Which of the following factors does NOT contribute to slope failure?

The factor that does not contribute to slope failure is the use of proper drainage techniques. Proper drainage is crucial in managing water flow and reducing the accumulation of water in soil, which can weaken the slope and lead to failures. By directing water away from slope areas or ensuring water does not pool, drainage techniques help maintain the stability of the slope and prevent erosion or saturation.

In contrast, factors such as removing vegetation, excessive weight from buildings, and increasing slope length by cutting the bottom of the slope can significantly increase the risk of slope failure. Removing vegetation decreases soil cohesion and stability, excessive weight can lead to added pressure on the slope, and altering the slope's geometry by cutting at the bottom can create an unstable condition, making these factors directly related to slope failure risks.