Proper amount of geotechnical investigation

The situation is like this: A major problem occurs in a bridge abutment and significant differential settlement between abutment and road is observed. The Owner decides to investigate the situation and assigns the job to a joint collaboration between a University and a Geotechnical Consultancy Firm.

The collaboration requests the execution of three boreholes to a depth of 30m, execute a number of consolidation tests some in a private laboratory and some in the laboratory of the University, together with other appropriate soil tests such as gradation, shear strength etc.

The collaboration provides a report in which it is stated that the previous geotechnical investigation did not evaluate properly the soil conditions because only one (1) drilling of 20m depth was executed in the abutment and did not evaluate properly the thickness of a compressible clay layer. Also based on the 15 consolidation tests executed by the collaboration, the coefficient of consolidation and the preconsolidation pressure estimated by the previous Geotechnical Consultant were optimistic. The previous consultant had executed three (3) consolidation tests.

So the conclusion of the report was that the problem was due to the optimistic evaluation of settlements made by the previous Geotechnical Consultant which had executed only one (1) drilling of twenty (20) meters and limited consolidation testing.

It is very easy to come to a “correct” solution after a significant amount of geotechnical investigation (money spent) has been executed in an area where a problem has occurred. The problem is known, some geotechnical information is available and the investigation can be targeted appropriately.

But how easy is this to be done from the start of a project? Most people involved in geotechnical investigation know how difficult is to persuade the Owner, Contractor etc to execute even the minimum required investigation not to mention the increased difficulty to persuade for additional investigation in an area where a hint of geotechnical problem is speculated.

In the fast track way that most projects are executed these days how can the geotechnical investigation and design produce “accurate” results?

How can we persuade the Clients that less is not more in geotechnical investigation and design? Food for thought.

About Chrys Steiakakis

Chrys Steiakakis is a practicing geotechnical engineer with more than fifteen years of experience in the field of geotechnical engineering. He earned his bachelor and master in mining engineering from the Technical University of Crete, Greece and a second master’s degree in Civil Engineering from Virginia Polytechnic Institute and State University, USA. He has been the technical director of engineering department of General Consulting ISTRIA for four years and now he is a partner and also provides his own consultancy services via Geosysta ltd. He has been involved in numerous highway, railway and mining projects. Chrys with his long term collaboration with the Technical University of Crete has participated in numerous research projects in the field of geotechnical engineering and rock mechanics and has provided self sustained seminars of geotechnical engineering in related areas for the Industry. His main field of experience covers all aspects of tunnel design, earthworks design and monitoring (slope stability, embankment in difficult ground, reinforced embankments and retaining walls), landslide investigation and mitigation, foundations for bridges and structures, risk assessment in geotechnical projects and value engineering in large projects.