FOUNDATIONS The term foundation is frequently used indifferently for either the lower courses of a structure of masonry or the artificial arrangement, whatever its character, on which these courses rest. For greater clearness, the term foundation will here be restricted to the artificial arrangement, whether timber or masonry, which supports the main structure; and the prepared surface upon which this artificial structure rests will be called the bed of the founda tion. There are some cases in which this distinction can not be adhered to strictly.
The foundation, whether for the more important buildings or for bridges and culverts, is the most critical part of a masonry structure. The failures of works of masonry due to faulty workmanship or to an insufficient thickness of the walls are rare in comparison with those due to defective foundations. When it is necessary, as so frequently it is at the present day, to erect gigantic edifices—as high buildings or long-span bridges —on weak and treacherous soils, the highest constructive skill is required to supplement the weakness of the natural foundation by such artificial preparations as will enable it to sustain such massive and costly burdens with safety.
Probably no branch of the engineer's art requires more ability and skill than the construction of foundations. The conditions governing safety are generally capable of being calculated with as much practical accuracy in this as in any other part of a construction; but, unfortunately, practice is frequently based upon empirical rules rather than upon a scientific application of fundamental principles. It is unpardonable that any liability to danger or loss should exist from the imperfect comprehension of a subject of such vital impor tance. Ability is required in determining the conditions of stability;
and greater skill is required in fulfilling these conditions, that the cost of the foundation may not be proportionally too great. The safety of a structure may be imperiled, or its cost unduly increased, accord ing as its foundations are laid with insufficient stability, or with provision for security greatly in excess of the requirements. The decision as to what general method of procedure will probably be best in any particular case is a question that can be decided with reason able certainty only after long experience in this branch of engineering; and after having decided upon the general method to be followed, there is room for the exercise of great skill in the means employed to secure the desired end. The experienced engineer, even with all the information which he can derive from the works of others, finds occasion for the use of all his knowledge and best common sense.
The determination of the conditions necessary for stability can be reduced to the application of a few fundamental principles which may be studied from a textbook; but the knowledge required to determine beforehand the method of construction best suited to the case in hand, together with its probable cost, comes only by personal experience and .a careful study of the experiences of others. The object of Part III is to classify the principles employed in con structing foundations, and to give such brief accounts of actual practice as will illustrate the applications of these principles.