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Technical Presentations

    Prefabricated vertical drains for

               Soil Consolidation

          Vertical drai...
What is a PVD
• Prefabricated Vertical Drain - PVD

• Typically 95 -100 mm wide by 3 - 5 mm thick

• Synthetic core wrappe...
PVDs shorten drainage path

• 90% Consolidation time reduced from >15 years to 1 year




                                ...
Why use PVD over sand drain

•    Installation of PVDs typically 6,000 linear meters per day and result in
     a lower pr...
Why use PVD over sand drain

• PVD’s have high discharge capacities, typically 30 x 10-6 m3/sec to
  90 x 10-6 m3/sec comp...
Vertical drain design




• Terzaghi T90 time factor = 0.848 while assuming soft clay with ch = 2 m²/year:

• without PVD ...
Vertical drain design

• by using:
  - Colbonddrain CX1000
  - 1.6 m triangular centers



  90% consolidations
  in 12 mo...
Equivalent PVD diameter
• calculation assumes PVD cylindrical and draining effect dependent on
  periphery

• PVD effectiv...
Drain spacing


•    triangular spacing standard
      π D2        1
    ---------- = ---- S2 √ 3
        4         2

   ...
Kjellman formula

        D2
• t = ---------
       8 Ch
                  [         D        3
                          ...
Discharge capacity
• maximum flow observed from PVD = 5 x 10-6 m3/s = 158 m3/year.
  Hydraulic gradient approximately 0.1
...
Discharge capacity

•    qw = Q / i   Darcy’s Law (valid for laminar flow only)



where qw is constant: qw ≥ 140 x 10-6 m...
Discharge capacity

• Effect of i on qw : plot of discharge against hydraulic gradient at 360 kPa
                      co...
Disclaimer




  The technical data set forth in this slideshow reflect our
   best knowledge at the time of issue. The sl...
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Pvd Soil Consolidation Design

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Some information and design guide about prefabricated vertical drains

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Pvd Soil Consolidation Design

  1. 1. Technical Presentations Prefabricated vertical drains for Soil Consolidation Vertical drain design www.geosyntheticsworld.com Page 1 of 14
  2. 2. What is a PVD • Prefabricated Vertical Drain - PVD • Typically 95 -100 mm wide by 3 - 5 mm thick • Synthetic core wrapped with geotextile • Many types of core www.geosyntheticsworld.com Page 2 of 14
  3. 3. PVDs shorten drainage path • 90% Consolidation time reduced from >15 years to 1 year www.geosyntheticsworld.com Page 3 of 14
  4. 4. Why use PVD over sand drain • Installation of PVDs typically 6,000 linear meters per day and result in a lower project cost. • No risk of PVDs breaking during installation - sand drains can have discontinuities if mandril is withdrawn too fast. • No risk of shear failure of PVDs during settlement - sand drains are vulnerable to shear failure during settlement. www.geosyntheticsworld.com Page 4 of 14
  5. 5. Why use PVD over sand drain • PVD’s have high discharge capacities, typically 30 x 10-6 m3/sec to 90 x 10-6 m3/sec compared to a ∅ 0.35 sand drain with a discharge capacity of 20 x 10-6 m3/sec (Van Santvoort, 1994). • When installed with purpose designed mandril, smear effects are much smaller for PVDs than for the large diameter sand drains. Zone of smear is directly proportional to the diameter of mandril used for installation. • PVD’s are consistent factory produced whereas sand drains are subject to quality variance of naturally occurring sands. www.geosyntheticsworld.com Page 5 of 14
  6. 6. Vertical drain design • Terzaghi T90 time factor = 0.848 while assuming soft clay with ch = 2 m²/year: • without PVD settlement for U = 90%: T90 d2 0.848 x 10² t = ------------ = ------------------ = 42 years cv 2 www.geosyntheticsworld.com Page 6 of 14
  7. 7. Vertical drain design • by using: - Colbonddrain CX1000 - 1.6 m triangular centers 90% consolidations in 12 months. www.geosyntheticsworld.com Page 7 of 14
  8. 8. Equivalent PVD diameter • calculation assumes PVD cylindrical and draining effect dependent on periphery • PVD effective periphery is 2 x width x f, where f is a correction factor allowing for: − less favorable inflow to possible disturbance & smear effect to soil during installation π • Delft laboratory finds f = ------- 4 2b π b => d = ------ x ------ = ---- π 4 2 where d = equivalent diameter of PVD b = width of PVD www.geosyntheticsworld.com Page 8 of 14
  9. 9. Drain spacing • triangular spacing standard π D2 1 ---------- = ---- S2 √ 3 4 2 D=S √ 2√3 --------- π = 1 . 05 S • for a square grid : D = 1.128 S www.geosyntheticsworld.com Page 9 of 14
  10. 10. Kjellman formula D2 • t = --------- 8 Ch [ D 3 ] ln ( ---- ) - ---- d 4 1 ln ---------- 1 - Uh • where: t = consolation period (years) D = diameter of drained soil cylinder (m) d = equivalent diameter of drain (m) Ch = horizontal consolidation coefficient (m2/year) Uh = average horizontal consolidation degree www.geosyntheticsworld.com Page 10 of 14
  11. 11. Discharge capacity • maximum flow observed from PVD = 5 x 10-6 m3/s = 158 m3/year. Hydraulic gradient approximately 0.1 • reduction in discharge capacity from : – deformation and creep of filter into core – permeability reduction due to clogging of filter and core – bending and kinking of PVD during settlement – pressure on PVD www.geosyntheticsworld.com Page 11 of 14
  12. 12. Discharge capacity • qw = Q / i Darcy’s Law (valid for laminar flow only) where qw is constant: qw ≥ 140 x 10-6 m3/s from test ASTM D4716 www.geosyntheticsworld.com Page 12 of 14
  13. 13. Discharge capacity • Effect of i on qw : plot of discharge against hydraulic gradient at 360 kPa confining pressure for filament core PVD. 70 60 Discharge,Q (ml/s) 50 40 30 20 10 0 0 0.2 0.4 0.6 0.8 1 1.2 Hydraulic gradient, i Q qw = --------- Maximum actual gradient 0.1 i www.geosyntheticsworld.com Page 13 of 14
  14. 14. Disclaimer The technical data set forth in this slideshow reflect our best knowledge at the time of issue. The slideshow is subject to changes pursuant to new developments and findings, and a similar reservation applies to the properties of the products described. We do not undertake any liability for results by usage of these products and information. We do not take any responsibilities. This slideshow is only for general information. www.geosyntheticsworld.com Page 14 of 14

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