Reactive Clay Time Bombs

Reactive clay soils can have severe impacts on Solar Farm foundation systems due to soil suction processes. These processes include ‘heave and shrink’ behaviour, depth of influence and soil cracking.

Dependant upon the site environment, composition and hydrostatic nature of the given clay, soil suction can lead to an effect we have discussed in a previous article known as ‘hydraulic jacking’. This effect over time causes the installed piles of a Solar Farm to quite literally eject from the soil.

Solar Farm sites that contain very high to extreme reactive clay soils and are dealt with incorrectly are what we refer to as ‘Reactive Clay Time Bombs’.

So, how do you determine whether or not your project is one of them?

First we must understand what is defined as incorrect in terms of dealing with these sites.

For starters, in any event that the piles for a given site are inadequately designed or installed for the real world levels of reactivity in the soil, medium-to-long term hydraulic jacking is highly likely.

If the encountered clays are in a dry, hard state during installation and traditional pre-drilling processes are applied, it is likely that a sump will be created that greatly increases the level of soil suction and reactivity around the pile, well above what was originally designed for.

Induced events such as prolonged wetting or droughts, deforestation, excessive civil works or pre-drilled soil sumps, can significantly alter the natural clay soil condition and processes of a given site.

These altered conditions and processes can increase the long-term aggression of the reactive clay soils and almost guarantee the eventual failure of piles from hydraulic jacking.

A quick method to determine whether your site may be a time bomb is through the checklist below:

1- Does your project site contain highly (H2) (>60mm Ys) or extremely (E) reactive clay soils ?

2- Is the reactive zone of influence (Hs) at a depth greater than 50% of the pile’s founding depth?

3- Were any end-bearing pile anchoring methodologies applied to the piles?

4- Was a pre drilling process required to enable the install of the piles?

5- Was there a prior plantation or forest on the site before piling works commenced?

6- Was pile load testing only considered from the immediate lateral and vertical load results, without consideration for seasonal soil strength changes and movement from wetting, drying and cracking?

The medium-to-long term effects for piles can quite often take 5 to 10 years to become fully evident, as the site cycles through its natural seasonal wetting, drying and hydraulic jacking soil suction processes.

Any project on an aggressive clay site that has not made the correct design determinations or installation considerations is at severe risk of long-term failure.

Significant preventative management plans or pile reconstruction are optional methods to prolong the operation of a Solar Farm project, to enable it to survive its intended design life.

If you would like to read more about how we can help Solar Farm developers, EPC’s and array suppliers, visit our ‘work with us’ page or contact us today.

Written by Solar Pile International.

Published 14/1/2019

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