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

Generic:

• compacted aggregate pier

• compacted aggregate caisson

• compacted aggregate column

Basic Concept

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

Two Project Applications

1.The Park

2.Park Place

The Park Apartments

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 Apartments

Park Place

San Diego Creek

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

MARSH DEPOSITS Older Alluvium

Groundwater

Structure

Younger Alluvium

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

Discussion/Questions