CHAPTER VII. COBBLE AND STONE-BLOCK PAVEMENTS. WITHOUT doubt pavements originated from the necessity of improving low places in roads, which become impassable in wet weather on account of the traffic. This was done successfully, and seemed so desirable that when traffic increased the pavement was extended, and in time it became a necessity over the entire road. To the ancient Romans must be given the honor of being the first to construct roads in Europe on any general system, and to their credit be it said that the work was done in a thorough and substantial manner. These old Roman roads were practically works of solid masonry construction, built of irregularly shaped stones, but finished to a smooth and true surface. A full description of the method of construction of one of these is taken from the French Encyclopedia of 1836. "1st. A cement of chalk and sand one pouce in thickness. "2d. On this cement, for the first bed, large stones six pouces thick were placed on one another, and backed by hard mortar. "3d. A second bed, eight pouces thick, of small round stones, mixed with other broken pieces of building material not so hard, and mixed with a binding cement. "4th. A third bed, one foot of cement, made of rich earth mixed with chalk." An ancient pouce was 1.09 inches, and an ordinary pouce 1.06. Fig. 3 shows the ground-plan of a Roman road on the Septimer, as taken from a consular report. Figs. 4 and 5 show sections of other Roman roads. The Romans constructed these roads all over their conquered provinces, and in after-times the discovery of their remains was taken as proof of former Roman occupation. That the Romans' work was well done is shown by the roads themselves, as the one previously described is said to have been in good condition fifteen centuries after it was built. The early pavements, however, were constructed in a different manner, the material being in almost every case what is now termed cobblestone. This was natural, as the cobblestones were the most available, and were known to have great durability. As cities grew, and the needs and desires for better streets increased, the rough cobblestone did not satisfy the people, and improved methods were demanded. Attempts were then made to construct a smoother pavement by forming the stones into rude irregular blocks, at first of no particular shape, but endeavoring to give a comparatively smooth surface. This was the beginning of the modern block pavement. As time passed on, the blocks were made better and the pavements, consequently, were improved. In Europe, in many cities, the blocks were made several square feet in area, and at first were laid lengthwise of the street, but as traffic increased it was demonstrated that, the long joints being parallel to the wheel traffic wore rapidly, and the pavement soon . became rough and uneven. To obviate this, the blocks were made square and were laid as is shown in Fig. 6, which shows a recent SIDEWALKS SURFACE OF STREET SIDEWALKS street in Catania, Italy. These blocks are of hard lava, 16 × 20 inches square and 8 inches thick. It was soon discovered, also, that these large blocks were not suitable for heavy traffic. It was difficult to get them so bedded on any foundation that they would maintain their position under heavy loads, and the blocks themselves soon became displaced. This caused the blocks to be made smaller still, and the greater portion of the European cities adopted a block about 6 x 8 inches square, and of depths varying according to traffic. In this country, however, the original pavements were all of cobble. The cities, as a rule, were poor, the cobblestones were available and naturally came into quite common use. They gave very good service, but were necessarily rough, uneven, and very noisy. The Russ blocks spoken of in a previous chapter were probably the only large square blocks that were ever laid in an American pavement to any great extent, though some were used in New Orleans and Boston. Following the cobblestone, and in response to the demand for an improvement on them, came what has always been known in this country as the Belgian block. The name is given to it because it was first used in Belgium, and it came to be quite generally adopted in Europe. In shape it was a truncated pyramid, with base about 5 or 6 inches square, and a depth of from 7 to 8 inches, the bottom of the block being of dimensions not more than 1 inch different from the top. This was an improvement on the cobblestone, and when well shaped and of proper material made a very good pavement. In New York and vicinity it became quite popular soon after its adoption, about 1850. The trap-rock forming the Palisades of New Jersey is easily cut into blocks of this shape, and being so near New York, it makes a very cheap and durable paving material. As the blocks became more common, deviations were allowed from the specifications, and the resulting blocks were too small on the base to allow a solid bearing, and under traffic they soon got out of position, and in consequence the pavement became rough. An improvement on the Belgian block was to make the block an exact cube. This was done in the old country, and many cities there at the present time lay blocks that are of that shape. The question of proper paving material became of so much public importance in Philadelphia that in 1843 a committee of eminent engineers was appointed by the Franklin Institute to examine into the subject and make a report upon the best material for the city of Philadelphia to adopt. After a very careful and thorough investigation of the material being used both in this country and in Europe at that time, the committee made an exhaustive report to the society. After speaking of several experiments of different kinds that had been made in the city, and showing where they were faulty, they finally made the following recommendations for the material to be adopted for the Philadelphia streets. Streets of the First Class.—These should be paved with dressed stone blocks laid in diagonal courses to the street, upon a subpavement of pebbles. These blocks were to be exactly 8 inches deep and from 7 to 9 inches wide, and 8 to 10 inches long. The estimated cost of this pavement at that time was $3 per square yard. This pavement was recommended for streets of heavy traffic when the grade was 29/10 per cent or less. Streets of the Second Class.-The pavement for these streets should consist of two stone tramways built in each street to accommodate traffic in both directions, and the spaces between the trams and curbs to be paved with cobble. It was estimated that this would cost for laying transversely on the streets already paved, and repaving the old material, about $1 per square yard over the entire surface between the curbs. Streets of the Third Class, including all Lanes and Alleys.—For this the then method of paving with cobbles was recommended, adopting the improvements suggested in the report, which consisted of using more regularly formed stones and thus having the average depth 6 inches. The committee reported as the best shape for the cobblestone "that of a prolate spheroid generated by an ellipse, of which the major axis is double the length of the minor." A tramway street similar to that proposed for those of the second class had been laid in London in 1825 on the Commercial Road, and the Philadelphians had had an opportunity of seeing one that had been made a short time previous to 1843 on Arch Street. How much attention was given to this report can be seen from the fact that in 1884 (forty-one years after it was made) ninetythree per cent of the entire pavements of Philadelphia (535 miles) was then paved with cobblestone, as has been before stated. It did not require, however, many years' experience with Belgian blocks to demonstrate to New York City that the proper pavement had not yet been discovered, and many experiments were made with a view to improvement. About 1865 a patent was issued by the United States to Mr. Charles Guidet for laying granite pavements. The distinctive points of this pavement, and upon which Mr. Guidet based his patent, were: First, stones bounded by six faces, the two opposite faces being parallel with each other. Second, the width of the joints running transversely to the street is comparatively wide. Third, the width of the joints running longitudinally to the street is comparatively narrow. |