An Advanced Software for the Geotechnical Design of Foundations

Prof. Dr. Nainan P.Kurian, Ph.D., D.Sc. Retd. Professor of Civil Engineering, IIT Madras.

Introduction

There are two phases to the complete design of any foundation system, whether it is a foundation (shallow or deep), retaining structure or substructure. These are the 'geotechnical design' and the 'structural design' phases. The purpose of geotechnical design is to satisfy the geotechnical requirements, i.e., requirements from the soil side, in the case of foundations, and stability of the system in the case of retaining structures. In fact the structural part of design can be taken up only when the geotechnical phase of design is satisfactorily completed.

More specifically, the aim of geotechnical design in the case of foundations, for example, a shallow foundation such as an individual footing, is to arrive at the plan dimensions in such a manner that it simultaneously satisfies the requirements pertaining to 'bearing capacity' and 'settlement' from the soil side.

On the other hand, the aim of structural design is to cater to the structural action developing in the foundation in the process of load transmission, the adequacy of which has been ensured in the geotechnical phase of design. By way of example, in the case of an SB software for Foundation individual footing, the structural action is 'flexure' under the concentrated column load and the distributed soil reaction. The result of structural design is the thickness of the footing and the quantum and location of reinforcement. In the case of a deep foundation such as a pile, the geotechnical design phase gives both the length and cross section, so much so, the role of structural design is confined to designing the reinforcement. So also is the case with a retaining structure, such as a cantilever retaining wall, in whose case the cross sectional dimensions are fully established in the geotechnical design phase, which normally takes the form of a stability analysis aimed at satisfying the various aspects of stability of the system.

(One may note in this connection that design for 'bearing capacity' and 'settlement' in the geotechnical design phase of a foundation is analogous to design for the 'limit state of collapse' and 'deflection' respectively, of a structural member such as a beam.)

Since any number of softwares are available at the moment for structural design of foundations, the same is not included in the softwares developed here which is therefore confined to geotechnical design, but taking it to a very sophisticated level consistent with the current state of the art as it pertains to geotechnical engineering and satisfying all the relevant codal requirements currently in force. As regards sophistication, it comes a long way from the age old method of determining plan dimensions by dividing the column load by a so called 'fictitious' bearing capacity, which is incorrect and inconsistent with the current status of geotechnical engineering as a distinct discipline of civil engineering.

The following sections describe the features of the advanced software which has been developed for the geotechnical design of shallow foundations, deep foundations and retaining structures, based on the principles and detailed procedures of design enunciated in the author's book (Kurian 2005). Hence a reasonable acquaintance with the same is deemed as necessary to appreciate the usefulness and value of the software.