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Archive for April, 2006

Significance of Geotechnical Engineering – Part I – Differential Settlement

Posted by Kshitija Nadgouda on April 5, 2006

Geotechnical Engineering is the study of soil in relation to man-made structures that stand on it. Every structure that is built, has a foundation that rests on the soil underneath and transfers the load (weight) from the structure to the ground. It is the job of the geotechnical engineer to assess the properties of the soil and determine wheather the structure is feasible at the proposed location.

Soil in its natural state is very heterogenous and non-uniform. It can vary greatly from place to place and also with depth. Soil investigations need to be performed to determine the type of soil present at a location. Based on the collected data, the geotechnical engineer determines the soil bearing capacity and estimated settlement of the structure.

The bearing capacity of the soil is simply the capacity of the soil to bear the weight (load) of the structure built on it, without undergoing failure. The settlement of the structure is the amount the structure will “sink” during and afer construction. It is the role of the geotechnical engineer to ensure that this settlement is within tolerable limits.

Settlement is broadly classified as total settlement and differential (uneven) settlement. Total settlement refers to the uniform settlement of the entire structure and occurs due to weight of the structure and imposed loads. Differential or uneven settlement can occur if the loads on the structure are unevenly distrbuted, variations in the soil properties or due to construction related variations.

Probably the most talked about and classsic “failure” in terms of differential settlement is La Torre Di Pisa (The Tower of Pisa) in Italy. Imagine a building meant for habitat (residential or commercial) structure showing so much inclination!!!

Leaning Tower Of Pisa

Leaning Tower of Pisa
(Courtsey Wikipedia )

The Leaning Tower of Pisa is the bell tower of the Cathedral. Its construction was commenced in 1173 and contiued haltingly over a period of 200 years! The tower began “leaning” soon after construction began in 1173. The inclination of the tower is attributed to the non-uniform, sponge-like saturated clay soil on which the foundation of the tower rests. The softer area within this strata has settled more causing the tilt.

Several engineers have proposed plans to “straighten” the tower. However, with its 800+ years of “leaning” history, locals do not want the tower to be straightened. Every few years some form of restoration is performed to ensure that the tower does not become unstable or collapse.

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