For locations on a relatively clean sand either a ietted-in anchor 



18 

 or a screw anchor is useful. The jetted-in anchor shown in Figure 4a 



has a 6-inch fluke diameter. The shaft and hose diameter are usually 



dependent upon available equipment. Embedment of the fluke to a depth 



of 8 feet and rodding to densify the sand as it is backfilled will give 



a design pullout capacity of 500 pounds. To achieve this capacity, it 



is extremely important that the sand which is backfilled into the hole 



created by the jetting, be compacted to a dense state. Rodding 



(repetitiously thrusting and removing a 10-foot length of 3/4-inch- 



diameter pipe, or similar, into the sand as it is filled into the 



hole) is one practical means. 



A second type of anchor which can be used in either sand or 

 cohesive soils (clays, silts, muds, and oozes) is a screw anchor. 

 Figure 4b shows a single-flight type which can be installed by a diver. 

 When this 8- inch- diameter screw is embedded 4 feet in cohesive soils, 

 a design capacity of 120 pounds is achieved. In sands a 4-inch-diameter 

 can be used and only 2 feet of embedment is necessary to develop a 

 240-pound design capacity. In order to assure these capacities, these 

 screw-in anchors should always be torqued to the diver's maximum 

 capability, which may result in slightly larger penetrations at some 

 locations. Higher capacities can be achieved by designing with larger 

 diameter anchors and deeper embedment, however, the torque required 

 during installation in either case would usually be beyond a diver's 

 capability. 



Another configuration which can be used in cohesive soils is a 

 simple mini-pile, Figure 4c. A usable design is a 2-inch-diameter 

 pipe, an open end is satisfactory, about 8 feet in length. This can 

 be driven with an 18-inch- length of larger diameter pipe with a plate 

 welded on one end. This drop hammer driver should weigh about 20 pounds. 

 Simply driving the mini-pile until the penetration per blow is less 

 than 1/4 inch will give a design capacity of 120 pounds. Penetrations 

 will typically be 8 feet or less. 



Explosive embedment anchors, Figure 4d, can be used where large 

 capacities are required and other anchor types either singly or in 

 groups, are not satisfactory. Reference 19 discusses their use and 

 capabilities. 



For a rock bottom, none of the previously mentioned configurations 

 are directly applicable (one exception is the explosive embedment anchor, 

 several variations of which have recently been developed for rock) . One 

 acceptable tiedown system on rock is the rock bolt, Figure 4e. Various 

 types are available; however, most require the drilling of a hole in 

 the rock with a diameter of from 1/4 to 1 inch and to a depth of from 

 2 to 10 inches. Design load capacities of these range from 100 to 2000 

 pounds when properly installed in sound rock. Values in coral may be 

 somewhat less. Another technique, Figure 4f , involves the drilling of 

 a 1 to 2-1/2 inch diameter hole from 6 to 48 inches into rock. A steel 

 rod, such as a standard concrete reinforcing bar, is positioned in this 

 hole which is then backfilled with a cement grout. Load capacities of 



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