ART. 53. WORK DURING CONSTRUCTION

Giving Line. Since a sewer-trench is seldom more than 12 inches wider at the bottom than the sewer to be placed in it, it is necessary that the trench itself be carefully aligned. For giving alignment, the method recommended is to drive stakes or spikes along the center line of the proposed trench at intervals of about 50 feet. (Spikes may be used in joints of block pavements.) These spikes or stakes should be a uniform distance apart to facilitate finding them.

Giving Grade. For laying pipe sewer, the best method is by means of a cord stretched vertically over the center line of the

FIG. 59.-METHOD OF SETTING GRADE PLANK.

proposed sewer and parallel to its grade. The preferred plan for supporting a cord in this position is to fasten it to a standard or strip of wood that is nailed in a vertical position to a plank which stands upon edge with one end resting upon the ground upon each side of the trench. This plank should extend at least 18 to 24 inches beyond the trench on each side and should be firmly bedded in solid ground so that it cannot possibly settle, and be held upright by a stake driven at each side of it at each end, or by stones and earth banked solidly around the ends. When excavating machinery is used, these planks cannot ordinarily extend above the surface, but can be sunk into the ground entirely below the surface; or the vertical strips that carry the cord can be nailed to the trench bracing. The cord should be strong fish-line or a similar material whose light weight will

prevent unnecessary sagging. If stretched tightly between the grade planks, the amount of sag will be inappreciable unless these planks are too far apart. To minimize the sag, the grade planks should be not more than 33 feet apart, and 25 feet would be better. After the planks on a given stretch of sewer have been set firmly in place, the center line of the sewer is marked on the top edge of each plank, and a standard (a strip of wood about 1 inch by 2 inches by 24 inches) is nailed to each plank so that one edge is just at the center line mark and is truly vertical, the latter being determined by means of a plumb-bob. On this edge is placed a mark exactly a whole number of feet above the sewerinvert immediately beneath it, and a slight notch is cut here to receive the cord. All the notches in each stretch of sewer are placed at the same distance above the sewer-invert and the cord is stretched from one to the other, and is therefore at every point the same distance above the sewer-invert and vertically over it. If it is desired to change this distance above the sewer-invert,

FIG. 60.-GRADE ROD.

such change is made by cutting in the edge of one of the grade standards two notches to receive the grade cord which are exactly 1 or 2 feet apart in elevation, as may be desired. A grade plank must of course be placed at every change of line or grade.

In measuring from the cord to the sewer-invert, a grade rod is used, consisting of a rod of white pine or other light wood, to the bottom of which is attached an offset piece which can rest on the inside of the end of the pipe. Such an offset is preferably made of a piece of wrought iron about or of an inch thick, and stiffened by being bent back upon the rod as shown in the illustration.

Another method employed for giving grade is to drive stakes to grade along the center line in the bottom of the trench. A third methodi to drive stakes in the ground surface near the edge of the trench, their tops a uniform or stated distance

above the sewer grade, such distance being measured down to the sewer by means of rod and spirit level. Neither of these is recommended for pipe sewer, but the former may be used to advantage in setting templets for constructing concrete or brick sewers. If the grade board method is used for sewers built in place, the cord may be stretched only when the templets or forms are being set, being removed at other times so as to be out of

the way.

Grade planks should be tested for grade and line at least once a day, and the inspector should keep close watch to see that they are not disturbed and that the cord is kept taut. Where running sand is found in the trench, the banks may settle several inches during construction, carrying the grade planks with them; and where this occurs it may be necessary to keep a level constantly on the ground and check the grade planks every few minutes during the time pipe is being laid.

Inlet- and house-connections should be laid as truly to line and grade and in the same way, as the sewer itself.

Keep careful notes of all instrumental work connected with giving line and grades. (See Art. 54.)

It is convenient to keep in the level notebook a list of all bench marks in the sewer district in which it is to be used.

Passing Obstructions. Inspector, engineer and contractor should watch for the first indication of the existence in the trench of an obstruction to the sewer, so that preparation may be begun immediately for a change in line and grade, if necessary, to pass the obstruction. Such change, if in line, may necessitate inserting one or two additional manholes; if in grade, it may sometimes be made by a flattening of grade in one stretch and an increase of grade in the next, or by an inverted siphon. If possible, the change should be made in the obstruction and not in the sewer.

Locating Branches. The inspector should see that branches for house-connections and inlet connections are inserted at the proper points and the exact locations noted; which locations the engineer must make note of and reference to some fixed point, usually the center of the nearest manhole, to make possible the

ready finding of the branches in the future. This is very important, and should be faithfully attended to. In addition, some engineers bury in the trench a stake or steel rod standing vertical above each branch and rising to the surface or a few inches below it, which can be found by a plumber soon after he begins to excavate for a connection.

Inspector's Duties. Among these are the following:

Be on hand before work is begun, at morning or noon, to see that no partly set mortar is worked over, and that the new mortar is properly proportioned and mixed.

See that grade boards are not disturbed and that grade lines are taut.

See that no dirt enters or remains in the sewer while being laid.

Examine each pipe before it is lowered into the trench, and each load of brick, sand, cement or other material as it is delivered on the work, to see that they meet the specification require

ments.

See that each pipe or each templet is set to grade, using grade rod and plumb-bob for this purpose.

Mark the position of each branch for house- or inlet-connection by a stake driven in the bank directly opposite it, indicating the side of the street toward which the branch points. See that covers are cemented in each branch (to prevent dirt or ground water from entering the sewer).

See that arch centers and concrete forms are set solidly to proper line and grade and do not spring or settle, and are not removed before the concrete is sufficiently set.

See that backfilling is placed and tamped as required by the specifications.

Keep a record of all extra work, of foundations and of sheathing left in trench or similar work that cannot be measured after the completion of the sewer.

See that no ground water flows over concrete or brick-work or through the pipe laid, except as may be ordered by the engi

neer.

Engineer's Duties. The engineer or his assistant should visit

each part of the work at least once a day and give necessary instructions to inspector and contractor, as well as giving and testing line and grade.

See that each inspector makes a daily written report of the work done in his section, preferably upon blanks furnished for

the purpose.

Decide where and how much sheathing shall be left in the trench.

Classify materials excavated, measuring promptly any classified as rock.

Measure each stretch of sewer and the depth of each manhole as soon as completed.

See that the contractor keeps streets and sidewalks open where possible, places such shoring and sheathing as may be necessary to prevent accidents to property or lives, provides pumps adequate for handling all ground water encountered, uses laborers in sufficient number and of the requisite skill, uses excavating machinery where necessary; and in general, that he conforms to all requirements of the specifications.

ART. 54. NOTES AND RECORDS

Each manhole, lamp-hole, flush-tank, and inlet should be designated by a number. It is almost impossible otherwise to correctly count and keep track of these, especially the manholes, so many of which are each common to two lines of

sewers.

A final-estimate book should be kept, in which is entered an exact statement of each piece of work as it is completed, but not before then. The measurements should be classified under the items for which bids were received, and the location of each given; thus: