(B) Allowable deviation of alignment and grade. The horizontal deviation of the sewer from the line shown on the plans shall be not more than three inches. The sewer grade shall not deviate from the profile shown on the plans, and the grade shall be maintained during and after backfilling operations. Sewer grades with deviations exceeding one-half inch shall be removed and replaced at the contractor’s expense. If deviations less than one-half inch from the design grade occur, pipe joints may be deflected to bring the invert back to grade. Grade corrections shall be made gradually to prevent sags in the pipe invert at low spots. Pipe shall be installed to be free draining (no sags) between any two points. No reverse (adverse) grade will be allowed.
(C) Lasers.
(1) When laying main sewers, unless otherwise approved by the Engineer, the contractor shall use a commercial laser grade setting system.
(2) The following requirements and conditions must be met:
(a) The contractor shall have the responsibility of providing an instrument operator who is qualified and trained in the operation of the laser and said operator shall adhere to the provisions of the State Construction Safety Orders, issued by the Division of Industrial Safety. Attention is particularly directed to §§ 1514, 1800 and 1801 of said orders for applicable requirements.
(b) The laser shall be connected firmly to a tripod, set firmly on compacted soil. The laser height of instrument shall be taken from one offset hub and checked with at least two more hubs, until two or more hubs show consistent readings or until readings coincide. This shall be done every time the laser is set up or disturbed.
(c) The laser and level instruments shall be properly calibrated within six months prior to use. A laser or level instrument found to be out of calibration, or without records showing it has been calibrated within the last six months, shall be removed from the job site until it has been properly calibrated.
(D) Grade line.
(1) When laying pipe for laterals, in lieu of a laser grade setting system, the contractor may use a grade line. When laying the pipe, except where vertical curves are shown on the plans or otherwise authorized by the Engineer, the contractor shall use a grade line with at least two adjacent runs in place at all times in order to detect any variation from a straight grade.
(2) The grade line must be established over the center of the trench in vertical trenches and over the center of the pipe in V-type trenches during the laying operations and grade line shall be maintained until the pipe grade is checked by the Engineer.
(3) The grade line shall be accurately and securely fastened at each staked station to securely erected batter boards and be kept taut at all times.
(4) The measuring pole shall be a solidly constructed straight pole with a metal foot at one end at right angles to the pole. The batter board construction, string line and measuring pole construction shall be approved by the Engineer prior to start of sewer pipe laying.
(5) In caving ground and in other circumstances when the above are not practicable, and when so authorized by the Engineer, the pipe must be checked by surveying instruments under the direction of a registered civil engineer or land surveyor who shall accept the responsibility for the pipe being installed on the proper grade.
(E) Sewer pipe plugs. Sewer pipe stubs, or other open ends, which are not to be connected immediately, shall be plugged or capped with standard watertight plug or cap as approved by the Engineer for use in the particular installation. The plugs or caps may only be removed when so authorized by, and in the presence of, the Engineer.
(F) Joint deflections and minimum radius. When approved by the Engineer, curved sewers shall be in conformance with the following requirements.
(1) Rigid pipe: no deflection of rigid pipe will be allowed.
(2) Flexible pipe: horizontal curves shall be achieved only with approval of the District Engineer and with the use of fused pipe. The minimum allowable bending radius is shown in the following table, which follows the equation radius equals 300 multiplied by pipe diameter. Smaller radii may be approved by the Engineer.
Pipe Diameter (Inches) | Minimum Radius (Feet) |
Pipe Diameter (Inches) | Minimum Radius (Feet) |
4 | 100 |
6 | 150 |
8 | 200 |
10 | 250 |
12 | 300 |
15 | 350 |
18 | 450 |
(G) Verification of existing sewer or structure. Where connection is to be made to an existing sewer or structure, said existing sewer or structure shall be uncovered and checked for location and elevation prior to submitting cut sheets. Discrepancy between the plans and field information shall be reported immediately to the Engineer.
(H) Commencement of new sewer pipe line. Unless otherwise authorized by the Engineer, the laying of the pipe in finished trenches shall be commenced at the lowest point of the project, with the spigot ends abutting and pointing in the direction of the flow. The joints shall be carefully centered so that when laid to proper grade and alignment, as designated on the plans, they will form a sewer with a uniform invert.
(I) Sewer pipe line through manholes. Sewers shall be laid continuously through proposed manhole locations on all straight runs and at angle points. A minimum drop of 0.1 feet is required for mains of the same size. When mains on the upstream and downstream connections to the manhole are different size pipes, the upstream and downstream pipe crowns should be at the same elevation. When excavation is made below the pipe for manhole construction, care must be taken that the pipe spanning this area is firmly supported.
(J) Flexible couplings at manholes. For all pipes, a flexible pipe coupling, such as Gripper Gasket Max Adapter coupling, shall be installed at a point one to three feet outside of the manhole base block on both upstream and downstream sides. In all cases, the flexibility of the coupling must be maintained by keeping all concrete away from the joint or coupling. A bell joint is not acceptable for this requirement.
(K) Placement of fill/grading. Grading of fill in order to change the grade of a parcel shall be placed up to three feet above where the outside of the pipe would be and laterally to a width of the pipe outside diameter plus six feet centered on where the pipe would be and compacted prior to trenching for sewer lines. The compaction requirements, as specified by the agency governing the fill, shall be considered adequate, except that not less than 90% relative compaction per ASTM D-1557 “Modified Proctor” shall be achieved. Evidence of these results in the areas concerned shall be furnished to the District from an approved testing laboratory prior to construction of the affected sewer.
(L) Handling of pipe.
(1) Pipe shall be protected during handling against impact shocks. Prior to making pipe joints, all surfaces of the portion of the pipe to be joined shall be cleaned, dried, primed or otherwise prepared as called for in these specifications. The interior of all pipe shall be kept free from all dirt and foreign matter as the work progresses.
(2) At the close of each day’s work, and at such other times when the pipe is not being laid, the ends of all open pipes shall be closed with a watertight plug or cap. Any modification of this requirement must be approved by the Engineer. (M) Field cutting pipe. Unless otherwise permitted by the Engineer, pipes that must be cut in the field shall be cut with mechanical cutters or as recommended by the pipe manufacturer.
(Ord. 2019-02, passed 4-25-2019)