Cone penetration testing of offshore soils. Advantages and disadvantages Печать E-mail


Cone penetration testing (CPT) has not only been spreading last years but it is becoming the main kind of marine soil investigation.

The tendency will go on on the way to deep water regions of the World Ocean because of even more obvious efficiency of the technology at offshore soil investigation water depth of 1 to 2 km (South Atlantic. Mexico Gulf. North Sea). The test has been one of the standard mean of over the world soil investigation practice (both shallow and deep water) right now and at least at the same scope as boring as sampling. Accordingly to Norwegian Geotechnical Institute CPT had covered more then 50% scope of work in North Sea since 1972 and some projects consisted of the test only.

Cone penetration testing is not the only way on in-situ soil investigation. Among them other methods of naturally stressed material can be noted: downhole vane, different kinds of pressure meter, dilatometer, standard penetration test, dynamic penetration test, density sounding, thermal sounding, T-bar, pressure and gas probing, electro conductivity, optical and sound probing etc. It should be noted CPT is not a single test but few of them. Piezo CPT, Seismo CPT and Temperature CPT are the main kinds among them.

Vast of majority of authors involved into business adopt priority and top status of CPT among all the rest of in-situ offshore methods. The advantage is based on CPT universality (the testing can be earned out in sand, clay and intermediate soils) and possibility to get number of soil properties (from soil type till straight and strain characteristics) applicable for design and engineering. Most of other in-situ methods allow estimating some properties and applicable at limited conditions and circumstances. Reliable results, continuous data, irreplaceable status at certain soils, higher safety can be additional advantages of the test.

On the other hand CPT as well as other in-situ methods is not enough spread in Russian offshore investigation practice. As a result standard and methodology basement of penetration testing is not equal to requirement in Russia nowadays. Issued not long time ago GOST 19912-2001 does not cover saturated marine soils factually because the procedure does not request pore pressure measurement at the test. Last official document for CPT data interpretation was made over 15 years ago and cannot include recent experience.

Probably the new issuing Code called SP 33-101-04 "Engineering Investigations at Continental Shelf for Oil and Gas Constructions" will contain certain recommendations for offshore cone penetration testing only. It should be noted as well the equipment for offshore CPT is not under produce in Russia. The noted disadvantages are the main items resulted or caused possibility and limitation of the testing at marine soil investigation.

At the same time CPT continue to spread more and more in the World. New equipment is developed and modified for the testing. There is special Technical Committee (TC 16) of soil in-situ testing within ISSMFE which organize conferences and seminars on a regular base. Results of multi year investigations in the area of penetration testing, its methodology and interpretation were published as a golden book by Mrs. Luime Т., Robertson P. and Powell J. in 1997 and has been re-issued twice since the time already. Importance of the test can be also noted by the fact of new combined European standard preparation a Eurocode on CPT/CPTU prEN 22476-1.10 and it is planned to be issued in 2006. Till that time IRTP (International Reference Test Procedure for CPT/CPTU issued in 1999 with corrections of 2001) is an official document for the procedure in Europe.



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