Foaming Additive for Tunnel Boring Machine Soil Conditioning
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Solution Overview
Problem
Current soil conditioning agents used in tunnel boring machines, such as bentonite and polymer suspensions, can increase soil water content, leading to liquid systems that are difficult to extract and may cause clogging, especially in clayey soils, reducing efficiency and causing cutterhead issues.
Innovation Solution
A readily biodegradable foaming additive comprising an alkyl ethoxy sulphate or laureth sulphate salt and a biopolymer like xanthan gum or guar gum, injected into the tunnel face to generate a stable foam that softens soil and maintains tunnel face stability, even in brine conditions, with a half-life that allows longer-lasting conditioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If bentonite and polymer suspensions are used as soil conditioning agents, then soil stability is improved, but water content increases causing liquid systems that are difficult to extract and may cause clogging
Solution Approach 1:
The invention uses foam as a conditioning agent instead of liquid suspensions. Foam is a gas-liquid dispersion that introduces air bubbles into the soil, changing the phase composition from purely liquid to gas-liquid-solid. This phase transition reduces the effective water content and prevents the soil from becoming overly liquid while maintaining stability.
Solution Approach 2:
The invention employs foam (a pneumatic system involving gas bubbles) rather than liquid suspensions (hydraulic system). The foam structure provides soil conditioning through the combined effects of gas bubbles and liquid film, reducing water content issues while maintaining soil stability and preventing clogging.
2Quantity of substance
If foam is used as a conditioning agent, then water input is reduced, but foam stability duration needs to be extended for longer-lasting soil conditioning
Solution Approach 1:
The invention modifies the chemical composition parameters of the foam by incorporating specific biopolymers (xanthan gum, guar gum) and surfactants in optimized concentrations. These parameter changes enhance the foam's structural stability and extend its half-life, allowing the foam to maintain its conditioning effect for longer periods while keeping water input low.
Solution Approach 2:
The foam conditioning agent is formulated as a composite system combining multiple components: biopolymers (xanthan gum or guar gum), surfactants (alkyl ethoxy sulphate or laureth sulphate salts), and water. This composite structure synergistically enhances foam stability and extends duration of action while maintaining low water content.
3Strength
If more water is added to soil conditioning agents, then soil softening is improved, but extraction difficulty increases and clogging occurs
Solution Approach 1:
By using foam instead of liquid water, the invention introduces gas phase bubbles that soften soil through mechanical action and gas pressure without adding excessive liquid water. This phase transition approach achieves soil softening while avoiding the clogging and extraction difficulties associated with high water content.
Solution Approach 2:
The foam-based pneumatic system delivers softening action through gas bubble expansion and collapse, combined with limited liquid film presence. This pneumatic-hydraulic combined approach softens soil effectively while maintaining low overall water content, preventing clogging and facilitating easier extraction.
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 additive provides improved soil conditioning stability and prevents clogging, maintaining efficient excavation by reducing water input and extending the duration of effective soil conditioning, ensuring consistent tunnel face support and cutterhead performance.
Implementation Method 1
Aqueous foaming additives comprising a surfactant and a stabilising agent are known in the state of the art. Thus, in operation, the foam is directly injected into the cutterhead at the excavation interface.
Implementation Method 2
EP 0 070 074 describes a foaming additive consisting of an alkylpolysaccharide surfactant and a sulphate or sulphonate and/or carboxylate cosurfactant.
Data Source
AI summary
Disclosed is a liquid foaming additive for use in mechanised excavation by a tunnel boring machine, containing 5-40% by weight of one or more surfactants, 0.01-5% by weight of one or more biopolymers, and 55-94.09% of water.