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Laying down Line on 6 in. Ordnance Map. It being supposed that these points have been duly considered and determined, the best procedure is to lay down the line on the 6 in. Ordnance sheets in pencil, as nearly as may be judged from the contours. The bench marks and levels along public roads which are given in the map are also of assistance in doing this.
In laying down the line on the map in this manner, we first fix upon the position and level of the starting point and a gradient, then by scaling the proper distance between adjacent contours we arrive at the position of the line. A good way is to calculate the distance required to rise 50 or 100 ft. on the proposed gradient. For instance, if the gradient is 1 in 50, on this we can rise 100 ft. in a distance of 5,000 ft. Take now 5,000 ft. in the compasses and fit them in between successive 100 ft. contours, marking the points where each contour is intersected. Theoretically the line should follow these points, but this will seldom be possible, and the best that can be done is to put in the curves so as to follow this line as nearly as possible and with as little cutting or embankment as may be. In the hilly parts of the country the contours are only given 100 ft. apart vertically, in flatter parts 50 ft. apart, and in the easiest country every 25 ft. When 25 or 50 ft. contours are given, the distance required to rise or fall 25 or 50 ft., as the case may be, is to be calculated, and the compasses stepped between successive contours, as above described.
Fixing Gradients. The best gradient, when the ground permits of a flatter gradient than the ruling or maximum gradient, can only be found by trial, and as a rule will not be definitely fixed until the longitudinal section is plotted. For location purposes the gradient must be judged from the configuration of the ground as nearly as can be by estimation with the eye. This is therefore to a great extent a matter of practical experience and outdoor practice. In the first instance, however, the gradients to be tried must be found from a careful study of the map and the levels on it.
Reconnaissance and Sketching in Location on Map. -Having now the line thus laid down on the map, get the sheets pasted together, and cut into continuous rolls 15 or 18 in. wide, and as long as possible, or mounted so as to fold up like a pocket map. Taking this along, now walk carefully over the line and sketch in best location that will fit the ground as nearly as can be
judged, taking the pencil line already laid down as a basis. It is advisable to have a pocket scale and a pair of pencil bows and compasses; a hand level will often be useful on very steep ground for getting approximate differences of level. In locating a gradient up or down the steep hillside of a valley, a good plan is to first fix upon the valley or summit level, then calculate the levels of the gradient proposed to be run, and pencil them on the map at every 10 chains, or at fences approximately 10 chains apart. These figures may be pencilled on along the line already laid down on the map from the contours. The points on the ground where the surface level corresponds with these levels may be found by levelling from the nearest contour or other known level with the hand level or by judging with the eye. These points may then be fixed and marked on the map by measuring or stepping distances from fence corners, buildings, &c., shown on the map. A line joining these points is the line the railway should theoretically follow, and the straights and curves may be drawn on indoors so as to follow this line as nearly as possible.
Plotting Sketched Location.--Having thus gone carefully over the ground and sketched in the proper location by hand, taking care to use the compasses or pencil bows in the field so as to avoid sketching in curves of less than the minimum radius, next draw in the curves and straights to coincide with the line sketched in the field as nearly as possible, and mark on the chainage at every 10 chains along the line. It is also a good plan to scale the chainage of each fence crossed and figure it in pencil on the map, as this will save the leveller a considerable amount of time in taking the levels for the section.
Levelling the Longitudinal Section.-The next operation is to take levels over the line thus located. The leveller must be supplied with a map, with the line marked on it, and he takes levels at the points where the slope of the ground changes along the line, booking the chainage of each point where a level is taken. As a rule these levels will be taken at the points where the line intersects fences, and he will locate the exact position of the line on the ground by measuring the distance scaled off the map along the fences from the nearest corner or by directing the staff-holder to step so many paces from it. Points intermediate of fences will be fixed in like manner by measuring or pacing along the line from
the nearest fence or other object shown on the map. As already remarked, it will facilitate the levelling if the chainage of each fence crossed by the line is pencilled in figures on the map, as the leveller can then work to these chainages. The leveller should also be provided with a scale to scale distances or intermediate chainages on the map.
Owing to the limited time usually available for Parliamentary surveys, and as the location is by no means a final one, while the limits of deviation as rule leave ample room for alteration in the final location, the location above described is usually all that can be done on a Parliamentary survey. The method of making a proper final location will be found described on pages 225, 226, 227.
Correcting the 6 in. Ordnance.-The limits of lateral deviation prescribed by the Parliamentary Regulations are 300 ft. on each side of the centre line of the railway in the country, and 30 ft. in towns. They are the limits within which the centre line of the railway may be altered when the detailed or working survey is made after Parliamentary sanction has been given to the scheme. The limits of vertical deviation are 5 ft. in the country and 2 ft. in towns. As the Parliamentary plans must show all details correctly within the limits of deviation, it is necessary to pencil on the limits of deviation as well as the centre line, so that any corrections necessary may be made. As the date of the Ordnance Survey map may be a considerable number of years prior to the date of the railway survey in hand, in some cases a good deal of labour is necessary to correct alterations to existing features, such as fences, &c., survey and plot on new buildings, &c. When there is not much alteration the leveller may be able to correct the Ordnance within the limits of deviation while taking the levels, but as a rule it is more expedient for him to devote certain days to this. If there is much alteration, and the time is limited, it will be necessary to have a special assistant to correct the Ordnance. All buildings included within the proposed limits of deviation must be surveyed and plotted to a scale of not less than 400 ft. to 1 in. They are usually plotted on the 25 in. Ordnance sheets if not already shown on these. These sheets should therefore be obtained for those parts of the line where buildings are to be included, and handed to the assistant whose duty it is to correct the map within the limits of deviation.
Referencing. Every field, enclosure, building, road or path within the limits of deviation must be numbered on the plan and the numbers entered in a book of reference, together with owner or reputed owner, lessee or reputed lessee, and description, i.e., whether arable, pasture, &c. All parish and county boundaries are also to be shown on the plan, as well as the names of all the parishes and counties through which the railway passes. The work of referencing is done by the solicitors to the promoters of the scheme, to whom should be supplied a set of 6 in. Ordnance sheets corrected to date and with the limits of deviation and the centre line of the railway marked on. It will as a rule be necessary for the engineer to send an assistant out with the solicitor's clerk to number and identify fields, enclosures, buildings, &c., on the map.
Preparation of Parliamentary Plans.-The Parliamentary plans are usually prepared by tracing from the 6 in. Ordnance on which the line has been laid down. They are made of a uniform size in sheets each containing 4 miles of the railway. The section of the part on each sheet is shown underneath the plan. Where it is intended to include within the limits of deviation any building, yard, courtyard, or land within the curtilage of any building, or any ground cultivated as a garden, an enlargement of this must be shown to a scale of not less than 400 ft. to 1 in. These enlargements, as already stated, are usually taken from the 25 in. Ordnance sheets. The limits of deviation are shown on the plan by a dotted line. Any enlargements are drawn under or above the general plan at the points where the buildings, &c., to which they refer are situated.
The tracings are handed to one of the lithographic firms which make a specialty of this class of work, and they are retraced by their draughtsman in specially prepared lithographic ink, and the figures and writing neatly printed on in the usual conventional styles of printing. As Parliamentary surveys are often only decided on at the last minute of available time, the engineer and surveyor have not as a rule time to spend in elaborate printing and figuring, &c. The description and figuring on the tracings are therefore simply written on in ordinary plain handwriting, to be copied by the lithographic draughtsman in neat printing. The lithographic tracing having been impressed on the stone, proof sheets are sent for correction, and the corrected lithographs are then prepared and
bound up in proper order. The engineer retains some copies for his own use and sends the remainder to the solicitors for the proposed railway, who deposit copies with the various local authorities &c., as specified in the statutory regulations.
Preparation of Parliamentary Sections.-The section is plotted in the usual manner, the gradients and gradient lines representing the surface of the rails being shown on it, to the same horizontal scale as the plan, and to a vertical scale of 100 ft. to I in., which conforms to the Standing Orders. The section must be referred to a known datum which is usually one of the Ordnance bench marks near one end of the line. The rail level at each change of gradient must be figured on, together with the distances in miles and furlongs, point of commencement and termination of each railway and branch, with total length of each in miles, furlongs, and chains. All public roads, railways, and canals which are crossed, how crossed, i.e., whether by a level crossing or by a bridge, whether to be raised or lowered, and if so, how much, and the span and headway of each bridge, are also to be marked on the section. The extreme height of any embankment or depth of any cutting, where these exceed 5 ft., must also be figured on. Public roads crossed by level crossings must be levelled along for 200 yds. on each side of the point of crossing, and a section shown to an enlarged scale of not less than 5 chains to 1 in. horizontal and 40 ft. to 1 in. vertical. When many roads are thus crossed, they add very considerably to the leveller's work. Every public road the level of which is to be altered must have a cross section drawn to the same scales, and the greatest present and intended rates of inclination marked thereon in figures.
As already stated, the section of each 4 miles is shown on the same sheet as the general plan of that part of the line and underneath it. The sections of roads crossed are shown on a separate sheet or sheets placed at the end of the general plan and section. They are, however, sometimes placed above the general longitudinal section at the points where they occur.
Another point to be noted is that when a junction is intended with any existing or authorised railway, a plan and section of the existing railway must be shown for 800 yds. on each side of the point of junction, to the same scales as the general plan and section.