Engineering Surveys for Highway Alignment

Before a highway alignment is finalized in a new highway project, engineering surveys are to be carried out. These engineering surveys may be completed in the following four stages.

i) Map Study

ii) Reconnaissance Survey

iii) Preliminary Surveys

iv) Final Location and Detailed Surveys

1) Map Study

If the topographic map of the area is available, it is possible to suggest the likely routes of the road. In India, topographic maps are available from the Survey of India with 15 or 30 meter contour intervals. The main features like rivers, hills valleys, etc. are also shown on these maps. By careful study of such maps, it is possible to have an idea of several possible alternate routes so that further details of these may be studied later at the site. The probable alignment can be located on the map from the following details available on the map.

1. Alignment avoiding valleys, ponds or lakes
2. When the road has to cross a row of hills or mountains, possibility of crossing through a mountain pass
3. Approximate location of bridge site for crossing rivers, avoiding bend of the river, if any
4. When a road is to be connected between two stations, one of the top and the other on the foot of the hill, then alternate routes can be suggested by keeping in view that the design or ruling gradient and the maximum permissible gradient.

2) Reconnaissance

The second stage of engineering surveys for highway alignment is the reconnaissance survey. During the reconnaissance, the engineer visits the site and examines the general characteristics of the area before deciding the most feasible routes for detailed studies. A field survey party may inspect a fairly broad stretch of land along the proposed alternative routes of the map in the field. Only very simple survey instruments are used by the reconnaissance party to collect additional details rapidly, but not accurately. All relevant details which are not available in the map are collected and noted down. Some of the details to be collected during reconnaissance are given below.

1. Valleys, ponds, lakes, marshy land, ridge, hills, permanent structures and other obstructions along the route which are not available in the map.
2. Approximate values of gradient, length of gradients and radius of curves of alternate alignments.
3. Number and type of cross drainage structures, maximum flood level and natural ground water level along the probable routes.
4. Soil type along the routes from field identification tests and observation of geological features
5. Sources of construction materials, water and location of stone quarries
6. When the road passes through hilly or mountainous terrain, additional data regarding the geological formation, type of rocks, dip of strata, seepage flow etc. may be observed so as to decide the stable and unstable sides of the hill for highway alignment.

3) Preliminary Survey

The main objectives of the preliminary survey are:

1. To survey the various alternate alignments proposed after the reconnaissance and to collect all the necessary physical information and details of topography, drainage and soil.
2. To compare the different proposals in view of the requirements of a good alignment
3. To estimate quantity of earth work materials and other construction aspects and to work out the cost of alternate proposals
4. To finalize the best alignment from all considerations the preliminary survey is carried out to collect all the physical information which are necessary in connection with the proposed highway alignment.

The preliminary survey may be carried out by any one of the following methods.

i) Soil Survey

Soil survey is an essential part of the preliminary survey as the suitability of the proposed location is to be finally decided based on the soil survey data. The soil survey conducted at this stage also helps in working out details of earth work, slopes, suitability of materials, subsoil and surface drainage requirements and pavement type and the approximate thickness requirements. All these details are required to make a comparative study of alternate proposals.

ii) Material Survey

The survey for naturally occurring materials likes stone aggregates, soft aggregates, etc. and identification of suitable quarries should be made. Also, availability of manufactured materials like cement, lime, brick, etc. and their locations may be ascertained.

iii) Traffic Survey

Traffic surveys conducted in the region form the basis for deciding the number of traffic lanes and roadway width, pavement design and economic analysis of the highway project. Traffic volume counts of the classified vehicles are to be carried out on all the existing roads in the region, preferably for 24 hours per day for seven days. Origin and destination surveys are very useful for deciding the alignment of the roads. This study may be carried out on a suitable sample of vehicle users or drivers. In addition, the required traffic data may also be collected so that the traffic forecast could be made for 10 to 20 year periods.

iv) Determination of Final Centre Line

After completing the preliminary surveys and conducting the comparative studies of alternative alignments, the final centre line of the road is to be decided in the office before the final location survey. For this, the preliminary survey maps consisting of contour plans, longitudinal profile and cross sections of the alternate alignments should be prepared and carefully studied to decide the best alignment satisfying engineering, aesthetic and economical requirements. After selecting the final alignment, the grade lines are drawn and the geometric elements of the horizontal and vertical alignments of the road are designed.

v) Rapid Method Using Aerial Survey and Modern Technique Using GPS

Aerial photographic surveys and photogrammetric methods are very much suited for preliminary surveys, especially when the distance and area to be covered are vast. The survey may be divided into the following steps.

Taking aerial photographs of the strips of land to be surveyed with the required longitudinal and lateral overlaps. Vertical photographs are necessary for the preparation of mosaics.

1. The photographs are examined under stereoscopes and control points are selected for establishing the traverses of the alternate proposals. The control points are located on the maps.
2. Using stereo-pair observations, the spot levels and subsequently contour details may be noted down on the maps
3. Photo-interpretation methods are used to assess the geological features, soil conditions, drainage requirements etc.

4) Final Location and Detailed Survey

The alignment finalized at the design office after the preliminary survey is to be first located on the field by establishing the centre line. Next detailed survey should be carried out for collecting the information necessary for the preparation of plans and construction details for the highway project.

i) Location

The centre line of the road finalized in drawings is to be transferred on the ground during the location survey. This is done using a transit theodolite and by staking of the centre line. The location of the centre line should follow, as closely as practicable, the alignment finalized after the preliminary surveys. Major and minor control points are established on the ground and centre pegs are driven, checking the geometric design requirements. However, modifications in the final location may be made in the field, if found essential. The centre line stakes are driven at suitable intervals, say at 50 metre intervals in plain and rolling terrains and at 20 metre in hilly terrain.

ii) Detailed Survey

Temporary bench marks are fixed at intervals of about 250 m and at all drainage and under pass structures. Levels along the final centre line should be taken at all staked points. Levelling work is of great importance as the vertical alignment, earth work calculations and drainage details are to be worked out from the level notes. The cross-section levels are taken up to the desired width, at intervals of 50 to 100 m in plain terrain, 50 to 75 m in rolling terrain, 50 m in built up areas and 20 m in hilly terrain. The cross sections may be taken at closer intervals at horizontal curves and where there is abrupt change in cross slopes. All river crossing, valleys etc. should be surveyed in detail up to considerable distances on either side. All topographical details are noted down and also plotted using conventional signs. Adequate hydrological detail is also collected and recorded.

Drawings and Report

Drawings

The following drawings are usually prepared in a highway project.

i) Key Map

Key map should show the proposed and existing roads, and important places to be connected. The size of the plan generally should not exceed 22 x 20 cm. The scale of the map is chosen suitably depending upon the length of road.

ii) Index Map

Index map should show the general topography of the area. The details are symbolically represented. The index map should also be of suitable scale, the size being 32 x 20 cm.

iii) Preliminary Survey Plans

Preliminary survey plans showing details of the various alternate alignments and all information collected should be normally drawn to scale of 10 cm = 1 km to 25 cm =1 km.

iv) Detailed Plan and Longitudinal Section

Detailed plans show the ground plan with alignment and the boundaries, contours at intervals of 1 to 2 m in plain terrain and 3 to 6 m in hills, showing all details including existing structures. A scale of 1/2400 in close country and a scale of 1/1200 may be adopted for detailed plans. The size of the drawing may be A2 size or 60 x 42 cm approximately.

Longitudinal sections should be drawn to the same horizontal scale of the ground as in detailed plan. Vertical scale may be enlarged 10 times of the longitudinal scale. The longitudinal section should show the details such as datum line, existing ground surface, vertical profile of the proposed road and position of drainage crossings.

v) Detailed Cross Section

Detailed cross sections are generally drawn to natural scale of 1 cm = 2.0 to 2.5 m. Cross section should be drawn every 100 m or where there are abrupt changes in level. In hill roads the cross sections should be drawn at closer intervals. The cross-section drawings should extend at least up to the proposed right of way. The cross-section number, the reduced distances and the area of filling and/or cutting should be shown on cross section drawings.

vi) Land Acquisition Plans

Land acquisition plans and schedules are usually prepared from the survey drawings for land acquisition details. These plans show all general details such as buildings, wells, nature of gradients and other details required for assessing the values. The scale adopted may be 1 cm = 40m or less.

vii) Drawings of Cross Drainage and Other Retaining Structures

Detailed design for cross drainage and masonry structures are usually drawn to scale of 1 cm = 1 m. For details of any complicated portion of the structure enlarged scales up to 8 cm = 1 m or up to half full size may be employed. However, the size of drawing should not exceed the standard size. Cross sections of streams should be to a scale of not less than 1 cm = 10 m.

viii) Drawings of Road Intersections

Drawings of road intersections should be prepared showing all details of pavement, shoulders, islands etc. to scale.

ix) Land Plans Showing Quarries, etc.

Where quarries for construction materials are to be acquired for new projects, separate land plans should be prepared. The size of these maps and scales may be similar to those suggested under land acquisition.

Estimates

The project estimates should consist of general abstract of cost and detailed estimates for each major head. If the project work is proposed to be executed in stages, the estimate should be prepared for each stage separately.

Project Report

The first phase of project report soon after completing the preliminary surveys, feasibility and EIA studies is to prepare a 'Feasibility Report'. The Detailed Project Report (DPR) should be prepared after completing all the detailed studies including final location survey, preparation of longitudinal and cross sections, soil and material surveys, drainage studies, etc. The design details of the pavements and all Cross Drainage structures including major bridges should be carried out and the relevant drawings prepared as specified in the terms of reference for the project preparation.

Highway Projects

In a new highway project, the engineer has to plan, design and construct either a network of new roads or a road link. There are also projects requiring redesign and realignment of existing roads of upgrading the geometric design standards. Once a highway is constructed, development takes place along the adjoining land and subsequent changes in alignment or improvements in geometric standards become very difficult. A badly aligned highway is not only a source of potential traffic hazard, but also causes a considerable increase in transportation cost and strain on the drivers and the passengers. Therefore, proper investigation and planning are most important in a road project, keeping in view the present day needs as well as the future developments of the region.

New Highway Project

The new highway project work may be divided into the following stages.

1. Selection of route, finalization of highway alignment and geometric design details.
2. Collection of materials and testing of sub grade soil and other construction materials, mix design of pavement materials and design details of pavement layers.
3. Construction stages including quality control.

i) Route Selection

The selection of route is made keeping in view the requirements of alignment and geological, topographical and other features of the locality. However special care should be taken as regards the geometric design standards of the road for possible upgrading of speed standards in future, without being necessary to realign the road. After the alignment if finalized, the plans and working drawings are prepared.

ii) Materials and Design

The soil samples collected from the selected route during the soil surveys are tested in the laboratory in order to design the required pavement thickness and the design of embankment and cut slopes. The basic construction materials such as selected soil, aggregates etc. are collected from the nearest borrow pits and quarries and stacked along the road alignment after subjecting these materials to the specified laboratory tests. In order to design the mixes for the pavement component layers and to specify quality control test values during road construction, mix design tests are carried out in the laboratory.

iii) Construction

The construction of the road may be divided into two stages,

i) Earth work

ii) Pavement construction

The earth work consists of excavation and construction of the embankments. During the excavation for highway cuts, the earth slopes, their protection and construction of drainage network are taken care of. Highway embankments may be best constructed by rolled fill method by compacting the soil in layers under controlled moisture and density using suitable rollers. In the case of high embankments, the stability of the embankment foundation and slopes and the possible settlement of the embankment with time are to be investigated. The pavement construction is subsequently taken up starting with the preparation of sub grade and the construction of sub base, base and surface courses of the pavement.

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Highway Alignment

Once the necessity of the highway is assessed, the next process is deciding the alignment. The highway alignment can be either horizontal or vertical.

Alignment

The position or the layout of the central line of the highway on the ground is called the alignment. It is an arrangement in a straight line or in correct relative positions. Horizontal alignment includes straight and curved paths. Vertical alignment includes level and gradients. Alignment decision is important because a bad alignment will enhance the construction, maintenance and vehicle operating cost. Once an alignment is fixed and constructed, it is not easy to change it due to increase in cost of adjoining land and construction of costly structures by the roadside. A new road should be aligned very carefully as improper alignment would result in increase in one or more of the following

a) Construction cost

b) Maintenance cost

c) Vehicle operation cost

d) Accident rate

Requirements

The basic requirements of an ideal alignment between two terminal stations are that it should be:

a) Short

b) Easy

c) Safe and

d) Economical

a) Short

It is desirable to have a short (or shortest) alignment between two terminal stations. A straight alignment would be the shortest, though there may be several practical considerations which would cause deviations from the shortest path.

b) Easy

The alignment should be such that it is easy to construct and maintain the road with minimum problems. Also, the alignment should be easy for the operation of vehicles with easy gradients and curves.

c) Safe

The alignment should be safe enough for construction and maintenance from the view point of stability of natural hill slopes, embankment and cut slopes and foundation of embankments. Also, it should be safe for the traffic operation with safe geometric features.

d) Economical

The road alignment could be considered economical only if the total life cycle cost considering the initial cost, maintenance cost and vehicle operation cost is lowest.

Factors Controlling Alignment

It is not always possible to satisfy all these requirements mentioned above. Hence we have to make a judicial choice considering all the factors. For an alignment to be shortest, it should be straight between the two terminal stations. This is not always possible due to various practical difficulties such as intermediate obstructions and topography. A shortest route may have very steep gradients and hence not easy for vehicle operation. Similarly, there may be construction and maintenance problems along a route which may otherwise be short and easy. Roads are often deviated from the shortest route in order to cater for intermediate places of importance or obligatory points.

A road which is economical with lowest initial construction cost, need not necessarily be the most economical in maintenance or in vehicle operation cost. It may also happen that the shortest and easiest route for vehicle operation may work out to be the costliest of the different alternatives from construction view point. Thus, it may be seen that an alignment can seldom fulfil all the requirements simultaneously; hence a judicial choice is made considering all the factors. The various factors that control the alignment are as follows.

1) Obligatory Points

These are the control points governing the highway alignment. These points are classified into two categories. Points through which it should pass and points through which it should not pass. Obligatory points through which the road alignment has to pass are generally due to the topographic and other site conditions including natural obstructions. Some of the examples of this category include location of a mountain pass, suitable location of bridge to cross a river, presence of quarry or an intermediate town to be connected. These obligatory points necessitate deviation of the road alignment from the straight alignment with shortest or easiest path. Some of the examples are:

i) Bridge Site

The bridge can be located only where the river has straight and permanent path and also where the abutment and pier can be strongly founded. The road approach to the bridge should not be curved and skew crossing should be avoided as possible. Thus to locate a bridge the highway alignment may be changed.

ii) Mountain

While the alignment passes through a mountain, the various alternatives are to either construct a tunnel or to go round the hills. The suitability of the alternative depends on factors like topography, site conditions and construction and operation cost.

iii) Intermediate Town

The alignment may be slightly deviated to connect an intermediate town or village nearby.

These were some of the obligatory points through which the alignment should pass.

There are obligatory points through which the road should not pass and these locations may make it necessary to deviate from the proposed shortest alignment. The obligatory points which should be avoided while aligning a road include religious places, very costly structures, unsuitable land etc. Religious places like temple, mosque, church, grave or tomb have been protected by the law from being acquired for any purpose. Acquiring costly structures would mean heavy compensation resulting in increased cost. Marshy, peaty and water logged areas are generally unsuitable for road construction and should be avoided as far as possible. If a marshy land with peaty soil falls on the path of a straight alignment, it may be necessary to deviate the road alignment from the straight path and go around the unsuitable land or pond. The other alternative method is to resort to very expensive construction techniques. The points through which the alignment should not pass are given below.

i) Religious Places

These have been protected by the law from being acquired for any purpose. Therefore, these points should be avoided while aligning.

ii) Very Costly Structures

Acquiring such structures means heavy compensation which would result in an increase in initial cost. So the alignment may be deviated not to pass through that point.

iii) Lakes or Ponds etc.

The presence of a lake or pond on the alignment path would also necessitate deviation of the alignment.

2) Traffic

The road alignment should be decided based on the requirements of road traffic. Origin and Destination study should be carried out in the area and the desire lines be drawn showing the trend of traffic flow. The new road to be aligned should keep in view the desire lines, anticipated traffic flow, classified traffic volume, their growth and future trends.

3) Geometric Design

Geometric design factors such as gradient, radius of curve and sight distances also would govern the final alignment of the highway. If straight alignment is aimed at, often it may be necessary to provide very steep gradients. As far as possible while aligning a new road, the gradient should be flat and less than the ruling or design gradient. Thus, it may be necessary to change the alignment considering the design speed, maximum allowable super elevation and coefficient of lateral friction. It may be necessary to make adjustment in the horizontal alignment of roads keeping in view the minimum radius of curve and the transition curves. The absolute minimum sight distance, which should invariably be made available in every section of the road, is the safe stopping distance for the fast moving vehicles. Also, there should be enough distance visible ahead for safe overtaking manoeuvres of vehicles moving at design speed on the road. Hence the alignment should be finalized in such a way that the obstructions to visibility do not cause restrictions to the sight distance requirements.

4) Economics

The alignment finalized based on the above factors should also be economical. While working out the economics, the factors to be considered are,

i) initial construction cost of the road,

ii) regular and periodic maintenance cost of the road and

iii) vehicle operation cost in future years.

While trying to decrease the initial construction cost, either the future road maintenance cost or vehicle operation cost or both of these may increase considerably. Therefore, while carrying out economic analysis, it is essential to work out overall economics based on life cycle cost of the road project and not consider the initial cost of the road project only.

5) Other Considerations

Various other factors which may govern either the horizontal or vertical alignment of the road are drainage considerations, hydrological factors, political considerations and monotony. The vertical alignment is often guided by drainage considerations. The sub-surface water level, seepage flow and high flood level are the factors to be kept in view, while deciding the highway alignment.

Types of Alignment

1) Horizontal Alignment

Horizontal alignment in road design consists of straight sections of road, known as tangents, connected by circular horizontal curves. It is the design of the road in the horizontal plane. It consists of a series of tangents (straight lines), circular curves and transition curves. It should provide safe travel at a uniform design speed.

2) Vertical Alignment

Vertical alignment is the longitudinal section and it consists of straight grades joined by vertical curves. Vertical alignment specifies the elevations of points along the roadway. Once the road is aligned and constructed, it is not easy to change the alignment due to increase in cost of adjoining land and construction of costly structures by the road side, as the land value increases manifolds once the road is opened to traffic.

Principles of Highway Alignment

The alignment of a highway is a three-dimensional problem measured in x, y, and z coordinates. This is illustrated, from a driver’s perspective, in Fig.1. However, in highway design practice, three-dimensional design computations are cumbersome and the more important thing is the actual implementation and construction. As a consequence, the three-dimensional highway alignment problem is reduced to two two-dimensional alignment problems, as illustrated in Fig. 2. One of the alignment problems in this figure corresponds roughly to x and z coordinates and is referred to as horizontal alignment. The other corresponds to highway length (measured along some constant elevation) and y coordinates (elevation) and is referred to as vertical alignment. The horizontal alignment of a highway is referred to as the plan view, which is roughly equivalent to the perspective of an aerial photo of the highway. The vertical alignment is represented in a profile view, which gives the elevation of all points measured along the length of the highway.

Fig.1 Highway Alignment in Three Dimensions

Fig. 2 Highway Alignment in Two-Dimensional Views

Special Considerations while Aligning Roads on Hilly Areas

During alignment of hill roads, special care should be taken on the following points which pertain to the hill roads.

i) Stability of Hill Side Slopes

While aligning hill roads, special care should be taken to align the road along the side of the hill which is stable. A common problem in hill roads is that of landslides. The cutting and filling of earth to construct roads on hill-side causes steepening of existing slopes and this affect its stability of the hill slopes.

ii) Drainage of Surface and Subsurface Water Flowing from the Hill Side

Numerous hill-side drains should be provided for adequate drainage facility across the road. But the cross-drainage structure being costly, attempts should be made to align the road in such a way that the number of very expensive cross drainage structures is kept minimum.

iii) Special Geometric Standards for Hill Roads

Different sets of geometric design standards are followed on hill roads with reference to gradient, curves and speed, and they consequently influence the sight distance, radius of curve and other related features. The route should enable the ruling gradient to be attained in most of the length, minimizing steep gradients, hair pin bands and needless rise and fall.

iv) Resisting Length

The resisting length of a road may be calculated from the total work to be done to move the loads along the route taking the horizontal length, the actual difference in levels between the two stations and the sum of ineffective rise and fall in excess of floating gradient. In brief, the resisting length of the alignment should have kept as low as possible. Thus, the ineffective rise and excessive fall should be kept minimum.

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Classification of Roads

The roads are generally classified into two categories, depending on whether they can be used during different seasons of the year.

i) All-weather Roads

All-weather roads are those which are negotiable during all seasons of the year, except at major river crossings where some interruption to traffic is permissible up to a certain extent, but the road pavement should be negotiable during all weathers.

ii) Fair-weather Roads

Roads which are negotiable only during fair weather are called fair weather roads. On fair weather roads, the traffic may be interrupted during monsoon season at causeways where streams may overflow across the road.

Based on the type of the carriageway or the road pavement, the roads are classified as `paved roads' and `un-paved roads'.

i) Paved Roads

The roads with a hard pavement surface on the carriageway are called 'paved roads'.

E.g. Stones, Water bound macadam (WBM), Bituminous macadam (BM), Concrete roads

ii) Unpaved Roads

The roads without a hard pavement surface on the carriageway are called 'unpaved roads'. Earth roads and gravel roads may be called unpaved roads.

Based on the type of pavement surfacing provided, the roads may be classified as `surfaced roads' and `un-surfaced roads’.

i) Surfaced Roads

Road pavements with any type of bituminous surface or cement concrete are called surfaced roads.

E.g. BM road, Concrete road

ii) Un-Surfaced Roads

The roads which are not provided with a bituminous or cement concrete surfacing are called un-surfaced roads.

E.g. Soil or Gravel road

Methods of Classification of Roads

The roads are generally classified based on the following.

a) Traffic volume

b) Load transported or tonnage

c) Location and function

The classification based on traffic volume or tonnage has been arbitrarily fixed by different agencies and there may not be a common agreement regarding the limits for each of classification group. Based on the traffic volume or flow, the roads are classified as heavy, medium and low volume roads. These terms are relative and so the limits under each class should be clearly defined and expressed as vehicles per day or 'annual average daily traffic'.

The classification based on load or tonnage is also relative and the roads may be classified as class I, II etc. or class A, B etc. and the limits may be expressed in terms of tones per day. The classification based on location and function should therefore be a more acceptable classification method for a country as they may be defined clearly.

Road Classification Based on Location and Function

1) Road Classification as per Nagpur Road Plan

The Nagpur Road Plan classified the roads in India based on location and function into following five categories and are described below.

i) National Highways (NH)

National Highways (NH) are main highways running through the length and breadth of India, connecting major ports, foreign highways, capitals of large states and large industrial and tourist centres including roads required for strategic movements for the defence of India. All of the national highways are assigned the respective numbers. For example, NHI is the national highway connecting Delhi, Ambala, Jalandhar and Amritsar (up to Pakistan border); NH-4 connects Thane, Pune, Belgaum, Hubli, Bangalore, Chittoor and Chennai.

ii) State Highways (SH)

State Highways (SH) are arterial roads of a state, connecting the national highways of adjacent state, district headquarters and important cities within the state and serve as the main arteries for traffic to and from district roads. These highways are considered as main arteries of commerce by road within a state or a similar geographical unit.

iii) Major District Roads (MDR)

Major District Roads (MDR) are important roads within a district serving areas of production and markets and connecting with other major roads or main highways of a district. The MDR has lower speed and geometric design specifications than NH or SH.

iv) Other District Roads (ODR)

Other District Roads (ODR) are roads serving rural areas of production and providing them with outlet to market centres, taluk headquarters, block development headquarters or other main roads. These are of lower design specifications than MDR.

(v) Village Roads (VR)

Village Roads (VR) are roads connecting villages or groups of villages with each other to the nearest road of a higher category. It was specified that these village roads should be in essence farm tracks, but it was desired that the prevalent practice of leaving such tracks to develop and maintain by themselves should be replaced by a plan for a designed and regulated system.

2) Road classification as per third 20-year road development plan, 1981 -2001

The road classification system was modified in the third 20-year road development plan. The roads in the country are now classified into three classes, for the purpose of transport planning, functional identification, earmarking administrative jurisdictions and assigning priorities on a road network.

i) Primary System

ii) Secondary System

iii) Tertiary System or Rural Roads

Primary system consists of two categories of highways.

a) Expressways

b) National Highways (NH)

Expressways are a separate class of highways with superior facilities and design standards and are meant as through routes having very high volume of traffic. The expressways are to be provided with divided carriageways, controlled access, grade separations at cross roads and fencing. These highways should permit only fast-moving vehicles. Expressways may be owned by the Central Government or a State Government, depending on whether the route is a National Highway or State Highway. The National Highways form the other main category of primary system in the country.

The Secondary system consists of two categories of roads.

a) State Highways (SH)

b) Major District Roads (MDR)

(Explained above)

The Tertiary systems are rural roads and these consist of two categories of roads.

a) Other District Road (ODR)

b) Village Roads (VR)

(Explained above)

The roads have classified as follows in the order of increased accessibility and reduced speeds.

1) Freeways

Freeways are access controlled divided highways. Most freeways are four lanes, two lanes each direction, but many freeways widen to incorporate more lanes as they enter urban areas. Access is controlled through the use of interchanges and the type.

2) Expressways

They are superior type of highways and are designed for high speeds (120 km/hr is common), high traffic volume and safety. They are generally provided with grade separations at intersections. Parking, loading and unloading of goods and pedestrian traffic is not allowed on expressways.

3) Highways

They represent the superior type of roads in the country. Highways are of two types - rural highways and urban highways. Rural highways are those passing through rural areas (villages) and urban highways are those passing through large cities and towns, i.e. urban areas.

4) Arterials

It is a general term denoting a street primarily meant for through traffic usually on a continuous route. They are generally divided highways with fully or partially controlled access. Parking, loading and unloading activities are usually restricted and regulated. Pedestrians are allowed to cross only at intersections/designated pedestrian crossings.

5) Local Streets

A local street is the one which is primarily intended for access to residence, business or abutting property. It does not normally carry large volume of traffic and also it allows unrestricted parking and pedestrian movements.

6) Collectors Streets

These are streets intended for collecting and distributing traffic to and from local streets and also for providing access to arterial streets. Normally full access is provided on these streets. There are few parking restrictions except during peak hours.

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Highway Planning and Geometric Design

Planning is considered as a pre-requisite before attempting any development programme in the present era. This is particularly true for any engineering project, as planning is the basic requirement for any new project or an expansion programme. Thus there is a need for planned development of the road network and the links. Highway planning is of great importance when the funds available are limited whereas the total requirement is much higher. In developing countries like India it is important to utilize the available funds in the best possible manner by resorting to best planning principles. The objects of highway planning are briefly given below.

• To plan overall road network for efficient and safe traffic operation, but at minimum cost. Here the costs of construction, maintenance and resurfacing or strengthening of pavement layers and the vehicle operation cost are to be given due consideration.
• To arrive at the road system and the lengths of different categories of roads which could provide maximum utility and could be constructed within the available resources during the plan period under consideration.
• To divide the overall plan into phases and to decide priorities.
• To fix up date-wise priorities for development of each road link based on utility as the main criterion for phasing the road development programme.
• To plan for future requirements and improvements of roads in view of anticipated developments.
• To work out suitable financing system phases of highway planning.

Highway planning includes the following phases.

• Assessment of road length requirement for an area (it may be a district, state or the whole country)
• Preparation of master plan showing the phasing of plan in five year plans or annual plans. In order to plan the road system in the selected region, state or country, different studies and surveys are to be carried out to collect the data required. The data collected are to be processed and analysed to arrive at the best possible road network and to arrive at the optimum length of the road system.

Geometric Design

Geometric design for transportation facilities includes the design of geometric cross sections, horizontal alignment, vertical alignment, intersections and various design details. These basic elements are common to all linear facilities, such as roadways, railways and airport runways and taxiways. Although the details of design standards vary with the mode and the class of facility, most of the issues involved in geometric design are similar for all modes. In all cases, the goals of geometric design are to maximize the comfort, safety and economy of facilities, while minimizing their environmental impacts.

The geometric design of highways deals with the dimensions and layout of visible features of the highway. The features normally considered are the cross section elements, sight distance consideration, horizontal curvature, gradients and intersection. The design of these features is to a great extend influenced by driver behaviour and psychology, vehicle characteristics, traffic characteristics such as speed and volume. Proper geometric design will help in the reduction of accidents and their severity. Therefore, the objective of geometric design is to provide optimum efficiency in traffic operation and maximum safety at reasonable cost. The planning cannot be done stage wise like that of a pavement, but has to be done well in advance.

Factors Affecting Geometric Design

1) Design speed

Design speed is the single most important factor that affects the geometric design. It directly affects the sight distance, horizontal curve and the length of vertical curves. Since the speed of vehicles vary with driver, terrain etc., a design speed is adopted for all the geometric design.

2) Topography

It is easier to construct roads with required standards for a plain terrain. However, for a given design speed, the construction cost increases multi form with the gradient and the terrain.

3) Traffic Factors

It is of crucial importance in highway design, is the traffic data both current and future estimates. Traffic volume indicates the level of services (LOS) for which the highway is being planned and directly affects the geometric features such as width, alignment, grades etc., without a suitable traffic data it is very difficult to design any highway.

4) Design Hourly Volume and Capacity

The general unit for measuring traffic on highway is the Annual Average Daily Traffic volume, abbreviated as AADT. The traffic flow (or) volume keeps fluctuating with time, from a low value during off peak hours to the highest value during the peak hour. It will be uneconomical to design the roadway facilities for the peak traffic flow.

5) Environmental and Other Factors

The environmental factors like air pollution, noise pollution, landscaping, aesthetics and other global conditions should be given due considerations in the geometric design of roads.

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Origin and Growth of Town

Origin of Towns: Topographical Features

If a survey is carried out regarding the origin of some of the important existing towns and cities of the world, it can be easily established that any town or city has originated because of certain specific cause. The origin of towns can be broadly classified into two categories, namely, topographical and functional. The topographical features of origin of towns are as follows.

1. Conditions favorable for industrial units
2. Hilly areas to achieve the objects of defense
3. Plain areas useful for business activities
4. River banks
5. Sea or ocean fronts

The functional aspects of origin of towns are as follows.

1. Education
2. Health resorts
3. Political
4. Community

Growth of Town

The towns grow during passage of time in number of ways and various forces which contribute to the overall development of a town are transportation facilities, industries, safety for public, proximity of agricultural lands, availability of electric power, political importance, etc. Some of the reasons why the people would like to stay in urban areas can be enumerated as follows.

• It is quite likely that people have often found to stay in groups or societies to safeguard themselves from dangers of theft.
• The humans by nature are social animal and they get much satisfaction of living their life in the company of friends and community.
• An urban man can develop contacts and make friends with like-minded people having common interest.
• The urban dwellers can maintain a very high degree of privacy.
• The urban are provide with reliable water supply, good market for business, large amount of opportunities to succeed, etc.

Also the facilities of transport and communication increase the population and leads to the growth of towns. The means of transport may take up the following forms.

• Aerial ports : In some cases, the airports plays an important role in the growth of a town.
• Railways : If the town is connected with railways, there will be increase of passengers and goods traffic even from long distances.
• Roadways : The neighbouring area is connected with the town and it leads to overall expansion of trade and industry.
• Waterways : If facilities of waterways are available, the town can grow as a harbour with possibility of foreign trade and business.

The above mentioned means of transport have led to the horizontal growth of town. But the availability of mechanical lifts, escalators and elevators has made it possible to have vertical growth of town in the form of skyscrapers.

Fig. 1 Types of Growth of Towns

Types of Growth of Town

The growth of towns and cities can be studied in the following two ways.

I) Growth according to origin

II) Growth according to direction

1) Growth According to Origin

The growth of towns and cities according to the origin can be divided in two categories.

A) Natural Growth

Most of the towns in the past have grown in a natural way, that is, the development of the town as such has taken place without any future planning. The provisions of various essential amenities such as road system, parks, playgrounds, schools, industrial units, commercial centres, hospitals, cinemas, etc., are made in an irregular way without consideration for future expansion of the town. The natural growth of a town may be in the form of following four types.

a) Concentric spread

b) Ribbon development

c) Satellite growth

d) Scattered growth

a) Concentric Spread

• It is the natural tendency of the people to be as near as possible to town or city, therefore the town develops in form of concentric rings with nucleus as town.
• These type of growth create many complicated problems such as traffic congestion, narrow streets,concentration of population, improper housing, etc.
• The town growth is represented by a series of concentric circles or rings.
• The first zone represents central business like commercial and social life of the town.
• The second zone represents low-income housing, better-class residences and high-class residences are subsequently formed.
• The idea of concentric spread is based on the fact that similar or functionally related activities will be located at the same distance from the centre of an urban area.

Fig. 2 Concentric Spread

b) Ribbon Development

• It has been observed that because of improvement of road surface and growth of motor traffic, everyone build or occupy the places as near as possible to the main road.
• The building activity therefore expands in a natural way along the sides of main road and long fingers or ribbons of houses, factories, shops, etc., develop as shown in figure below.

Fig. 3 Ribbon Development

Disadvantages

• As houses extend in a long strip or ribbon, there is increase in cost of utility services such as water supply and electricity, postal deliveries, etc.
• It results into wastage of available resources.
• It lacks social life as ribbon development causes scatter of community.
• The future improvement becomes costly and difficult, in some place it becomes impossible.
• The interior place are left undeveloped which results in wastage of valuable land.
• It causes accidents and traffic delays (jams) due to pedestrians on the main road.
• The traffic capacity and efficiency of main road are reduced.
• The ribbon development spoils the countryside view as it becomes non-visible at least for road users.
• The problem of ribbon development is complex involving social-economic, political, technical and legal measures for its solution.

c) Satellite Growth

When a town reaches a certain size, satellite growth is bound to take place. The satellite town is mainly due to the metropolis and it indicate a body under the influence of a more powerful body but possessing its own identity. Development of satellite towns around the parent city is shown in the figure below.

Fig. 4 Satellite Growth

The features of a satellite town are as follows.

• It has its own local government and corporate life.
• It is a town in the full sense but it depends to a certain extent upon a nearby large town or city.
• It is connected to the parent city by local trains, buses, etc. in such a way the people can reach to the parent city easily.
• It is free to decide its economic, social and cultural activities.
• It is generally situated beyond the green belt of the parent city.
• It is mainly residential area having only local shops, schools for children, etc.
• No industries are permitted, the people will have to depend on the parent city for employment opportunities.
• It is neither a village nor a suburb.
• It need not have zoning regulations.
• Its size and development are controlled in such a way that it does not affect the parent town in future.
• The satellite may even be considered to be the part of market for some goods and services from the parent town.
• The workers living in particular satellite may belong to the labour force of a certain industry. It gives a wider choice to the employers of such industries for finding the best man for the job.

Disadvantages

• The main disadvantage of satellite growth is the necessity of the long journey to work. (It may be long journey in distance does not necessarily mean a long journey in time due to efficient modes of transport and traffic).
• Satellite growth may be deprived of entertainment and cultural activity.
• It is responsible for preventing the development of a community spirit.
• Lack of community centres and halls.

d) Scattered Growth

• The growth of the town takes place in very irregular way.
• It results in traffic congestion.
• Encroachment of industries on residential areas.
• Development of slums.
• Lack of parks and various other problems which prove to be too difficult to be solved in future.

B) Planned Growth

In case of a planned growth, a town develops in a pre-determined line as conceived by the town planner. The overall growth of the town is controlled by the enforcement of suitable rules and regulations. There is rational distribution of various blocks such as residential, industrial, commercial, etc.

The provision of various amenities such as widths of streets, drainage lines, water supply lines, parks, playgrounds, etc. is made to meet with the future requirements. The modern concepts of town planning can very well be seen and appreciated in some of the recent new towns in many parts of the world.

2) Growth According to Direction

With respect to direction, the growth of towns and cities can take place in the following two ways.

1. Horizontal Growth

The town expands and develops horizontally in all directions. It is clear that such a growth will be possible at places where land is available in plenty at nominal cost.

Advantages

• In general, there will be saving in cost as the buildings will usually consist of two or three floors.
• It does not require the service of high technical personnel.
• Maximum possible use of the natural light in the buildings.
• The density of the population can be restricted.
• There is economy of floor space as the provision of columns, lifts, etc. will not be required.
• The surrounding marginal space can be utilized for developing gardens.

Disadvantages

• It uses more land and hence, it will prove to be uneconomical where the land value are very high.
• The foundation cost per unit area will be more.
• There will be absence of group living.

2. Vertical Growth

The buildings of the town are designed and developed as multistoried flats. It is quite evident that such a growth will be possible at places where land is costly.

Advantages

• A sense of group living and unity develops as many families live in same building.
• The foundation cost will be distributed between all the floors, therefore the foundation cost per unit area will be in the reasonable limit.
• For floor above certain height, the natural sceneries such as sea view, river view, etc. can be enjoyed in a better way.
• It will be possible to make maximum use of the modern technology such as fire-proofing, sound-proofing, heat insulation, air-conditioning, high speed elevators, etc.
• There will be considerable saving in land and hence, it will prove to be economical where land values are very high.
• There will be economy in construction cost as the buildings will be designed as framed structures with repetition of a typical floor plan at each floor level.

Disadvantages

• In case of natural calamities such as earthquakes or fire, it will be difficult for the inhabitants (dwellers) of the upper floors to escape safely.
• The density of population will be more.
• The design of flats will be stereo-typed and there is no scope for personal likes or dislikes.
• The evils of group living will have to be tolerated.
• The failure of lift, pumps, etc. will cause great inconvenience.
• The people staying at upper floors will be deprived of natural living near the ground level.
• There will be some wastage of floor space as lifts, supporting columns, etc. will have to be provided.

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Town Planning Process

All stages of actions from defining the objectives till implementation and review of any planning project in the planning process. In plan preparation, the physical planning should associate with the socio-economical, geographical, political factors, for achieving the objective in desired direction. The various stages of planning process are as follows.

1.Identification and Definition of Problems

Various problems with reference to the results obtained by studies and surveys and with reference to the objectives are identified.

2. Defining the Objectives

Here the objectives of the planning are identified. The general objectives of any planning of urban area is

• To regulate growth
• To nullify the bad effects of past growth
• To improve the transportation facilities
• To optimize the resources utilization
• To balance population and economic activities
• To promote social integration among different categories
• To promote a convenient comfortable, beautiful and healthy environment

3. Studies and Survey

The following studies and surveys are taken up for plan preparation.

• Identification of growth (physical, economic, social, cultural, institutional, administrative and political)
• Identification of trend and direction of growth
• Traffic survey
• Study on demography
• Climate

4. Analysis of Data and Preparation of Study Maps

The data obtained is analyzed – observations and conclusions have to be derived out of the studies and surveys. The short-term objectives and long-term objectives are identified – various study maps, charts and graphs are prepared.

5. Forecasting

Period of demographic projection is prescribed. Forecasting of about migration, employment, industrialization and other rapid urbanization possibilities are to be made.

6. Design

This is an important aspect in the planning process. Need to relate existing pattern, interactions and trends is to be examined. Preparation of development plans, formulation of zones, alteration to the existing zoning regulations, widening of roads etc. are made in detail here. Alternatives are also made for effective and quick implementation of plan. The plan should also be able to cope with sudden and unexpected events. Possibility of changing from one strategy to another should be designed at the same time keeping in view its practicability and the total expenditure involved.

7. Fixation of Priorities

Since all the proposals cannot be taken up at one time due to financial and administrative difficulties, priorities should be fixed for taking up the implementation depending upon the importance and urgency.

8. Implementation

Implementation is the most important stage where all the earlier efforts to prepare plan is to be put into practice to achieve the objectives. The authority, which takes up the implementation, is to fulfill all the required legal obligations in time – zoning regulations, land acquisition for road widening and for other purposes is taken-up.

9. Review, Evaluation and Feedback

The work of implementation has to be monitored by taking – up periodical inspections and obtaining review reports. Feedback is essential periodically. The plan should be flexible for modifications depending upon the necessities.

Types of Surveys

Surveys can broadly be divided into two categories depending on the area upon which they are to be conducted. They are:

1. Regional Surveys

They are those surveys, which are done over a region dealing with physical factors like topography, physically difficult land, geology, landscape etc. Physical economic factors like agricultural value of the land, mineral resources and water gathering lands, areas with public services, transportation linkages etc. Social economic factors like areas of influence of towns and villages, employment, population changes etc.

2. Town Surveys

They are done at much small scale and apart from the above data collected from the regional surveys it also includes

• Land use surveys
• Density surveys
• Surveys for the age and condition of the buildings
• Traffic surveys

Other social surveys for conducting proper survey, primarily relevant enquiries should be framed in the form of questionnaires for presentation, when required.

Techniques of Surveys

1. Self-surveys (i.e. mailing questionnaires to the persons to be surveyed)

2. Interviews (i.e. by asking questions to the people to be surveyed)

3. Direct inspection (i.e. when the surveyor himself inspects the situations concerned)

4. Observers participation (i.e. when the observer himself participate in acquiring the data

required)

Approaches to Planning

1. Comprehensive planning

The traditional four-step planning process - the identification of problems and issues; the establishment of goals and objectives; data collection and analysis; and plan preparation and implementation.

2. Issue-oriented planning

Some communities do not get around to planning until a problem or a crisis has occurred. Issue-oriented planning focuses attention on the problems and issues of greatest concern to a community at a particular point in time. This is an “old-fashioned approach” to planning,

3. Functional planning

Functional planning is a slower version of comprehensive planning.

4. Strategic planning

Major emphasis should be placed on the selection and application of strategies to resolve identified issues and attain desired goals. The principal steps in strategic planning are

• Scan the environment and select key issues.
• Formulate goals or missions for the key issues.
• Analyze each issue, developing a list of community strengths and weaknesses.
• Develop strategies that are realistic and take into account those strengths and weaknesses.
• Implement strategies using public and private resources.
• Monitor and update the plan to ensure implementation.

5. Vision-based Planning

Imagines what a community should look like in the future and then develops a plan to achieve that vision. This visioning process is unique, but it is often included as an element of a variety of master plans. It is a positive approach to planning and can be very inspiring.

6. Urban Planning (urban, city, and town planning)

It is a technical and political process concerned with the control of the use of land and design of the urban environment, including transportation networks, to guide and ensure the orderly development of settlements and communities.

Elements of City/Town Planning

1.  Communication & Transportation
2. Built up Area
3. Open space (Parks, Playgrounds, Recreational unit)
4. Public utility services (Electricity, Gas, Telephone, Fire safety)
5. Public amenities (Post office, Bank, Police, Solid waste disposal, Petrol pump, Court)

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Principles of Town Planning

Town planning cannot be studied in isolation. It involves the study of various subjects such as engineering, architecture, surveying, transportation planning etc. The intention of the town planning is to satisfy the needs of our future generations and prevent the haphazard growth of the town. Some of the guiding principles of town planning are as follows. 

1. Zoning 

The town should be divided into suitable zones such as commercial zone, industrial zone, residential zone, etc. and suitable rules and regulations should be formed for the development of each zone. 

2. Green Belt 

Green belt is non-development zone on the periphery of the town. It prevents the haphazard sprawl of the town restricting its size. In essence, a green belt is an invisible line designating a border around a certain area, preventing development of the area and allowing wildlife to return and be established. Greenways and green wedges have a linear character and may run across the town and not around the town. 

3. Housing 

Housing has to be carefully studied and designed to suit the local population. Care should be taken to see that there is no development of slums since it would be responsible for degrading the life of the citizens. There are various types of housing styles. When a landuse plan is made, zones for independent housing, midrise buildings, high rise buildings are allocated. 

4. Public Buildings 

Public buildings should be well grouped and distributed throughout the town. Unnecessary concentration of public buildings should be avoided. Factors such as parking facilities, road widths have to be taken into consideration while allocating the space for public buildings. 

5. Recreation Centres 

Recreation centres have to be given importance while designing a town. They are necessary for the recreational activities of the general public. They include parks for walking and cycling, amusement parks etc. 

6. Road Systems 

Road network hierarchy is very important. The efficiency of any town is measured by the layout of its roads. A nicely designed road system puts a great impression in the minds of people, especially the visitors to the town. The provision of a faulty road system in the initial stages of town formation proves to be too difficult and costly to repair or to re-arrange in future. 

7. Transport Facilities 

The town should be provided with suitable transport facilities so that there is minimum loss of time from place of work to the place of residence. Efficiency in transport facilities includes both public and private networks. Public transportation network includes access to buses, trains, trams and trolleybuses. Efficiency in using the public transport will determine the success of that town in terms of design.

Objectives of Town Planning

The main objectives of the town planning may be summarized in three words viz. Health, Convenience, Beauty and Environment.

1. Health

To make right use of the land for the right purpose by proper division of land called zoning such as residential, commercial industrial, institutional and recreational etc. inorder to avoid the encroachment of one zone upon other for smooth and orderly development of the town or city without causing future conflicts. To create and promote healthy conditions and environments for all the people – rich and poor, to live, to work, to play or relax.

2. Convenience

The object of convenience is meant in the form of various needs of the community such as social, economic, cultural and recreational amenities etc. Public amenities requiredfor the proper upkeep of the citizens include water supply, sanitation, electricity, post,telegraph, gas etc., proper sites for industrial, commercial, business enterprises toencourage them in trade with cheap power, transport services, drainage etc. Recreational amenities include open spaces, parks, gardens and playgrounds, for children and town halls stadiums, community centers, cinema houses, and theatres for adults.

3. Beauty

To preserve the individuality of the town by developing it on its most suited natural conditions. To preserve the aesthetics in the design of all elements of town or city plan, which includes preservation of trees, natural greenery, improved types of domestic buildings and buildings of civic dignity and beauty, architectural control on public as well as semi-public buildings, ancient architectural buildings, temples, churches, mosques and buildings of cultural and historical importance.

4. Environment

It is an important factor in town planning. The environment of the town should be in such a way that people can lead their normal activities with least difficulty. The complex problems of modern society such as tiresome travel to work, long hours of work, limited time spent within the family and community, etc. has led to serious problems in the lifestyle of the people living in the towns, therefore, town planning is mainly concerned with brining about a better relation between man and his environment.

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Quarrying of Stones

The method of removal of stones from their natural bed by using different operations is called quarrying. The only operation involved in the production of natural stone is the quarrying process. The open part of the natural rock from which useful stone is obtained is known as quarry. While selecting a quarry site, the points to be borne in mind are availability of sufficient quantity of the stone of desired quality, proper transportation facilities, cheap local labour, problems associated with drainage of rain water, location of important and permanent structures in the vicinity and site for dumping refuse.

Stone Quarrying Tools

Some of the quarrying tools shown in Fig. 1 are wedge, pin, hammer, dipper or scraping spoon, tamping bar, priming needle, jumper, borer, claying iron, crow bar.

Fig. 1 Tools for Quarrying Stones

Methods of Quarrying

Rocks suitable for the manufacture of stone materials are called useful minerals and the operations involved in obtaining minerals are called mining. In the process of mining, voids formed are called excavations and the mined deposits are the quarries. The purpose of quarrying is to obtain stones for various engineering purposes. A knowledge of various quarrying methods is essential but does not make one very much more competent to choose or specify a stone for building work. Depending upon the nature and surface of rocks and the purpose for which stones are needed, quarrying is done by excavating, wedging, heating or blasting.

1) Excavation/Digging

Stones buried in earth or under loose overburden are excavated with pick axes, crow bars, chisels, hammers, etc. This method is used when the quarry consists of small & soft pieces of stones.

Fig.2 Digging of Stones

2) Wedging

This method of quarrying is suitable for costly, soft and stratified rocks such as sandstone, limestone, laterite, marble and slate. This method is used when the hard rock consists of natural fissure. When natural fissures are absent then artificial fissures are prepared by drilling holes. The tools used for wedging are

• Steel wedge
• Conical steel pin or plug
• Flat steel wedge
• Wooden plug
• Pneumatic drill

About 10–15 cm deep holes, at around 10 cm spacing, are made vertically in the rock. Steel pins and wedges or plugs (conical wedges) and feathers (flat wedges) as shown in Fig. 3 are inserted in them. The latter arrangement of plugs and feather is better. These plugs are then struck simultaneously with sledge hammer. The rock slab splits along the lines of least resistance through holes. In case of soft rocks, dry wooden pegs are hammered in the holes and water is poured over them. The pegs being wet swell and exert pressure causing the rocks to crack along the line of holes. Then, the wedges are placed on the plane of cleavage (the joint of two layers) on the exposed face of rock and are hammered. The slab is completely detached and taken out with the help of crow bars and rollers. In this method, the wastage is minimum and the slabs of required size and shape can be quarried.

Fig. 3 Quarrying by Wedging

3) Heating

Heating is most suitable for quarrying small, thin and regular blocks of stones from rocks, such as granite and gneiss. This method is used when the natural rock bed is horizontal and small in thickness. A heap of fuel is piled and fired on the surface of rock in small area. The two consecutive layers of the rock separate because of uneven expansion of the two layers. The loosened rock portions are broken into pieces of desired size and are removed with the help of pick-axes and crow-bars. Stone blocks so obtained are very suitable for coarse rubble masonry. Sometimes, intermediate layers are to be separated from the top and bottom layers. In such a case, the intermediate layer is heated electrically and the expansion separates it from the other two.

Fig. 4 Quarrying by Heating

4) Blasting

It is the process of removal of stones with the help of controlled explosives is filled in the holes of the stones. Line of least resistance plays very important role in the blasting process. Explosives such as blasting powder, blasting cotton, dynamite and cordite are used. The operations involved are boring, charging, tamping and firing.

a) Boring

Holes are drilled or bored in the rock to be dislodged. For vertical holes, jumper is used whereas for inclined or horizontal holes, boring bars are used. One person holds the jumper exactly in the place where hole is to be made. The other person strikes it up and down and rotates it simultaneously. Water is poured in the hole regularly during the operation to soften the rock and facilitate drilling. The muddy paste generated in the process is removed from holes by scrapping. For hard rocks, machine drilling is employed instead of hand drilling.

b) Charging

The holes are dried completely and the required amount of charge is placed in the holes. For drying the holes, rag is tied in the scrapper and is moved in the hole from where it absorbs the moisture, if any. In case it is found that water is oozing into the hole, water tightness is ensured inside the hole.

c) Tamping

After placing the charge in the hole, a greased priming needle, projecting a little outside the hole, is placed in the hole which is then filled up with damp clay or stone dust in layers tamped sufficiently with a braced tamping rod. The priming needle should be kept on rotating while tamping is going on. This is done so that the needle remains loose in the hole. The priming needle is then taken out and 60 to 75 per cent of space created by withdrawal of needle is filled with gun powder. A Bickford fuse, a small rope of cotton coated with tar, is placed just touching the needle. The other end of the fuse is kept of sufficient length so that the person igniting it can move away to a safe place. Blasting powder and cordite are ignited by means of a fuse, whereas gun cotton and dynamite are exploded by detonation.

Detonation is achieved with detonators. These are copper tubes about 5 mm in diameter and 25 mm long containing 5 to 20 grains of fulminate of mercury. These can be exploded by an ordinary fuse or by an electric current. An electric detonator is shown in Fig. 5. Tamping should be done very carefully otherwise the explosive fires back in the hole, since the line of least resistance (LLR) is the shortest distance (Fig. 6) from the explosive in the hole to the nearest rock face, fixture, crack, fault or plane of cleavage.

Fig. 5 Electrical Detonator

Fig. 6 Tamped and Charged Blast Hole

d) Firing

The fuses of blasting holes are fired by using electrical power supply or match sticks.

Precautions in Blasting

Accidents may take place during blasting. The following points to be considered while blasting process.

1. Blasting should not be carried out in late evening or early morning hours. The blasting hours should be made public and a siren should warn the workmen and nearby public timely to retire to a safe distance.
2. The danger zone, an area of about 200 m radius, should be marked with red flags.
3. First aid should be available.
4. The number of charges fired, the number of charges exploded and the misfires should be recorded.
5. Explosives should be stored and handled carefully.
6. Detonators and explosives should not be kept together.
7. Cartridges should be handled with rubber or polythene gloves.
8. A maximum of 10 bore holes are exploded at a time and that also successively and not simultaneously.

Storage of Explosives

The explosives should be stored in a magazine (a special type of building) which should be away from residential areas, petrol depots etc. The magazine should have ventilators at high levels and should have concealed wiring. It should be protected from lightning. Smoke or fire should not be allowed in the nearby area. Explosives should be protected from extreme heat or cold and also from moisture. They should be handled carefully and gently. The magazine should be surrounded by barbed wire and the entry should be restricted.

Quantity of Explosive Required

The quantity of explosive required depends upon several factors such as strength of explosive, method of blasting, number of bore holes and their size, position etc. and the type and mass of rock to be dislodged. It is very difficult to incorporate all the factors in an expression and obtain the exact amount of explosive required. A rough estimate can be made by the equation given below.

where  A = quantity of gunpowder or dynamite (g)

              L = length of line of least resistance (m)

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