IV. CORING PROCEDURE 



Vibracore sampling is divided into three steps: intrusion, extraction, and 

 packaging. 



1. Intrusion. 



For maximum penetration, the vibrator head should be attached near the top 

 of the unsharpened end of the 33-foot core barrel, while the barrel is lying 

 on the ground. As one individual of the coring crew keeps a foot on the 

 sharpened end to prevent movement away from the designated coring position, 

 one or preferably two other individuals push the core pipe into a vertical po- 

 sition. Initially, the core barrel will sink into the saturated sediment by 

 its own weight giving some stability. Unsaturated sediment can also be cored 

 with this system but depth of penetration may be limited. A quick start of the 

 engine will generally cause rapid penetration of the pipe into the sediment. 

 Tying a rope to the pipe and pulling down by adding weight will aid in getting 

 the pipe through resistant subsurface units such as rooted zones and oyster- 

 beds. Usually, 15 to 25 minutes is needed to penetrate 33 feet of sediment. 



2. Extraction . 



After removing the vibrator head, the remaining pipe is cut off with a 

 hacksaw about 1.6 feet (0.5 meter) above the ground surface. The distance to 

 the sediment surface inside and outside the pipe is measured to determine the 

 amount of sediment compaction. The pipe is then filled with water and a gas- 

 main sealer plug is inserted and tightened to prevent loss of sediment from 

 the core pipe as it is removed. 



The tripod is assembled and placed over the intruded pipe. Two come- 

 alongs are each fastened to the eyebolts at the tripod head and to a rope 

 securely fastened to the core pipe. Extracting the core with the come-alongs 

 (Fig. 3) is initially difficult but becomes easier once the core breaks free 

 from the bottom. The core is guided through the core pipe slot in the tripod 

 head and then rested against the tripod head to prevent falling over during 

 extraction. The filled core barrel, weighing approximately 10 pounds per foot 

 (15 kilograms per meter), cannot be gently lowered. Therefore, as mentioned 

 previously, when the core is completely out of the sediment, the come-alongs 

 are removed and the core pipe slot is opened by pulling the cord that moves 

 the spring-loaded slot gate. The core is then gently pushed so that it falls 

 freely to the ground (Fig. 5). The sample tube, completely filled except 

 near the top, falls onto a relatively soft beach, marsh or aqueous medium. 

 This prevents any disturbance except for the top 1 foot which may slump. 



3 . Packaging . 



The extracted core is usually too long for immediate shipment, so the core 

 is cut at the field site, using a hacksaw. Aluminum foil held securely with 

 duct tape is sufficient as core caps. Each core section must be carefully 

 labeled, indicating top and bottom, with a waterproof marker. 



The splitting, logging, and sampling of each core is done in the laboratory. 

 Immediate photographing of all the cores after opening is an important step that 

 should not be neglected (Fig. 6). Even under the best conditions, complete 

 preservation of a core is impossible. 



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