Table 5 











Subaqueous Soil Sampling 



Without Drill Rigs and Casing 





Device 



Application 



Description 



Penetration depth 



Comments 



Petersen dredge 



Large, relatively 



Clam-shell type grab 



To about 4 in. 



Effective in water 





intact "grab" 



weighing about 1000 lb 





depths to 200 ft. More 





samples of 



with capacity about 





with additional weight. 





seafloor. 



0.4 ft 3 







Harpoon-type 



Cores 1 .5- to 6-in. 



Vaned weight connected 



To about 30 ft. 



Maximum water depth 



gravity corer 



dia. in soft to firm 



to coring tube dropped 





depends only on 





soils. 



directly from boat. Tube 

 contains liners and core 

 retainer. 





weight. Undisturbed 

 (UD) sampling possible 

 with short, large- 

 diameter barrels. 



Free-fall gravity 



Cores 1 .5- to 6-in. 



Device suspended on wire 



Soft soils to 



As above for harpoon 



corer 



dia. in soft to firm 



rope over vessel side at 



about 17 ft. 



type. 





soils. 



height above seafloor 

 about 1 5 ft and then 

 released. 



Firm soils to 

 about 10 ft. 





Piston gravity 



2.5-in. sample in 



Similar to free-fall corer 



Standard core 



Can obtain high-quality 



corer (Ewing 



soft to firm soils. 



except that coring tube 



barrel 1 ft; 



UD samples. 



gravity corer) 





contains a piston that 

 remains stationary on the 

 seafloor during sampling. 



additional 10-ft 

 sections can be 

 added. 





Piggott explo- 



Cores of soft to 



Similar to gravity corer. 



Cores to 1-7/8 in. 



Has been used 



sive coring tube 



hard bottom 



Drive weight serves as gun 



and to 10-ft 



successfully in 





sediments. 



barrel and coring tube as 

 projectile. When tube 

 meets resistance of sea 

 floor, weighted gun barrel 

 slides over trigger 

 mechanism to fire a 

 cartridge. The exploding 

 gas drives tube into bot- 

 tom sediments. 



lengths have been 

 recovered in stiff 

 to hard materials. 



20,000 ft of water. 



Norwegian 



Good-quality 



Similar to the Osterberg 



About 35 ft. 





Geotechnical 



samples in soft 



piston sampler, except 







Institute gas- 



clays. 



that the piston on the 







operated piston 





sampling tube is activated 

 by gas pressure. 







Vibracorer 



High-quality sam- 



Apparatus is set on sea 



Lengths of 20 to 



Maximum water depth 





ples in soft to firm 



floor. Air pressure from 



40 ft. Rate of 



about 200 ft. 





sediments. Dia. 



the vessel activates an air- 



penetration varies 







3-1/2 in. 



powered mechanical vibra- 

 tor to cause penetration of 

 the tube, which contains a 

 plastic liner to retain the 

 core. 



with material 

 strength. Samples 

 a 20-ft core in 

 soft soils in 

 2 min. 





Box corer 



Large, intact slice 



Weighted box with closure 



To about 1 ft. 



Central part of sample 





of seafloor. 



of bottom for benthic bio- 

 logical sampling. 





is undisturbed. 



(Adapted from Hunt (1984)) 



Chapter 3 Field Data Collection and Observation 



45 



