Lime-Soil Stabilization

 

         Soil stabilization occurs when lime, fly ash, cement or bentonite clay is added to a reactive soil.  The resulting pozzolanic reaction between these materials and the soil develops a durable and stable bond between molecules in the soil.  This reaction can provide for long lasting stabilization of clay based soils.

Soil Stabilization is a simple process involving in-place mixing where an appropriate amount of lime, fly ash, cement or bentonite clay is spread over the ground surface, mixed to an appropriate depth.  Pulverization by our mixers thoroughly combines the lime and soil to depths of 12 to 18 inches.  For heavy clays, it is typical to complete a preliminary mixing, spreading lime and passing over the entire area, followed by 24 to 48 hours (or more) of moist curing.  This is followed by a second spreading of fly ash or lime, followed by final mixing.   During the final mixing faze the soil is compacted to develop the proper and intended soil strength and durability.

Materials used to stabilize soils including lime, fly ash and cement, are strong alkali and a caustic material.  They can burn the skin and are considered dangerous to the eye. 

APPLICATION OF SOIL STABILIZER:   Application of Lime, Fly Ash, Portland cement or bentonite clay follows three simple steps.  (1) Spreading Lime, Fly Ash and Portland cement  (2) Mixing Lime, Fly Ash or Portland cement and Soil (3) compacting. 

Spreading:  Truck mounted, and track spreaders are used to lay down the Lime, Fly Ash, Portland cement or Bentonite clay.   Spreader are equipped with curtains at the delivery point, to help control dusts generated as the material is emptied out of the hopper and spread across the ground.  Because of the exothermic reaction that takes place when the Lime, Fly Ash, Portland cement react with the water in the soil, it is common for steam to rise above the spread material.  Dusts created during spreading and transfer are controlled by filter bags covering the vents at the top of the spreaders and fixed curtains covering the point of delivery at the rear of the spreader.  Workers on site should not normally be affected by drifting clouds of dust due to the in place controls, but should take precautions and actions to avoid working near the spreading and mixing operations. 

Mixing:  Mixing is done by machine using drum mixers, pulverizing and mixing the soil to depths ranging from 12 to 18 inches.  The drum and mixing chamber are closed to the outside environment by use of fixed curtains along the sides of the mixer.  A water truck, attached, by hose, to the mixer is used to inject a steady stream of water into the mixing chamber. This supply of water helps to control the dusts and assures proper and complete chemical reaction.  All workers must stay clear of the mixer and spreading operations.   The operator has many variables to consider and may not see you approaching.  The operator does not anticipate people on the ground in this work area.  Save your life, stay clear of the equipment when it is in operation.  

Many jobs required two passes; the first pass through the site generally includes mixing the lime into the soil.  No compaction is done.  The lime is allowed to react for 24 to 48 hours and the soil to mellow.  During this process steam will be seen as the lime reacts with the water.  The heat generated in the soil 6 and 8 inches down is hot enough to cause thermal burns on the skin.  Keep your hands and other unprotected skin out of the soil. 

The Second pass through the site may include application of Fly Ash, which is spread and mixed the same as the lime.  Following the mixing of the fly ash, the ground is generally compacted.  

Compaction:  Initial compaction is generally performed with a sheepsfoot roller, in some cases followed by a pneumatic or flat wheel roller. 

Petroff’s Safety Plan Hand out can be found here: SAFETY CONSIDERATIONS AND PLAN FOR LIME 1_1