Assessing the soil formation (in layers), its in-situ condition, type of soil, In-situ penetration strength of soil below the proposed foundation and observing the fluctuation of water table which affects foundation soil
If the soil condition is not determined, we may happen to lay the foundation on a soil which we assumed as good by visual identification but we may not aware of the weak soil that present below the foundation. Load due to the building goes up to a depth equal to twice the width of footing. If there is loose soil in this region unnoticed, the foundation fails
(Once the foundation fails either repairing cost will be very high or building is to be demolished).
Definitely not. Soil investigation is a preventive measure like immunizing children against polio, small pox. Not all the children will be affected but all the children are immunized since prevention is better than cure. If once affected curing is not possible. And some buildings stand in the mercy of “factor of safety”.
Visual observation often leads to conservation. We can only assume the strength of soil. Designing based on assumption may be uneconomical or unsafe. Strength of the soil should be determined by on site penetration resistance below the proposed foundation. (Testing on actual soil condition)
Actual testing leads to safe and economic design to our satisfaction and mental peace.
If you are not aware of the soil condition you may happen to terminate your foundation on a poor soil which leads to cracks in the building and to the worst case the building may get collapsed
Disturbed samples are used only to know about the type of soil. They do not reveal the actual condition to estimate strength of soil below the foundation. Soil strength depends upon the degree of firmness and many conditions of the site. Since same soil for different compaction energy give different strength
At the minimum cost of 25,000 you can construct a stable building with the full confidence