Prestressed Hydroelectric Tunnel Segments Using Swelling Grout
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Hydroelectric power plant pressure tunnels excavated with tunnel boring machines face challenges in stabilization and sealing due to high internal pressures and pressure fluctuations, requiring effective prestressing and sealing methods to prevent water ingress and maintain structural integrity.
Innovation Solution
The method involves filling the annular gap between the cavity and segment components with multi-grain pearl gravel, followed by pressurized injection of swelling, waterproof grout for prestressing, and subsequent re-sealing with silicate resin injection to maintain and increase inward preload, while using multi-grain pearl gravel to densely fill gaps and reduce grout volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If segment components are assembled in a drilled cavity to form a closed tunnel wall, then the tunnel structure can be constructed, but the joints between segment components remain unsealed allowing water circulation
Solution Approach 1:
Sealing membranes are applied to the outer wall of the segment components before the annular gap is filled with grout. This preliminary sealing action ensures that joints between segments are protected from water ingress before the filling process begins, resolving the contradiction by establishing reliability upfront rather than as a subsequent measure.
Solution Approach 2:
The solution combines sealing membranes (flexible barrier) with grout filling (rigid structural material) to create a composite sealing system. The membranes provide immediate joint sealing while the grout provides structural support and additional sealing, together achieving reliable water-tightness without excessive construction complexity.
2Stability of the object's composition
If the annular gap is filled with grout to prestress the segment components, then the tunnel structure is stabilized, but the grout shrinks and creeps over time reducing the prestress effect
Solution Approach 1:
The patent specifies using grout with controlled swelling properties that expand by 0.5 to 1.5% during hardening. This parameter change in volume compensates for the shrinkage and creep that occur over time, maintaining the prestress effect and structural stability for the duration of the tunnel's service life.
Solution Approach 2:
The grout undergoes a phase transition from liquid state (when injected) to solid state (when hardened), accompanied by a controlled swelling transformation. This phase change and volume expansion counteracts the subsequent shrinkage and creep, ensuring long-term prestress maintenance.
3Quantity of substance
If multi-grain pearl gravel is used to fill the annular gap, then the gap is densely filled and grout volume is reduced, but the gravel alone cannot provide adequate sealing
Solution Approach 1:
The filling material is segmented into two components: multi-grain pearl gravel (for structural filling and volume reduction) and swelling grout (for sealing and prestressing). This segmentation allows each material to perform its optimal function while together achieving both economy and reliability.
Solution Approach 2:
The sealing membranes act as an intermediary between the gravel filling and the water pressure. The membranes are applied to the segment outer walls before gravel and grout filling, providing the primary sealing function while allowing the gravel-grout mixture to provide structural support with reduced material volume.
4Force
If high pressure is applied during grout pressing to achieve adequate prestressing, then segment components are preloaded, but the process requires excess pressure that may cause damage
Solution Approach 1:
Sealing membranes are applied beforehand to cushion and distribute the pressure during grout injection. These membranes prevent pressure concentrations that could damage segment components while still allowing adequate prestress to be achieved through the controlled swelling of the grout.
Solution Approach 2:
The grout's swelling property changes the pressure dynamics during and after injection. The grout continues to expand after initial pressing, maintaining prestress without requiring excessively high initial pressures that could damage the segment components.
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
This approach provides stable prestressing of segment components and rock, prevents water ingress, and allows for re-tensioning as needed, ensuring the structural integrity and sealing of pressure tunnels under varying pressure conditions.
Implementation Method 1
grouting mortar that swells and is waterproof when hardened is pressed into the gap under pressure
Implementation Method 2
The swelling process of the grout during hardening compensates for the shrinkage and creep of the segment components
Implementation Method 3
The sealing effect of the hardened grout simultaneously prevents the entry and exit or circulation of water
Implementation Method 4
For re-sealing and re-tensioning, hardening injection agent, preferably silicate resin, is injected into spaces between the outer walls of the tubbing components and the films covering them
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The method involves assembling lining segment components in a hollow space for forming a closed tunnel wall. An intermediate area between an inner wall of the hollow space and an outer wall of the components is filled with mortar or multi-grain Perl gravel. Waterproof injecting mortars are pressed into the intermediate area for generating additional bias on the components through sources of the mortars. A hardened injection medium is injected into the intermediate area, where foils are connected with outer walls of the components such that the foils are bulged outwardly by the medium.