Pre-Fabricated Vertical Drain (PVD)
1. General

Prefabricated Vertical Drains (PVDs) are a type of geocomposites which has got application in railway embankment. PVD can be defined as any prefabricated material or product consisting of a synthetic filter jacket surrounding a plastic core (Fig.01).

Fig. 01: Pre-fabricated Vertical Drain

For construction of embankment over soft sub-soils (Ev2 less than 20 MPa or Cu less than 25 kPa or N value less than 5), the sub-soil/ground has to be improved for :

  • (a) Reducing consolidation time & associated settlement; and
  • (b) To increase bearing capacity/shear strength of sub-soil.

Out of various techniques for "ground improvement", use of "Pre-fabricated Vertical Drains (PVDs)" is one of the widely used technique.

2. Pre-fabricated Vertical Drains Installation

Pre-fabricated Vertical Drains (PVD) are typically 95-100 mm wide by 3-5 mm thick. Synthetic core is wrapped with geo-textile. They are less bulky and easier to handle; but, require sophisticated installation techniques.Normally PVDs are manufactured in rolls of 200-300m length and are inserted into ground to required depths using special drain stitcher rigs (Fig.02).

Fig. 02 : Installation of PVD
Video on Pre-fabricated Vertical Drain

Their installation causes little disturbance to the neighbouring soil and are over sand drains. Large settlements of substrata do not destroy the drain continuity. Generally, installation takes place up to full depth of compressible soils.

Video on Installation of PVDs

PVDs have replaced conventional sand drains for the purpose of faster consolidation in soft compressible/slow draining sub-soils (by shortening the drainage path of the pore water from a low permeable layer to free water surface or to pre-installed drainage layer, thereby accelerating the rate of consolidation and associated settlement), due to their easy & speedy installation.

Video on Efficacy of PVD
3. Reference

(a) For guidelines regarding Design and Construction for Ground Improvement by Pre-Consolidation using Vertical drains, reference can be made to IS 15284 (Part 2) : 2004 (Reaffirmed-2020).

(b) For Specification of Pre-Fabricated Vertical Drains (PVD) for Quick Consolidation for Very Soft Plastic soil, reference can be made to IS 18309 : 2023.