BFC 31802 Chapter 4a - Copy.ppt

BFC 3042 HIGHWAY ENGINEERING Lecturer: Mr. Basil David Daniel
Chapter 4
ROAD CONSTRUCTION
1

2
SITE INVESTIGATION
SITE INVESTIGATION
Site investigation is carried in most cases as a preliminary to new works.
The reasons for site investigation are given below:
• Investigation of defects of existing roads
• Investigation to the safety of existing works.
• Investigation relating to the suitability and availability of materials for constructional purposes.
Investigation of defects of existing roads
This type of investigation is necessary to establish the cause of
the failure and to provide information indicative of remedy.
Measurements and observations of the structure are taken to
indicate whether or not the ground conditions are involved.
This investigation will reveal the level of ground water and the
true state of sub-strata.

3
SITE INVESTIGATION
Investigation to the safety of existing works
To investigate existing works and decide whether the latter will
adversely be affected by changes in ground conditions.
Existing works may be affected by the following:
• excavations may reduced ground support
• tunneling or mining which may cause subsidence
• vibrations ( eg. from piling operation) which may cause fractures
• extra load created by new works may overload stratum supporting
existing works
• soil movement due to heat induced by proximity to plant
installations.
• ground water lowering
• disturbed drainage path may cause flooding and instability of
slopes.

4
SITE INVESTIGATION
Investigation relating to the suitability and availability of
materials for constructional purposes
There are two quite different problems with the mass
movement of earth:
(1) Disposal
- e.g. in the case of spoil from cuts
(2) Acquisition
- e.g for large fill projects such as reclaimation
In both cases however, investigation is necessary to
establish the quantity and suitability of the soil for the
purpose for which it is to be used.

5
ROAD CONSTRUCTION PROCESS
 ROUTE SURVEY
 SITE INVESTIGATION

6
 SITE CLEARANCE
 EARTHWORKS

7
 SUBGRADE COMPACTION AND LEVELLING
 ESTABLISHING THE FORMATION LEVEL

8
 SUB-BASE CONSTRUCTION

9
 BASE CONSTRUCTION

10
 APPLYING OF PRIME COAT
 LAYING OF BINDER COURSE

11
 APPLYING OF TACK COAT
 LAYING OF WEARING COURSE
ROAD IS COMPLETED.

Activity Work Description Measurement
Clearing
Cutting, removal and disposal of
everything above ground level
including object overhanging the
area to be cleared
Levelling of obsolete dikes,
terraces, ditches
All stumps and roots be removed to a
depth of not less than 0.3 m below the
propose road.
This requirement also usually holds in
embankment areas where the height of
the feel not less than about 1.5 m.
In embankment section when the
embankment height is to be more than
1.5 m, tree and stump may be left in
place and cut off at ground level or at a
height of 75-150 mm above the existing
ground surface.
Grubbing
Removal and disposal of surface
vegetation, roots, underground
parts of the structure and other
obstruction
Stripping Removal topsoil or stockpiling
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EARTHWORKS
This process consists of clearing, grubbing and stripping in road construction
area. It also includes the demolition and disposal of soils to a formation level
(top of the sub grade).

13
EARTHWORKS
Excavation
Excavation increases the volume of material.
It is therefore necessary to use a bulking factor to determine the volume of material that will be
created by excavation.
Bulking factor is defined as:
Bulking Factor = Volume after Excavation / Volume before Excavation
Similarly a shrinkage factor is defined for the compaction of a soil at it's final destination:
Shrinkage Factor = Volume after Compaction / Volume before Excavation

14
EARTHWORKS
Earthmoving Equipment
Bulldozer - This is used primarily for pushing soil. Vehicles
are generally tracked and require large amounts of
traction. Many bulldozers incorporate hydraulic
attachments at the rear for breaking up soil and rock. The
best known of the vehicles.
Drag Line - This vehicle allows excavation below it's own
level. It is essentially a bucket on the end of a jib and is
used solely for bulk excavation as it is relatively
uncontrolled.
Dump Truck - These are wheeled vehicles and as such are
able to move much faster. This is offset by a lack of
traction and dump trucks are always the first to get stuck.
They are used for transferring material from one part of
the site to another.
Bulldozer
Drag Line
Dump Truck

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EARTHWORKS
Earthmoving Equipment
Shovels - These again are normally wheeled vehicles and
are used to fill up the dump trucks. Typically they take 2-3
loads to fill an average dump truck.
Hydraulic Excavators - These can be either wheeled or
tracked and are used again to excavate below truck level.
They have a very small capacity and are extremely
flexible.
Grader - Used to level out deposited fill, ready for
compaction.
Rollers - There are many different types of roller and they
are used for compaction. Different types include vibratory,
sheepsfoot and grid. Vibratory are the most common as
they have effectively double the effect.
Shovel
Excavator
Grader
Roller

16
MASS HAUL DIAGRAM
In order to minimize material waste or borrow, it is necessary to produce what is called a
Mass
Haul diagram.
This is essentially a plot of cumulative volume of soil against distance along the road,
often
called the chainage.
Cut volumes are taken to be positive and fill volumes to be negative.

17
MASS HAUL DIAGRAM
A rising curve indicates an increasing
volume (cut).
A maximum point on the curve represents
the end of a cut.
A falling curve represents a decreasing
volume (fill).
A minimum point represents the end of a
fill.
Areas at the end of the diagram represent
a waste or a deficit.







 )
(
2
1
2 nh
h
hb
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MASS HAUL DIAGRAM
Calculation of Cross Sectional Area
The first stage in the production of the Mass Haul Diagram is the calculation of the cross
sectional areas of cut or fill at different points along the road.
For a cut or fill on horizontal ground
Assuming a cut such as the one above, the cross sectional area is given by:
Area =
= hb + nh2
= h(b + nh)

n
S
nh
b
S








2
n
S
nh
b
S








2
n
b
W
W
n
b
h G
L
4
)
(
2
2
1 2









19
MASS HAUL DIAGRAM
For a cut or fill on sloping ground
Assuming a cut such as the one above, the cross sectional area is found firstly by
calculating WL and WG:
WL =
WG =
Thus Area =

20
MASS HAUL DIAGRAM
Example Calculation
The table below shows ground levels and formation levels for a proposed road construction.
Embankments are to be built with side slopes of 1:2.5 and cuttings with slopes of 1:3.0. The
embankment crest width and cutting base width is 13m. It may be assumed that the ground
is horizontal across the section.

21
(a) Construct a Mass Haul diagram for the project given the following:
Bulking Factor = 0.8
Shrinkage Factor = 1.0

MASS HAUL DIAGRAM
-90000
-80000
-70000
-60000
-50000
-40000
-30000
-20000
-10000
0
10000
20000
30000
40000
50000
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Chainange (m)
Cumulative
volume
(cubic
meter)
22

23
MASS HAUL DIAGRAM
-90000
-80000
-70000
-60000
-50000
-40000
-30000
-20000
-10000
0
10000
20000
30000
40000
50000
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Chainange (m)
Cumulative
volume
(cubic
meter)
(b) A river breaks up the project at chainage 1160m. Calculate the volumes of
waste material and borrow for this scenarios:
(i) Material cannot be moved across the river
Fill Cut Cut Fill Fill Fill Cut
150 280 500 740 1160 1280

24
Distance (m) 150 130 220 240 420 120 220
Cut (m3) 15,000 36,000 49,000
Fill (m3) 15,000 36,000 68,000 11,000
Haul (m3) 15,000 36,000 11,000
Borrow (m3) 68,000
Waste (m3) 38,000
River
Borrow = 68,000 m3
Waste = 38,000 m3

25
MASS HAUL DIAGRAM
-90000
-80000
-70000
-60000
-50000
-40000
-30000
-20000
-10000
0
10000
20000
30000
40000
50000
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Chainange (m)
Cumulative
volume
(cubic
meter)
(b) A river breaks up the project at chainage 1160m. Calculate the volumes of
waste material and borrow for this scenarios:
(ii) A Bailey bridge is constructed allowing material to be transported across the river
Fill Cut Cut Fill Fill Fill Cut
150 280 500 740 1280

26
Distance (m) 150 130 220 240 540 220
Cut (m3) 15,000 36,000 49,000
Fill (m3) 15,000 36,000 79,000
Haul (m3) 15,000 36,000 49,000
Borrow (m3) 30,000
Waste (m3)
Borrow = 30,000 m3
Waste = 0 m3

27

28
SUBGRADE PREPARATION
The subgrade is the in-situ material upon which the pavement structure is placed.
The subgrade can often be the overriding factor in pavement performance.
Increasing the load-bearing capacity of the subgrade soil will most likely improve pavement
load-bearing capacity and thus, pavement strength and performance.
Additionally, greater subgrade structural capacity can result in thinner (but not excessively thin)
and more economical pavement structures.
The finished subgrade should meet elevations, grades and slopes specified in the contract
plans.

29
Subgrade Performance
A subgrade’s performance generally depends on two interrelated characteristics:
(1) Load bearing capacity
- The subgrade must be able to support loads transmitted from the pavement structure.
- This load bearing capacity is often affected by degree of compaction, moisture
content, and soil type.
- A subgrade that can support a high amount of loading without excessive deformation
is considered good.
(2) Volume changes
- Most soils undergo some amount of volume change when exposed to excessive
moisture.

30
Improving Subgrade Performance
Poor subgrade should be avoided if possible, but when it is necessary to build over weak soils
there are several methods used to improved subgrade performance:
(1) Removal and replacement (over-excavation)
Poor subgrade soil can simply be removed and replaced with higher quality fill
(2) Stabilization with a cementitious or asphaltic binder
The addition of an appropriate binder (such as lime, portland cement or emulsified
asphalt) can increase subgrade stiffness and/or reduce swelling tendencies.
(3) Additional base layers
- These layers spread pavement loads over a larger subgrade area
- When designing pavements for poor subgrades the temptation may be to just design a
thicker section with more base material because the thicker section will satisfy most
design equations.

31
Good Practices in Subgrade Preparation
(1) Ensure the compacted subgrade is able to support construction traffic
If the subgrade ruts excessively under construction traffic it may cause premature
pavement rutting and will result in variable paving thicknesses.
(2) Remove all debris, large rocks, vegetation and topsoil from the area to be paved
These items either do not compact well or cause non-uniform compaction and mat
thickness.
(3) Treat the subgrade under the area to be paved with an approved herbicide
This will prevent or at least retard future vegetation growth, which could affect subgrade
support or lead directly to pavement failure.

32
SURFACE PREPARATION
Before a pavement is placed the surface to be paved must be prepared.
Pavements constructed without adequate surface preparation may not meet
smoothness specifications, may not bond to the existing pavement (in the case of
overlays) or may fail because of inadequate subgrade support.
Surface preparation generally takes one of two forms:
Preparing the subgrade and granular base course for new pavement
Involves activities such as subgrade stabilization, over-excavation of poor
subgrade, applying a prime coat or compacting the subgrade.
Preparing an existing pavement surface for overlay
Involves activities such replacing localized areas of extreme damage, applying a leveling
course, milling, applying tack coat, rubblizing and setting.

33
SURFACE PREPARATION
Prime Coats
The granular base layer can be prepared with a prime coat if necessary. A prime coat
is a sprayed application of a cutback or emulsion asphalt applied to the surface of
untreated subgrade or base layers in order to (Asphalt Institute, 2001):
1. Fill the surface voids and protect the subbase from weather.
2. Stabilize the fines and preserve the subbase material.
3. Promote bonding to the subsequent pavement layers.
Tack Coats
A tack coat is a thin bituminous liquid asphalt, emulsion or cutback layer applied
between HMA pavement lifts to promote bonding. Adequate bonding between
construction lifts and especially between the existing road surface and an overlay is
critical in order for the completed pavement structure to behave as a single unit and
provide adequate strength. If adjacent layers do not bond to one another they
essentially behave as multiple independent thin layers.

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SURFACE PREPARATION
COMPACTION
Compaction is the process by which the volume of air in an Hot Mix Asphalt (HMA) mixture is
reduced by using external forces to reorient the constituent aggregate particles into a more
closely spaced arrangement.
Compaction is the greatest determining factor in dense graded pavement performance.
Inadequate compaction results in a pavement with decreased stiffness, reduced fatigue life,
accelerated aging/decreased durability, rutting, raveling, and moisture damage.

35
SURFACE PREPARATION
Compaction Equipment
There are three basic pieces of equipment available for HMA compaction:
(1) Paver screed
(2) Steel wheeled roller
(3) Pneumatic tire roller.
Paver Screed Steel Wheel Roller Pneumatic Tire Roller

36
QUALITY ASSURACE & QUALITY CONTROL
Quality assurance
Planned and systematic actions necessary to provide confidence that a product or facility will
perform satisfactorily in service.
Quality assurance addresses the overall problem of obtaining the quality of a service, product,
or facility in the most efficient, economical, and satisfactory manner possible.
Quality assurance involves continued evaluation of the activities of planning, design,
development of plans and specifications, advertising and awarding of contracts,
construction, and maintenance, and the interactions of these activities.
Quality control
Those quality assurance actions and considerations necessary to assess production and
construction processes so as to control the level of quality being produced in the end
product.
This concept of quality control typically includes sampling and testing by the contractor to
monitor the process but usually does not include acceptance sampling and testing by the
agency/owner.

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QUALITY ASSURANCE & QUALITY CONTROL
Acceptance
Sampling, testing, and the assessment of test results to determine whether or not the quality
of produced material or construction is acceptable in terms of the specifications.
Independent assurance
A management tool that requires a third party, not directly responsible for process control or
acceptance, to provide an independent assessment of the product and/or the reliability of
test results obtained from process control and acceptance testing.
The results of independent assurance tests should not be used as a basis of product
acceptance.

38

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