Question

A geotechnical engineer has determined that the factor of safety of a sand slope is equal to 0.9. This means that the slope is not stable. Geotechnical field investigations have shown that this low factor of safety is due to the high position of the groundwater table. The geotechnical has decided to install horizontal drains in the slope to drop the groundwater table, and thus increase the factor of safety from 0.9 to 1.1 (required design factor of safety). Determine the following design parameters of the horizontal drains by using the design charts for 0.5<Hu<0.7
- Optimal drain length (L)
- Optimal drain spacing (S)
- Optimal drain inclination
- Optimal drain type (made of PVC or steel)
Data: slope height (H) = 20 m; Slope length > 4H

Answer 1