Question

Which of the following is provided to check the piping through the foundation of a soil conservation structure?
A. Toe wall
B. Cutoff wall
C. Wing wall
D. Headwall
Choose the correct answer from the options given below

• A. A Only
• B. A and B only
• C. B and C only
• D. C and D only

Hint:

Cutoff wall (upstream/headwall) + Toe wall (downstream apron) increase percolation creep length to eliminate foundation piping.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Piping failure in hydraulic structures is subterranean erosive conduit formation caused by excessive exit hydraulic gradients in foundation seepage lines.
Key Formula or Approach:
\[ L_{\text{creep}} = L_{\text{horizontal}} + 2 \sum d_{\text{vertical cutoff}} \]

Step 2: Detailed Explanation:
To safeguard permanent soil conservation drop spillways and check dams against subsurface piping failure:
1. Cutoff Wall (B): A vertical wall extended below the headwall foundation into impermeable strata to lengthen the subsurface seepage path and reduce exit hydraulic gradient.
2. Toe Wall (A): Constructed at the downstream end of the stilling basin apron, penetrating into the foundation to prevent undermining and exit piping.
(Wing walls and headwalls support earth embankments and retain channel banks).

Step 3: Final Answer:
Thus, Toe wall and Cutoff wall (A and B only) check foundation piping, matching option (B).