7.1 GENERAL REMARKS
7.2 DIVIDER SETTING
7.3 PLOTTING THE ROAD LINE
7.4 CROSS SECTIONS AND DETERMINATION OF CUT VOLUMES
Formerly a considerable amount of time was spent on drawings of road projects since the roads were manually constructed. For mechanical road construction in steep terrain simpler drawings are sufficient.
At present, tracing paper is used for all drawings, this being mainly in pre-cut sheets of a standard size. Drawings can be copied in pencil as well as in ink. Careful lettering is important and is done in ink using lettering sets so that detail will not be lost.
The following drawings should be prepared for a forest road:
- Section of a topographic map at a scale of 1:25 000 or 1:50 000. The planned road is generally outlined in this section. On the copies the road is drawn in red, the forest area in green.- Detailed plan at a scale of 1:2 000 up to 1:5000. The plotted road line is adjusted to the situation on the map.
- Standard cross-sections at a scale of 1:50.
- Profile of the zero (grade) line. This drawing can be substituted by a written profile.
- Road construction details at a scale of 1:25 or 1:50. Most of these details (culverts, retaining walls, cattle grids, etc.) should be prepared in standard drawings.
A divider setting method is used for plotting a zero line with the required gradient on a contour map. Even on a topographic map with a small scale this method can be applied to obtain a rough idea as to whether a route can be found, taking into account the steepness of the terrain and the allowable grades.
The following simple proportions are used to calculate the divider opening based upon the contour interval, the allowed grade and the map scale.
FIGURE 36 Cross - section Between Two Contour Lines for Divider Setting
The contour lines on large scale maps are generalized, more like form lines, and do not reflect all breaks in the topography, therefore, it is necessary to add 10 percent of ds to the measured distance up from 7 percent grade to obtain proper zero lines.
TABLE 7
Example
Divider Opening for Maps with a scale of 1:50 000 and 40 m Contours
|
g % |
ds |
ds+10%(m) |
Divider Setting |
|
3 |
1330 |
- |
26.5 |
|
5 |
800 |
- |
16.0 |
|
7 |
570 |
630 |
12.6 |
|
9 |
445 |
490 |
9.9 |
|
10 |
400 |
440 |
8.8 |
|
12 |
330 |
360 |
7.2 |
Example: v = 40 m, scale 1:50000.... ds-4000/g
To draw a zero line on a 1:50 000 map with a vertical contour interval of 40 m set the divider points 9.9 mm apart for a 9 percent grade and then, starting at a control point, successively mark off the distances ds as shown in Figure 34.
If the trial zero line does not hit the terminal contour point reset the divider and mark off a second trial line. A zero line with a constant grade can be easily and quickly drawn by means of this simple method.
FIGURE 37 Drawing a Zero Line on a Contour Map with a Divider
The zero line is the first drawing which is prepared for the detailed plan. First, the distances recorded in the field notebook are added to obtain the total length. It is recommended that intermediate sums for all control points and check points of the map be noted. A printing electronic calculator is useful for this purpose so that checks for errors may be made quite easily.
The zero line is plotted with protractor and ruler at the scale of the map. Normal working scales are 1:2 000 or 1:5 000. If a ruler with these scales is not available the required scale is calculated and dawn on the tracing paper.
Transparent tracing paper of the best quality should be used and a sheet of the required size should be fixed to the drawing board. A sheet of cross-section paper should also be used as a pad between the drawing board and the tracing paper so that the vertical lines indicate the magnetic North direction (0) and allow the plotter to adjust the protractor accurately at each point of the open-ended polygon.
PHOTO NO. 20 Plotting a Zero Line with Protractor and Ruler
Equipment required: Field notebook with data, tracing paper and cross-section paper, protractor, ruler and scale, medium-hard and hard pencils and an eraser.
Working Procedure
(a) Mark the total length of the open-ended polygon on the paper and estimate the average bearing of the whole line. This way you can determine the size of the tracing sheet needed and how to fix the northern direction in order to save paper.
FIGURE 38 Tracing Paper and Pad for Cross Section Paper
(b) Begin by drawing in the starting point (Point 1) of the zero line. check to see whether the direction of plotting is equal to the direction of surveying. The bearing from 1 to 2 must be equal to the plotted Azimuth from 1 to 2.
First, the bearing along the circumference of the protractor is marked on the tracing paper, then the protractor is removed and Point 1 is connected by a thin line with the mark of bearing. The distance between points 1 and 2 is marked on the line and Point 2 is marked. Plotting is continued in this way from 2 to 3 and so on, until the last point has been plotted.
FIGURE 39
Plotting Bearing 45 and Distance 20 m from Point 1 to Point 2, Scale 1:2 000
First: Bearing
Second: Distance
(c) After plotting the line, the tracing paper is removed from the pad and drawing board. If a detailed map of the planning area is available at the same scale, the plotted line is checked against main points of the map by laying the tracing paper which contains the plotted line over the detailed map. The traverse is converted into the final road line by drawing in the centre line using free parabolic or circle curves. A plastic curved template with the minimum radius at the required scale is very useful.
FIGURE 40 Zero Line and Centre Line
The final road line (centre line) is traced onto a transparent copy of the detailed forest map. Culverts, bridges and other structures are shown by use of simple symbols. The hundred-metre stations (hectometre) are marked using the measuring divider and checking the points of the intermediate sums. Gradients can be drawn with arrow symbols.
FIGURE 41 Detail of the Final Drawing of the Road Line
Layout of the Detail Plan
Because the original draft is prepared on transparent tracing paper, copies can be reproduced. When drawing the original use only black in and/or pencil. The base map and all details which should be black on the copy are drawn in black ink. All lines which should be coloured on the copy are drawn only with thin pencil lines.
On dyeline copies the road line is drawn with red ink, the creeks and rivers with blue ink and the forest symbols in green. Signs for the planned logging system (landings, cable corridors, etc.) can be drawn on the map in addition to the road system.
FIGURE 42 Section of a Detail Plan
A cross-section of road is a profile which is at right angles to the centre line. For curves, the cross sections are drawn in the direction of the radius.
FIGURE 43 Birds eve view of Cross-Section
Individual cross-sections for forest roads which will be mechanically constructed are normally not drawn. However, it is necessary to draw some standard cross-sections, based upon the road standard, steepness of terrain and local logging and transport conditions so that these can be used as references during construction.
A normal truck road with one-way traffic and turnouts has a formation width of from 4 to 5 m (including ditch) and a width of carriageway (surface) of from 3 to 3.5 m. Landings and turnouts are constructed at all suitable places, especially on ridges and on gentle parts of the slope, unless otherwise dictated by length of haul and logging sequence. An example of a cross-section is given in Figure 44.
FIGURE 44 Example of a Standard Cross-Section
Besides these cross-sections which are required as standards for the construction, norm sections are drawn for different slopes and different types of subsoil (earth or rock) and are used to determine the volume of cuts to be used for estimating costs.
The following explanations and examples outline this calculation:
Norms of Cross-Section
Norms can be altered according to local conditions and requirements.
First, the slope grade is drawn on cross-section paper and then the zero line point is marked. The horizontal line of formation is drawn, the width of formation consists of a part inside the cut and a part on the fill8. These dimensions depend mainly on the steepness of the terrain, since the portion of cut increases with increasing slope (see the examples). The slopes of cut and fill are drawn from the edges of the formation with the required grades. The grades of slopes are given in percent or in the proportion height:
base (- tangent of the base angle) - h/b - say 2/3 or 1/1
8 Except in certain soil types in steep terrain when the formation should be full bench (not in fill).
FIGURE 45 Different Slopes
Calculation of the Cut Volume
The volumes of cuts are accounted for by 1 m of road lengths expressed in cubic metres per metre (m3/m). The volume of the cut is calculated as the volume of a triangular prism with the base of the cut triangle of the profile and the height of 1 m (which is really 1 m of running length along the road).
FIGURE 46 Example of Volume Calculation
The volumes of earth and rock profiles are different, corresponding to the different angles of the cut slopes which vary with the material to be cut.
Total Volumes
The average grades of slopes between the stakes and the zero line are measured in the field during the location and noted in the field notebook. See sample notes in Figure 35. From stake to stake the volume of the cuts is calculated as a triangular prism with the average volume per m (table) and the distance between stakes.
General example:
Volume of cut between stake 1 and 2 - V1 - v1 (cbm/m) x d1 (m)
-" - 2 and 3 - V2 - v2 (cbmm) x d2 (m)
to be continued to the terminal point
Sum of volumes (point 1 - terminal point) - Total Volume
It is recommended that standard form sheets be used for this calculation. Two examples of these sheets are shown along with norm sections in the following pages.
Example for Calculation of Cut Volumes for Mechanical Road Construction
The cut volume is calculated in the following manner:
(a) Enter the distances from the field notebook on the form "Distribution of distances for calculation of mass" (see Figure 48), distributing them according to slope grades and percentage of rock. For a long road several form sheets will be required. After distribution is completed, the sections are added up. In the example this calculation is performed for the stakes 1 to 10 (see example of a page of the field notebook, Figure 35).
(b) Calculate and write in the form of "Calculation of Mass", Figure 49, the volume per m (m3/m) corresponding to the Norms of Cross Sections (see Figure 47). Here the calculator must be careful since he must consider the percentage of earth and rock and distribute the volumes correctly.
The total volume per m road is divided according to the percentage parts of earth and rock. The rock percentage has been estimated and noted in the field. The figures of the norm section "Earth" are used for rock percentage, 0 percent, 25 percent and 50 percent (batters 1:1.5 to 1:2). For the sections with higher rock components of 75 percent and 100 percent use the figures of norm sections "Rock" (batter 5:1).
Example:
G = 50%, rock component 75%
v = 2.5 cbm/m (norm profile "rock")
|
|
Distribution: |
|
v (earth) = 2.5 x 25/100 - 0.6 m3/m (cbm earth = h per m) |
|
|
v (rock) -=2.5 x 75/100 -1.9 m3/m (cbm rock per m) |
|
|
|
2.5 |
|
m3/m | |
These figures can be calculated with the accuracy of a slide rule and figures can be rounded up or down. the figure 0.6 m3/m is written in the form "Calculation of Mass" to the section G (slope of ground) - 50 percent, 75 percent rock in the first column of "Earth", the figure 1.9 m3/m in the first column of "Rock", the form "Calculation of Mass" is completed by calculating these figures for all grades and rock percentages. If the used Norms of Cross Sections are adequate for several areas, the adjusted form can be used permanently.
(c) The sums of distances in the "Distribution of Distances" are inserted in the columns "d" of both sections "Earth" and "Rock", the figures of m3/m are multiplied with the sums of distances, the products are inserted in the columns "sum m3". These columns are then summed up and the total sums of earth and rock are obtained.
The third section of the form "Calculation of Mass" is determined for the established additional mass, the figures having been obtained from the field notebook.
The grand total of the three columns represents the total volume, pro-rated between earth and rock. These figures are then used to estimate the costs of bulldozer work and blasting.
FIGURE 47
Standard Cross-Sections for Mass Calculation of Forest Roads
Scale 1:50
|
Width of Formation |
5.0 m (Slope Grade 10 - 60%) |
|
|
4.5m (- " - 70 - 80%) |
|
|
4.0 m(- " - 90 - 100%) |
Slope Grade 30%
Slope Grade 40%
Slope Grade 50 %
Slope Grade 60 %
Slope Grade 70 %
Slope Grade 80 %
Slope Grade 90%
Slope Grade 100 %
PROFILE OF THE ZERO (GRADE) LINE
The lengthwise profile (profile) of the grade line can be written or drawn. A written profile can be calculated easily as shown in the following form. The distances... uniform grades are summed up.
FIGURE 50 Written Profile of the Grade Line
Remark: Numbers of stakes and stations not typical. Stake No. 1 is the terminal point of the road.1 C. 50/8 stands for culvert of 50 cm ø and 8 m length
A drawn profile takes more time. However, it gives a better overall view of the... grades and the quality of the planned zero line.
The scale of the horizontal distances should be the same as the detail plan (1:2 000 1:5 000), the vertical scale is drawn 10 times that of the horizontal scale (1:200 to 1:5000).
The elevations of the points of the zero line are not calculated for a simple project..... grades are drawn in a graph and directly transferred to the profile by means of set... (see Figure 51).
FIGURE 51 Profile of Grade Line
DETAILED DRAWINGS OF ROAD STRUCTURES
As far as possible standards of culverts, retaining walls, gates and drainage structures should be drawn on tracing paper at a scale of 1:50 or 1:25. Copies can be... in the project work papers as guides for uniform construction.
Individual plans should be drawn for all special structures, such as bridges and unusually large culverts. These drawings should only be made in pencil. Lettering is in ink with a lettering set.
Figure 52 shows a detail plan of a box culvert with masonry abutments.
