Anchored sheet pile, free earth procedure

Uses of sheet piles

• Retaining walls for waterfront structures (quay walls, bulkheads, jetties).
• Temporary support of excavations (braced cuts and trenches).
• Cofferdams for bridge piers and underwater foundations.
• Cut-off walls under dams, seepage control, flood protection.
• Protection against scour and for river training, and landfill containment.

Free earth support method (granular soil)

Assumption: the pile tip is free to rotate (no fixity); the active pressure acts on the full height $(H+D)$ on the back, passive pressure acts only in front; the wall is simply supported by the anchor and the passive resistance.

1. Compute $K_a = \tan^2(45^\circ-\phi/2)$ and $K_p = \tan^2(45^\circ+\phi/2)$; use $\gamma'$ below water table and include surcharge and water pressure.
2. Draw the active pressure diagram on the back from top to depth $H+D$ and the passive pressure diagram in front from the dredge line to depth $D$ (using $K_p/FS$ if a factor of safety is applied to passive resistance).
3. Find the active resultant $P_a$ and its lever arm from the anchor level.
4. Find the passive resultant $P_p$ (in terms of $D$) and its lever arm from the anchor.
5. Take moments about the anchor point: $P_a\, l_a = P_p\, l_p$ and solve for the embedment $D$ (trial and error).
6. Find the anchor force per metre $T$ from horizontal equilibrium: $T = P_a - P_p$.
7. Increase $D$ by 20-30% for the design depth, then find the maximum bending moment (at zero shear) and select the sheet pile section from $Z = M_{max}/\sigma_{allow}$.