Active Jacking Force Calculation for Tunnel Undercrossing Station
Solution Overview
Problem
Current methods for determining the active jacking force during tunneling under existing railway stations lack theoretical support, leading to potential uplift and damage due to excessive stress, as they rely on empirical determinations without stress control.
Innovation Solution
A method using a beam-on-elastic-foundation model and Mindlin's solution to calculate the active jacking force, which controls the settlement of the existing station by determining the vertical stress and deflection, allowing for theoretical determination using site-collected parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If empirical determination is used for active jacking force without theoretical support, then the design process is simple, but the existing station is prone to uplift and damage due to excessive stress
Solution Approach 1:
The patent transforms the empirical determination approach into a theoretical calculation method by changing the parameters from experience-based estimates to scientifically derived values. The Mindlin solution provides exact stress distribution parameters, and the beam-on-elastic-foundation model provides deflection parameters, enabling precise control of the active jacking force to prevent both uplift and insufficient support.
2Reliability
If active jacking force is increased to prevent settlement, then the settlement control effect is improved, but the existing station will be uplifted and damaged
Solution Approach 1:
The patent establishes a feedback control mechanism where the active jacking force is calculated based on the actual stress distribution (Mindlin solution) and deflection requirements (beam-on-elastic-foundation model). The theoretical model provides real-time feedback on the optimal force magnitude, allowing precise adjustment to achieve settlement control without causing uplift or damage to the existing station.
Solution Approach 2:
The patent changes the control parameter from empirical estimation to theoretically calculated values that explicitly account for the balance between settlement prevention and uplift avoidance. The Mindlin solution parameters and beam deflection equations provide the scientific basis for determining the optimal active jacking force magnitude.
3Object-affected harmful factors
If active jacking force is too small, then the station structure is safe from uplift, but the settlement control effect is not obvious
Solution Approach 1:
The patent changes the active jacking force parameter from insufficient empirical values to theoretically optimized values. The Mindlin solution provides the stress distribution parameters, and the beam-on-elastic-foundation model provides the deflection control parameters, ensuring the active jacking force is large enough to achieve effective settlement control while remaining within safe limits to prevent uplift.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively controls the settlement of the existing station within safe ranges, preventing uplift and damage by providing a theoretical calculation for the active jacking force, ensuring safe construction practices.
Implementation Method 1
The existing station is simplified as a section of homogeneous long beam to form a beam-on-elastic-foundation model; vertical stress on the existing station under the combined action of unloading stress and the active jacking force is solved by Mindlin's solution
Data Source
AI summary
Determining an active jacking force of a tunneling closely undercrossing existing station, includes: acquiring design parameters of stations, and geological parameters of a construction site; obtaining a stress solution expression of the active jacking force on the existing station to obtain a stress solution of any point in a semi-infinite space under the action of a vertical load, replacing the vertical load with a vertical load acting on the existing station, and obtain a vertical stress solution of the existing station; obtaining a relational expression between the deflection and the stress solution of the existing station; and substituting the stress solution expression of the active jacking force into the relational expression between the deflection and the stress solution of the existing station according to boundary conditions at both ends of a beam on elastic foundation to obtain the active jacking force that controls the deflection of the existing station.