Vibro-replacement

[edit] Introduction

Vibro-replacement is a ground improvement technique that can be used to transfer structural loads to suitable levels in poor ground conditions. Another term that can be used for this technique is vibro stone columns (VSC).

The effect of vibration consolidates and strengthens the ground, helping to stabilise granular soils that would otherwise be unsuitable for construction.

It can be a cost-effective alternate method to piled foundations and grouting that can be used for structures such as buildings, embankments, dams, tanks and towers. However, the site must be large enough to accommodate and justify the plant that is required.

The amount of stone fill material must be carefully calculated to ensure that the process does not become uneconomical compared with conventional piles which also have the advantage of having higher bearing capacities.

Another similar method is vibro-compaction.

[edit] Technique

Vibro-replacement works by using a crane-suspended downhole vibrator to construct stone columns through weak soils, improving their load-bearing and settlement capacities. The vibrator is usually up to 4 metres long, although sometimes it may be necessary, if strata are particularly dense, to pre-drill down to the design depth. There are two processes that can be used:

[edit] Dry process

Weak soil is penetrated to the desired depth and stone used to fill the cavity through a feed pipe attached to the vibrator. The vibrator is then used to compact the stone and ensure it interlocks tightly with the surrounding ground. Successive charges of stone are added and compacted to form a column that is built up to ground level.

[edit] Wet process

Weak soil is penetrated to the design depth by means of the vibrations as well as water jetting from the vibrator’s tip. The stone backfill is then inserted as the vibrator is removed and then used to compact the stone. A water supply of 10,000-12,000 litres per rig hour is usually required for this method.

Both processes can be aided by computers on-board the rigs that monitor specific parameters, allowing operators to respond quickly to any deviations that may occur.

[edit] Related articles on Designing Buildings Wiki

• Driven piles.
• Geothermal pile foundations.
• Grouting in civil engineering.
• Micropiles.
• Pile foundations.
• Retaining walls.
• Screw piles.
• Underpinning.
• Vibro-compaction.

[edit] External references

• Hayward Baker – Vibro-replacement techniques
• ‘Introduction to Civil Engineering Construction’ (3rd ed.),HOLMES, R. (1995), The College of Estate Management