It is a planning tool used to aid pavement management decisions. PMS software programs model future pavement deterioration due to traffic and weather.It recommends maintenance and repairs to the road’s pavement based on the type and age of the pavement and various measures of existing pavement quality.
Measurements can be made by persons on the ground, visually from a moving vehicle or using automated sensors mounted to a vehicle.PMS software helps the user create composite pavement quality rankings based on pavement quality measures on roads or road sections.
Recommendations are usually biased towards preventive maintenance.Typical tasks performed by pavement management systems includes inventory pavement conditions, identifying good, fair and poor pavements .
It assign important ratings for road segments based on traffic volumes, road functional class and community demand.It schedule maintenance of good roads to keep them in good condition and schedule repairs of poor and fair pavements .
Research has shown that it is far less expensive to keep a road in good condition than it is to repair it once it has deteriorated. Pavement management systems place the priority on preventive maintenance of roads in good condition rather than reconstructing roads in poor condition.
In terms of lifetime cost and long term pavement conditions, this will result in better system performance. Agencies that concentrate on restoring their bad roads often find that by the time they’ve repaired them all, the roads that were in good condition have deteriorated.
The State of California was among the first to adopt a (PMS) in 1979. First PMS was based in a mainframe computer and contained provisions for an extensive database. It can be used to determine long-term maintenance funding requirements and examine the consequences on network condition if insufficient funding is available.
5.3 Pavement evaluation, roughness, present serviceability index, skid resistance, structural evaluation, evaluation by deflection measurements
Pavement evaluation:
A study of various factors pertaining to pavement, such as subgrade support, pavement composition and its thickness, traffic loading and environmental condition, is referred to as pavement evaluation. Aim of pavement evaluation is to assess as to whether and to what extent the pavement fulfills the design requirements.
Based on the evaluation, the maintenance and strengthening works could be planned .Study is used to investigate the structural adequancy of pavements and also the requirements for providing safe and comfortable traffic operations.
Although several methods are used, the four methods categorized below are the basic ones:
1.Structural Evaluation of pavements
2.Evaluation of pavement surface condition
3.Present serviceability index
4.Visual Rating.
Roughness of Surface:
Apart from different aspects, the riding quality of a pavement is a function of the specifications adopted for the surfacing . Roughness is one among them. A measure of the pavement performance can be obtained by monitoring its roughness.
Smooth riding surface brings about many advantages, viz., higher speeds, less fuel consumption, less wear and tear of tyre, less consumption of spare parts, riding comfort and safety. In performance evaluation, rigidity of surface play a vital role.
Present Serviceability Index:
A rating system was developed by AASHO involving the measurement of permanent deformation, riding quality and the extent of cracking and patching. Rating is well-known by the term Present Serviceability Index (PSI). It is the most widely used pavement rating measure.
Following equations give the value of PSI for flexible and rigid pavements,
1.Flexible Pavements:
2.Rigid Pavements:
Where,
SV = Slope variance giving an index of the longitudinal profile.
RD = Rut depth under a 4 ft straight edge
C = Cracking distress in terms of lineal feet of cracks per 1000 sq.ft. area.
P = Patched area in sq.ft. per 1000 sq.ft. area.
Skid Resistance:
Though smooth surface has various advantages it is dangerous to traffic, especially when the surface is wet and the vehicles move fast. It is normal to construct reasonably skid-resistance surfaces. Passage of vehicles polish the aggregates and excess Bitumen tends to fatten the surface and render it slippery.
Hence it is essential to evaluate the skin resistance of the surface at periodic intervals to ensure that the roughness level has not fallen to dangerous low levels. It is accomplished by periodic measurement of skin-resistance. Skin resistance is measured using Towed fifth wheel pump integrator, Car-mounted roughness measuring device, etc.
Structural Evaluation of Pavements:
Plate bearing test can be conducted for both flexible and rigid pavements to assess the structural capacity. Assessment may be made by the load carried at a specified deflection at a place or by the amount of deflection at a specified load on the plate.Performance of a flexible pavement is closely related to the elastic deformation under loads or its rebound deformation.
Under the existing conditions of a pavement, the deflection of pavement under the design wheel loads serves as an index to carry traffic loads.Benkelman Beam is the most commonly used method.
Before conducting the Benkelman Beam measurements, a rating survey of the road is performed by dividing the road into homogeneous sections of approximately similar serviceability.
Deflection Measurement:
It occurs due to various factors such as subgrade soil type, moisture content and compaction level of subgrade, pavement thickness and drainage conditions, pavement surface temperature and wheel load.
Measured using a suitable equipment such as Benkelman Beam, Lacroix Deflectograph, Dynaflect and Deflectome.
5.4 Strengthening of Pavements
Strengthening of existing pavements:
A highway is expected to have adequate stability to withstand the design traffic under prevailing climatic and subgrade conditions. If the design load and the anticipated traffic are maintained, the planned maintenance will be fruitful.
If the pavement is to support increased wheel loads and load repetitions, the pavements cannot be maintained properly but undergo large distress.Only solution to manage the increased traffic is either to direct the traffic on some adjacent roads or to strengthen the existing pavements.
Strengthening may be done by providing additional thickness of pavement provided the subgrade is strong enough.Construction of one or more layers over the existing pavement is called overlay. If the distress of the road is excess, construction of overlay will not help. The road has to be reconstructed.
Types of Overlays:
An overlay may be either flexible or rigid. Flexible overlays are generally bituminous surfaces.It can be constructed over existing flexible pavements or existing concrete pavements. A bond breaker comprising of a granular base is used between a concrete base pavement and overlay. Deflection is also reduced to some tolerable level.
Rigid overlays may consist of plain, simply reinforced or continuously reinforced concrete pavements. Provision of a bond breaker may or may not be necessary.Following are the combination of overlays:
Existing pavement
Overlay
Cement concrete
Cement concrete
Cement concrete
Bituminous
Bituminous or flexible
Cement concrete
Bituminous or flexible
Flexible or Bituminous
Choice of overlay depends on various factors including total thickness of overlay required, Wheel load, Subgrade strength, etc.
5.5 Types of maintenance
Types of Maintenance:
Maintenance operations of highways fall under three categories noted below.
1.Routine maintenance
2.Special repairs
3.Resurfacing
1.Routine Maintenance:
All types of pavements are exposed to climatic changes and adverse weather conditions, evidently these would wear out. To avoid further deterioration and to reduce further heavy expenses, it is mandatory to maintain the highway in time.
The following works are to be maintained routinely:
i)Upkeeping of carriage way
ii)Shoulders
iii)Subgrade
iv)Side drain clearance for silt accumulation
v)Highway geometric and traffic control
vi)Ancillary works like culverts, bridges, etc.
2.Special Repairs:
Adverse weather conditions and other causes may demand special repairs of the pavement which would have been damaged. Need may arise for special repair of some sub-surface drainage system and cross drainage structure.
3.Resurfacing:
It arise due to the expiry of the life of the pavement or surface being heavily damaged.
5.6 Highway Project formulation.
Highway project formulation:
A new highway project comprises of design and construction either at network of new roads, or a road link.There may also be projects which require redesign and re-alignment of existing roads of upgrading the geometric design standards.A new highway project formulation may be divided into the following stages
1.Selection of route and survey of possible alignment of roads.
2.Finalisation of highway alignment.
3.Collection of materials and testing of subgrade soil and other construction materials.
4.Design aspects.
5.Construction stages.
Selection of Route and Surveys:
Based on the points to be connected ,different routes are tried. Selection of route ,the requirement of alignment and the geological, typographical and other features of the locality are kept in mind.Surveys to be conducted for selection of route comprises of the following steps:
1.Map Study:
This is the preliminary stage of the project.
At this stage the help of available maps of the area are studied.
2.Reconnaissance Survey:
Tentative alignments are primarily looked into keeping in various factors. To decide the correct alignment a reconnaissance survey is conducted. Following are the points to be considered during the reconnaissance survey:
1.The alignment should be such that necessary cutting and banking are avoided.
2.Obstructions to be faced along the alignment are looked into.
3.Gradients and length of curves to be provided in the alignment.
4.The alignment should avoid any cross-drainage work.
5.The alignment should not be taken through agricultural land completely.
6. The type of soil along the route should be looked into.
7.The sources of construction materials along the route to be assessed.
8.The type of terrain to be noted.
9.The magnetic bearing of the alignment are measured by compass.
10.Nature of ground on either side of the alignment and the highest flood level are noted.
3.Preliminary Survey:
The preliminary survey or the preliminary location survey of the highway project is carried out with the following main objectives:
1.Various alternate alignments.
2.Estimation of the quantity of earthwork materials and other construction aspects.
3.Compare different proposals.
Following surveys are conducted during the preliminary survey:
1.Primary traverse.
2.Topographical surveys.
3.Levelling work.
4.Collecting hydrological data.
5.Soil surveys.
6.Establishment of permanent benchmarks by running a fly levelling.
7.Intersection of canals, of rivers are to be properly located.
8.Drawings are prepared following route survey, longitudinal and cross- sections, mass hall diagram, contour map of the strip and design of curves.
9.At the office ,the cost estimate of different works such as land compensation, flyovers, culverts, bridges, earthwork, etc., are prepared.
Finalization of Highway Alignment:
After the preliminary surveys, the final alignment is decided and is first located on the field by establishing the center line. Next the detailed survey should be carried out and the geometric design details are made.The detailed survey involves the following:
1.Centre line is marked at intervals of 30 m.
2.Fixing temporary benchmarks along the route for every 300 m.
3.Cross-section details are taken for 30 m on either side of the central line.
4.All details of cross drainage works are taken.
5.Topographical details are taken.
6.Detailed soil survey is carried out.
7.Total land width required is marked by pillars at regular intervals.
8.Tangent points and intersection points of the curves are properly marked by pillars.
Collection of Materials and Testing:
Soil samples collected during the survey along the selected route are tested in the laboratory in order to design the pavement and the design of embankments and cuttings.Selected construction materials from borrow areas are also tested for the required properties.
Mix-design tests of materials are conducted in the laboratory to explore the possibility of using them for the pavement component layers.The possibility of using low-cost construction material like soil aggregate mixes, soft aggregates, stabilised soil and concrete mixes, in the sub-base or base course layers of pavement should also be fully explored.
Design Aspects:
After the survey and investigation are over, a new project involves in the following design steps:
1.Identifying the class of road to be designed and the terrain over which it has to pass.
2.Design speed selection appropriate to the class of road and the terrain.
3.Selection of cross-sectional elements keeping in view the future traffic requirements.
4.Selection of appropriate geometric design standard suitable to the class of road, terrain and design speed.
5.Design of alignment and profile.
6.Alignment design of embankments and deep cuts.
7.Choosing of appropriate pavement based on the need and material availability.
8.Design of pavement.
9.Design of surface and subsurface drainage system and erosion control.
10.Design of cross-drainage structures.
11.Design of road junctions.
12.Estimation of various quantities of items and the total cost.
13.Estimation of road use cost.
14.Estimation of maintenance cost.
15.Comparing various alternative and selecting the optimal solution.
16.For the selected route, preparation of final drawings and estimates.
17.Preparation of final project report.
Construction Stages:
The construction of the road may be divided into two stages, viz.,
(i)Earth work and
(ii)Pavement construction.
The earthwork comprises of excavation and construction of embankments.
During the excavation process for highway cuts, protection of earth slopes and construction of drainage works are taken care of and construction of highway embankment by rolled-fill method is preferred.Compaction of soil in layers under controlled moisture and density are done using suitable layers.In situations of high embankments special checks such as stability of the embankment foundation and slopes, settlement, etc. are to be done.