Well, countless words have been written on the importance of site investigations. Unforeseen ground conditions can cause at best project delays, budget overruns of millions and at worst catastrophic failure. Shallow groundwater, soft soils, heaving clays, shallow rock, unstable slopes can all spell disaster for a project. We here at GeoZone are providing peace of mind.
Expansive clays cost the British economy an estimated £400 million per year, the US economy $15 billion annually, and the South African economy an unknown amount.
Some clays are more active than others
Clays take up moisture in the wet season, and lose it in the dry. Some clays are more active than others, and the amount of soil heave is a function of its activity, and the thickness of the deposit. A thin layer of highly expansive clay may have a lower cumulative heave than a thick layer of low expansive material.
The load is initially carried by the water
Clays may also be subject to consolidation when loaded. A complex subject indeed, but in broad terms, settlement and failure may occur when a soil is subjected to load. The clay particles will rearrange themselves to accommodate the applied stresses, sometimes catastrophically. Should the soil be saturated, the load is initially carried by the water between the particles, but over time this water will drain away due to the applied loads and the pore pressures will dissipate. The load will then be carried by the soil particles themselves and consolidation and settlement may occur.
Sites can be incredibly difficult to model
Sands have their own challenges in terms of founding thereon, but are generally easier to deal with than their clay counterparts. Sites underlain by clays, sands and silts can be incredibly difficult to model and characterise, especially when they begin to interact with each other in terms of shear strength and drainage characteristics.
It allows us to determine the engineering properties of the soils
In view of the challenges broadly outlined above, a geotechnical investigation is important. It allows us to establish the thickness and distribution of the various soils which underlie a site, to determine the engineering properties of these soils, the groundwater levels, and depth to a suitable founding horizon and depth to bedrock. A geotechnical investigation can range from a simple study comprising no more than a couple of shallow test pits for a lightly loaded foundation for a house, to a comprehensive drilling and test pitting programme for a power station where it is imperative that the geotechnical conditions are well understood.
The engineer will over design the foundations
The old saying, “You pay for a ground investigation whether you have one or not” is very true. Normally it is understood to mean that unforeseen ground conditions can lead to expensive delays, claims, or potential failures, which will require a geotechnical investigation to solve should they occur. However it can be argued that the engineer will over design the foundations if she doesn't have good geotechnical information. This is to ensure that all the eventualities are covered, leading to increases in concrete, reinforcing steel, design and construction time, with the possibility of failure still present with the beefed up design still relying on guesswork and assumptions.
Need geotechnical advice?
If you need some help characterising the geotechnical properties of your site, leave us a message below, or email us on info(a)geozone.co.za or phone us on 082 9260626.