Subsoil improvements

[edit] Introduction

Many techniques are available to improve subsoil. The aim of soil improvements can be:

• To increase its bearing capacity by improving the shear strength.
• To enhance the soil stiffness and density so that liquification can be avoided.
• To prevent excessive settlement, in particular in the construction of roads, runways and so on.
• To stabilise or immobilise contaminants within the soil.

Some of the available techniques are described below.

[edit] Land drainage

The purpose of this method is to lower a high-water table and to dry out the ground to improve its bearing capacity. The technique might involve water entering into a flexible perforated drainage pipe in the ground and being directed away. A layer of shingle might be added to assist.

[edit] Grouting

Soft subsoil is a serious problem for maritime construction. A solution can be to inject a cement-based mixture into the subsoil under pressure. The mixture will expand and fill any voids and eventually form a strengthened base with improved the permeability.

For more information see: Grouting.

[edit] Vibroflotation

A vibrating probe is lowered into the ground by vibrating jets causing vibration. After the probing process is complete a granular hardcore mixture is poured into the hole and further compacted by the probe. Once the probe is slowly removed, further hardcore is pushed in until a column is formed. This process requires specialist plant and cranes.

[edit] Compaction with rollers

Plant rolling machinery is used to compact soil.

For more information see: Roller

[edit] Dynamic compaction

A method that is used to increase the density of soil deposits. The process uses specialist plant and cranes to drop a heavy weight repeatedly on the ground at consistent intervals.

[edit] High energy impact compaction

A method that is used in low strength soils. Specialist plant is used with big hexagonal-shaped rolling attachments in a controlled dynamic drag along site.

[edit] Vacuum consolidation

Prefabricated vertical drains were originally used with surcharge fill to manage residual settlement in soft ground. This method was extended to include vacuum application for better results. This method uses stress transfer and surface loading techniques and is carried out by specialist contractors.

[edit] Geotextiles

Geotextiles are permeable fabrics that can be used to filter, reinforce, separate, drain or protect. They work by allowing filtration or separation of granular layers in-ground applications. They are commonly used in construction and are a relatively easy way to improve soil characteristics.

For more information see: Geotextiles.

[edit] Related articles on Designing Buildings Wiki

• Alluvium.
• Bearing capacity.
• Geotextiles.
• Groundwater.
• Grouting.
• Insitu testing of soils.
• Roller.
• Soil compaction.
• Soil survey.
• The importance of soil analysis.
• Types of soil.
• Vibro-compaction for ground improvement.
• Water table.

[edit] External references

BTEC National Construction - Pearson