Drainage Engineering and Salt Management

In synthetic and gravel envelope design for corrugated plastic drainage tubing, the bridging criterion (preventing base soil piping into envelope voids) requires that envelope $D_{15}$ and base soil $d_{85}$ satisfy:

Options:

• (A) $\frac{D_{15}}{d_{85}} \le 4 \text{ to } 5$
• (B) $\frac{D_{15}}{d_{85}} \ge 50$
• (C) $D_{15} = d_{85} \times 100$
• (D) $D_{15} \le 0.001 d_{85}$