GRI-GC16 Standard Specification for Prefabricated Vertical Drains (PVDs)

• also called “wick drains”, or “strip drains”

• usually deployed vertically, but other orientations are sometimes used

• provides for rapid in-situ consolidation of saturated foundation soils; no depth limitation

• the function is drainage of excess pore water

• both theory and testing are fully developed

General PVD Properties

• generally 100 mm wide and 3 to 5 mm thick

• length wrapped on coils is 100 m or longer

• drainage core is either PP, PS or PA

• many available surface patterns

• geotextiles encapsulate core; usually HB-NW

• GTs are thermal bonded or adhesive seamed

• many products are available worldwide

Test Properties Included in Spec

Entire Composite; Drainage Core and Geotextile 1. dimensions (all measured directly) 2. discharge capacity 3. tensile strengths at 5%, 10% and 50% (or break)

Geotextile by itself 4. permittivity 5. apparent opening size 6. grab tensile strength and elongation 7. puncture strength (CBR) 8. trapezoidal tear 9. UV resistance

1. Dimensions

• width and thickness are measured by caliper

• length by tape measure

Assortment of prefabricated vertical drains (PVDs)

2. Discharge Capacity

• follows ASTM D4716; the transmissivity test

• actually measures planar flow rate

• flow box width must be modified for a single PVD; alternatively use three PVDs side-by-side

• normal stress is 50 kPa (using soft boundaries)

• flow is measured at a hydraulic gradient of 1.0

• value must be 6.0 lpm (1.6 gpm)

A flow rate testing device

Schematic diagram of flow rate testing device

Transmissivity device for measuring discharge capacity (parallel or in-plane flow)

Test

specimen

3. Tensile Strength

• evaluate composite PVD; i.e., core and GT covering

• follows ASTM D4595 (using single PVD)

• requires tensile strength at 5%, 10% and 50% elong.

• if break occurs below 50% provide commentary

Photographs of Tensile Strength of Various PVDs

PVD-A Max Load: 2.694 kN

PVD-E Max Load: 1.417 kN

PVD-M Max Load: 2.940 kN

4. Permittivity of GT

• follows ASTM D4491

• uses deaired water ( 6 ppm dissolved oxygen)

• measures flow rate/unit area

• constant head of 50 mm (2.0 in.)

• results in permittivity, = (k)(t)

• value must be 0.8 sec-1

ASTM D4491 – Water Flow Rate (Permittivity) Device

Specimen Being Placed

Adjusting Hydraulic

Head

Measuring Flow Rate

5. Apparent Opening Size of GT

• a dry bead sieving test per ASTM D4751

• AOS is sometimes called EOS

• it’s a maximum value, i.e., “MaxARV”

• converted to either 095 in mm, or closest equivalent U. S. sieve size

• must be 2.10 m

• this is equivalent to #70 sieve size

ASTM D4751 AOS Test Sieves

Being Shaken

Bottom Pan With

Beads That Passed Fabric

6. Grab Tensile Strength of GT

• follows ASTM D4632

• 10 specimens MD & XMD across width

• 100 mm wide; gripped in center 25 mm

• must avoid slippage or grip failure

• strength 500 N (112 lb) and elongation 50%

D4632 - Grab Tensile Test

7. Puncture Strength of GT

• California Bearing Ratio (CBR) is a soil strength test adopted for the puncture of geosynthetics

• follows ASTM D6241 using the same device but modified with bolted flanges

• probe is 50 mm (2.0 in.) diameter

• container is 150 mm (6.0 in.) diameter

• 10 specimens across roll width

• strength must be 550 N (125 lb)

D6241 - Puncture (CBR) Strength

8. Trapezoidal Tear Strength of GT

• follows ASTM D4533

• tear propagates from an initial cut

• maximum value is recorded

• 10 specimens in MD and XMD across roll width

• take average value of lowest peak

• strength must be 245 N (55 lb)

D4533 - Trapezoidal Tear Strength

9. Ultraviolet Resistance of GT

• uses commercial laboratory weathering devices

• follows ASTM D7238

• called “ultraviolet fluorescent device”

• 20 hr. UV cycle at 75°C, then 4 hr. condensation at 60°C at 340 mm wave length

• requires 70% grab tensile strength after 1000 hr.

• frequency is once per year

ASTM D7238 Ultraviolet

Fluorescent Weathering Device

Regarding Individual Test Frequency

• composite PVD frequency is per specific test method to obtain minimum average

• GT (by itself) is based on MARV, except AOS which is MaxARV

• this is a negotiated concept, but accepted throughout GT industry… but only for GTs

• complete details shown in GSI White Paper #10

Regarding MARV

• minimum average roll value

• accommodates variation in GT manufacturing properties

• statistically it’s the “-2” value

• MaxARV is the “+2” value

• procedure shown in next screens

SAMPLE

Field Sampling to Obtain

Average Roll Value

Roll

Width

1.0 m

S-1 S-2

S-3 S-4

S-5 S-6

S-7

Roll

length

XMD

MD

MD

1.0 m

Sample

XMD

Take Specimens from above Sample and Test as Required

Test

Number

Roll Number

1 2 3 4 5 6

1

2

3

4

5

6

7

Average =

643N

627

652

629

632

641

662

641

627N

615

621

616

619

621

622

620

637N

643

628

662

646

633

619

638

642N

646

658

641

635

642

658

646

652N

641

639

657

642

651

641

646

637N

624

631

620

618

633

641

629

This is the MARV Value!

Property ASTM Method Value MQC Testing Frequency

Composite Product

Discharge capacity1

Roll length

Roll width

Tensile strength @ 5%

Tensile strength @ 10%

Tensile strength @ 50 % or break

D4716

direct measure

direct measure

D4595 (modified)2

D4595 (modified)2

D4595 (modified)2

6.0 lpm (1.6 gpm)

200 m (660 ft.)

100 mm (4.0 in.)

500 N (110 lb)

700 N (150 lb)

1000 N (225 lb)

2500 m (8200 ft)

2500 m (8200 ft)

2500 m (8200 ft)

2500 m (8200 ft)

2500 m (8200 ft)

2500 m (8200 ft)

Geotextile (by itself)

Permittivity

Apparent opening size

Grab tensile strength

Grab tensile elongation

Puncture strength (CBR)5

Trapezoidal tear

UV resistance after 1000 hr.

D4491

D4751

D4632

D4632

D6241

D4533

D7238

0.8 sec-1

210 m (#70 sieve)

500 N (112 lb)

50%

550 N (125 lb)

245 N (55 lb)

70%5

MARV3

MaxARV4

MARV

MARV

MARV

MARV

yearly

1. In an as-received condition with a normal stress of 50 kPa (72 psi) and hydraulic gradient of 1.0. In this regard, core kinking (ASTM D6918) reduction of discharge capacity must be independently evaluated and included in the design as a reduction factor (this is a design decision; see DwG for a procedure)

2. Modification to ASTM D4595 is changed from 200 mm (8 in.) to 100 mm (4 in.) wide specimen 3. Minimum Average Roll Value (ASTM D4439) 4. Maximum Average Roll Value (ASTM D4439) 5. Refers to grab tensile strength of geotextile by itself

Table 1. Prefabricated Vertical Drain (PVD) Specification