Working With Clay - polymer paving

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October 05 2:20 PM | Articles

 

How to address and remediate the problem of clay soils

 

Clay has a large amount of fine particles; logically one would assume this is a desirable trait to obtain cohesion. However clay particles are not granular.

 

As engineers we prefer to obtain cohesion through straight gradation of interlocking rocks and granular sieve 200 fines because this provides a long term result with adequate weight support.

 

The problem with Clay

 

The basic structural unit of most clay minerals consists of one silica tetrahedron and one alumina octahedron. Because they are thin but have considerable lateral size they form in sheets. These sheets carry negative charges. Without going into details, this creates a water retention effect called double layer which we experience as mud at our level of perception. Because there is no direct (soil to soil) contact between the sheets suspended between these layers of water which surround the clay sheet, clay as a material is not suitable for compaction because water cannot be forced to take up less volume.

(Craig, 1974)

 

This problem can be resolved by replacing the soil, or sometimes very successfully with a chemical treatment intended to create hydrophobicity in the clay medium. The latter (chemical repair) is highly recommended for bases and subgrades because it reduces the sometimes astronomical cost of removing clay, finding a place to dump it, then buying and bringing in suitable base material to fill the void created by the clay removal.

 

The cheapest way to treat clay is with lime; this creates quick dissecation (drying). Lime treatment also causes non-reversible reactions which may continue for days, months or sometimes years, such as cementation (a.k.a. pozzolanic) reactions.

(Nicholson, 2014)

 

Some components of soil organic matter, such as natural humic substances, will adsorb to mineral surfaces, making them hydrophobic. Synthetic materials such as cationic organic surfactants can displace inorganic cations and make surfaces hydrophobic.

(Boyd et. al. 1989, 1990)

 

Electro-osmosis (electro-kinetic dewatering)

Applying an electrical current to a saturated soil will cause the water to travel towards the cathode (negative terminal). If this water is then pumped away, the result is reduced water content and a better, improved consolidation of the soil mass.

(Hausmann, 1990)

(Holtz, 1989)

 

Electro osmosis is a somewhat controversial practice with mixed reviews, due to cost and inconsistent results. However in the last few years it's been making a comeback as an excepted alternative stabilization method of clay or muddy soils.

 

From our perspective, osmosis is a temporary fix and it doesn't address the issue of what happens when water returns.

 

As with any scientific process nothing beats hands on experience. Treating small batches of identical soil with different methods will allow you to experience hands-on what type of results you should expect out in the field.

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