05-455B TRENCH EXCAVATION, BEDDING AND BACKFILL SECTION

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1 SECTION GENERAL 1.1 SCOPE: A. This work consists of trench excavation, trench foundation, pipe bedding, pipe zone material, trench backfill and removal or disposal of material in the installation of sewer lines, culverts, conduits, conductors and appurtenances. This work also includes but is not limited to sheeting, shoring, bracing, dewatering, importing of material and disposal of unsuitable material. B. Unless otherwise provided in the contract, other work required under this item shall include the removal of structures or portions thereof, grubbing of structure sites which are in the trench zone, the construction and removal of shoring or cofferdams, the dewatering of excavated areas, and the placement and compaction of excavated or imported material. Work under this section shall conform to all federal, state, and local safety regulations. 1.2 RELATED DOCUMENTS: A. Drawings and general provisions of the Contract, including General Conditions and other Division 1 specification sections, apply to work of this section. B. Section 02205: Soil and Aggregate Materials 1.3 MATERIAL APPROVAL: A. All backfill, fill, and other construction materials shall be approved prior to their use. All sampling and testing necessary for the Contractor to receive approval by the Engineer and substantiate compliance with the material specification requirements shall be done at the Contractors expense. B. Approval of construction materials shall be based on an inspection of the onsite material and documentation submitted by the Contractor to the Engineer. All materials delivered to the site prior to approval by the Engineer are at the Contractors risk. If variations in materials occur or if materials appear to depart from the specifications, testing by the Contractor may be directed by the Engineer. The Engineer reserves the right to independently sample and test construction materials prior to their use.

2 SECTION C. Material that does not conform to the specification requirements and is placed on site or in the work shall be removed and replaced at the Contractors expense. 1.4 QUALITY ASSURANCE: A. Codes and Standards: Oregon State Highway Division (OSSHC), Standard Specifications for Highway Construction, Current Edition. B. American Association of State Highway and Transportation Officials (AASHTO) C. American Society for Testing and Materials (ASTM). 1.5 JOB CONDITIONS: A. Existing Utilities: The locations of existing underground utilities are shown in an approximate location only and have not been independently verified by the Owner or its representative. The Contractor shall determine the exact location of all utilities before commencing work, and agrees to be fully responsible for any and all damage, which might be occasioned by the Contractor s failure to locate and preserve any and all underground utilities. B. Should piping or other utilities be encountered during construction, notify Engineer immediately for direction or procedure. C. Do not interrupt existing utility service unless permitted in writing by Engineer and then only after temporary utility services have been provided. D. Repair damaged utilities to the satisfaction of the Owner at Contractor s Expense. E. The Contractor shall be responsible for all backfill, utility placement, compaction, surface replacement and all other activities associated with utility installation.

3 SECTION MATERIALS 2.1 TRENCH FOUNDATION STABILIZATION: A. Foundation stabilization shall be 3 inch minus rock, pit run or bar run, well graded from coarse to fine, and free from excessive dirt or organic material. Foundation stabilization shall be the same as Type D fill as listed in Section PIPE BEDDING: A. Pipe bedding material shall be crushed rock with a maximum size of 1 inch, clean sand, or pea gravel, well graded from coarse to fine. Pipe bedding shall be the same as Type B or Type C fill as listed in Section TRENCH BACKFILL MATERIAL: 3.0 WORKMANSHIP A. Standard trench not located in vehicular traffic areas shall be Type A fill as listed in Section 02205, clean native or common material. B. Trenches under vehicle travel ways shall be backfilled with granular material consisting of Type B or C fill. Native material may be substituted in trench lines for Type C fill, only approved in writing by the Engineer. Native material utilized in place of Type C fill shall be clean native sand. 3.1 PREPARATION OF RIGHT-OF-WAY: A. Where clearing of the right-of-way is necessary, it shall be completed prior to the start of trenching. B. The contractor shall exercise care not to unnecessarily remove existing tree limbs, or shrubbery on public or private property, unless they are within five feet of the pipe centerline, without written permission from the Engineer. Overhanging signs, canopies, or structures shall not be removed without written permission from the Engineer. 3.2 PAVEMENT, CURB. AND SIDEWALK REMOVAL:

4 SECTION A. Pavement, curb and sidewalk to be removed in the course of construction shall be neatly cut regardless of thickness, prior to excavation of the trenches. Equipment used for cutting shall be a pavement saw, jackhammer, hydrohammer, or approved pavement cutter. Width of the pavement cut will be the 6 inches wider than the width of the trench at the ground surface. Pavement removed shall be removed from the site and not used for trench backfill, unless they meet the requirements for backfill specified herein. 3.3 OPEN TRENCH LIMIT: A. The length of open trench shall be kept to a minimum. In normal cases, the open trench shall not exceed 300 feet. The Engineer may allow longer segments based upon work conditions. Related construction such as pavement, road gravel, concrete restoration, etc., shall be completed as soon as possible but within no more than 1000 feet of the open trench. 3.4 TRENCH WIDTH: A. Trench width at the ground surface shall be kept to a minimum, but in no case shall be less than 12 inches. Sheeting requirements shall be independent of trench width. As a standard, trench width shall provide a minimum clear working space of 4 inches outside the maximum diameter of the pipe on each side in the pipe zone. B. When approved by the Engineer, the Contractor may, at no additional cost to the Owner, use pipe of greater strength or install a superior pipe base in lieu of maintaining the trench widths as shown. C. Confine trench widths to a minimum, dispose of excess material in designated disposal sites or off site. 3.5 TRENCH GRADE: A. The Contractor shall excavate the trench, or supervise the excavation, to the lines and grades shown or as approved by the Engineer with proper allowance for pipe, bedding, and base thickness. If the trench is excavated below the required grade, correct the part of the trench which is over excavated at no additional cost to the Owner with the type of material specified for pipe base or bedding. Place the material over the full width of the

5 SECTION trench in layers not exceeding 8 inches deep and compact each layer to a density of 95 percent of maximum as determined by ASTM D-698 to the established grade. 3.6 DISPOSAL OF EXCESS MATERIAL: A. Excess material remaining after the completion of trench backfill, or material not allowed to be placed in the backfill will be hauled away and placed at locations and in such a manner that it does not create a hazard to pedestrian or vehicular traffic, or interfere with the function of existing drainage. Wasted material shall be neatly placed, compacted, and graded to match existing ground as much as possible. Disposing of all excess materials shall be considered incidental to trench excavation. 3.7 TRENCH PROTECTION: A. The Contractor shall provide the materials necessary to protect the trench at all times. Sheet and brace the trench when necessary to prevent caving during excavation of unstable materials, or to protect adjacent structures, property, workmen, the public, and paving. Excavated materials shall not obstruct any private or public traveled roadways, streets or driveways longer than necessary and shall be located as to not exceed the safe loading of the trench. The method of trench protection used shall according to the contractor s design, and meet all applicable safety requirements of the federal, state, and local safety codes. 3.8 COMPACTION CONTROL AND TESTING: A. All trench shall be compacted in layers and to the densities specified herein. Maximum density, as used in these specifications, shall be defined as the maximum density obtained by ASTM D 1557 (AASHTO T-99), Method A or C, Standard Proctor using a 5.5 pound hammer and 12 inch drop. In place density of compacted backfill will be determined in accordance with ASTM D 1556, or by nuclear density test procedures in accordance with ASTM D 2922 and ASTM D B. It shall be the responsibility of the Contractor to achieve the specified compaction for all classifications of backfill. The Contractor shall control his operations by conducting his own confirmation tests as required to verify and confirm that he is

6 SECTION complying at all times with the requirements of these specifications concerning compaction control and testing. C. The Contractor shall demonstrate the adequacy of compaction equipment and procedures before exceeding the original 200 lineal feet of trench backfill. Once the Contractor has established his method as meeting the requirements of this section, and as long as the backfill or character of the trench does not materially differ, additional testing is not required unless the Engineer's random testing demonstrates the trench compaction does not meet the specified requirements. If the backfill, trench conditions, or the Contractors compaction methods change, the Engineer may require the Contractor to re-demonstrate his methods as achieving the specified compaction requirements. Failure of the backfill to achieve the specified density will be just cause for rejection of all or any portions of the backfill tested. D. If compaction fails to meet the specified requirements, the Contractor shall remove and replace the backfill or fill at the proper density or shall bring the density up to specified level by other means acceptable to the Engineer. Costs of excavating, backfilling, and compaction in connection with compaction testing specified shall be borne by the Contractor and considered incidental to the trench excavation and backfill. 3.9 BACKFILL METHODS: A. Backfill Types: 1. Type A Backfill: Type A backfill shall be used in areas without surface improvements, other than vegetation. Backfill the trench above the pipe zone with backfill material. Determine and provide the type of compaction equipment, method to use, and the amount of compaction to prevent subsequent settlement. The backfill shall be slightly mounded so that at the end of the performance period the excavated and backfilled area finished surface meets the existing adjacent grade. 2. Type B Backfill: Type B backfill shall be used in areas where specified on the drawings, or in crossings of the Oregon State Highways. Backfill the trench above the pipe zone with backfill material. Top of rock elevation shall be held

7 SECTION down at least the thickness of the of the paving in areas to receive pavements. All type B backfill will be placed in 8 inch lifts and compacted to 95 percent of optimum density in accordance with AASHTO T Type C Backfill: Type C backfill shall be used in areas where specified on the drawings, or in any area under paving or sidewalk area that is not specified otherwise. Class C backfill shall be used above the pipe zone and below the base rock. All class C backfill shall be placed in 12 inch lifts and compacted to 95 percent of maximum density in accordance with AASHTO T Type D Backfill: Type D backfill shall be used as foundation stabilization or where specified on the drawings. Type D backfill shall be used as pipe zone base material, or between the pipe zone and the pavement base. Type D backfill shall not be used in the pipe zone. All type D backfill shall be compacted to a minimum of 92 percent relative density. B. Foundation Stabilization: When voids or other subsurface conditions unsuitable for support of pipe are present, over excavate the trench to remove unsuitable material as directed and backfill the trench to the pipe base with Type D backfill. Minimum depth of foundation stabilization shall be 6 inches. C. Removal of Water: Take all precautions to prevent water from entering the excavation. At all times provide and maintain ample means and devices to promptly remove and dispose of water which enters the trench during the time the trench is being prepared for pipe laying, the pipe laying and during backfill operations. Dispose of the water in a manner to prevent damage to adjacent property, silting in of other pipes and contamination of groundwater. D. Pipe Zone Material: Pipe zone material shall be a minimum of 4 inches below the pipe, the full width of the trench, and a minimum of 6 inches above the pipe. Prior to placing the pipe zone material, remove all loose or foreign materials form the trench. Hand grade the trench to proper grade ahead of the pipe laying. Pipe zone material shall be compacted as specified for Type C Backfill, with allowance for pipe laying requirements when using mechanical compaction equipment. Hand compact the pipe zone material around the pipe. Impact compactors shall not be used until

8 SECTION sufficient cover, as recommended by the pipe manufacturer, has been placed over the top of the pipe. E. Trench Backfill Above Pipe Zone: When backfill is placed mechanically, push the backfill material onto the slope of the backfill previously placed and allow to slide down into the trench. Do not push backfill into the trench in such a way to allow free fall of the material until at least two feet of cover is provided over the top of the pipe. Under no circumstances permit sharp, heavy pieces of material to drop directly on to the pipe or the compacted material around the pipe. F. Interfering Structures or Obstructions: Where rock, stumps, logs, or structures are encountered in the excavation and not shown on the plans which cannot be efficiently removed with the Contractors equipment, the Engineer may, if requested, make changes in the alignment of the trench. The cost for removal of such structures or obstructions will be considered extra work IF, in the Engineer s sole and absolute judgment, the obstruction or structure could not be efficiently removed and could roots, logs, stumps and debris shall be removed with out additional compensation by the Owner. G. Tunneling, Boring, or Jacking: Tunneling, boring, or jacking may be used as a method in lieu of open trench excavation if approved by the Engineer. The Contractor shall first show just cause and furnish the Engineer with a construction schedule outlining methods, time schedule and proposed safety measures to be incorporated in the construction. If this method is approved, the Contractor shall pothole the construction every 50 feet or as approved by the Engineer to demonstrate that the proper line and grade is being followed. 3.9 SURFACE REMOVAL AND REPLACEMENT: A. Topsoil: When specified and where reasonable topsoil conditions exist, the Contractor shall remove the topsoil to the specified depth and place the material in a stockpile. The Contractor shall not mix the topsoil with other excavated material. After the trench has been backfilled, the topsoil shall be replaced. 1. In lieu of stockpiling the existing topsoil, the Contractor may substitute approved imported topsoil to a depth specified, at no expense to the Owner.

9 SECTION The Contractor shall maintain the finished grade of the topsoil level with the area adjacent to the trench until final acceptance of by the Engineer and shall repair any damage to adjacent topsoil caused by work operations. B. Pavements, Curbs, and Sidewalks: All surface improvements shall be trimmed back to a neat edge and any damaged, lifted, or broken pavement shall be removed. Base course shall be placed and compacted in place. Base thickness shall be in accordance with the standard details incorporated into these specifications. When asphaltic concrete is to be placed, all manholes, pavement edges, valve boxes, curb faces, cleanout frames, etc., shall receive an asphaltic tack coat. Surface improvements shall be placed and compacted in place in such a manner that if a straight edge is placed across the patched area and along the edges of the old surfacing and the new surface, the new surface shall not deviate from the straightedge more than 1/4 inch. 4,0 MEASUREMENT AND PAYMENT 4.1 Measurement: No separate measurement shall be made for the Work described in this section. 4.2 All work associated with trenching for drainage piping, water piping, electrical improvements an miscellaneous improvements shall be included under the lump sum items for Drainage Improvements or Furnish & Install Irrigation Piping or other lump sum items, whichever is appropriate as listed in the proposal. END OF SECTION