Hi dear colleagues,
To ensure the stability of the built structures, it will be necessary to make a good geotechnical study of the soil and consequently to adopt a good foundation for them. However, the financial envelope allocated to the project doesn’t allow us to make an adequate geotechnical study of the project. In fact, just after one or two years at most, we notice the appearance of cracks on the walls due to an inadequate selection of foundations or caused by other factors that I don't know. My question is what are the factors determining the minimum number of laboratory and in-situ tests to perform a good geotechnical investigation of soils? If not, are there any standards that require a specific number of tests for making a better geotechnical study of soils?
Thank you in advance
Hello Mr. Gadouri,
to read a standard about the geotechnical investigations take the EN 1997-2, the Eurocode 7: Geotechnical design - Part 2: Ground investigation and testing.
Kind regards,
P. C. Quasten
As Mr. Patrick mentioned, Eurocode 7 Part 2 provides the general requirements for a number of commonly used laboratory and field tests for structural stability. The characteristics of soil can vary significantly, depending on location and can affect the stability of the foundation. Therefore, it is important to plan the geotechnical investigation such that maximum amount of information can be obtained at a minimum cost.
Dr. Hamid
concerning the two questions, we can refer to Eurocodes as guidance. For instance, revisions are under development, also for Ground investigation (focused on more practical information for a wider range of tests) ans on Foundations, slopes, and ground improvement (devoted to practical rules for design of these structures). Comments on Eurocodes are provided in the Designer's Guide by Frank et al. Th.Telford publ. 2004.
Generally the focus for field engineers and geologist involved in the characterization is concentrated on the expected failure and/or deformative process that can determine the behaviour of the structure, also during the construction phases. Scale effect, heterogeneity at the site, peak-residual behaviour and changes in the GWT conditions claim for an increase in the number of samples and testing modes. A careful practice in sampling and in the lab are necessary to obtain reliable values. Rarely, despite good sampling and characterisation, bad practice in construction could affect the final performances.
In conclusion, stability and deformability are both features to be studied, working in lab at the proper stress level, in comparison with reality of the final structure.
Best Regards
C.O.
Hi dear Dr. Claudio Oggeri,
Thank you so much for the very good news related to the revisions that are under development made on the ground investigation, foundations, slopes, and ground improvement.
I appreciate your valuable response.
Best wishes
following factors should be considered to determine number of laboratory or field tests to be performed for geotechnical investigation.
1. Type and importance of structure, loading conditions ( light /heavy/impact), area of building /structure etc
2. general classification of soil based on sieve analysis preliminary tests or sample observation ( type of soil/ rock,), variation of soil properties/ geological formation in the land on which structure is to be constructed.
3. Selection of type of foundation ( shallow / deep , raft etc)
4. depth ( location) of compressible layer and its thickness.
5 effect of ground water table variation.
6 Modifications/ improvements in existing soil properties are proposed or not.
7. Variations in factors which will affect bearing /strength properties and settlement/ deformation of the soil.
Though above mentioned factors makes difficulty in decision in selecting number of lab and field tests to be performed since cost of geotechnical investigation, facilities available , data and experience available on geotechnical investigation on similar type of soil are also important factors need to consider.
I agree with Dr Claudio Oggeri ' s opinion. The prevailing codes will give guidelines for number of tests to be performed. However, revisions in codes or standards under development will be of great help since they will consider research experiences in geotechnical investigations, effect of change in soil conditions and the performance of existing structures.
Thank you so much dear Dr. Ishwar Sonar for the clarification given above.
Soil being a very complex substance especially in presence of moisture is very difficult to characterize with higher accuracy. Answering your question, in a Nutshell, we can say that, the minimum numbers of tests required for Geotechnical investigations mainly depends upon the type of structure and Ground conditions there. If the site conditions vary there over a single season, then you might need more no of tests as compared to a more normal climatic and ground condition in the area.
Secondly, you must do some research on the soil investigations already done for the similar projects in that vicinity to decrease the number of your soil investigations tests.
Best regards.
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