Bore Hole Location Plan in Transmission Line Projects – A Complete Guide

When it comes to Overhead Transmission Line (OHTL) design, one of the most crucial steps before foundation design is the preparation of a Bore Hole Location Plan. This drawing ensures proper planning for soil investigation at exact tower locations, helping engineers design safe and cost-effective foundations for both suspension and tension towers.

In this article, we’ll cover:

• What is a Bore Hole Location Plan?
• Why it is required in OHTL projects.
• Reference drawings needed for preparing a Bore Hole Location Plan.
• Details included in the drawing.
• Example of bore hole depths in high-voltage lines.

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What is a Bore Hole Location Plan?

A Bore Hole Location Plan (BHLP) is a detailed engineering drawing that specifies the exact locations where soil investigation bore holes must be drilled along the transmission line route.

It is prepared during the design stage of an OHTL project and approved before soil investigation begins. The plan ensures that soil samples are collected at correct tower locations, reducing the risk of errors in foundation design.

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Importance of Bore Hole Location Plan in OHTL Design

The soil condition directly influences the type, size, and depth of tower foundations. A well-prepared Bore Hole Location Plan helps in:

• Identifying correct bore hole points at each tower location.
• Matching bore hole coordinates with the plan & profile (P&P) of the transmission line.
• Avoiding discrepancies between route alignment and soil investigation data.
• Ensuring compliance with utility/authority requirements (for example, minimum bore depths in high-voltage projects).

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Reference Drawings Required to Prepare Bore Hole Location Plan

To create a BHLP, the following reference drawings and documents are used:

1. Drawing Control Sheets – To decide bore hole location plan drawing number and maintain control of revisions.
2. Overall Route Key Plan – For matching Point of Intersection (PI) coordinates and line deviations.
3. Plan & Profile (P&P) Drawing – To correlate bore hole points with the line route.
4. Structure List – Contains details of tower types, locations, and spans.

These references ensure that the bore hole locations are aligned with actual tower positions.

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Information Included in Bore Hole Location Plan Drawing

A typical Bore Hole Location Plan drawing sheet includes:

• Tower Locations: Marked as BH T1, BH T2, etc. along with span lengths.
• Coordinates: Easting and Northing of each tower location.
• Elevation Details: Ground elevation at bore hole location.
• Span Ahead: Distance between consecutive towers.
• Stationing/Accumulated Distance: Cumulative distance from the start of the line route.
• Bore Hole Number: To identify each bore hole uniquely for soil investigation reports.

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Bore Hole Depth Criteria

The minimum bore hole depth depends on the voltage level and type of tower:

• Suspension Towers – Usually 15 meters (for 380 kV lines in the Kingdom of Saudi Arabia).
• Tension/Angle Towers – Usually 20 meters (for 380 kV lines in the Kingdom of Saudi Arabia).

These depths may vary depending on utility specifications and geotechnical requirements.

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Notes and Standards in the Drawing

Every Bore Hole Location Plan must include standard notes, such as:

• All dimensions are in meters unless otherwise specified.
• Minimum bore hole depth for suspension and tension towers.
• Any special geotechnical or environmental considerations.

This ensures clarity for the geotechnical team carrying out the field investigation.

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Conclusion

A Bore Hole Location Plan is a key document in transmission line soil investigation and foundation design. It ensures accurate drilling locations, proper geotechnical data collection, and ultimately safe tower foundations.

At OHTL Design, we specialize in creating detailed engineering drawings, including Bore Hole Location Plans, Plan & Profile, and Structure Lists, ensuring compliance with international standards and utility requirements.