asce geopier presentation march 2015
TRANSCRIPT
Ground Improvements for Challenging Sites in Orange County
Compacted Aggregate Piers (Geopier/Rammed Aggregate Pier)
Outline
1. Compacted aggregate pier basics
2. Two Case Studies
• The Park Apartments
• Park Place Apartments
3. Construction QA/QC
4. Questions and Discussion
Proprietary (Trade Names):
• Geopier - Rammed Aggregate Pier
• TerraRam
• GeoRam
• VibroPier
• Earth Pier
• Etcetera Etcetera Pier
Geopier drill
Geopier Tamper
Skid steer
Mobile crew (4 people, 3 machines)
Rapid installations (30 – 50 per day)
Safe, clean, dry process (no jetting!)
Installation depths up to 30 feet
Geopier GP3™ Construction
Engineering Aspects
• Not a foundation system
• Improve near surface soil
• Increased bearing capacities below foundations and slabs-on-grade
• Reduced settlements
Settlement Within Compacted Aggregate Zone
Design based on spring analogy:
Rigid footing: Geopier deflection & matrix soil deflection
Stiff spring (RAP element) takes more load than soft spring (matrix soil).
Use conventional geotechnical analysis approaches:
Estimate footing-induced stress (Westergaard, Boussinesq, etc)
Estimate soil compressibility
Traditional elastic or consolidation design methods.
Add lower zone and upper zone for total settlement
Settlement Below Aggregate Piers (Lower Zone)
B
2B
HLZ
HUZ
Design Process
• Foundation Loads
• Settlement tolerances
• Onsite soil properties
• Collaboration
– Geotechnical consultant
– Structural engineer
– Aggregate pier designer/builder
The Park Project • 1500 apartment units on 29-acres
• 4-story wood framed apartment buildings over 2 levels of partial subterranean parking (podium)
• Column loads 380 to 1156 KIPS
The Park---site conditions
• Relatively flat site
• Historically used for agriculture
• Explored with hollow-stem borings and CPT’s
• Groundwater wells.
• Underlain by deep alluvium
• Interlayered silts, sands, clays
• Groundwater at 15 to 30 feet BGS
Geotechnical Issues
• Groundwater below subterranean levels
(5 to 10 feet)
• Reduced bearing capacities
• Differential foundation loads and differential settlements
Alternatives
× Piles infeasible
× Remedial Grading---groundwater
× Matt foundation ($7 million)
Ground improvement---aggregate piers
Geopiers at The Park
• 2,400 piers
• 30-inch diameter
• 11 to 13 feet deep
• 50 to 60 working days
• Savings over mat foundation: $3 million
Acknowledgements
Project Owner: Irvine Company
Specialty Contractor: Geopier
Structural Engineer: Van Dorp Chow
Park Place Project
• 980 units on 14-acres
• 4-story wood framed buildings
• 2-levels, partially subterranean, reinforced concrete parking below
• Column loads: 94 to 807 kips
• Wall loads: <12.5 kips/l.f.
Park Place --Site Conditions
• Relatively flat site
• Formerly MARSHLAND (swamps)
• Underlain by PEAT/organic clays, alluvium
• Groundwater at 20 to 30 feet BGS
Geotechnical Issues
• Very low bearing capacities
• 4 inches total settlement in alluvium (2 inches differential)
• Mat foundations infeasible over marsh soils
• Conventional aggregate piers inadequate in marsh deposits (peat)
Geopiers at Park Place
• 4,798 piers
• 24-inch diameter
• 9 to 13 feet deep
• Cement Treated Piers (474)
in MARSH Deposit areas
• Cement Treated Piers---up to 30’ deep
Acknowledgements
Project Owner: Irvine Company
Specialty Contractor: Tensar-Geopier (Western Ground Improvement)
Structural Engineer: HCDA Engineering, Inc.
Construction QA/QC
• Aggregate properties
• Surface logging of excavated soil
• Pier depths
• Pier locations
Purpose: Measure Stiffness (kg)
W-Beam
Uplift Anchor Rod
100 Ton Jack
Uplift Anchor Pier Telltale Compression Pier
Insitu Modulus Test