"A slope on a road was identified as being potentially unstable. The situation worsened when tension cracks were sighted near crest of the slope. Incessant rainfall was thought to be part of the factors contributing the instability. The stability of this particular slope was critical because it was located immediately across the road from two blocks of apartments, each housing approximately 5,000 people.

the steep slopes on the left and the apartment blocks on the right which shows a 60 m high slope with three 20 m high benches. The overall slope angle is 50° and the individual bench faces are inclined at 70° to the horizontal. The affected slope’s length is 250 m. Tension cracks are frequently observed behind the crest of slopes. The critical slip line was estimated to be at 35° from the horizontal."

how can i determine the number of borings to be perfomed? and how can i determined the depth of the borings should be??