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Evaluating Wick Drain Performance in Virginia Soils

Evaluating Wick Drain Performance in Virginia Soils

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Evaluating Wick Drain Performance in Virginia Soils

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  1. Evaluating Wick Drain Performance in Virginia Soils Susan E. Burns Matthew J. Cline

  2. Prefabricated Vertical Drain Study Tasks • Review of literature to assess the current state of knowledge on PVD testing in the laboratory. • Acquisition of soils and PVDs for the test program. • Laboratory characterization of the soils. • Quantification of the flowrate through the PVDs with the drains in the vertical position and with a 90 bend. • Quantification of the flowrate through the PVDs as a function of applied lateral stress after compaction in each of the soil types studied. • Quantification of the consolidation properties of four soils with and without the presence of PVDs.

  3. PVD Core Types Tested

  4. PVD Properties *All fabric and cores made from polypropylene**Amerdrain – ASTM D 4632; Mebra-Drain – ASTM D 638*** ASTM D4716

  5. Soil Characterization • Clay samples from: • Route 1/I-95 Interchange Alexandria, VA (VDOT) • West Point, VA (VDOT) • Craney Island, VA (VGS) • Silty sand (Charlottesville, Virginia)

  6. Silty Sand

  7. Atterberg Limits for Clay Samples

  8. Compression Indices from Consolidation Testing (Clay Samples)

  9. PVDs Used in Crimp Testing

  10. Vertical Discharge Capacity - Hydraulic • Vertical water flow • Constant head 1 kPa (1.45 psi) • Measure flowrate through wick • Crimp with a 90° bend, measure flowrate • Measure flowrate through empty heat shrink Flow Flow

  11. Vertical Discharge – PVD Methodology • PVDs encased in heat shrink tubing • Uniformity critical • Insert wick into heat shrink • Clamp into aluminum plates, with spacers • Heat aluminum to shrink tubing

  12. PVD Discharge Capacities

  13. Flow Reductions for Six PVDs - Crimped

  14. Summary - Crimp Testing • Tests with flow from bottom to top (saturated flow) did not show significant differences in result • Uncrimped: • Highest flowrates: Mebra-Drain MD-88 and MD-7407 • Lowest flowrates: AD407 and AD407F • Crimped • AD607 (high strength fabric) and MD-88 (fin core) had highest flowrate • Experienced a lower reduction in flowrate in the crimped position compared to other drains • AD407F (drain with the lowest flowrate in the uncrimped position) also had the greatest percentage reduction and lowest flowrate in the crimped position

  15. Discharge Capacity Under Lateral Stress • Conforms to ASTM D4716 • Compact soils at optimum water content; apply range of stresses confining PVD • Flow water using constant head reservoir with a gradient of 1 • Measure discharge under increasing lateral stress up to 276 kPa (40 psi) • Data normalized to flow at zero lateral stress

  16. Stress Applied to PVD Lateral Stress Test Cell

  17. Ongoing Lateral Pressure Test

  18. Lateral Pressure Test Results Craney Island West Point

  19. Lateral Pressure Test Results Woodrow Wilson Bridge Silty Sand

  20. Summary – Lateral Pressure Tests • Corrugated and fin cores - essentially no dependence on lateral stress • Up to 276 kPa (40 psi) • AD417 Dimple core drain • Consistently reduced flowrates of 25% to 50% compared to the value measured at zero applied lateral stress

  21. Quantification of Consolidation Properties with and without PVDs • Six consolidation tests (5 with PVDs and 1 control) were run in each soil type (24 tests) • Clay samples slurry packed at liquid limit • Silt compacted at optimum water content and soaked to saturate

  22. Preparation of Consolidation Samples Slurry packed clay with partial wax cover (forces drainage through PVD).

  23. Preparation of Consolidation Samples Clay specimen ready for consolidation testing. Completed wax layer is covered by sand drainage blanket. Loading plate rests on drainage blanket.

  24. Typical Consolidation Test Results

  25. Consolidation Test Results • t90 for each test in the clay soil was calculated using the square root of time method • t90 defined for the case of vertical drainage, the graphical construction technique provided a useful method to compare the different tests performed. • PVDs in the soil consistently reduced the value of t90 to between 7% and 20% of the t90 values determined in the control tests • Amerdrain 407F & 607 provided the lowest t90 values, while the Mebra-Drain MD-7407 provided the highest values of t90, even with the exceptionally low value measured for the MD-7407 in the West Point soil

  26. t90 Values Determined for Each Consolidation Test

  27. t90 Values by Soil Type

  28. PVD Performance Data in Terms of t90

  29. t90 Values by PVD Type

  30. Summary – Consolidation Testing • Amerdrain 407F and 607 produced the most consistent and the lowest values of t90 (averages of 11% and 9% of the control values, respectively) • Mebra-Drain MD-88 and Amerdrain AD417 produced intermediate values (averages of 17% and 19% of the control values, respectively) • Mebra-Drain MD-7407 produced the highest value of t90, at an average of 24% of its control test value.

  31. Test Summary / Conclusions (1/3) All costs quoted for 2003

  32. Test Summary / Conclusions (2/3)

  33. Test Summary / Conclusions (3/3) • Amerdrain AD607 consistently exhibited superior performance: • Largest average reduction in t90 (t90 with the drain  9% t90 of control) during consolidation testing • One of the lowest reductions in flow capacity in the crimp test (20%) • $0.14/ft • Mebra-Drain MD-88 also performed well: • Least reduction in flow capacity in the crimp test (17%) • Good performance in the consolidation tests (t90 with the drain  17% t90 of control) • $0.11/ft