Textbook of
Forest Engineering
A.G KOPPAD Associate Professor (Forest Engineering) College of Forestry (UAS), Sirsi, Dharwad (Karnataka) 581401
3MJT ICAR
Published by
Directorate of Knowledge Management of Agriculture Indian Council of Agricultural Research Krishi Anusandhan Bhavan, Pusa, New Delhi 110 012
Printed : June 2011
Project Director : Dr T.P. Trivedi
Incharge (English Editorial) : Dr R.P. Sharma Editing : Dr Sudhir Pradhan
Chief Production Officer : Dr V.K. Bharti Technical Officer (Production) : Ashok Shastri
Š All Rights Reserved of Agricultural Research, New Delhi
2011, Indian Council
ISBN : 978-81-7164-105-5
Price : Rs 300.00
Published by Dr T. P. Trivedi, Project Director, Directorate of Knowledge Management in Agriculture, Indian Council of Agricultural Research, New Delhi 110 012. Typeset at M/s Print-O-World, 2579, Mandir Lane, Shadipur, New Delhi 110 008, and printed at M/s Chandru Press, D-97, Shakarpur, Delhi 110 092.
CONTENTS 1.
INTRODUCTION
1
2. CHAIN SURVEYING Objectives and principles of surveying, Scope of surveying in forestry, Traversing and triangulation, Equipments used in chain surveying, Survey station and other lines, Offsets and their types, Obstacles in- chaining, Methods to overcome the obstacles in chaining, Ranging of survey lines, Cross staff surveying, Chaining a survey line on flat and sloppy land, and Errors in chaining and their correction.
3
3. COMPASS SURVEY Compass traverse, Types of compass survey, Meridians and bearings, Methods of compass survey, Local attraction, Determination of interior angles, and Balancing of closed traverse.
29
4. PLANE-TABLE SURVEYING Principles of plane-tabling, Plane-Table and its accessories, Advantages and disadvantages of plane-tabling, Setting of the plane table, Methods of Orientation, Methods of plane-table survey, Sources of error in plane-tabling and their corrections, and Practical application in forest survey. 5. DUMPY LEVEL SURVEY Leveling instrument, Principles of Levelling, Booking staff reading, Methods of computation of reduced level, and Types of Leveling. 6. THEODOLITES Transit theodolites, Non-transit theodolites, Parts of Theodolite, Adjustments of theodolite, Methods of theodolite traversing, and Sources of error in theodolite survey. 7. BUILDING CONSTRUCTION Building materials, Building foundation, Building walls, Doors and windows, and Slabs and plastering. 8. FOREST ROADS Classification of forest roads, Forest Road Alignment, Road design, Drainage of Roads, and Road Curves.
51
62
81
94
125
9. BRIDGES General information about bridges, and Simple wooden bridge.
REFERENCES SUBJECT INDEX
138 147 149
CHAPTER
1
INTRODUCTION T每OREST ENGINEERING is an art and science of surveying and X map making for integrated planning and development of forest area. This mainly includes the surveying of existing features, laying out of proposed structures, such as roads, bridges and buildings, and planning for development activities etc. Surveying is the science and art of determining the relative position of various points above on or below the surface of the earth. The relative positions are determined by measuring horizontal distance, vertical distance (elevations) horizontal angles, and vertical angles using various surveying instruments.
Surveying, deals with both horizontal and vertical plane, is classified on the basis of whether the curvature of the earth is considered or whether the earth is assumed to be a floatplane as plane surveying and geodetic surveying. The straight-line and the curved surface of the earth in small area are almost same hence the curvature of the earth is neglected in plane surveying. The area to be covered under plane surveying is restricted to 250 km2. Whereas the Geodetic surveying is being used for large area, hence the curvature of the earth is considered as curved. Among the different methods of surveying, chain, compass and plane-table surveying are being used for determination of measurements in horizontal plane. The dumpy level and theodolite surveys are being used for determination of measurement in vertical plane. The survey is primarily classified as plane surveying and geodetic surveying. For ordinary surveys in forest area where high degree of precision is not required in such places only plane surveying is adequate, therefore plane surveys are discussed in this book. The secondary classification of surveying are made based on nature of field survey, nature of methods of survey, based on instruments used and based on objects of survey. This book deals with surveys based on
2
Textbook of Forest Engineering
instruments used such as chain surveying, compass surveying, plane table surveying, dumpy level surveying and theodolite surveying. The details about the building material, building construction in forest area, the forest roads and bridges their design and layout in forest area for integrated planning and development of the forest area is elaborated in separate chapters in this book. The forest officers generally required to carry out different surveys mentioned above for recording the existing features and planning for future development of the area. This book is most useful for the undergraduate students of Forestry, and the forest officials for their workings.
CHAPTER
2
CHAIN SURVEYING /每iHAIN SURVEYING is the method of land surveying in which V-每only line measurements are taken with the help of chain and no angular measurements are recorded. This method is being used for small and open areas having simple details. It is simple and quite useful for land surveying to establish the boundaries of a piece of land. It is generally used to prepare the plans of estate and field on a large-scale when the area is small and the ground is fairly level and open and this method is not suitable for large and crowded areas.
OBJECTIVES AND PRINCIPLES OF SURVEYING The objectives of survey are as follows: 1. To take measurements to determine the relative positions of the existing features on or near the ground. 2. To layout or to mark the position of the proposed structures on the ground. 3. To determine areas, volumes and other relative quantities.
The principles of surveying are enumerated here. 1. Always work from the whole to part.
2. Always choose the method of survey that is most suitable for the purpose. 3. Always make provision of adequate checks. 4. Always record field data carefully. The entire area to be surveyed is divided in to a network of triangles. All the sides of the triangles are measured. Knowing the sides, the network is plotted and checked with the help of check lines. The internal details are filled with respect to the plotted lines.
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Textbook of Forest Engineering
SCOPE OF SURVEYING IN FORESTRY Knowledge of theory and practice of surveying and map reading are an important part of a forester’s training. The forest officials have the responsibility of protection, management and administration of a forest and often they are required to map out fire-burnt areas, demarcate and or check forest boundaries, layout felling coupes, prepare plantation maps and stock maps, detect and rectify encroachments and illicit possessions. Prepare plans of areas to be cleared or fenced or planted; again extraction roads and paths and for a variety of other purposes connected with their duties. They must plan for proper road, drainage and layout bridges in the forest which in turn helps to transport the wood materials from the forest. Unless proper plan is prepared for the forest area sustainable usage is not met, hence there is an immense scope of surveying in the forestry field. TRAVERSING AND TRIANGULATION Traversing It is defined as a series of connected lines in which the lengths and direction of all the lines are known. There are two kinds of traverse: (a) Close Traverse, and (b) Open Traverse. Close Traverse: In close traverse survey, a polygon is formed which may have any number of sides. In this survey the polygon finish at the point from where the survey was started. Open Traverse: In open traverse survey, a polygon is not formed. Traversing is better when there are few details inside the polygon. In this survey the polygon finish at the point other than the starting point
Triangulation In this method the whole area to be surveyed is enclosed by a triangle or a chain of triangles. The triangles should be well condition that is equilateral as far as possible and the entire area should be covered by triangles. The sides of the triangles should be near the main objects. The base-line should also be quite long. Triangle, only geometrical figure which can be drawn when the lengths of all its sides are known, may also be plotted when the angles of the triangles are known. The lengths of the sides of the triangle are not measured because there is bound to be some mistake in the actual measurement. Different types of the chain or tape bound to give error due to variation in temperature,- pressure and other factors. Correction due to sag in the tape, correction due to the spherical shape of the earth. It is therefore advisable to measure only one side (base line) and measure all the
Chain Surveying
5
angles of the triangles. The angle can be measured with the help of theodolite and by knowing the length of one side and the angles of the triangle, the length of other sides of the triangles can be calculated trigonometrically by using the formula. Sin A
Sin B b
Sin C
where A, B and C are angles a, b, c are sides of the triangle
EQUIPMENTS USED IN CHAIN SURVEYING The equipments that are used in chain surveying are: Chain (metric, engineers or gunters), Measuring tape, Ranging rods or pole, Arrows, Offset staff, Cross staff, Optical square and Trough compass. Apart from these instruments, other accessories required for chain surveying are field-book, drawing-sheet, pencil, eraser, setsquare, scale divider etc.
Chains Chains, commonly used for measurement of distance where a high accuracy is not required, consist of number of large-links made of galvanized mild steel wire. Each end of the links is bent in to a loop for easy connection to next link by rings. There are 3 rings: outer rings are of oval in shape and the central ring is circular. These rings help for easy folding of the chains. Each chain having 100 links, both the end of the chain have brass handles which are used for pulling and dragging the chain. For easy counting the links of the chain a brass tallies or tags are attached at every tenth link from end of the chain. The tallies are provided with 1 edge, 2, 3 and 4 edged or forked and attached at every tenth link serially from both the end of the chain such that 10th and 90* link have one-edge tallies, similarly 20* and 80* have two edge, 30* and 70* have three edge and 40* and 60* link have four edged tallies. At the centre a round brass tally is attached.
Types of chain Metric chain: It is 20 m long, and has 100 links, each link being 20 cm. The tags are placed ofter every tenth links from either end of the chain and at centre round tally is attached. Engineers’ chain: It is 100 ft (30 m) long with 100 links, each being one foot in length after every 10* feet there are tags to help count the number of links. The engineers’ chain was earlier used mainly by the engineers in carrying out the survey work, hence it is called engineers’ chain.
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Textbook of Forest Engineering
Gunter’s or surveyor chain: It was introduced by a scientist by name Giinter during 1620. It is 66 ft (19.8 m) long. It has 100 links each being 7.92 inches (0.198 m). Bigha chain: It is 30 ft (9 m) long, it is small and handy. Revenue chain: It is 33 ft (9.9 m) long and is mainly used for measuring the field in cadastral surveys. Measuring tapes: These tapes are used for measuring horizontal or vertical distances. Metallic tape: The tape is called metallic tape because throughout its length it is water-proof or synthetic threads inter woven with noncorrosive brass or bronze wires in its breadth. They are available in 25 ft, 50 ft, 66 ft, 100 ft as well as 15 m and 30 m. Steel tape: The steel tape is being used where great precision is required, it is made of steel or stainless steel. They cannot be folded because they break folding. They are available in length 10 m, 20 m, 30 m and 50 m. Invar steel tape: Invar is an alloy of steel and nickel (64:36). It is little affected by changing temperature because the alloy has a low coefficient of expansion. It is used for base line measurements in
triangulation survey. Ranging rods They are also called as ranging poles. They are made of fiberglass, steel or wood with a pointed iron shoe to help it fix easily in the ground. The height of the ranging rod is 6 (1.8 m), 8 (2.4 m) or 10 (3 m) ft every foot is alternatively coloured with white and black. Different bands of colour make it clearly visible against any sort of background. Arrows
They are also called as marking pins; they are 10 to 18 (25 to 45 cm) inches long made of mild steel round wire 1/5 to 3/16 inches in dia. It is pointed at one end and a loop of about 1.5 inch (3.75 cm) diameter at the other end. They are fixed in the ground after hvery chain length while surveying.
Offset staff It is a round or squared wooden staff of 3 m length which is alternatively coloured in 3 colours, 30 cm length for each colour and has got iron shoe to help it fix in the ground also. To make them handy there is a screw type arrangement in the middle from where they can be separated into 2 parts. Some of them have a brass hook at the top end with the help of which the chain can be dragged.The main purpose
Chain Surveying
7
of the offset staff is that short offset or the perpendicular distance from the chain line to the object can be easily measured.
Cross staff It is a handy small instrument having 8 to 10 cm2. It has four metallic arms cut with vertical slit or small holes at right angles to each other. An iron or wooden rod is fixed on the hole provided at the bottom of the instrument. The main purpose of this instrument is that the offsets are taken at a long distance from the chain line.
Optical square This is included in the category of reflective instrument. It is more accurate than the cross staff. This is used for more accurate work especially for long offsets. There are two mirrors making an angle of 45° with each other. One is called the index mirror and is fully silvered. It is placed vertically erect. The other mirror is called the horizon glass. The lower portion of the glass is silvered but the upper half is un silvered through which it can be seen across.
Trough compass Trough compass is instrument designed to find the magnetic north direction, or angles from magnetic north. Field-book: The field notes are entered in a type of note book called field-book. This is usually about 19 cm x 12 cm which opens length-wise. It has 2 red lines at its center 2.5 cm apart drawn lengthÂŹ wise. It is supposed to be a chain line. The distances measured along the chain line are recorded between 2 red lines from below upwards. The distance of offsets is recorded on either side of the lines based on the objects present in the respective direction. The objects are also recorded with the conventional symbol along with the details such as diameter, length, width or radius etc depending upon the object which helps while drawing the objects on the drawing sheet with suitable scale. The common conventional symbols used while drawing the sketch of the filed is shown in Fig. 2.2. Drawing-sheet: Size of the drawing sheet generally used in survey work is 76 cm x 56 cm.
SURVEY STATION AND OTHER LINES For conducting the chain survey in the field, we have followed 4 steps: (a). Reconnaissance, (b). Marking stations, (c). Running survey lines, (d). Taking offsets.
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Textbook of Forest Engineering
Reconnaissance Preliminary inspection of the area to be surveyed to get some idea about terrain and the principal features of the ground.
Marking stations If the survey is of temporary character, the stations are generally marked by fixing a ranging rod at each station. If the stations are to be marked permanently, a block stone is fixed below the ground surface and a cross is marked on its top. Running survey lines Survey lines are run to measure the distance between main stations and to locate the adjacent details by offsets. Base line: It is the primary-line which forms the base of the triangulation scheme. This line is generally the longest line passing through the center of the area. The accuracy of the network depends upon the accuracy of the base-line. This line is also called survey-line or chain-line which joins the main survey stations. Check line: This line is selected to check the accuracy of the plotted network of triangle. It joins the apex of a triangle to some fixed point on the opposite side. This line can be any other line also, such as joining two-fixed points on the sides of the triangle. The measured length should match with its length on the plotted plan. These are the lines which are run to check the accuracy of the framework of the triangles; these are also called as proof lines. Subsidiary line: This line is joining the subsidiary station other than main stations.
Taking offsets The objects present on either side of the survey lines are located by measuring the distance from the survey line to the objects known as offsets. Chain survey is generally carried out by three persons: surveyor, leader and follower. A surveyor: One who directs the work and records the measurement. A leader: One who is dragging the chain from the front end of the chain. A follower: One who is holding the handle of the chain at rear end and collecting the arrow at every chain length. If there are only 2 persons, the surveyor oneself works also as follower. First the ranging out of the base-line is done and is followed by
Chain Surveying
9
unfolding chain and spreading it on the line. The follower holds one handle of the chain at the station at the beginning of the base-line and the leader drags the chain towards the other end. After properly stretching the chain on the chain-line, the leader places an arrow at the end of the chain. The surveyor records the length of the offsets and the respective distance from the starting station in the field book. The survey lines crosses important features such as drains, fences, roads etc should also be recorded in the field-book. The frame work of chain survey is explained in Fig. 2.1. Offsets
Well
C
B
O Base
gp Buildin
>
J f
D
t Fig. 2.1
f
Cf - Subsidiary line/check line ABCD - Main survey stations e,f,g - Subsidiary stations
A
Frame work of chain survey.
Conventional signs: Signs, abbreviations or symbols to indicate various features are more or less standardized by custom and usage and are known as Conventional signs. Some of the common symbols and signs are given in Fig. 2.2. Scale: Scale of the drawing is indicated on the sheet before starting the drawing. The scale may, however, be drawn later, as the use of scale on the plan by means of dividers will disfigure the plan. Alien the drawing is completed the diagonal scale may be drawn, to read in the desired units and fractions thereof, somewhere just inside the border at the bottom of the sheet. Border: A neat plain border of about 1.5 mm thick single black line preferably with a thin line inside is the best. A margin of about 2 cm on the outside of border improves the appearance. Title: A suitable wording of the title is decided and then its location on the sheet. It is not essential to have it in the centre, though it is best to have it so placed. Sometimes drawings are better balanced with title on the corner.
Textbook of Forest Engineering
10
Symbol
Feature
Feature
Foot path
Orchard
Bridle path
Hedge
Road.
River, Stream, Canal
Gate
oo or
Symbol
9 9 9 9 9 9
Lake or Pond
Post and Rail fence.
Temple.
&
Bridge, Culvert
Forest chauki
ft
Ch. Line and Svy. stn
'Oi
M
Forest rest house
Railway line.
Govt, forest boundary
Rly. Embankment
Bench Mark
6.T&tl9Sยง
Rly. Cutting
Forest pillar
o
Isolated tress
tan
Contour lines.
Forest (woods).
Profile of land
Brushwood
Building
Rough pasture.
Tunnel
Marsh or Swamp.
North direction
v P>ri
(
rfJ
Fig. 2.2 Conventional signs and symbol.
North direction: North point must be shown on the plan, preferably at the top, pointing upward. Lettering - Printing: A drawing is not complete without a printed title or heading, etc. A really good printing adds considerably to the finish of a drawing. Lettering must be distinct, well spaced and balanced, of pleasing appearance, simple and easy to execute. Selecting scale: The scale to which the plotting is to be done is decided upon by the extent and purpose of the survey. The size of the drawing-sheet which is to contain this will also effects the final selection. Plotting details: After proper verification of the framework, the details are plotted. The chainage of the points from where the offsets have been taken are marked on the survey lines. The lengths of the offsets are then scaled-off with the help of a set square or mini-drafter
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