TM 5-818-1 / AFM 88-3, Chap. 7
Table 14-3. Design Considerations for Braced and Tieback Walls
Design Factor
Comments
1. Earth loads
For struts, select from the semiempirical diagrams (fig . 14-10); for walls
and wales use lower loads - reduce by 25 percent from strut loading.
Tiebacks may be designed for lower loads than struts unless preloaded to
higher values to reduce movements
2. Water loads
Often greater than earth load on impervious wall.Should consider possi-
ble lower water pressures as a result of seepage through or under wall.
Dewatering can be used to reduce water loads
3. Stability
Consider possible instability in any berm or exposed slope.Sliding po-
tential beneath the wall or behind tiebacks should be evaluated. Deep
seated bearing failure under weight of supported soil to be checked in
soft cohesive soils (fig. 14-12)
4. Piping
Loss of ground caused by high groundwater tables and silty soils.
Difficulties occur due to flow beneath wall, through bad joints in wall,
or through unsealed sheetpile handling holes. Dewatering may be
required.
5. Movements
Movements can be minimized through use of stiff impervious wall supported
by preloaded tieback or braced system. Preloads should be at the level
of load diagrams (fig. 14-11) for minimizing movements
6. Dewatering - recharge
Dewatering reduces loads on wall systems and minimizes possible loss of
ground due to piping. May cause settlements and will then need to re-
charge outside of support system. Not applicable in clayey soils
7. Surcharge
Storage of construction materials usually carried out near wall systems.
Allowance should always be made for surcharge, especially in upper
members
(Continued)
14-15
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