Force employed at Sycamore Chain, reduced to days' service. In building dam and preparing it for the work of excavation: The engineers were employed in running the pumps to keep the area clear of water; blacksmiths in sharpening tools; carpenters in repairing tools, &c. The ice was stripped from the rock-bed, as shown in my report. Upon the entire work, then, including building dams, stripping ice, and excavating rock, we have Superintendents Foremen .. Engineers.. Days' service. 348 1, 093 431 700,000 feet (board measure) of lumber used in construction; 3,800 yards of stone for cribs; 14,000 yards of puddling, of which 750 flat-boat loads were brought from distances averaging one mile. The remainder of the filling was wheeled from the shore, and used simply to give additional weight to the structure. The original intention had been to extend the dam three hundred feet further down, but as the contractors feared that they would be unable to close it before the advent of extreme cold weather, if they were forced to go this distance, and as they then had a great deal of risk upon their hands, I was willing to permit them to leave it over for the present season, upon their assurance that they would put in another dam below, and resting upon the large one, as soon as the work could be resumed in the spring. This new dam was commenced in the March following, and finished in April, but, on account of the spring rise, it could not be pumped out before the early part of June, when the river lowered sufficiently to enable them to do so with safety. About four hundred yards of rock were taken out of this inclosure, when, the river rising again, work had to be temporarily suspended. Days' service in building small dam at Sycamore Chain, putting up pumps and preparing it for the work of excavation. Superintendents Foremen .. Engineers (steam). Carpenters. Laborers... Total.... and one steamer, one dredge, and two flats. Davs' service. 77 77 55 77 77 525 898 Six days' work in excavating rock from the area, up to and including June Total amount of rock excavated from the bed of the river to date. Grand aggregate of all hands employed in building dams, chiselling, dredging, blasting, quarrying, and wheeling for the year ending June 30, 1869. Moline Chain.... Grand total.... Cubic yards, 20, 963 2, 112 23, 642 46,717 The improvement of the channel through Campbell's Chain was contemplated this season, but in consequence of there being three works already in progress, and the probability that the construction of the necessary coffer-work would be carried into the winter, thus endangering its safety, and the lack of necessary funds to push the work as desired, it was abandoned for the season. From the nature of the rock bottom upon the various chains, their diversity of shape, the composition, dip, and stratification of the rock blasting, to a theoretical plane has been very difficult of attainment. The proportionate charges of powder found by experience upon one chain to be correct, could not be relied upon for another. The blasts threw off more or less from each particular point than was actually necessary or desirable, in order to give the depth sought, viz: four feet at lowest water, the depth required at all the chains. Take the case of a horizontal stratum two feet in thickness, and suppose that a depth of one foot and eight inches below its upper surface is to be reached. The drill, for precaution, penetrates only to one or two inches of the depth required; the blast will throw out the rock to the depth of its bed, and the entire stratum must be taken out. In cases where the rock has a decided dip, the drill must penetrate to the depth of the theoretical plane of excavation, and the effect of the blast is to throw out a large prism of rock below the theoretical plane, and to leave in a prism above it which must be drilled and blasted again, repeating the error, if it may be called so. The extra rock thus thrown out by the blasts must necessarily be removed, unless it chances to be broken into small fragments, when it may be left where it falls, provided its surface is not above the plane of the bottom established. This is seldom the case, however, and the masses must be broken by sledges into pieces suitable for handling, and then either wheeled away, or drawn by means of stone boats. In either case expense occurs in the handling of it, and as this is something that is unavoidable, the contractors claimed compensation for it. In working the chain at Duck Creek and Moline, notwithstanding the great irregularity of the bottom of the former, the proportion of over-excavation to the desired excavation was very small; at Moline Chain it was five per cent. of nearly 17,000 yards, showing not only faithful work upon the part of the contractors, but also faithfulness upon the part of my assistants in keeping the excavation so close to the original estimates. Work of this nature cannot be carried on over such large areas, and the excavation kept to close limits, unless the hammer and chisel are used, which of course is out of the question. A close examination of the bottom, as shown at Sycamore Chain, its great irregularity of surface, and the dip of the strata, convinced me that it would be impossible, by the closest attention to blasting, to prevent over excavation. I desired Colonel Ulffers, civil engineer and assistant, who is a professional geologist, to take a geological survey, and to report what in his opinion would be the necessary amount of overexcavation in getting out the estimated quantity of rock. He reported an average extra depth of sixty-six hundredths of a foot, which, multiplied by the area worked over, would give nearly 5,000 yards additional. There had always been a tacit understanding, from the time the work was commenced, that the necessary extra excavation would be considered in your office, leaving the question of compensation open, to be decided by superior authority. The surveys at the conclusion of the work at Sycamore Chain showed that the average depth to which the blasts had been carried below the theoretical plane was 0.926 feet, but as a large proportion of this broken rock was left in, and spread over the area in small fragments, it could not all be taken into consideration. The quantity of solid rock actually removed below bottom of excavation was 3,533.25 yards, and the actual cost per yard to the contractors for this portion was estimated, from the best information in the possession of this office, to be $8 79. * The contractors claimed payment for this at contract prices, viz: $13 per yard, basing their claims upon the text of the contract of June 28, 1867, drawn up before I was connected with the work. It says: * * "That the said parties of the second part shall furnish all the boats, machinery, and materials of every sort required, which shall be of good and sound quality, and perform all the labor necessary to excavate and remove from the bottom of the Mississippi River, at such place or places on the upper or Rock Island Rapids of the Mississippi River as may be designated by the engineer in charge of the work, all rock or other material necessary to make a continuous channel through said rapids." * * * * * Further on it says that the channel shall not be less than four feet deep in the lowest stages of the river. The claim turned upon the word "necessary;" the contractors contending that as the rock was necessarily removed in order to give the channel required, and that as the depth to which they blasted was unavoidable in order to give even a less depth of channel, they were entitled to full price per yard. They also referred to the paragraph in Colonel Hains's report of the survey of the rapids in 1866, and the accompanying estimate of quantities to be removed, in which the words "It may appear at the first glance that the percentage I have added for contingencies in excavating is rather large, but after a careful consideration I can only say that I am convinced it is not. occur: * * * * "Experience has taught us that in excavating rock at the lower rapids, the cost is materially increased by the more or less favorable seasons for working, and, moreover, the rock being in strata of various thicknesses, if, in deepening a part to four feet, we should come to a stratum two feet thick, the entire stratum must be taken out." I have made this extract as it seems necessary to a full discussion of the subject. The evident meaning is that if the upper surface of the stratum should be a few inches above the required depth, and the remainder of the stratum below, the whole must be taken out. I think the report has been misprinted, and that it should read: "If in deepening a part two feet we should come to a stratum four feet thick, the entire stratum must be taken out." Still the meaning is evidently the same in both. As soon as the estimates of work done were made I submitted the question with a statement to your office. By you it was submitted to the department, and then to the Secretary of War, and returned with the approval of your recommendation to pay to the contractors the cost to them of removing the rock. I have not inserted any of the correspondence or figures, as you have them in your office. The field work during the season has been extensive, consisting in the observations of currents, locating buoys for the erection of dams, triangulating and establishing base lines for laying out lines of excavation, dams, &c., and in taking additional topography of the country bordering the rapids. Additional soundings have also been made upon the portion of Duck Creek Chain worked over by the chisel boats, the soundings reduced, and new maps made, showing the condition of the chain at that time, in all about six thousand soundings. St. Louis Chain was also thoroughly sounded in November, by means of a steamer and attached skiffs, and twelve thousand soundings taken, reduced, and platted. About five thousand soundings were also made in January, upon the portion of the river immediately above the coffer-dam at Sycamore Chain, and added to the charts of that chain. The maps finished in the office have comprised sounding and contour maps of the different chains, a general map of the rapids, small reduced maps of the chains, and working sheets and sketches. The draughting has been mainly done by assistants C. J. Pauli and J. H. Harlow. Water gauges have been established at convenient points, and their daily readings recorded. The summer, fall, and winter were generally favorable for work, but this spring has been the reverse, heavy rains and high water prevailing. The proportions of powder used to rock blasted have been as follows: At Duck Creek Chain, seven-thirteenths pounds of powder to one yard of rock. At Moline Chain, one pound of powder to one yard of rock. At Sycamore Chain, two pounds of powder to one yard of rock. The excess of powder at this latter chain is in part due to the work having been done in the winter, the broken rock being frequently frozen together during the night, and the conglomerate mass having to be blasted again in the morning. The method of constructing and putting in the dams has been the same as described in my last report, viz: First, a line of cribs sunk above the head line of the dam and connected with each other by heavy timbers, against which planks were rested on the up-stream side, their lower ends abutting against the bottom of the river. The planks were as close together as possible, and inclined at an angle of about forty-five degrees with the horizontal. A breakwater was thus formed, which, being extended some distance beyond either end of the head line of the coffer, gave comparatively still water below it. |