Modern Gasworks Practice

£- MODERN GASWORKS PRACTICE The work done per unit volume of displacement increases as the angle of taper decreases, but when the taper approaches 0, or is 0, then the work done is less than when the angle of taper is larger. When a disk is forced into clay, the sides of the hole do not crush in (unless a certain critical depth be attained) because the pressure of fluidity of the clay having been attained immediately under the disk, the clay flows laterally ; but the moment it has escaped from beneath the disk the pressure is reduced to the statical pressure corresponding to the local head of clay, and when this is less than the pressure of fluidity the clay does not flow into the hole made by the disk. If, however, the penetration of the disk be carried far enougli, then ulti-mately the statical head of clay will be equal to the pressure of fluidity and the sides of the hole near the bottom will crush. in. To-day, the favourite method of dealing with average compressible soil is by means of some type of floating foundation in the form of a raft, often with. stifEening ribs as in a large ceiling. That is to say, the weigh.t of the superstructure is dis-tributed over a large area, so that the unit loading on the soil is within the recognized limit. In such cases the distribution of loading must be as equal as possible ; other- wise, if sinking occurs, the whole may go slightly out of level. In this respect it must be remembered that it is fre-quently impossible to avoid a little sinking; but unequal sinking is the great danger. The once familiär type of grillage foundation, embrac-ing an elaborate network of joists bolted together, is now 1 IG. 3.—Typical Reinforced Ratt Foundation fob Vbktical Retort Bench. giving way to reinforced concrete work, this having proved to be the most economical form of foundation which can be employed under most circumstances. An alternative but more expensive method is that of employing one of the many forms of metal sheet piling, thus completely enclosing the space to be built over. A very light raft spread over the enclosed area will then suffice. This is certainly an admirable way of dealing with soils of a spongy character. As an illustration of its efficacy, it may be mentioned that in America buildings have been erected on what has practically amounted to a body of water, the latter, being incompressible, aff ording an ideal support so long as lateral movement is efEectively restrained. Some few years ago it was a common practice to set down raft foundations constructed from timbers tied together, also from fascines ; but such methods may now be looked upon as things of the past. As an example of the modern slab foundation, an illustration of a method adopted for the erection of a vertical retort beuch and house is shown in Fig. 3. Fig. 4 shows such a foundation with the rein-forcement in position before the concrete is inserted. Here the slab is of a more or less shallow nature, but is heavily reinforced by means of indented bars. The