## Thursday, December 6, 2012

### DESIGN CHARTS FOR ANCHORED BULKHEADS IN SAND.

Hagerty and Nofal ( 1 992) provided a set of design charts for determining

1. The depth of embedment
2. The tensile force in the anchor rod and
3. The maximum moment in the sheet piling

The charts are applicable to sheet piling in sand and the analysis is based on the free-earth support method. The assumptions made for the preparation of the design charts are:

1. For active earth pressure, Coulomb's theory is valid
2. Logarithmic failure surface below the dredge line for the analysis of passive earth pressure.
3. The angle of friction remains the same above and below the dredge line
4. The angle of wall friction between the pile and the soil is 0/2

The various symbols used in the charts are the same as given in Fig. 20.15 where,

ha = the depth of the anchor rod below the backfill surface
hl =the depth of the water table from the backfill surface
h2 - depth of the water above dredge line
H = height of the sheet pile wall above the dredge line
D = the minimum depth of embedment required by the free-earth support method
Ta = tensile force in the anchor rod per unit length of wall

Hagerty and Nofal developed the curves given in Fig. 20.18 on the assumption that the water table is at the ground level, that is h1 = 0. Then they applied correction factors for h1, > 0. These correction factors are given in Fig. 20.19. The equations for determining D, Ta and M(max) are

The theoretical depth D as calculated by the use of design charts has to be increased by 20 to 40% to give a factor of safety of 1.5 to 2.0 respectively.

Figure 20.15 Depth of embedment of an anchored bulkhead by the free-earth
support method (method 1)

Figure 20.18 Generalized (a) depth of embedment, Gd, (b) anchor force Gt,and (c)
maximum moment Gm (after Hagerty and Nofal, 1992)

Figure 20.19 Correction factors for variation of depth of water h1 (a) depth
correction Cd, (b) anchor force correction Ct and (c) moment correction Cm (after
Hagerty and Nofal, 1992)