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

Transcription

1 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

2 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

3 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

4 1. Dimensions width and thickness are measured by caliper length by tape measure Assortment of prefabricated vertical drains (PVDs)

5 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)

6 A flow rate testing device Test specimen Schematic diagram of flow rate testing device Transmissivity device for measuring discharge capacity (parallel or in-plane flow)

7 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

8 Photographs of Tensile Strength of Various PVDs PVD-A Max Load: kn PVD-E Max Load: kn PVD-M Max Load: kn

9 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

10 ASTM D4491 Water Flow Rate (Permittivity) Device

11 Specimen Being Placed Adjusting Hydraulic Head Measuring Flow Rate

12 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 0 95 in mm, or closest equivalent U. S. sieve size must be 2.10 m this is equivalent to #70 sieve size

13 ASTM D4751 AOS Test Sieves Being Shaken Bottom Pan With Beads That Passed Fabric

14 6. Grab Tensile Strength of GT follows ASTM D 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%

15 D Grab Tensile Test

16 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)

17 D Puncture (CBR) Strength

18 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)

19 D Trapezoidal Tear Strength

20 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

21 ASTM D7238 Ultraviolet Fluorescent Weathering Device

22 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

23 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

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25 MD Roll length XMD Field Sampling to Obtain Average Roll Value SAMPLE 1.0 m Roll Width 1.0 m S-1 S-2 S-3 Sample XMD S-4 MD S-5 S-6 S-7 Take Specimens from above Sample and Test as Required

26 Test Number Roll Number N 627N 637N 642N 652N 637N Average = This is the MARV Value!

27 Table 1. Prefabricated Vertical Drain (PVD) Specification Property ASTM Method Value MQC Testing Frequency Composite Product Discharge capacity 1 Roll length Roll width Tensile 5% Tensile 10% Tensile 50 % or break Geotextile (by itself) Permittivity Apparent opening size Grab tensile strength Grab tensile elongation Puncture strength (CBR) 5 Trapezoidal tear UV resistance after 1000 hr. D4716 direct measure direct measure D4595 (modified) 2 D4595 (modified) 2 D4595 (modified) 2 D4491 D4751 D4632 D4632 D6241 D4533 D 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) 0.8 sec m (#70 sieve) 500 N (112 lb) 50% 550 N (125 lb) 245 N (55 lb) 70% m (8200 ft) 2500 m (8200 ft) 2500 m (8200 ft) 2500 m (8200 ft) 2500 m (8200 ft) 2500 m (8200 ft) MARV 3 MaxARV 4 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