A LABORATORY STUDY OF THE STABILITY OF SAND-FILLED 

 NYLON BAG BREAKWATER STRUCTURES 



hy 

 Robert Ray 



I. INTRODUCTION 



1 , Background . 



In the late 1960's, several small shore protection structures using 

 sand-filled nylon bags were constructed by private homeowners and commu- 

 nities on the east coast of the United States. A partial list of those 

 structures is given in the Appendix. Nylon was known to be strong, dura- 

 ble, and resistant to rot and fouling, but susceptible to damage by long 

 exposure to the ultraviolet light in sunlight. Although nylon sandbags 

 had been used in Europe for a number of years, little was known about the 

 engineering design criteria of the nylon bag for application to shore pro- 

 tection structures. The Coastal Engineering Research Center (CERC) began 

 investigating the use of the bags as a low-cost solution to erosion problems 

 in locations where sand was more available than riprap, or where the cost 

 of building a riprap structure was beyond the financial resources of the 

 property owner. After studying the performance of some of the small bag 

 structures and receiving inquiries concerning the design of submerged 

 breakwaters using nylon bags, CERC initiated a project in the fall of 1968 

 to investigate the stability and effectiveness of sand-filled nylon bag 

 breakwaters under the attack of shallow-water waves. This study describes 

 all aspects of the investigation to provide an understanding of the complex 

 phenomena taking place. 



2. Nature and Purpose of Study . 



The sandbag breakwater project involved full-scale laboratory tests 

 using commercially available standard-size bags 5 feet (1.52 meters) wide 

 by 8 feet (2.44 meters) long when empty. The tests were conducted to 

 investigate: 



(a) Effects of random bag placement on structure config- 

 uration. 



(b) Changes in nylon sandbag performance by increasingly 

 severe wave conditions as the structure crest elevation and 

 width were increased. 



(c) Changes in the sand bed, especially settlement and 

 scour, at the base of a breakwater built of randomly placed 

 sand-filled nylon bags with no underlying filter layer. 



(d) Changes in structure configuration by increasingly 

 severe wave conditions for structures of varied design con- 

 figuration. 



