session 30 johan ullberg

ROADEX approach on deterioration of low volume roads

Johan Ullberg, VägverketPauli Kolisoja, Tampere University of Technology

Introduction of the ROADEX project

Classification of rutting modes on low volume roads

Basic solutions to rutting problems

ROADEX design approach against rutting

Conclusions

OUTLINE OF THE PRESENTATION

Three phases 1998-2007 ”Northern periphery”

Similar problemsRoad technology

WWW.ROADEX.ORG

ROADEX

We can define three modes of rutting, depending on how and where the plastic strain accumulates

- Mode 0 = Compaction strain in upper layers

- Mode 1 = Shear strains in the near-surface layers

- Mode 2 = Shear strains in deeper layers (especially the subgrade)

THREE MODES OF RUTTING

MODE 0 - COMPACTION

SoilAggregate

MODE 1 – NEAR-SURFACE SHEAR

AggregateSoil

MODE 1 – NEAR-SURFACE SHEAR

During spring thaw:

- deeper soil / sub-base is frozen

- upper aggregate is thawed

- upper aggregate can’t drain due to frozen underlayer, so tends to contain excess moisture

- thus upper aggregate prone to Mode 1 rutting

MODE 1 RUTTING DURING THEEARLY SRPING THAW

Frozen

MODE 2 – DEEPER SHEAR

Soil

Aggregate

MODE 2 – DEEPER SHEAR

BASIC SOLUTIONS TO RUTTING – DRAINAGE;A TYPICAL DRAINAGE PROBLEM AREA

ProblemSolution

BASIC SOLUTIONS TO RUTTING – DRAINAGE;AN EXAMPLE OF A PROPER DRAINAGE STRUCTURE

Use a stronger base layer if Mode 1 (upper layer) rutting is the problem

- Inappropriate if Mode 0 or Mode 2 is the problem

Use a stiffer base layer if Mode 2 (lower layer) rutting is the problem OR Use same material in thicker layer

- Inappropriate if Mode 0 or Mode 1 is the problem

BASIC SOLUTIONS TO RUTTING

Structures to be analysed are unsurfaced/thinly sealed

Enables different wheel configurations/tyre inflation pressures to be analysed

Is based on a mechanistic analysis approach

Is still simple to use; at least shouldn’t assume the availability of sophisticated computational tools

Determination/estimation of the required design parameters should be a ’reasonable’ task

REQUIREMENTS SET FOR THE DESIGN APPROACH

Wheel configuration: dual wheel/super single

Tyre inflation pressure: 800 kPa/400 kPa

Thickness of the unbound layer (in relation to radius of the loaded area)

Aggregate stiffness/subgrade stiffness ratio

Mohr-Coulomb strength parameters (c and ϕ) for the unbound base course aggregate

Undrained shear strength of the subgrade

VARIABLES/PARAMETERS CONSIDERED IN THE ROADEX III DESIGN APPROACH

DESCRIPTION OF THE DIFFERENT WHEEL LOADINGS IN THE ANALYSISDual wheel Super single

800 kPa

400 kPa

An analysis of stress corresponding to the actual loading case is made; in practise a simple parameter Sis determiner by using a set of graphs or tabulated values or a spreadsheet tool

Strength of the base course material is described by a parameter Sf (derived based on the values of c and ϕ)

S/Sf ratio should not exceed 0,90 in dry conditions and 0,75 in wet conditions

BASIC IDEA OF MODE 1 RUTTING ANALYSIS

GRAPHICAL DETERMINATION OF S

1.3

4

242.9kPaDifferent

graphs are available

for different wheel

configurationsand tyre inflation

pressures.

DETERMINATION OF S USING THE TABULATED VALUES

Table continues for 800kPa/DT, 400kPa/SS and 800kPa/SS

DETERMINATION OF S USING THE SPREADSHEET TOOL

Vertical stress acting on top of the subgrade is estimated using a set of ready-made graphs.

Undrained shear strength of the subgrade is determined/estimated.

Vertical stress should not exceed 4 x undrained shear strength of the subgrade.

BASIC IDEA OF MODE 2 RUTTING ANALYSIS

GRAPHICAL DETERMINATION OF THE STRESS AT THE TOP OF SUBGRADE

0

50

100

150

200

250

300

350

400

450

500

1.0 1.5 2.0 2.5 3.0 3.5

Agg.Thickness/Load Radius Ratio

Str

ess

at th

e to

p of

sub

grad

e (k

Pa)

Sup. Singles - 800kPa - Ebas/Esub=2






SS-800-R:2

SS-800-R:4

SS-800-R:8

SS-400-R:2

SS-400-R:4

SS-400-R:8

Different graphs are available

for dual wheel and super

single wheel configurations.

TOOLS FOR ASSESSING THE INPUT PARAMETRS LIGHTWEIGHT FWD / DYNAMIC PBT

Rutting is clearly the dominating structural problem on the Low Volume Roads of the Northern Periphery Area

Efficient design requires a correct diagnosis of the failure mechanism – identification of the different phases of the seasonal freeze-thaw and respective rutting modes

A fundamental study has been performed to develop a sound but easy-to-use design approach that is based on simple laboratory and in-situ tests

See more details at: www.roadex.org

CONCLUSIONS

http://www.roadex.org/

The most cost-effective method to improve the condition of a Low Volume Road is to ensure that it has a functioning drainage system

New solutions to the rutting problems are provided by:- non-traditional stabilizers- TPCS technology and special axle configurations- accurate timing of weight restrictions based on in-situ monitoring of spring thaw and new type ofinterplay between road users and owners

See more details at: www.roadex.org

CONCLUSIONS (2)

http://www.roadex.org/

http://www.roadex.org

THIS PROJECT IS BEING PART- FINANCED BY THE EUROPEAN UNIONEuropean Regional Development Fund

www.roadex.org