Understanding the interaction between the plasticity of muddy soil and earth pressure is vital for ensuring tunnel stability and anticipating ground behavior during earth pressure balance (EPB) shield tunnelling, a prevalent method of underground excavation. A team of researchers from Shibaura Institute of Technology has developed a small-scale experimental model coupled with moving particle simulation-based computer-aided engineering analysis. This approach effectively predicts the plasticity of soil and its related factors while avoiding the expenses and time associated with field studies.
Grasping the connection between the plasticity of muddy soil and earth pressure is essential for preserving tunnel integrity and forecasting ground behavior during earth pressure balance (EPB) shield tunnelling, a commonly used underground excavation technique. Researchers at Shibaura Institute of Technology have created small-scale experimental models integrated with moving particle simulation-based computer-aided engineering analysis, which reliably forecasts soil plasticity and its associated factors without incurring the high costs and time delays typical of direct field analyses.
Infrastructure often faces significant damage due to both natural geotechnical hazards such as floods and earthquakes, as well as human-induced issues like underground construction and excavations. Civil engineering and disaster risk management have intensely explored strategies to mitigate these risks and continue to seek more effective methods for preventing large-scale deformations that accompany such hazards. With the introduction of computer-assisted simulations, researchers now utilize particle-based techniques like moving particle simulations (MPS), which offer a valuable resource for independent deformation analysis across larger areas. Although this method has gained traction recently, it has yet to be widely implemented in predicting ground behavior during the design or construction phases.
By merging small-scale experimental models and computer-aided engineering (CAE) analysis via moving particle simulation (MPS), a research team from Shibaura Institute of Technology, led by Professor Shinya Inazumi from the College of Engineering, has delved into various mysteries surrounding earth pressure balance (EPB) shield tunnelling in their recent study published in Tunnelling and Underground Space Technology on 21 August 2024.
EPB is a widely adopted technique for tunnel construction that leverages the excavated muddy soil to provide support for the tunnel face. This process involves the use of foam, slurry, or other additives to plasticize the excavated material to ensure it is impermeable and easily transportable.
The researchers discovered that despite its popularity, there is limited understanding of how the plasticity of muddy soil, modified by mixing the excavated soil with plasticizing additives like bentonite solution, influences the earth pressure within the tunnelling chamber. Understanding these relationships can significantly enhance the likelihood of preventing ground deformations while also ensuring efficient sediment management throughout the tunnelling process.
“Urban areas are becoming increasingly dependent on underground infrastructure, so we aimed to create a predictive tool that enhances the resilience of urban infrastructure while minimizing costs associated with delays and structural damages caused by unstable tunnelling operations through effective soil plasticity management,” Prof. Inazumi explains the purpose behind this study. He also pointed out that since the research lab associated with this investigation aligns with the UN’s sustainable development goals, they looked into the environmental impact resulting from large amounts of excavated materials and the application of chemical additives like bentonite to identify ways to enhance the sustainability of construction projects.
The experimental configuration featured a sealable soil tank that simulates a chamber, along with descending and ascending phases of an agitation blade model achieved by incorporating a twin-pair earth pressure gauge in a shield tunnelling machine. This setup, in conjunction with calculations from a computer-aided analysis system based on moving particle simulation (MPS), accurately replicated the tunnelling process and measured changes in earth pressure in response to variations in plasticity caused by the agitation of muddy soil.
The findings indicated that earth pressure serves as a reliable metric for assessing soil plasticity, along with related factors such as vane shear strength and slump value, which together influence tunnel stability and machinery operation. Supported by MPS, the CAE analysis system proposed by the researchers accurately reflects experimental data, affirming its effectiveness in evaluating and visualizing the plasticity and fluidity of muddy soil during tunnelling.
Assessing earth pressure in real field scenarios by examining the plasticity state of muddy soil under various conditions can be resource-intensive and costly. However, the combination of small-scale experimental modeling with computational capabilities demonstrated in this study can be a significant asset for optimizing EPB shield tunnelling operations and enhancing sediment management strategies. This could lead to new innovative approaches that greatly improve the safety and efficiency of underground construction projects, especially within urban settings.
“The outcomes of this study could directly impact the construction of subway systems, underground utilities, and roads in densely populated urban regions by facilitating controlled operations that minimize disruption to the surrounding ground. We also aspire for our proposed strategies to be implemented to reduce the environmental consequences of the tunnelling process and bolster safety protocols in areas vulnerable to earthquakes or other geotechnical threats,” concludes Prof. Inazumi.
