Forming China’s new great wall

Concrete pouring operations at the Three Gorges project in China are reaching a new level of intensity this year, as contractors aim to pour some 5.4M m3 of concrete at an average rate of 450,000m3/month. More than half of this will be flowing into Doka formwork to create the spillway and one intake section of the 2.3km long dam across the Yangtze river.

China Gezhouba Construction Group Corporation (CGGC) is now constructing the spillway and dam along with the Ching Yung Joint Venture. The China Force Army Construction Company and the 378 Joint Venture Company are responsible for the power house.

All four contractors are using Doka’s standard D22 dam formwork, with the majority supplied to CGGC. The D22 system is suitable for block heights up to 3m and can cope with anchor tensile forces up to 220kN. It can also accommodate the dam’s 1:0.65 and 1:0.75 inclined faces while maintaining a horizontal working platform. A combination of 3m x 1.2m x 2.1m panels enables the contractors to work with 1.5m pours at the base, 2m pours in the middle section and 3m pours at the top.

The formwork element, dam formwork scaffold and working platform are joined together in a single unit that can be used from the first casting step, without the need for any additional material. This facility for all-in-one shifting makes moving the formwork fast and easy. To strike the formwork, the element is simply tilted backward to allow for preparation of anchor points for the next step, then the complete unit is raised in a single crane lift.

Hubei Gezhouba Doka has already delivered some 7000t of formwork and expects the total to reach more than 10,000t by the end of the project.

Two specially-built potain MD2200 Topbelt tower cranes are being used at the project for the high volume concrete pouring. The cranes, each with a lifting capacity of 60t or 22.8t at 80m, are the biggest units ever manufactured by Potain and rank among the largest in the world for a construction application.

The two MD2200s are operating on the dam sections. Each unit is equipped with a conveyor system that can pour concrete over a distance of up to 105m at a rate of 300-400m3/hr or over a 80m radius when fitted with a 6m3 bucket. The conveyor system, designed by Nippon Conveyors, comprises a 97m x 760mm rubber belt, with one end supported by the crane hook, the other by a platform fixed to the crane mast and a mid-point support, also connected to the mast. Concrete is fed to the platform from the ground by a locally manufactured conveyor.

Four major batching plants supply concrete to these conveyors via a main distribution conveyor system.