Final answer:
In geotechnical engineering, natural sources that can contribute to increased slope shear strength include vegetation roots, cohesive soils, and rock formations. These elements help stabilize slopes and prevent erosion, making 'All of the above' the correct answer.
Step-by-step explanation:
In geotechnical engineering, natural sources that can provide a slope with greater shear strength include: a) Vegetation roots, b) Cohesive soils, and c) Rock formations. Therefore, the correct answer is d) All of the above. Vegetation roots help bind soil particles together and reduce erosion, which can stabilize slopes. Cohesive soils contain clay and silt that, due to their intrinsic properties, tend to stick together and resist shear forces. Rock formations, when present, provide a more durable, stable structure that supports the overlying materials on the slope.
Natural events like erosion by rivers, glaciers, or ocean waves, saturation from snowmelt or heavy rains, earthquakes, and volcanic eruptions can weaken slopes and lead to failures such as landslides. However, the presence of strong natural elements like vegetation, cohesive soils, and rock formations can mitigate these effects by providing increased stability and shear strength to the slopes.