Table of Contents
A track, Path use for access to any area is known as a road. (Roads have a specific width, gradient, and structure)
Importance of road:
- Extraction of forest produce
- Silvicultural needs
- Control of fire
- Exposed the area
- Watershed management (Afforestation)
Planning Forest Roads:
Following points have to be taken into consideration while planning forest roads:
- Forest to be opened up (Stand, Species, Volume)
- The flow of harvested wood (Quantity, Volume of traffic)
- Terrain (Formation, Gradient, Roughness, Soil quality)
- Climate & period of road use (Rainy periods, Water damages, Soil moisture)
- Environmental requirements (Existing restrictions, Sensitivity of the area, Landscape)
- Infrastructure (Existing roads, Communication, Services)
- Multiple uses of forests
- Government policy & regulation
Classification of roads:
According to material
- Metalled road
- Non-metalled road
According to the duration
- Temporary roads (Secondary roads)
- Permanent roads (Main roads)
- Fair-weather roads (Seasonal roads)
According to Gradients & Nature of traffic
- Main cart roads (Access roads). Generally, the width of road 12-25 Feet, Metalled 12 Feet
- Forest cart Roads (Earth roads, Gravels). Width 12-16 Feet
- Forest motor roads (When the forest is near the plains, metalled preferably). Width 12-14 Feet
Bridle paths (6-8 Feet)
- Inspection Paths (2-4 Feet). Visit the working area
Principles of projects:
- Knowledge of the area
- Knowledge of the subject
- Common sense
Roads alignments mean:
- Saving the cost of construction
- Saving in the cost of maintenance
- Traffic along the road is quicker
- Traffic along the road is easier
- Cost of forest products
- Future road development can be made without much trouble and expenses
Alignment of roads:
Selection of exact route on which the road or path is followed is known as alignment.
Factor influencing location
- The object of road construction
- Physical and topographical features
- The position of the market
- Existing roads
- Availability of road material
- Coast of construction
- Probable radii of curvature
- The position of a population center
Procedure for road alignments
Marking out alignment on the contour map, on the contour map you go for the following steps.
- Decide the width of the road
- Decide the obligatory points
- Average gradient
- Ruling gradient
- Find the vertical interval of the contour
- Draw several such traces
- Existing footpath and tracks
- Keeping the ruling gradient in a view
- Details of minor accidents which affect the Average, Maximum and Ruling gradient
- Particulars of rivers, canals, and streams
- Administrative information
3. Preliminary alignment for selection of one or two probable alignments
- Once the possible alignments have been decided on paper, the actual ground has to go over.
- Go for detailed study.
- From the data collected during road reconnaissance, one or two possible alignments can be selected. Notes would be made regarding
- Provisional control points in the nature of ridge and valley crossings. Main physical and topographical features
- Probable radii of curvature
- Cross section of any cutting. (Cut and fill)
- Number of culverts and bridges
- Geological formation, the tendency to landslides
- Flood levels
Selection of final alignment after more detailed survey
Final location or setting out alignment on the ground
Points to observe in good alignment:
- Re-entrants, Culverts, and bridges should be on level surface
- Spur, The projection from the mountain
- Increase the length to avoid the cutting and high embankments
- Height should not be lost
- Starts from the highest points downward
- Remembered the objectives of roads
- Timber extraction
- It should be followed valley rather then the ridges
- Near to lower boundary of the working area
- For communication
- It should follow the top ridges for better drainage
- Avoid streams in that case
Special points of interest in road alignments:
- Road should never rise or fall Un-necessarily between two obligatory points
- Alignment should not be taken above and below the obstacle
- The uniform gradient should be taken
- Avoid zigzags
- They are difficult to layout
- Sharp turn dangerous to traffic
- Cannot be use for higher class traffic
- Drainage is difficult
- The sunny side should be taken in a moist area
- In hot areas select the shady side
- Gradient should be maintained
- Maximum gradient should not be exceeded, Stretch of maximum gradient up to300 Feet
- A long stretch of gradient should be avoided
- Avoid landslide areas
- Water supply in the construction of road is regular
- Rest places
Procedure for road alignment:
- Trace or route
- Pegs, for a distance
- Requirements for instruments
- Layout the gradients on the trace
Alignment of plain roads:
Survey of plain roads
- Traverse the proposed route in straight lines
- Measure length of straight line
- Angle between straight lines
- Locate all the feature related to this line
- Take cross section
Alignment of plain roads
- Careful observation and reconnaissance
- Shortness with least rise and fall
- Ruling gradient
- Gentle curve
- Economical earth work, Culverts
- Water source, villages
- Contour plan plot the grade, Grade contour, Ruling gradient
Setting out on ground
- Straight lines
- Special points of interest
- Obligatory points
- Cross Drains
Metalled car road
Acquisition of land
Design of roads:
- Type of road
- Selection of route
- Type and thickness of Base and surface course (Materials, time, Availability of labor, Traffic)
- Gradients (Present in Ratio, Percentage, Degree)
- Ruling gradient
- Maximum gradient
- Average gradient
- Earth works
- Traffic requirements
- Widths (Carriage way)
- Earth road (7-8 Feet)
- Gravel road (6-7 Feet)
- Concrete road (7-9 Feet)
- Metalled road (9-10 Feet)
- Extraction road (8-9 Feet)
- Track ways (2.5-4.5 Feet)
- Concrete route ways (2’3″-2’6″)
- Bridle paths (6-8 Feet)
- Foot paths (4-6 Feet)
- Passing places
- Super elevation
- Type of traffic
- Coast of construction
- Types of road (Hilly area, plains)
Types of curves
- Horizontal curve
- vertical curve
- Simple curve
- Degree of curve
- D=100/R*180/π Or 1/R*5730 degrees
Object of earth work is to enable a road to be constructed to the desired width and gradient and to provide drainage.
Operation that carried out in earth work:
- Formation of cuttings by excavating through high ground
- Formation of embankments by filling over low ground
- Shaping the ground surface as formed to true formation Level
- Excavating for drainage works
Angle of repose:
The natural slope of any slope of any soil is termed the angle of repose.
The angles which slope makes with the horizontal.
Measurements in earth work:
- Construction of parks
- Access Road
- Catch water drains
- Preparation of culverts and improvement of out falls
- Cut and Fill
- Side drains
- Sub grade treatment
- Bridges and Culverts
- Top Coat
- Base Coat
Various Road Constructions
Earth Road includes
- Earth Work
- Ditches (Carry off the Surface water)
- Verges or Shoulders
“Soil Stabilization means any process which aims at increasing and maintaining the resistance of a soil”
- The raising of bearing capacity of the material by the addition of aggregate or binder
- The preserving of stability of material by the use of water proofing techniques
- Improvement of natural soil for use as earth roads or runways.
- Prevision of an improved sub grade under a correspondingly reduce thickness of base and surfacing
- Prevision of base courses for use under any conditional surfacing.
It composed of weak concrete in-which clay silt and sand from the mortar and stones from the coarse aggregate.
Metalled Roads (Macadam Roads)
- Material and construction
- Trenches (For excavation)
- Laying the Soling
- Laying of the foundation course.
- Early layer of soling laid access the road.
- On the top of the soling the broken road metal is laid. One or more layer is found permanent
First layer 3-4 inch, Gage 1-3 inches
Second layer 2-3 inch, Gage ½-1.5 inch
- Top layer is well rolled
- The top dressing should be well watered and rolled 20 to 30 times
- Top layer with tar and bitumen for greater water proof effects
- Repairs to metalled roads
Rut ways or Track ways
Material use on these roads
- Gravel, Furnace, Ash etc
- Road metal or broken bricks
Types of rut and Track ways
- Gravel or road Mattle Track ways
- timber track ways
- Concrete rut ways
- 2 inches Base
- Aggregates; Sand, Cement, Gravel, Steele
- Joints; Expansion and contraction
Roads in swampy areas
Principle of roads construction:
- Good alignments, the visibility
- Easy gradients
- Sufficient width
- Properly designed curves
- Stable sub soil
- Proper drainage
- Adequate foundation
- Wearing course, surface
- Correct camber and Supper elevation
- Economical constriction in materials, labor, and Transport
- Must be efficiently drained and kept dry i-e drainage
- Good formation, foundation well prepared, drained and consolidated
- Foundation to be firm and hard i-e Base
- Surfacing. Hardy wear by traffic
“Water is the great enemy of roads” It soft in material of road construction, Due to expansion and freezing. It Disintegrates the road bed.
The necessity of road drainage:
- Water standing on the-road, interfere with the movement of the-road traffic
- Standing water cases damage to the road surface-even pot holes are created
- water excess in the sub soil reduce its bearing capacity, failure of road due to sinking
- Frost action
Source of water:
- From rain directly falling n the road surface
- Discharge from the surface of adjoining land
- Flooding of water courses
- Percolation through the soil under the road
Type of water:
- Surface water
- Subsurface water
Type of road drainage:
- Surface water drainage
Factor affecting the Design
- Catchments area
- Runoff factors= Runoff/ Total rainfall
- Disposal of surface water
- Side drains (Open ditches) Q=AV (Q=Runoff in cusecs, A=Cross Sectional area Sq Feet, V=Velocity Feet/Sec
- Piped surface water drains
- Catch-water drains: (Interception ditches)
- Cross drainages
- Culverts (A culvert is a drain provided to convey water transversely under a road way). Types of culverts
- Pipe culverts
- Stoneware pipes (2 Feet Dia)
- Concrete pipes (5 Feet Dia)
- Cost iron pipes (4 Feet Dia)
- ARMCC “Circular corrugated iron sheets” (8,12,18,24,34,36,60,64 inches)
- Box culverts
- RC slab (use for span of 4 Feet)
- Stone slab (Size up to 4 Feet)
- Timber box culverts (12*12,18*18,24*24,30*30,36*36)
- Arch culverts
- Brick masonry arch
- Catch pits
- Irish bridge
- Cause ways
- Sub soil drainage
Forest Roads Important Terms
Parts of the-road generally used by vehicles.
Space on each side of the carriageway which is, in fact, the part of carriageway and almost at the same level.
Highest portion of the road in cross-section, (only in camber carriageway).
The difference in level between the crown and the edge of the carriageway or the transverse convexity given to the surface of a pavement or formation.
The transverse slope in the road provided at the curves to balance the centrifugal force.
Drains running parallel to the road on either sides or only one side, to collect and remove water from the carriage way, verge and side slopes.
Sub-Grade: The ground or foundation upon which the pavement is built. Its top surface is called the formation which is trued up by the graders or labor before laying on the sub-base.
A Layer of material placed between the base and the formation. It is not always necessary.
- It assists drainage.
- It avoids penetration of base into sub-grade.
The layer of hard material resting on the formation and through which the weight of the traffic is distributed to the formation.
The coarse of hard material laid on the base to withstand abrasion. This is a part of surfacing.
A thin coat of water proof material applied to the upper surface of the road to fill voids in wearing surface and make it water proof.
The term refers to the soil underlying the road. Its surface, when formed to shape, is known as “the formation”. Its function is to provide adequate, continuous and uniform support for the road structure and the leads imposed thereon. The design of the road structure is largely governed, therefore, by nature and supporting power of the sub-grade.
The modern tendency in road construction is to devote a maximum of the effort on the improvement of a subgrade with the object of reducing to a minimum the materials and labor required in the road base and surfacing. To ensure continuous, adequate and uniform supporting power sub-grades should be treated as follows:
- All pockets of soft soil should be removed and granular material substituted.
- Sub____ drainage should be provided where necessary.
- Thorough compaction should be effected by sheep-foot or smooth-wheeled rollers.
- Plastic and cohesive soils should be stabilized mechanicals by mixing them with granular materials.
Certain subgrades require covering with a compacted layer of granular material prior to the laying of the base proper. This Layer is known as for the “sub-base”, and its function varies with the character of the subgrade. A sub-base is not always required. When provided, it is a layer of granular material placed between the base and the formation. Its functions are:-
- To separate the subgrade from the base, so that moisture from the subgrade cannot rise into the base and so that large stones from the base cannot sink into the subgrade.
- Champervious subgrade soils, to assist the drainage of the formation.
- On hard, rough subgrade to true up the formation so as to provide an even bearing for the base.
the function of a base in road pavement is to transmit the applied lead from the surface to the subgrade or sub-base. The base provides the main strength of the pavement.
A vehicle wheel subjects a relatively small area of the pavement surface to a heavy pressure and the base must be capable of so spreading and reducing the intensity of this pressure that it does not exceed the bearing capacity of the subgrade. Excessive Loading will cause deformation and rutting of the subgrade and the structure of the overlying pavement will begin to fail.
Types of Base:
There are two main categories of base course, the rigid and the flexible.
- Rigid base: The rigid type is made of concrete either with or without the addition of a separate wearing surface, all other terms of construction are regarded as flexible.
- Flexible Bases: A wide variety of natural materials can be used either as found or after removal or crushing of oversize fragments, or after the blending of two or more types.
Commonly used materials are:-
- Stone pitching. ii) Hardcore. Iii) Macadam.
- Gravel and/or sand v. Stabilised soil.
- Limestone, Coral and cementaceous material.
Choice of type:
In cases of emergency, the choice of base material will obviously depend upon the local resources and the time. Plant, transport, and labor available.
Rigid bases are preferable where:
- Heavy traffic is anticipated.
- Material and plant are available.
- Repairs must be kept to a minimum over a long period.
Flexible bases the quicker and easier to lay than concrete and they can usually be constructed of local materials. They are generally more readily reconditioned and they can accept traffic soon after, or even during repair.
A road surfacing may be defined as the layer or layers of road material applied to a base to form a carriageway or other pavement, and upon which the traffic is sustained. Its main functions are:
- To provide a smooth running surface suitable for carrying the slane and intensity of traffic anticipated.
- To protect the base from abrasion and from the effects of rain and frost, and
iii. To afford reduction in the live load pressure transmitted to the base and subgrade.
Surfacing may be omitted from the construction altogether in cases where very light traffic only is anticipated, or where the base itself possesses the principal qualities required in road surface; e.g., it is unusual to provide a concrete road with surfacing for this reason, and the use of such materials is normally confined to flexible bases.
A road surfacing material should possess:
- Fon-slip texture
Type: Surfacings may be divided into four main types:
- Water-bound surfacings: Consist of a mineral aggregate usually broken stone or gravel – cemented together by means of a clay, stone dust or similar material.
- Bituminous surfacings: This class embraces a number of types in which tar or bitumen is used to bind mineral aggregate together. The principal types are grouted macadam, bituminous macadam, sand mixes, and the bituminous carpet.
- Pertland cement concrete surfacings: Cement concrete when adopted is generally made thick enough to act both as surfacing and base.
- Pavings: Comprised surfacing of separate block fitted closely together and laid upon a carefully prepared base. These are costly.
By Javed Iqbal Pakistan Forest Institutue Peshawar