Modern Gasworks Practice

Frø. 2.—Pisk Foundation. FOUNDATIONS, GASWORKS BUILDINGS, ETC. 43 the foundation. For buildings, etc., the piers may be so much. as from 20 to 25 feet apart, rough arches being thrown from pier to pier by digging out the ground, so as to form a centering. When dealing with retort beuch foundations it is usual to drop down a pier beneath eacli supporting wall of the main setting-arches ; hence in such cases the piers are pitched at about 8 to 10 feet centres. When the subsoil necessitates sinking to a greater depth than 12 feet, it is ad visable to discard the pier method, and to drive down reinforced concrete piles, which may be employed. in the form of continuous piers, or spaced at equal distances apart. In the latter case the stability of the upper slab should be ensured by running some type of rein-forcement, such as old railway metals, from head to head of the piles, or by introducing one of the many systems of special bars or metal. In faet, any method may be employed which has the efEect of forming a continuous slab by binding the lieads of the piles together, thus ensuring equal loading. As regards the construction and use of piles, it has been shown by experiments carried out by A. S. E. Ackermann that, for equal depths, tapered piles support a greater load per unit volume of the pile than piles having parallel sides. This, in particular, refers to piles driven into clay. The reason is that in the case of tapered piles their surfaces keep in more intimate contact with. the clay, with the result that the support due to the friction on their sides is greater than is the case in parallel piles. In order to inerease the resistance of piles they should be corru-gated as well as tapered. The reasons why parallel piles with blunt ends are not so efficient per unit volume is that the pile in entering the clay rubs the surfaces ncar the top of the hole so much that the friction (or cohesion) is reduced tliere, and also because the clay in sqtieezing laterally from under the end partially loses contact with the sides of the pile, thus also reducing the friction on which the supporting capacity of a pile depends. The mean intensity of friction for the same depth. of penetration on the sides of parallel piles is greater in the case of piles of small cross section. than in the case of larger ones ; but if the diameter of the pile be reduced beyond a certain amount (the depth of penetration being constant), tlien the mean intensity of the friction appears to decrease again. Consequently for a given quantity of material of which. to make piles a large number of small piles is more efficient than a smaller number of large ones. Pointed piles are more efficient per unit volumes of pile than blunt ones because the points cause a more gradual lateral displacement of the clay, thus leaving it in more intimate contact with the sides of the pile. The action of the point of a pile is to cause the pressure of fluidity to be attained on its surface, whereupon the clay flows out of the way. The resistance to penetration is considerably greater the lower the temperature of the clay, probably because the pressure of fluidity inereases as the temperature decreases. The density of clay decreases as the percentage of water inereases.