Part 3 (2/2)
Some of the advantages of the pole road are that it is tough and strong and does not crack, split or break easily so that if it is properly put in it lasts and requires but little maintenance. The material for its construction is found along the right of way and being small in diameter is less expensive than other road materials.
_Fore and Aft Plank Roads._ This type of road is constructed by placing cross-ties from eight to ten feet apart, center to center, upon which are placed lengthwise for each wheel, two or three sawed timbers not less than six inches in thickness and from twelve to fifteen inches in width. A good road of this type will deliver 150 million feet of logs at a conservative estimate.
The grading is usually light and in many places entirely unnecessary.
Second-grade six by eight ties with the eight inch face placed down, or hewn poles are laid about eight feet apart. Where the road bed is soft, the ties are placed closer and in some places as near as two and a half feet apart. Over very swampy ground, the road known as the fore and aft puncheon road is used. It consists simply of cedar puncheon placed crosswise of the road with the usual planking nailed securely to it. The plank used should never be less than six inches in thickness in the main road as it has been proved that four inch plank very soon give way under the heavy loads. On the spur lines it is practicable to use four inch plank because the road is used only a short time.
The total width of the road is eight feet and the plank are laid on top of the ground, but if they are sunk nearly to the level of the ground the road is made considerably more firm and enduring, and of course is safer. The ends are adzed smooth to present an even surface, drift-bolted to the ties, and all joints broken.
The plank in the track are kept together by means of a three by four inch timber driven tightly between the tracks on top of the cross-ties at each joint, and a block nailed to the outside of the tie at each joint with a wedge-shaped piece of wood driven between it and the plank.
(See ill.u.s.tration on page 33.) This wedge is driven in from time to time as occasion may demand. If, in addition to this construction, dirt or gravel is filled in the center to the level of the track, the road is made very solid.
[Ill.u.s.tration: Fore-and-aft plank road with wedges on cross ties to facilitate the re-aligning of the planks.]
With a good road of this type and a bearing surface of thirty inches, the trouble and expense of a guard rail may be eliminated. When a light truck is used for a small body of timber such a wide and heavily constructed road is not practical. In this case, a four inch plank with a fifteen inch surface and an eight inch pole for a guard rail would be used. Here again the track must be made wider on the sharp curves, often as wide as three and a half feet. Usually, the inner rail is made wider than the outer one. On very sharp curves the track may have to be planked solid to keep the trailer from running off. By sawing out chips from one-half to one inch wide two-thirds of the way through the plank, and about six feet apart on the inner side, a long plank may be bent around quite a sharp curve. The ties, of course, should be placed so as to allow the cut sections of the plank to rest squarely on them. This does away with the short pieces and so strengthens the track.
The company logging at Camano Island, Was.h.i.+ngton, operates over a road of this type, an ill.u.s.tration of which is shown on page 38. The difficulties encountered in the construction of this particular road were very considerable as a cut through very hard shale, in some places as much as seven feet, was necessary. The maintenance on this road is heavier than is usual. Two men are employed to work on it continually.
The work consists of blocking up the loose ties and plank, making any necessary repairs and keeping sand and gravel on the steep grades. The cost of this work is good insurance as it keeps the road in the best of condition at all times and saves on other operating expenses.
[Ill.u.s.tration: Detailed view of fore-and-aft plank road, showing method of wedging.]
_Cost._ The first cost of a road of this type is high but it more than pays in the long run if a large body of timber is to be hauled over it.
The timber used in its construction amounts to about 160 thousand feet per mile. Second grade material can be used at a cost of approximately $5,500 a mile for the plank. The total cost per mile varies from $6,000 to $8,000. The plank road at Camano Island cost $20,000 for two and three-quarter miles, which includes the cost of the plank, the grading and labor of putting the plank in place. This is at the rate of about $7,275 a mile, or approximately $138 a hundred foot station. The overhead charge for the road at this operation is $.75 a thousand feet of timber hauled over it. Plank roads of lighter construction have been built for $4,000 a mile. The length of life is about the same as that of a pole road, three to four years.
The fore and aft plank road is one of the best roads that can be put in where the timber is of sufficient quant.i.ty to justify the expense. The big advantage is the speed that can be made and the saving in the equipment. Such a road is very free from b.u.mps and the jar and vibration on the truck is no greater than on a city pavement. The depreciation on a truck depends to a great extent upon the road operated over. With the above type, depreciation on the truck will not be less than five years.
In addition, tire mileage will be double that obtained over a pole road, and the gasoline and repair expense will be very materially cut. Owing to the very small vibration, a load of logs can be brought to the landing as fast as it is safe to let the truck glide on a down grade.
Speeds as high as 20 miles an hour can easily be taken without excessive vibration. The traction is greater on this type of road than it is on the pole road, due to the greater bearing surface. Traction on grades up to 12% is easily secured by sanding the plank.
_Concrete Roads._ Concrete has been suggested as an ideal road material.
However, up to the present time, loggers have not been very enthusiastic about this type of road on account of the cost of construction, which is somewhat more expensive than the other types of roads, and on account of the permanence of the finished road which is beyond that needed. To the writer's knowledge, there is no company operating in the Northwest over a concrete road of their own building. In the future such roads may be used to a limited extent on the main haul by companies which have operations extending over at least a five year period. The spur roads will probably always be of some other material.
In building such roads two tracks of concrete, one for each wheel are provided. The sub-grade should be well ditched in the center with cross ditches every fifty feet, as is done with the pole road. It has been suggested that the ditches holding the track be six inches deep and twenty-six inches wide. They are filled to the top with concrete and built with a lip four inches high and four inches wide along the outside on top of the main surface to serve as a guard rail. No forms are necessary except for the guard lip.
A word of caution here may not be amiss. Concrete roads of this nature must be regarded as only experimental, for no specific data are available for determining the proper section of concrete to be used for carrying heavy loads on so narrow a bearing surface. It is evident that the carrying capacity of such strips of concrete would be greatly affected by the character of the sub-base. It will therefore be impossible to specify a standard that can be used under all conditions.
The use of the concrete guard rail is one of the disadvantages of this road. The edges of the rail cannot be made rounding except by special forms and the rubbing of the tires against this rough surface would greatly reduce the tire mileage. In addition, the rail is so exposed to weather and hard wear that it cannot be relied upon to serve effectively for any great length of time. The placing of forms is also a considerable item of expense in building such a road. A method which would eliminate such an expense and at the same time provide a more practical rail would be an advantage.
[Ill.u.s.tration: Figure 2. Cross section of concrete road. Scale--1 inch equals 2 feet.]
It has already been said that guard rails are unnecessary with a thirty inch track except on sharp curves and otherwise dangerous places.
However, where rails are necessary the wooden rail fastened by bolts embedded in the concrete as ill.u.s.trated above, is quite effective and readily installed. This consists of a four by six inch plank placed on edge and drift-bolted to the concrete every three to five feet by a three-quarter inch bolt. These bolts are placed in the concrete when it is poured and should be embedded six inches. This will provide a rail less expensive to build than a concrete rail and one which will last longer and save on tires. Replacements are easily made by removing the nuts and placing a new plank in place of the old. With a guard rail of this type, there is left a twenty-six inch track for the wheels to run in.
Experiments by W. D. Pence (Journ. West. Soc. Eng. Vol. VI, 1901, Page 549) on 1:2:4 concrete give an average value of 0.0000055 inches per degree Fahrenheit for the coefficient of expansion. The richer the concrete, the greater the change in dimension. Due to the expansion, in laying the concrete the track must be broken every twenty-five or thirty feet by placing a half-inch board in the ditch when the concrete is being filled in. Later this board is removed and the joint filled with asphalt so that the concrete may expand without danger of cracking the road.
_Cost._ The best mix to use in building this road is what is known as the 1:2:5. For one cubic yard of concrete, the following amounts of materials will be used for the above mix: 1.21 barrels of cement, 0.46 cubic yards of sand, and 0.92 cubic yards of stone. At the present prices, the cost for the materials for this road is about twenty cents a cubic foot or about $4,400 a mile. The total cost of the road including the necessary grading, ditching and labor, will be from $7,000 to $9,000 per mile.
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