Soil Mixing

The Process

The in situ soil mixing system keeps site disturbance to an absolute minimum, eliminating contaminated spoil disposal, minimising the release of volatile compounds into the atmosphere whilst chemically fixing contaminants in the ground. The system uses cementitious and pozzolanic materials together with additives such as organophilic clays. A design mix of the constituents is mixed in situ with the contaminated ground using a specially adapted auger. The treatment grout is injected through the hollow stem of the auger and thoroughly mixed with the soil. This provides both chemical fixation and mass physical encapsulation and can improve the geotechnical properties of soft/loose ground. Soil columns are overlapped to ensure complete mass treatment or to provide a secure barrier.

The mixing process can also be applied ex situ if site constraints dictate, using on site batching/mixing plant.

Organophilic Clays

The structure of the naturally occurring Bentonite clays, often used in the process, consists of complex layers of molecules loosely bonded together by exchangeable cations. The process of modification creates an organophilic environment for the fixation of organic contaminants particularly PCBs and PAHs. Organophilic clays together with cementitious materials can be used together to provide an effective permanent chemical and physical fixation of organics, inorganics and heavy metals.

Permeable Reactive Barriers (PRBs)

A more open clay structure allows groundwater to flow through the clay, enabling it to act as a molecular sieve, as contamination is effectively removed by sorption within the modified clay structure.

Hot Spot Treatment / Passive & Active Containment Applications

A combination of permeable reactive and low permeability passive containment together with hot spot treatment can be implemented to manage the on-site and off-site migration of contamination in groundwater flows. This is particularly useful where the site being treated forms part of a wider contaminated area.

Advantages of the Soil Mixing Process:

  • Wide spectrum of applications
  • Rapid implementation and effect
  • Treatment for organics, inorganics and heavy metals In situ and ex situ process
  • Active containment to treat contaminated groundwater with PRBs
  • System uses well proven application techniques – cut off walls, augers and capping layers
  • Treatments can be engineered to meet the requirements of individual sites
  • On completion specific sites can be capped with an impermeable material to prevent further water ingress or provided with capillary break layers and top soiled to suit the development