The geotechnical engineers face many problems while designing the structures over soft, weak and marshy soil. The properties of soft soils are low shear strength, high compressibility and the most critical property is the low drainage which causes the slow process of consolidation. So, where there is a large infrastructure such as airfields, road embankments, commercial complex etc. has to be construct in shorter time in such soft soil it may takes a years due to slow consolidation process because of low permeability of soil. So, to speed up the consolidation or construction process, an artificial path has to build to increase the rate of consolidation process. This can be done by installing of TECHDRAIN_TM, prefabricated vertical drains (commonly called PVD, band drains or wick drains)..

Consolidation occurs very slowly in saturated, fine grained soils because the low permeability of theses soils impedes the escape of pore water in the soil voids. Even under large temporary surcharge loads, settlement can take many years because of this slow water movement and the ground distance the water must move to exit the soil. Without some sort of special treatment construction is usually impractical due to unpredictable long term-settlement. To achieve rapid consolidated settlement it is necessary to create shorter paths for movement of the water.

The installation of TECHDRAIN_TM, a prefabricated vertical drains (commonly called PVD, band drains or wick drains), creates artificial paths as well as greatly reduces the distance the water must travel to reach a free drainage path, and therefore accelerates consolidation rate. Using TECHDRAIN_TM, can cut the time required for primary soil consolidation from 20 to 25 years without the use of vertical drains to just a few months. Most settlement can occur during construction, thus keeping post-construction settlements to a minimum.

By installing wick drains in a designed pattern as shown in Fig.1, the distance that the water must travel to escape the pressure is reduced considerably, and reduces the travel time of the water to just weeks or months as shown in Fig. 2.

Fig.1 (a) Without PVD drains	(b) With PVD drains

TECHDRAINTM band drains are installed vertically to depths exceeding 65m. The drains are usually placed in a square or triangular configuration of 1 to 1.50m depending on the desired consolidation time.

Fig.2. A plot of time Vs settlement curve with and without PVD drains

The installation of vertical drains are done by driving mandrel and then extracting the mandrel and placing the PVD drains as shown in Fig.3. Under excess hydrostatic pressure, water has only to travel the horizontal distance to the nearest drain to reach a free drainage path.

Consequently the higher horizontal permeability of the clay is also taken to advantage. The water flows through the filter fabric of the drain and into the channels of the drain core where it can flow vertically out of the soil. This flow may be either up or down to intersecting natural sand layers or to the surface where a sand drainage blanket or prefabricated strip drains are provided.

Vertical drains are normally used in conjunction with preloading with surcharge embankment or vacuum pressure.

Fig. 3. Installation of PVD drains.

TECHDRAIN_TM has engineered a range of product that optimally meets most PVD project requirements.

• TECHDRAIN_TM TD-420F is the benchmark PVD with 4mm X 100mm corrugated core profile for a broad range of soft soil conditions.
• TECHDRAIN_TM TD-F450U is the benchmark PVD with 4mm X 100mm fin-profile core profile for a broad range of soft soil conditions.
• TECHDRAIN_TM TD-520F is a heavy duty 5mm X 100mm corrugated core for special conditions like deep installations, high surcharge, large settlements, or situations requiring large flow rates.

Fig.4. TECHDRAINTM Pre-fabricated vertical drains.

TECHDRAIN_TM is predictable, in both technical and financial terms. PVD technology has proven itself in hundreds of projects in the last thirty years. Over 1 Billion linear meters of similar prefabricated vertical drains have been installed worldwide.

TechDrain PVD’s (Pre Fabricated Vertical Drains) as per global standards are now being manufactured and being supplied from India.