Underground Transmission Civil Works in Korea: Ducts, Manholes, Tunnels

Underground transmission civil works in Korea prepare the route for underground transmission cables: duct construction, installation of manhole hardware and construction of cable tunnels (전력구). Because this work builds the path the cable will occupy, duct level and compaction, hardware spacing and tunnel waterproofing determine the quality of later cable pulling and operation. This guide covers three stages — ducts, underground hardware and cable tunnels.

Contents

• Common Pre-Work Review
• 1. Duct Construction
• 2. Underground Hardware Installation
• 3. Cable Tunnel Construction
• Ducts vs Cable Tunnels
• FAQ
• Reference Standards
• Summary

Common Pre-Work Review

Before work, review the design documents, method statement, road occupancy permit and KEPCO design standards and field manuals. Prepare an earth resistance tester, utility locator, coating thickness gauge, survey instruments, total station, staff and level, plus cranes, excavators, forklifts and winches. Safety equipment includes gas detectors, site partitions, guidance signs, fall-prevention nets and fences, hard hats, safety vests, safety shoes, harnesses and lanterns; on roads, set out traffic signs, cones, beacons and barrier ropes. Materials include formwork, H-beams, anchor bolts, hangers, sand or stone dust, concrete, hardware and corrugated ducts with couplers.

1. Duct Construction

1. Set the trench location according to the design documents.
2. Check the surroundings and decide materials, plant and labor.
3. Use a locator to confirm water, sewer, gas and telecom lines.
4. Confirm the duct burial method — trench depth and width — from the design documents and excavate.
5. For manholes, install formwork for concreting and to prevent trench collapse.
6. Fill with sand or stone dust for level, compaction and settlement prevention, then lay the ducts.
7. Install cable protection slabs and warning tape to prevent damage from future excavation by others.
8. Backfill to restore the site after duct work.
9. Install earthing for hardware inside manholes to achieve the required earth resistance, and measure it.

After trenching, lay sand under the ducts to prevent settlement and set the level, then cover the ducts with sand again after laying to protect them.

2. Underground Hardware Installation

1. Secure and transport the materials needed, considering site and working conditions.
2. Drill and install set anchor bolts for manhole steps and cable support brackets.
3. Confirm support sizes from the design documents and install the supports.
4. Check support spacing and verticality against the design documents.
5. Fit hangers of the right size for the cable load.
6. Adjust manhole covers level so road traffic is not affected.

3. Cable Tunnel Construction

1. Prepare safety measures covering road occupancy permits, safety facilities, materials and plant.
2. Use a locator to confirm water, sewer, gas and telecom lines.
3. Drill the ground to install soldier H-piles for shoring.
4. Install lagging boards to secure working space and prevent collapse.
5. Excavate along the tunnel route as designed.
6. Install formwork for concreting and to prevent trench collapse.
7. Place concrete considering strength and curing as designed.
8. Waterproof the tunnel so water cannot enter, then backfill.
9. Install earthing for hardware inside the tunnel to achieve the required earth resistance, and measure it.

Tunnel safety measures include safety fencing, traffic signs, cones and ventilation. Take concrete samples before placing for slump and strength tests.

Ducts vs Cable Tunnels

	Ducts and manholes	Cable tunnels
Key sequence	Trench → sand bed → lay ducts → sand cover → protection slab and tape → backfill	Drill → H-pile and lagging → excavate → formwork → concrete → waterproofing → backfill
Quality points	Duct level, compaction, settlement; support spacing and verticality	Concrete strength and curing; waterproofing
Safety points	Utility checks; traffic control	Shoring; ventilation; fencing and signs
Earthing	Earth manhole hardware and measure resistance	Earth tunnel hardware and measure resistance

Piece test (피스테스트): if a duct continuity test falls short of spec, a sample of the same cable type (about 6 m) is pulled through the duct to confirm the cable can be installed.

FAQ

Reference Standards

• Electricity Business Act (전기사업법) — law.go.kr
• Electrical Safety Management Act (전기안전관리법) — law.go.kr
• Electric Technology Management Act (전력기술관리법) — law.go.kr
• Electrical Construction Business Act (전기공사업법) — law.go.kr
• Occupational Safety and Health Act (산업안전보건법) — law.go.kr
• Korea Electro-technical Code (KEC, 한국전기설비규정) — law.go.kr
• KEPCO design standards; field practice manuals for transmission and distribution work; Korean Industrial Standards (KS)
• NCS competency unit Underground Transmission Civil Works (지중송전공사, 1901070219_22v4; NCS is Korea’s National Competency Standards) — ncs.go.kr

Summary

The most common mistakes in underground transmission civil works are skimping on the sand bed and compaction so ducts settle, and leaving tunnel waterproofing until the end. Ducts depend on level and protection, hardware on spacing and load, and tunnels on shoring, concrete and waterproofing. Cable jointing is covered in Underground Transmission Cable Jointing. For pre-construction preparation, see Transmission Line Construction Planning. A Korean version of this guide is available here.

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This article restructures the Korean NCS competency unit ‘Underground Transmission Civil Works’ (지중송전공사, code 1901070219_22v4) as a practical reference. Actual work must follow applicable standards and the judgment of qualified professionals; always confirm specific values, deadlines and criteria against the latest regulations and client standards.

Written/reviewed by VOLT · Last updated 2026-10-25