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Design/Construction Considerations

for Tied-back Shoring Systems

Structural Engineers Association of Ohio

September 11, 2014

Presented by

Richard Goettle, Inc. Jonathan Huff, P.E.

A. Tieback Wall Components

B. Lateral Earth Pressure Design Considerations

C. Soldier Pile / Anchor Design

D. Lagging Design

E. Anchor Testing Requirements

F. Bottom of Excavation Considerations

G. Case Study

Design/Construction Considerations

for Tied-back Shoring Systems

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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No need to factor lateral earth pressures

derived from these pressure envelopes

in LRFD designs!!!

Design Criteria

• Moment Reduction in Soldier Piles

• 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

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.

Soldier Pile / Anchor Design

Often, the wood or precast lagging is designed by experience, by the contractor

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 470-

471 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.

Lagging Design

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Queen City Tower – Cincinnati, OH – 65’ excavation with 3” thick wood lagging

Lagging Design Lagging Design

• 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 Considerations Anchor Testing Considerations

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?