World's longest main span

World's largest number of lanes

World's tallest main tower

World's largest anchorage diameter

World's largest main cable scale

West cable tower anchorage pit of the Shiziyang Channel (photo by Binglan Baqie)

On July 11, the diaphragm wall construction of the west cable tower anchorage pit of the Shiziyang Channel, which holds five world No. 1 records, was declared complete. The diaphragm wall works for this anchorage pit section were undertaken by Zhejiang Yitong Special Foundation Engineering Co., Ltd., using a full fleet of four Jintai SX-series air-lift reverse circulation dual-wheel cutters. The high rock-penetration efficiency, precise construction accuracy, and fast service response left many industry experts in disbelief!

Rendering of the Shiziyang Channel (photo by Binglan Baqie)

It is reported that the Shiziyang Channel has a total length of about 35 km, of which the river-crossing section adopts a double-deck bridge about 12.5 km long, making it the first double-deck river-crossing passage at the Pearl River Estuary. The controlling project, the Shiziyang Bridge, is a double-deck steel truss suspension bridge with a main span of 2,180 m, making it the world's longest-span double-deck suspension bridge. The bridge's cable towers are designed at a height of 342 m, with a total of 16 lanes on the upper and lower decks and a design speed of 100 km/h. The circular diaphragm wall of the bridge anchorage foundation has an outer diameter of 130 m, and a single main cable is about 3,832 m long with a diameter of nearly 1.5 m. Once completed, it will set five world No. 1 records: main span length, number of lanes, main tower height, anchorage diameter, and main cable scale.

West cable tower anchorage pit of the Shiziyang Channel (photo by Binglan Baqie)

The main strata at the west cable tower anchorage pit project include: miscellaneous fill, silty fine sand, silt, strongly weathered argillaceous sandstone, moderately weathered argillaceous sandstone, and slightly weathered argillaceous sandstone. Construction of the west cable tower anchorage pit requires rock penetration of about 20 m, roughly 10 m more than the east cable tower anchorage pit handled by the pump-suction dual-wheel cutters.

According to the project manager, the west anchorage pit uses a circular diaphragm wall foundation with a wall thickness of 1.5 m and an outer diameter of 130 m. The diaphragm wall for this project is divided into 90 panels in total, including 45 Phase I panels and 45 Phase II panels. Phase I panels are 6.671 m long, 1.5 m wide, and 44.15 m to 49.1 m deep; Phase II panels are 2.8 m long, 1.5 m wide, and 44.15 m to 49.1 m deep. For Phase I and Phase II panels, 0.25 m of concrete is milled on one side along the diaphragm wall axis, with a cover layer thickness of 0.15 m on one side and vertical accuracy of better than 1/300.

For the same panels, the average construction depth of the west cable tower anchorage pit is slightly deeper than that of the east cable tower by 3–5 m, and the rock-penetration depth is twice that of the east cable tower. So why did the air-lift method lead the pump-suction method by more than 20 panels?

The east cable tower used a total of three dual-wheel cutters—imported pump-suction and domestic pump-suction units—while the west cable tower used a full fleet of four Jintai SX50S and SX50 air-lift reverse circulation dual-wheel cutters. In the early stage of construction, with the same number of trench cutters, the east cable tower started 10 days earlier than the west cable tower, yet the west cable tower overtook it by 7 panels and ultimately led by more than 20 panels in the later stage, completing construction half a month ahead of expectations. An objective analysis shows that the main reasons for its lead lie in the Jintai dual-wheel cutters' high torque, fast rotation speed, resistance to wheel clogging, fewer bucket-lifting and cleaning cycles, and large-diameter slag discharge. The Jintai SX50S and SX50 have torques of 16 t·m and 15 t·m respectively, rotation speeds of 25 r/min and 15 r/min, an average penetration rate of over 2 m/h in soft strata from 0 to 26 m, and an average penetration rate of 1.5 m/h to 3 m/h in rock after 26 m.

Amid the construction boom oriented toward the Greater Bay Area, the achievements of this coordinated on-site operation of four Jintai SX-series air-lift reverse circulation dual-wheel cutters at the west cable tower anchorage pit of the Shiziyang Channel are just one microcosm among many classic cases. At present, nearly 20 dual-wheel cutters are working on major water resource projects in the Greater Bay Area and on metro lines along the Guangzhou-Shenzhen corridor. With their unique air-lift reverse circulation technology and absolute advantages in price and operating cost, Jintai dual-wheel cutters have become the main force in diaphragm wall projects in the Greater Bay Area.