2.2 Groundworks measurement rules

Section 4 of the ANZSMM sets out the measurement rules for groundworks. The sections that follow present detailed requirements for each corresponding subsection within this category. For a comprehensive understanding of the applicable measurement procedures and pricing considerations, readers are advised to refer to Section 4 of the ANZSMM.

2.2.1 Excavation

In excavation, provisions for activities such as taking samples, conducting tests, and keeping excavations free from rainwater and percolating water, using pumping or other methods, need to be allocated as preamble items. 

The excavation works comprise site works, surface excavation to reduced levels, basement excavation, pit excavation, trench excavation, backfilling, disposal of surplus excavated materials, bored excavation, cuttings, tunnelling, surface preparation, working space, and designing shoring. However, this chapter focuses on the most common items encountered in building construction; bored excavation, cuttings, tunnelling, surface preparation, and designing shoring are not discussed. According to Measurement and Pricing Rule P1 of the ANZSMM, all items under the Excavation section are deemed to include associated activities such as levelling, grading, trimming, compacting, and other similar tasks. 

Site works include activities such as site clearing; removal of trees completed with stumps and roots; protection and retention of existing trees and shrubs; stockpiling of turf or vegetable soil; removal of tree suckers, roots, and similar materials; and the treatment of general ground areas and the sides and bottoms of trenches. This chapter explains the measurement rules related to site clearing, tree removal, protection and retention of existing trees and shrubs, and the removal of turf or vegetable soil.

Site clearance involves removing smaller vegetation to create sufficient space for equipment and labour. This is the first step in any construction project. Figure 2.1 illustrates an example of site clearance using plant and machinery.

Site clearance area must be measured in square metres (m²) and must include the removal of trees with a girth of 0.5 metres or less, together with their stumps and roots. In accordance with  standard, tree girth is to be measured at a height of 0.5 metres above ground level, as illustrated in Figure 2.2.

Trees with a girth greater than 0.5 m must be measured separately by number (no.) under the item “removal of trees complete with stumps and roots.” These trees should be classified in 0.5 m girth increments. For example, a tree with a girth of 0.65 m would fall into the 0.5–1 m category. Additionally, existing trees and stumps that are to be protected and retained on site must also be measured separately, either by number (no.) or as a distinct item where required.

Turf or vegetable soil is generally soft, contains more moisture, and is readily compressible. It can often be reused for landscaping and is therefore typically removed before any other excavation work. Consequently, the removal of topsoil is an important item on the groundwork checklist following site clearance. The Figure 2.3 shows a typical soil profile, highlighting the vegetation, topsoil, and subsoil layers (part a), as well as the removal of topsoil using machinery (part b).

Topsoil removal must be measured in square metres (m²), with the average depth specified in the item description. A typical depth for topsoil removal ranges between 100 mm and 150 mm. 

Figure 2.4 illustrates sample images of a basement excavation (part a), a pit excavation (part b), and a trench excavation (part c), which are commonly encountered in building construction. For all excavation types, the total depth must be identified and measured from the commencing level to the base of the excavation. Once determined, the depth should be expressed in 1 m increments within the description. For example, if the total depth is 3.5 m, the appropriate depth category would be 3 m – 4 m.

Surface excavation to reduced levels, basement excavation, pit excavation, and trench excavation are measured in cubic metres (m³). All volumes should be measured as net areas, as outlined in the drawings. When different classes of material are encountered during excavation, each class must be measured separately. Notably, rock excavation is measured as an “extra over” item when occurring within another class of material. 

It is essential to specify the commencing level of the excavation, such as the existing ground level, the bottom of topsoil excavation, the reduced level excavation, or the basement excavation. Additionally, any required working space beyond the face of the excavation must be explicitly included in the item description.

For surface excavation to reduced levels, the area must be stated in the item description. If preliminary trenches have been measured separately, this should be clearly indicated in the description for basement excavation. When measuring pit excavation, the area of each pit must be calculated. If a pit has an area of less than 1 m², this must be noted in the description, and the number of such pits should be indicated in brackets within the item description.

For trench excavation, it is important to specify whether the trench is intended for a strip footing, ground beam, or a similar structural element. Figure 2.5 demonstrates sections of a strip footing (part a) and a ground beam (part b), which are measured under trench excavation.

Backfilling refers to filling the excavation with excavated materials as shown in Figure 2.6. The area highlighted in grey indicates the portion that requires backfilling.

Backfilling is measured in cubic metres (m³) and must be recorded separately for different applications, such as trenches. The depth of backfilling should be classified based on the total depth – up to and including 1 m, and thereafter in 1 m increments.

The disposal of surplus excavated material from all types of excavation is typically carried out at a nominated location. In accordance with the standards, the distance to the disposal site must be stated in kilometres (km).

Figure 2.7 demonstrates the provision of working space in trench excavation.

Working space must be measured in all cases, and a special note is required where excavation for working space is not possible for a given item. When measuring working space, the total depth range and purpose must be specified in the item description. The quantity of working space is measured in square metres (m²) by multiplying the girth along the outside line of footings by the depth of excavation.

2.2.2 Filling and hardcore

This category covers items as filling in beds, filling behind retaining walls, filling over the site, filling to slopes, filling to trenches, and surface preparation. As per the standard, all items in the filling and hardcore section are deemed to include related activities such as levelling, grading, and trimming. 

In construction projects, layers of compacted material are used to create a stable base for subsequent works. These materials may include soil, crushed stone, brick, or concrete, depending on the project’s stability requirements. The Figure 2.8 shows examples of sand filling (part a) and hardcore filling (part b).

Filling in beds is measured in square metres (m²) when the thickness is less than 250 mm, with the thickness stated in the description. When the thickness exceeds 250 mm, it is measured in cubic metres (m³), with the corresponding area specified in the description. For filling in trenches, the total depth is categorised as less than 1 m, 1 m – 2 m, and thereafter in 1 m increments. In all cases, the description must include the type of material, the thickness of the layers, and the method of compaction. 

2.2.3 Paper or plastic membranes

This category comprises items as paper, plastic, and similar membranes. All types of membranes are measured in square metres (m²) and must specify whether they are installed horizontally, on a slope, or vertically. Measurement rules require that all measurements be taken as the net area covered, including horizontal breaks and turning ups of 500 mm or less. The description must include information on laps and joining requirements. Measurement and pricing are deemed to include dressing around and sealing all penetrations. The Figure 2.9 shows an example of laying a plastic membrane prior to slab placement.