BRIDGE ANCHORAGE (Contd)
LENGTH OF DEADMAN
Deadmen are designed to have lengths which enable them to resist the breaking
strength of the cable attached to them. The required length and thickness are based
on allowable soil bearing with 1 ft (0.3 m) of length added to compensate for the width
of the cable trench. The formula for the determination of deadman length Dt is:
Dt = CC + 1
(HP x Df)
where CC is cable capacity (breaking strength) HP is the required
holding power of the deadman.
Df is the deadman face in feet (for log deadmen, use log diameter).
This is the general formula for the determination of the required deadman length in
all circumstances. In Appendix C of TC 5-210, the values for CC and HO have been
divided by 1,000 for ease of calculation. Actual breaking strengths (CC) or cables were
provided in table 7. The actual holding power of deadmen in loamy soil is provided in
Table 9 assumes the deadman will be buried in loamy
soil. For rock or hardpan soil, multiply the values in
table 9 by a factor of 5. For fine-grained or sandy soil,
multiply these values by a factor of 1/2.
The tower-to-deadman slope used in table 9 represents an approximation of the
slope of the cable running from the tower to the deadman, as shown in figure 16. Since
this value cannot be accurately measured until the exact location of the deadman is
known, an estimation is made. The tower-to-deadman slope should fall between a 1:1
slope (45 degrees) and a 1:4 slope (14 degrees). If it is not possible to obtain an accurate
estimate, then assume the worst case (1:1) slope.
REQUIRED HOLDING POWER (HP) IN LB/SQ FT
DEPTH OF DEADMAN (DD)
Notes: 1. For hardpan or rock, multiply the HP by 5.
2. For fine-grained soils with high moisture content, multiply the HP by
Table 9. Holding Power of Deadmen in Loamy Soil.