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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.

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mto empirical pavement design

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

there are
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

example 1
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.
slide5

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

slide6

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)
example 1 b
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

slide8

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

example 2
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?

slide10

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

slide11

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

example 212
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