§ 15.01.590. Corrugated metal (CMP) storm sewer pipe.

A.

CMP general description. This specification covers the manufacture and installation of corrugated metal pipe, for use in storm drains. CMP shall not be used within city road right-of-way unless approved by the city engineer and/or city public works director.

For hydraulic design considerations, a Mannings n value from the following table shall be used for helical two and two-thirds × one-half inch corrugations.

CMP Pipe Diameter (inches)	Manning's n Value
12	0.011
15	0.012
18	0.013
24	0.015
30	0.017
36	0.018
42	0.019
48	0.02
54 and larger	0.021

 

Mannings n values for other corrugation types and sizes can be found through the National Corrugated Steel Pipe Association web site at: (http://www.ncspa.org/pdf/hydraulics.pdf)

B.

CMP material. The steel coils shall conform to the applicable requirements of AASHTO M 274 or ASTM A 929.

C.

CMP pipe. Pipe size shall not exceed twenty-four inches in diameter. The pipe sizes, and gauges shall be as shown on the project plans. Gauges shall be a minimum of fourteen gauge.

D.

Handling and assembly. Shall be in accordance with NCSPA's (National Corrugated Steel Pipe Association) recommendations.

E.

Installation. Shall be in accordance with AASHTO Standard Specifications for Highway Bridges, Section 26, Division II or ASTM A 798 and in conformance with the project plans and specifications. In general, granular (non-plastic) backfill will be required a minimum of twelve inches beyond the pipe O.D. with twelve-inch cover over the top of the pipe. Granular fills must meet AASHTO A-1, A-2, or A-3 and be no larger than one and one-half inches in size. If there are any inconsistencies or conflicts, the contractor must bring them to the attention of the project engineer.

It is the contractor's responsibility to follow OSHA guidelines for safe practices.

Where pipe product is provided with a joint system intended to allow for segmental installation of piping materials, joints shall be closed tightly such that gasket system is fully engaged and no more than one-half inch of gap section between overlapping joint material (bell and spigot or another approved method) is visible via a televised inspection methods. Contractor shall meet with city designated inspection representative prior any construction commencing to review city standards relative to installation of piping system.

F.

Construction loads. Construction loads may be higher than final loads, follow the manufacturer's or NCSPA's guidelines.

G.

CMP pipe joints. Joints shall be made with re-rolled annular ends, with bolt, bar and strap connector, including O-ring gaskets.

H.

CMP pipe laying. All pipe installation shall proceed upgrade on a stable foundation, with joints closely and accurately fitted.

Pipe shall be installed with uniform bearing under the full length of the barrel, with suitable excavations being made to install the gasketed strap connector. Corrugated metal pipe shall be so laid that flow is over the lap of the sheets.

Select material shall be compacted around the pipe to firmly bed the pipe in position. Haunching material (bed to springline) should be carefully worked under the haunches of the pipe and compacted from the pipe to the trench wall (with minimum trench widths sufficient to provide ninety percent compaction). In embankment conditions two and one-half pipe diameters on each side of the pipe will be required to ensure support. If adjustment of position of a pipe length is required after being laid, it shall be removed and re-jointed as for a new pipe. When installation is not in progress, the ends of the pipe shall be closed with a tight-fitting stopper to prevent the entrance of foreign material.

In addition to the above requirements, all pipe installation shall rigidly adhere to the specific requirements of the pipe manufacturer.

All pipe shall be unloaded and handled with reasonable care. Pipe shall not be rolled or dragged over gravel or rock and shall be prevented from striking rock or other hard objects during placement of the bedding. Pipe with protective coatings shall be handled with special care to avoid damage. Interior denting of the pipe that shows violation of this requirement shall cause the pipe to be removed and replaced at the contractors sole expense.

I.

Gravel foundation for CMP pipe. Wherever the subgrade material does not afford a sufficiently solid foundation to support the pipe and superimposed load, and where groundwater must be drained, the subgrade shall be excavated to such depth as may be necessary and replaced with crushed rock or gravel compacted into place.

Gravel for pipe foundation shall be clean crushed rock or gravel with one hundred percent passing a one-inch screen and no more than five percent passing a three-fourths-inch sieve.

J.

CMP pipe bedding. All pipe sewers and drains shall be protected from lateral displacement and possible damage resulting from impact or unbalanced loading during backfilling operations by being adequately bedded.

A groove shall be excavated in the bottom of the trench to receive the bottom quadrant of the pipe. Before preparing the groove, the trench bottom shall be excavated or filled and compacted to an elevation sufficiently above the grade of the pipe so that, when completed, the pipe will be true to line and grade.

Pipe bedding materials placed at any point below the mid-point of the pipe shall be deposited and compacted in layers not to exceed six inches in uncompacted depth. Deposition and compaction of bedding materials shall be done simultaneously and uniformly on both sides of the pipe. Compaction shall be accomplished with hand or mechanical compactors. All bedding materials shall be placed in the trench with hand tools or other approved method in such a manner that they will be scattered alongside the pipe and not dropped into the trench in compact masses. Bedding materials shall be loose earth, free from lumps; sand or gravel, free from rocks larger than one-and-one-half inch diameter; with all materials free from roots, sod, or other vegetable matter.

In the event trench materials are not satisfactory for pipe bedding, modified bedding will be required. Modified bedding shall consist of placing compacted granular material on each side of and to the level of twelve inches above the top of the pipe.

Modified bedding material shall be graded as follows: One hundred percent passing a three-fourths-inch sieve and forty to seventy percent passing a No. 4 sieve and ten to twenty percent passing a No. 50 sieve and less than ten percent passing a No. 200 sieve.

The haunching area of the pipe shall be installed with the modified bedding (See ASTM B788) with compaction being accomplished by hand, without the use of mechanical compaction equipment.

When soft material is encountered and must be removed in order to maintain pipe on grade during construction, it must be removed for at least three pipe widths.

K.

Manhole connections. Manhole riser connections shall be made with re-rolled annular ends, with bolt, bar and strap connector, including O-ring gaskets.

L.

Special considerations. Hydrating cement, grout or concrete mixtures are not allowed to come in contact with the aluminized steel pipe under any circumstances. Noncompliance with this requirement shall cause the contractor to remove and replace the impacted pipe section(s).

(Ord. No. 2007-07-31, §§ 6.8—6.8.12, 7-10-2007; Ord. No. 2010-11-24, § 2, 11-23-2010; Ord. No. 2011-06-17, § 1, 6-28-2011)