GROINS 



GENERAL CONSID ERATIONS 



U36. Scope. - In the past, groins generally have been built., not 

 designedp As the result^ many have been too light to withstand the forces . 

 to be met and have failed. Others have been overbuilt to such an extent 

 as to be uneconomic. Because of the many unknowns involvedj this section 

 on design is an attempt at standardization on a safe basis rather than any 

 presentation of an exact design analysis. The types of structures analyzed 

 include a steel sheet pile groin^ a concrete block groin and a rubble- 

 stone groin. Modifications of these would be similarly designed. 



I4.370 Type and Descript ion of Groins. - Nearly as many different 

 types of groins have been constructed as there sre people to design and 

 build them. The following list includes a few of the more representative 

 types which have been found satisfactory through actual experience. The 

 selection of the type to use is dependent on many interrelated factors. 

 The various types of groins listed below are not necessarily in the order 

 in which they would be recomniended. 



a. Concrete permeable: 



b. Concrete impermeable j 



c. Steel sheet pilej 



d. Rubble-stonej 



e. Stone blockj 

 ■ f. Timber 



lj.38. Concrete Perm-eable Groins . - Of the various t3'"pes of permeable 

 concrete groins^ that patented by Sydney M. Wood probably has been the 

 most widely used. Accordingly^ it has been taken as typical of this 

 type of groin. This groin consists of precast reinforced concrete units 

 shaped like flat dumbbells. See Figure 137. These units are threaded 

 on piles to form cribs. The piles contribute materially to the stability 

 of the groin and may be used to support erecting equipment. As part of 

 the theory of perm_eable groins is that the permeability may be varied^ the 

 longitudinal members may vary with respect to the number of vertical 

 lugs. The lengths of the units range from 6 to lU feet and the correspond- 

 ing weights from 3/U to if tons. The width of the groin is equal to the 

 length of the units. The li|.=foot lengths are used below waterj_ varying the 

 lengths from the surface of the water to the top of the groin makes a slop- 

 ing side and a top width of 6 feet. The piles serve as guides to position 

 the units and lock them together. Each group of four piles and connecting - 

 units comprise an independent crib unit^ permitting a measure of unequal 

 settlement without failure of the structure, 



U39» Concrete Imper meable Groins. =• Impermeable concrete groins may 

 be either articulated or solid throughout their entire length. In general, 

 the articulated type appears to be the most practicable as it will permit 

 of unequal settlement, llsoj being handled in smaller units,, it is 



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