1. Set up the instrument at B; turn the wing angle from G; set reference stakes H and I; measure distances BH and BI. Set up at A and repeat this procedure to establish J and K. Use reference lines FG, BH, and AJ to set temporary stakes marking the corners of the excavation for the foundation. Then the method described earlier for abutments is followed. If abutment or wing-wall faces are battered (inclined, rather than vertical), lines are established for both top and bottom.

2. To stake out wing walls for askew abutments to the center line of a bridge, follow the procedure described for askew abutments. Set up the instrument over N (fig. 10-15); sight on R; turn the wing angles; set reference stakes to establish the wing line from N. Establish the wing line from M in the same manner.

Piers. After the center line of the bridge is established, locate the piers by chaining if possible. If chaining is impracticable, locate the piers by triangulation. Set stakes establishing the center line on each side of the river. Lay out CD and EF approximately at right angles to the center line, as shown in figure 10-17. For well-proportioned triangles, the length of the base lines should equal at least one-half CE. To

locate piers at A and B, you may use the following procedure:

1. Establish base lines CD and EF and carefully reference them.

2. Measure the length of each base line with a degree of accuracy suitable for the required accuracy of the line CE.

3. Measure all angles of the triangles CDE and EFC.

4. Compute the distance CE from the triangle CDE and check against the same distance computed from triangle EFC. The difference in computed lengths must be within the prescribed limits of error.

6. Draw a triangulation diagram, showing computed angles and distances and measured angles and distances.

7. Turn the computed angles BDC, ADC, BFE, and AFE.

8. Set targets DA and DB on the far shore and FB and FA on the near shore so that the intersecting lines can be reestablished without turning angles. Carefully reference these points.

Piles. You may be required to position piles, record pile-driving data and mark piles for cutoff. Figure 10-18 shows points A and B established as a reference line 10 feet from the center line of a bridge. Stretch a wire rope between points A and B with a piece of tape or a wire rope clip at each pile-bent position (such as C or D).

If it is impractical to stretch a wire rope to the far shore, set up a transit at a convenient distance from the center line of the bridge. Position the piles by sighting on a mark located the same distance from the center line of the template. Before driving piles, you must measure the length of piles. Measure the distance between the piles by chaining.

During pile driving, keep a complete record of the following: location and number of piles, dimensions, kind of woods, total penetration, average drop of hammer, average penetration under last five blows, penetration under last blow, and amount of cutoff. Mark elevations on the two end piles by nailing two 3- by 12-inch planks to guide the saw in cutting the piles to the specified height.