CIU 07471: CONSTRUCTION

TECHNOLOGY:
 1:Describe Procedures used in
Construction of Access Roads in
Irrigation Scheme;

a. To describe different types of access roads.

b. To explain appropriate method of road

construction.
TYPES/CLASSES OF ACCESS ROAD:
 There are several classes of road depending
on their pavement strength.
(i) Earth roads and Gravel roads.
(ii) Soil stabilized roads.
(iii) Water bound macadam (WBM) roads.
(iv) Bituminous or Black-top roads.
(v) Cement concrete roads.
FACTORS CONSIDERED IN THE
CHOICE OF TYPES/CLASSES OF ROAD:
1. Type and Intensity of traffic.
2. Availability of Fund for construction and
subsequent maintenance.
3. Sub-grade soil and drainage condition.
4. Availability of construction material.
5. Climatic condition.
6. Plants and equipments available.
7. Time available for completion of project.
Note; The main factor is the traffic volume
or intensity
PHASES OF ROAD CONSTRUCTION
Road construction project may broadly
divided into two phases.
1. Earthworks and preparation of
subgrade.
2. Pavement structure
The earthwork mainly consists of preparation
of subgrade, to be suitable to receive the
subsequent construction of pavement
structure.
EARTHWORKS
 Aim of earth work; is to bring the subgrade to
the desired grade, camber and compacting
adequately.
 The sub-grade it may be either in

embankment or in excavation, depending on

the topography and the finalized vertical
alignment of the road to be constructed.
 Embankment is constructed where required

to raise the grade line of the road above the

existing ground level.
REASONS TO RAISE GRADE LINE
 Grade line may be raised due to any of the
following reasons;
i) To keep the sub-grade above the high ground
water table.

ii) To prevent damage to road due to surface water

or capillary.

iii) To maintain the design standards of the road with

respect to the vertical alignment.
1:CONSTRUCTION OF EARTH ROAD.
 An Earth Road is the cheapest type of the
roads prepared from natural soil.
 Made with soil available at site and at near by

borrow pits
 The camber is very steep, ranges between 1

in20 to 1 in33: Maximum slope of 1in20 is

recommended to avoid erosion due to rain
waters and formation of ruts.
MATERIAL SPECIFICATION
 Soil of the BASE Wearing
following COURSE Course
properties are Clay <5% 10 to 18%
considered Contents
satisfactory for Silt 9 to 32% 5 to 15%
construction of Contents
Earth Roads Sand 60 to 80% 65 to 80%
Contents
Liquid Limit <35% <35%

Plastic <6% 4 to 10%

Index
CONSTRUCTION PROCEDURE.
 The construction of Earth Road may be divided
in the following steps
(i) MATERIAL; carry out soil survey to determine
suitability of soil and suitable location of
borrow pits within economic haulage
distances.
(ii) LOCATION; Establish the centre line and road
edges alignment by driving wooden pegs.
Note: Reference pegs are driven to help the
contractor to follow the desired vertical profile
of the road during construction.
Cont…. procedure
(iii) PREPARATION OF SUBGRADE.
Various operation involved in the preparation of sub-grade are as
follows;
a) Clearing site
b) Excavating and constructing of fills to bring the to a desired grade.

c) Shaping of the sub-grade.

(iv) PAVEMENT CONSTRUCTION. The borrowed soil is dumped on the
prepared sub-grade and pulverised. The field moisture is checked
and addition of water is added if necessary to bring it up to OMC.
Then mix, spread and rolled in layers not exceed 10cm to 15cm for
compaction based on the soil type, compaction amount and
equipment available. Check required camber and correct it if
necessary to
(v) OPENING TO TRAFIC: The compacted earth road is allowed to dry
for a few days before opening to traffic.
2: CONSTRUCTION OF GRAVEL
ROADS.
 The Gravel road are considered superior to
earth roads as they can carry heavier traffic.
 Its carriage way is constructed with gravels.
 Its camber is between 1in25 and 1in30.
 It is fairly resilient and not become slippery

when wet.
 There are two types of construction method.

i) Feather edge type. I

ii) Trench type.
Gravel Road cont……….
 Feather edge type is  In the trench type, the
constructed over the sub-grade is prepared
sub-grade with varying by excavating a shallow
thickness so as to trench or constructing
obtain the desired trench by
cross slope for concrete/blocks or cab
pavement surface stone along the .
 Since there is better
confinement for the
gravel, the trench is
preferred.

Feather Edge Type Trench Type

Construction Procedure:
 Note: Stage (i) to (iv) in Earth road are done; then;
1. Material: Gravel to be used is stocked along the proposed
road.
2. Location: Pegs are driven in the earth road.
3. Preparation of sub-grade: Trench is formed according to
the width of carriage way.
4. Pavement Construction: Crushed Gravel are placed
carefully to avoid segregation. Then spread to obtain the
desired camber. Rolled using smooth wheeled rollers
starting from edge to center with overlap of at least half
the width of roller in longitudinal direction.
5. Opening to traffic: After final rolling in 24hrs the road is
opened to traffic:
3. CONSTRUCTION OF (WBM) ROADS:
 The water Bound Macadam is the construction known
after the name of John Macadam.
 The term macadam in the present means, the pavement
base course made of crushed or broken aggregate
mechanically interlocked by rolling and the voids are
filled with screening and binding materials with the
assistance of water.
 It may be used as the sub-base, base course, or surfacing
course.
 Note; when used as surfacing course, deteriorate rapidly
due to traffic and weather, it is desirable to provide a
bituminous surfacing course over the WBM layer to
prolong its life.
CONSTRUCTION PROCEDURES:
1. The foundation: Is prepared to the required grade
and camber; it may be Sub-grade, Sub-base, or base
course.
2. Course aggregate are spread uniformly to proper
profile to even thickness upon the prepared
foundation and checked.
3. Compaction is done by three wheeled power roller of
capacity 6-10 tones.
4. Then dry screening are applied gradually over the
surface to fill the voids in three or four applications.
Then sprinkled with water swept and rolled. Wet
screening are swept into the voids by hand brooms.
WBM Cont…..
5. After application of screening and rolling,
the binding material is applied at a uniform
and slow rate at two or more successive
layers. After that, water is sprinkled and wet
slurry swept with brooms to fill the voids.
This is followed by rolling
6. After final Compaction the WBM course is
allowed to set for over-night. No traffic is
allowed till the WBM layer sets and dries
4:CONSTRUCTION OF BITUMINOUS
PAVEMENTS
 There are two main construction
techniques/types/method used.
 1. Surface dressing and seal coat.

 2.Premix.

In these methods, the bituminous binders used are either

straight run bitumen, road tar, cutback or emulsion, The
choice depend on type of construction, availability of
materials and equipment, and Climatic condition.
Bitumen and Tar, require heating to bring them to the
proper viscosity of their use.
Cutback and Emulsion do not normally require heating, are
therefore applied cold, and the Technique is known as
“Cold Mix”
General Construction Procedure;
1. Interface Treatment; is the treatment which is
necessary to provide the necessary bond
between the old and the new layers.
In which, the existing pavement is to be cleaned
to remove dust and dirt, and a thin layer of
bituminous binder is to be sprayed before the
construction of any type of bituminous layer
over this surface;
The interface it may either be a prime coat or a
tack coat, and in some cases the prime coat
followed by a tack coat.
a). Prime Coat
 Bituminous Prime coat, is the first application of low
viscosity liquid bituminous material s over an existing porous
or absorbent pavement surface like WBM base course.
 The main Objectives/ Function of priming;
i) Provide base with temporary protection against rainfall and
light traffic till the surfacing can be laid.
ii) Strengthen the base by binding the finer particles of
aggregates together.
iii) Help to seal /plug the surface pore/voids in the base so it
reduce the absorption of the first spray of the binder of the
surface dress
iv) It assist in promoting and maintaining adhesion between the
road base and surface dressing.
b). Tack coat.
 Bituminous Tack coat, is the application of
bituminous materials over the an existing
pavement surface which is relatively
impervious like an existing bituminous
surface or a cement concrete pavement or a
previous surface like the WBM which has
already been treated by a prime coat.
 Tack coat is usually applied by the spraying

bituminous of higher viscosity like the hot

bitumen.
1: (a).SURFACEDRESSING METHORD:
 Bituminous Surface Dressing (BSD) is
provided over an existing pavement to save
as thin wearing coat. Done in Single coat or
Double coat.
 The main function of BSD are;

i) To provide a water proof seal to road surface.

ii) Arrest deterioration of an existing road surface.
iii) Skid resistance to an existing road surface.
iv) To provide a dust free and durable running
surface.
CONSTRUCTION PROCEDURE
 Single coat surface:
 It consist of a single application of bituminous binder material
followed by spreading of aggregate cover and rolling.
 Seal Coat.
 Usually recommended as the top coat over a certain
bituminous pavement which are not impervious, such as open
graded bituminous constructions like premixed carpet, or over
a bituminous pavement which is worn out.
 The selection of material required must be done very careful
especially in properties of binder and chipping compared to the
nature of material, road surface temperature, Characteristic of
the road, type of binder and the cost of available material.
5: PREMIX METHORD.
 In this method the aggregate and the bituminous
binder are mixed thoroughly before spreading and
compaction. Depending on the gradation of aggregates
chosen, premix may be classified as.
i) Open graded mix,
ii) Semidese mix,
iii)Dense mix.
The common types of premix bituminous construction
are
a. Bituminous Macadam,
b. Bituminous Carpet
c. Bituminous concrete
Construction Procedure;
 Bituminous Macadam Bond; Is the premix consists of
one or mare courses of compacted crushed aggregates
premixed with bituminous binder, laid immediately after
mixing.
 Premix Carpet; consists of coarse aggregate of 12.5 to
10mm size premixed with bitumen or tar binder, are
compacted to a thickness of 20mm to serve as a surface
course of pavement.
 Bituminous Concrete or Asphalt Concrete; Is a dense
graded premix bituminous mix, which is well compacted
to form a highly pavement surface course. It consists of a
carefully proportioned mixture of aggregates, fine
aggregates; mineral fillers and bitumen.
 Procedure cont……..
1. Prepare the existing surface by removing pot holes or ruts if any.
2. The irregularities are filled with premix chipping seven days
before laying surface course.
3. Apply Prime coat.
4. Apply Tack coat as a binder.
5. Preparation and application of the premix. This must de applied
at the required temperature (150 – 177) degree at transport, and
(121 – 165) degree at spreading.
Verify camber and thickness of min 30mm to max 50mm by
one layer.
6. Rolling; Thoroughly after spread, then initial rolling by 8 to 12
tones roller then, Intermediate rolling is done with pneumatic
tyre roller of 15 to 30 tones.
7. After this final rolling the road is open to traffic.
Procedure cont………
1. Preparation of site & Placing of different layers.
i. Proper profile, ruts depression are rectified.
ii. Made surface free of dust and loose material.
iii. Apply prime coat to the surface.
iv. Apply binder uniformly. (note; excessive binder will course
bleeding)
v. Apply Stone chippings as per requirement to cover the surface
uniformly.
vi. Rolling of first or final coat.
vii. If the Second coat is applied then; the binder is applied and
stone chipping and rolling is done again.
viii. Finishing and opening to traffic: Check for profile longitudinal
and cross. Then variations greater than 6mm are corrected then
after 24 hrs the road is opened to traffic.
 LABOUR BASED ROAD
CONSTRUCTION TECHNOLOGY.
 CONSTRUCTION PROCEDURE;
1. SITE CLEARANCE AND SETTING OUT:
i) Heavy bushes clearing; involves cutting down and
removing trees, digging roots and removing root systems to
prevent re-growth.
ii) Boulder removal; this can involve hand carrying small
boulders, rolling clear, breaking or digging and burying of
large boulders.
iii) Top soil removal; is usually only needed where the
topsoil is deep(10 – 15cm) very organic and obviously much
lower strength than the soil below.
iv) Setting of Center line; Centerline and the width of the
road, including side drain setting is done before earth work.
2. Earthworks
 Basically, earthworks involves digging drains
and using the materials to built up the
camber.
 There are two situations to consider;

1. Flat Terrain.
2. Sloping terrain.
1.Flat Terrain
 Earth work for flat terrain is not so difficult,
the consideration is taken for camber
formation between the drains by excavating
the side drains and use of those materials to
form a camber;
 After use of those materials, if there is a need

of addition of materials it can be done by

importation of materials from the
surrounding area borrow pits. (consider fig 1 on pg
5)
2. Sloping Terrain.
 For sloping terrain, there is a need to cut and fill before
forming a camber. After setting out to see the road
formation( see fig 2 on page 5), The road construction will
have the following features;
i. The high side drain will have to be dug deep.
ii. The low side drain have to filled, no drain needed on that side.
iii. The road will be build on cut and filled surface.
There are two stages to be followed.
Stage 1. Cutting the high side and fill / built up the
lower side.
Stage 2. Excavate the high side drain and form a camber.
(see fig 1&2 on page 6)
Advantages of working in stages
method due to slop terrain
 1. Filling materials is balanced during
excavation/citing.
 2. Filling material can be obtained close as

possible to where it is needed, so reducing

the need for longitudinal haulage cost
 No need for drain on the low side. Since the

edge of the road sloping down to the natural

ground.
DRAINAGE
 Drainage in general deals with means of water control.
 Since water is the main contributor to the wear and damage low
volume rural roads; then it must be controlled well.

 Water to be controlled may be form of,

i) Ground water.
ii) Surface water (streams and rivers)
iii) Rain water

 There are two ways on which water can damage the road, which
are;
1. By washing away the soil (scouring or erosion)
2. By making the road body weak or less strong to traffic
(lowering the road bearing capacity).
DRAINAGE COMPONENTS:
 1. Road surface drainage =>
Enables the water to flow off the road surface.
 2. Side Drains and mitre drains=>
It collect and lead the water away from the road.
 3. Catchwater drains =>
The one which catches surface water before it reaches the road.
 4. Scour Checks =>
The structures which prevent the erosion in the ditches by slowing
down the flow of water.
 5. Culverts =>
Is the structure which lead the water from (upper) side drains
under the road to the other (lower) side.
 6. Small bridges and drifts.=>
Are structures which allows the road to cross small rivers and
streams in a controlled manner throughout the season.
ROAD SURFACE DRAINAGE
 This is achieved by installing a camber on the
road carriage way, which will enable the surface
water to run off to the side drains.
(See fig on page 22 5.5.2)
The camber is the slope formed both sides of
the road from the centre line towards the road
shoulder. Slope varies according to the materials
used. For Earth and Gravel road it ranges from 5
to 10 per cent to obtain sufficient run-off. All
road ruts and pot holes must be treated before
camber formation to the existing road.
SIDE DRAINS
 These are structures constructed to collect all
rain water from the road carriage way and
dispose it quickly and in a controlled manner
so as to minimise damage to the road.
 It can be constructed in three forms

1. V-shaped.
2. Rectangular shape
3. Trapezoidal shape
(See fig on page 22 5.5.3)
EROSION CONTROL STRUCTURES
 The high speed of the water through the side
drains and large quantity cause erosion. This
can be controlled by introducing the
following
1. Mitre drains,
2. Scour checks,
3. Cut-off Drains.
MITRE DRAINS
 These are diverting structures used to control
erosion by reducing the water flowing
through the drain
 Where possible provided at every 100m or

less and
 Where the gradient of the road is very small,

provide at every 50m along the side drain.

 The angle between mitre drain and the side

drain should never be greater than 45degree.

An angle less than 30degree is ideal.
SCOUR CHECKS
 These are structures used to reduce the
speed of the water and prevent the water
from eroding the road structures.
 Provided where the slope of the exceed 4%,

because the drainage water have a tendency

of gaining speed which will erode the side
drains.
 Are constructed with natural material

available along the road sides such as natural

stones, wooden or bamboo atakes.
CUT-OFF or INTERCEPTION DRAINS
 These are structure used for channeling away
water from the high side road in sloping
terrain.
 Are particularly useful to surrounding area

such as Drift, Culverts and Bridges.

 Purpose of it is to prevent the water from

reaching the road, or to direct water to

where it can cross the road safely at a
constructed water crossing.
Consideration with Cut-off drains
 The water are usually carries a lot of silt and
if not properly built can silt up quickly,
 As they are off the road they will probably

receive less maintenance especially when

they are difficult to maintain.
 When they fail, water will break through in a

concentrated flow causing damage.

 They may be ploughed up or blocked off by

the people using the land.

CULVERTS
 Allow water to cross underneath the road to a place where it can be safely
discharged.
 The water may be from natural streams or from run-off surface water from the

road surface.

LOCATION or SITING: For existing road, look places where;-

1. Small gullies have been formed because water has been crossing the road.
2. Sand has deposited on the road surface because of standing water.
3. Drain have been badly damaged because they have been carrying too much water.

DIMENSION: Most is single line of concrete pipe, Dia not less than 0.6m. Up to 0.8m.
Note. Smaller Dia are difficult to maintain. Instead of using large Dia, two or more
rows of smaller dimension can be used.

See Fig on pg 29.

DRIFTS.
 These are structures used to provide an efficient
and economic method of allowing water to cross
from one side of the road to another.
 Water is allowed to pass over the surface of the
road. So the road need special protection to stand
up to the flow of the water.
 The protection is done by, stone parked or concrete
surface where water will pass. And the level of the
drift must be lower than the road on each side to
make sure that water does not split over onto the
unprotected road surface. See fig on
pg 31.
TYPES OF DRIFT STRUCTURES;
 There are three types of structures that together Known
as drifts
1. Splashes= Are minor crossing, that carry water from a
side drain across the road to the lower sides. Are located
at low points along the road alignment and when the side
drains cannot be emptied by mitre drains and the water
has to taken across the road.
2. Drifts= Are crossing at large drainage channels and small
rivers. They may have to take strong flows of water.
3. River Crossings= Are large crossings over a sand river
bed. Usually, the river bed would consist of deep sand
and the crossing has to be built with a firm foundation.