CE 353 Lab Week 6: Spiral Curves

Objectives

The objectives of this lab are to learn the theory of spiral curves for horizontal alignment, obtain hands-on experience with procedures for establishing these curves in the field and to assess quality of measurements by doing field checks. Groups will be assigned to develop appropriate curve data for circular and spiral curves. The curves will be layed out adjacent to each other so the curvature variations can be examined.

Project

The TS of a 200 foot spiral curve is at Station 21+50 . The delta angle is 30 degrees and the degree of curvature for the circular curve componenet will be assigned to each group, which has two crews (Crew A and Crew B. Each group is to layout two curves, starting at the same point, one spiral curve and one circular curve, so that differences can be observed.)

Computations: (note, all curves turn to the right)

1. Determine the key components of the spiral curve to include P, K, Ts, Es, Xs, and Ys, as well as the stationing for SC, CS and ST. For these equation, use theta(s) in radians.
2. Determine the deflection angles for each full and half-station as well as the backsight and foresight angles that would be needed to orient the theodolite if we need to set up on the point 150 feet from the TS in order to set the SC station. (Use theta(s) in degrees for the backsite and foresite deflection angles.) Consider that you sight back on TS to obtain your orientation.
3. Determine deflection angles and chord distances for laying out a simple circular curve of degree D, every 50 feet for 200 feet. (For laying out purposes, the circular curve also starts at station 21+50).

Field Procedure: (reminder, all curves turn to the right)

1. Two crews are used for each curve. The instructor will establish the line for each curve. Crew A sets up on TS, and tapes down the tangent to establish Xs.
2. After Crew A establishes Xs, Crew B sets up on Xs to turn and establish Ys.
3. While Crew B is setting up on Xs, Crew A will layout the spiral using the tape for measurements to the 50, 100 150 and 200 foot points. Note that the 200 foot point in the SC, and has already been established by Crew B. Therefore, there will be two pins at the SC (hopefully fairly close to one another).
4. After crew A finishes the 150 point of the spiral, Crew B will move their instrument to the 150 point of the spiral and set the SC for a third time, using the computed backsite and foresite angles. Now there are three pins at the SC (again, hopefully close to one another).
5. While crew B is working on the SC, Crew A will layout another curve from the TS. This time, layout a simple circular curve of degree D (at 50, 100, 150 and 200 feet).
6. Check the placement of your three methods of placing the final point (SC). Comment on any differences observed.
7. Before leaving the groups will inspect all other curves.

Report