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GEOSYNTHETICS
AFRICA

Prefabricated Vertical Drains (PVDs)

GeoDrain PVD is a prefabricated band drain - a corrugated or fishbone polypropylene core wrapped in a filter geotextile - installed vertically into soft, compressible ground. It shortens the pore-water drainage path from metres to centimetres, cutting consolidation of soft clays and silts from years to months under surcharge or vacuum preload. Supplied in 100 mm widths, 300–350 m rolls, with discharge capacities to 100 × 10⁻⁶ m³/s at 300 kPa.

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Technical Specification of Prefabricated Vertical Drains (PVDs)

Prefabricated vertical drains (PVDs), also called band drains or wick drains, are geocomposite strips installed vertically into soft, compressible soils to accelerate consolidation. Each drain consists of a channelled polypropylene core wrapped in a filter geotextile: the core carries pore water vertically to a surface drainage blanket, while the filter admits water and excludes soil fines that would otherwise clog the flow channels. Because consolidation time varies with the square of the drainage path length, replacing a vertical path of several metres with a horizontal path of under a metre reduces primary settlement time from years to a matter of months.

GeoDrain PVD uses a polypropylene core in two channel geometries. The corrugated core presents continuous parallel flow channels on both faces and is the general-purpose configuration for most embankment and reclamation work. The fishbone core uses a herringbone channel pattern that maintains flow paths under lateral confinement and drain buckling at depth. Both are 100 mm wide (±3.0 mm) with a nominal 3.0–4.0 mm thickness, and are wrapped in a nonwoven filter — polypropylene or polyester depending on grade - selected for an apparent opening size of 75 microns or finer to retain fines while sustaining permeability under confining stress.

PVD design is governed by drain spacing rather than drain capacity in most soils. Spacing is set from the target degree of consolidation and the available preload period using radial consolidation theory (Barron, Hansbo), with typical grids of 0.8 m to 2.0 m in triangular or square patterns; triangular gives more uniform pore pressure dissipation for the same drain count. Three effects should be checked against the datasheet values: well resistance, where discharge capacity must remain adequate at the design confining pressure and at depth; smear, the remoulded annulus created by mandrel penetration, which reduces horizontal permeability near the drain; and filter retention against the in-situ particle size distribution.

PVDs are specified wherever soft clays, silts or hydraulically placed fills must gain strength and complete settlement before permanent works proceed — port and container terminal reclamation, highway and rail embankments on soft ground, storage tank and warehouse pads, tailings and landfill platforms, and airport aprons. Installation depths of 10–25 m are routine, with 40 m achievable on suitable rigs. PVDs do not by themselves cause settlement: they provide the drainage path, and a driving load must be applied by surcharge preload, staged embankment construction, or vacuum consolidation. Design should always pair drain layout with a surcharge programme and an instrumentation regime of settlement plates and piezometers.

Typical Values for PIPES DRAINAGE DUCTING

Width
100 mm ±3.0
Thickness
3mm – 4mm
Discharge Capacity
up to 100 × 10⁻⁶ m³/s
Tensile Strength
≥2.5 kN full width
Filter Opening
75 micron max
Roll Length
300m / 350m

Properties & Dimensions

PropertyTest MethodUnitGD-3070C / 3070FGD-3520UGD-3540T
Core / filter material--PP / PETPP / PPPP / PP
WidthIS 1954mm100 ±3.0100 ±3.0100 ±3.0
Thickness, minASTM D 5199mm3.0 ±0.5 (core)4.0 (overall)4.0 (overall)
Discharge capacity — straight, 300 kPa, i=1.0ASTM D 4716×10⁻⁶ m³/s1009080
Tensile strength, full width, minASTM D 4595kN2.51.52.0
Filter tensile (MD), minASTM D 4595kN/m6.03.06.0
Apparent opening size (O₉₀), maxASTM D 4751Micron757575
Roll lengthIS 1954m300 / 350200 / 250 / 300200 / 250
Download Full Technical Datasheet for Prefabricated Vertical Drains (PVDs) (PDF)

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Three Questions To Ask Before You Order

1.What is a prefabricated vertical drain (PVD)?
A prefabricated vertical drain is a 100 mm wide geocomposite strip — a channelled polypropylene core wrapped in a filter geotextile — installed vertically into soft compressible soil to accelerate consolidation. Also called a band drain or wick drain, it gives pore water a short horizontal path to the nearest drain instead of a long vertical path to the surface, then carries that water up to a drainage blanket. PVDs are used on soft clays, silts and hydraulic fills where settlement must be completed before permanent works begin.
2.How much faster do PVDs make consolidation?
Consolidation time scales with the square of the drainage path length, so the gain is large. A 20 m soft clay layer draining vertically to one boundary might need eight to ten years to reach 90% consolidation. With drains at 1.5 m spacing, the governing path becomes roughly 0.75 m horizontally and the same stratum reaches 90% within a single preload season of three to six months. The exact time depends on the horizontal coefficient of consolidation, drain spacing and the surcharge applied.
3.What is the typical PVD spacing?
Typical spacing is 0.8 m to 2.0 m, set by design rather than by rule of thumb. Spacing is calculated from the target degree of consolidation, the time available for preload and the soil's horizontal coefficient of consolidation, using radial consolidation theory. Triangular grids give more uniform pore pressure dissipation than square grids for the same drain count and are generally preferred. Closer spacing accelerates consolidation but increases drain quantity and installation time, so spacing is the main cost lever in a PVD design.
4.Do PVDs work without a surcharge?
No. PVDs provide a drainage path but they do not generate the load that drives consolidation. A driving load must be applied through surcharge preload, staged embankment construction, or vacuum consolidation. Installing drains without a surcharge programme achieves nothing beyond the settlement the existing ground stress would eventually cause. Any PVD design should specify drain layout, surcharge height and duration, and a monitoring regime together.
5.How deep can PVDs be installed?
Depths of 10 m to 25 m are routine and 40 m is achievable with suitable rigs and mast configurations. The practical limits are rig capacity, mandrel buckling in dense layers, and whether the drain can maintain discharge capacity under confining pressure at depth. For deep installations, the buckled-condition discharge capacity matters more than the straight-condition figure, and a fishbone core is generally preferred over corrugated.
6.What is the difference between corrugated and fishbone PVD cores?
A corrugated core has continuous parallel flow channels on both faces and is the general-purpose choice for most embankment and reclamation work, offering the highest straight-condition discharge capacity. A fishbone core uses a herringbone channel pattern that keeps flow paths open when the drain is laterally confined or buckled - the condition that governs at depth and under large settlements. Both are 100 mm wide with the same filter specification, so they substitute directly without changing mandrel tooling or design spacing
7.What discharge capacity does a PVD need?
Enough that well resistance does not govern the design. Discharge capacity is measured at a stated confining pressure and hydraulic gradient - typically 300 kPa and i = 1.0 - and quoted for both straight and buckled conditions. Required capacity depends on drain length, soil permeability and the flow that must be carried; for most projects a straight-condition capacity of 80 to 100 × 10⁻⁶ m³/s is adequate, but long drains in more permeable soils need checking against the design flow. Always compare like with like: confining pressure and condition must match between quoted figures.
8.What is the smear zone and why does it matter?
Driving the mandrel remoulds a zone of soil around each drain, reducing its horizontal permeability. This smear zone slows radial drainage and is one of the main reasons field consolidation rates fall short of theoretical predictions. Its effect is accounted for in design by assuming a smear zone diameter of two to three times the equivalent mandrel diameter with a reduced permeability ratio. Using the smallest practical mandrel section and avoiding unnecessary re-driving limits the impact.
9.How are PVDs spliced and installed?
Drains are threaded through a hollow mandrel with an anchor plate or shoe at the base, driven to design depth, and the mandrel withdrawn leaving the drain anchored in the soil. The drain is cut off 150 to 300 mm above the drainage blanket. When a roll runs out mid-installation, drains are spliced by overlapping 200 to 300 mm with filter over filter and core over core, stapled or secured so the flow channel remains continuous. Depth, position and verticality are recorded per drain as the QA record.
10.What should I specify when ordering PVDs?
State grade and core type, total linear metres, roll length preference and delivery programme. Ask for discharge capacity in both straight and buckled conditions at the design confining pressure, filter apparent opening size against your soil's particle size distribution, and full-width tensile strength for installation loads. Request current third-party test certificates rather than datasheet values alone. Our engineering team can review your ground investigation data and advise on grade selection and spacing before you finalise the specification.

Specification For The Design, Installation Of Prefabricated Vertical Drains (PVDs)

Installation begins with a working platform and a horizontal drainage layer. The platform must carry the rig, typically 30 to 60 tonnes on tracks, over ground that is by definition soft - this usually means a granular fill layer, often reinforced with a woven geotextile or geogrid separator to prevent loss of fill into the subgrade. The same layer serves as the drainage blanket that receives water discharged by the drains, so it must be free-draining sand or aggregate, generally 0.5 to 1.0 m thick, with an outlet to collection drains or a filter-protected edge. Water discharged from the drains has nowhere to go without a functioning blanket, and a blocked or contaminated blanket is one of the most common causes of underperformance on site.

The drain grid is set out to the design spacing and pattern, with each position marked and referenced. Drain is threaded through a hollow steel mandrel and secured at the base with a disposable anchor plate or shoe, sized to grip the soil on withdrawal and to seal the mandrel against soil ingress. The mandrel is driven to design depth by static push or vibration, then withdrawn, leaving the drain anchored at depth. The drain is cut off 150 to 300 mm above the blanket surface so it discharges freely into it. Where a roll is exhausted mid-drain, splices are made by overlapping 200 to 300 mm with core over core and filter over filter, secured so the flow channel remains continuous and soil cannot enter at the joint.

Drains alone do not produce settlement; a driving load must be applied. Surcharge is placed as fill above the drainage blanket to the design height, or vacuum consolidation is applied beneath a sealed membrane where surcharge fill is unavailable or stability limits its height. On soft deposits, surcharge is usually raised in stages, with each lift held until the underlying soil has gained sufficient shear strength to permit the next - placing fill faster than strength develops is the principal cause of embankment failure on PVD-treated ground. Surcharge height and duration are set together with drain spacing in design, and one cannot be varied on site without reassessing the other.

Performance is verified by instrumentation, not assumed. Settlement plates track surface movement, piezometers record pore pressure dissipation in the treated stratum, and inclinometers monitor lateral movement at the embankment toe where stability governs. Settlement and pore pressure data are used to estimate the degree of consolidation achieved, commonly by Asaoka or hyperbolic methods, and surcharge is released on that evidence rather than on elapsed time. Installation records for each drain - position, depth achieved, date and any obstruction or refusal - together with the instrumentation record form the acceptance documentation for the works.

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