoring sections |
| 01.050 | Compacted subbase, 20 cm thick, under the slab that bears on the ground | m³ | 144.00 | Basement slab detail |
| 02.010 | Blinding concrete, 5 cm thick, under the raft and the ground-bearing slab | m² | 860.00 | Foundation detail |
| 02.020 | Void formers under the suspended slab, according to the detail | m² | 260.00 | Basement slab detail |
| 01.020 | Excavation in rock | m³ | Missing | Missing |
| Check | Formula and result | Conclusion |
|---|---|---|
| Pile count: perimeter divided by spacing | =ROUND(142.00/2.10,2) = 67.62 ⟶ =ROUNDUP(142.00/2.10,0) = 68 | Matches the count on the plan: 68 |
| Theoretical concrete volume in the piles | =ROUND(ROUNDUP(142.00/2.10,0)*16.00*PI()*(0.60/2)^2,2) = 307.62 | Appears in the bill once only |
| Anchors per row | =ROUNDUP(142.00/3.40,0) = 42 · =ROUNDUP(142.00/3.40,0) = 42 | Two rows, 84 in total |
The rock excavation line stays "missing". Until the soil report arrives there is no way to know whether there is rock and at what depth, and a zero in this line would look like an answer that nobody gave.
What a professional quantity surveyor checks below ground
A quantity surveyor who comes from the field, an engineer or a registered building technician who worked on site, like Yaakov Avital, reads the soil report and the structural drawings together. For example: the soil report requires soil replacement for the whole footprint of the building, while the structural drawing marks it for only part of it. Measuring by the marking alone will put only the marked part into the bill. A professional check flags the gap as a question to the geotechnical consultant and the structural engineer, and they decide. In the same way, questions such as who removes the temporary anchors at the end of the works, or whether cutting down the pile heads is included in the item, are asked before the tender. A full example is on the page professional BOQ.
In an excavation and shoring BOQ, the quantity takeoff depends on the soil report and the shoring plan together. When one of them changes, the quantity calculation has to be updated too, not only the drawing.
Frequently asked questions
What is excavation and shoring?
Excavation and shoring are the works that make it possible to build a basement: digging the pit, and shoring that supports its sides so that the ground and the neighbouring buildings stay stable. The design is done by the project's designers, usually based on the geotechnical consultant's recommendations, and the bill describes and measures what was designed.
Why is the excavation not measured from the model?
Most models have no ground, no natural levels and no shoring line. The excavation usually comes from the survey map and the shoring plan, and the model is used for checking.
What happens when the soil report changes?
The pile type, the depth and the rock layer can change, and the quantities with them. So every quantity in this part should be linked to the revision of the report and of the drawing it was measured from.
Is this relevant to a contractor pricing a tender?
Yes. A contractor checking an excavation and shoring BOQ in a tender can use the same checks: the pile count against the perimeter, concrete counted once, and subbase only under the ground-bearing slab. More on this on the page quantity surveyor for contractors, and on the basics on the page quantity surveyor for construction projects.
Have a project? Tell me briefly what the project is and what already exists. When the project is a good fit, I usually reply with focused questions and a written quote.
Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.