Page:Architectural Review and American Builders' Journal, Volume 1, 1869.djvu/428

 350 Sloan's Architectural Review and Builders' Journal. [Nov., country, it is otherwise ; and this secret underground action must be the study of the Architect. This subject is a very interesting one, and although it must be evident to all, that such a lodgement of water is a positive source of danger to foundations, and there is no doubt but to such source can be traced some, otherwise unaccountable, bad settlements of large buildings ; yet, how few of our professional brethren ever dream the possibilhiy of such a cause. To make this matter more plain, let us suppose a case, in which the Archi- tect has probed his site throughout, to say ten feet, and found it apparently sound. Now, at one point, which may be the locality of a corner, we will suppose a large boulder to be down twelve feet, or two feet below his prob- ing, and under this boulder a lodgement of water increasing or decreasing with the state of the weather. The ground immediately over such boulder will be firm and compact enough, to resist the probe sufficiently to inspire the examiner with confidence. The building is erected, and, perhaps, finished, without any ap- pearance of defective foundation. But the secret action saps beneath. The boulder at last, under the pressure now on it, sinks down in its moistened bed ; and the fated building, fractured at its corner, is irredeemably injured, — per- haps made so dangerous, as to oblige its being taken down. A similar fate lurks in the sand stra- tum, which underlies an apparently firm footing for foundations ; and calls for the cautious skill of the examining Architect. A knowledge of Geology might here be made available ; but how very few give sufficient attention to the subject, the most being too anxious to hurry forward the erection of their design, or too careful of putting their patron to what, to him, might seem unnecessary expense. The surest safe- guard, against such hidden dangers, is to be found in piling, and such work, when efficiently done, is well worth the outlay, whatever it may be. There are other methods, which are good, but we place piling foremost in the rank of precautionary measures, and shall now describe it. When the necessary excavations are made for cellar, or sub-cellar, as the case may be, the trenches for the foun- dations are dug of the required breadth, and from two to three feet deep, down- ward, from the bottom of the cellar. In these trenches the piles are to be driven ; and they must be of lengths propor- tioned to the penetrability of the soil. The average length may be found by driving five or six piles at fair distances ; and, when the hammer stroke ceases to drive, mark the length of pile-drives ; and, thus driving and marking each, the average of required length of pile is arrived at. Then have your piles, say two feet longer, than the longest. This will provide for " soft spots." Set them three feet from centres. Piles should be of sound, hard wood. White Oak is excellent for the purpose. They should be pointed at the entrance end, and not less than nine inches in diameter. An iron ring should be tem- porarily set on the upper end, to pre- vent the continued strokes of the ham- mer splitting the pile, and to give a uniform surface, to receive the strokes, until the pile is driven completely home. This ring can then be transferred to a fresh pile, and so on, throughout the operation. When the point of the pile rests upon any hard stratum, it is at once evidenced by the fact that the hammer, in its stroke, rebounds from the pile, without driving it. The last pile being driven, they should be all cut off, to the required level of the bottom of footing course, which will leave their heads, say, eight inches over ground. This eight inches should be filled up in two equal courses : first, of well-rammed dry gravel ; second, of good, well-mixed concrete, composed