It is becoming increasingly common to use vibratory techniques, during construction, to improve the load bearing capacity of the ground in preparation for foundations.

With vibratory ground improvement a cheaper alternative to traditional methods such as piling, it’s no surprise it’s becoming so popular!

So what does vibro compaction involve and what are the potential limitations that need to be taken into account before changing the way you provide support for your structures?

Let’s start with the basics.

What is ‘Vibratory Ground Improvement’?

Vibro ground improvement strengthens the load bearing capacities of weak or filled soils to provide adequate support for foundations.

How does it work?

This is done by lowering large high powered vibrating probes from a specially designed rig into the targeted ground. The ground is then back filled with highly compacted aggregate or soil, causing the configuration of the ground to become denser thus making the soil more stable.

Wait… here’s the important bit!

What foundations can be used with vibro compaction?

Vibro compaction on its own is not substantial due to the localised nature of the process and the different soil types. Therefore, it needs to be supported by reinforced foundations which should be:

  • Either reinforced concrete strip foundations, or a raft/semi raft foundation
  • Designed by a structural engineer and comply with the minimum requirements for areas of reinforcement as defined by BS 8110
  • Include suspended ground floors
  • Where the treated ground comprises cohesive soils, measures must be taken to mitigate the potential effects of vegetation (i.e. subsidence or heave). Refer to Section 5.2 of our Technical Manual for further guidance

So which is better vibro compaction or traditional piling? Let’s compare the two methods.

Vibratory Ground Improvement vs Piling

To the untrained eye the stone columns left by vibro compaction can be mistaken for piles. However, these stone columns derive their strength from the surrounding soil as opposed to piles which are more than 10 times stiffer than stone columns.

That’s 1-0 to piling! So why would you choose vibro compaction over piling?

Benefits of vibro compaction

  • It is much quicker than piling and follow-on works can be started straight away
  • It is cheaper than piling
  • It provides a flexible option for different types of soils
  • It is one of the most sustainable techniques and thus the most environmentally friendly
  • It decreases the chances of liquefaction

Limitations of vibro compaction

  • It does not work with all soil types so an extensive analysis into the soil should be carried out which is not required for piling
  • It requires specialist equipment and expertise which would need to be contracted in.
  • Certain types of vibratory techniques are unsuitable for contaminated land for example when water jets are used as they may spread the contamination further

If you are considering vibratory ground improvement techniques for your build why not take a look at Section 5.1 of our Technical Manual for more information.

 

By Craig Ross