How to Install MPP Pipes Without Excavation: Full Guide
I. Management Regulations for Trenchless Construction of MPP Power Conduits
In power engineering, cable installation often employs trenchless techniques such as "pulling pipe" or "pipe jacking" due to routing constraints, construction schedules, and other objective factors. While trenchless methods offer advantages like minimal traffic disruption and shorter construction periods, they also present safety and management challenges. This is because trenchless technology remains relatively new for power utilities and utility sectors nationwide, lacking unified construction standards and technical codes. Additionally, geographic variations and complex underground utility networks further complicate implementation.
To standardize trenchless construction management within the power sector and ensure cables can be easily maintained after commissioning, the following management regulations are provided for reference, based on relevant technical documents from various power companies and input from operational departments:
The power supply unit’s engineering management department (hereinafter referred to as the "power department") should, by default, avoid using trenchless construction for cable laying unless under special circumstances.
If site surveys confirm that open-cut construction is not feasible (e.g., across railways, rivers, busy roads, or other obstacles), trenchless technology may be used. In such cases, the power supply plan must clearly indicate the route and length of the trenchless section.
II. Pre-Construction Design and Planning
Contractors performing trenchless pipeline work must possess the required design and construction qualifications and strictly comply with the requirements specified in the construction project planning permit. Otherwise, the power department will not approve acceptance or energization. The power department shall clearly inform customers in advance and be responsible for verifying the contractor's qualifications.
The contractor shall provide its own trenchless construction specifications or technical standards to the power department and jointly determine the construction plan based on feedback.
Prior to external power cable construction, the power unit’s project manager shall urge the customer to contact the local power station in advance. The power station shall organize a coordination meeting involving the customer and the contractor (or contracted company) for trenchless cable laying.
At least one week before preliminary or construction drawing design review meetings, the contractor shall submit the following materials related to the project scope to the power department: construction specifications or outline; site plan; cross-section drawings; data on existing underground utilities; geological survey reports; and the pipeline project planning permit. The project manager must also be clearly identified.
The power department reserves the right to review and reject construction designs.
The contractor shall provide a clear commitment on construction quality in written agreement form, including: warranty period for construction quality; legal liability for power failures caused by poor workmanship; commitments to rectify defects during the warranty period; and consequences for failing to meet these commitments.
III. Materials and Equipment
Power cables shall meet the cable selection and procurement technical requirements of the respective power supply units.
Trenchless cable conduit (MPP pipe) shall comply with the Technical Specifications for MPP Pipes Used in High-Voltage Cable Installation.
IV. Installation and Construction
The customer shall notify the power department two days prior to construction, who will then inform the local power station to send personnel for on-site supervision.
Construction must strictly follow approved design drawings and urban planning routing, adhering to mandatory construction standards, codes, and quality acceptance criteria to achieve first-time pass quality. On-site measuring instruments and construction equipment must meet regulatory requirements.
If design changes are necessary due to unforeseen difficulties, the contractor must obtain approval from the local power station and issue formal design change documentation.
The underground route of MPP conduits should fully consider soil and geological conditions and minimize crossings with other underground facilities to prevent damage from mechanical stress, chemical corrosion, vibration, heat, stray currents, pests, or other hazards.
Trenchless depth shall be determined according to design and ground elevation, not temporary surface levels, ensuring actual construction aligns with design. For future ease of cable operation, and in accordance with geological conditions and standards for crossing railways or rivers, the pipeline burial depth should generally be no less than 8 meters.
Before cable installation, verify cable specifications, check for recent test certification, and inspect cable ends and sheaths for damage. Address any issues through appropriate treatment and testing before proceeding.
Prior to laying, determine intermediate joint locations based on cable reel length. Joints should be placed inside manholes, avoiding intersections, building entrances, crossings with other pipelines, or narrow, inaccessible areas.
A manhole should be excavated approximately every 120 meters to prevent excessive friction during cable pulling or difficulty replacing cables during maintenance. Manholes may be constructed as open or closed types depending on site conditions.
Manhole dimensions must accommodate cable bending radius and allow space for joint installation. The height should allow workers to stand and operate comfortably.
During directional drilling or guided drilling, the borehole curvature must satisfy the minimum bending radius requirements of both the cable and the MPP conduit.
During pullback and hole enlargement in trenchless operations, the borehole diameter should be 1.2–1.5 times the outer diameter of the conduit, based on subsurface geology. This prevents undersized holes (hindering conduit insertion) or oversized holes (causing soil collapse and conduit compression). Drilling parameters and pump rates should be adjusted according to soil layer changes to ensure uniform hole diameter and smooth, flat borehole walls.
When using trenchless directional drilling, guided drilling, or pipe jacking, the mechanical pulling force during conduit installation shall not exceed 70 N/m.
When pulling cable through MPP conduit, a pulling head shall be attached to the cable, and measures taken to minimize friction and abrasion. Personnel must monitor both ends of the cable to prevent damage.
After cable installation into the MPP conduit, the cable need not be pulled taut. It should be laid loosely in a wave-like or serpentine pattern, with slack approximately 0.5% of the total length.
After completing pullback and hole enlargement, take precautions to prevent debris such as bricks or stones from entering the borehole. After cable installation, seal the MPP conduit ends to prevent water ingress and animal intrusion.
Minimum horizontal and vertical clearance distances, burial depth, and minimum crossing distances with other utilities must comply with the Urban Engineering Pipeline Comprehensive Planning Code (National Standard of the People’s Republic of China GB50289-98). The depth from the top of the MPP conduit to railway tracks or road surfaces shall be no less than 1 m; to the bottom of drainage ditches, no less than 0.5 m; and to urban street surfaces, no less than 1 m. Conduit length should extend at least 2 m beyond the width of the road or track being crossed. In urban streets, conduits shall extend beyond the roadway. Open or closed manholes shall be installed at both ends of roads and tracks. When running parallel to standard railways, the minimum allowable distance from the track shall be no less than 3 m.
Cable terminal heads at both ends and within pullback manholes shall be fitted with nameplates indicating cable number, start and end points, voltage, length, and cross-section. Clear surface markers shall be installed.
V. Final Acceptance
The power supply unit’s engineering management department and local power station are responsible for accepting trenchless cable installations.
Trenchless construction must meet the following conditions for acceptance:
Entry point location is accurate;
Exit point horizontal error does not exceed ±0.5 m;
No surface or borehole collapse;
Actual underground construction path conforms to original design.
Any defects identified during acceptance—especially those affecting commissioning—must be rectified before energization. Projects failing to meet standards will not be energized.
After completion, the power department shall require the customer to submit as-built documentation within one month of cable commissioning, for archiving by the local power station.
As-built documentation shall include:
A cable layout map drawn on a 1:500 topographic map per power cable operation regulations;
1:50 cross-sectional drawings;
Records of construction and installation activities.
The power station shall properly archive, categorize, and maintain all submitted drawings and records, establishing equipment ledgers and operational logs.
Conduits connected via onsite hot-melt welding shall have smooth, flat inner joints capable of withstanding external pressure and operating temperatures equivalent to the base pipe material.
