Shenzhen Galaxy Twin Towers 

Introduction:

Recently, the west tower of Shenzhen Galaxy Twin Towers, constructed by Shanghai Construction No.4 Group, passed completion acceptance 45 days ahead of schedule and stands firmly on Shenzhen's central axis, adding another super high-rise landmark to the city. The west tower is set to open on June 30, a full 3 months ahead of plan.‍

The west tower has 74 floors above ground and is 356 meters tall. Construction started on May 16, 2019. During the process, No.4 Group fully leveraged its core capabilities in super high-rise, super deep foundation pit, and reverse construction method, and innovatively developed key construction technologies tailored to the project's characteristics and difficulties, efficiently completing the construction of China's tallest equal-height twin towers.

The Galaxy Yabao High-tech Innovation Park Plot 3 general contracting project is constructed by Shanghai Construction No.4 Group, including a 74-story, 356-meter-tall super high-rise tower (the west tower of the twin towers), a 1,200-seat cultural activity center, and a 5-story underground commercial building of 160,000 square meters, with a total construction area of 322,000 square meters. It is a giant high-tech comprehensive industrial project integrating R&D offices, commercial center, and art center.

This project has great difficulties in construction organization, many technical difficulties, tight schedule requirements, and high safety risks. No.4 Group optimized construction organization, ensured efficient output of project construction through "top-down and bottom-up construction methods" and "flow operation", innovatively responded to project characteristics, overcame "extra hard rock", stabilized the "core tube", led high-quality construction with technical breakthroughs, and set a new height for projects in South China.

"Top-down and Bottom-up Construction" and "Flow Operation"

Ensure Efficient Construction‍

The project site is small and close to the under-construction subway, with high subway protection requirements and early handover of relevant work faces required. At the same time, it is constructed in the same pit simultaneously with adjacent sections and shares the only ramp to the pit, making construction organization difficult. In response, the project optimized the layout from the overall construction organization and adopted partitioned and block construction for the structure.

Section diagram

Construction in top-down area

The side adjacent to the subway adopts the top-down method, with the negative second floor slab as the interface between top-down and bottom-up construction. First, earth and rock are excavated to below the negative second floor slab, then bottom-up construction is carried out to ground level and backfilled, the site is handed over to the subway party, and finally the basement is completed by top-down method.

Top-down area completed and handed over to subway party in 6 months

The bottom-up area adopts the overall construction deployment concept of "tower first, podium later", "north area first, then south and central areas", and "south area constructed as slope is removed". During the process, temporary sites, roads, and facilities were adjusted multiple times according to different stages and conditions. Under the premise of ensuring subway construction safety, the subway area was handed over in 6 months, ensuring the subway's scheduled operation.

For tower construction, the project team optimized the construction organization route, formed vertical flow operation, created a reasonable vertical flow layer difference, created work faces, maximized schedule compression, saved time, and improved construction safety.

Vertical construction flow of tower

The luffing jib crane is placed inside the core tube to reduce the impact of typhoons.

Customized large-span load-bearing beams and non-standard internal climbing support frames

The B2-1 floor of the tower basement was changed to steel structure, and a steel platform was installed during the basement stage to form vertical flow in advance.

Steel platform during basement stage

The external climbing frame was installed in segments in the air, saving the time for erecting the bottom support frame.

Segmental installation of attached integral lifting scaffold in the air

Through these measures, the tower construction achieved a speed of one floor every 4 days at the fastest, and the tower core tube was topped out 1 month ahead of schedule.

Tower core tube topped out

The optimization of construction organization ensured the rapid progress of the project. The project completed the construction of more than 10,000 cubic meters of large foundation slab concrete in 2.5 days, completed the superstructure construction in the top-down area and handed over the work face to the subway in 6 months, completed the removal of the ramp containing 37,000 cubic meters of extra hard rock in 6.5 months, and completed the construction of the 74-story tower in 18 months, achieving efficient output of project construction.

The project won the 2021 second-half Shenzhen Construction Project Safety Production and Civilized Construction Excellent Site Award and the 2022 Guangdong Province Construction Project Quality Structure Award.‍

Overcome "Extra Hard Rock" and Stabilize "Core Tube"

Ensure Project Quality‍

Completely different from the soft soil geology of the Yangtze River Delta, South China is mostly rocky geology. The Galaxy project encountered typical rocky foundation during deep foundation pit construction: shallow rock surface, large volume, high hardness, and difficult excavation. The large area is slightly weathered granite, with an average uniaxial compressive strength of 76.5 MPa, equivalent to C75 concrete hardness. Rock excavation takes a long time and is costly. How to handle the extra hard rock became a key problem to be solved in project construction.

By comparing the effects of "water drill mining" and "static crushing mining", the project team adopted the efficient "water drill rock excavation" process and self-innovated a new vertical adjustment technology for one-column-one-pile, achieving high-precision hoisting of steel pipe columns on steep rock walls.

Construction technology of one-column-one-pile on high and steep rock

At the same time, through track cranes and pushing to the bottom slab, the basement car ramp was flexibly used for earth and rock transportation, improving transport efficiency and saving schedule.

Even so, the excavation volume of extra hard rock was still considerable, and the required schedule was still long. The technical team conducted research and discussion again, trying to solve the problem from the root, and proposed a basement exterior wall construction technology based on rock wall as formwork, retaining the complete rock from the retaining pile to the basement exterior wall, and directly connecting the top-down horizontal structure with the rock reliably. This not only reduced disturbance to the support structure and surrounding environment, but also reduced rock excavation by about 3,500 cubic meters, effectively shortening the schedule by nearly 4 months.

Process flow of rock wall as formwork

In the vertical construction flow of the tower, the construction of the core tube is the top priority. The sudden change of the core tube requires the steel platform to efficiently complete deformation in the air.

For this, the project designed the frame body in the corresponding area of the steel platform as unitized quick-release modules. On floors where the wall limbs disappear, the corresponding frame body is entirely removed, so that the sudden change of the core tube did not affect the schedule, ensuring the core tube construction speed of one floor every 4 days at the fastest.

Unitized quick-release modules

Simulated stress state

At the same time, the stress state of the core tube under tower crane dynamic loads, wind loads, etc. was simulated, and the feasibility of the thin-walled core tube in a "hollow" state leading the outer frame by 15 floors was safety demonstrated, ensuring safe and efficient construction of the tower.‍

"Veterans" and "New Generation"

Accelerate Local Integration‍

As a strategic high-quality large project in South China, cultivating a high-quality young talent team is another major work goal of the project.

In 2018, under the call of nationalization, project backbone members from various brother units in Shanghai went to Shenzhen and, together with local employees who had just joined the company at that time, formed the Galaxy project management team.

The team aimed at streamlined and efficient operation. At peak times, there were only more than 40 management personnel, with local employees accounting for over 80% and young employees accounting for nearly 70%. With both young and local characteristics, the Galaxy project became a large platform for young people to learn and inherit excellent experience, technology, and culture, and also an in-depth practice of local integration development.

The project party branch, together with the project team and various lines, created a platform for young people, adhered to "mentorship" work, actively carried out professional training in technology and construction lines, led young people to study and overcome technical difficulties, and helped young people improve their personal abilities. During project construction, 7 young talents were promoted, some grew into regional project deputy managers, regional project engineers, project manager assistants, and some went to other regional markets to continue striving.