5. Placement Methods . 



a. General . Stone should be placed hy equipment and methods suitable 

 for handling materials of the size specified. Placement of the stone should 

 begin at the bottom of the section and should continue in a manner so as to 

 produce a graded mass of material with maximum interlocking and minimum 

 voids. In general, the larger stones should be placed so that vertical 

 joints are broken with the long axis of the stone set approximately normal 



to the structure slope and pointing inward toward the center of the structure 

 section. Stone should be placed to the lines and grades shown on the con- 

 tract drawings. Typical extreme tolerances for finished surfaces, as cur- 

 rently contained in various Corps of Engineers specifications, are ±30 

 centimeters (12 inches) when placing under water and ±15 centimeters (6 

 inches) when placing in the dry. Tolerances of ±7.5 centimeters (3 inches) 

 may be required for smaller underlayer and bedding layer stone. Up to 45 

 centimeters (18 inches) may be allowed for large armor stone. The extremes 

 of tolerances for underlayer stones and large armor stone should generally 

 not be continuous over areas of structure surface greater than approximately 

 18.5 and 93 square meters (200 and 1 000 square feet) respectively (U.S. 

 Army Engineer Division, North Central, 1978). Rubble-mound structures 

 exposed to wave action during construction should be completed in sec- 

 tions (including placement of armor stone) to minimize damage. Particular 

 care must be taken when building structures such as groins and jetties that 

 pass through the surf zone. Placement of extra stone on and around the end of 

 the structure as it progresses seaward may be required to prevent damaging 

 scour in the surf zone during construction. Damage to unprotected dikes is 

 generally the responsibility of the contractor. 



To firmly place stone, particularly in the armor layer, it must be 

 placed or seated on the underlying stones so that it does not tend to slip, 

 tilt, or wobble, either under wave attack or from the weight of stone 

 placed on top of it. This is commonly known as seating the stone. Small 

 armor stone and armor stone placed in areas of very rough seas may have to 

 be randomly placed. If so, design allowance must be made for a less stable 

 structure. Controlled placement methods are preferred for the best use of 

 armor stone; this depends to a great extent on the skill of the contractor 

 personnel . 



b. Filter, Bedding, and Core Material . The method used in placement 

 of filter, bedding, or core material should be such that the soft and 

 organic materials on the bottom are displaced outward toward the extreme 

 outside toes of the required sections of the structure and in the direction 

 of the construction. The stone should be handled and placed in such a 

 manner as to minimize segregation and provide a well-graded mass. If the 

 materials are placed by clamshell, dragline, or other similar equipment, 

 the stone should not be dropped from a height exceeding about 0.6 meter (2 

 feet) above the existing bottom or previously placed material. The use of 

 bottom dump scows and self-unloading vessels may be permitted with the 

 vessel in motion along the centerline of the structure and the material 

 dropped as near to and directly over its final location as possible. The 

 finish surface of the material should be free of mounds or windrows. 



In areas where the stone is to be placed on geotextile filter cloth, 

 care should be taken so as not to rupture the cloth and the stone should 



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