Annular Grout Composition for TBM Backfilling
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Solution Overview
Problem
Current tunnel boring machine backfilling technologies face challenges with long set times, high carbon footprint, and cost inefficiencies, particularly with cement-based grouts, which are brittle and lack durability and adhesion, while alternative alkali-activated aluminosilicate materials require heat and have high rheology, limiting their use as drop-in replacements.
Innovation Solution
A fluidized bed combustion ash-based grout composition combined with sodium silicate, optionally including additives like lime, gypsum, and ordinary Portland cement, which reacts quickly to form a strong seal, addressing viscosity and gelation issues, and can be formulated to match existing equipment and cost standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ordinary Portland cement-based grout is used, then compressive strength is achieved, but carbon footprint increases and brittleness occurs
Solution Approach 1:
The invention changes the chemical composition parameters by replacing ordinary Portland cement with fluidized bed combustion ash and using sodium silicate as an alternative binding mechanism. This substitution maintains compressive strength while eliminating the high carbon footprint and reducing brittleness associated with traditional cement-based grouts.
Solution Approach 2:
The invention creates a composite grout system combining fluidized bed combustion ash, sodium silicate, and optional additives like lime and gypsum. This composite approach achieves the desired mechanical properties while incorporating sustainable materials that reduce environmental impact and improve durability.
2Object-affected harmful factors
If alkali-activated aluminosilicate materials are used, then sustainability improves, but set time increases and rheology becomes too high
Solution Approach 1:
The invention optimizes the rheological and temporal parameters by carefully controlling the sodium silicate concentration (5-20 wt%), water-to-solids ratio, and particle size distribution of the fluidized bed combustion ash. These parameter adjustments ensure the grout remains pumpable during transport while achieving rapid setting and gelation at the application site.
Solution Approach 2:
The invention introduces sodium silicate as an intermediary accelerator that mediates between the sustainable alkali-activated aluminosilicate system and the required rapid setting performance. The sodium silicate enables quick gelation and strength development without requiring external heat input, thus maintaining sustainability while reducing set time.
3Ease of operation
If grout viscosity is reduced for pumping, then transportability improves, but gelation time increases
Solution Approach 1:
The invention creates a dynamic grout system where viscosity and gelation time are not fixed but evolve over space and time. The grout maintains low viscosity and pumpability during transport, then rapidly increases in viscosity and gels upon mixing with sodium silicate at the application site, achieving both transportability and quick setting.
Solution Approach 2:
The invention segments the grout delivery process into two distinct phases: transport phase with low viscosity achieved through controlled water-to-solids ratio and particle size distribution, and setting phase with rapid gelation triggered by sodium silicate mixing. This segmentation allows optimization of each phase independently.
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 fluidized bed combustion ash-based grout provides a quick-setting, cost-effective, and durable solution for tunnel annular gap filling, offering improved compressive strength and sustainability compared to traditional cement-based systems, while being compatible with existing tunnel boring machine equipment.
Implementation Method 1
Once the components are mixed together, the low viscosity grout begins to form a stiff gel in under a minute. The gel then develops strength and within an hour to form a solid that has sufficient strength
Implementation Method 2
aluminosilicate powders such as Class C fly ash, Class F fly ash, ground granulated blast furnace slag, pumice and metakaolin can be reacted with an alkali source such as sodium silicate and/or sodium hydroxide as well as their potassium counterparts to create a cement alternative. These cement alternatives are referred by different names including geopolymers, inorganic polymers, and alkali-activated aluminosilicates
Data Source
AI summary
A method and composition are provided for backfilling the annular gap created as a tunnel boring machine advances through the ground. The fill material is comprised of two components that are combined and mixed together just prior to entering the annular gap. The first component is non-cement slurry consisting of a fluidized bed combustion ash such as coal ash. The second component consists of an alkali silicate such as sodium silicate. Additionally, ordinary Portland cement and/or metakaolin can be added to the grout composition.