Question

List 3 key assumptions made in the infinite slope safety calculation method. State whether each of the assumptions would lead to a safe or unsafe design.

Answer 1

"A civil engineer can't burry his mistakes in a grave like a doctor, neither can he hide it with greenery like an architect, nor can he justify it by philosophical justifications like a philospher".....but still our design are based on assumptions and secured by factor of safety.... The various assumptions made in infinite slope approach are ;

• shallow landslides are infinitely long (in a down slope direction)
• the soil properties for all identical depths below the surface are same i.e l soil profile is homogenous and failure always occurs at the base
• Non variable ground water conditions and failure lane is parallel to the surface of the slope and the limit equilbrium method can be applied readily

The first assumption is usually considered valid for natural landslides on the basis that they are generally long relative to their depth. however, this is rarely justified, because the critical length/ depth ratio (l/h)ratio below which edge effects become important are unknown

the random field analysis showes that there is a significant probability that the critical mechanism will occur above the base of the soil column where the factor of safety is lower

The third assumtion is also just a over simplication of things are the non variable ground water assumption and parallel failure surface in most unlikely to happen in real conditions

all the three assumptions won't lead to any catastrophe because they are backed by the famous securing tool of civil engineers called as factor of safety and the design based on these assumptions has high probability of success and tolerance within the desigh period but the conclusion follows that we as civil engineers should further secure our design and a new trending method of probabilistic and finite element approach must be synchronised with old approach to add to simplification and realiblity of our design