Wing

The specifications under which these abutments were built, when block-stone masonry was the material of construction, required as follows: "1. Bed-plate pedestal blocks to be 2 feet thick, and placed symmetrically with regard to the plates. 2. Coping under pedestal blocks to be 18 inches thick for all spans exceeding 100 feet, 16 inches for 90 feet, and 14 inches for spans under 90 feet,— said coping to be through stones, and spaced alike from both sides of abutment. 3. Distances from front of dirt wall to front of bridge seat, and from grade line to top of bridge seat, and thickness of dirt wall, to vary for different styles and lengths of bridges. 4. Front walls to be 22 feet wide under bridge seat for all spans of 100 to 160 feet inclusive. 5. Total width of bridge seat to be 5i feet, for all spans. 6. Steps on back of walls to be used only when necessary to keep thickness - of the height. 7. In case piling is not used, footing courses may be added to give secure foundation. 8. Length of wing walls to be determined by a slope of 14 to 1 at the back end of the walls—as shown by dotted line in front elevation,—thence by a slope of 1 to 1 down the outside—as shown on side elevation—to the intersection of the ground line with face of abutment. This rule may be modified in special cases. 9. Dimensions not given on the drawing are determined by the style and length of bridge, and are to be found on special sheet." Abundant drainage should be provided for the material between the wings of the U abutment, by inserting farm tile or per forated iron pipe vertically at intervals along the back of the wings and allowing them to discharge through weep holes through the face of the wing or connecting them to horizontal tile or pipes in the filling near the bottom which can discharge at the free end of the wings. Cinders or sand and gravel are sometimes used to fill in between the wing walls to give a better drainage, and also to decrease the lateral thrust of the filling.

New York Central Standard.

Fig. 135, page 545, shows the standard U abutment of the New York Central and Hudson River Rgilroad.* The official drawing contains the following notes: "1. For depth of 9 ft. from the top of the coping, the thickness of the wing is to be in accordance with the standard retaining wall [i 1056]; and from that point down, the back of the wing is to be plumb. 2. The back

filling is to be cinders or other porous material. 3. Weep holes are to be provided with vertical blind drains in the rear." In addition to the items in the preceding paragraph, items 1 and 5 to 9 of § 1076 also apply to this abutment.

T ABVTazirr. Fig. 136, page 546, shows the type of T abutment ordinarily used by railroads when such structures were made of coursed stone masonry. The tail wall is usually 10 or 12 ft.

wide, and of such length that the foot of the slope of the embankment will just reach to the back of the head wall. The batter on the head wall is 1 to 12 or 1 to 24 all around. The tail wall is gen erally built vertical on the sides and the end. Notice the batter at the top of the free end of the tail wall. This is known as the "frost batter," and is to prevent the frost from dislocating the corner of the masonry. The' drainage of the ballast pocket should be provided for by leaving a space between the ends of two stones. Formerly the tail wall was sometimes only 7 or 8 feet wide, in which case the ties were laid directly upon the masonry without the in tervention of ballast; but this practice has been abandoned, as being very destructive of both rolling stock and masonry.

According to the common theories for retaining walls, T abut ments with dimensions as above have very large factors of stability against sliding, overturning, and crushing.

1083.

Fig. 137 and 138, page 547, show two methods of decreasing the amount of masonry in a T abutment. The designs were made for an abutment in the Cairo Bridge approach on the Illinois Central Railroad to be built against a pier already constructed.* The plan and the front elevation of these two designs are identical, and the earth fill required is almost exactly the same. Fig. 137 was adopted. The estimate for Fig. 137 was as follows: Another modification of the U abutment proposed for the same position consisted in making the side walls lighter than in the ordinary U abutment and in tying them together at intervals with rods. The rods were to be encased in concrete which was to be supported by light concrete arches resting on the side walls. The estimate for this design was: T Abutment. Fig. 139 shows a mod ified form of T abutment employed on the South Bend and Southern Michigan Railway (electric interurban).*