Services > Ground Improvement > Injection Systems for Expansive Soils
Injection Systems for Expansive Soils
Injection Stabilization is an in situ method of treating expansive clays by pressure injection of an aqueous solution of water, lime slurry, or potassium chloride.

  • Typical injection depths are 7 to 12 ft deep under building foundations and up to 40 ft deep or greater under railroad subgrades and landfills
  • An economical, in situ stabilization system with a 30 year history of treating cohesive soils. Injection methods vary according to the type of material being injected
Three Fundamental Types of Injection
The Injection Process
Acceptance Based On
  • Increasing in situ moisture contents to the plastic limit plus 2 to 3 moisture points
  • Reducing pocket penetrometer readings to 3.0 tsf or less
  • Reducing average swell to 1.0% or less in the treated zone

* Acceptance testing method is dictated by the material being injected

Water Injection, a preswelling technique, is a method of introducing water into expansive clay in order to swell the clay as much as possible prior to construction
  • Water and surfactant (surface active agent) are injected into expansive clay to preswell the clay. Each injection “pass” is performed on 5 ft centers. Several passes are required to effectively preswell a site. Preswelling is typically used for large (50K+) buildings and large areas of pavement. Water injection is inexpensive, fast and easy to use
  • A surfactant is added to the water to reduce water tension and increase the rate of adsorption of the water by the clay

Methodology

Several conditions combine to make water injection an effective technique.

  • As water is added to the clay by the injection process, it is adsorbed by the clay particles due to the presence of hydrating ions located in the spacing between the particles of clay

  • Eventually, the clay will adsorb an amount of water that satisfies the clay particle’s charge, at which point the swelling process is complete

  • A plane of shear develops at the outer envelopes of the clay/water system which corresponds to an overall reduction in shear strength of the clay. For this reason, measurements of shear strength, such as those obtained with a pocket penetrometer, can be a fast and effective way to determine the success of injection



Lime Injection is the injection of lime slurry at high pressures (50 to 200 psi) resulting in a coating of the dessication pattern of the clay with slurry
  • Additionally, the surface of the building pad will be covered with lime slurry as a result of the process
  • This material is mixed with the soil to form a working platform after injection
  • Lime injection is typically followed by water injection to preswell the clay and further distribute the lime into the soil
Lime Injection
  • Lime is injected to fill the dessication pattern of expansive clay with slurry and stabilize the surface of the pad for workability
  • Lime injection is used for building pads as well as streets, parking lots and runways
Methodology
  • When the calcium hydroxide is in contact with the clay surface in the dessication pattern of the soil, it reacts with the silica and alumina in the clay to form calcium silica hydrates and calcium silica aluminates

  • These cementing compounds represent new molecules and are non-expansive



Potassium Chloride Injection (CIS) is the mixing together of potassium chloride and ammonium lignosulphonate in an aqueous solution that is injected to greatly limit future heave of an expansive clay soil.
  • Unlike preswelling, potassium injection limits the amount of water a clay will adsorb. For this reason, potassium injection also is a method of arresting heave occurring in existing structures
  • Typically, potassium injection is limited to use in existing structures as well as those that are highly sensitive to movement such as residences
Potassium Chloride Injection
  • Is mixed with ammonium lignosulphonate and injected into expansive clays to chemically treat clay and dramatically reduce its affinity for water
  • Is typically injected prior to construction of highly sensitive structures as well as through the floors of existing structures to reduce ongoing heave
Methodology

Several conditions combine to make water injection an effective technique.

  • The amount of water a clay will adsorb is dictated by the predominant ion located in the spacing between the clay particles

  • By changing the predominant ion, the clay/water system’s behavior can be altered

    Potassium and ammonium are ions that can satisfy the clay particle’s potential energy and not have excessive hydration


Lime/Fly Ash Injection is the blending of lime and fly ash into a slurry and injection into low strength soils to improve bearing capacity and trafficability.
  • In less reactive soils, Geocem is also used to improve the strength of the soil
  • Geocem is a blend of 80% fine ground limestone and 20% Portland cement klinker. These two materials are injected to improve conditions beneath railroad subgrades, pavements, and landfills
Lime/Fly Ash Injection
  • Is used to treat lower strength clays and silts to improve bearing capacity by lowering moisture content and increasing dry density and shear strength
  • Is used to treat railroad subgrade problems in high fills. It is also used to improve subgrade conditions in pavement structures such as runways and bridge approaches
Methodology
  • When lime/fly ash is injected into a low strength clay or silt, it displaces water which is trapped in the soil
  • The material will then react chemically with the soil resulting in further increases in shear strength
  • By injecting lime/fly ash or Geocem it is possible to lower the moisture content of the soil and improve the dry density which both contribute to shear strength.
©2003 Hayward Baker, All Rights Reserved. Privacy Policy
Site Design by HindSite Interactive, Inc.