DEEP DRIVEN GROUND RODS FOR POLES

Transcription

1 Project Procedure DEEP DRIVEN GROUND RODS FOR POLES 07/25/2011 PAGE 1 OF PURPOSE The purpose of this procedure is to provide guidance for the need for and direction on the installation of deep driven ground rods. Supplemental earth grounding within right-of-way limits reduces footing resistance of structures to acceptable levels in penetrable soils. Deep driven ground rods are an alternative for areas where counterpoise cannot be utilized or where an improvement is warranted, but physical obstructions (roads, sidewalks, creeks, etc.) disrupt continuity of right-of-way. Deep driven ground rods may also be preferred in situations where Clients are concerned that plowed counterpoise may damage or devalue right-of-way property. Low lying areas or areas of damp soil are areas to be considered first when installing deep driven ground rods. A target footing resistance of 10 ohms is typically sought for structures that are being improved with deep driven ground rods. Further improvements are not necessary once this condition is met. If multiple installations do not yield target value for footing resistance, both the work effort performed and the value obtained for footing resistance measurement shall be documented on form QF A, Deep Driven Ground Rod Documentation (see Form 8.1). This information shall be sent to the Project Engineer for evaluation. Installation crew should then continue on to next structure. If additional improvements are deemed necessary, the Project Engineer will indicate. If ground resistance measurements are not available at the time of installation, the Deep Driven Rod (DDR) crew shall install, as a minimum, the installation shown in Attachment 7.1, or shall install a DDR configuration that conforms as closely to Attachment 7.1 as varying field conditions will allow. 2.0 SCOPE The scope of this procedure applies to Pike construction activities. This procedure may also be applied to Contractors when invoked by Contract documents.

2 PAGE 2 OF REFERENCES 3.1 Project Procedure P-1-4, Quality Control Functions and Responsibilities (Construction Site) 3.2 Project Procedure P-1-5, Quality Control Personnel Assignments (Construction Site) 4.0 DEFINITIONS None 5.0 RESPONSIBILITIES Personnel responsibilities are as defined in the procedures P-1-4, Quality Control Functions and Responsibilities (Reference 3.1), and P-1-5, Quality Control Personnel Assignments (Reference 3.2). 6.0 PROCEDURE FOR INSTALLING DEEP DRIVEN GROUND ROD ASSEMBLY See Attachment Measure out 15 from pole along a line parallel with conductor Mark end of trench. 6.2 Dig a trench with a backhoe from pole ground to where the end of the trench was marked Trench should be approximately 18 deep for uncultivated soil and 30 deep for cultivated soil. 6.3 Measure out 10 along the same trench and mark location DDR A. 6.4 Dig a 2 diameter hole with a backhoe at site targeted for DDR A. 6.5 For a pole, dig trenches between poles or beside down pole ground at base of pole. 6.6 Secure Stanley GD47 Rod Driver or equivalent. 6.7 Depress jaw release trigger to open clamping jaws. 6.8 Insert a ground rod section through jaws of driver until 18 to 30 protrudes beyond bottom end of tool. 6.9 Release jaw trigger to grip ground rod Position driver with rod into excavation located 10 from pole.

3 PAGE 3 OF Depress and hold impact trigger to drive rod Drive rod into ground until the end of the driver is a few inches from soil in excavation. Note: Keep head and moving parts of driver out of dirt and clean as possible for reliable operation With upward lifting pressure on driver, depress jaw release trigger to open clamping jaws Lift driver as high as possible and release jaw release trigger Depress and hold impact trigger to repeat driving cycle Repeat Paragraphs 6.11 through 6.15 until ground rod is within 6 of ground line Depress jaw release trigger and remove driver from rod If possible, measure ground resistance after each ground rod and continue to add ground rods until desired ground resistance is achieved. Drive up to five ground rod sections or until driver can no longer penetrate soil before proceeding to next rod location. Install ground rods as shown in Attachment 7.1 for particular structure in alphabetical order (i.e., Ground Rod A first, Ground Rod B second, Ground Rod C third, and Ground Rod D last) Drive rod splice coupling onto driven rod. Note: Hard nylon hammer should be used to drive coupling onto driven rod to avoid damage to coupling Lift driver and place opening in bottom of driver on top of coupling Depress jaw release lever and slide another ground rod into driver Slide rod through driver and into coupling Release jaw release trigger Lift driver as high as possible Repeat Steps 6.11 through 6.15 until each rod is within 6 of ground line Repeat Steps 6.11 through 6.22 until enough rods have been driven to reach desired depth of 40. Note: Last ground rod installed in excavation shall be 18 below ground line in uncultivated soil and 30 in cultivated soil.

4 PAGE 4 OF Lay out enough copperweld wire into bottom of trench to connect from down pole ground to deep driven ground rod Secure a wire-to-rod grounding clamp Position clamp 1 from the top of the rod Insert wire into the top of the clamp on the rod and extend wire 1 out of the bottom of the clamp Tighten grounding clamp Position ground wire in bottom of trench. Note: Separate ground wire from rod and verify no wire protrudes above top of ground rod Clean down pole ground(s) where connection(s) will be made using wire cleaning brush Clean pole end of DDR lead using wire brush Install split bolt connector onto down pole ground Insert DDR lead into split bolt connector on down pole ground wire Tighten split bolt connector Push wire into the bottom trench keeping copperweld wire away from pole Repeat Paragraphs 6.29 through 6.33 for any other DDR leads to be connected to pole Measure structure footing resistance Record information such as depth of rod assembly and structure resistance readings, etc., in the appropriate spaces on form QF A, Deep Driven Ground Rod Documentation (see Form 8.1) Draw a sketch in the space provided that fully portrays the location of deep driven rod(s) in relation to the structure and each other. Give all dimensions in feet. Also, appropriately label each deep driven rod assembly to correspond with previously recorded data (DDR A, DDR B, etc.). The beginning and ending points of the line should be indicated at the top and bottom of the sketch. Note: If footing resistance is more than 10 ohms and field conditions permit, extend the trench to a length equal to the depth of DDR A and repeat above procedure for DDR B, DDR C, and DDR D. If field conditions significantly limit separation distance between rod locations, it is permissible to deviate from a straight line and proceed at an angle toward the next rod location. Connect each assembly together using copperweld wire.

5 PAGE 5 OF Once all deep driven rods have been installed, backfill all excavated areas with 6 of soil and tamp Repeat Paragraph 6.38 until trench is completely backfilled. Note: Tamping is a vital step that re-compacts soil around ground rods and wire. Tamping helps to control soil erosion and can significantly lower the footing resistance value of final installation Distribute grass seed over disturbed soil areas Data Collection Data collection form is always required with this procedure. 7.0 ATTACHMENTS 7.1 Steel Pole Ground Wire Connections 8.0 FORMS 8.1 Quality Form QF A, Deep Driven Ground Rod Documentation 9.0 REVISIONS AND APPROVALS Revision Level Revision Date Revision Description Department Head (Approver) 0 09/10/2010 Original Issue Audie Simmons 1 07/25/2011 Updated logo and company name N/A

6 ATTACHMENT 7.1 STEEL POLE GROUND WIRE CONNECTIONS PAGE 1 OF 1 Note: The top of ground rods, connections, and buried jumpers shall all be installed at least 12 below the surface in uncultivated soil and 30 for cultivated soil.

7 FORM 8.1 PAGE 1 OF 1 DEEP-DRIVEN GROUND ROD DOCUMENTATION Project: Project Number: Job Number: Client: Location: Drawing/Rev: Date: Description: Line Name: Pole #: Date: Project Wid.: Sta. No.: Structure Resistance Readings Sketch Reading before DDRs: Reading after DDR A: BP Reading after DDR B: Reading after DDR C: Reading after DDR D: Temperature: F Soil Type Sand Clay Rock Other Moisture Wet Moist Dry Very Dry Row Shielding Completely exposed: Partially exposed: Shielded: Structure Location/Elevation Flat: Hillside: Depth of Deep-Driven Rod (DDR) Hilltop: DDR A Ft. Valley or Depression: DDR B Ft. # of Deep-Driven Rods Installed: DDR C Ft. Depth of Leadwire to Rod(s) Ft. DDR D Ft. Remarks: EP Signature Print Name Date Performed By: Approved By: Accepted By: Quality Form QF A, Rev. 1 Last Revised: 07/25/2011 Project Number: Project Procedure P Page 1 of 1