"SECTION 2000 – TRENCH EXCAVATION AND BACKFILL"
SECTION 2000 – TRENCH EXCAVATION AND BACKFILL TRENCH EXCAVATION AND BACKFILL PART 1 – GENERAL 1.01 Section Summary A. Trenching, backfilling, and compacting of underground infrastructure. 1.02 References A. North Dakota Department of Transportation “Standard Specification for Road and Bridge Construction” 2008 Edition, As Revised. 1.03 Submittals A. Gradation of each granular borrow material B. Compaction Test results 1.04 Definitions A. Bedding Material: Soil material surrounding the pipe that provide structural support, and secures the pipe true to line and grade. B. Pipe Foundation: Soil material below the pipe that provides support. C. Improved Pipe Foundation: Material used when unstable materials are encountered and added pipe support is needed. D. Pipe Zone: The area of the trench measured from 1 foot above the pipe to the bottom of the excavation. E. Sand Cushion: Aggregate bedding used around the pipe in the trench. 1.05 Warranty A. Any trench settlements that occur during the warranty period shall be repaired in a manor acceptable to the Owner and at the expense of the Contractor. PART 2 – PRODUCTS 2.01 Pipe Bedding Material A. Bedding material shall be screened pit run or crusher run sand. 1. No onsite granular material may be used for bedding. 2010 City of Minot 1 Trench Excavation and Backfill 2. Gradation shall be a material that is graded from course to fine such that the portion passing the #200 sieve divided by the portion passing the 1 inch sieve may not exceed 10 percent by mass. 2.02 Improved Pipe Foundation A. Conform to NDDOT Spec 816.03B Class 2 Permeable Trench Backfill. 1. No onsite granular material may be used for improved pipe foundation. 2.03 Trench Backfill Material A. Suitable excavated materials from trench excavation shall be used. B. Material shall be free from organic materials, frozen clumps, large rocks, concrete and bituminous chunks, rubbish, and other materials deemed unsuitable. C. Questionable materials shall be reviewed by the Engineer before backfilling shall begin. The Contractor shall proceed at their risk if the Engineer was not consulted. PART 3 – EXECUTION 3.01 Existing Utilities A. The Contractor shall protect all utilities that interfere with trench excavation. The Contractor shall be required to remove and restore or protect the utility. B. The inverts of existing utilities shall be protected during construction. The Contractor is responsible for inspecting and cleaning, if necessary, all lines which have been compromised by construction activities. C. Backfill and compact around all existing utilities to 100 Percent Standard Proctor Density. D. Report and repair damage to utilities prior to backfill operations. 3.02 Trench Construction A. Construct trench to line and grade shown on the drawings or as directed by the Engineer. B. Excavate to a depth 6 inches below the bottom of the pipe to allow for bedding materials to be placed. 2010 City of Minot 2 Trench Excavation and Backfill C. Apply bedding materials in 6 inch lifts and compact to 95 Percent Standard Proctor Density or as recommend by the pipe manufacturer, whichever is denser. D. Remove any bedding and backfill that enters the pipe. E. Check line and grade of pipe for conformance to the drawings. Correct any deficiencies. 3.03 Trench Backfill A. Backfill material around all manholes, catch basins, valve boxes, curb boxes, and hydrants shall be compacted with hand operated motorized compactors. The maximum lift thickness shall be 6 inches. B. All manholes, catch basins, valve boxes, water vaults, and miscellaneous structures shall be backfilled with granular bedding material and shall be compacted with hand operated motorized compactors. C. Flexible Pipe Materials 1. Granular bedding shall be provided, placed and compacted around the pipe to an elevation 12 inches above the pipe the full width of the trench. Bedding shall be compacted to 95 Percent Standard Proctor Density. D. Rigid Pipe Materials 1. In ordinary trench conditions, granular bedding shall be used to the haunch line and compacted to 95 Percent Standard Proctor Density. E. All trench backfilling operations shall use suitable backfill and shall be compacted to 95 Percent Standard Proctor with ± 3% optimum moisture content except the top 3 feet below the subgrade elevation which shall be compacted to 100 Percent Standard Proctor with ± 3% optimum moisture content. F. Imported backfill shall be used as directed by the Engineer. The imported backfill shall be mixed with the onsite material to obtain the proper soil compaction. If in the Engineer’s opinion, the onsite material cannot be compacted to specification, the Engineer shall direct the onsite material to be removed as muck excavation. 3.04 Field Quality Control A. Density tests shall be taken as specified in Section 600 of this Specification. The Engineer may determine that additional tests should be taken. The Contractor shall assist the Engineer in conducting the tests. 2010 City of Minot 3 Trench Excavation and Backfill B. Any failing tests shall be excavated and re-compacted until the density requirements are met. 3.05 Measurement and Payment A. Trench Excavation: Excavation and backfill of trench and pipe bedding shall be included in the price of pipe provided. B. Improved Pipe Bedding: Shall be paid for by lineal foot (LF) 6 inches deep below the pipe bedding. Payment shall include Geotextile fabric. The required overlap and sewing of the joint shall be incidental. 1. For example, if a 2 foot thickness of improved pipe bedding is required, the payment would be for 3 – 6 inch lifts totaling 3 feet of quantity for each lineal foot of pipe installed. 2. No payment will be made unless directed by the Engineer. 3. No payment will be made for rock used for dewatering purposes unless specified. C. Imported Backfill: Shall be measured by the cubic yard (CY) compacted and will include all labor and costs to excavate, load, haul, and place the materials. The Engineer will cross section the original material and final cut and the average end area will be used to compute the volume excavated. D. Temporary Bracing or Sheeting: Considered part of excavation costs and no extra payment shall be provided. E. Dewatering: Shall be considered incidental unless a bid item is provided. F. All other work and costs of this Section shall be incidental to the Project. END OF SECTION 2010 City of Minot 4 Trench Excavation and Backfill