MTO EMPIRICAL PAVEMENT DESIGN

1. The following presentation contains references to Tables 6.02 and 6.03, and “MTO Empirical Design Examples”, all of which are posted under subsection 2.6 of the course notes on the instructor’s website. Viewer discretion is advised as some scenes contain material of a tabular nature. MTO EMPIRICAL PAVEMENT DESIGN

2. ANY QUESTIONS?

3. There are? Subgrades range from: STRONGEST to weakest Same old subgrades OK, well here’s a little more… • You may have noticed that there were two design charts: • The first is for “Kings” Highways and Expressways • The second is for secondary highways • So, a) has 5 levels (rows) of traffic (AADT) which are different than the 6 for b) • The 6 columns for different subgrade types are the same for both • Each cell has a conventional pavement design AADT>200 vpd AADT<3000 vpd

4. Example 1 A 2-lane county road is expected to have an initial AADT of 1750 vpd and is to built over a silty sand subgrade with 30% Passing the No. 200 sieve. • Determine a conventional flexible pavement design. • A couple of subsections require the use of a deep strength design using cement treated base and no subbase. Give the appropriate layer thicknesses.

5. For a county road with an AADT of 1750 vpd, try Table 6.03b • for AADT of 1750 use second row • for silty sand with 30% passing no. 200 use second column • And the winning design is: HM: 50 mm B: 150 mm SB: 250 mm GBE: 415 mm

6. Lets calculate the GBE for this design: Total Granular Base Equivalency (mm): 417.5 • The tabulated GBE was 415. • The tabulated GBE’s have been rounded to the nearest 5 mm. • Now on to part b)

7. Example 1 b) • Part b) calls for a deep strength design • This would require that the base and subbase be replaced by a cement treated base layer (CTB) • The strength of the base and subbase is 150 + 167.5 = 317.5 mm of new Granular A • The Equivalency Factor for CTB is… 1.80

8. Example 1 b) • If the required thickness of CTB isTCTB, then the GBE of the CTB is 1.80TCTB=317.5 mm • Solving,TCTB=≈ • So the deep strength design would be: 180 mm 176.4 Total Granular Base Equivalency (mm): 424

9. Example 2 A 12 km stretch of Highway 99 has 75 mm of hot mix over 180 mm of granular base over 300 mm of granular subbase. If the AADT has grown to 2500 vpd, the sandy subgrade has 22% passing the No. 200 sieve and the hot mix has lost 65% of its strength, what minimum thickness of hot mix overlay will restore the pavement to its required strength?

10. For a highway with an AADT of 2500 vpd, try Table 6.03a • for AADT of 2500 use third row • for silty sand with 22% passing no. 200 use second column • The required design is: HM: 90 mm B: 150 mm SB: 300 mm GBE: 530 mm

11. Therecommendeddesign: Total Granular Base Equivalency (mm): 531 Theexistingdesign: 65% of HM strength lost EF of HM = 2-(2-1)*0.65=1.35 Existing GBE (mm): 386.25

12. Example 2 Extra Strength Required = 531 –386.25 =144.75 mm of new Granular A Since overlay will be with new Hot Mix, only halfof this thickness of new hot mix will be needed. Overlay Thickness Required = 144.75/2=72.375≈80 mm of new Hot Mix