gri-gc16 standard specification for prefabricated...
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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