All rock removed which has not been measured by the engineer will not be estimated as rock excavation. Measurement for rock excavation will be limited to 6 inches on either side of the sewer, and trench-slopes of 8 vertical to 1 horizontal. In all cases of blasting the blast shall be carefully covered with heavy timbers chained together, and the engineer may limit the number of simultaneous discharges. Not more than 30 pounds of dynamite shall be kept on hand at one time in any one place.. No blasting shall be done within 40 feet of the finished sewer or 10 feet of an uncovered gas- or water-pipe, and the end of the finished sewer shall be covered or stopped with plank or earth during each blast. (If the sewer-end is not so protected there is a possibility of stones flying into the sewer and also of the concussion of air opening the joints.)

ART. 53.

CONSTRUCTION.

Paragraph 19. Foundations.

When timber or pile

foundations other than those shown in the plans are necessary, in the opinion of the engineer, special designs will be furnished the contractor, who, in accordance with such designs, shall place such foundations in position satisfactory to the engineer. Planking in platforms shall be laid in the manner directed, closely joined, and each plank spiked to each cap or sill with nails or spikes of a length at least 2 times the thickness of the plank. If cradles or platforms are laid directly upon the ground this must be graded perfectly even and smooth to receive them and give a good and firm bearing throughout. If caps or sills are used the spaces between them and under the planking must be filled with good earth thoroughly rammed.

Where piles are used they shall be driven to refusal, unless extending more than 10 feet below the foundation, when they

shall show a penetration in inches under the final blow not wh greater than L

1, in which L is the weight to be borne

by each pile, w is the weight of the hammer in pounds, and h its fall in feet. After driving, the piles shall be sawed off truly and evenly at the proper elevation for receiving the caps, which shall be fastened to them with 1-inch drift-bolts of a length twice the depth of the sill, holes for such bolts having first been bored with a 3-inch bit. If any pile shall be out of line more than the diameter of its upper end the engineer may refuse to estimate it and may order another driven in its place.

Concrete or stone-masonry foundations shall be constructed where ordered in a manner similar to that specified for "Concrete" and "Stone Masonry."

Paragraph 20. Concrete. - Concrete, unless otherwise specified, shall be composed of I part by bulk of natural cement, 3 parts of sand, and 5 parts of broken stone, gravel, or furnace-slag of approved quality, free from dust and dirt and broken so as to pass in every way through a 2-inch ring. All material shall be actually measured for each batch, the cement compacted in barrels as received (or, if received in bags, an equivalent quantity as ascertained by trial), the sand and stone in similar barrels or specially prepared boxes. In mixing, the sand shall be spread out upon a suitable platform or box and the cement deposited upon this; these shall then be thoroughly mixed dry until the whole is of an even, uniform color, when sufficient clean water shall be added to form a thick paste. The stone, which has previously been thoroughly wet, shall then be added and the whole shall be quickly and thoroughly mixed, until every stone is coated with mortar, water being gradually added by sprinkling, if necessary, to obtain a better consistency. If mixing be done by machinery it shall produce a mixture equally as good as by

the above method. Concrete must not be mixed in quantities greater than required for immediate use, and any which has begun to set shall not be retempered or used in any way. Concrete shall be deposited in layers not to exceed 9 inches in thickness, and settled by thorough light ramming, sufficient to bring water to the surface. One course shall follow another as rapidly as possible. Where fresh concrete is to be placed in contact with that already set or partly set all loose stone or concrete not thoroughly compacted shall be removed from the surface of the latter, which shall be washed clean of all dirt and given a thin coat of mortar. If such a surface be hard set it shall previously be thoroughly water-soaked. When concrete is in place all wheeling, working, or walking on it must be prevented until it is firmly set, and until such time it shall be kept damp and protected from the sun.

Such forms and centres as may be necessary to give the finished concrete the desired form shall be furnished by the contractor without extra charge. These shall be sufficiently stiff and substantial to retain the concrete firmly in place, and shall not be withdrawn until the same has set to the satisfac tion of the engineer. No concrete shall be made or used when the temperature is below 35° Fahr. without the permission of the engineer, whose instructions and restrictions for such use shall be followed. (When an entire sewer is composed of concrete a better quality, generally made of Portland cement, is used for the invert, and the inside is plastered.)

Paragraph 21. Stone and Brick Masonry.-Stone and brick masonry, unless otherwise specified, shall be laid with mortar composed of 1 part by measure of natural cement to 2 of sand, mixed as specified for concrete mortar. No mortar shall be used after it has set or partially set.

Stone masonry must be laid true and by line and built of the exact dimensions shown in the plans of the work. All stones shall be laid upon their natural beds and roughly

squared on the joints, beds, and faces, the stone breaking joints at least 6 inches, and with at least one header for every three stretchers. Headers shall be at least 3 feet long or extend entirely through the wall. No stone once bedded shall be lifted by spalling, but any spalls used must be embedded in the mortar before setting the stone. Each stone shall be floated to place in a full bed of mortar and every joint thoroughly filled with the same. No dressing of stone upon the wall will be allowed. (For river- or retaining-walls further specifications should be added as to thickness of joints, character of face dressing, etc.)

For brick masonry in straight walls or sewers none but whole, sound brick shall be used. For manholes, flush-tanks, and similar work a limited number of half brick may be used, not to exceed of the whole in any case. Unless the engineer direct otherwise each brick shall be thoroughly wetted immediately before being laid. (If the brick absorbs practically no water this wetting should be omitted, as likely to cause the brick to slide on the mortar and cause uneven work.) It shall be laid with a full, close joint of cement mortar on its bed, ends, and side at one operation. In no case is mortar to be slushed in afterward. Special care shall be taken to make the face of the brick-work smooth, and all joints on the interior of a sewer shall be carefully struck with the point of a trowel or pointed to the satisfaction of the engineer. Where pipeconnections enter a sewer or manhole " bull's-eyes" shall be constructed by laying rowlock courses of brick around them, the cost of such construction being included in the regular price bid for the sewer or appurtenance. Around pipe more than 15 inches in diameter 2 rowlock courses shall be laid.

Brick-work in sewers shall be laid by line, each course perfectly straight and parallel to the axis of the sewer. Joints appearing in the sewer shall in no case exceed inch in width. Sewers shall conform accurately in section and dimensions to

the plans of the same. All inverts and bottom curves shall be worked from templets accurately set, the arches are to be formed upon strong centres accurately and solidly set, and the crowns keyed in full joints of mortar. No centres shall be drawn until the arch masonry has set to the satisfaction of the engineer and refilling progressed up to the crown. They shall be drawn with care, so as not to crack or injure the work. The extrados is to be neatly plastered with cement mortar inch thick, the arches being cleaned and wetted just before plastering. The end of each section of brick sewer shall be toothed or racked back, and before beginning the succeeding section all loose brick at the end shall be removed and the toothing cleaned of mortar. All brick-work shall be thoroughly bonded, adjacent courses breaking joints at least the exposed length of the brick.

Stone blocks shall be laid in Portland-cement mortar composed of equal parts by measure of cement and sand. Joints shall not exceed & inch in width. The face of the masonry shall be such that there shall be no projection beyond the general surface exceeding inch. All joints shall be cleaned out to a depth of inch and pointed with neat Portlandcement mortar. All stone-block work shall be laid in other respects as specified for brick-work.

If there should be any distortion of the sewer before acceptance this shall be corrected by tearing down and rebuilding. No local patching will be allowed, but when repairs are necessary a section shall be removed at least 3 feet long and including the entire arch, or the entire sewer if the defect is in the invert. Leakage of ground-water into the sewer shall be similarly corrected, unless it can be prevented by calking the joints with oakum saturated in cement, with wooden plugs, or other material acceptable to the engineer.

Paragraph 22. Laying Pipe Sewers.-Previous to being lowered into the trench each pipe shall be carefully inspected,