which will be begun about May 1962. Sufficient experience has not been obtained to form definite conclusions regarding the advisability of their general use, but limited experience indicates that concrete components may be superior to stone in some hydraulic aspects but inferior in durability and strength. As the units are constructed on site, the cost of the components will vary widely in various regions of the country depending on the cost and availability of concrete aggregate at that location. In addition, a royalty fee of $3 per cubic yard of concrete used is charged by Neyrpic, Inc., for the privilege of using the tetrapods design. Tribars and quadripods are royalty free to the U.S. Government.

Sealing of permeable jetties and groins. Some stone structures designed for wave breaking purposes would furnish additional benefits if they were more impermeable and would interrupt sand or silt moving

along the shore. Other stone structures have lost their impermeability. Various methods of grouting and forcing of asphaltic concrete or asphalt compounds into the interstices have been attempted by the Corps of Engineers at several locations, including jetties at Mission Bay, Calif. and Galveston Harbor, Tex. This has, at least temporarily, sealed the jetties above the waterline but is generally unsuccessful beneath the water surface. The cost of grouting the jetty at Galveston Harbor was about $41 per linear foot. This cost would vary according to access, sea conditions, and other factors at other locations. In general, it is considered that the use of either concrete or asphaltic mixes have not been fully satisfactory. The material separates, solidifies, or changes in characteristics upon being forced into water. Radioactive tracers have been used by the corps in studies to determine the permeability of structures or to determine the manner in which littoral materials enter the channel so that proper corrective action may be taken. South of Galveston Harbor gold 198 was inserted and traced through the jetty and through a small boat opening in the structure. This procedure is considered successful for short duration tests. There are definite limitations to the use of radioactive tracers because of their possible damaging effect to animals. To insure safety of the population, a complex system of permits is necessary and a short half-life material, such as gold 198 must generally be used. Further information on tracers is contained under the subject "Utilization of Radioisotopes in Sediment Transport Studies." Small scale-model investigations are planned by the corps for radioactive and fluorescent (nonradioactive) tracers.

Consolidation of stone structures. In many areas stone is obtainable in small sizes but not in sizes large enough to be stable under the wave conditions of the area. This material could be utilized if a reliable bonding material were available to consolidate the structure after construction. Also existing unstable structures might be so stabilized. Both asphaltic and concrete mixtures have been used by the corps at several locations including the mouth of the Columbia River, Oreg., Galveston Harbor, Tex., and Panama City, Fla. The materials studied to date have lacked the bonding capability, strength or resistance to the elements and their use has not been effective.

Filters and bedding layers.—In porous structures the construction material near the base must be graded down to smaller sizes, nearing that of the foundation material, to prevent scour by currents around and beneath the stones. Such a mat also spreads the load and deter settlement of the structure. Several plastics and fabrics or combina tions thereof have been proposed by manufacturers for this purpose Some of these materials have been used by States or other local govern mental agencies in the State of Florida. These structures are being observed by the Corps of Engineers to ascertain durability of th material and its possible application in civil works structures. Furthe discussion of these materials including "Filter X" is given under th subject "Fiber and Plastic Materials.

Protection of timber and steel piling in ocean waters.-The life of bot timber and steel are relatively short in salt water. Most paints an coatings to prevent corrosion of steel are tested, principally at the pain laboratory at Rock Island, Ill. Although many have been used i structures by the Corps of Engineers, improved coatings are needed

Timber deterioration is due to decay in wet and dry portions, to marine borers and abrasion when placed in sandy or gravelly shores. Creosote, salts, and gunite have been used as aids in reducing decay and borer damage. The preventive measures may be defeated by bruising of the surface of the timber. Metal jackets have been proposed for borer and abrasion control, but in general are expensive methods. A plastic wrapping for timber piles as protection against borer damage is under observation at an installation in California.

CHANNEL STABILIZATION

Asphalt paving. This material has been used extensively for bank protection on Mississippi River levees. It has been used to a very limited extent for revetment in flood channels of moderate velocity. The paving material consists of a mixture of hot asphalt, sand and gravel, which is placed in a layer 3 to 6 inches thick on the bank to be protected. Field experience by the corps has proven that this type of paving is effective on the Mississippi River, but that in rapidly rising and falling streams of moderate velocities the paving has a very short life. In the latter case, the porosity of the asphalt paving is not sufficient to relieve uplift pressure which results in cracking and rapid deterioration of the paving. The cost of asphalt paving for bank protection ranges from about 20 to 40 cents per square foot, depending upon the thickness and placing conditions. The material is abundantly available in most parts of the United States.

Articulated concrete bank protection. This type of bank protection has been used extensively by the corps to prevent erosion of banks and levees on the Mississippi River. The revetment consists of large mattresses of small concrete units, held together by light steel reinforcing bars or wire mesh. In general, this type of bank protection has been effective, but when the articulated concrete slab is subjected to pressure pulsations due to stream turbulence, foundation materials pass through the spaces between the individual concrete units, causing settlement and damage to the bank protection. The cost of this bank protection is about $1 per square foot.

Kelner jetties. This type of channel protection is used in some sandy streams where velocities are moderate and other types of protection would be too costly. Kelner jetties (fig. 13) consist of a number of steel jacks that are tied together with cables and located along banks to reduce velocities, thereby preventing bank erosion. Each jack is made of steel angle bars that are bolted together at their midpoints and tied together by wire at their ends. Field tests by the Corps of Engineers on the Rio Grande and Arkansas Rivers have shown the jetties to be at least partially effective in reducing stream bank erosion. The life of Kelner jetties is limited because it is impractical to do maintenance painting. The cost of bank protection by Kelner jetties is in the order of one-fourth of the cost of protection by riprap.

Fiber and plastic materials. Several types of fiber and plastic materials have been proposed by manufacturers for use as bank protection. Nylon sheets have been used to replace the filter layer under rock bank protection. "Filter X," a cloth woven from polyvinylidene chloride resin monofilament yarns, has been used as the filter

85639 062 -5

NOTES. (1) Unit is usually 16'x4"x4"x4" angle iron laced with No. 6 wire. (2) Cables are usually 4 p. (3) Above unit is placed 122' on centers.

layer for offshore breakwaters and beach protection seawalls and revetments by the State of Florida. Tests by the manufacturer have proven the material to be resistant to all sorts of chemical and biological substances. Heavy loads, such as rock in a breakwater, may damage the thin sheets of material and thus limit its life. "Filter X" is manufactured by Carthage Mills, Inc., located in Cincinnati, Ohio. Its cost ranges from about 20 to 30 cents per square foot, depending on the size of installation. Although the Corps of Engineers has not yet used these materials, it appears that they may have application to some corps projects, and a test program to establish their suitability to corps needs is planned.

STRUCTURAL DESIGN

PRESTRESSED CONCRETE

Tainter gate anchorages.-Perhaps the most important application to date of prestressed concrete in Corps of Engineers civil works structures has been in anchorages for tainter gates. In addition to the advantages of reduced deflections between the noload and loaded conditions and the resulting more favorable stress condition in the concrete piers, the use of prestressed anchorages has resulted in a significant economy over conventional anchorages.

Other applications.-Prestressed concrete is also being utilized in the construction of bridges and powerhouse roof slabs.

NEW STEELS

Carbon steel. The increased use of welding led in 1954 to the issuance of ASTM Specification A373 which provides carbon and manganese controls to insure better weldability. This change was incorporated into Government construction by the adoption in 1955 of Federal Specifications QQ-5-741a. A more recent carbon steel, A36, which was adopted in 1960, has a higher yield point leading to a significant contribution to the economy of steel construction. At Corps of Engineers projects, A36 steel is approved for use in buildings (using welded, bolted, or riveted construction), crane runways, lock and dam gates, stoplogs, and bulkheads.

High strength steels.—In recent years high strength steels have been introduced to civil works construction and have led to greater economy. The ASTM designated A242 and the more recent A441 have been used in the fabrication of control gates. Savings are achieved not only by a reduction in steel cost but also through the resulting need for lower hoist capacities.

Penstock steel. The steel presently specified for power penstocks and surge tanks is the ASTM designated A-201, grade B, firebox quality. It is a carbon silicon steel for pressure vessels and has a slightly higher yield strength than the principal steel, A285, previously used for this type construction. It is also a better quality steel having improved notch toughness and better weldability.

ALUMINUM

Where savings are indicated, aluminum is being used for bulkheads and stoplogs at the corps water resources projects. Economy is achieved principally from the reduction in the required hoisting capacity. Other uses of aluminum include spiral stairs, handrails and grating where service conditions are corrosive and lightweight is desired.

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