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3. There are two methods in general use for filling bridge openings:
1. By use of side or center dump cars, or both.
3. By grab buckets swung from cable way. In lesser degree:
4. By endless belt conveyor.
6. By hydraulic excavation and leveling by sluicing. 4. Where foundation is good, and in case of low trestles, where it is not good, fills can be made by dumping directly from the structure to be filled. Good results may be obtained by use of a ditching machine in
conjunction with two 16-yd. air dump cars for jobs of approximately 5,000 cu. yds. or less, and by steam shovel and air dump cars for jobs of over 5,000 cu. yds., though this dividing line is by no means fixed, as it depends on the haul, the depth of cuts from which material is available, and the relative need for ditching the cuts in the vicinity of the structure. The double benefit derived from the use of a ditcher often justifies a greater total expenditure than would be involved in the use of a steam shovel.
5. Before dumping from trestle, wooden guard timbers should be removed and plank about 2 in. by 2 in. should be spiked on top of ties, close by rail, to prevent ties from bunching. This applies to side dumping. When center dumping is employed, the same method may be followed with the addition of cutting out alternate ties between the inside line of the stringers.
6. When dumping large rocks, care should be taken not to damage essential members of the structure. It is sometimes advantageous to install inverted “V” shaped wooden shields with comb located under the center line of track. This accomplishes a dual purpose; first, it affords protection to members which may otherwise be damaged by heavy filling
VIEW OF FILLING OPERATIONS INVOLVING Heavy CONCRETE CONSTRUCTION, Viz., ARCH OVER HIGHWAY AND TROLLEY AND Two ARCHES OVER STREAM. NOTE THE High DROP OF FILLING MATERIAL: THE CONCRETE WAS PROTECTED BY CUSHION OF ONE OR Two MAN
STONE OVER BARREL OF EACH ARCH.
material from a high drop; secondly, this approximates to the side dump method which results in less disturbance to the structure. The shields must be removed when the filling has progressed so far that the dirt will not fall free of the shield.
7. When filling high trestles where foundation is very bad and appears liable to give trouble due to settlement, and traffic may be sufficiently heavy to justify it, it may be advisable to build temporary trestles on each side of the main trestle, say from one-third to one-half ihe height of main trestle, and located so that material dumped from same will spread to cover the area of the completed fill. The use of grab buckets from cable way or use of endless belt conveyor may be employed to advantage in making fills of this character. Then by dumping simultaneously from all three trestles, or dumping simultaneously from main trestle and cable ways, the settlement may be reduced and kept fairly uniform.
8. It is often advisable to haul filling material further, in order to obtain a better grade of material to stabilize the fill and reduce cost of future maintenance.
9. Sufficient material should be deposited in fill to allow for shrinkage of embankment and subsidence of foundation. Fills made adjacent to and subject to erosion by rivers may be made more compact and repellent to water action by having the dirt spread by teams in layers over the entire area to be covered.
10. It is considered good practice when filling trestles of over approximately 25 feet in height to install a small pump, if there is water available at the opening, and run a pipe line underneath the lies through the center of the trestle, having valves at intervals so that the trough formed by dumping on both sides of the trestle, or the central core when center dump cars are used, is kept continually wet. In this way settlement occurs gradually as the filling is deposited, with the result that the filled trestle is not carried so badly out of line and surface, but also when the fill is completed there is a solid puddle core from the bottom to the top to carry the weight of trains.
11. Immediately after the completion of the filling of low trestles, the stringers should be removed, but in cases of high trestles, the stringers should not be removed until the fill has settled about all it will without the load of trains; except that, if trestle has become so badly out of line and surface that it cannot be resurfaced and relined, it is better to remove the stringers at once and put the load on the green fill, even if this requires considerable watching and resurfacing of track for some time.
12. Care should be taken to avoid the formation of a trough which will hold water when removing stringers. This may be done by filling openings left by stringers with a good grade of clay, and tamping and crowning same before applying ballast.
13. On account of its cheapness, and ease of handling, track should be ballasted on engine ashes until new fill has entirely stopped settling.
14. Where engine ashes or commercial dirt is used for making fill, great care should be taken that the fill does not catch fire. When engine ashes are collected from water pits the fire hazard is very greatly reduced, but where cars are loaded from hot ash pits and the fires are not quenched by the ash pit shovelers, the cars should be run under the water plug in order that the live coals may be deadened. In handling commercial dirt, yard scrapings, shop cleanings, and filling of that general character, all paper, sticks, planks, greasy rags, oily waste, etc., should be removed during the unloading process, for if allowed to remain, spontaneous combustion will probably set in with disastrous results; particularly is this the case where live coals in the engine ashes become a part of the fill. On a large job of this kind it is always well to have a good sized force pump installed with sufficient fire hose to overcome fire, which may start in the fill when least expected.
15. It is recommended that in making fills of great height, or when unusual conditions are anticipated, that an Inspector with full authority be kept continuously on the work.
Filling by Hydraulics 16. Water is diverted from the most convenient mountain stream and carried along the mountain side parallel with the line of track and usually about 200 feet above same, from which it is taken for use in the hydraulic “monitor or giant” employed in this work. The jet used is from three to four inches in diameter, depending upon the amount of water available. The material is carried to the trestle in ordinary rectangular box Aumes and the discharge outlet is varied from time to time to meet the requirements. The building of the levee is a special feature. It is usually constructed of alternate layers of earth and straw or hay, tough marsh grass is suited best for this purpose. The material is spaded from the inside and the hay is distributed by a man walking along the dike and shaking same down neatly. The next layer of earth compacts the hay and while this might appear to be quite porous, it is in fact very quickly puddled by the action of the water. The embankment is usually constructed to within 3 or 4 feet of its finished elevation, and is then completed by train. Banks constructed in this manner are remarkably solid and subsidence is unusual other than that arising in some cases from the compression of the original soil on which it rests; also the hay or straw on the levee has the advantage of protecting the newly made bank not only during the first year but subsequently as the seeds germinate and form a sod. The cost of the process varies with the local conditions, but this method is very satisfactory in that there is no interruption to traffic by work trains during the greater part of the work. This method has been largely used on the Northern Pacific Railway.
Photographs of actual working conditions received from E. F. Gorman and C. W. McFarland.
Bibliography REPORT OF E. H. McHenry, Chief Engineer, Northern Pacific Railway,
dated August 14, 1899. This report relates to filling bridges by
sluicing. Similar report of November 30, 1896. 0. E. S. BULLETIN No. 249, Part 1, by Samuel Fortier, Chief of Irriga
tion, Department of Agriculture, pages 74 and 77, inclusive, dealing with filling of bridges on the Northern Pacific Railway, by hydrau
lics in the Cascade Mountains, Washington, between 1890 and 1897. The 1920 Report of the American Bridge and Building Association, on
Maintenance of Bridges during Filling, pp. 149 to 162, inclusive. ARTICLE in the Engineering News-Record of January 20, 1921, descriptive
of filling by dumping from cars and spreading by sluicing, as practiced recently on the Minneapolis, St. Paul and Sault Ste. Marie
Railway. Article in the Engineering News-Record, January 16, 1921, descriptive
of filling of high iron and steel viaducts and the preparation of the same to withstand the unusual stresses set up in the structures during filling operations and the methods whereby such difficulties may be lessened and in many cases overcome. This article by P. S. Baker, Engineer Bridges and Buildings, is descriptive of work of this character on the Philadelphia & Reading Railway.