PP2-Execution Methodology of Flexible Pavement
PP2-Execution Methodology of Flexible Pavement
PP2-Execution Methodology of Flexible Pavement
By
Steps involved in widening of the road formation: Pre levels are to be taken before widening. The CBR values of existing sub grade material is to be obtained @ 4 places per KM. Atleast @ 3 places per KM. The existing sub grade height and the thickness of sub base and base at different mileages are to be noted. Widening is to be done both sides of the road, if the water bodies are not adjacent to the road. Widening is to be done only one side i.e., fields side, if any canal or drain or minor irrigation tank is existing other side. Water bodies side, the stabilized slopes shall not be disturbed. As far as possible the formation of road over irrigation bund is to be avoided. Before widening, vegetation on the side slopes and on berms is to be removed along with its roots. Then widening with suitable soils is to be done and it is to be rolled with Vibro or 8 to 10 tonnes roller upto OMC level as per standards and specifications. Then proper sectioning of the side slopes is to be done. If the CBR value of sub grade material is less than 2%, sub grade stabilization is to be done or a continuous layer of medium sand with 100mm thick is to be provided across the total width of the road formation to drain off the seepage water. If the sub grade material is clayee and have CBR less than 3, then also a continuous layer of medium sand with 100mm thick is to be provided across the total formation width of the road. After construction of sub grade to the required height and width, final levels are to be taken to compute the total earth work executed.
Sub Base:
Sub base granular material shall be properly selected with the following properties: P.I. value shall be less than 6. CBR value shall be more than 20. Atleast it shall be more than 15. It shall confirm the MORD specifications clause 401. If the naturally available gravel is not having the said properties, it shall be mixed with local sand or quarry dust (whichever is economical) in the required proportion to attain the said qualities. In case of sub base over B.C. or clayee sub grade soils, half the thickness of granular sub base or minimum 100mm thick shall be extended throughout the width of the road, if the sand is not provided as the drainage layer. In case of sub base over very poor (CBR less than 2) sub grade material, graded chips confirming to MORD specification 401 may be used over modified sub grade material. It is costly material compared to natural gravel. Hence, usage of this material shall be justified. The required granular sub base material as per designs shall be properly compacted in layers using 8-10 tonne roller and proper curing is to be done. Simultaneously earth work for shoulders to support the sub base material is to be done and it is to be properly compacted in layers using 8-10 tonne roller and OMC is to be attained. It shall be properly cured along with sub base. The minimum thickness of sub base shall not be less than 100mm.
Clause 402 of MORD SPECIFICATION Construction of granular sub base/shoulders by providing well graded material (i.e., stone aggregates (Gravel) of 9.50mm to 4.75mm size 66% and sand of size <2.36mm - 34%), spreading in uniform layers with motor grader on prepared surface, mixing by mix in place method with rotavator at OMC and compacting with three wheel 80-100 KN static roller capacity to achieve the desired density, complete as per technical specification clause 402.
Base:
The base material as per the designs shall be provided in layers usually in two layers of different graded materials (Grade-II & Grade-III of 75mm compacted thickness of each layer). The base material should have the following properties:
Impact value shall be less than 20. Well graded material as per the specifications shall be used. WBM shall confirm to MORD specifications clause 405. The screening and binding materials of required quantities with required specifications shall be used. Wet Mix Mecadam (clause 406) and Crusher Run Macadam (clause 411) can be used.
Grade- II material, screening and binding material shall be collected of required quantities. Then it is to be spreaded over granular sub base and is to be properly compacted and watered to push the screening material into the voids. Later Grade-III material, screening and binding material shall be collected of required quantities. Then it is to be spreaded over Grade-II material and it is to be properly compacted and watered to push the screening material into the voids. Simultaneously Gravel Shoulders are to be provided in layers and is to be rolled and watered along with grade-II material and grade-III material. The minimum thickness of base shall not be less than 150mm.
Grade-III Providing, Laying, Spreading for a compacted thickness of 75 mm, using stone aggregates of Grade - III as per Table 400.80 of MORD specification with 40-45 mm @ 82%, 19-22.4 mm @ 18% HBG Metal for Water Bound Macadam specification including cost, conveyance and seignorage charges and spreading in uniform thickness, hand packing, rolling with Power Road Roller 8- 10 Tonnes in stages to proper grade and camber applying and brooming requisite type ' B ' screenings and binding materials such as Stone Dust so as to fill up the interstices of coarse aggregates, watering and compacting to the required density for finished item of work as per MORD specification clause 405 (3) (A) by manual means and as directed by the Engineer-inCharge.
63mm to 45mm
53mm to 22.40mm
63mm
53mm
95-100
45mm
22.40mm 11.20mm
65-90
0-10 0-5
TABLE 400.20 : AGGREGATE GRADING REQUIREMENTS FOR CRUSHED RUN MACADAM BASE Per cent Passing by weight Sieve Size 53mm Max. Size 63 mm 100 37.5 mm Max. Size
45 mm
22.4 mm 5.6 mm 600 micron 75 micron
87-100
50-85 25-45 10-25 2-9
100
90-100 35-55 10-30 2-9
Specifications and sieve analysis of screening material Screenings to fill voids in the coarse aggregate shall generally consist of the same material as the coarse aggregate. However, where economic considerations so warrant, predominantly non plastic material (other than rounded river borne material) may be used for this purpose provided liquid limit and plasticity index of such material are below 20 and 6 respectively and fraction passing 75 micron sieve does not exceed 10 percent. The screenings shall not contain any of the undesirable constituents lists in clause 301.2.3 which would render it unsuitable as a fill material. Screenings shall conform to the grading set forth in table 400.9. The consolidated details of quantity of screenings required for various grades of stone aggregates are given in table 400.10. The table also gives the quantities of materials (loose) required for 10m2 for sub base compacted thickness of 100/75mm.
13.2mm
11.2mm
APPROXIMATE QUANTITIES OF COARSE AGGREGATES AND SCREENINGS REQUIRED FOR 100/75MM COMPACTED THICKNESS OF WATER BOUND MACADAM (WBM) SUB BASE/BASE/SURFACING COURSE FOR 10m2 AREA
Classification Size Range Mm Compacted thickness Mm Loose Quanti ty m3 Stone Screenings Gradin g Classifi cation & Size Type A 13.2 For WBM sub-base/ Base course (Loose qty) m3 Crushable screenings such as moorum or gravel Properties Loose Quantity m3
Grading 1
90 to 45
100
1.21 to 1.43
0.27 to 0.30
0.30 0.32
to
Grading 2
Grading 2 Grading 3
63 to 45
75
0.91 to 1.07
0.91 to 1.07 0.91 to 1.07
Type A
13.2
0.12 to 0.15
-do-
0.22 0.24
-do-
to
63 to 45
75
Type B 11.2
0.20 to 0.22
-do-
53 22.4
to
75
Type B 11.2
0.18 to 0.21
-do-
-do-
4. Bituminous Surfacing:
It serves the following purposes: Improves the riding quality. Seals the surface, thus preventing the entry of water which would otherwise weaken the pavement structure. Protects the granular base from the damaging effects of traffic. 20mm thick open graded premix carpet as per clause 508 is to be provided and it is to be properly compacted. Care shall be taken to maintain required temperature while laying of the carpet in case of hot mix. Also to ascertain that sufficient quantity of bitumen is mixed with graded chips of standard sizes.
Then 6 mm thick seal coat is to be provided over the OGPC and ascertain proper grade of the materials, required quantity of BT, compaction, completion of wearing coat over OGPC every day, day end. Gravel Shoulders shall be done before BT surfacing only. After laying of wearing coat, 20mm level difference of BT and shoulders is to be leveled with gravel on shoulders.
Rolling Terrain
Mountaineous Terrain
Steep Terrain
Minimu m
Ruling
Minimu m
Ruling
Minimu m
Ruling
Minimu m
Rural Roads
50
40
40
35
25
20
25
20
Camber (in percentage) for different surface types Low Rainfall (Annual Rainfall < 1000mm) 4 3.5 3 2 High Rainfall (Annual Rainfall > 1000mm) 5 4 3.5 2.5
Surface Earthen WBM & Gravel Thin Bituminous pavement Rigid Pavement
Super elevation: e = V2 225R where e = Super elevation in meters V = Design speed in km/hour R = Radius of curvature in meters
Limiting value of super elevation in percentage
Plain and Rolling Terrain Snow bound area Hilly area but not snow bound 7 7 10
0.9m
0.6m
Nil
3.30%
Plain & Rolling Mountainous Terrain and Steep terrain having elevation less than 3000m above the MSL Steep terrain having elevation more than 3000m above the MSL (1 in 30) 5% (1 in 20)
5%
(1 in 20) 6% (1 in 16.7)
6%
(1 in 16.7) 7% (1 in 14.3)
6% (1 in 16.7)
7% (1 in 14.3)
8% (1 in 12.5)
Quantity of material required for 10sqm of road surface for 20mm thick pre mix carpet using Penetration Bitumen or Cut back
Requirement of Aggregates:
a) b) Nominal metal size 13.2 mm (passing 22.4 mm sieve and retained on 11.2 mm sieve) Nominal metal size 11.2 mm (passing 13.2 mm sieve and retained on 5.6 mm sieve) Total : 0.18m3 0.09m3 0.27m3
Requirement of Bitumen: a) b) For 0.18 m3 of 13.2mm nominal size metal chips @ 52 kgs.bitumen per m3. For 0.09 m3 of 11.2mm nominal size metal chips @ 56 kgs per m3 Total : 9.5 Kgs 5.1 Kgs 14.60kgs
Bitumen (Kgs)
9.8
12 to 14
6.8
10 to 12
9 to 11
Type of Surface
Normal Bituminous Surface Dry and Hungry Bituminous surface Granular surface tread with primer
2 - 2.5
2.5 - 3
2.5 - 3
Drainage:
Scientifically worked out drainage design is a vital part of design of a pavement system. Proper cross slopes are to be provided over the carriageway and road side shoulders to shed off the rain water quickly. Proper camber plates are to be used while construction of Grade-II and Grade-III layers. The surface of the road shall not be wavy or there shall not be any ditches over the BT surface. If any water stagnates over BT surface, the BT surface looses adhesive and cohesive forces and the BT particles will come out. The BT surface shall not be provided over (i) where there is proper drainage of water is not possible i.e., village limits (ii) where there are steep gradients and (iii) in water logging areas. Where 1000mm dia vent culverts are required, it is preferable to provide Slab Culvert.
In case of field channels, it is enough to provide 450mm dia or 600mm dia pipes without body walls. High level causeways and High level bridges are preferable to low level causeways. Low level causeways may be provided on unimportant roads crossing shallow depth and less discharge streams. Construction of road dams are to be avoided. Slab culverts are to be constructed in place of road dams. The body walls of pipe culverts shall be of minimum possible length and minimum possible height. Construction of retaining walls are to be avoided as far as possible. Revetment may be provided in such cases.
Design of Culverts
Calculation of mean velocity (v) (Mannings Formula) V = 1 R2/3 S1/2 n where V = Velocity in meters/sec R = Hydraulic mean depth = A = Cross Section area P Wetted perimeter S = Slope of Energy gradient (bed slope) n = Co efficient of Rugosity of the river Q=AXV
Sl. No.
Value of n
Perfect
Clean, straight bank, full stage, no rifts or deep pools Same as (1) but some weeds and stones Winding, some pools and shoals clean Same as (3) lower stages more ineffective slope and sections Same as (3) some weeds and stones Same as (4) stony sections Sluggish river reaches rather weedy or with very deep pools Very weedy reaches
Good
Fair
Bad
0.025
0.0275
0.030
0.033
0.030
0.033
0.035
0.040
0.035
0.040
0.045
0.050
0.040
0.045
0.050
0.055
0.033
0.035
0.040
0.045
0.045
0.050
0.055
0.060
0.050
0.060
0.070
0.080
0.075
0.100
0.125
0.150
Calculations of Discharge
Dickens Formula (applicable to Rayalaseema and Telangana Areas) Q = CM3/4 where Q = The peak run-off in cum/sec. M = The catchment area in sq. km. C = 11 to 14 where annual rainfall is 60 -120 cm. Ryves Formula (applicable to Coastal Area) Q = CM2/3 where C = 6.8 for areas within 25 Km of coast. C = 8.5 for areas between 25 and 160 KM of coast. C = 10 for limited areas near the hills.