Imágenes de páginas

Ti (pagird on December 12 20.4 was at the same locality as the 656 bine in thran anlampry dmtruyed the two lower 165 11.2**: 1*-2 2nd train aivo mention-d. This cave was si ta 1.2 115 i wiele in the middle, but on Dyktestele 17 15.0 125.1.2. 6ing to rely ar-tion, extended until it poartar a trtai dönyt! o pary Tow) fort. Soundings taken a fer dare aitwe yair dapibus a one the outer edge of the 1652 work of from tom tr, mil fangot, whom the original depths had been but 41 to 41 fut, shrning that the ran of the failure was scouring under the outas mies of the mat. To repair this fault, two mats, aggregating 3.7 hy 110 fort, wupp plared.

Work *as thon bun on revetting across the mouth of Jound City (hute; One mat, 210 by 140 feet, was sunk arross the upper half of the chute, and in order not to interrupt the steamer then plying the chute anothor mat, 253 by 140 feet, was built above and dropped with lines across the lower half of the chute. The lines wore then scured and the mat ballasted. But in attempting to sink it, the current was very strong, and the tug handling the stone barge fouled its wheel in the mat and in trying to get loose brought an additional pull on the already overstrained mooring lines and broke them, when the mat drifted away and was lost.

The work of this season comprised the construction of thirteen river mats, and of these two were lost in sinking. The total length built was 11,751 feet, of which 1,260 feet were lost and 10,491 feet sunk. Of the mats sunk, nine, aggregating 9,515 linear feet, extended the revetment downstream; one, 210 feet long, extended it upstream, and one, 766 feet long, was placed to make repairs of old work, and, including the work of the previous year, the river mats in place at the close of the season covered 10,450 linear feet of the bank; all continuous except a small gap in Mound City Chute near the head.


There being no large grader available, the grader built for the Delta Point (Vicksburg) work was obtained. This was a small machine and entirely inadequate for the work, and while it worked quite efficiently from September 1 to the end of the season, and was assisted for some time by the still smaller pumps of a pile driver, the grading could not be kept up with the subaqueous work. All grading was done after the mats were sunk, and as the grader had not the capacity to cut the entire bank to the top to a 3-to-1 slope


No. 10. An overhang is made on the mat barge to lap the mat on the bank. The steamer shown is carrying the Mississippi River

Commission on an inspection trip and has no connection with the work.

and keep up with the work, the slope was made steeper, or from 1 on 2 to 1 on 21/2, and a shoulder from 6 to 10 feet in vertical height was left at the top. In all, 9,290 linear feet of bank was graded, extending to within 1,000 feet of the end of the river mats.

The upper bank protection was placed along the entire 1882 work extended along the work of the present season to within 4,25) feet of the end, its total length being 5,700 feet. The construction was similar to the 1882 work along the Memphis front and consisted of two layers of brush and a wire grillage. When the work had to be extended over the water to properly lap the river mat, it was temporarily supported on stakes driven in the water, and poles were used in lieu of wires for the grillage, and where the subaqueous mats were too far from shore, as in a pocket, to admit of this construction a connecting mat, similar to the river mat, was used, and, owing to irregularity of the bank line, quite a number of these were required. Not all of the bank revetment was built as above, for the shortage of brush compelled the use of only one layer of brush over a considerable length. The width of the work placed wholly on the bank was from 40 to 45 feet, and the total bank work constructed, including connecting mats in the pockets, was 4,282 squares, placed along 5,760 linear feet of bank.


The high water of the spring of 1884 caused a slight damage to the revetment where completed, but farther downstream, where no upper bank work had been placed, the upper bank was cut away, thus completely flanking the river mats. At the lower end of the subaqueous mats the caving amounted to fully 500 feet; so the lower 4,250 feet, where no upper bank work had been placed, was entirely lost; the work remaining effective extended to 6,400 feet below the head. But even the revetment which had held intact during high water of this year began to fail when the river reached a low stage in the fall. One cave just below Mound City Chute destroyed all that remained of the 1882 work, and about 450 linear feet of complete revetment, with river mats 150 feet wide, were required for its renewal. Another cave at 4.600 feet below occurred in the shore work back of the river mats. This was at first 240 feet long, but afterwards increased until it required a mat 1,800 feet long and 100 feet wide to repair it; and still another cave of the same character, and a short distance below this, was repaired with

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No. 11. Shows construction of fascine mattress at Caruthersville, 1898.

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a mat 200 feet long by 75 feet wide, and along these caves uppur bank revetment was placed.

The experience gained by previous work showed conclusively the necessity for carrying the revetment to or near the top of the bank, and of extending it under water practically to the foot of the slope to prevent caving by under-scour. Moreover, some caving appeared to have had its initial point at the junction of the river mats and the shore work on account of improper connection there, and this must be remedied by making a proper connection or a sufficient lap. The mats as previously constructed were quite open and should be made closer to avoid such large interstices and prevent scour through them, for even thus early it was thought that some settling of the work was due to the scour through the mats. In order to prevent the tearing of a mat in sinking, the strength of the longitudinal poles must be increased, and to prevent the loss of an entire mat in sinking, it must be anchored to the bank with more and stronger lines. These ideas were embodied in the following changes in the method of construction: The mats were made 150 feet wide, the shore edge being held against a line of piles driven at about the 5-foot contour line below low water, or an average of about 25 feet farther outstream than the mats of the previous year. This, with the 10 feet additional width, increased the total width of the subaqueous work about 35 feet. Instead of weaving one brush at a time over and under the poles for its entire length, a number of pieces were handled at once; these were spread out in a horizontal layer, with their butts over one pole, which they lapped about 2 feet. The brush was then passed under the next pole and over the second, and the tops were then thrown over on the mat already constructed. The tops of the brush thus woven were inclined upstream at a considerable angle. Other bunches of brush were placed in the same manner, with their butts shifted two poles apart, until a strip was woven entirely across the mat. Then the direction of the brush was reversed and another strip woven, the butts this time being placed over the poles intermediate to those on which the butts of the first strip were placed and the tops thrown over on the first weaving, which they crossed at an angle, thus making practically a double thickness of brush. This was called the diagonal method of weaving, and, while making a considerably thicker mat, it still contained many and fairly large holes. The top binding poles were then placed as heretofore and transverse poles wired on at 8-foot intervals. To increase the strength of the mat, five iron rods, one

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