chapter 1 handout

JIGJIGA UNIVERSITYRoad & Bridge Construction

Chapter 1: Introduction

IMPORTANCE OF TRANSPORTATION

Transportation contributes to the economic, industrial, social and cultural development of any country. Transportation is vital for the economic development of any region since every commodity produced like clothing, industrial products or medicine need transportation at all stages from production to distribution.

Types of Transportation.1. Railways2. Roadways3. Airways4. Water ways5. Pipe lines

Importance of Roadways1. Roads can cover the wide geographical areas.2. Roads can be constructed at lower initial costs, compared to railways.3. Road transport offers quick deliveries and hence time can be saved.4. Road transport offers door to door service.5. Road transport has a high employment offers.

Classification of Roads

The types of roads are classified into 3 categories, depending upon weather, pavement surface and depending upon the function.

Depending on weather All weather roads: Roads which can be used during all the weather conditions. Fair weather roads: Roads which can be used during summer and winter season but

not during the rainy season.

Depending upon the pavement surface Surfaced roads: Roads which are provided with the asphalt or concrete surfacing. Unsurfaced roads: Roads which are not provided with the asphalt or concrete

surfacing.

Instructor : Shivaraj B S 1


Depending upon the functionThe functional classification of roads in Ethiopia includes five functional classes.

Trunk Roads (Class I) Link Roads (Class II) Main Access Roads (Class III) Collector Roads (Class IV) Feeder Roads (Class V)

Trunk Roads (Class I)Centers of international importance and roads terminating at international

boundaries are linked with Addis Ababa by trunk roads. They are numbered with an "A" prefix: an example is the Addis-Gondar Road (A3).

Link Roads (Class II)Centers of national or international importance, such as principal towns and urban

centers, must be linked between each other by link roads. They are numbered with a "B" prefix. An example of a typical link road is the Woldiya- Debre Tabor- Woreta Road (B22), which links, for instance, Woldiya on Road A2 with Bahir Dar of Road A3.

Main Access Roads (Class III)Centers of provincial importance must be linked between each other by main

access roads. They are numbered with a "C" prefix.

Collector Roads (Class IV)Roads linking locally important centers to each other, to a more important center,

or to higher class roads must be linked by a collector road. They are numbered with a "D" prefix.

Feeder Roads (Class V)Any road link to a minor center such as market and local locations is served by a

feeder road. They are numbered with an "E" prefix.

Roads of the highest classes, trunk and link roads have, as their major function to provide mobility, while the primary function of lower class roads is to provide access. The roads of intermediate classes have, for all practical purposes, to provide both mobility and access.



STANDARDS OF ROADSAll roads can not be constructed on the same standards. There are different standards for the different classified roads. Each country has its own standards and classification off roads. Similarly the design standard of Ethiopia is given below.

DESIGN STANDARD 1 FOR NORMAL & TOWN SECTIONS (DS1)

DESIGN STANDARD 1 FOR PAVED DUAL CARRIAGEWAY (DS 1)



DESIGN STANDARD 2 FOR NORMAL & TOWN SECTIONS (DS2)

DESIGN STANDARD 2 FOR TOWN SECTION OF DESIGN STANDARD (DS2)



PavementsThe surface of the road should be stable and it should allow the heavy wheel load of road traffic to move with the least possible rolling resistance. The surface should be even smooth along the profile. The earth roads may not be able to fulfill any of the above requirements, especially in varying weather conditions. So the pavement is most essential part in the construction of the roads.

Types of PavementsBased on the structural behavior, pavements are generally classified into two categories:

1. Flexible Pavements2. Rigid Pavements3. Composite Pavements

Flexible Pavement: A flexible pavement is one, which has low flexural strength, and the load is largely transmitted to the lower layers or to subgrade soil. Thus if the lower layer of the pavements or subgrade is undulated, the flexible pavement surface also gets undulated. The flexible pavement thickness is designed such that the stresses on the subgrade soil are kept within its bearing capacity. The strength and smoothness of flexible pavement structure depends to a large extent on the deformation of the subgrade soil.The cross section of flexible pavement is shown below,



Rigid Pavement: Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below. Compared to flexible pavement, rigid pavements are placed either directly on the prepared sub-grade or on a single layer of granular or stabilized material. In rigid pavement, load is distributed by the slab action, and the pavement behaves like an elastic plate. Rigid pavements are constructed by Portland cement concrete (PCC). The major factor considered in the design of rigid pavement is the structural strength of the concrete. The cross section of rigid pavement is shown below,

COMPOSITE PAVEMENTS: Composite pavements are pavements composed of cement concrete as a bottom layer and hot-mix asphalt as a top layer. The cement concrete slab provides a strong base and the hot-mix asphalt provides a smooth and non reflective surface. However, this type of pavement is very expensive and is rarely used as a new construction. Composite pavements include rehabilitated concrete pavements using asphalt overlays, and asphalt pavements with stabilized bases. A disadvantage of this construction is the occurrence of reflection cracks on the asphalt surface due to the joints and cracks in the rigid base layer.



ROAD DRAINAGEProvision of adequate drainage is an important factor in the location and geometric design of highways. Drainage Facilities on any highway or street should adequately provide for the flow of water away from the surface and subsurface of the pavement.

EFFECTS OF DRAINAGE Serious damage to highway structure

Reduce pavement strength. Swelling heave. Stripping of asphalt. Cause pumping in rigid pavements. Frost heave and reduction of bearing capacity when melting.

Traffic operation problems Slow traffic movement by accumulated water on the pavement. Cause traffic accidents as a result of hydroplaning and loss of

visibility from the splash and spray.

REQUIREMENTS OF HIGHWAY DRAINAGE SYSTEM The surface water from the road surface and shoulder should be effectively drained

off without allowing it to percolate to subgrades. The surface water from the adjoining land should be prevented from entering the

roadway Seepage and other source of ground water should be drained off by the subsurface

drainage system.

TYPES OF DRAINAGE SYSTEM

Surface Drainage: Surface water which occurs as rain or snow. Drainage for runoff water on the surface from this source is referred to as surface drainage.

Sub-Surface Drainage : Ground water, is that which flows in underground streams. This may become important in highway cuts or at locations where a high water table exists near the pavement structure. Drainage for seepage water and underground streams is referred to as subsurface drainage.


chapter 1 handout

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