Objectives: To address the problem that single-type cement grouting cannot simultaneously achieve reinforcement and anti-seepage in local adverse geological bodies of high-pressure tunnels, and to fill the research gap that grouting parameters under ultra-high water heads lack systematic guidance, a transferable design and construction method for cement-chemical composite grouting was established. The method was intended for new pumped-storage projects where otherwise competent rock masses contain local faults, altered dikes, densely jointed zones, or microfracture networks.

Methods: Design documents, field tests, construction records, quality inspections, and initial-operation data from the Meizhou, Yangjiang, Shenzhen, and Qingyuan pumped-storage power stations were compared. The maximum static heads ranged from approximately 426 to 800 m. Rock-mass classes, fracture scales, permeability, grouting pressures, hole spacing, hole depth, epoxy properties, pressure-flow histories, lining deformation, and post-grouting permeability were jointly examined. The relationship between water head and process parameters was analyzed by separating two controls. Water head was treated as the external hydraulic demand governing anti-seepage reserve, material verification level, and target pressure range. Geological quality and lining safety were treated as internal constraints governing hole density, treatment depth, allowable pressure, pressure-rise rate, and intermittent grouting need.

Results：Composite grouting was shown to be appropriate only after rock cover, minimum principal stress, and overall stability had satisfied the applicability requirements of a rock-bearing lining. Cement grout was used first to fill medium and large fractures, restrict uncontrolled grout loss, and form a macroscopic load-transfer skeleton. Low-viscosity modified epoxy grout was then used to penetrate microcracks, weathered contacts, mud-filled interfaces, and residual seepage paths. For preliminary design, head ranges of 100~400, 400~600, and 600~800 m were associated with progressively higher material-performance requirements; however, grouting pressure was not determined by head alone. Weak or highly altered rock required closer holes, shorter stages, lower pressure-rise rates, and stricter pressure limits, whereas competent rock under an ultra-high head could accept higher terminal pressures after full-scale field verification. The verified engineering ranges were 1.5~3.0 m for row spacing, 3~12 m for normal hole depth, 8~20 m for fault-zone reinforcement depth, 0.5~10 MPa for cement grouting pressure, and 2~8 MPa for chemical grouting pressure. When the internal water pressure exceeded 5 MPa, additional verification of splitting tensile strength (not less than 10 MPa) and elastic modulus (greater than 300 MPa) of the epoxy grout was recommended. The Meizhou project adopted differentiated chemical pressures of 2~6 MPa for altered dikes and faults; post-grouting permeability was below 1.0 Lu, ultrasonic velocity increased by 3%~10%, and initial filling was successful. The Yangjiang project used 8~10 MPa cement grouting and chemical grouting up to 8 MPa under an approximately 800 m head, with pressure-flow product and lining-uplift controls. Shenzhen verified full-hole chemical grouting for holes not deeper than 7 m, and Qingyuan treated kaolinized Class V rock by pressure-limited, intermittent, same-hole composite grouting. Cement-grouted zones generally reached 2.0~3.0 Lu, whereas chemically strengthened zones could be controlled within 1.0 Lu.

Conclusions: A practical workflow was formed comprising hydraulic and geological zoning, applicability verification, treatment-object identification, material selection, productive field testing, parameter design, dynamic construction control, and multi-index acceptance. The results demonstrated that water head should define the required performance level, while geology and structural response should determine the executable process parameters. This dual-control distinction prevented both insufficient reinforcement and unsafe pressure escalation. The core innovation lies in the water-head-geology dual-control criterion and the differentiated parameter system established through multi-project comparison, which provides a quantitative basis for grouting design. The proposed workflow can guide engineers in deciding where composite grouting is necessary, how holes and materials should be selected, how pressures should be increased and limited, and how the final treatment should be verified in a new high-pressure tunnel.