Preventing Pre-mature Rutting

Preventing Pre-mature Rutting

Dr Greg ArnoldEngineering Policy ManagerTransit New Zealand

Preventing Premature Rutting

• Rutting – where and why• Preventing rutting from compaction

– Strong construction platform– Changes to TNZ B2

• Preventing rutting from shear movement within materials

• Choosing the best pavement appropriate for traffic and environment

• Lowest initial cost or lowest whole of life costs, considering risk of failure

Rutting – Forestry road - Scotland

Thicker ThinnerThicker

From my supervisor’s presentation –Andrew Dawson – University of Nottingham





Rutting – shear in base

AggregateSoil

b

b/3

Rutting – compaction in base

AggregateSoil

b

Rutting – shear in subgrade

Aggregate

Soil

Rutting

Thin aggregatehigh shear on subgradesubgrade rutting

Thick aggregatehigh shear on aggregateaggregate rutting greater if

poor quality and/orwetpoor compaction

AC=25mm; Aggregate=275mm AC=25mm; Aggregate=750mm

AC=200mm; Aggregate=275mm AC=200mm; Aggregate=750mm

Rutting• Aggregate movement predominant

contributor to surface rutting• Aggregate proportion of rutting is

– greatest when aggregate thickest– as much as 100% in some places– >40% even when subgrade has rutted

• Rutting –– Compaction related– Shear related

Rutting

0

5

10

15

20

0 500 1000 1500 2000 2500 3000

Laps ('000's)

Rut

Dep

th (m

m)

Shear2mm per 1M

Compaction andConsolidation (build up of residual stresses

CAPTIF Results• Two pavements same subgrade

and aggregate – two depths• Both the same life• 50% rutting occurred in aggregate• 320mm – 2.4 million ESA life• 250mm – 2.4 million ESA life

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Cptf_A

03_4

0_l

Cptf_A

03_6

0_l

Cptf_B

03_4

0_l

Cptf_B

03_6

0_l

Cptf_C

03_4

0_l

Cptf_C

03_6

0_l

Cptf_D

03_4

0_l

Cptf_D

03_6

0_l

Cptf_E

03_4

0_l

Cptf_E

03_6

0_l

Cptf_A

01_4

0_l

Cptf_A

01_5

0_l

Cptf_B

01_4

0_l

Cptf_B

01_5

0_l

Cptf_C

01_4

0_l

Cptf_C

01_5

0_l

Cptf_D

01_4

0_l

Cptf_D

01_5

0_l

Pave

men

t Life

, whe

el p

asse

s (1

06 ) Linear Extrapolation - Lower 90th %ile

RC

C

Rep

aire

d

Rou

nded

agg

rega

te

CAPTIF Results

320m

m

250m

m

250m

m

320m

m

320m

m

300m

m

RLT tests

0.0

0.5

1.0

1.5

2.0

0 50,000 100,000 150,000 200,000 250,000

Loads

Per

man

ent S

train

(%)

RLT Extrapolation (to N of interest)(i) 0 to 25k; (ii) 25k to 100k; (iii) 100k to 1M; and (iv) >1M

Cumulative Permanent Strain

y = 1.5x0.6

0

2000

4000

6000

8000

0 200000 400000 600000 800000 1000000

Loads

Per

man

ent m

icro

-str

ain

100k - 1M

25k - 100k

RLT data(up to 50k)

>1M

0 - 25k

Curve fitted to RLT data -

Material Testing stress Permanent strain

Permanent strain rate (tangential)

TEST p q 25k (magnitude)

25k –100k

100k – 1M >1M

- - - - - - -

- - - - - - -

Tabulate RLT permanent strain rates with test stress

Fit data to Two parameter model Eqn7.10: εrate = e(a) e(bp) e(cq) - e(a) e(bp)

Eqn 7.4 Permanent strain


Constants 25k (magnitude)

25k –100k

100k –1M >1M

a - - - -

b - - - -

c - - - -

RLT tests

0.0

0.5

1.0

1.5

2.0

0 50,000 100,000 150,000 200,000 250,000

Loads

Per

man

ent S

train

(%)

RLT Extrapolation (to N of interest)(i) 0 to 25k; (ii) 25k to 100k; (iii) 100k to 1M; and (iv) >1M

Cumulative Permanent Strain

y = 1.5x0.6

0

2000

4000

6000

8000

0 200000 400000 600000 800000 1000000

Loads

Per

man

ent m

icro

-str

ain

100k - 1M

25k - 100k

RLT data(up to 50k)

>1M

0 - 25k

Curve fitted to RLT data -

Material Testing stress Permanent strain


TEST p q 25k (magnitude)

25k –100k

100k – 1M >1M

- - - - - - -

- - - - - - -

Tabulate RLT permanent strain rates with test stress

Fit data to Two parameter model Eqn7.10: εrate = e(a) e(bp) e(cq) - e(a) e(bp)

Eqn 7.4 Permanent strain


Constants 25k (magnitude)

25k –100k

100k –1M >1M

a - - - -

b - - - -

c - - - -

Transit NZ• Aim to develop a RLT test methodology

to classify basecoarse (those in top layer) aggregates for:

• High, medium or low traffic for both wet and dry conditions

• Currently favour Arnold simplified for this

Preventing Pre-mature Rutting

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