William Brown - New Business Manager
In New Zealand we’re lucky to enjoy a wide variety of outdoor
environments – mountains of rock forced up by earth movement, ancient
forests, rocky rivers carrying stones and sand onto open plains, wetland areas,
sandstone cliffs and beautiful sandy beaches. As much as we like to get out in
these environments, we also like to build in them, and the ground beneath our
feet can be as varied as the view from above.
If you’re building, you will probably be expected to get a
geotechnical report, but how do you know that your report will be enough to
design the foundation that holds up your building, and minimise the chance of
nasty surprises (and hidden costs) when you start building?
Something that we often see when a customer first makes
contact is that their current geotechnical investigation isn’t detailed enough
to design deep foundations, and more investigation is needed. Often this is a
valid approach – geotechnical investigation can be quite an iterative process
and the first round of investigation often focuses on shallow foundations – why
would you look deep if you don’t need to? However, often the need for
additional investigation comes as an unplanned expense and time delay, which people
could do without. Choosing a geotechnical engineer who is familiar with local
conditions can be helpful to reduce surprises in this area, as they may have an
idea of what foundation types have worked in your area in the past.
So why bother with the additional investigation?
The simple answer is so that you know what you’re dealing
with before you start building. Is that ‘hard’ layer 7 metres below the surface
strong enough? Is it thick enough? Does it vary in depth and thickness across
the building site, or does it disappear altogether? Will the ground liquefy in
an earthquake? Just as rivers meander across the ground, conditions underground
can vary from one side of a building to the other. Other times the ground
beneath can be quite consistent. Although a geotechnical investigation is only
ever an indication of what lies beneath, the more information you have
the clearer this picture becomes.