Colmix - Deep Soil Mixing (DSM)
COLMIX is the process of installing soil cement columns by grout mixing of insitu soils.
Hiways pioneered the COLMIX application for slip remediation and slope stability. Over the past decade, Hiways GeoTechnical has provided COLMIX stabilized soil mixing solutions for a wide range of geotechnical applications throughout New Zealand. Numerous ground improvement, foundations and liquefaction prevention projects have been completed. The majority of these sites have been completed as design and build projects.
Principle
The COLMIX process relies on three
distinct phenomena occurring separately or combined.
- A destruction (and subsequent reconstruction) of the insitu soils is performed under the mechanical effect of a desegregating tool enhanced by the physical and chemical effects of the addition of hydrating binder(s), typically Lime, Cement or blends.
- A thorough incorporation of the binder (with quantity and hydration degrees) designed specifially for the characteristics of the treated soil and to the specified results.
- A mechanical recompaction of the final mix, in order to rebuild or improve the original soil density.
The COLMIX process presents similarities with the Lime Column Technique (LCT) and the Japanese "Deep-Mixing" process. However, it has fundamental differences and advantages in two aspects:
- The degree and fineness of the homogeneity of the soil-binder mix.
- The possibility to recompact in place the final soil-binder mix.
Description
COLMIX uses twin, counter rotating augers with opposite pitches and overlapping auger flights.
These twin augers are located at the end of two drill rods driven in opposite revolving motion at synchronized speed by twin motors. Each auger features a desegregating drill head tool with a grout outlet port.
The rotation of the interlocked helixes induces a lengthwise movement of the soil.
Destruction of the soil and incorporation of the binder are performed simultaneously or successively, in one or several drives during the first phase of drilling, when the materials are going upward, or during withdrawl phase in reverse rotation when the materials are going downward.
Destruction of the soil can be made significantly easier by incorporating a lime special binder blends which induces instant spreading of the clay particles during the drilling phase.
Incorporation of one or several binders through two hollow rods and homogenization of the mix are made easier by the motion of the materials along the twin augers.
The recompaction effect is obtained during the last phase when the double auger is reversed and withdrawn under a constant thrust. The mix is thus forced down and subsequently recompacted. The thrust applied to the augers is a function of the degree of compaction expected.
Implementation
The Equipment: The COLMIX process involves specific equipment including;
- A drilling mast allows continuous auger drilling. The maximum depth acheivable is 11.5 meters.
- Twin motors allowing direct or reverse synchronized revolution of the twin hollow drill rods.
- A servo-control system maintains a constant thrust or a constant traveling speed of the tools.
- A drilling parameters recording system to synchronize the injection of binder and the drilling speed to ensure constant column strength through variable material types.
- A modified 35 tonne excavator base machine to provide maximum maneuverability, stability and reach for column construction.
The Binder: Binders are generally either lime hydroxide, cement or both, depending on soil characteristics and column design requirements. The binder is incorporated by pumping as a grout after being mixed with water (wet process) using an onsite batch mixing plant.
Lime provides a particle floculation and strength gain in clay soils through combining an ion exchange phenomenon during the first phase and a pouzzolanic type reaction on a long-term basis.
Cement action is due directly to its hydraulic binding characteristics.
Binder selection and quantity is selected in accordance with the mineral characteristics of the soil, its water content and design strength of the COLMIX columns.
Edgecumbe SwitchYard Foundations
Quality Control
COLMIX is a fully controlled process providing thorough Quality Control documentation. Pre testing of soils is carried out to ensure that target design characteristics of the COLMIX columns are achieved in the field. Appropriate binders and application rate designs are pre selected from laboratory and site testing.
An on board computer provides monitoring and recording to ensure the accurate delivery of grout injection and to record full drilling records and parameters.
Field of Application
The COLMIX process is a fast and inexpensive technique for soft soil strengthening.
Its major practical applications include:
- Improvement to slope stability (slips).
- Embankment strengthening and mechanical stabilization (trenches, causeways, embankments for rail or road, river or canal banks, etc).
- Reduced settlement control for structures.
- Foundations of building with distributed load (rail or road beds, bulk material storing yards).
- Foundations for light industrial buildings, housing areas.
- Containment of contaminated soils.
- Impervious barrier walls.
- Foundation designs to mitigate liquefaction
Earthfill dam foundations incorporating COLMIX columns
Rodney District Council - Slip remediation site
