Evaluation factors that can be used on selected conceptual wall designs include the following:
• Constructibility
• Maintenance
• Schedule
• Aesthetics (appearance)
• Environment
• Durability or proven experience
• Available standard designs
• Cost
The sum of all weight factors should be 100 points. To simplify the selection process, minor factor(s) may be removed from the rating matrix. This is readily achieved by assigning the same score for minor factors on all the selected feasible wall types.
8.1.1 Notes on Using the Worksheets (Figs. 8.2, 8.3, and 8.4)
1. Factors that can be evaluated in percentage of wall height
A. Base dimension of spread footing
B. Embedded depth of wall element into firm ground
|
FIGURE 8.5 Requirements for wall cost study. (From Bridge Design Manual, Section 5, Colorado Department of Transportation, Denver, Colo., with permission) |
2. Factors that can be described as “large (high),” “medium (average),” or “small (low)”
A. Quantitative measurement
(1) Amount of excavation behind wall
(2) Required working space during construction
(3) Quantity of backfill material
(4) Effort of compaction and control
(5) Length of construction time
(6) Cost of maintenance
(7) Cost of increasing durability
(8) Labor usage
(9) Lateral movement of retained soil
B. Sensitive measurement
(1) Bearing capacity
(2) Differential settlement
3. Factors that can be appraised with “yes,” “no,” or “question” (insufficient information)
A. Front face battering
B. Trapezoidal wall back
C. Using marginal backfill material
D. Unstable slope
E. High water table or seepage
F. Facing as load-carrying element
G. Active (minimal) lateral earth pressure condition
H. Construction-dependent loads
I. Project scale
J. Noise or water pollution
K. Available standard designs
L. Facing cost
M. Durability
4. Factors that can be approximated from recorded height
A. Maximum wall height
B. Economical wall height
