The document describes the functions of each layer in a flexible pavement. The subgrade is the bottom-most layer that supports the loads from above layers. The subbase layer spreads loads from the base to prevent overstressing the subgrade. The base layer further distributes loads from the surface to prevent subgrade deformation. The surface layer provides a smooth, durable riding surface and protects lower layers from traffic loads and water infiltration.

1. Describe briefly the functions of flexible pavement by each layer.<br />SUB-GRADE<br />Sub-grade is a layer of natural soil or filled soil, ready to receive the pavement material over it. Traffic load moving on the surface of the road is ultimately transferred to the sub-grade through intermediate layer of sub-base, base and surface layer. For the success full construction of the road, it is necessary that the soil sub-grade should never be over stressed. Stress intensity on the sub-grade should not be of the magnitude that may cause excessive deformation in the sub-grade. It is this reason that the strength properties of the soil sub-grade should be evaluated. The pavement design assumes sub-grade strength as the basis for designing the pavement. If strength properties of the sub-grade are inferior to the expected ones, it is given suitable treatment to impart improvement in its performance.<br />There are a number of tests which can be used to measure strength properties of the soil sub-grade. All these tests are empirical and are useful in their correlation in the design. Following are some of the standard tests, used to evaluate the strength properties of the soil.<br />C.B.R test<br />Plate bearing test<br />Triaxial compression test<br /> SUB-BASE<br />Sub-base is one course that is constructed with quality materials. This is the lowest layer of pavement that is constructed onto the sub-grade. The functions of sub-grade:<br />Support the road base and spreads the force to the sub-grade.<br />Prepares the drainage using rough materials.<br />Prepares a cover at any layer that is constructed.<br />Bears the pressure from heavy vehicles so the sub-grade will not crack.<br />Prevent the sub-grade from traffic flow.<br />BASE<br />Base or road base is the main course to absorb force from surface directly and spread the force to the thickest layer. This layer is normally made from broken stones which may be bounded or unbounded. It is used to help spread traffic load on large area of sub-grade so that the stress intensity remains within the capabilities of the sub-grade. Thus undue deformation caused by the consolidation of the sub-grade is prevented. This layer is evaluated by plate bearing test or stabilometer test.<br />SURFACE<br />The surface is the top layer in a pavement. The pavement is divided into two layers that is Base course and wearing course on the top.<br />In resurfacing, this layer is usually known as a binder course. It is the second layer before the wearing course. The function is to spread the force from the surface. The wearing course is the top most layers in a pavement. The functions of this layer are as follows:<br />Provides smooth and dense ridding surface.<br />Takes up wear and tear due to traffic.<br />Provides water tight surface against filtration of surface water.<br />Provides hard surface which can withstand the pressure exerted by tyres of vehicles.<br />The road surface is constructed with bitumen material. Describe the road surface construction include the compaction work.<br />The road surface is constructed with bitumen materials, such as concrete asphalt, macadam bitumen and so on. The constructed should be free from dust and waterproof. To construct the surface layer, the base course must be prepared first. Prime coat is poured onto the road base surface to be a binder between the road bases and the base course. To pour the prime coat, the temperature must be according to the specifications stipulated.Base course is built on one layer only with a pavers’ machine. After this layer is constructed, it is placed before it is compacted. The surface is checked and corrected if there are any differences.The compacting must be done immediately. It should be compacted from the side towards the middle of the road. It there is a super elevated bend, then it should be compacted from lower part to higher part. The type of compactors must be according to the specifications.Finally wearing course is prepared. Like always, base course should be cleaned before tack coat is poured. The compacting job is done the same way as the base course.<br />State the functions of wearing course are as follows:<br />The wearing course is the top most layers in a pavement. The functions of this layer are as follows:<br />Provides smooth and dense ridding surface.<br />Takes up wear and tear due to traffic.<br />Provides water tight surface against filtration of surface water.<br />Provides hard surface which can withstand the pressure exerted by tyres of vehicles.<br />