ULMA Construction supplied its MK underground tunnel carriage system for the construction of the Air Cushion Surge Chamber at the San Gabán III Hydroelectric Project. The structure, executed by China International Water & Electric Corp (CWE), forms part of the hydraulic headrace system designed to regulate transient pressures.
The chamber is a reinforced concrete structure measuring 92.4m in length and 18.5m in height, with 1.1m wall and slab thicknesses. The slab was executed in two stages: an initial 0.7m pour with embedded perimeter steel inserts, followed by a 0.4m layer to complete the section. The internal radius is 5.7m and the external radius 6.1m, with an overall geometry optimised for dynamic load distribution during flow oscillations.
For the second-phase slab works, ULMA provided the MK tunnel carriage, a 60-ton mobile formwork unit incorporating two wheeled axles, integrated access platforms, and guardrails. The carriage enables sequential casting in 6m sections and combines formwork and support elements into a single structure. Its modular design and use of standard reusable components simplified assembly, transport, and repositioning within the confined work environment, the company said.
The MK system employed 6mm steel panels to achieve the required surface finish and dimensional tolerances. Concrete compaction was performed using 24 vibrators arranged in three rows. The formwork was advanced with two 3200kg towing winches.
Each construction cycle lasted approximately 48 hours per section. After pouring, front molds were dismantled after 12 hours (3–4 hours operation time). At 24 hours, the formwork was lowered using 16 hydraulic jacks rated at 20 tons each, the internal components were removed, and the carriage was repositioned. Reinstallation and preparation for the subsequent pour required an additional 3–5 hours.
The structure was completed within schedule, meeting the specified geometric tolerances and surface quality standards. The MK carriage allowed precise, repetitive operations under constrained access conditions, ensuring efficient execution of the concrete works for the Air Cushion Surge Chamber.
