Suitable Method (Empirical Analytical and Numerical Method) to Evaluate the Requirements for the Elephant Feet, Temporary Invert and permanent Invert

A. Objective of ThesisAs per NATM philosophy, the controlling the deformation is important part of the NATM philosophy and the same should be done in construction stage.In soft ground conditions during heading excavation, techniques like Elephant's foot, micro-piles, and temporary invert are recommended.These methods help to control the deformation through ring closure and provide significant support for the top heading shell.Additionally, Elephant's foot and micro-piles ensure stability throughout the benching phase, making the excavation process more secure and effective.The use of elephant's feet and micro piles is a specialized technique in tunnelling.The elephant's feet refers to the widened base of top heading support system distributes loads more effectively, preventing excessive settlement.Micro piles are small-diameter, high-strength steel pipes or bars drilled and grouted into the ground to provide additional support to the structure.while constructing tunnels, maintaining stability during excavation is important.The top heading method involves excavating the upper portion of the tunnel first, followed by the lower sections.During this process, it's essential to support the newly exposed surfaces to prevent collapses or excessive deformation.The application of temporary and permanent invert closures helps manage these challenges.An invert is the lowest point inside the tunnel cross-section, and closing it off temporarily or permanently provides a solid base and resists the inward pressures from the surrounding ground, which can lead to "squeezing" conditions.Squeezing occurs when the tunnel walls deform inward due to high pressure from the surrounding rock or soil.Implementing these measures helps maintain tunnel stability and ensures safe and efficient construction progress.Despite their benefits, the implementation of techniques such as the Elephant's Foot, micro-piles, temporary invert and permanent invert in real projects often leads to debates due to the associated costs and time requirements. Cost Implications: The use of these advanced support techniques can significantly increase the overall cost of the project.This includes the cost of materials, specialized equipment, and additional labour required for their installation. Time Requirements: Installing these support systems can also extend the project timeline.The additional steps involved in setting up micro-piles or constructing a temporary invert require careful planning and execution, which can delay the overall project completion. Technical Complexity: Implementing these techniques requires specialized knowledge and expertise.Ensuring that they are installed correctly and function as intended adds another layer of complexity to the project.Considering the significance and challenges associated with the implementation of the Elephant's Foot, micro-piles, temporary invert and permanent invert in soft ground tunnelling conditions, the primary objective of this thesis is to determine the actual requirement based on empirical, analytical and numerical method.