With the continuous development of urban underground spaces

More and more high-rise buildings appear with narrow and ultra-deep foundation trenches

Considering project progress, quality, safety

and cost, among other factors

Conventional foundation trench backfill technology can no longer meet the demands

Carry out new technology integration for the construction waste resource utilization industry chain

Explore suitable and efficient construction waste resource utilization

This is an unchangeable fact

Aerial view of Qujiang·Yunsongjian>>>

The Qujiang·Yunsongjian project undertaken by Shaanxi Construction Engineering First Construction Group

in collaboration with Shaanxi Provincial Institute of Building Research for a pilot project

innovatively adopts high-fluidity, vibration-free, lightweight recycled concrete

for foundation trench backfill, effectively solving technical problems such as lateral pressure and settlement in foundation trench backfill

Achieving resource utilization of construction solid waste

Enhancing the sustainable development of the construction industry

Deep foundation pit backfill of Yunsong Project

Depth reaches 20 meters, narrowest width only 0.5 meters

If traditional lime-soil backfill is still used

It is difficult to operate in terms of manpower, cost, quality, and safety

The project team, after multiple discussions, came up with a new plan

Adopting a new technological ecological model—

First use of 20,000 cubic meters of recycled concrete

High-quality, efficient, energy-saving, and safe solution for ultra-deep foundation pit backfill

Recycled aggregate concrete, as a green building material

Not only can it solve the problem of waste concrete disposal from the source

but it also saves natural aggregate resources

Alleviates the contradiction between supply and demand

Greatly meets the requirements of sustainable development

Has significant social, economic, and environmental benefits

Foundation trench backfill process flow

In response to the narrow site of super high-rise buildings and the need for ultra-deep foundation trench backfill before the horizontal structure is closed, Shaanxi Construction Engineering First Construction Group and Shaanxi Provincial Institute of Building Research actively promoted pilot project collaboration at the Qujiang·Yunsongjian project, innovatively using high-fluidity, vibration-free, lightweight recycled concrete for deep foundation trench backfill, effectively solving technical problems such as lateral pressure and settlement in foundation trench backfill. The produced recycled concrete is used in building construction, realizing resource utilization of construction solid waste. A total of 2.89 million tons of construction waste has been processed, reducing carbon dioxide emissions by more than 50,000 tons.

Schematic of soil lateral pressure

Analysis of Recycled Concrete for Deep Foundation Backfill

Rendering of Qujiang·Yunsongjian

01. Comparison of Construction Techniques

3:7 lime-soil backfill: Complex process, high construction difficulty. Process flow: 3:7 lime-soil mixing → lime-soil transport → layered spreading → manual compaction → sampling and testing;

Recycled concrete backfill: Simple process, convenient construction. Process flow: side formwork erection → recycled concrete pouring.

02. Comparison of Construction Period

3:7 lime-soil backfill: According to the quota, manual backfill of 100m³ requires 70 people working for one day or 1 person working for 70 days;

Recycled concrete backfill: The construction period required for pouring 100m³ of recycled concrete is 4 hours, and the concrete requires no vibration.

03. Comparison of Quality Control

3:7 lime-soil backfill: The backfill soil has lateral pressure, and the garage structure needs to be strengthened to resist lateral horizontal forces. The quality of manual backfill cannot be guaranteed, and there is a risk of water seepage in the basement later. The strength of backfill soil is about 200KPa;

Recycled concrete backfill: After the recycled concrete solidifies, there is no lateral pressure. It provides a barrier for waterproofing membranes, which is beneficial to the waterproofing effect of the basement. The strength of recycled concrete is about 10MPa.

04. Comparison of Green Construction

3:7 lime-soil backfill: Conventional process, no green construction content;

Recycled concrete backfill: Advocated by the state, reduces construction waste transportation and disposal costs, and can recycle construction waste, meeting green construction requirements.

05. Comparison of Economic Benefits

For deep foundation pit backfill in narrow areas, the comprehensive cost of using recycled materials is less than that of 3:7 lime-soil backfill.

Recycled aggregate and recycled concrete have certain differences from ordinary concrete in basic performance and working performance. However, by improving the production process of recycled aggregate and reasonably determining the mix proportion of recycled concrete, the prepared recycled concrete can meet the strength requirements and has engineering practicality. From a long-term development perspective, recycled concrete can fundamentally solve the problem of waste concrete disposal, save resources, greatly meet the sustainable development requirements of society, and have important social, environmental, and economic benefits.