Modification by Inclusion
The modification by inclusion (or ground reinforcement) is the construction or inclusion of ‘vertical reinforcement’ elements in the ground with the main benefit resulting from the structural aspect of the elements themselves. These elements operate as stiff but compressible columns embedded in weaker soils. The soil-column composite that interacts through friction and adhesion increase the bearing capacity and enhance stability.

The reinforcement elements can be natural inclusions (e.g. sand, stone, etc.) or semi-rigid inclusions (e.g. cement grout, mortar, etc.) The common reinforcement methods used as follow:

• Vibro Stone Columns (SC)
• Dynamic Replacement TM (DR)
• Controlled Modulus Columns TM (CMC)
  

The choice of suitable technique depends on the bearing capacity requirement, existing soil conditions in particular the undrained shear strength, availability of inclusion materials, environmental concerns and the costs.

Vibro Replacement (VR)
The vibro stone columns (SC) techniques began as an adaptation of the vibro compaction technique, and uses identical vibroflots. It involves replacing 15 – 30% of the cohesive soil with stones in the form of columns.
The vibroflot penetrates the ground aided by water jeting in the wet method or compressed air in the dry method. Stone backfill is compacted in controlled lifts, either from the surface down the annulus created by penetration of the vibroflot as in the top feed system or thought feeder tubes directed to the tip o the vibroflot as in the bottom feed system. Thanks to the equipments developed by its parent company, Menard Geosystems Sdn. Bhd. is resourceful to install stone columns using both wet and dry method.

Generally, stone columns are used in soils with undrained shear strength, Cu, great than 15 kPa. For weaker soil (Cu < 15kPa), one has to reduce the bearing load and/or allow higher post construction settlement. Alternatively, one can increase the column diameter as in the case of dynamic replacementTM columns or introduce cohesion in the column materials as in the case of controlled modulus columnsTM to reduce the column bulging effect.

Dynamic ReplacementTM (DR)
]Dynamic ReplacementTM (DR) is an extension of the dynamic compaction technique. This technique starts out by producing a crater with light pounding. The craters are then backfilled with hard, durable, inert materials such as aggregate, stone, gravel or rock pieces (up to 300mm size) that will lock together under subsequent heavy pounding. This followed by subsequent pounding which results in large diameter columns (2.5 to 4m) with depth up to 7m and behave like mushroom pillars.

DR columns are normally used to improve the strength of soft saturated cohesive soils (e.g. clay and silt) and organic soils (e.g. peat). In addition, DR columns also act as large vertical drains which accelerate consolidation process while providing structural support.

Design values up to 80 tons per column are typical for DR columns in soft to medium stiff clays compared with 20 – 30 tons in vibro stone columns. Apart from that, DR columns do not bulge easily as compared with stone columns due to the larger diameter and better bearing capacity. Thus, DR column is usually adopted when heavy loading needs to be place on soft compressible ground with low undrained shear strength.

Controlled Modulus ColumnsTM (CMC)
The use of deformable foundation such as stone columns is often an economical alternative to rigid foundation because of its ability to improve the soil sufficiently at a lower cost. However, this technique reaches its limits, when the soil is too soft and does not offer a sufficient lateral support, or when the settlement reduction ratio is too small in case of high applied loads. In view of this, Prof. Cognon of Menard Soltraitement has developed the controlled modulus ColumnsTM (CMC), which is an intermediate between rigid foundation and deformable foundation in the sense that it presents the advantages of both.

CMC consists of reinforcing the soil by means of semi-rigid cemented columns. This technology provides a good control of the settlement and of the equivalent deformation modulus of the treated ground, and it is, at the same time, an economical solution adapted to about all types of compressible soils and to a very wide range of loads. In addition, this technology is also designed to be very clean and environmental friendly.
CMC has been first implemented in France and have then been successfully introduced in other countries such as Great Britain, Spain, Germany, United States of America, Egypt and Malaysia.