24 



THE CUBA REVIEW 



THE VALUE OF PRECAST PILES 



The precast and weight-driven concrete 

 pile, so effectively used by Mr. Aldrich 

 Durant, the engineer in charge of constructing 

 the great piers in Havana, gives the Engineer- 

 ing News an opportunity to give an expert 

 opinion on the use of such piles in general, 

 and in connection with the work of building 

 the Havnan docks in particular. 



The work which has been going on for 

 several years has been fully described and 

 illustrated in previous issues of the Cuba 

 Review, and was also the subject of a lengthy 

 report by U. S. Consul-General Rodgers of 

 Havana, which appeared in the April, 1914, 

 issue of this publication. 



The Engineering News finds that the 

 ])recast and weight-driven concrete pile is 

 now such a necessity in the construction of 

 foundations that engineers are apt to forget 

 how recent a development such a pile and 

 with what hesitancy its introduction was 

 accepted. It is only a few years since such a 

 pile was only an innovation frowned upon 

 by conservative builders who feared, not 

 without reason, that the repeated shocks of 

 a heavy hammer must of necessity shatter 

 so slender a concrete column or, at least, 

 destroy that bond between the concrete and 

 steel which confers the sometimes necessary 

 columnar strength to the loaded pile. To 

 allay these fears, ingenious inventers devised 

 different types of cast-in-place concrete piles 

 in the construction of which no shock came 

 upon the structure of the pile. A few of 

 them have proved very successful and are in 

 extensive and ever-increasing use. At the 

 same time they are not applicable to certain 

 kinds of work, particularly in subaqueous 

 foundations, and the precast pile has been 

 continuously tried until there is httle doubt 

 as to its usefulness under many and varied 

 conditions. 



The continuous use of the precast pile has 

 pretty thoroughly allayed the once-held fears 

 as to its integrity under the blow of the 

 hammer. While there have not been re- 

 ported many cases where driven piles were 

 exposed or withdrawn, the few tests available 

 have shown that the concrete pile withstands 

 the shock of driving remarkably well, and 

 that, when well made, and when not ob- 

 structed by some impenetrable stratum or 

 individual boulder which is driven against 

 for a number of blows after refusal, the 

 concrete column of the pile can be counted 

 on to be intact thi-oughout its length, which 

 is one of the important requirements in a 

 foundation pile. 



In another respect the precast concrete 

 pile is of advantage and that is the extreme 

 length to which it can be successfully driven. 

 The piles used in the Havana piers were some 

 of them 80 ft. long and in similar work at 

 Halifax, reported in these columns some 

 weeks ago, piles only a few feet shorter were 

 employed. In marine work where the pile 



extends through water many feet above 

 bottom a necessary penetration requires a 

 pile length often far in excess of the econo- 

 mical production of wooden piles, even in 

 places where a wooden substructure is allow- 

 able, and the possibility of making and using 

 concrete piles for such lengths solves a 

 number of heretofore complicated problems 

 in pier and wharf work. The main difficulty 

 in such piles is the danger in handling them 

 and this is avoided, as noted in the Havana 

 work, by designing the reinforcement to 

 care for the stresses induced by a certain 

 method of suspension and then providing 

 hooks or rings so that the pile cannot be 

 suspended in any other manner. 



Unfortunately, there is nothing in the 

 precast concrete pile that reheves the un- 

 certainty as to safe loading common to all 

 piles. For wooden piles, numei'ous formulas 

 have been devised, theoretically designed to 

 deduce a safe loading from the behavior of 

 the pile under driving, but such formulas 

 have a value largely dependent upon empiri- 

 cal coefficients which individual engineers 

 develop through experience. Such experience 

 has not been sufficient to warrant the applica- 

 tion of proper coefficients to concrete piles, 

 though it has been enough to prove that the 

 coefficients common to wooden piles will not 

 hold for the heavier concrete pile. It seems 

 hardly possible that any formula for driving 

 can be devised which will cover all kinds of 

 concrete piles in all kinds of ground, so it 

 remains a fact for concrete pile work, as reallj' 

 it should be for wooden pile work, that no 

 loading assumption should be made without 

 a satisfactory and fanly extensive loading 

 test of typical piles in typical ground under 

 typical conditions of driving. 



How the precast piles were driven into 

 the bottom of Havana harbor is thus told 

 by the Engineering Record of New York: 



"The pile driving was done with a floating 

 equipment, the piles being handled both in 

 horizontal and vertical position by pairs of 

 slings fastened to the gas-pipe holes and at- 

 tached to a bridle suspended from a derrick 

 boom. Care was taken to keep the pile with 

 the marked side up and they were driven by 

 a 6-ton No. 1 Vulcan steam hammer seated 

 on the top of the pile and attached to it by 

 slotted vertical links allowing the whole 

 maximum pile weight of 17 tons to be ef- 

 ficient for settling it from 10 to 20 ft. into 

 the mud and while the hammer was still sup- 

 ported by the derricks and afterward allow- 

 ing the hammer to be entirely supported on 

 the piles. A rope mat was used to cushion 

 the hammer and the piles were driven by an 

 average of 500 blows to a penetration in the 

 hard stratum of J^ in. or less for the last 

 ten blows. The estimated length of most of 

 the piles was correct, but a few of them 

 were found too long and were cut off by 

 pneumatic chipping hammers. 



