8/27/2014
Design/Construction Considerations for Tied-back Shoring Systems Structural Engineers Association of Ohio September 11, 2014 Presented by
Richard Goettle, Inc.
Design/Construction Considerations for Tied-back Shoring Systems A. B. C. D. E. F. G.
Tieback Wall Components Lateral Earth Pressure Design Considerations Soldier Pile / Anchor Design Lagging Design Anchor Testing Requirements Bottom of Excavation Considerations Case Study
Jonathan Huff, P.E.
Design/Construction Considerations – Soldier Piles
Design/Construction Considerations – Soldier Piles
Design/Construction Considerations – Soldier Piles
Design/Construction Considerations – Soldier Piles
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Design/Construction Considerations - Tiebacks
Design/Construction Considerations for Earth Retention Systems
Design/Construction Considerations for Earth Retention Systems
Design/Construction Considerations for Earth Retention Systems
Proper Site/Subsurface Exploration
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Design Criteria
Design Criteria – Lateral Earth Pressure
Design Criteria
Design Criteria
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Design Criteria
Soldier Pile / Anchor Design • Moment Reduction in Soldier Piles
No need to factor lateral earth pressures derived from these pressure envelopes in LRFD designs!!!
Soldier Pile / Anchor Design
• With multiple rows of highly loaded anchors, must check soldier pile as a beam-column • Must check the soldier pile embedment for resistance to vertical component of the anchor load(s).
Soldier Pile / Anchor Design
• Design the stressing zone length to ensure the bond zone is beyond the potential failure plain. • Bond zone material considerations • Anchor grout considerations, ie: non-shrink, sufficient strength prior to testing. • Overstressing of the anchors verifies the strength of the surrounding components, ie: wedge plates, bearing plates, etc.
Lagging Design
Lagging Design Foundation Design, Wayne C. Teng; Prentice Hall, Inc., 1962 Chapter 13, page 396. The most significant sentence states “Lagging is seldom subject to high bending stress, even if the calculated value is high.” Foundation Engineering by Peck, Hanson and Thornburn, 2nd Edition, 1974, Chapter 27 applies to our discussion. On pages 470471 the authors offer a suggested method for the design of lagging. However, they state that the results are likely to be over conservative because of arching. The suggest that the dimensions of the lagging should be selected on the basis of experience.
Often, the wood or precast lagging is designed by experience, by the contractor
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Lagging Design
Lagging Design
Queen City Tower – Cincinnati, OH – 65’ excavation with 3” thick wood lagging
Anchor Testing Considerations
Anchor Testing Considerations
• Ensure that properly sized and recently calibrated ram, jack, load cell, etc are used. Keep all observers away from the testing operation. • Some specifications require that tieback anchors be proof tested to 150% of the design load. • Since all anchors are tested, this requirement is too high and adds no benefit. • The industry standard specification for anchor tendon material indicates that the maximum design load cannot exceed 60% GUTS and the maximum test load should not be greater than 80% guts. • Dividing the two limits indicates that a 133% test load would satisfy both requirements (.80/.60=1.33). Specifying a higher test load requires a larger anchor tendon just to satisfy the test load. • Since all anchors are tested, is it really worth the extra cost just to test to 150%?
Anchor Testing Requirements
Bottom of Excavation Considerations
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Bottom of Excavation Considerations
Bottom of Excavation Considerations
Case History
Case History
Case History
Case History
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Case History
Case History
Case History
Case History
Case History
Case History
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Thank You! Questions?
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