CONTENTS ABSTRACTINTRODUCTIONINVESTIGATIONS, DESIGNS AND IMPROVEMENTS TO ROADSOILS FOR CONSTRUCTION STEPS OF CONSTRUCTION FOR SECTION WITH

AMENDED PAVEMENT STRUCTURECONSTRUCTION OF PRIME COAT AND SURFACE

DRESSING (SAND SEALS) Prime Coat Surface Dressing (Sand Sealing)

MAINTENANCE OF ROADPRESENT STATE OF ROADCONCLUDING REMARS

Technical Paper to Study the feasibility

Basically for To make use of locally available material Minimize the estimated cost To suit a Low volume road Where Labourers freely available for

maintenance. Where Regular maintenance is possible

To Adopt standard design to suit the site condition .

Advantages by adopting design Low Cost construction method in Low volume

traffic road

Least project Cost Environmental friendly construction

methods Sustainable Improvements to suit

the site conditions Achieving Objectives & Goals of Ro

ad Development Authority (RDA)

Replacement of Standard Design Standard Design

1. Sub-base of compacted 225mm Gravel layer (CBR>20)

2. Base of 150 mm ABC (CBR>80)

3. Priming4. SBST (surface dressing)

Modified Design 1. Scarifying & mixing with

gravel to Existing & re-grading surface to a compacted thickness of 150 mm

2. Sub-base of 150-300 mm thickness of gravel (CBR- 19-22)

3. Base with Gravel compacted thickness of 150 mm (CBR-19-22)

4. Priming5. Sand Sealing (surface

dressing).

Years of Conflict has resulted in the Years of Conflict has resulted in the deterioration of most of the road infrastructure deterioration of most of the road infrastructure in Sri Lanka’s Northern Province and adjacent in Sri Lanka’s Northern Province and adjacent areas. As a result, some roads have become areas. As a result, some roads have become functionally impassable, through direct damage functionally impassable, through direct damage and/or destruction or due to lack of preventative and/or destruction or due to lack of preventative maintenance. The existing roads in these areas maintenance. The existing roads in these areas need significant rehabilitation in order to need significant rehabilitation in order to facilitate freedom of movement, and revive the facilitate freedom of movement, and revive the economy in the area.economy in the area.

INTRODUCTIONINTRODUCTION

PROJECT DETAILS

Name of Road :- Paranthan-Mullaitivu (A-035) Section :- 2.00 km to 52.13 km (50 km) TEC :- 50.0 million Source of Funds :- GOSL Period of Construction

Start :- June -2003

Completion :- April 2004 Scope of works :- Scarifying existing surface

and mixing gravel & re-grading to a compacted thickness of 150 mm and gravel sub-base overlay of compacted thickness of 150mm-300mm and gravel base overlay of 150 compacted thickness with priming & sand sealing surfacing

Existing Road Condition Consisting of doubled layers of

50mm single sized aggregate with extremely large potholes without aggregateThe available platform width of road 6-8 m Carriageway width of 4-5m

Not motor able poor & dilapidated condition

Climate Condition

Dry Zone

Annual average Rainfall - <1500 mm

Ambient Temperature -25-35°C

Works Entrusted to ….

Chief Engineer, RDA Mullaitivu No Contractual system was introduced due to

non-availability of competent Road Experience Contractors

Entire improvement Works executed by RDA direct lab our system

Field Laboratory set-up and attached with Chief Engineer’s office by Research & Development Division, RDA/ Ratmalana.

Standard Pavement Design a.) estimating the amount of traffic (and its axle load distribution) that will use the road over the selected design life,

b.) assessing the strength of the sub grade soil over which the road is to be built and that of the material to be used as sub-base.

c.) taking into account a) and b), selecting the most economical combination of pavement materials and layer thickness that will be sufficient to provide satisfactory service over the design life of the pavement with only routine maintenance.

Investigations & Designs

Estimated Traffic in 2004 -500 veh /day

Design Life -10 years

Axle load traffic – 0.1 million cumulated standard axles

Annual Traffic growth rate -4%

Standard Pavement Design……. Existing Sub-grade CBR varied 3-8 range Sub-base gravel 4 days soaked CBR >20

with 225 mm compacted minimum thickness. Base with Dense graded aggregate base

coarse with compacted thickness of 150 mm with 4 days soaked CBR >80

Prime Coat Single Bitumen Seal treatment (SBST)

Constraints with standards pavement Design construction…… The length of road section -50 km Limited funds allocated for improvements -50

million Limited Project duration to less than 1 year Difficult in handling through RDA direct labour DGABC is not readily available locally and to be

transported to a distance of more than 150 km No competent bidders in tendering No suppliers for DGABC

Standard Pavement Design Adopted to … Adopted Pavement Design

1. Scarifying & mixing with gravel to Existing & re-grading surface to a compacted thickness of 150 mm

2. Sub-base of 150-300 mm thickness of gravel (CBR- 4 days soaked range 19-22)

3. Base with Gravel 150mm compacted thickness (CBR- 4 days soaked range 19-22)

4. Priming

5. Sand Sealing (surface dressing).

SOILS FOR CONSTRUCTION ( Four number of Borrow pits selected) Gravel for Base, Sub-base Sub

grade & Embankments considering the followings1. Maximum Dry Density 2. Engineering Properties

1. CBR 2. Atterberg limits3. Mechanical Properties (Particle size Distribution)

Engineering Properties of Soils selected….

ID Mark LL PL PI OMCMAX DD

CBR (%)

Kalliyady-1 40 22 18 11.8 1.96 17

Vaddakachchi

33 14 19 10.2 2.01 19

Kalliyady-2 37 19 18 11.2 1.98 21

Kokavil 39 22 17 15.0 1.93 22

Step 1- Drainage works 1.Cutting Earth drains

2.Repairs to Existing structures3. Re-construction of Minor

structures4.Construction of New minor

structures where ever required

Step 2- Sub Grade Construction Moistened Existing Damaged

surface & scarified and mixed with gravel and laid, spreaded, graded rolled & compacted to the standard compaction

Step 3- Embankments fillingWherever road widened to minimum 7.4

m width and raised to the required levels and this was done by removing the loose sand and gravel on existing unpaved road, grass and loose soil on shoulders, verges and side slopes of embankments. Then benching the side slopes and road foundations and compacting of layers of suitable soils of compacted thickness of 150mm to the required densities

STEP 4-Embankment Construction

where no widening or raising was done, the top 150mm layer of existing soil was compacted to 100% standard density.

STEP 5-Sub-base Construction Over the compacted sub grade to

the full width of carriageway, a sub-base of thickness 150 to 300mm in layers of 75 to 150mm compacted thickness was constructed with gravelly soil compacted to 100% standard density

STEP 6-BASE CONSTRUCTION

Over the compacted sub-base to the full width of the road formation, a Gravel Soil Base of thickness 150mm was constructed & compacted to 100% standard density.

STEP 7 Priming & Surfacing

Over the compacted base to the width of carriageway of 5.0m, a prime coat and a sand seal were applied.

Priming

On newly constructed road bases a prime coat is required , prior to applying the surface dressing, to bind the surface together and ensure good adhesion of the binder film.

Prime Coat A prime coat is an application of low

viscosity asphalt to a granular base in preparation for an asphalt surface course. The prime coat is designed to perform the following functions:

1. - To coat and bond loose mineral particles on the surface of the base.

2. - To harden or toughen the surface.3. - To waterproof the surface of the

base.4. - To plug capillary voids.5. - To provide adhesion between the

base and the next course.

Prime Coat GSB was shaped and compacted to the

correct longitudinal and transverse profile. The compaction was carried out with standard 8 tonne vibrating and 8-10 tonne smooth wheeled rollers. After shaping and compaction, dust and loose materials on the surface were well brushed and removed. Then the gravel surface was lightly sprinkled with water to moisten the surface. The bituminous material was then sprayed uniformly over the gravel surface.

Prime Coat The material used -CSS-1 Mixed with an equal amount of water. The rate of application of the diluted

emulsion was 1.0-1.5 l/m2. The spraying was done at the ambient

temperature of not below 15 ºc by using a 4000 l bitumen distributor

Closed for traffic -24-48 hrs min 3 hrs After lapse of the period, surface

blinded with Coarse sand as blotting material with light rolling

Surface Dressing (Sand Sealing)

This is a traditional Sri Lankan periodic maintenance technique which effectively SEALS the road surface, but does not improve its skid resistance. However, Sri Lankan climate is suitable for good surface dressing or sand seals with long dry periods and generally predictable rainy seasons..

Surface Dressing (Sand Sealing)

A sand seal comprises a thin film of binder, generally bitumen, which is sprayed on to the primed road surface and then covered with a layer of coarse sand and rolling using a pneumatic tyred roller

The thin film of binder acts as a water proofing seal and prevents the entry of surface water into the road structure.

Surface Dressing (Sand Sealing) 1. Provide a water proof seal to a road

surface, thus preventing the ingress of surface water to the lower layers of the road pavement.

2. Arrest the deterioration of an existing road surface that is showing signs of distress.

3. Restore the skid resistance to an existing road surface.

4. Provide a dust-free and durable running surface for a previously untreated mechanically stable road base.

Surface Dressing (Sand Sealing)

A sand seal was constructed on the primed gravel surface after a lapse of about 3-4 days.

This increased the useful life of the road. The primed surface was dried, and any loose

material swept and removed from the surface.

Surface Dressing (Sand Sealing) Material Used - CRS1 Temperature - Ambient

temperature>15ºC

Spray Rate - 0.75-1.00 lit/sq.m

Covered Sand rate - 8 cu.m/1000sq.m

Rolling -Std 9 wheeled PTR

Damages immediately after construction

several small patchessurface peeled off

Regular Maintenance Drainage facilities Verges and the side drains

Present Road Condition…….. After completion of 3 years time,

1. Road surface looks satisfactory condition in more than 95% of the area

2.No edge failures more than 80% of the area3.Drainage system is under control4.No inundation5.Shoulders in more than 90% area is

satisfactory without erosion.6. Drainage structure are functioning properly7.During the period all damaged major

structures were newly constructed by Ministry of Nation Building using Bailey Bridge Components

Performance of road…….. Road now in good condition Replacing by above method gives following

advantages

1. Money savings

2. Time savings

3. Easy maintenance

4. Environmental friendly construction methods

5. Sustainable developments

Overall Benefits by the Construction ……1. Travel time reduced from 3hrs to 45-60 min2. Vehicle operating cost considerably reduced3. National Network in linked by linking district

capitals4. No detours& passable during rainy seasons5. Contributed to the great extend of GDP &

Economy growth of the area.6. Facilitated freedom of movement, and cilitated freedom of movement, and

revived the economy in the area.revived the economy in the area.7.7. Achieved the Goals & Objectives of RDAAchieved the Goals & Objectives of RDA8.8. The success of the project inline with Vision The success of the project inline with Vision

and Mission of RDAand Mission of RDA