Vibro Stone Columns

Vibro stone columns are one of many ground improvement solutions used at the early stages of construction.

Much like in cases of vibro compaction, dynamic compaction and dynamic replacement, vibro stone columns are used to improve shallow low strength and stiffness soils.

Adopting a vibro stone column approach allows the use of lightly reinforced ground bearing slabs, pads & strip foundations. This offers significant cost efficiencies when compared against a traditional piled approach.

Through the combined effects of densification, reinforcement stone columns can be successfully used to improve:

• Fine grained (Clay)
• Coarse grained (Sand & Gravel) soils.

To construct the columns, imported stone is compacted into voids formed using a displacement process. This helps produce zero spoil arisings. GeMech operates a fleet of top feed vibro stone column rigs, with fixed mandrels ranging in length from 4.5m up to 7.0m.

With prior approval, the columns can be formed using recycled aggregates, offering environmental sustainability benefits.

Vibro stone columns can be used on a wide range of construction projects, from low rise housing, commercial warehousing to large scale Civil Engineering.

Advantages

• Suitable for a wide range of soils profiles
• More cost effective than most other piling methods, particularly when the whole foundation package cost is considered
• Faster than other traditional methods of piling
• Zero spoil arising
• Minimal site preparation requirements in comparison to traditional piling methods
• Recycled aggregates can be used in column construction, offering environmental sustainability benefits. 

Vibro stone columns expedite the consolidation of fine-grained soils, such as clays and silts, after installation. This is a lesser-known benefit of this method. This is because the columns work effectively as vertical drains, reducing the time period required for achieving primary consolidation.

The stone columns can be used in tandem with static surcharging to provide efficient solutions on sites with challenging ground conditions.

The Vibro Stone Column Process

Ahead of commencement on site GeMech will complete a detailed ground improvement design and prepare a stone column layout. This is typically based on a set of construction issue foundation drawings – supplied to us in DWG format by the Client.

Step 1 – Prior to the rig arriving to site the client surveys the area for a suitable working platform. Numbered pins are then driven into the working platform at each pile position.

Step 2 – A health and safety briefing will take place, the rig will be prepared to work, and moved to the first pile position.

Step 3 – A delivery of stone arrives at the site and is then tipped onto the working platform. We ensure that this is placed within close proximity to the piling rig. GeMech will move stone from the stockpile to the individual columns using a 360 excavator.

Step 4 – The fixed mandrel, with an appropriate length, will be set up over the numbered stone column position. The mandrel is then progressed to a predetermined design depth, or refusal at a maximum hammer pressure.

Step 5 – Stone is placed in the void formed by the mandrel in a series of layers, with each layer successively compacted by the vibro mandrel during the column construction process.

The top part of the column doesn’t get compacted much during construction. This isn’t a problem for stone columns under foundations, as this material is taken out during digging.

For columns below slab areas, it is important that the surface of the improved soil is subjected to heavy compaction prior to slab construction. This will compact the material at the head of the stone columns.

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FAQs

Q – What foundations are vibro stone columns used with?

A – Vibro stone columns are commonly used with shallow foundations such as strip footings or raft foundations. This helps to provide an improved ground support and load distribution.

 

Q – Do Vibro Stone Columns connect to structures foundation?

A – When using vibro stone columns, the foundation designer should approach the design in a similar manner to the way they would approach a traditional ground bearing foundation design. Vibro stone columns reinforced the soils, improving shear strength characteristics, and reducing settlement potential. The columns should not be considered as discreet bearing points. There’s no requirement for any form of connection between the foundations and the column heads.