A Treatise On The Principles And Practice Of Dock Engineering

SUPPORTING POWER. 65 Ihe majority of the formulæ enunciated for dealing with the question of the supporting power of piles are of a very complicated nature, and comprise elements which are but remotely connected with it. Mr. C. H. Haswell has the following pertinent remarks upon the subject * :— ^e resistance opposed by a pile to the blow of a ram is the measure of its value to sustain stress whatever may be its diameter, weight, length, or modulus of elasticity. The diameter and length of a pile do not affect the question, their effect is to limit penetration. The weight of the pile is 0^ consideration only as affecting the weight of the ram employed. the relative elasticity is of little moment, for when a pile approaches the milt of its penetration its head is dressed off, if broomed, and if split or ■able to be so, it is confined by a ring. In fact, the weight of the ram being proportioned to the duty required of it, the diameter, length, and elasticity or the pile are inconsiderable, where so great factors of safety ranging, in various formulæ, from ^ to 1, are employed,” Mr. Haswell’s own formula is 32w7H C (4) in which the constant (C) has values ranging between 3 and 6, according to the nature and condition of the soil, the character of the piles, and the excellence of their driving. The following table exhibits a comparative view of the results obtained the foregoing expressions, assuming a depression of, say, J inch from the hnal blow of the ram in each case. Sectional area of pile = 100 square inches: — Safe Load in Lbs. Rankine. Saunders. Trautwine. Haswell. 1,000 Ibs. falling 20 feet, . 66,425 60,000 / 46,609) / 47,6801 I 7,768/ 1 23,840) 2,000 Ibs. falling 25 feet, . 129,249 150,000 / 100,296 ) / 106,666 1 1 16,716/ 1 53,333 ) 3,500 Ibs. falling 9 feet, 93,312 94,500 / 124,974 1 / 112,000 — 1 20,829/ 1 56,000/ Rankine’s empirical rule for the safe load on a pile, driven till it reaches rm ground, is 1,000 Ibs. per square inch of area of head. The author con- 81 10 CWtS'Per square inch we]1 within the limit of practical safety. A When the arrangement of the strata is such that it is impossible to reach ■ni ground with a pile, the conditions of equilibrium are different. The pi e will then only be able to sustain a superimposed weight by reason of the ° 1011 of the ground against its sides. Under such circumstances Rankine ecommends 200 Ibs. per square inch as the maximum load. Mr. Hurtzig Haswell on “ Formulas for Pile Driving,” Min. Proc. Inst. G.E., vol. cxv. 5