A. General: This section includes the requirements for excavation, pipe bedding and backfilling for pipelines, services and appurtenances.
B. Materials:
1. Type I pipe bedding shall be in accordance with type I pipe bedding per the current edition of the Idaho standards for public works construction, section 305, Pipe Bedding. Pea gravel and poorly or uniformly graded crushed stone shall not be allowed.
2. Type II pipe bedding shall be in accordance with type II pipe bedding per the current edition of the Idaho standards for public works construction, section 305, Pipe Bedding.
C. Execution:
1. Clearing The Right Of Way: Where clearing of the right of way is necessary, it shall be completed prior to the start of the trenching. Brush shall be cut as near to the surface of the ground as practicable and removed to an approved disposal area. The contractor shall observe all federal and state laws relating to hauling permits and local regulations relating to burning and/or otherwise disposing of such materials. Under no conditions shall excavated materials be permitted to cover brush prior to clearing and removing same.
2. Obstructions: This item shall refer to obstructions that may be removed and do not require replacements. Obstructions to the construction of the trench, such as, but not limited to, tree roots, stumps, abandoned concrete structures, and debris of all types shall be removed by the contractor. The city engineer may, if requested by the engineer, allow changes in alignment to avoid major obstructions if such alignment changes can be made without adversely affecting the intended functioning of the facility.
3. Removal Of Topsoil:
a. In all cases where trenches cross cultivated fields or other areas on which topsoil exists, the topsoil shall first be removed for the depth of twelve inches (12") for the full width of the trench to be excavated. This topsoil shall be stockpiled to one side of the right of way and not mixed with the remaining excavated material. The topsoil shall be replaced in the top one foot (1') of the backfilled trench.
b. The surface of the trench and other disturbed areas shall be brought to a true and even grade to match the adjacent lawn or cultivated areas. All rocks, debris, roots, clods and deleterious material unearthed or encountered shall be removed and disposed of. The finished surface shall be free from humps, depressions and other irregularities.
4. Trenches:
a. Trench excavation shall be to line and grade as established by the engineer. The bottom width of the trench shall be as shown on the city of Hailey standard drawings for the size of pipe installed.
b. The trenches shall be adequately and properly timbered or shored and constructed in conformance with all applicable regulations. It shall be the contractor's responsibility to provide and install all shoring, sheeting and bracing, and he shall be responsible for the adequacy of the same. Where the bottom of the trench encounters a material which, in the opinion of the city engineer or his representative, is unstable and not adequate to provide a suitable foundation for the pipe, the trench shall be over excavated to remove the unstable material and then backfilled with an approved pipe bedding material to bring the bottom of the trench back up to grade. Excavation shall extend to at least four inches (4") below the line of the pipe bell and then backfilled with an approved pipe bedding material to form a cradle for the pipe. The final or finished grade, including bell holes, shall be made just ahead of pipe laying. All irregularities in the trench bottom shall be removed by appropriate excavation and backfilled to provide a minimum of four inches (4") of pipe bedding material under the pipe. Bell holes shall be excavated for bell and spigot pipe of sufficient dimensions to permit pipe laying to work freely and to positively avoid the bell carrying any weight or loading stresses and so that the pipe shall have a firm bearing of not less than three-fourths (3/4) of the length of the barrel. Trenches shall be kept free of water until the pipe is laid, joints completed, and thereafter until jointing material is adequately set.
5. Location Of Excavated Materials: During trench excavation, the contractor shall locate the excavated material so it will not completely obstruct a traveled street or roadway. Unless otherwise approved by the city engineer, all streets and roadways shall be kept open to at least one-way traffic.
6. Removal Of Water: The contractor shall provide and maintain ample means and devices with which to promptly remove and dispose of all water entering the trench excavation during the time the trench is being prepared for the pipe laying, during the laying of the pipe, and until the backfill at the pipe zone has been completed. The contractor shall dispose of the water in a suitable manner without damage to adjacent property, drainageways or irrigation ditches.
7. Gravel Bedding For Foundation Stabilization: If trenches are hampered by unstable, wet parent material or excessive water on the bottom, the trench shall be over excavated and material that meets the requirements of type II pipe bedding per the current edition of the Idaho standards for public works construction, section 305, Pipe Bedding, shall be placed for pipe subgrade. Once the pipe is placed on the bedding and the compaction and stability of the bedding material approved by the city engineer, initial backfill may commence.
8. Initial Backfill: After the pipe lengths have been jointed and jointing material has been properly set to the city engineer's or his representative's approval for backfilling, the bell holes and sides of the pipe shall be carefully backfilled with pipe bedding material and thoroughly compacted with approved tampers. The contractor shall exercise care in placing the initial backfill to ensure the pipe remains centered in the trench. Initial backfill material shall contain no particle larger than one inch (1") for all sizes of pipe. The initial backfill shall be continued in layers of not to exceed six inches (6") in thickness until the backfill is six inches (6") above the top of the pipe using approved pipe bedding material. Each layer of backfill shall be compacted to a minimum of ninety five percent (95%) of maximum density as determined by ASTM D698, as shown on the city of Hailey standard drawings. A copy of the soil inspection report from a certified inspector for this requirement shall be provided to the city engineer. A minimum of one test per two hundred fifty feet (250') of installed pipe shall be performed. Compaction tests shall be performed at the contractor/developer's expense. Under no conditions will puddling be permitted for this initial backfill.
9. Trench Backfill: After initial backfill, trenches may be backfilled with the material excavated provided rocks larger than eight inches (8") and other deleterious material, if present in the excavated material, are removed. Material containing frost shall not be used for backfill. The first one foot (1') of backfill above the initial backfill shall be given careful attention as to composition. The backfill shall be placed in horizontal lifts. The entire backfill shall be firmly compacted by mechanical methods approved by the city engineer or his representative. Compaction shall be to a minimum of ninety five percent (95%) of the maximum density as determined by ASTM D698. A copy of the soil inspection report from a certified inspector for this requirement shall be provided to the city engineer. A minimum of one test per two hundred fifty feet (250') of installed pipe shall be performed per lift. Compaction tests shall be performed at the contractor/developer's expense.
10. Excess Excavated Material: All excess excavated materials from excavation and backfill operations shall be hauled and disposed of by the contractor at locations obtained by the contractor.
11. Surface Runoff Water: The contractor shall at all times protect any open trench from the entrance of surface runoff water within the work area. In the event that water does enter a trench, the city engineer or his representative may require the contractor to furnish foundation stabilization gravel to provide a suitable foundation for laying the pipe. (Ord. 1116, 2012)