currents racing along the jetty. The slope blocks then settle in the sand and, exposing the crest blocks to wave action, they are rolled down the side of the jetty. It would be necessary to place this extra width either from barges or to use a light derrick with skips on a car. The barge method would probably be cheaper. The barge would be anchored fore and aft along the line of the jetty; and with lines moved across the line of the jetty, distributing the material uniformly.

On top of the apron is placed a core of quarry run of the stone weighing between 15 pounds and 2 tons. This portion of the jetty

Fig. 8. Unloading Stone for South Jetty, Aransas Pass, Texas

is drawn as the mound. It is unloaded from the cars by manual labor (Fig. 8), the larger pieces being pushed cver the sides of the flat cars by pinch bars, pieces of steel about 5 feet long, drawn to a sharp point at one end and at the other flattened to a wedge shape and about 4 or 5 inches, bent to an angle of 45 degrees. This overlaps the apron on each side by about 6 to 10 feet. The mound extends to 1 foot above mean low water. As placed from the cars its top width is about 23 feet, with side slopes of 1 on 1.

The slopes below mean low tide are covered about 6 feet thick with stone weighing not less than 3 tons, with average weight of 5 tons; but increasing in weight as the work advances gulfward to a minimum weight of 6 tons and average of 10 tons. Next is

placed the crest covering of three rows of blocks, placed on a bedding of small stone at an elevation of 1 foot above mean low water, and so arranged that the pieces bond together, to prevent any direct flow of water through the crest. The top of the crest is 5 feet above mean low water, and the width varies from 15 feet to 20 feet.

The slopes above water and alongside the crest are the last to be placed. These blocks and the crest blocks are approximately the shape of a rectangular parallelopipedon and weigh at the inner

Fig. 9.

View of Completed Jetty, Aransas Pass, Texas end of the jetty 5 and 8 tons, and for the outer half 8 to 12 tons. The side slopes are about 1 on 2.

The slope and crest blocks are handled by a derrick, which is built on a standard flat car and operated by a 25-horsepower hoisting engine. Its capacity is from 10 to 12 tons. The car is secured to the trestle by chains and clamps, and loaded cars are brought to it one at a time by the locomotive to be unloaded. About 12 cars per day can be unloaded. In placing, the inspector uses care to see that the various pieces dovetail into each other with the minimum amount of voids. Large cavities and gaps between the blocks are filled up with smaller stone.

Where the incompleted structure is liable to serious damage from

waves, as small a length of jetty as practicable is under construction at any one time. Generally, the trestle is 200 feet in advance of the apron; the apron should be 1,000 feet in advance of the mound, and the mound protected below water as fast as possible. The portion above water can wait. In winter, the work should be kept well closed up. The profiles of the South Jetty show that when the apron is kept about 1,000 feet ahead of the mound in 15 feet of water the amount of scour when the mound is placed is about 3 feet, but when, owing to the stone failing to arrive from the quarry in correct proportions, the mound is advanced to within 200 or 300 feet of the end of the apron, the scour is as much as 7 feet. The groin on land was built of a mound of riprap, of stone weighing from 15 pounds to 2 tons, without crest or slope covering. Its top was 8 feet above mean low water, width 14 feet, and slopes 1 on 2. Before placing the stone, the sand was removed under the central portion of the groin to an elevation of 3 feet above mean low water. On either side, trenches 10 feet wide were excavated to the level of mean low water, extending to the outside edges of the groin. These trenches were then filled with small riprap to an elevation of 3 feet above mean low water. The object was to carry the foundations well below the level of ground water and thus prevent undermining by the washing out of the sand on which the stone was placed.

The cars of stone are weighed on standard railway scales, furnished by the contractor, and the place in the jetty that the stone on each car goes is noted. From this the cost per linear foot of the jetty is determined. Generally, it is given in 100-foot lengths. Up to Station 30 (that is, for a length of 3,000 feet), the jetty was built under contract at the following unit prices: riprap (including apron, mound, and side slopes), $3.50 per ton, properly placed on work; crest stone, $4.37 per ton; railway trestle and track, complete, $6.35 per linear foot. Beyond Station 30, the prices were: for riprap, $3.08 per ton; crest stone, $4.09 per ton; railway trestle and track, $7.50 per linear foot. The following table gives the cost per linear foot between the stations named:

Cross sections of the completed jetty are shown in Fig. 10. The theoretical apron and mound are shown in dotted lines, based upon the original depth when the apron was begun, with top width

Fig. 10. Cross Sections of South Jetty, Aransas Pass, as Actually Built. retical Outline of Riprap Mound Shown in Broken Lines

Theo.

of mound of 23 feet and side slopes of 1 on 1. These sections show a decided filling of sand on the Gulf side, and on the channel side a scour at the inner end, but a filling at the outer end. They also show that the jetty after standing a while bears little resemblance

to the theoretical cross section. The changes in the sections are due to settling in the sand and to consolidation. In making estimates for a new work, it is necessary to allow for these changes, and if the sequence of work is properly carried out, the estimate should be based upon building the jetty in 3 feet of water greater than shown on the map. In calculating the amount of stone required for the apron and the mound, where all sizes of stone are used, the amount of voids is about 40 per cent, so that for limestone the weight per cubic yard in place would be 3,174 pounds. The crest blocks have a smaller percentage of voids. Measurements just taken over the outer end of the jetty, near Station 60, give the average width of crest as 17.3 feet; average depth of crest, 4.1 feet; average cubic yards per linear foot, 2.63; average tons per linear foot, 4.5. There are 1.71 tons of stone per cubic yard in the crest in place. As the weight of 1 solid yard of the limestone is 2.3 tons, the percentage of voids in the completed crest is 25.

Ice Accumulation on Wires

The accompanying cut shows to actual scale the amount of ice collected by a No. 9 steel telephone wire in a sleet storm on January 14, 1911, at Keokuk, Iowa. The total area of the figure is 0.5575 square inch. The area of the wire itself is 0.0103 square inch, making the total area of the cross section of the ice 0.5472 square inch. From the above figures it will be found that the volume of ice per linear foot of wire is 0.00381 cubic foot. Assuming the average specific gravity of ice to be 0.92 (Trautwine), the weight of ice per running foot of wire is 0.2185 pound.

These figures will be of considerable interest to engineers concerned in transmission lines in northern climates.

The above information is furnished from the United States Engineer Office at Rock Island, Ill., by Maj. Charles Keller, Corps of Engineers.