SECTION 660: EXCAVATION, TRENCHING, AND BACKFILLING FOR UTILIT IES
660.1 Description
This Work consists of performi ng excavation, trenching, and ba ckfilling for underground utility lines.
660.2 Materials—Reserved
660.3 Construction Requirements
660.3.1 Trenching and Excavation
Grades for underground utility lines are the invert (inside bo ttom of the pipe) unless the Contract specifies otherwise. During excavation, the Contract or shall pile Material suitable for backfill in an orderly manner far enough away from the banks of the trench to avoid ov erloading and to prevent slides or cave-ins. The Contractor shall perform grading necessary to prevent surf ace water from flowing into trenches or other excavations; the Contractor shall remove water that has accumulated by pumping or with other approved methods. The Contractor shall perform trenching far enough in advance o f pipe laying to allow the Project Manager to make necessary grade changes. Unless otherw ise specified in the Contract, the Contractor shall begin backfilling immediately af ter laying pipe and keep pace with pipe-laying operations.
660.3.1 1 Trench Widths
The Contractor shall ensure that trenches are wide enough to p roperly lay, align, grade, and joint the pipe. The Contractor shall dig trenches to at le ast 24 inches wide, but in no case should they exceed 1.4 times the outside diameter of the pipe, plus 24 inches, plus twice the thickness of shoring Structures, at the level of the top of the pipe. The Contractor may use excavation for concrete Structures as t he outside form, if approved by the Project Manager. If trenching is behind a curb, in lawns, or adjacent to Sidewa lks or walls, the Contractor shall ensure that the trench is not wider than the outside diam eter of the pipe plus 24 inches at the trench top. The Contractor shall provide sheeting or braci ng as necessary. The Department will consider over depth excavation not ordered by the Project Manager as unauthorized. The Contractor shall fill the unauthorized ex cavation with granular or compacted embedment Material or concrete, as directed by the Pr oject Manager at no additional cost to the Department.
660.3.1 2 Shaping Trench Bottoms
The Contractor shall accurately grade trench bottoms for pipe six (6) inches or smaller to provide uniform bearing and support throughout the length of ea ch section of pipe. The Contractor shall finish the bottom of the trench by excavating a shallow concave groove at the line of the pipe and shape it appr oximately to fit the pipe. Section 660: Excavation, Trenching, and Backfilling for Utiliti es Page 731 The Contractor shall excavate t rench bottoms for larger pipe t o below the grade line, as necessary, to allow the installation of granular embedment foun dation Material for the pipe. The Contractor shall dig bell holes and depressions for joints after grading the trench bottom so that the full length of the pipe rests on the prepare d bottom. The Contractor shall make these depressions the length, depth, and width necessary t o properly fit the particular type of joint. The Contractor shall not excavate below the specified final tr ench bottom elevation, unless the Contract requires granular embedment foundation Mate rial.
660.3.1 3 Foundations
The Contractor shall remove wet or otherwise unstable soil, in capable of properly supporting the pipe, and backfill the trench to grade with gran ular embedment foundation Material or other suitable Material. If the Contractor excavates deeper than the specified grade, t he Contractor shall backfill the trench to grade with granular embedment foundation Material or other approved Material. The Contractor shall thoroughly tamp the replacement foundation Material to provide a solid bed for the pipe. The Project Manager will determine if Materi al from the trench is Acceptable.
660.3.1 4 Rock Excavation
The Contractor shall remove rock that is not rippable with a r ip tooth, or that occurs in masses larger than 1/2 yd 3 or ledges at least four (4) inc hes thick in accordance with Se ction 203, “Excavation, Borrow, and Embankment.” If the Contractor encounters solid rock during excavation, the Contractor shall excavate to a depth six (6) inches below the outside bottom of the pipe and backfill the trench to the proper grade. If Materials cannot be handled or compacted as earth (includin g rock), the Contractor shall separate them from excavated Materials that the Contracto r shall use as fill or Embankment Material. The Contractor shall dispose of rock separated from fill Mater ial as approved by the Project Manager. 660.3.1.5 Wet Excavation Requirements The Contractor shall keep trenches and other excavations free of water by bailing, pumping, or draining during cons truction operations. The Contr actor shall keep water away from concrete or cement joints until the Materials attain initi al set. The Contractor shall provide the following, as necessary: 1. Cofferdams; 2. Pumps; 3. Drains; 4. Ditches; 5. Well points; and 6. Other means for removing water from the excavations or other parts of the Work and for preventing excavated sl opes from sliding or caving. Section 660: Excavation, Trenching, and Backfilling for Utiliti es Page 732 The Contractor shall dewater for at least 24 h in the vicinity of concrete to allow the concrete to set properly. The Contractor shall dispose of wate r by pumping it into ditches, storm drains, or sanitary sewer s in accordance with applicable regulations.
660.3.2 Bracing and Sheeting
The Department will allow the Contractor to cut trench banks o n slopes to prevent sliding and caving where the increased trench width will not interfere with surface features or encroach on Right of Way limits. Slopes may not intersect vert ical trench walls more than 12 inches above the top of pipe. The Contractor shall not remove sheeting and bracing until suf ficient backfill is in place to protect the utility Structures and the adjacent Roadway from ca ving damage. The Contractor shall leave sheeting in place if necessary and approved in writing by the Project Manager. The Contractor shall cut off sheeting left in place at least one (1) ft below the ground surface.
660.3.3 Bedding and Backfill
The Contractor shall provide bedding and backfill for utilitie s in accordance with Section
663.1 1, “NMSSPWC Appurtenant Stipulations,” except, the Contractor shall provide
compaction within four (4) ft of pipe and utility appurtenances , under the Roadway Prism, to 95% of maximum dry density as determined by AASHTO T 180 (Modif ied Proctor), Method D (TTCP Modified). If backfilling uncased pipe, the Contractor shall not break, c hip, crush, crack, or otherwise damage the pipe. The Contractor shall backfill polyvinyl chlor ide pipe only if the pipe is 75 °F or below.
660.3.3 1 Backfill Material
The Contractor shall provide backfill Material that, after pla cement and compaction, is capable of supporting the design l oads. The Contractor shall p rovide backfill Material that is free of lumps, debris, other Del eterious Materials, and sharp r ocks, stones, or other objects that might damage the pipe.
660.3.3 2 Backfill Compaction Operations
The Contractor shall compact backfill Material placed around i rregular areas with hand- operated tamping Equipment. The Contractor shall compact ancho r loads for pipe testing and other backfill placed before the regular trench backfill.
660.3.4 Contractor’s Responsibility for Protection of Public Ut ilities
The Contractor shall repair damage to Structures, pipelines, c onduits, cables, sewers, storm drains, or other utilities encountered in or adjacent to the excavation, due to the Contractor's negligence. The Contractor shall use reasonable m easures and precautions, including Blue Stake or One Call, to protect utilities. The Contractor shall locate underground utilities before excav ating and provide support to protect these utilities and av oid damage or interruption in functions. At least seven (7) Days before beginning excavation; the Contr actor shall provide written Section 660: Excavation, Trenching, and Backfilling for Utiliti es Page 733 notification to owners of public utilities that may be affected by construction, so that the owners may make necessary arrangements. The Contractor shall restore or rebuild property damaged by co nstruction operations to at least the condition that existed before the construction operat ions. The Contractor shall get the Project Manager’s approval to rel ocate trench lines to avoid known obstacles. The Contractor shall permanently plug the dea d ends left in the trench from removed abandoned pipes, conduits, or sewers.
660.3.4 1 House Service Connections
The Contractor shall not disturb or damage existing house late ral connections to utility mains. The Contractor shall replace broken lateral connections with the same type pipe or better, at no additional cost to the Department.
660.4 Method of Measurement—Reserved
660.5 Basis of Payment
The Department will pay for aut horized rock excavation in acco rdance with Section 203, “Excavation, Borrow, and Embankment.” The Department will pay for sheeting left in place at the dire ction of the Project Manager at an agreed price that does not exceed the actual Material cos t. Section 662: Manholes Page 734