This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
When the soft superstratum is of indefinite or very great thickness, and not hard enough to "float" the building upon it, by extending the area of the foundation, it must be supported upon piles or piers, carried sufficiently deep that the friction on their sides will be enough to carry the weight. In the case of piling, they should be closer together than in the former case, and the heads of the piles, besides being connected together with timber framework, should be surrounded with a mass of masonry or concrete, to distribute the weight and add to the resistance. If piers are employed they may be of masonry, sunk in the manner that wells are formed, and which are used as foundations by the natives in India, or they may be hollow cylinders of iron.
When the ground is exceedingly soft, there is considerable danger of the pressure on the part underneath the building causing the part surrounding it to rise above its original level; to counteract this, as far as possible, the piling or piers should be extended beyond the area of the foundation, and the ground in the immediate neighbourhood should be consolidated or weighted with stones or concrete, and as few excavations as possible should be made in the natural soil. It is also necessary in these cases to equalize the pressure all over the area of the foundation, because there is sure to be a settlement, however small, and the smallest irregular settlement will cause a break in the structure. Equalization of the pressure on the foundation will not, however, prevent an absolute settlement, nor a rising in the neighbouring ground, which latter can only be counteracted by piling and counterbalancing the pressure by weighting the surrounding parts.