A marginal parcel can often be built on economically, but only if the ground investigation happens early enough to change the design rather than confirm it.
The standard sequence on a marginal parcel is to run a conventional structural design, price it, and walk if the number is bad. The trouble is that the number is bad by construction. A foundation designed without knowing what the ground permits is sized for the worst case the soil report allows, which on variable ground is a long way from what the site actually requires. The project is then declined on the strength of a cost that was an artefact of the sequence.
Investigating first changes what is on the table. Ground improvement matched to the actual bearing deficiency rather than to the worst layer encountered. Foundation systems selected against the measured profile instead of defaulted to from habit. Anchors specified for layered ground rather than for a single assumed stratum. Construction sequenced around seasonal ground behaviour, which on Alberta clays is the difference between a workable summer programme and a spring nobody costed.
None of this is unusual engineering. It is ordinary geotechnical work moved earlier in the programme, which is a scheduling decision rather than a technical one. It costs an investigation up front against a foundation package that may not need to be as large as the default assumed.
| Investigating first changes what is on the table. Ground improvement matched to the actual bearing deficiency rather than to the worst layer encountered. Foundation systems selected against the measured profile instead of defaulted to from habit. Anchors specified for layered ground rather than for a single assumed stratum. Construction sequenced around seasonal ground behaviour, which on Alberta clays is the difference between a workable summer programme and a spring nobody costed. On a recent solar project in Canada, a geotechnical investigation encountered sedimentary bedrock and the default foundation solution provided by other third party engineers was to use micropiles in the shallow bedrock areas and helicals in the deep overburden areas . PRI’s pre-production pile testing program verified that driven round HSS (hollow structural sections) could be advanced into the soft sedimentary bedrock and provide adequate uplift resistance to support the PV racking system, resulting in the owner saving $3,500,000 in material costs alone across 5,000 piles. None of this is unusual engineering. It is ordinary geotechnical work moved earlier in the programme, which is a scheduling decision rather than a technical one. It costs an investigation up front against a foundation package that may not need to be as large as the default assumed. Which means a parcel declined as unbuildable has usually been declined on incomplete information, and the developer has paid for a conclusion rather than an investigation. Contact PRI’s geotechnical practice to discuss a constrained site. |