In-situ Tests on Soil

In situ testing is a division of field testing corresponding to the cases where the ground is tested in-place by instruments that are inserted in or penetrate the ground. In-situ tests are normally associated with tests for which a borehole either is unnecessary or is only an incidental part of the overall test procedure, required only to permit insertion of the testing tool or equipment. The role of specialized in-situ testing for site characterization and the research and development of in-situ techniques have received considerable attention over the last 15 years or so. The use of specialized in-situ testing in geotechnical engineering practice is rapidly gaining increased popularity. In Europe, specialized in-situ testing has been commonly used for more than 25 years. Improvements in apparatus, instrumentation, and technique of deployment, data acquisition and analysis procedure have been significant. The rapid increase in the number, diversity and capability of in-situ tests has made it difficult for practicing engineers to keep abreast of specialized in-situ testing and to fully understand their benefits and limitations.

Advantages

• Tests are carried out in place in the natural environment without sampling disturbance , which can cause detrimental effects and modifications to stresses, strains, drainage, fabric and particle arrangement
• Continuous profiles of stratigraphy and engineering properties/characteristics can be obtained.
• Detection of planes of weakness and defects are more likely and practical
• Methods are usually fast, repeatable, produce large amounts of information and are cost effective
• Tests can be carried out in soils that are either impossible or difficult to sample without the use of expensive specialized methods
• A large volume of soil may be tested than is normally practicable for laboratory testing. This may be more representative of the soil mass.

Disadvantages

• Samples are not obtained; the soil tested cannot be positively identified. The exception to this is the SPT in which a sample, although disturbed, is obtained.
• The fundamental behavior of soils during testing is not well understood.
• Drainage conditions during testing are not known
• Consistent, rational interpretation is often difficult and uncertain
• The stress path imposed during testing may bear no resemblance to the stress path induced by full-scale engineering structure
• Most push-in devices are not suitable for a wide range of ground conditions
• Some disturbance is imparted to the ground by the insertion or installation of the instrument
• There is usually no direct measurement of engineering properties. Empirical correlations usually have to be applied to interpret and obtain engineering properties and designs