Back at the Hagerbach Test Gallery

For more than 15 years, underground construction experts from all over the world have participated in our popular workshops at the Hagerbach Test Gallery in Switzerland. After a short break due to the Covid-19 lockdowns, we are back with our injection and sprayed concrete workshops. We were happy to welcome 82 underground construction experts from Germany, Turkey, Slovenia, South Africa, Romania, Poland, the United Arab Emirates, and the United Kingdom to this year's training sessions. These two workshops are always a great opportunity to learn together and exchange knowledge about our technologies.

It's all about rock bolting performance and solutions for injection

The first two days were all about our solutions for rock bolting and the skilful selection of injection materials. Our participants were able to experience the unique thixotropic behaviour of our fast-reacting two-component polyurea silicate injection resin MasterRoc MP 368 TIX. They also learned how pre-injection technologies help prepare the ground ahead of the advancing face to avoid water ingress occurring, while also stabilizing the ground.

How safely a mine can be developed is a critical factor for fast, efficient mining. Developed for the placement of cable and rock bolts in underground mines, our innovative solutions improve cycle times for both cable and rock bolt installation.

One of the products we also focused on is our fast-reacting, solvent free two component polyurea silicate resin series MasterRoc RBA 38X, specifically designed for rock bolting it demonstrates excellent thixotropic behaviour straight after mixing, making overhead applications possible without additional sealing.

The benefits of MasterRoc RBA 380:

• Excellent thixotropic properties for secure and precise application

• Application flexibility based on unique thixotropic properties and long-distance pumping capability

• Full-size grouting for increased reliability

• Easy to mix even at low temperatures > 5 °C

• High structural strength combined with flexibility

• Excellent adhesion to damp and low-friction substrates

• Does not react or absorb water for a constant volume

• Fast curing and early strength development for safe working conditions

How can we avert water ingress, while at the same time stabilizing the ground?

There are several challenges that we need to consider while planning stages of mining and tunnelling projects:

• The avoidance of unforeseen and excessive water ingress reduces the costs associated with unexpected water removal.
• The avoidance of ground collapse during difficult excavation conditions creates a safer working environment and improves tunnel face stability
• The tunnel design should facilitate the construction of permanent sprayed concrete linings as a fast and durable safety solution
• Reduce the risk of lowering the groundwater table through the injection of environmentally friendly materials.

To address the above challenges, we discussed the following solutions that consider the pre-injection method used, ground consolidation and permeability reduction as well as time and cost benefits for projects.

Pre-injection method:

• Solving technical challenges ahead of the tunnel face to enhance the tunnelling productivity
• Systematic probe drilling (ahead of tunnel face) to identify zones with complex ground and water structures
• Pre-planned and detailed drill hole patterns combined with appropriate injection technologies

Ground consolidation and permeability reduction

• High-performance injections systems to improve technically challenging ground conditions with minimum effort

Time and cost benefits

• The pre-injection method offers predictability and significantly reduces costs in comparison to post-injection remedies.
• The priority should be performance parameters such as grout stability and penetrability as well as the ability to control setting times. 

Sprayed concrete - what are the do's and don'ts?

The last two days were dedicated to sprayed concrete and its effective use and application. We discussed the do’s and don'ts in a hands-on training environment where we demonstrated how to responsibly and sustainably spray concrete to reduce CO₂ emissions in underground construction.

Sprayed concrete must be applied by qualified personnel to ensure that the desired and designed quality is achieved. Correct application results in the minimum amount of dust and rebound, and the maximum bonding and compaction for a durable and strong lining. These factors are greatly influenced by the nozzle angle and distance in relation to the substrate.

Do's

• The angle of the nozzle should be perpendicular to the receiving surface (i.e., as close to 90 degrees as possible)
• Spraying should be carried out in such a way as to minimize the risk of loose blocks falling and the concrete sagging or dropping – any loose block hanging in mesh reinforcement must be removed
• Pre-fill all over-breaks and weak zones, such as fissures, faults, and gravel zones in weaker ground
• Begin spraying on the walls from the bottom up, moving from both sides to the tunnel crown to form an arch.
• If more than one layer of sprayed concrete is required, apply only when the previous layer can support it – allow previous layers to harden slightly to prevent separation and minimize the risk of falling concrete
• Use fibre-reinforced sprayed concrete for hard rock rather than mesh. Fibre-reinforced concrete is generally a much faster and cost-effective method because it follows the contours of the excavation and consumes less material.

Don'ts

• An incorrect angle of the nozzle will significantly increase rebound and create undulating surfaces, reducing compaction and lowering the strength of the hardened concrete.
• Do not capture rebound, especially in soft ground tunnelling, as the overall stability depends on the integrity of the lining
• Do not move the nozzle in an uncontrolled manner
• Try to avoid spraying concrete through overlapping meshes as this can result in spray shadows, voids and low concrete compaction – if this is unavoidable, special care must be taken.

Operator skill testing with the Edvirt® VR Shotcrete Simulator™

The Edvirt® VR Shotcrete Simulator™ allows our experts to demonstrate the effective use and application of sprayed concrete in a virtual mine setting and lets participants test their own operator skills. It also shows how good concrete mix design and the impact of the chemistry used can influence results.

Originally, the Edvirt® VR Shotcrete Simulator™ was designed to help spray operators learn about spray parameters and help them to improve their skills in achieving the correct layer thickness and reducing rebound. Our Principal Expert in Tunneling and Mining, Wolfgang Aldrian, together with our Global Technical Manager for Sprayed Concrete, Roland Mayr, came up with the idea of incorporating concrete knowledge into the simulator. New software was developed by Edvirt based on the data provided by our experts so that parameters such as the influence of cement quality, accelerator type and concrete temperature can also be incorporated into the simulation. The simulation now takes concrete parameters, cement suitability, accelerator type and their influence on the spray result, rebound and strength development into account.

Determining the setting time for cement mixtures with the Vicat test method

Further to testing their concrete spraying abilities, participants learned how to test cement mixes with the Vicat needle test. The objective of the test is to determine the setting time performance between different cement and set accelerator combinations. The test begins with the weighing and mixing of the materials for the preferred cement mixture: water, superplasticizer, and accelerator. Both the initial and final sets of the mixture are then determined. 

The initial setting is tested by placing the Vicat needle on the surface of the paste, carefully leaving the Vicat needle to stand freely to penetrate through the paste under its own weight. The final setting is achieved when the Vicat needle leaves a barely visible indentation (< 0.2 mm deep). The test results give a good impression of the interaction between cement and accelerator and make it possible to test different dosages with small amounts of materials without having to test large batches on site. A good indicator of suitable results is between an initial setting time of 2-3 minutes and a final setting time between 5-6 minutes after the addition of the accelerator.

The workshop is not just about our injection and sprayed concrete technologies, participants and instructors spent the evenings having dinner together and exchanging ideas and expectations regarding the workshops. Participants also had the opportunity to enjoy a four-course meal at the Sargans castle and learn about the history of the 15th century castle from a distant descendant.

“Hereby I would like to appreciate you all for preparing such wonderful workshops for us. The workshops were very well organized and informative. I found the combination of both theoretical as well as practical parts amazing.”   

DR. A. TAYEBI, Customer

To gain a more comprehensive understanding of our products and solutions, we invite you to explore our brochures on Injection and Sprayed Concrete.

References:

[1] Permanent Sprayed Concrete Linings; Aldrian W., Thomas A., Chittenden N., Holter K.G.; ITA Working Group n°12 and ITAtech AG Lining, Support & Waterproofing, Lausanne 2020