engineer. In this case the drawings usually are self-explanatory even to the extent of indicating the materials to be used, so that the written specifications need not describe the work as to its form and dimensions, but are only descriptive of the work in a general way.

117.

Specifications Accompanying a General Plan Only. In this case the bidder is asked to submit detail plans for the work in submitting his bid, the specifications being so framed, however, as to reduce all designs which fully comply with these requirements to a common standard of value. To accomplish this purpose the engineer must be able to foresee practically all the various designs which may be submitted, and to anticipate all the advantages in economy which are likely to control the preparation of these designs, and to make such requirements in the specifications as, when complied with, will in his opinion give products of equal efficiency, capacity, and permanency. In this way the engineer gets the advantage of the experience and of the inventive genius of all the persons bidding upon the work, with the chance that he may secure a better design than he himself would have been able to prepare, and also one which may cost materially less than his own design. As an illustration of this kind of specification, we may have a bridge or roof truss of a particular general design, the outline drawing showing simply the general dimensions, and the location of the members, this fixing the general style of truss, which for some particular reason the engineer wishes complied with. The contractor is then asked to build a truss on these general lines in compliance with the accompanying written specifications.

118. Specifications Unaccompanied by Plans, Known Commonly as General Specifications. In this case no plans whatever are submitted, but only the most general requirements to be satisfied. As, for instance, in the case of a bridge, the total span, the loads to be carried, the

character of the stream to be bridged (this determining the character of false works required, and often determining the character of the superstructure itself), the kinds of materials to be used in its construction, the maximum unit stress allowed in the various parts, etc. Or if the contract is for machinery, the specifications may define the amount and kind of work to be done, which fixes the capacity of the apparatus. They would also define the efficiency or economy of operation of the plant, and make various requirements in regard to the material used, and methods of construction which would be supposed to govern its permanency. In this case, as in the one preceding, the engineer must have constantly in mind in writing the specifications the possibility of complying with them with some kind of cheap product which, while fulfilling the letter of the requirements of the specifications, would not be at all what he hopes to obtain, or what would be consistent with the more standard forms of construction.

ILLUSTRATIVE SPECIFICATIONS OF VARIOUS ELEMENTARY PORTIONS OF ENGINEERING WORK.

119. Scope and Purpose. It is proposed in the following articles to give illustrative examples of what is considered good practice in describing many of the more common elements of engineering construction. The practice pursued in discussing the general clauses in engineering specifications, of first considering the purpose of the clause, and then giving an illustrative example, will be followed here. Frequently, however, more than one illustration will be given, and the sources from which they are obtained will also be indicated. It is thought this arrangement will serve a better purpose than

to give a series of complete specifications of various kinds of engineering work, without a detailed discussion of the several clauses. By the arrangement here used duplication of parts is avoided, and the reasons for the particular descriptions can be given in their proper connection. These reasons will perhaps be more useful to the young practitioner than the particular specifications themselves.

SPECIFICATIONS ON EXCAVATIONS AND EMBANKMENTS.

120. Earth Work, Excavation, and Grading. A specification for excavation, or grading, should satisfactorily cover the following ground:

(a) Location and general description of the work.

(b) As full a description of the character of the materials to be excavated as can be furnished.

(c) A classification of the materials which will be employed, and the methods of measurement.

(d) A description of the lines of limits of excavation and fill, including borrow pits, and waste banks.

(e) The disposition to be made of the excavated materials. (ƒ) The distance to which the material is to be transported, commonly included under the general head of "Haul."

It is always wise for the engineer to determine in advance approximately the character of the material to be encountered and to give to the contractor the benefit of such information. It is not wise, however, for him to guarantee the quality of the material to be as indicated, since this furnishes to the contractor grounds for claims which the engineer will find it difficult to adjust. The character of the material is usually learned approximately by borings along the line of the work. In the case of railroad work it is not customary to do this, but from

the general knowledge of the geologic formations, the various kinds of materials can be fairly anticipated.

The specifications should be very explicit and clear beyond all possibility of doubt in the matter of grades or classification of materials to be encountered, and the methods which will be used in measuring the quantities. Innumerable difficulties are constantly arising in the carrying out of engineering specifications from misunderstandings on these points. Materials encountered in excavation are not only various as to quality, but all gradations are found, so that it is practically impossible to determine where one classification or kind of material ends and another begins. In fact two engineers will often classify the same materials differently under the same specifications, and there is no possibility of determining such questions, except by agreeing to abide by the decision of the engineer. It is best not to have too many classes of materials, and all kinds of materials are usually grouped under three general heads, namely: Earth, loose rock, and solid rock.*

121. Grading. The following specifications for railroad grading are used by the Pennsylvania Railroad:

Under this head will be included all excavations and embankments required for the formation of the roadbed; cutting all ditches or drains about or contiguous to the road; the foundations of culverts and bridges, or walls; the excavations and embankments necessary for reconstructing turnpike or common roads, in cases where they are destroyed or interfered with in the formation of the railroad; and all other excavations or embankments connected with or incident to the construction of said railroad.

All cuttings shall be measured in the excavations, and estimated by the cubic yard, under the follow heads, viz: Earth, Loose Rock, Solid Rock.

Earth-will include clay, sand, loam, gravel and all other earthy matter, or earth containing loose stone or boulders intermixed, which do not exceed in size three cubic feet.

*In the specifications used on the Chicago Drainage Canal but two classes of materials were named, "Solid rock" and "Glacial drift." Where no solid rock was anticipated, but one class was named and this was called "Excavation." Sometimes more than three classes are recognized and provided for when the grades are distinct and well marked.

Loose Rock-shall include all stone and detached rock lying in separate and contiguous masses containing not over three cubic yards; also, all slate or other rock that can be quarried without blasting, although blasting may be occasionally resorted to.

Solid Rock-Includes all rock occurring in masses exceeding three cubic yards, which can not be removed without blasting. The roadbed will be graded twenty feet wide in earth cuttings and fifteen feet in fillings, except where otherwise directed by the engineer, with side slopes of such inclination as the engineer shall in each case designate, and in conformity to such depth of cuttings and fillings as may have been or may hereafter be determined upon by said engineer.

Earth, gravel and other materials taken from excavations (except when otherwise directed by the engineer), shall be deposited in embankments, the cost of removing which will be included in the price paid for excavation. All material neces

sarily procured from without the road and deposited in the embankments will be paid for as excavation only. In procuring materials for embankment from without the line of the road, the place will be designated by the engineer in charge of the work; and in excavating and removing it, care must be taken to injure or disfigure the land as little as possible. The embankments. will be formed in layers of such depth (generally one foot), and the materials disposed and distributed in such manner as the engineer may direct, the required allowance for settling being added.

No borrow pits will be opened nearer than four feet from base of embankment slope, and will receive same slope as corresponding embankment. All borrow pits will be excavated in a regular manner and so as to leave no holes for standing water, generally with a descent at bottom to allow free passage of

water.

Wherever the excavations furnish more material than is required for embankments, the surplus will be used to increase width of embankment, or deposited in spoil banks or waste piles, as and where the chief engineer may direct.

The roadbed, in cuts and on banks, to be made in a workmanlike manner; to be perfectly even and regular according to grade stakes as set from time to time by the engineer in charge, and to be exactly of the width directed.

All slopes to be formed even and straight, according to slope stakes, and to such incline as directed in each case.

All ditches in cuts or along banks to be made of such width

and grade as the engineer in charge may direct.

If the contractor shall make excavations or embankments in excess of the directed width, then such excess shall not be paid for.