6.1 GENERAL
6.2 SURVEYING INSTRUMENTS
6.3 ROAD RECONNAISSANCE
6.4 ROUTING TECHNIQUES
6.5 FIELD NOTEBOOKS
Hand held instruments are now used for surveying forest roads in steep terrain. These optical instruments combine accuracy with low weight and volume, thus allowing high output even in difficult terrain and dense forests.
Except for bridge construction, tunnelling and other special projects, theodolite, and levelling instruments are not used, since their use is too slow for the accuracy required, in addition to which they are expensive and fragile.
6.2.1 Clinometers
6.2.2 Compasses
6.2.3 Tapes
6.2.4 Barometric Altimeters
6.2.5 Additional Equipment
When planning forest roads in steep terrain, the following instruments are used
Instruments
Clinometer
Magnetic compass
Tape
Barometric altimeter
Items to be Surveyed
Gradients or grades
Bearings or azimuth (direction)
Distances
Altitudes or elevations
This equipment, along with proper survey methods, has proved to be suitable... practical for surveying roads in forests in mountainous terrain.
The clinometer is the basic instrument for routing a forest road in steep terrain. The vertical axis of a pendulum instrument corresponds to the direction of gravity an angle of 90 the horizontal level (collimation line) of the instrument is optically fixed, from which vertical angles (in percent or degrees) can be measured. There are several types of clinometers which can be used to determine gradients but basically are all the same, based on the principle of gravity.
The percent scale of the clinometer is used to determine the gradients of the road and to measure side slopes since it is much simpler for future calculations than use of angles measured in degrees.
FIGURE 8 Side view of Meridian Clinometer
"Percent" means "part of a hundred". For example, 1 percent is one part of a hundred (equal to 1/100 or 0.01); 45 percent is 45 parts of a hundred (equal to 45/100 or 0.45). The gradient of a straight line in percent can be drafted by the height of a right angled triangle with a base of 100 units:
FIGURE 9 Example of a gradient, in percent
Gradients can be measured directly, independent of the distance between clinometer and target. Thus lines (routes) with required gradients can easily be found. The so-called "zero line" or "grade line", which is one of the basic criteria for locating a forest road in steep terrain, is determined by use of the clinometer. A word of caution with regard to the use of clinometers is, never mix up readings of percent and degrees, since both functions are normally given on the instrument scales. The percent readings correspond to the tangent functions of the degrees and are quite different, and if the two are mixed while reading the scale, it will lead to errors in calculations and grade lines.
FIGURE 10 Triangular Functions
TABLE 5
Conversion of Degrees into Percent
|
Grade in Degrees |
Grade in Percent |
Grade in Degrees |
Grade in Percent |
|
1 |
1.8 |
11 |
19.4 |
|
2 |
3.5 |
12 |
21.3 |
|
3 |
5.2 |
13 |
23.1 |
|
4 |
7.0 |
14 |
24.9 |
|
5 |
8.8 |
15 |
26.8 |
|
6 |
10.5 |
16 |
28.7 |
|
7 |
12.3 |
17 |
30.6 |
|
8 |
14.0 |
18 |
32.5 |
|
9 |
15.8 |
19 |
34.4 |
|
10 |
17.6 |
20 |
36.4 |
Example of an error by triangular form, i.e. 8 or 14% if 8% was your maximum grade:
An erroneous reading of 8 degrees instead of 8 percent leads to a grade of 14 percent: (see conversion table)
FIGURE 11 Drawing Explaining Grade Difference Between Degrees and Percent
FIGURE 12 Triangle showing 100% (45°)
Remark: 100% grade corresponds to an angle of 45°
|
Note: The intervals of the percent scale of the clinometer are smaller than the intervals of the degree graduation. |
Two types of clinometers are recommended for forest engineering and surveying work.
These are:
a) Meridian clinometer (made in Switzerland)
A pendulum device with a fixed optical system, the most suitable model (MC1002) has two optical lenses for separating uphill (+) and downhill (-) readings to 100 percent both ways.
PHOTO NO. 3 Meridian clinometer
FIGURE 13 Elevation Scale of the Meridian Clinometer (according to Meridian)
How to use the Meridian Clinometer
First, hang the instrument from your thumb, as shown in Photo No. 4. Then place the instrument close to your eye and keep it plumbed. You cannot see through the instrument, but you see the bright, translucent scale. The percent scales are seen on both edges of the ocular lenses of Model MC 1002. The left lens is for uphill (+) (see scale as shown in Figure 13); the right lens is for downhill (-) reading. By simultaneously looking through the lens and alongside the clinometer you can align the objective (target) (see Figure 14) with the reading by an optical illusion. You must keep both eyes open. Be sure to read the correct number on the scale and remember + (elevation) or - (depression).
FIGURE 14 Target and Scale of Meridian Clinometer
PHOTO NO. 4 Meridian clinometer in working position
b) Suunto Clinometer (made in Finland)
The Suunto instrument has an aluminium housing with a moving scale card. This moving part is immersed in a damping liquid inside a sealed plastic container. The liquid does not freeze or evaporate. It is recommended that Type PM-5/360 PC with scales of percent and 360 degrees be used. The percent scale has a graduation from + 150 percent to -150 percent.
FIGURE 15 Scales of the Suunto Clinometer
PHOTO NO. 5 Suunto Clinometer PM-5/400 with Case
PHOTO NO. 6 Use of the Suunto clinometer during Training Course in Bhutan
How to Use the Suunto Clinometer
Place the instrument close to the eye and move it in a vertical arc until the horizontal index line is aligned with the objective (target). By an optical illusion the index line seems to protrude from the side of the instrument. Align this line with the centre of the target and simultaneously read the gradient on the scale. Both eyes must be kept open since one cannot see through the Suunto. Since the Suunto has scales in degrees as well as in percent, the surveyor must be sure to read the record the correct scale reading. It is necessary to have the height of the instrument and the target with identical distances above the ground.
FIGURE 16 Clinometer and Target on Poles (Rods)
Use two poles (or rods) with flat bases so that the poles do not penetrate the round and so that their height will be constant. The clinometer (zero point) and target (middle line) are adjusted to the same height with the two poles on level ground. The height of the instrument pole is adapted to the comfortable eye height of the instrument....
Adjusted Meridian clinometer and target
Use two poles (or rods) with flat bases so that the poles do not penetrate the ground and so that their height will be constant. The clinometer (zero point) and target (middle line) are adjusted to the same height with the two poles on level ground. The height of the instrument pole is adapted to the comfortable eye height of the instrument man.
PHOTO NO. 7 Adjusted Meridian clinometer and target
PHOTO NO. 8 Suunto clinometer and adjusted target
The target can be made of aluminium sheet or plywood to a size of about 30 x 20 cm. It is best painted with white - red or yellow - red, water-resistant colours to obtain the best visibility possible. Special flourescent colours are very helpful.
FIGURE 17 Home-Made Target
Checking
The clinometer and target must be checked, before use to ensure that the vertical heights of the clinometer and the target are equal. Two points are fixed on the ground at an average distance of 20 - 25 m and the gradient is measured in both uphill and downhill. If both readings are equal, then the instrument and the target adjustment are correct.
Checking
The clinometer and target must be checked before use to ensure that the vertical heights of the clinometer and the target are equal. Two points are fixed on the ground at an average distance of 20-25 m and the gradient is measured in both uphill and downhill. If both readings are equal, then the instrument and the target adjustment are correct.
After setting out the zero line by means of clinometer and stakes, the line must be surveyed in order to make a plan of the route. There are numerous hand-held compasses of modem design which can be used. These are of two main types, those with protractor base and surveying needle and those with a swinging needle card without a protractor base.
Compasses with a Protractor base
These instruments have a swinging needle and a circular scale and can be used for direct mapping. There are universal types for reconnaissance and use of maps but they are not as accurate as surveying compasses of the second type.
Examples of this type are the Bezard (made in Germany) and the Silva (made in Sweden).
PHOTO NO. 9 Bezard Compass
FIGURE 18 Silva Compass (Type 16)
Surveying Compasses without Protractor Base
These instruments have swinging needle card with scale and optical reading. They are suitable and accurate for surveying and can be recommended for forest road surveys.
The Suunto compass is one of the best instruments the author has used for road surveying. A solid housing encases the needle card in a damping liquid (similar to the Suunto clinometer). The readings are accurate to 0.5 degrees (scale in half degrees) and the readings can be estimated to 10 minutes. By an optical illusion the vertical index line appears to project above the compass case. Align the index line with your target (vertical rod) and simultaneously read the bearing both eyes must be kept open because one cannot see through the instrument. Hold the compass horizontally in a comfortable working position.
PHOTO NO. 10 Suunto Compass KB-14-RT-360
FIGURE 19 Scale of a Suunto Compass
The use of the Suunto type KB-14-RT-360, illustrated above, is recommended. It has a clockwise degree graduation 0-360 in black, and a reverse scale in red (code R). The instrument-man must be sure to read the correct scale.
The reverse scale is useful for controlling the measurement on the line (see 2.4.5 "Routing Process). The instrument also has an illuminated scale by Bray (code T) for easier reading in dense forests or during twilight.
PHOTO NO. 11 Rod with flagging as compass target
PHOTO NO. 12 Suunto compass being used in the field
General Remarks on Compass Survey
The needle of a compass shows the magnetic north direction (magnetic meridian) due to the influence of the magnetic forces of the globe. The Azimuth angle between magnetic north (0) and the surveyed direction is called the BEARING.
The compass scale is read in a clockwise direction in four quadrants which are shown in Figure 20 to give the student the relationships between the compass degree readings and his more familiar nomenclature for direction.
FIGURE 20 System of Compass Scale
The magnetic North Pole is not the same thing as the Geographic Pole of the globe The deviation (difference) between the magnetic meridian and the direction "True North" of the map is called the DECLINATION. Declination is different in different places of the northern hemisphere, depending on the geographic longitude and latitude, so that the compass must be adjusted for the region where it will be used in order that everyone in an area surveys to the same base.
When ordering a Suunto compass, the geographic data for country of use must be given with the order, since the instrument can only be adjusted during its production at the factory.
Some needle compasses can be adjusted easily with a set screw in the field; however, one must be careful with waterproofing.
When using a compass it is important that the surveyor keeps the instrument free from attractions caused by magnetic influences, such as steel parts of spectacles, wrist-watches or iron tools and equipment. The surveyor must avoid surveying close to electric wires and iron ore deposits. There are methods for testing the magnetic influences caused by ore bodies but this will not be gone into here.
A measuring tape for rough use in the forest must be strong, reliable and must not stretch when tightened. The use of fibreglass or steel tapes with metric graduations and a length of 50 m (fibreglass) or 30 m (steel) is recommended. Steel tapes are more expensive and heavy, and they should be stainless to avoid rusting. Recently the preference has been for fibreglass tapes which are cheaper and lighter than steel and are not magnetic.
Tapes must be handled as carefully as other instruments, do not drag them on rough surfaces, unless they are steel, clean and dry the tape after use and it will last for many years.
PHOTO NO. 13 Fibreglass tape
PHOTO NO. 14 Steel tape in a reel
These instruments are used to determine relative altitudes of control points during the field reconnaissance. The principle of barometric instruments is based on the decreasing of air pressure with increasing altitude.
In forest engineering, relative differences in heights (in other words the difference between two or more points but not necessarily correct in relation to external points) are used in order to determine the correct or best gradient between control points the instrument is adjusted to an average altitude at the starting point, according to the topographic map, and all following measurements will be relative but accurate to this first adjustment.
Modem barometric altimeters have an evacuated aneroid diaphragm which is highly sensitive. The displacement of this diaphragm caused by changing air pressure is transmitted without friction to the indicator and the scale from which readings are obtained. These sensitive instruments must be handled carefully. Information on two of the types used in forestry is given below.
Pocket Altimeters
The Thommen altimeter (made in Switzerland) is an excellent pocket instrument with an accuracy of ± 10 to 20 m. Several types with altitude ranges up to 5 000 m are available.
FIGURE 21 Scales of Thommen Altimeters
PHOTO NO. 15 Thommen pocket altimeter
The Thommen pocket altimeter can be adjusted easily by turning the scale, the altimeter scale is divided in units of 10 m from 0 to 1000m. The intervals of 1 000 m are accounted in the central display.
Precision Altimeters
The Paulin precision altimeter (made in Sweden) is a very accurate but lightweight instrument. The accuracy of this fully compensated altimeter is in the order of ± 5 m.
In order to avoid damages to the instrument the measuring system of the instrument must be locked during transport by turning the central button anticlockwise. In the measuring position the central button is turned clockwise until the needle point balance indicator indicates the reading position. Then the main needle shows the altitude on the circular scale (minimum scales are 5 or 10 m depending on type). The instrument can be adjusted to actual heights.
PHOTO NO. 16 Paulin Palab altimeter with case
FIGURE 22
Available Types of Paulin Altimeters (according to Paulin)
|
TYPE |
ALTITUDE SCALE |
BAROMETER SCALE |
||
|
Range |
Graduations |
Range |
Graduations |
|
|
External diameter mm (4 5/8") |
||||
|
PALUK |
- 350 to + 725 m |
1 m |
- |
- |
|
PALER |
- 220 to + 1400 m |
2 m |
650 to 790 mm Hg |
0.2 mm Hg |
|
PALAB |
- 220 to + 3420 m |
5 m |
510 to 790 mm Hg |
0.5 mm Hg |
|
PALON |
- 150 to + 6750 m |
10 m |
350 to 790 mm Hg |
1 mm Hg |
|
PALIB |
- 800 to + 5000 ft |
5. ft |
25" to 31" Hg |
0.01" Hg |
|
PALAN |
- 900 to + 12300 ft |
10 ft |
19" to 31" Hg |
0.02" Hg |
|
PALYD |
- 500 to + 23700 ft |
20 and 50 ft |
13" to 31" Hg |
0.05" Hg |
Range Poles (or Ranging Rods)
Range poles are used for setting out the Centre Line of a forest road on level ground and in other special cases where the Zero Line system cannot be used. They are actually used for sighting on by the compass man. Range poles are also required for setting out the foundations of bridges, culverts and retaining walls the poles, made of wood or aluminium in detachable sections, are painted red and white or red and yellow. These sections can be carried in a bag and can be put together to form the full length of the rod.
PHOTO NO. 17 A set of ranging poles with bag
Nylon Rope
A nylon rope, to 8 mm in diameter and about 50 m in length, is a useful dragline to determine rough distances between control points during reconnaissance. This rope can also be used as a securing aid in very steep and rocking terrain.
Pocket Steel Tape
Normally, a pocket steel tape has a length of 2 to 3 m and is graduated in cm and mm. It is used for measurements of short distances during field work and especially for construction works.
6.3.1 Planning Area
6.3.2 Maps And Aerial Photographs
6.3.3 Fieldwork And Cooperation
6.3.4 Work Procedure
6.3.5 Field Control
Reconnaissance is the basic tool of forest road location and design. This preliminary work provides the knowledge of terrain and the forests which enables the engineer to determine the most feasible and economic road alignment.
In the mountains the planning area for a road network can be easily determined because the area is naturally bounded by ridges and creeks. A planning unit is usually defined by the boundaries of a watershed, or it can be only a part of a watershed, and similarly several watersheds can be put together to form one large planning area. -
A topographic map is almost a necessity for road planning. Topographic maps show planimetric details such as rivers, roads, fences, etc., as well as elevations presented in the form of contour lines.
The usual scales of maps produced by governments are at a scale of 1:50 000 or 1:25 000 and these scales are good for general planning purposes. For detailed logging and road planning, however, maps at scales of 1: 5 000 or less are usually required, or will give better results. These latter maps are seldom readily available unless made specifically for the operation and usually by the operation.
Topographic maps derived from the evaluation of aerial photographs are reasonably accurate.
Aerial photographs complement but cannot substitute for a good topographic map, Normally, aerial photographs are at a scale of about 1:15 000 and show details of terrain and forest stands. Using a pocket stereoscope in the field, pairs of aerial photographs provide a stereoscopic view of the terrain.
GIS and aerial photography are major recent innovations for the improvement of survey and planning information. This guide would only wish to indicate the value of these methods of gathering information on the characteristics of the site. The subjects are to wide ranging to include details.
Aerial Photography continues to provide a satisfactory source of spatial information. Digitising the aerial photograph and entering its information into a computerised processing system will produce significantly more consistent results than direct interpretation This use of aerial photographs can become one of the important GIS data layers.
These photographs are subject to detailed photo-interpretation. The importance of this stage cannot be over-emphasised. To produce an accurate map requires the use of a specialised instrument known as a stereoplotter, along with stereo aerial photography. The benefit in using a stereoplotter is that it allows all distortions to be removed in the photography.
It should be emphasised that aerial photographs are not maps, and they contain large distortions. The stereoplotter is specially designed to rectify the photography so that every detail which is then recorded is precisely located.
Additionally, the photography is viewed stereoscopically which allows a comprehensive range of features to be mapped which cannot be achieved using a single photograph (even when it is enlarged). A crude interpretation can be produced using a pocket stereoscope but not only is this exercise more time consuming - requiring the observations to be manually transposed onto a map, it also makes no allowance for the inherent distortions which exist in aerial photography.
As has been the case in all aspects of life, the use of computers has become far more widespread in recent years. There are probably two main reasons for this: the first is that the cost of hardware and software has fallen, and the second is that the various software packages have become much easier to use and more accessible to the non-expert.
The collation of data concerning the spatial distribution of significant properties of the earth's surface has long been an important part of the activities of organised societies. From the earliest civilisations to modern times spatial data have been collated by navigators, geographers and surveyors and rendered into pictorial form by the map makers or cartographers.
The history of using computers for mapping and spatial analysis shows that there have been parallel developments in automated data capture, data analysis and presentation in several broadly related fields. These fields are cadastral and topographical mapping, thematic cartography, civil engineering, geography, mathematical studies of spatial variation, soil science, surveying and photogrammetry, rural and urban planning, and remote sensing and image analysis.
Essentially all these disciplines are attempting the same sort of operation -namely to develop a powerful set of tools for collecting, storing, retrieving, transforming and displaying spatial data from the real world for a particular set of purposes. This set of tools constitutes a 'Geographical Information System'. Some replicate (and ease) things that have traditionally been carried out manually using paper maps, tables of data and cartographic techniques.
PHOTO NO. 18 Pocket stereoscope for field work
Maps and photographs are a prerequisite for any preliminary study and the planning process for an area, but in addition it is necessary to study the terrain and the forest area on foot. Only by intense walking can a sufficient knowledge of the planning area be obtained. This part of the work, called "reconnaissance", requires a lot of time but is the most important and is the best investment.
In planning a forest road it is necessary to cooperate with the local staff and residents of the planning area who know the terrain and local conditions best. Cooperation and sharing of information form the basis for good results.
When a planning exercise is to start, the engineer should look for all maps, aerial photographs, management plans and other information available on the planning area. In order to save original planning material, copies should be used. At the same time the forest staff responsible for the planning area should be contacted in order to gather more detailed information and the timing of field work from them.
Using the contour maps one or several variants of a road system which seems to be feasible should be plotted. Account must be taken of existing public roads, their junction and terminal points, the logging system and the transport situation, ownership and boundaries of property, and so on.
Fieldwork should be carefully planned corresponding to the general road system as drafted. Divide large planning areas into several planning units. Consider problems of travelling, housing, food and drinking water, etc. The timing of the fieldwork is important. In the subtropical zone of the country the dry season should be used.
In order to carry out a field reconnaissance the following will be required:
- Engineer's jacket with pencils, eraser, ruler and scale, divider, etc.
- Field notebook with cross-section paper
- Maps and aerial photographs 5
- Altimeter, clinometer, compass (with protractor base)
- 50 m drag rope, pocket stereoscope for aerial photography 65,6 If they are to be used in the field.
During the first field reconnaissance the engineering crew must walk the main and side valleys and then check the slopes and ridges relative to the preliminary map plan (s) as drafted. Important characteristics are grades, soils, rock, control points and logging units.
Positive control points are important as well as advantageous places for road construction and logging, such as bridging points, gentle parts in slopes which are suitable for curves, switchbacks and better alignment, log landings and easier construction, similarly gravel deposits are extremely important, as are saddles for crossing from one watershed to another.
Negative control points are very steep slopes (>80%), rock, swamps, landslides, deep canyons and excessive ridging:
Very steep slopes are mostly rocky and should not be crossed for distances of longer than about 200 m. The considerable excavated material can cause damage to the forest below and when not rock, erosion and siltation with all their negative impact on the environment can ensue.
During the first reconnaissance the actual situation in the field is carefully checked against the map and photographs. Details of terrain and control points, field data and sketches are noted in the field notebook.
By means of the barometric altimeter the relative altitudes of all important control points can be determined. The instrument is adjusted to the actual altitude of the starting point which can be identified on the map.
After the first field reconnaissance the preliminary paper locations can be improved and unsuitable variants of the plan can be discarded.
In mountainous terrain the engineer tries to develop a road system which will allow for the downhill transport of products, in order to use the natural forces of gravity, it is also important to find suitable junction points with the public road system.
Beginning from roads in the main valley bottom, the road system is developed up into the slopes. Road spacing depends on the type of logging and transport systems (see General Planning) which will be used.
After general cost considerations and comparisons and perhaps more field reconnaissance have taken place, the most feasible and economic variant of the road system is selected. This selection should be discussed with the local staff and the authorities before final detailed work commences.
A common problem of design is to determine whether or not a road line can be obtained which fits within the elevations of the terminal points, bearing in mind the maximum allowable gradient. On a fairly exact contour map, a draft of a general zero line (grade line) can be drawn by divider setting (see 6.2). Usually the gradients between control (terminal) points are checked by calculation, the distance being taken from the map and the relative altitudes being obtained from the barometric survey. An example is given below.
FIGURE 23 Sketch of a Lengthwise Section (Example)
In spite of intense reconnaissance it is necessary to check the selected main roads out in the field to be sure that they can in fact be realized. Therefore, the second part of reconnaissance is more detailed work along the generally designed route by means of clinometer and drag rope. One target man and 1 to 3 brush cutters are required for this work, during which the line is marked on trees by means of plastic flagging. In this phase unexpected obstacles may be found and by careful re-routing the general layout can be improved and actually become feasible. This is often called a preliminary grade line.
Reconnaissance for general planning of a forest road network demands personal interest, years of experience and careful work. A high degree of responsibility is connected with this task.
6.4.1 Introduction
6.4.2 Personnel (size of location crew)
6.4.3 Instruments and Equipment
6.4.4 General Rules for Road Location
6.4.5 Method of Location
6.4.6 Special Problems
6.4.7 Right of Way
It is recommended that the "zero line" (or "grade line") method be used in locating a forest road in steep terrain. The term "zero line" is derived from the German language and means that on this line there is neither cut nor fill. It is the intersection line between the planes of the original slope and the eventual formation. The difference between a zero line and a centre line is shown in Figure 24.
FIGURE 24 Zero Line and Centre Line
The zero line can be applied as an element of location only on slopes. It is determined by the use of a clinometer and is marked on the ground with stakes. The zero line is like an unclosed polygon with the required gradients which is adapted to the shape of the terrain and to the desired alignment. This polygon is the guideline for the bulldozer operator during road construction. The formation is cut with free bends close to the shape of the terrain. This type of work is known as "sidecasting".
The zero line marks the gradient of the road and also the alignment in the slope provided the distance to the centre line is relatively short. This distance decreases with increasing slope grade. This does not mean that the alignment of the road can be ignored and special consideration must be given at points for tight curves, embankments, long cuts and in areas with gentle slopes. In such cases it is recommended that the centre line also be located.
Lastly, it must be emphasized that intensive training, personal capacity and years of practical experience are needed to be successful in road location which is one of the most important tasks in any forest operation.
-1 engineer, responsible for the work
-1 target man
- 2 helpers for driving stakes and measuring distances
- 2 to 3 brush cutters (number depends on type of forest)
A checklist of instruments (see 5.2) and equipment which are also required for road engineering are given below.
- 1 clinometer (Meridian or Suunto) 1 compass (Suunto)-1 tape (30 m stainless steel or 50 m fibreglass)
-1 target with screws or nails to fix it to the target rod
-1 pair of poles to adjust clinometer and target
-1 set of ranging poles in a carrying bag
-1 field notebook
-topographic map; if available, aerial photographs and a pocket stereoscope
-layout of planned road, if available
-1 engineer's pocket (leather or canvas) with pencils, eraser, scale and other small utensils like graphite markers for stakes, plastic flagging, pocket measuring tape, pocket knife.
- set of tools, bush knives, 1 axe or hammer to drive stakes into the ground, gloves to protect hands.
- 1 first-aid kit
- snake bit serum and syringe (can be purchased from Haffkine Institute, Bombay, India
- suitable personal equipment. Heavy leather boots are best since steep slopes must be traversed. "Mountain boots" protect and support the feet best. A raincoat. Daily food ration (in a plastic box or bag), and a hot drink (in a thermos) carried in a rucksack.
PHOTO NO. 19 Engineer's Pocket with clinometer, compass, altimeter, steel tape. pocket tape. ruler and scale, pencils
A work programme should be planned carefully, in advance of field work, and in accordance with, and taking into account, the layout of the road system. Such a system may be divided into several types of roads, and lengthy roads may be divided into several sections for practical purposes. The sequence of location starts with the main roads of the planned system, and the feeder roads (lowest standard) are located last.
A long road is best divided into sections corresponding to the control points within the line (for instance, switchbacks, bridges, saddles, etc.), provided they are not too close together. In locating sections, start from the positive control points which should be connected accurately to the control points which are not so crucial and where there is space. In this manner work can proceed uphill or downhill within the different sections of a long road, depending on the control points.
The engineer usually walks ahead and looks back at the target. In this way he can check the line and the terrain since he is most experienced, and find the most suitable points for the location of the stakes.
The gradient between two control points should be kept fairly constant. The maximum gradient for downhill transport in steep terrain should not exceed 9 to 10 percent (main roads) or 12 percent (feeder roads), a 12 percent gradient should be absolute maximum, having due regard to erosion and maintenance. Where uphill transport is required the maximum gradient should not exceed 6 to 8 percent.
A minimum gradient of 2 to 3 percent is required for proper drainage. Never use a level grade (0 percent) over long distances.
Information about the terrain where the road will be located is known from the reconnaissance, so that the road engineer has some ideas about the general conditions, the control points and the ruling grades of the various sections.
Nevertheless, time will be wasted by driving in stakes during the preliminary location since corrections are usually necessary. It is therefore recommended that the location work and the survey work be divided into four parts:
First part: Flagging of a zero line with the estimated ruling grade and with sighting distances as long as possible. Do not use target and poles. Sight from man to man at the eye level of the clinometer man. Use the drag rope to roughly determine the distance between terminal points. Remember that these lengths of rope must be recorded. The line is marked by flagging on trees and saplings. During careful general planning this "first part" has been done for the main routes. The first trial will not reach the desired control point exactly, since the estimated gradient used in the trial may have been too great or too little.
FIGURE 25 First Trial "Forward
Correction of the Gradient
(a) Estimate or measure the height difference of the terminal points. Bigger differences can be measured using the clinometer with a pole of known length as a simple levelling device.
FIGURE 26 Measurement of Height Difference in the Terminal Point 2
(b) The correction of the gradient is attained by means of the determined height difference and the distance (drag rope totals).
Correction of grade ± g (%) = h/d x 100
It should be mentioned that the difference between slope and horizontal distances of the location line is so small that it can be neglected. Therefore, regard the actual distances of the zero line as horizontal distances.
Second Part: In case of major differences, locate a second route using the improved gradient by working backwards. A different colour flagging must be used to avoid confusion. Over long distances a minor difference may again be found and thus a final correction of gradient must be made.
FIGURE 27 Second Trial "Forward"
Third part:
The two preceding trials (parts 1 and 2) are carried out to determine the correct zero line and can be regarded as a "detailed reconnaissance". Theoretically at this point all details are known and the final location can be started. The clinometer and the target are used in order to obtain exact gradients. The distance between stakes should not exceed 20 to 25 m and should be approximately equal. The stakes are numbered continuously. The engineer notes the following data in his field book during this part:
Numbers of stakes, gradients between stakes, representative slope (percent) of terrain between the stakes, estimated rock component, additional mass of earth and rock which is not given by the Norm Profiles, description of peculiarities of terrain, culverts and structures required.
FIGURE 28 Location "Forward"
Fourth part: The located zero line is surveyed by means of compass and tape. Again, the engineer walks ahead and looks back at the target. Thus the correct bearings corresponding to the form in the field notebook are obtained. By using a second target ahead, the bearings can be checked by means of the reverse scale of the compass. In the case of a careful survey both bearings7 are noted and differences should not exceed 1 degree.
7 backsight and foresight
The engineer can also read the distances on the tape and should do the recording. It is recommended that a tape crew of three men be trained for this task. The readings of distances are rounded to full decimeters (1/10 of a metre).
During the fourth part the engineer only has to determine the bearings and distances.
Location of Embankments and Cuttings
As mentioned before, the zero line follows the shape of terrain in consideration of the desired alignment and the gradient. In each case of major distances between zero line and the centre line the differences between the planned and the actual gradient will be obtained.
In the case the zero line crosses valleys or ridges the centre line should be marked. It is recommended that the centre line also be located if the terrain conditions are irregular and difficult.
When locating the zero line, the gradient should be lowered in the curves.
FIGURE 29 Zero Line and Centre Line in a Slope
A common mistake made by inexperienced personnel is to set stakes too far up valleys or on the outside of ridges, as shown in Figure 29. the minimum radius should be checked using a 20 m tape or rope.
Feasible crossing points along creeks and torrents must be selected. Bridge embankments require a lot of fill material which the bulldozer cuts close to the site, out of the flanks of the valley. The bulldozing distance should, if possible, not exceed 20 m.
Alteration of Gradient
If it is necessary to reduce or to increase the gradient, the maximum difference between the two gradients should not exceed 3 percent. In this way a smooth road profile will be obtained. This rule must be especially observed for the layout of switchbacks and the transition from elevation to depression ("crest") or vice versa ("valley").
FIGURE 30 "Crest" in the Lengthwise Profile, average distance between the stakes 20-25 m
Torrents which will endanger the road during heavy rainfall should be located in a "valley" of the profile, with a 0% grade at the crossing. Thus, overflow water is limited to this crossing section.
FIGURE 31 Lengthwise Profile - Road Crossing a Torrent
"Crests" and "valleys" of the profile of a forest road should be located within curves because they are not as visible here as along straight parts of the road. According to practical experience, it is recommended that a crest within a curve be located on a ridge, and a valley within a curve be located in a valley.
Routing Switchbacks
A switchback is generally a narrow bend in a slope where the general direction of the road is altered by a vertex angle of the bend smaller than 90 degrees. The minimum radius for truckable forest roads should be at least 11 m.
FIGURE 32 Functions of Road Curves
Switchbacks are often required in order to get to the top of a planned road. These curves are disadvantageous for transport in that the truck must slow to round the curve and thus transport costs are affected. Therefore, an important part of planning is to minimize the number of switchbacks on a road. Several switchbacks in a so-called "zig-zag system" should be avoided if possible because of the danger of land slides. Switchbacks should be located only if they cannot be avoided, and their distance from each other in steep terrain should be as long as possible.
FIGURE 33
Examples of Correct and Wrong Serpentine Systems
Cooperatively planned roads CORRECT
Individually planned roads WRONG!
Suitable places for switchbacks are positive control points. The hillside slope in these places must not exceed 40 percent.
A switchback is located as shown in Figure 33. It is recommended that in addition the centre line be marked, using the tape to mark the radius of the curve.
FIGURE 34 Zero Line and Centre Line of a Switchback -Average distance of the stakes 20-25 m
Invisible Target
During the location of a forest road the target may frequently be invisible because of big trees or ridges. Three empirical methods are suggested in order to overcome these obstacles:
a) Use intermediate points for the clinometer and the target without driving in stakes. This simple method is mainly used for crossing small ridges. During the compass survey the target is elevated above the invisible point until it is visible.b) If the target is visible from a slightly higher clinometer point, the pole is put at this point and the clinometer is moved down along the pole until the correct reading is found. Then the clinometer is fixed by hand at this height on the pole, and the target is adjusted downward (to 0 percent). The foot point of the target pole is the correct point. This method is used to pass by big trees or other obstacles.
c) For long cuts across ridges which obstruct the sight, the clinometer is used as a levelling instrument to transfer the elevation of the last point around the ridge using 0 percent sights. The distance between the terminal points of the cut is determined by means of the tape and the centre line is marked. By means of the gradient and the distance the difference in elevations can be calculated easily using the formula:
h(m) - g(%) x d(m)/100
The final terminal point is located from the transferred 0 percent point using the calculated difference in elevations.
The right of way has to be marked before the trees are felled and the construction area is cleared. This work can be done roughly without an exact survey, except if there are other land owners. The engineer walks along the zero line and two helpers mark the upper and lower borders according to his instructions, he having estimated the required distances from the following table:
TABLE 6
Right of Way for Forest Roads
|
Slope Gradient |
Actual Distances from Zero line |
||
|
Uphill |
Downhill |
||
|
Earth |
Rock |
||
|
30% |
4 m |
4 m |
4 m |
|
40% |
5 m |
4 m |
6 m |
|
50% |
6 m |
5 m |
6 m |
|
60% |
7 m |
5 m |
8 m |
|
70% |
8 m |
6 m |
10 m |
|
80% |
9 m |
6 m |
12 m |
|
90% |
10 m |
7 m |
12 m |
|
100% |
12 m |
7 m |
12 m |
For reconnaissance a field notebook with cross-section paper should be used. This type of paper is suitable for general notes and sketches.
For location a special notebook should be used. The following form is recommended and has stood the test of time for the zero line method.
FIGURE 35 Example of a page of a Field Notebook
|
Stake |
Gradient |
Distance |
Bearing |
Rock Component |
Notes and Sketches |
||
|
from |
to |
g (%) |
d (m) |
B (c) |
R (%) |
||
|
1 |
2 |
-5 |
37.7 |
240 |
40 |
- |
1. Connection with Slope Road, Switchback, Subbase culvert 50 cm, 8 m long. Additional fill material, 300 m3 earth required. |
|
3 |
-8 |
19.5 |
227 |
40 |
- |
||
|
4 |
-9 |
35.1 |
208 |
50 |
- |
||
|
5 |
-9 |
32.0 |
199 |
60 |
50 |
||
|
6 |
-10 |
25.5 |
205 |
60 |
50 |
||
|
7 |
-10 |
24.4 |
207 |
80 |
75 |
||
|
8 |
-10 |
38.0 |
202 |
80 |
75 |
||
|
9 |
-10 |
24.5 |
205 |
80 |
75 |
||
|
10 |
-10 |
25.8 |
200 |
100 |
75 |
||
