Horizontal Directional Drilling/On-grade Gravity Bore

1205-1      SCOPE:

1205-1.1  Description:  This Specification covers the installation of pipe or conduit by horizontal directional drilling.  Horizontal directional drilling is a Trenchless excavation method which is accomplished in two phases.  The first phase consists of drilling a small diameter pilot hole along a designed directional path.  The second phase consists of enlarging the pilot hole to a diameter suitable for installation of the pipe or conduit, and pulling the pipe or conduit into the enlarged hole.  Horizontal directional drilling is accomplished using a specialized horizontal drilling rig with ancillary tools and equipment. 

   This application is for gravity sewer pipe, which has a vertical precision much greater than that required for pressure pipe or for waterway or street crossings.  Only Accu-Bore  is the accepted on-grade gravity boring method for this project .  The CONTRACTOR shall use DCI Digi-Trak Eclipse Tracking System to check elevations at 25 foot intervals or less, and shall provide these elevations to the ENGINEER during the course of the work.  Should these elevations show that the installed pipe does not meet the tolerances specified herein, the ENGINEER may stop the work and direct the CONTRACTOR to take remedial measures or to abandon a pipe section at no cost to the OWNER.  The CONTRACTOR shall use Innovative Trenchless System (ITS) pull back equipment for the installation of carrier pipe.

 1205-1.2    Existing Facilities and Utilities:

   A. CONTRACTOR shall undertake the following steps prior to commencing drilling operations in this project location which contains existing underground facilities.

                          1) Contact the utility location/notification service, for the construction area. 

                          2) Locate and stake all existing lines, cables, or other underground facilities. 

                          3) Modify drilling practices and down hole assemblies to prevent damage to         existing facilities. 

             B.         CONTRACTOR shall be responsible for locating any and all underground facilities regardless of any previous efforts in this regard. 

1205-1.4     Contractor Submittals:

              A. Procedure and materials descriptions shall be submitted for approval by the ENGINEER not less than three weeks prior to commencing any horizontal directional drilling activities. 

1205-2        PRODUCTS

 1205-2.1      Pipe:

A.          The installed pull section shall be as described in the Section entitled Gravity Sewer Pipe.  The CONTRACTOR has the option of using either high density polyethylene pipe or restrained joint PVC Pipe. 

1205-2.2      Tolerances: 

A.          Description:  The pilot hole shall be drilled along the path shown on the plan and profile drawings to the tolerance listed.  Regardless of the tolerance achieved, no pilot hole will be accepted if it will result in any or all of the pipeline being installed in violations of right-of-way restrictions.  Any cause for concern regarding conflicts with adjacent utilities and/or structures shall be immediately communicated to the ENGINEER.  Listing of tolerances does not relieve CONTRACTOR from responsibility of safe operations or damage to adjacent utilities and structures. 

B.          Line and Grade: 

             1) When excavation is off line or grade, make alignment corrections to avoid reverse grades in gravity sewers.  A belly in the pipe which will hold water is not acceptable.

             2) Acceptance criteria for the sewer pipe shall be plus or minus 6 inches in horizontal alignment from the theoretical at any point between manholes, including the receiving end, and plus or minus 1 ½ inches in elevation from the theoretical.  The slope of the sewer line may not be less than the slope shown on the drawings. 

             3) Pipe installed outside tolerances will not be accepted.  This pipe shall be abandoned and shall first be fully grouted. 

             4) Pipe may not be bent to a radius greater than that recommended by the pipe manufacturer.  The CONTRACTOR shall obtain written recommendations from the pipe manufacturer. 

C.        As-Built Survey:  At the completion of the project, CONTRACTOR shall provide a tabulation and sealed drawings of coordinates, referenced to the drilled entry point, which accurately describe the location and elevations of the pipe.

 1205-2.3      Ream and Pull Back:

 A. Pre-Reaming: Pre-reaming operations shall be performed so the final pre-ream leaves only 2” of annular space greater than diameter of carrier pipe to be installed. The CONTRACTOR is responsible for maintaining this tolerance and it is at the discretion of Engineer to approve final pre-reaming.  All provisions of this Specification relating to simultaneous reaming and pulling back operations shall also pertain to pre-reaming operations. 

B. Pulling Loads:  The maximum allowable tensile load imposed on the pull section shall be equal to 80 percent of the product of the specified minimum yield strength of the pipe and area of the pipe section.  If more than one value is involved for a given pull section, the lesser shall govern. 

C. Torsional Stress:  A swivel shall be used to connect the pull section to the reaming assembly to minimize torsional stress imposed on the section. 

D. Pull Section Support:  The pull section shall be supported as it  proceeds during pull back so that it moves freely and the pipe and corrosion coating are not damaged. 

E. External Collapse Pressure:  The pull section shall be installed in the reamed hole in such a manner that external pressures are minimized.  Any damage to the pipe resulting from external pressure during installation shall be the responsibility of the CONTRACTOR.

F. Buoyancy Modification:  Buoyancy modification shall be used at the discretion of CONTRACTOR.  Any buoyancy modification procedure proposed for use shall be submitted to the ENGINEER for approval.  No procedure shall be used which has not been approved.  CONTRACTOR is responsible for any damage to the pull section resulting from buoyancy modification.   

G.  CONTRACTOR shall provide a sufficient number of rollers, cradles and motorized equipment to support the pipe and
prevent over-stressing due to sags or bends during the pull back Procedure.

 1205-2.4         Drilling Fluids:

   A.  Composition:  The composition of all drilling fluids proposed for use shall be submitted to the ENGINEER for information only.  No fluid may be utilized that does not comply with permit requirements and environmental regulations.

     B.      Water:  CONTRACTOR is responsible for obtaining, transporting, and storing any water required for drilling fluids.

      C.    Recirculation:  CONTRACTOR shall maximize recirculation of drilling fluid surface returns. CONTRACTOR shall provide solids control and fluid cleaning equipment of a configuration and capacity that can process surface returns and produce drilling fluid suitable for reuse.  The CONTRACTOR will be solely responsible for solids control and cleansing equipment performance or for treatment of excess drilling fluid and drilled spoil.

   D.    Proportional Displacement: CONTRACTOR shall provide a dual mandrill/pull-back head that is capable of displacing 90% of the drilling fluids used in boring process towards the pull pit to be collected during disposal process.  10% of the drilling fluids will be diverted thru ports machined into pull back head to lubricate carrier pipe during installation process.

    E.    Disposal:  Disposal of excess drilling fluids and cuttings is the responsibility of    CONTRACTOR and shall be conducted in compliance with all environmental regulations, right-of-way and workspace agreements, and permit requirements.  CONTRACTOR shall maintain all annular circulation of drilling fluids.  Recovery of fluids other than entry and exit points will be minimized. In the event that annular circulation is lost, CONTRACTOR shall take steps to restore circulation. If inadvertent surface returns of drilling fluids occur, they shall be immediately contained with hand placed barriers (i.e. hay bales, sand bags, silt fences, etc.) and collected using pumps as practical.  If the amount of the surface return is not great enough to allow practical collection, the affected area shall be diluted with fresh water and the fluid will be allowed to dry and dissipate naturally.  If the amount of the surface return exceeds that which can be contained with hand placed barriers, small collection sumps (less than 5 cubic yards) may be used.  If the amount of the surface return exceeds that which can be contained and collected using small sumps, drilling operations shall be suspended until surface return volumes can be brought under control. 

1205-3       EXECUTION:

 1205-3.1    Trench Safety: 

 A. The CONTRACTOR shall comply with all OSHA and State of Mississippi requirements in te performance of all work.  The CONTRACTOR shall be responsible for the design, installation, maintenance and removal of any sheeting and shoring necessary for the drilling operation, including fluid containment and permitted disposal practices.

 1205-3.2    Noise Abatement

 A.   Noise produced by construction operations shall be kept to a minimum.  Noisy operations shall be conducted wherever possible during daylight hours and scheduled to minimize duration.  The CONTRACTOR shall comply with all applicable Federal, State, and Local noise pollution control regulations.

   B.  Noisy equipment shall be kept as far as possible from noise sensitive equipment.  Noisy   operations shall be limited to day hours and scheduled to minimize their duration.  Equipment not in use will be turned off to eliminate unnecessary idling. 

1205-4         POST TELEVISING OF COMPLETED SECTIONS

A.   The Contractor shall provide the Owner a color video tape taken by a 360 degree radial view camera for close up view showing the completed work, including the condition of the restored taps. Post Televising is incidental to the cost of the replacement pipe.

B.  Television inspections, tapes and reports, etc., shall be in accordance with applicable sections of the specifications. Upon completion of the installation work and testing, the Contractor shall restore/clear the project area affected by his operations. No trash, rubbish, etc. shall be stored at any site, whether the work is in progress or not.

C. Defects which may affect the integrity or strength of the pipe in the opinion of the Engineer shall be repaired or the pipe replaced at the Contractor’s expense.

 1205-5          WARRANTY

 A. All work performed under this Contract shall be warranted to be free from defects in material and workmanship for a period of one year from the date of final acceptance by the Owner.  If the engineer determines that the process has failed (including but not limited to the service connections), the Contractor shall perform any and all repairs at no additional cost to the Owner.

 1205-6            MEASUREMENT AND PAYMENT

 A.          The length of the sewer line installed will be measured by linear foot along the center line of the completed sewer from center line to center line of manholes, as designated on the Drawings; and to the end of stubs or the termination of the pipe; and to the inside face of lift station and treatment plant works.  The installation of the sewer within the limits of a  structure other than manholes will not be considered as specified or as shown on the    Drawings.

B.     Payment will include and be full compensation for labor, equipment, materials, and supervision for construction of the sewer and excavation, complete in place including disposal of excess materials, sheeting, shoring or bracing, utility adjustments, connections to existing sewers, grouting (if required), test, backfilling, clean-up, and other related work necessary for construction as specified or as shown on the Drawings.

 C.   Payment for the installation of the sewer will be authorized by the ENGINEER in two parts. Pay estimates for partial payments will be made as measured above according to the following schedule.

1)  90 percent payment will be authorized on a linear foot basis for the amount of sewer pipe installed (including grouting when specified.

2) 100 percent payment will be authorized when the sewer pipe has been inspected in accordance with Section 1205-4.

D.  Cost of all submittals as specified in Section 1.05 along with all labor equipment, and     materials necessary to complete those items are incidental to and shall be included and paid for under unit price for installed sewer pipe.  Monitoring of line, grade, surface settlement, and critical structures are also incidental to and shall be included and paid for under the unit price for installed sewer pipe.

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