Flexible Road Construction Method Process Step by Step in civil engineering
We have worked on various project’s and after working on them, i thought to provide article Flexible Road Construction Method Process Step by Step to help the fresher engineer in getting road construction step by step process.
First method of Flexible Road Construction is Alignment of Road-
What are the fundamental principles of alignment?
Masonry pillars shall be erected at suitable points in the area which is visible from the
Largest area to serve as bench mark, for the excavation of the work. Necessary profiles with Iron or wooden pegs, strings or ‘Burjis’ shall be made to show the correct formation or correct alignment levels before the work is started.
Ground levels shall be taken at 5 to 15 metres in uniformly sloping ground and at closer intervals where local mounds, pits or undulations are met with. The ground levels shall be recorded in field books and plotted on plans. The plans shall be drawn to a suitable scale as decided by the Architect.
Road construction Earth work excavation Measurements-
1. The length, breadth and depth shall be measured correct to a cm. in case the measurements are taken with tape. If the measurements are taken with staff and level, the level shall be recorded correct to 5 mm and depth of cutting and heights of filling calculated correct to 5 mm. The Measurements should be worked out to the nearest two places of decimal.
2. Where excavation is in fairly uniform ground, the measurements of cutting in trenches or barrow pits shall be made.
3. Where the ground is not fairly uniform or where the site is required to be levelled, levels shall be taken before the start and after the completion of the work and during the billing the quantity of excavation in cutting calculated from these levels.
4. Where it is not possible or suitable to take measurements from barrow pits or cutting, excavation should be worked out from filling. The exact measurements of the filling earth should be calculated by taking levels, of the Natural ground Level before start of the work after site clearance and after compaction of the filling at suitable intervals and the quantity of earth work so computed shall be reduced by 10% in case of consolidation fills, 5% in case the consolidation is done by machinery to calculate net earth work quantity.
Deduction not required in case of:
i) Consolidation done by heavy machinery at optimum moisture contents
ii) Consolidated fillings in confined situation such as under floors.
What is the subgrade in road construction?
The formation surface for a width of sub base, which should be 10cm or 15 cm. more on either side of base course (depend upon thickness in drawing ), should first be cut to a depth equal to the combined depth of such base (stone soling), base and surface courses below the proposed finished level (due allowance being made for consolidation).
It shall be cleaned of all foreign substances and sub grade dressed off parallel to the finished profile and compacted. The density to be achieved shall not be less than 98% of the Modified Proctor Density.
The Final finished surface should be uniform , properly compacted and conform to the lines, grades and typical cross section shown in the drawings.
It shall be ensured prior to actual execution that the material to be used in the subgrade satisfies the requirements of design CBR. Subgrade should be compacted and finished as per the design strength consistent with other physical requirements.
Preparation of sub-grade With GSB
Grading of GSB should be as per morth grading III with CBR>20. The size of stone aggregate should not be more than 22.5 cm nor less than 10 cm. in any direction, and height equal to the soling course with tolerance of 25 mm.
After the preparation of sub grade, stone soling shall be laid. Care shall be taken that stones are laid on edges and packing with small stones shall be done as soling work proceeds binding material shall then be spread and consolidation done with vibratory roller (8 – 10 Tons).
Irregularities in surface shall be corrected as consolidation proceeds. Rate shall include the cost of all materials and labour required for all operations mentioned above.
The density to be achieved shall be as per CPWD/ IRC specification of the density obtained in the laboratory (Proctor Method).
Road construction (WBM) Water bound macadam (Flexible Pavement)
Base (WBM) Water bound macadam
1st layer: It contains WBM with stone aggregate ranging from 90 mm to 45 mm size. This also contains coarse aggregate properly interlocked by rolling, and voids filled with screening and binding material with the assistance of water, laid on a prepared subgrade, sub base or the case may be coarse aggregate. WBM of 100 mm approximate compacted thickness of WBM base coarse in one layer with grading I.
2nd layer: Water bound macadam with stone aggregate 63 mm to 45 mm size. This also contains coarse aggregate properly interlocked by rolling, and voids thereof filled with screening and binding material with the assistance of water, laid on a prepared sub base or the case may be coarse aggregate. WBM of 75 mm approximate compacted thickness of WBM sub base coarse in one layer with grading II.
No segregation of large or fine particles should be done and the coarse aggregate as spread should be of uniform gradation with no fine material.
Road construction Spreading coarse aggregate
Road construction Spreading coarse aggregate should be spread uniformly and evenly upon the prepared base in required quantities with a twisting motion to avoid segregation. It should be not allowed to dumped in heaps directly on the area where these are to be laid nor should their hauling over a partly completed base.
The aggregates should be spread uniformly to proper profile by using templates placed across the road. The levels along the longitudinal direction up to which the metal shall be laid, shall be first obtained at site and these shall be adhered to. The surface of the aggregate spread should be carefully levelled up and all high or low areas should be remedied by removing or adding aggregate as required.
The WBM sub-base shall be normally constructed in layers of 100 mm compacted thickness. No segregation of large or fine particles should be done and the coarse aggregate as spread shall be of uniform gradation with no fine material.
Road construction rolling work for Compaction
Road construction Rolling work for Compaction after spreading of the coarse aggregate, it should be compacted to the full width by rolling with either a three-wheel-power-roller of 8 to 10 tonnes capacity or an equivalent vibratory roller. During Start, light rolling is to be done, which should be stopped when the aggregate is partially compacted with sufficient void space in them to permit application of screenings.
The rolling should start from the edges with the roller running forward and backward and adding the screenings simultaneously until the edges have been firmly compacted. The roller should move from the edges to the centre, parallel to the centre line of the road and overlapping uniformly each preceding rear wheel track by one half width and shall continue until the entire area of the road course is rolled by the rear wheel.
Rolling should done until the road metal is thoroughly keyed with no creeping of metal ahead of the roller. Only Slight sprinkling of water is to be done during rolling, if required. On super elevated curves, the rolling should be done from the lower edge and progress gradually continuing towards the upper edge of the pavement.
Rolling should not be done when the sub grade is soft or yielding or when the rolling causes a wave like motion in the sub-base or sub-grade due to water logging or wet earth. When rolling develops irregularities that exceed 12 mm when tested with a three meter straight edge, the irregular surface shall be loosened and then aggregate added to or removed from it if required and the area should be rolled until it gives a uniform surface conforming to the desired cross-section and grade.
The surface should be checked transversely by slope for camber and any irregularities corrected in the manner described above.
Test for consolidation due to Rolling –
A piece of about 25 mm stone is put on the consolidated surface and roller passed over it, it will be driven in if the consolidation is incomplete.
Measurements (WBM) Water bound macadam (Flexible Pavement)
The length and breadth shall be taken to the nearest centimeter and thickness to the nearest half centimeter. The consolidated cubical contents shall be calculated in cubic metres correct to two places of decimals.
Road construction Wet Mix Macadam method
Wet Mix Macadam laying method contains of laying spreading and compacting of clean, crushed, well-graded granular materials on a prepared and Granular sub-Base. For Wet Mix Macadam material is well mixed with water and then rolled to a dense mass. It should be laid on one or more layers as per line and level,grade and cross section shown in the good for Construction drawing .
Wet Mixed Macadam (WMM) Base thickness of single compacted should not be less than 75 mm. WMM shall be laid in layers of 75mm or 100mm as per thickness.
Road construction Tack Coat method
Bitumen in RoadConstruction : This shall be straight-run bitumen of penetration value 80/100 @ 0.2-0.25 kg/sq. mt conforming to IS 16-2008 & IS 8887 specifications.
Cleaning Prior to the application of bitumen, all vegetation, loose sealing compound, caked mud,animal dung, dust, dirt and foreign material shall be removed from the entire surface of the pavement and also from the existing dummy, construction and expansion joints (wherever existing) by the method of mechanical sweepers and blowers, otherwise it can also done with steel wire brushes, small picks, brooms.
Weather and Seasonal Limitations Road construction Tack Coat method-
The tack coat should not be applied nor any bitumen work done during rainy weather or when the surface is damp or wet or when the atmospheric temperature in the shade is not more than 16o C.
Process of Application of tack coat in Road construction-
Heating : Bitumen shall be heated in a boiler to a temperature of 165 deg. C to 9.75 deg. C and maintained at that temperature. Temperature shall be checked at regular intervals with the help of a thermometer. Hot bitumen should be applied evenly to the clean, dry surface by means of a pressure sprayer at specified rate. Distribution of bitumen should be even and uniform.
Bitumen should be applied longitudinally along the length of the pavement and never across it. Excessive deposits of bitumen caused by stopping or starting of the sprayer or through leakage or any other reason shall be suitably rectified.