Hydraulic Modification
The consolidation method is used to increase the bearing capacity and to reduce the settlements so that areas covered by very soft clay, silt or organic soil (e.g. mangrove swamps or ponds filled with slime) can be used for housing and industrial development and construction of infrastructure facilities (e.g. road, railways, harbors, airfields, etc.)
The hydraulic modification process is aimed to improve fine, grained saturated cohesive soil by consolidation resulting in a net decrease in the water content of the soil mass. The common consolidations methods are as follow:

• Prefabricated vertical drains (PVD)
• Menard vacuum consolidation (MVC)

The selection of a particular technique depends mainly on the purpose of the ground improvement works, the soil condition in particular undrained shear strength, the construction time and the cost.

Prefabricated vertical drains (PVD)
Preloading is often the most economical technique for treating soft soils as compare to other ground improvement techniques. However, for most projects sufficient time is not available for preloading. Hence, the primary use of prefabricated vertical drains (PVD) is to accelerate the rate of consolidation.

The consolidation rate can be further increased with an overload (surcharge) whereby the applied load from the fill exceeds that from future permanent load. In doing so, besides accelerating the rate of consolidation it also accelerate the rate of strength gain and reduce post construction settlement.

Menard Geosystems together with its parent company Menard Soltraitement International has developed its own range of vertical drains installation equipment to cope with wide variety of subsoil conditions. We have experience using static, vibratory and jetting methods to install PVD. We can also incorporate preaugering and special downhole draining to penetrate difficult surface layers including true stiff clays, rubble, concrete, slag and other fill items.

Menard vacuum consolidation (MVC)
Menard vacuum consolidation (MVC) consists of installing vertical and horizontal vacuum transmission pipes under an airtight impervious membrane over the soft saturated cohesive soils deposit to be consolidation. By evacuating the air below the membrane, atmospheric pressure is imposed on the soil. This technique is often used as a replacement for all supplement to placing surcharge fills. It is most suitable for ultra soft soils where stability and speed of construction is of major concern.

The advantages of using MVC are as follow:

• Significant time saving over other consolidation methods
• Loading and construction can proceed as early as two weeks after process has started
• Isotropic consolidation reduces the risk of failure under the additional loading of the permanent construction
• No risk of slope instability beyond boundaries
• Controlled rate and magnitude of loading and settlement
• Elimination of transporting massive amounts of surcharge fill materials