Aggregate Pier Design & Construction Wentworth Institute of - - PowerPoint PPT Presentation

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Aggregate Pier Design & Construction Wentworth Institute of - - PowerPoint PPT Presentation

Sep 18, 2022 523 likes •801 views

haywardbaker.com Aggregate Pier Design & Construction Wentworth Institute of Technology | Beatty Hall | Boston, MA Kevin Dawson, PE, Vice President, New England Area Manager Presentation Outline What Wrap Up Why How When Design

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haywardbaker.com

Aggregate Pier Design & Construction

Wentworth Institute of Technology | Beatty Hall | Boston, MA

Kevin Dawson, PE, Vice President, New England Area Manager

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Presentation Outline

What Why When How

  • Design
  • Installation

Wrap Up

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What

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Vibro Piers = Aggregate Piers

  • Also known by names such as GeoPier, Rammed

Aggregate Pier, Short Aggregate Pier, Compacted Aggregate Piers, Stone Column and others

  • Piers or columns of dense aggregate installed as

foundation elements to support light to medium loads

  • Often referred to as an intermediate foundation

system, i.e. not shallow but also not deep

  • Usually about 24 to 42 inches in diameter and

about 10 to 30 feet deep

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Aggregate Piers: How they work

  • Aggregate piers form a composite

system with the surrounding soil

  • When confined laterally, the

aggregate pier is much stronger and stiffer than the surrounding soil

  • Higher modulus columns attract

load and dissipate it gradually with depth

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This Not This

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Why

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reduce total & differential settlement Increase allowable bearing capacity

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When

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Selection of Ground Improvement Techniques

Soil Type Governs the Ground Improvement Technique

Mine Spoils Loose Sand Undocumented Fill Low Strength Cohesive Soils

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Commercial & Industrial Historic Land Use

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Filled Land & Former Industrial & Commercial Land Use

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Private Industrial Site Redevelopment

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Public Redevelopment – Filled Industrial Land

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When Summary

  • Undocumented fill or loose soil less than 30’ thick
  • Appropriate loads (deep foundations or alternate ground

improvement technique not required)

  • Less expensive alternate ground improvement techniques not

viable

  • Cost/schedule impact of excavation and replacement not viable
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How; Design

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Aggregate Pier Design Methodology Design based on spring analogy:

– Rigid footing: aggregate pier deflection equals matrix soil deflection – Stiff spring (aggregate pier) takes more load than the soft spring (matrix soil)

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www.HaywardBaker.com

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Total Settlement = Settlement from the Improved Zone + Settlement from the Unimproved Zone

IMPROVED ZONE UNIMPROVED ZONE

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Pier Testing: Modulus Verification Test

Testing done either with a load frame and anchors or utilizing the vibratory rig as a counterweight

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How; Installation

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Wrap Up

  • Cost effective intermediate foundation solution

for fill & loose native soil sites

  • Know the limits of the system
  • Alternate ground improvement systems or deep

foundations may be best match for thick soft soil deposits or if improvement depth > 30’

  • Market is extending the use of aggregate piers
  • Understand the risk/reward relationship