Ground improvement methods | Deep compaction method of dynamic compaction

Ground improvement methods:

Following are some of the methods to improve the conditions of the ground. These methods may be used separately or simultaneously.

• Deep compaction.
• Pre-loading.
• Drainage and GWT control (consolidation).
• Injection grouting.
• Soil freezing.
• Use of geotextiles (Geo-fibers).

1)      Deep compaction:

Deep compaction can be performed by a number of methods which are listed below:

• Consolidation or dynamic compaction.
• Vibroflotation or vibro compaction.
• Terra probe compaction
• Compaction piles

Dynamic compaction:

Dynamic compaction is actually a type of laboratory compaction method; in this method soil is compacted by introducing high intensity impacts on it, these impacts are generated by dropping 10 to 20 tons of weight freely from a height of about 30 meters with the help of cranes. A French engineer L. Menard developed this method in 1970’s. The soil particles are made denser and in more compact state by the impact of the shock waves created by the heavy weight, these shock waves travel considerably deeper. The soil depths of 15 m have been treated using this technique and further using other special equipments and the heavy loads further compaction is possible. This method results in the increase in shear strength and reduction in compressibility and thus improve the bearing compressibility.

Advantages:

• Suitability for large variety of soil.
• Allow treating soil below water table.
• It is a rapid treatment.
• Low in cost.

Disadvantages of dynamic compection:

The process is expensive and relatively time consuming; due to the development of the pore pressure in the fine grained soil its applicability is reduced.

This method is not valid for populated or fully developed areas because the shock waves generated by this method may affect other underground utilities or the adjoining structures. This can be avoided, while working in crowded or populated areas by using small weights, which reduces the intensity of vibrations, produced; it can also be done by dropping the weights from smaller heights. It is reported by experienced contractors that they the soil can be treated as close as 3 m from underground services and can be treated 6 m from the sound structures.

• The treatments may be complicated when GWT is about 2 m below the ground level, for the success of the treatment the level of whole site is to be raised up by the use of imported materials.
• It causes environmental pollution by making noise, gusts of air, vibrations and permanent deformation of the soil.