Recovery & Recycling of Excavated Tunnel Waste

Rock excavated in an average tunneling project is often considered waste and mostly finds its way to a landfill. Depending on the geology and excavation method used, the extracted material can have significant quality deviations and may be unsuitable for use as construction aggregates because of varying geometric, physical, and chemical characteristics. However, if this waste is suitably treated and processed, it can be recycled and used as a substitute for conventional mineral aggregates at a construction site.

The processing of tunneling rock wastes into usable products is popularly known as tunnel excavation rock recycling. The most common application of the processed material is as aggregates for concrete or as a sub-base for road building, which is good for both environment and business. Benefits include:
  • Generates more value than simply being dumped in a landfill or to fill up old quarries
  • Utilisation of rock is usually near a processing facility or a concrete batching plant which significantly reduces the need for transporting aggregate
  • Lesser need for landfills creates a positive environmental impact
  • The project being almost self-sustained in construction aggregates results in the investment cost of the facility getting repaid quickly.
TBMs: Tunnel Boring Machines are one of the most popular methods of tunneling. TBMs create rock particles with excessive fines - a problem affecting the quality for both sub-base and concrete aggregates. Mechanical screening (scalping screener), which usually is the first stage of processing tunnel rock in a TBM removes rock particles below 16-20mm diameter. This process aims to get rid of the high amounts of fines that are created by tunneling in hard rock.

By 2018, there were seven confirmed projects worldwide that were recycling tunnel rock on an industrial level. These projects are all placed in hard rock, the details of which are given in table:

recycled material

The above data indicates that, on an average, around 20% of the tunnel debris was successfully recycled. The low percentage of recycled material can be attributed to the large portion of fines generated during the drilling process. In industrial concrete, such fines destroy the flow of the concrete in its fresh state due to agglomeration that adversely affects concrete batching.

One of the ways to increase the yield from tunneling waste is to create concrete aggregates of 8 mm or 4 mm fractions that are free of silt. It requires a more advanced processing facility for size control of finer particles. It also needs an accurate classification technique to achieve the desired particle size range for concrete making. Removing fines is often done using water as a medium, which requires a water treatment plant to clean the water and recirculate it into the system.

Recovery & Recycling of Excavated Tunnel Waste

Apart from silt removal and generating products as per specified particle size distribution, treating excavated waste needs prior removal of contaminants like various types of scrap (wood chips, plastic, and other trash material) most likely to be generated during drilling. In many cases, depending on the characteristics of the rock, there could be incidences of low specific gravity minerals and various particles with flat elongated structures. Special techniques are necessary to address these.

The environment-friendly, patented wet processing technology from CDE Asia addresses all the issues and has the following key features:
  • Zero waste discharge to atmosphere
  • 95% re-circulation of process water
  • Removal of scrap such as wood chips, plastic, other trash material
  • Minimum space for installation
  • Skid mounted portable units
  • Suitable for shifting from location to location
  • Minimum unit power requirement
  • Less than 80db noise level
It can recycle finer materials of under 20mm fractions and generate construction-grade aggregates and sand, both for concrete and plaster. Bentonite, an expensive mineral used in the drilling process, can also be recovered and recycled from the finer particles. The increased utilization of excavated material can have a significant positive financial impact on the project.

References: Wikipedia
CRCHI Creates World Record - Deploys 52 TBMs at Guangzhou Metro Construction
The construction project of Guangzhou Metro Line 18/22 - the largest metro investment in China - has attracted much attention. CRCHI has tailored 52 φ8.8m EPB/Slurry TBMs for the project, creating a world record of the largest TBM construction group

Read more ...

Managing Geological Complexity in BVC and PAC of Tehri PSP
Tehri hydroelectric project is located on the left bank of River Bhagirathi in the state of Uttarakhand. Tehri Pumped Storage Project (PSP) comprising 4 reversible pump-turbine units of 250 MW each, involves construction of an underground Machine Hall

Read more ...

New-Gen DRAMIX® Fiber Reinforced Precast Segment Allows Eco Efficiency & Performance
As mentioned in the fib bulletin 83 on Fibre Reinforced Precast Segment: for sustainable use of structural concrete, environmental and mechanical performances of concrete structures must have the same importance. Through sufficiently high mechanical

Read more ...

Breakthrough by two 15.01m Slurry TBMs of CRCHI in two projects
On March 12th 2023, the breakthrough by the largest slurry TBM in China’s Hunan Province marked the completion of the right line tunneling of the Xiangya Road river-crossing tunnel in Changsha City. It represents the largest diameter shield machine tunnel

Read more ...

Sela Tunnel Project - Overcoming The Impossible
The responsibility for construction and maintenance of Balipara-Charduar-Tawang (BCT) Road has been entrusted to Border Roads Organisation (BRO). The 317.520 km long road connects West Kameng and Tawang districts of Arunachal Pradesh to the rest

Read more ...

Slurry TBM ‘Channel Express’ launched by CRCHI for working in Water Supply Tunnels in Singapore
On February 1, 2023, CRCHI attended the launching ceremony of its Slurry TBM ‘Channel Express’. It will be used in the construction of key water supply tunnel project TWRP Pipeline Contract 1 in Singapore where it will bore 1.6km with the inner diameter

Read more ...

China’s Largest TBM - With Panda Face Emerges From Tunnel
On 12 December 2022 ‘Jinxiu’ - China’s largest EPB TBM developed by CRCHI - marked the first smooth breakthrough of the Jinxiu Tunnel, a key control project of the Chengdu-Zigong high-speed railway. Jinxiu is China’s largest diameter EPB TBM with

Read more ...

STRUCINSPECT Technology Transforms Inspection of Los Angeles Metro Tunnel Network
With drones, multispectral optics, and AI, Austrian joint venture transforms tunnel inspection in the US. The world’s first infrastructure lifecycle hub taps the rapidly growing global market for infrastructure inspections. The remarkable thing about

Read more ...

CRCHI showcases total solutions of Underground Engineering Equipment
China Railway Construction Heavy Industry Corporation Limited (CRCHI) brought the whole industry chain products and solutions to bauma CONEXPO INDIA 2023. CRCHI exhibited TBMs, drilling and blasting method equipment, cotton pickers, and other

Read more ...

Sandvik sets up new factory; hands over first ‘made in India’ tunnelling jumbo to KSR Group, Hyderabad
In a historic event held on 30th January, 2023 Sandvik proudly presented the key of the first ‘made in India’ DT820 Tunnelling Jumbo to Mrs. and Mr. Koneru of KSR Group, Hyderabad. The machine was rolled out from Sandvik’s newly set-up state-of-the-art

Read more ...

CRCHI Slurry TBM ‘Avni’ Helps Make a Breakthrough in Bangalore Metro Project
The 6.6m Slurry TBM developed by CRCHI exited the tunnel at Vellara Station, Phase II of Bangalore Metro in India, becoming the first TBM to complete the breakthrough for the whole line of the project. Avni is one of the four slurry TBMs provided by CRCHI

Read more ...

The Bolter Miner - A Technology Revolution for Roadway Development in Underground Coal Mining
In India, coal is still the primary source of energy; over the past few years, there has been quantum jump in coal production level, but it was mostly due to the high percentage share from the opencast sector. The country is witnessing a fast

Read more ...

CRCHI emerges as provider of total underground engineering equipment and solutions
China Railway Construction Heavy Industry Corporation Limited (CRCHI) showcased its comprehensive range of equipment and products at bauma that included solutions for the whole industry chain in the field of

Read more ...

Herrenknecht AG wins bauma Innovation Award 2022 for development of continuous tunnelling
Herrenknecht AG won the highly coveted award bauma Innovation Award 2022 in the category “Machine Technology” for the new development of continuous tunnelling. The award was given for the next innovation boost in the mechanized

Read more ...

The Genesis of Underground Engineering
Regardless of the tunnelling technology used, tunnel designers decide the future success or failure at an early project stage. In fact, designers are the real managers of tunnel construction. The choice of design together with selected contract model is

Read more ...

Managing Geological Complexity in BVC and PAC of Tehri PSP, India - A case study
Tehri hydroelectric project is located on the left bank of River Bhagirathi in the state of Uttarakhand. Tehri Pumped Storage Project (PSP) comprising 4 Nos of reversible pump-turbine units of 250 MW each, involves construction of an underground Machine Hall

Read more ...

TBM driving under low overburden by adopting innovative methodology
TBM mining in urban areas particularly under low overburden (less than 0.5D, D = tunnel Dia) is a big challenge to design team as well as execution team. While working in a Lucknow metro project, the metro authorities encountered a stretch where TBM had to cross

Read more ...

Tunnel Ventilation System Basic Concepts and Designing Principles
The term ventilation combines several functions such as smoke extraction, pollution ventilation, and ventilation for environmental purpose. The design of a ventilation system is usually based on three scenarios: During construction: to provide external

Read more ...

CRCHI Mega Slurry TBM ‘Jinghua’ Assists the First Tunnel Section Breakthrough of Beijing East Sixth Ring Road Reconstruction Project
In September 2022, the Beijing East Sixth Ring Road Reconstruction Project reported another good news: the CRCHI mega slurry TBM ‘Jinghua’ smoothly reached the intermediate air shaft, marking the project’s achievement. The maximum excavation diameter

Read more ...

TERRATEC EPBMs ready to tackle Kanpur Metro’s 1st Underground Section in India
TERRATEC celebrated the successful site acceptance testing of two 6.52m diameter Earth Pressure Balance Tunnel Boring Machines (EPBMs) for Uttar Pradesh Metro Rail Corporation (UPMRC) for Corridor-1 of Kanpur MRTS Project (KNPCC-05) in India. The two 6.52m

Read more ...