Liquefaction Mitigation using GeoComposite Vertical Drains Kyle Rollins and Joshua K.S. Anderson Brigham Young University Civil & Environmental Engineering Dept Provo, Utah, USA
Acknowledgements • NCHRP-IDEAS Program • Nilex, Inc. • ConeTec, Inc.
Liquefaction Mitigation by Densification Versus… Vibro-Compaction Stone Columns Dynamic Compaction Compaction Grouting
Liquefaction Mitigation by Drainage Liquefiable Sand Drains
EQ Drain Anchor Plate Hollow Steel Mandrel Drain Installation
Potential Problems with Conventional Densification • Expensive and time consuming effort • Cost increases and success decreases as fines content increases. • Cost of improvement increases as initial blow count increases. • Improved density may be overestimated by conventional penetration correlations.
Potential Advantages of Earthquake Drains • Reduced cost of installation • Shorter installation time • Greater flow capacity than stone columns • Densification during drain installation • May provide mitigation for silty sands that are difficult to densify
PROJECT OBJECTIVES • Evaluate ability of drains to dissipate excess pore pressures. • Evaluate ability of drains to reduce liquefaction-induced settlement. • Provide case histories to validate/calibrate computer models.
Test Site Locations Vancouver, B.C. Treasure Island, CA
Treasure Island Test Site Downtown San Francisco Test Site
Cluster 4 Cluster 3 Cluster 5 (Wick Drains) Cluster 2 (Wick Drains) Cluster 1 Cluster 6 Cluster 7 Blast Holes Cluster 8 Settlement Stakes Blast-Induced Settlement in Treated Area
Cluster 4 Cluster 3 Cluster 5 (Wick Drains) Cluster 2 (Wick Drains) Cluster 1 Cluster 6 Cluster 7 Blast Holes Cluster 8 Settlement Stakes Blast-Induced Settlement 20 40 60 80 100
Vancouver BC Test Site Vancouver CANLEX Test Site EQ Drain Test Site MasseyTunnel
1.22 m 4 Blast Holes at 5 m radius Layout for EQ Drain Test Areas
Comparison of qc with Time Low Vibration High Vibration
ANALYSIS OF TEST RESULTS • Calibrate model with measured response from blast event. • Compute expected response from earthquake event.
Input Parameters for FEQDrain Analysis • Soil Layering • Hydraulic Conductivity, K • Modulus of Compressibility, Mv • Drain Properties • Nq/NL, Stress Cycle Ratio • Td, Earthquake Duration
Keep Ru in this Range Variation of Compressibility (Mv) with Ru (Seed et al,1976)
Conclusions Relative to Drains • Significant densification provided. • Rate of dissipation increased. • Settlement can be reduced for low Ru. • Drain layout must be designed for anticipated earthquake.