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Underpinning and Strengthening of Foundations

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Instructor Information: Alexander Newman, P.E., F.ASCE

Course Length: 1.5 Hours

This webinar was co-sponsored by ASCE's Structural Engineering Institute and ASCE Continuing Education 

Purpose and Background

Many renovation projects involve strengthening of foundations. Whenever an increase in gravity loading or a lateral load retrofit is proposed, foundation strengthening is likely to follow. Underpinning – lowering or enlarging an existing foundation – is a basic technique of foundation strengthening. Underpinning of existing foundations is particularly common when new construction occurs nearby.

There are few standards dealing with strengthening of foundations, and many designers are looking for some relevant references. Whether you are one of them, or simply want to validate the practices that your firm follows, this webinar will help. The webinar’s objective is to provide a concise yet practical primer on foundation strengthening and underpinning practices in the United States. The presentation offers a broad overview of everyday challenges associated with this work, supplemented by a host of practical design details and several case studies.

The webinar begins with an overview of the reasons foundations require strengthening. After explaining the basic philosophy of foundation strengthening and underpinning, the instructor examines the available approaches in detail. The first one is an often overlooked but typically cost-effective method of adding structural supports in lieu of strengthening existing foundations. Next on the agenda is shoring and replacement of foundations with larger or deeper ones, followed by other techniques.

The largest webinar segment is devoted to underpinning, including both the “pit” variety and the various methods using drilled piers, micropiles, and proprietary piers. The webinar concludes with final questions and answers from the audience.

Learning Outcomes/Benefits

  • Learn various methods of strengthening building foundations
  • Understand where pit underpinning might be appropriate and where other strengthening methods should be more useful
  • Examine the available techniques for strengthening rubble foundations
  • Find out how minipiles and proprietary piers can help strengthen foundations
  • Learn about the modern methods of soil improvement that can be used in lieu of the conventional underpinning techniques

Intended Audience

Structural and civil engineers and other design and construction professionals seeking to learn about underpinning and strengthening of foundations will benefit from this webinar.

Webinar Outline

  • Introduction: Why strengthen foundations
  • General approach and methods
  • Adding supports
  • Shoring and replacement
  • Underpinning
    – Pit underpinning
    – Using drilled piers, minipiles, proprietary piers
  • Enlarging footings
  • Other strengthening topics
  • Modifying soil properties
  • Conclusion