ROAD MATERIALS AND PAVEMENT DESIGN


DESIGN OF ROAD SECTION ALONG UDASA-UDSM ESTATE.


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
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.



Post a Comment

0 Comments