Geotechnical Engineering. Hills District.

The brief. A two-storey brick veneer home with an in-ground pool and spa on a vacant lot, the base of the pool shell about two metres below the existing ground.

On the ground. Two rig boreholes to 3.0 metres and two penetrometer tests. Up to 0.5 metres of fill over stiff to very stiff residual clay, then extremely weathered material and very low strength shale from 1.4 to 1.5 metres, proven to the base of both holes.

The outcome. Class P as it stands, because of the fill. Reclassified Class M once the fill is cleared from beneath the footings and slab, with foundation parameters for the house and the pool.

The brief. A consultancy needed boreholes for the classification of a rural lot ahead of a new home and shed. We drilled, tested and logged; the consultancy wrote the classification.

On the ground. Three boreholes with the 4WD-mounted rig and three penetrometer tests. Thin topsoil or fill over clayey sand and sandy clay with ironstone gravel, with auger refusal at 0.6 to 1.2 metres, two of the holes on very low strength sandstone. All three were dry.

The outcome. The field logs were issued on the day of drilling, for the consultancy's report.

The brief. A two-storey home with a granny flat, gym, cabanas, pool and spa, and terraced entertaining areas, across about five metres of fall on a rural lot.

On the ground. Eight rig boreholes and eight penetrometer tests across both terrace levels, set out around livestock and the existing house. High-plasticity residual clay over clayey sand, with auger refusal on inferred extremely weathered sandstone at 0.9 to 2.1 metres. Every hole was dry.

The outcome. NATA-accredited laboratory testing confirmed a reactive clay, but the clay mantle is thin and the rock shallow, which limits the movement it can deliver. Class M, with the upper bound of the class adopted for design.