There are three principle factors to consider before choosing the most appropriate type of foundation for a given structure. These are as follow
Function of the structure and loads it must carry
The sub surface condition
Cost of foundation in comparison with cost of the superstructure
Because of these factors, there exist several acceptable solutions for a foundation problem. So the judgment of an engineer plays an important role in foundation engineering. The role of an engineer is to findout the most suitable type of foundation considering both the subsurface condition and the function of the structure. Thereafter considering the economy he makes his final decision.
If an engineer is new to this field or has less experience, then it is better for them to rely on scientific studies and experience of other engineers related to this field. The 5 steps given here, if followed in a logical manner, then it will help an engineer to arrive at a most suitable type of foundation, without the danger of serious error.
The steps to follow are given below.
Obtain at least approximate information concerning the nature of the superstructure and the loads to be transmitted to the foundations.
Determine the subsurface conditions in a general way
Consider briefly each of the customary types of foundation to judge whether they could be constructed under the existing conditions, whether they would probably be capable of carrying the required loads, and whether they might experience detrimental settlements. Eliminate, in this preliminary way, obviously unsuitable types.
Make more detailed studies and even tentative designs of the most promising types. These studies may require additional information concerning the loads and subsurface conditions and generally must be carried far enough to determine the approximate size of footings or piers or the approximate length and number of piles required. It may also be necessary to make more refined estimates of settlement in order to predict the behavior of the structure.
Prepare the estimate of the cost of each promising type of foundation, and choose the type that represents the most acceptable compromise between performance and cost.