INTRODUCTION;
The site is located near Mlimani Primary school, where the
length of road section is 87 meters and its average width is 8metres, Features
surrounding the sites 20 meters apart are
·
Trees
·
One residential house
·
Vegetation
The site utility includes electricity and water, where the
nature of the road section is gravel with a drainage system at one side. The
main purpose of UDASA-ESTATE ROAD is to provide the access for users which are
students and staffs of Mlimani Primary School, Magufuli Hostel, Estate office
and residential houses located near the area .
DESIGNING PROCESS;
ASSUMPTIONS;
·
Designing for flexible pavement.
·
Designing weight of road section considered to
be greater than 3 tones to 8 tones.
·
Design life of 10 years is considered
·
Demolishing of existing road section will be
done up to the formation level.
·
Road section will contain four layers (sub-grade,
sub-base, base course, surfacing course.)
·
Drainage system provided both sides of the road
section.
sub-grade
layer ;
Material; soil
Required depth; 150mm thick
The purpose of having subgrade is
to provide support to the pavement as its foundation. where by the minimum of
100% of standard proctor compaction should be attain in subgrade. For clay soil
95% and ,moisture content of 2% in excess of optimum value. Soil below subgrade
should be compacted to 97% of standard proctor compaction.
CBR test is followed where a
sample is taken into 3 different
position, if CBR less than 2% for 100mm thickness then minimum CBR of 10% is to
provided to the sub base for CBR of 2%. If CBR more than 15% no need to provide sub-base.
Sub- base course;
The function of sub – base is to
distribute the stresses over a wide area of the subgrade imposed by the traffic
where by selected materials placed on subgrade which is compacted to 98% of
heavy compaction.
The CBR test of sub – base should
be 15% and must passing through 425 micron IS sieve.
Base course;
Layer above sub-base course where
thickness of this layer range between 100 to 150mm and is governed by
underlying layer properties. Generally consisting of a specific type of
aggregate, it is placed by means of attentive spreading and compacting to a
minimum of 95% relative compaction , thus providing the stable foundation
needed to support either additional layers of aggregates or the placement of an
asphalt concrete wearing course which applied directly on top of the base
course.
Surface course;
The surface course of a flexible
pavement protects the underlying base course from traffic and water while also
providing adequate tire friction, generating minimal noise and giving suitable
light reflectance for night time driving. Thickness of of surface course
depends upon the traffic volume and type of material used for it. For gravel
roads like ESTATE-UDASA ROAD SECTION extra thickness due to the traffic action. The impact value of
bituminous wearing course not exceeding 30% in order to reduce degradation of
aggregates by crushing.
EARTHWORKS;
By definition; earthworks the
process of excavate the existing land to a suitable level so that road
construction may begin. Normally in road design project both will be necessary
and movement of earth from one part of the site to the next will be necessary.
DESIGN REQUIREMENTS;
DESIGN CRITERIA
Earthwork must be designed to meet
the specified performance criteria for;
(a)
Volumetric
change;
i/ settlement due
to consideration in embankments and material under subgrade in cut.
ii/ non load
dependent soil volumetric changes, including reactive soil movements .
(b)
Slope
stability;
i/ batters are
stable and will not display any detectable instability or evidence of impending
loss of stability during the design life.
ii/ overhanging
loose or unstable material in cuts is prevented for slipping or failing.
iii/ any material
which becomes detached is prevented from reaching the road shoulder.
(c)
Durability
and maintainability;
i/
detrimental effects from water example
erosion, ponding of water, are kept to the minimum practicable.
ii/ there is no
undermining of any existing batter slopes.
iii/ maintenance
that would normally be required of the road and environs can be readily and
economically undertaken.
DESIGN LIFE;
Earthwork must be design for the following
design life;
ELEMENT
|
DESIGN
LIFE (YEAR)
|
Embankments, including reinforcement embankments
|
100
|
Cut batters including batter treatments.
|
100
|
![](file:///C:/Users/MUSSA/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png)
DESIGN OBJECTIVES;
The design must achieve the
following;
·
Providing safe run off area for errant vehicles
·
Providing a natural fit into the surrounding terrain.
·
Minimizing maintenance costs.
·
Providing safe environment for personnel undertaking.
·
Minimizing the length of traffic barriers consistent
with safety requirement.
DRAINAGE DESIGN;
GENERAL CONSIDERATIONS;
Roads will
affect the natural surface and subsurface drainage pattern of a watershed.
Road
drainage design has as its basic objectives such as,
·
The reduction and elimination of energy generated of
flowing water.
·
The destructive power of flowing water, water must not
be allowed to develop sufficient velocity so as to cause excessive wear along
ditches or along exposed running surfaces, cuts, or fills.
·
Provision for adequate drainage is of paramount
importance in road design and cannot be overemphasized.
The
presence of excess water within the roadway will affect the engineering properties
of the materials which is constructed. Cut or fill failures, road surface
erosion, and weakened subgrades followed by a mass failure are all products of
inadequate or poorly designed drainage. Many drainange problems can be avoided in
the location, and design of the road.
DESIGN CRITERIA;
A road drainage system must satisfy
two main criteria if it is to be effective throughout its design life.
·
It
must allow for a minimum disturbance of the natural drainage pattern.
·
It
must drain surface and sub surface water away from the roadway and dissipate it
in a way that prevents excessive collection of water in unstable areas and
subsequent downstream erosion.
WALKWAYS;
Walkways or sidewalks ËŠpedestrian lanes’ that provide space for people to travel the
public right-of-way that separated from roadway vehicles. They also provide
places for children to walk, run, skate, ride bikes, and play.
Purpose of pedestrian lane;
·
Create
the appropriate facility for the walking area of the public right-of-way.
·
Improve
pedestrian safety.
Walkways are typically made of
concrete, less expensive walkways may be constructed of asphalt, crushed stone,
or other materials if they are properly maintained and accessible. The minimum
width of walkways is 1.5m according to the institute of transportation
engineers (ITE).
KERBSTONES;
Kerbing improves delineation of road
edges and contributes to the appearance and safety of the road.
Barrier kerbs; the type kerb that selected to be used to
UDASA-ESTATE ROAD are design to prevent vehicles encroachment on the roadsides.
Where by its dimensions is 450 x 300 x 150 mm.
The purposes for kerbs construction
are;
·
To
assist drainage
·
To
protect pedestrians
·
Improvement
of aesthetics values of the road alignment
·
To
reduce maintenance of shoulders.
·
To
provide a boundary to landscaping treatments.
ROAD MARKINGS;
Pavements lines are lines, symbols, words, colors, or other
devices except sign and power operated control devices, set into surface of
applied upon or attached to the roadway.
Requirements;
·
Specified
colors are identifiable day and night
·
Minimum
visibility standard are maintained throughout the materials lifetimes.
Road markings are 4 inches wide. Where the factors that
considered in selecting markings are;
·
Durability
·
Workability
·
Drying
·
Accommodation
of heavy traffic volumes.
Yellow color are used to
separate two lane and white color used to separate pedestrian and carriage way
REFERENCES;
1. Main roads supplement to austroads
GRP Pat 6. Road side design, safety and barriers.
2. Pedestrians and cyclists facilities-
MRWA
3. AS 2876-2000- concrete kerbs and
channels – manually or machine placed.
0 Comments