The following geotechnical analysis presents the Finite Element modelling of an embankment stabilized with prefabricated vertical drains installed in soft clay foundations. The adopted modelling strategy is based on several fully instrumented case histories selected from Thailand as described in detail by Indraratna and Redana (2000). 

The embankment studied is the test embankment TS1 for the Second Bangkok Internal airport which has been constructed and stabilized with 12 m long PVDs installed in a square pattern using vertical FloDrain® (100 mm × 4 mm) installed with a spacing of 1.5m. The drains were installed using a mandrel (125 × 45 mm) which was continuously pushed into the soil using a static weight (in lieu of vibration) to reduce soil disturbance (smear zone) as much as possible. 

The subsoil is relatively uniform, consisting of a top weathered crust (1.5 m thick) overlying a layer of soft clay approximately 12 m thick. A stiff clay layer underlies the soft clay and extends to a depth of 20–24 m below the ground surface. During wet seasons, the area often is flooded, and the soil generally retains a very high moisture content. The subsoil variation and the vertical drain pattern at this location are shown in Figure 1. The embankment load was applied in stages. Stage 1 loading was equivalent to 18 kPa, which included a sand blanket and clay sand having a total height of 1.0 m placed over 15 days. The load in stage 2 was raised to 45 kPa (over 10 days), followed by stage 3 (up to 54 kPa over 5 days) and stage 4 (up to 75 kPa over 20 days), giving a total fill height of 4.2 m.

The definition of equivalent vertical permeability is crucial in the context of 2D plane strain analysis of Prefabricated Vertical Drains (PVD).The concept of equivalent horizontal permeability arises from discrepancies between 3D reality and 2D plane strain models in the context of drainage field analysis due to the difference of drainage lengths. This is particularly relevant in modeling Prefabricated Vertical Drains (PVD) and must be dealt with first as presented in the article  “Definition of the equivalent permeability for a 2D plane strain analysis of PVD”.