Observations as to Various Causes of Wear and Deterioration of Roadways'
Page 17
If you've noticed an error in this article please click here to report it so we can fix it.
In the Open Country (Country Roads).
By Councillor Pietzeb, Chemnitz (Saxony). Wear Produced by the Weather.
'The author is of opinion that since 1908 nothing specially important has been learned as to deleterious effects of the weather. Ordinary roads are only able to resist ordinary weather changes, not such unusually dry or wet spells as those of 1911 and 1912. Roads with tarred surfaces and tar-macadam roads are much better able to ithstand extraordinary 1,vcather conditions, but surface tarring is no protection against severe winter weather.
Traffic Effects.
Road traffic, especially motor traffic, has increased in Germany since 1908, and totally different methods et' construction will 'have to be adopted in many cases. The following consideratimis are based upon reports from all parts of Germany, materially in agreement, and supported by the author's U NA' It experience.
Light smearears.—These vehicles are injurious chiefly on account of their high speeds. Abnormal wear is only produced under speeds exceeding 25 kiloms. (15 miles) an hour ; but 40 to 50 kiloms. (24 to 30 miles) an hour are ordinary speeds and are often exceeded. These conditions must be accepted by road engineers. The wear caused by wift motorcars is due to (1) the abstractien of fine binding material, (2) mechanical crushing under blows from studs and other non-skid devices, and (3) loosening of the top layer by a slipping motion of the times at sharp bends. The manner in which the wheels abstract binding material is a moot point, but the opinion that no such action takes place must be rejected. It is the surface actually touched by the tires which suffers. The author attributes the effect to suction, produced partly by the tires and partly by the whirling of the wheels, eddies being formed " comparable to two wind spouts rapidly progressing in a horizontal direction." On tarred, or paved roads light, fast-running motorcars cause less damage than horse-drawn vehicles.
Fleury moor vehicles.—The results of observations of the effects of heavy motor vehicles are somewhatdisconcerting. Speeds of 30 kiloms. (18 miles) an hem are reached by vehicles of this class. Other factors causing damage ire heavy axle leads, high centres of gravity, and the use of iron tires; and effects produced are (4) the road surface is ground away and the stones loosened; (5) hollows are formed by the pounding caused by swaying; (6) the stones on the surface are crushed by iron tires; (7) ruts are formed by regularly running vehicles following the same track. All reports agree that hollows are formed on ordinary macadam roads used by a considerable number of heavy motor wagons or a regular service of motor omnibuses, and this is known—as in the case cf horse-drawn vehicles—to be due to sway. In the author's opinion the effect is enhanced by high centres of gravity, and he believes that the holes cannot be repaired effectually. The email diameter of the front wheels of omnibuses is another factor of importance; the mini-mum allowed should be 75 cm. (say 30 ins.).
Iron tires cause serious damage. Heavy motor vehicles do nct wear out the roads; they destroy them; and ordinary macadam roads are not suited for the regular traffic of motor waons or motor omnibuses. As regards the value of tar-macadam in this respect further trial is necessary. Roads well paved with small setts have, so far, not shown signs of extraordinary wear under heavy motor traffic.
Tire-width and Loads for Animal-drawn Vehicles.
By Julius Duhm, Austria. Read and Revised by Phillip Krapp.
The author begins his paper with references to the earlier regulations in Austria, theie neglect after the introduction of railways, and the revival of interest in the subject which attends the present-day developments of read traffic. He th.2n deals with some of the difficulties in the way ot drawing up suitable regulations, and the differences between vatious road crusts, depending not only on the materials but on tb '2 methods of construction. Attention is drawn to the limitations imposed upon increase of width of tire in proportion to the loads carried. The limits proposed by Morin and Emery would be to low for the limestone roads of the Tyrol, if there can be any question of a limit for macadam roads. The value of a maximum width depends partly on the extentto which it is effective when aoads are soft, and regulations for tire width are more conveniently applied in mountain regions with a large rainfall than they are in the plains. Ae regards the use of springs, this factor becomes -more important in the case of motor traffic than with horse-drawn wagons, but the author regards the introduction of regulations calling for the use of springs as likely to meet with considerable opposition. With respect to the influence of diameter, the formula C =. 150 C being in kilograms and d flu metres, would require modification for the roads of the Tyro!, a better co-efficient being 120; hilt the author considers that rules for tire width based on diameter might be too complicated to be handled in practice. The paper includes regulations for tire width suggested by the Administration of Imperial Roads in the Tyrol.
In Town and Suburban Districts.
By William H. Connell, U.S.A.
The author recognizes that the newness of the problem has, in -many instances, been it cause of deterioration of roads end pavements, but considers that a snore frequent cause is to be found in a lack of application of the principles of highway engineering to construction and maintenance; a failure to recognize the need for qualified expert supervision. Bridges, and other engineering works, are not undertaken until the conditions have been studied. The two items, foundations and probable loads, should be studied in the rase of a proposed road as well as in designing a bridge, and if this wore done, and drainage carefully studied, failures would he minimized. The most important considerations in the preliminary studies for suburban roads and town pavements are: drainage, traffic, and probable future traffic, foundation, gradient, and wearing surface. After referring to the great importance of the first two, the author discusses foundations, and gradients, and at considerably greater length, the wearing surface. (To be continued.)