Soil Stabilisation (or Lime Treatment of Soils)

Soil stabilisation by Lime Treatment can be achieved by applying a controlled dose of quicklime, hydrated lime or liquid lime to soil.

Cohesive soils can be stabilised using quicklime or hydrated lime but only quicklime causes drying of the soil. This process enables unacceptably wet or cohesive materials to be treated and used for construction purposes. Different treatments are available to suit virtually every soil type and can produce a range of different strengths according to use.

Lime Improvement is a quick and simple operation that can be incorporated into any earthmoving contract no matter how large or small. Because the nature of the soil is quickly changed to improve the handling characteristics, productivity is often enhanced. The segregation of unacceptable material is also eliminated. This is simply treated with lime as it is identified to obtain the soil properties that are required.

One of the great advantages of improving soils with quicklime is the ability to retain all material on site. This eliminates the need to remove material to tip and saves the cost of tipping and haulage charges. This often has an impact on the construction programme as it is usually considerably quicker to treat soils on site rather than dig, dump and replace.

The mechanisms of Lime Treatment of Soils

1. Improvement (quicklime addition only)

Once quicklime is mixed with the moisture bearing soil an exothermic (heat producing) reaction takes place.

CaO                 + H₂O              =          Ca(OH)₂                +          1,140 kJ/kg CaO
quicklime         water                            hydrated lime               heat produced

In a homogeneous mixture, the quicklime reacts with the moisture present in the soil. This exothermic reaction generates significant amounts of heat energy which will dry the soil (temperatures can reach in excess of 100ºC) as well as chemically binding 32% of it’s own weight of water as hydroxide.

2. Modification (quicklime or hydrated lime / liquid lime addition)

The next steps, Modification and Stabilisation only occur with clay soils. When quicklime or hydrated lime is added to a clay soil, the clay platelets go through an ion exchange process, which introduces calcium into the clay surface and causes a change in the way the clay platelets align, as shown in the pictures below. This gives an increase in soil strength and will normally occur quite rapidly (usually within two hours of mixing but can take up to a day depending on site conditions).

3. Stabilisation (quicklime or hydrated lime / liquid lime addition)

The silica and alumina contents of the clay soil will react with the calcium present in the lime to form calcium silicate hydrates or calcium aluminate hydrates. This reaction is slow to proceed and is similar to the reactions that occur when cement cures. The strength gain can continue for over 10 years.

The Process

The process is simple and can range from basic plough and disc harrow through to purpose built lime spreaders and rotovator. This allows lime treatment work to be carried out from small to major sites.

Process Advice

Contact the British Lime Association members who have extensive experience of Lime Treatment of Soils and are available to help with your project.

Advantages of Lime Treatment

• Save ££££'s - Reduce Project Costs.
• Save Time - Bring your project back on schedule or even finish early !
• Least Environmental Impact - Minimise vehicle movements and disturbance to the
• surrounding areas.
• Minimise - Waste generation, tipping and aggregate fill demand.
• Avoid - Aggregate and Landfill Taxes.
• Simple - process and equipment requirements.
• Long History of Use - Used widely for many years throughout the World.

Lime Treatment of unsuitable or contaminated soil is a simple process which is being used to strengthen, dry out or remediate unsuitable ground. There is a long history of use on large and small projects alike.

Main Contractors are saving considerable amounts of time and money by using Lime Treatment, which avoids the need for dig and dump by treating material in situ. This reduces imported aggregate and landfill costs and can often be done with simple, readily available equipment either by an earthworks contractor or a specialist subcontractor.