The Fourth James K. Mitchell Lecture: The CPT in offshore soil investigations - a historic perspective

Figures & data

Figure 1. Worldwide progression of water depth for offshore drilling (adapted from [email protected]).

Figure 2. Fugro's Seabull rig (courtesy of Fugro).

Figure 3. Fugro's Seacalf rig (from Zuidberg 1974).

Figure 4. NGI/McClelland's CPT operation at Ekofisk (from Eide 1974).

Figure 5. McClelland's Stingray rig (from McClelland 1975).

Figure 6. Diving bell operated by Delft Soil Mechanics Laboratory (from Vermeiden 1977).

Figure 7. APvdBerg's ROSON rig (courtesy APvdBerg) (a) Heavy weight version (b) Principle of ROSON.

Figure 8. Fugro/McClelland's TSP rig (from Power & Geise 1994).

Figure 9. IFREMER's Penfield rig (copyright IFREMER).

Figure 10. Benthic's PROD rig (courtesy of Benthic Geotech) (a) PROD on deck (b) Cone penetrometer with pushrod.

Figure 11. Geo's Geoceptor rig (courtesy of Geo).

Figure 12. DATEM's Neptun 3000 rig (courtesy of DATEM).

Figure 13. Fugro's Wison (after Zuidberg 1972).

Figure 14. McClelland's Dolphin system (Peterson & Johnson 1985).

Figure 15. CPT while drilling, CPTWD (after Sachetto 2004) (a) principle (b) Picture.

Table 1. Summary of the main developments for seabed rigs

Penetration mechanism/main advance development	Date	Equipment	Company	Note	Reference
Discontinuous push Hydraulic cylinder	March 1972	Dead weight operated from platform	NGI/McClelland	Max 4 m penetration reached in dense sand	Eide (1974)
	March 1972	Seacalf	Fugro	25 m penetration reached in 130 m water depth	Zuidberg (1972)
	1974	Stingray	McClelland	Push on drill pipe, not on cone rod	McClelland (1975)
	1976	Diving bell	Delft Soil Mechanics Laboratory (Deltares)	600 kN reaction force, 60 m penetration achieved	Vermeiden (1977)
	1991	SCOPE	Geo, Denmark	Self leveling	Denver & Riis (1992)
Continuous push	1983	ROSON	APvandenBerg/ D'Appolonia	Roller wheels	Berg (1984)
	1984	Modified BORROS rig	McClelland	Synopticated hydraulic cylinders	Amundsen et al. (1985)
	1984	Wheeldrive Seacalf	Fugro	Roller wheels	Zuidberg et al. (1986)
	2010	DeepCPT	Gregg Drilling & Testing	Suction anchor; 200kN thrust capacity, 10 and 15 cm^2 cones	Boggess & Robertson (2010)
Coiled rod (on full size rods)	2000	Penfeld	IFREMER	Selfpowered by lead batteries. Can penetrate to 30 m	Meunier (2000)
Seabed founded drilling, testing and sampling rigs	2001	PROD	Benthic	Rods stored in carousel on sea bottom	Kelleher et al. (2008)
Combined rig	1997	Searobin	Fugro	Can take sample to 1 m and do 10 cm^2 CPT to 2 m in one deployment	Hawkins & Marcus (1998)
	2001	Geoceptor	Geo, Denmark	Can take sample to 6 m and do 10 cm^2 CPT to 10 m in one deployment	Brinch-Clausen (2010)
Minirigs	1992	Seascout	Fugro	Coiled rod, wt < 1 ton, 1 cm^2 cone penetrometer	Power & Geise (1994)
	2000	Neptun	DATEM	Coiled rod 5 and 10 cm^2 cones; up to 20 m penetration	Steggar (2009)
	1999	MiniCPT	Gregg Drilling & Testing	Coiled rod; 2 cm^2 cones up to 12 m penetration
ROV mounted	1983	Mini Wison	Fugro	1 m stroke, 5 cm^2 cone penetrometer	Geise & Kolk (1983)

Table 2. Summary of the main developments of down-hole type CPTs

Pushing mechanism	Year	Equipment	Company	Note	Reference
Hydraulic cylinder	1970	WISON	Fugro	First 1.5 m stroke, extended to 3 m	Zuidberg (1972)
	1973/4	WISON APvandenBerg	APvandenBerg		Berg (1984)
	1974	Stingray	McClelland	Push on drill pipe	McClelland (1975)
	1982	Swordfish	McClelland	Functions like WISON	Meyer et al. (1982)
Mud pressure	1984	Dolphin	McClelland	Data stored in memory unit	Peterson & Johnson (1985)
	1994	WISON - XP	Fugro	Data stored in memory unit	Power & Geise (1994)
	2007	WISON - EP	Fugro	Data stored in memory unit and real time	Peuchen & Raap (2007)
Seabed founded drilling, testing and sampling rigs	2001	PROD	Benthic	Cones pushed by drill rods	Pennington & Kelleher (2007)
Advanced by drilling	2001	CPTWD	SPG and ENVI	Data stored in memory unit	Sachetto et al. (2004), Sachetto (2010)

Figure 16. Fugro's 15 cm² piezocone with pore pressure on cone face (after Zuidberg et al. 1982).

Figure 17. Compensated shear load cell design (from Bogess & Robertson 2010).

Figure 18. Results of CPTUs from four organizations at Onsøy.

Figure 19. Examples of parallel CPTU by different companies (a) Norwegian Sea (b) Offshore Africa.

Figure 20. Unequal end area effects on friction sleeve.

Figure 21. McClelland's triple element piezocone and special cones (from Bayne & Tjelta 1987).

Figure 22. Results of triple element piezocone from Gullfaks C (from Bayne & Tjelta 1987).

Table 3. Some CPTU add on devices that have been used offshore

Additional sensor/tool	Main purpose	Key offshore related reference	Comments on use
Electrical resistivity ECPT	In situ density; assessment of contamination	Kroezen (1981)	Used on some projects
Nuclear density NDP	In situ density of cohesionless soils	Tjelta et al. (1985)	Used on only few projects
Seismic cone SCPT	Shear wave velocity in addition to CPT parameters	Campanella et al. (1986)	Frequently used 1985–1995, now used occasionally
Cone pressuremeter	Stress strain properties in situ horizontal stress	Withers et al. (1986)	Very seldom used
Lateral stress cone	In situ horizontal stress	Jefferies et al. (1987)	Used only on a few projects
T-bar/ball	Intact and remoulded shear strength of very soft clays	Randolph et al. (1998)	Used on several deep water projects with very soft clays

Figure 23. Combined results of piezocone test and nuclear density test at Gullfaks C in the North Sea (from Tjelta et al. 1985).

Figure 24. Schematic layout for seabed seismic cone testing (from Peuchen et al. 2002).

Figure 25. Results of G_max measurement (from Lange et al. 1990).

Figure 26. CPT penetrometer, T-bar and ball.

Figure 27. Example of down-hole CPT with faulty zero readings.

Figure 28. Recommended scheme for reporting deck to deck readings for seabed CPTUs in new ISO standard.

Figure 29. Example CPTU profile for wind farm project.

Figure 30. Clay sites investigated by NGI and Fugro (Lunne et al. 1976).

Figure 31. Cone factors based on vane shear strength (Lunne et al. 1976).

Figure 32. Deepwater example with undrained shear strength interpreted from CPTU and CAUC triaxial tests.

Table 4. Recommended N-factors (adopted from Low et al. 2010)

		Recommended N-factor
N factor/Nrem factor	Definition	Mean	Range
Nkt,suc	qnet/suc	12.0	10.0–14.0
NΔu	(u2 – u0)/suc	6.0	4.0–9.0
NT-bar,suc	qT-bar/suc	10.5	8.5–12.5
NT-bar,rem,UU	qT-bar,rem/sur,UU	20.0	13.0–27.0
NT-bar,rem,fc	qT-bar,rem/sur,fc	14.5	12.5–16.5
NT-bar,rem,vane	qT-bar,rem/sur,vane	14.0	12.0–16.0
Notes: sur,UU, sur,fc, sur,vane (remoulded UU, fall cone and laboratory vane).

Figure 33. Schmertmann's original q_c, σ_vo', D_r chart (from Schmertmann 1971).

Figure 34. Assessment of relative density in sandy layers from Figure 30.

Figure 35. Correction of fine content for liquefaction analyses (adapted from Seed and de Alba 1986 and Stark and Olson 1995).

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