2-67 SECTION 209 – TRENCHLESS CONSTRUCTION
209.01 DESCRIPTION . This work shall consist of performing trenchless construction as specified in the
Contract and in accordance with standard industry practice.
209.02 SUBMITTALS . The Contractor shall submit a detailed work plan that encap sulates a wide range
of procedural precautions necessary to ensure a proper trenchless installation. The work plan shall be submitted to the Engineer for acceptance in accordance with Subsection 105.0 6(c)(2) prior to the beginning of any work associated wi th the trenchless work. The work plan shall contain, at a minimum, entry and exit points, entry and exit angles, any horizontal bend radii, a profile showing points of tangency and curvature, vertical radii, the depth of the bore along the proposed alignm ent, equipment details and specifications, anticipated duration of the drill and assembly, and the Contractor’s qualifications. The qualifications, at a minimum, shall be three projects in the last 5 years where the Contractor or subcontractor performing t he work has successfully used the trenchless construction method for projects of similar diameter, length, and difficulty as required for this project. The work plan shall also indicate if the Contractor intends to do any preliminary subsurface investigati on.
209.03 Equipment Requirements .
a.Horizontal Directional Drilling . Horizontal directional drilling equipment shall consist of a directional drilling rig of sufficient capacity to perform the bore and pull -back, a drilling fluid mixing and delivery sy stem of sufficient capacity to successfully complete the work, and a guidance system to accurately guide drilling operations. Equipment shall include a vacuum trailer to withdraw excess drilling fluid and a drilling fluid cleaning system truck for mixing a nd recycling bentonite. All equipment shall be in good and safe operating condition with sufficient supplies, materials, and spare parts on hand to maintain the system in good working order for the duration of the work.
1.Drilling System .
a.Drilling Rig . The directional drilling machine shall consist of a hydraulically powered system to rotate, push, and pull hollow drill pipe into the ground at a variable angle while delivering a pressurized fluid mixture to a guidable drill head. The machin e shall be anchored to the ground to withstand the pulling, pushing, and rotating pressure required to complete the work. The hydraulic power system shall be self -contained with sufficient pressure and volume to power drilling operations. The hydraulic sys tem shall be free of leaks. The drill rig shall have a system to monitor and record maximum pull back pressure. 2-68 b. Drill Head . The drill head shall be steerable by rotation direction changes and through drilling fluid jets.
c.Mud Motors . Mud motors, wh en required, shall be of adequate power to turn the required drilling tools.
d.Drill Pipe . Drill pipe shall be constructed of high quality AISI 4130 seamless tubing, Grade E or better, with threaded box and pins. Tool joints shall be hardened to between 3 2 RC and 36 RC.
2.Guidance System . The guidance system shall be of a proven type and shall be set up and operated by personnel trained and experienced with the system. If using a magnetic system, the operator shall be aware of any magnetic anomalies and shall consider such influences in the operation of the guidance system. The guidance system shall be capable of identifying the exact location of the drill head, horizontally, vertically, and degree of inclination, at all times during drilling operations. The guidance system shall be capable of accurately monitoring the location of the drill head beneath a reinforced concrete slab.
3.Drilling Fluid System .
a.Mixing System . The drilling fluid mixing system shall be self -contained, closed, and be of suffi cient size to mix and deliver drilling fluid composed of bentonite clay, potable water, and appropriate additives. The mixing system shall be able to molecularly shear individual bentonite particles from the dry powder to avoid clumping and ensure thorough mixing. The drilling fluid reservoir tank shall be of sufficient size for the work. The mixing system shall continually agitate the drilling fluid during drilling operations.
b.Drilling Fluid . Drilling fluid shall be composed of clean water and an approp riate additive. Water shall be from a clean source with a pH of 8.5 to 10. Water of a lower pH or with excessive calcium shall be treated with the appropriate amount of sodium carbonate or equal. The water and additives shall be mixed thoroughly and be fre e of any clumps or clods. No hazardous additives shall be used. Drilling fluid shall be maintained at a viscosity sufficient to suspend cuttings and maintain the integrity of the bore wall. 2-69 c. Delivery System . The mud pumping system shall have sufficie nt capacity and be capable of delivering the drilling fluid at a constant pressure to meet the needs of the work. The delivery system shall have filters in -line to prevent solids from being pumped into the drill pipe. Connections between the pump and the d rill pipe shall be relatively free of leaks. Used drilling fluid and drilling fluid spilled during drilling operations shall be contained and properly disposed of. Pumps or vacuum trucks of sufficient size shall be in place to convey excess drilling fluid from containment areas to storage facilities.
4.Other Equipment .
a.Pipe Rollers . Pipe rollers, if required, shall be of sufficient size to fully support the weight of the pipe while being hydro -tested and during pull back operations. A sufficient number of rollers shall be used to prevent sagging of the pipe.
b.Restrictions . Devices or placement systems for providing hydraulic thrust other than those previously defined shall not be used unless approved by the Engineer. Consideration for approval will be made on an individual basis for each specified location.
209.04 CONSTRUCTION REQUIREMENTS . The Contractor shall notify the Engineer at least 48 hours
prior to starting work. The trenchless work shall not begin until the Engineer is present at the job site and agrees that preparations are in place as specified in the approved work plan. The Engineer’s approval for beginning the installation shall in no way relieve the Contractor of the ultimate responsibility for the satisfactory completion of the work as authorized under the Contract.
a.Horizontal Directional Drilling Requirements.
1.Site Preparation . Prior to any alterations to the work site, the Contractor shall photograph or video the entire work area, including entry and exit points, one copy o f which shall be provided to the Engineer and one copy of which shall remain with the Contractor. The work site shall be graded or filled to provide a level working area. No alterations beyond what is required for operations shall be made. The Contractor shall confine all activities to designated work areas. Prior to anchoring the drilling rig to the ground, the Contractor shall confirm locations of all underground utilities in the area of the drilling rig. 2-70 (2) Drill Path Survey . The entire drill path shall be accurately surveyed, with entry and exit stakes placed in the appropriate locations within the areas indicated on the Plans. If the Contractor uses a magnetic guidance system, the drill path shall be surveyed for any surface geo-magnetic variation s or anomalies.
3.Environmental Protection . The Contractor shall adhere to all applicable environmental regulations and install any EPSC measures necessary to contain all drilling material and fluid around the drilling operation, drilling fluid mixing systems, entry and exit pits, and drilling fluid recycling system. EPSC measures shall be shown on the EPSC plan submittal, or on the work plan if pay item 653.0100 is not included in the Contract. At a minimum, the plan shall show perimeter control s that will contain the drilling material and fluid.
4.Drilling . If a deviation greater than 5% of depth occurs, the Engineer may require the Contractor to pull back and re -drill from the location along the bore path before the deviation. In the event t hat drilling fluid fractures, inadvertent returns, or return losses occur during the pilot hole drilling operations, the Contractor shall cease drilling, wait at least 30 minutes, inject a quantity of drilling fluid with a viscosity exceeding 120 seconds a s measured by a March funnel, and then wait another 30 minutes. If mud fracture or returns continue, the Contractor shall cease drilling operations and notify the Engineer. The Engineer and the Contractor will discuss additional options and work will then proceed accordingly.
5.Reaming . Upon successful completion of the pilot hole, the Contractor shall ream the bore hole to a minimum diameter 25% greater than the outside diameter of the pipe to be installed using the appropriate tools. The Contractor shal l not attempt to ream at one time more than the drilling equipment and mud system are designed to safely handle.
6.Pull Back . The Contractor shall pull the pipe, casing, or sleeve through the bore hole. In front of the pipe shall be a pull head and swive l to connect to the drill rig for pull back. Once pull back operations have commenced, operations shall continue without interruption until the pipe is completely pulled into the drill hole. During the pull back, the Contractor shall not apply more than th e maximum safe pull pressure at any time. In the event that the pipe becomes stuck, the Contractor shall cease pulling operations to allow any potential hydro -lock to subside and shall then re -commence pulling operations. If the pipe remains stuck, the Co ntractor shall notify the Engineer. The Engineer and the Contractor will discuss options and then work will proceed accordingly.
7.Inlet Grouting . Upon the completion of the installation, the inlet of the casing shall be sealed and capped to the satisfac tion of the Engineer. 2-71 209.05 SITE RESTORATION . Following trenchless operations, the Contractor shall demobilize equipment and restore the work site to its original conditions. All excavations shall be backfilled with material from excavation or borrow, u nless otherwise specified. The material shall be compacted to 95% of the material’s maximum dry density as determined in accordance with AASHTO T 99, Method C . Landscaping shall be restored to the original conditions, or to the satisfaction of the Engineer .
209.06 RECORD KEEPING . The Contractor shall maintain a daily project log of trenchless operations
and a guidance system log with a copy given to the Engineer at the completion of the work. At a minimum, the logs shall include the date, location of work, description of work, and pitch and depth of trenchless operations. The Contractor shall also give to the Engineer, at the completion of work, a revised work plan that shows any deviations made during construction.
209.07 METHOD OF MEASUREMENT . The quanti ty of Trenchless Excavation, Horizontal Directional
Drilling of the type and size specified to be measured for payment will be the number of linear feet of drilling performed in the complete and accepted work.
209.08 BASIS OF PAYMENT . The accepted quantit y of Trenchless Excavation, Horizontal Directional
Drilling will be paid for at the Contract unit price per linear foot. Payment will be full compensation for all work required for a complete installation, including clearing, site preparation, excavation o r grading needed, site restoration, grubbing, erosion control, excavation, excavation support, dewatering, drilling, removal of tailings, backfilling, compaction and flushing; and for furnishing all labor, tools, equipment, and incidentals necessary to com plete the work. Payment will be made under: Pay Item Pay Unit 209.0100 Trenchless Excavation, Horizontal Directional Drilling .......................... Linear Foot 2-72 SECTION 210 – MILLING
210.01 DESCRIPTION . This work shall consist of the removal, disposal, and clean -up of bituminous
pavements by coarse -milling or fine -milling.
210.02 Equipment and Operation .
a.General Requirements . Milling equipment shall be power -driven, self -propelled, and of a size and shape to allow traffic safe passage through areas adjacent to the work. The equipment shall have grade and slope controls capable of operating from a ski and based on mechanical or sonic operation. The equipment shall have a positive means for controlling cross sl ope elevations. The equipment shall have sufficient weight to perform milling without lifting, and sufficient and positive down pressure on the drum assembly at all times when milling. The equipment shall also have conveyors capable of side or front loadin g to transfer the removed material from the roadway to a truck and an effective means of preventing dust from escaping into the air. The cutting head shall use carbide or polycrystalline diamond (PCD) tipped cutting teeth designed for milling bituminous p avement to close tolerances. The cutting head shall be properly maintained so that the depth of cut is within a tolerance of 1/8 inch throughout the width of the head. The grinding and texturing mandrel shall have multiple wraps of flighting with a weld -on or quick - change block system that accepts carbide or PCD tipped cutting bits. Bituminous surfaces adjacent to objects such as drop inlets and curbs that are inaccessible to milling equipment shall be milled with equipment designed for that purpose.
b.Coarse -Milling Equipment . Equipment used for coarse milling shall have a cutting head with the teeth arranged in a manner such that the final pavement surface will have a center -to-center transverse pattern of 5/8 inch between each strike area . The target difference between ridge and valley (RVD) measurements of the mat surface shall not exceed 5/16 inch. The maximum axial distance between the tips of the teeth shall be 5/8 inch.
c.Fine-Milling Equipment . Equipment used for fine milling shall have a cutting head with the teeth arranged in a manner such that the final pavement surface will have a center -to-center transverse pattern of 3/8 inch between each strike area. The target difference between ridge and valley (RVD) measurements of the mat surface shall not exceed 3/16 inch. The maximum axial distance between the tips of the teeth shall be 3/8 inch.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 207–211 of 1,380.