Overview
In order to reduce the construction time and in some case to achieve an economically viability of the project, underground traffic routes are often excavated by tunnel boring machines (TBM). Squeezing ground may slow down or even obstruct TBM operation and, if occurring over frequent tunnel intervals or persisting over longer portions of a tunnel, may be decisive for the economic viability and the feasibility of a TBM drive. The specific problems are sticking of the cutter head, jamming of the shield, extensive convergences of the bored profile or even destruction of the support in the back-up area. In several cases feedback effects between the different problems are possible.
Important basic research results – related to the issue "TBM drives in squeezing ground" – have been already obtained at the ETH Zurich. These will represent the basis for the proposed research project. In particular, the specific developed mathematical models and computational methods will be utilised. The main goals of the proposed research project are the formulation of basic principles for the decision-making and the provision of design tools for the planning of TBM drives in squeezing ground. For the assessment of the feasibility of a TBM drive the project engineer bases on experiences, on plausibility considerations and on static calculations. The work packages of the proposed research project take this procedure of decision-making into account.
The main objective of the project is formulation of basic principles for the decision-making and provision of design tools for the planning of TBM drives in squeezing ground:
- Reviewing and uniform description of case histories, which are documented in the literature;
- Improving understanding of the geotechnical and technological interrelationships, representation of the specific hazards and the technical solutions, classification of the relevant influencing factors and structuring of the numerous interactions;
- Creation of nomograms for the simple determination of the necessary thrust force and for the assessment of the shield jamming risk;
- Evaluation of the pros and cons of the different TBM types and tunnel support concepts depending on the tunnel diameter.
In a first phase, the experience of completed projects, which are documented in the literature, and worked up according to uniform criteria (geology, TBM-type and diameter, etc.) are analysed.
Thereafter, the geotechnical and process engineering connections for the various TBM types are recognised conceptually, the specific hazards and building solutions presented, organised the relevant factors and the numerous interactions structured and analysed qualitatively.
Although experience and plausibility considerations in planning are essential, certain aspects only by quantitative analysis can be assessed. Based on the work already done research of ETH-Z selected issues are studied (work packages 3 and 4).
In work package 3 decision aids are provided under the simplified assumption of a mountain without time dependent material behavior. This assumption means that the rock deformations not delayed relative occur for propulsion, and is therefore tend to be on the safe side. For this relatively simple limiting case, the relationship between the required feed force and the mountain and tunnel-side factors (mechanical properties of the rock, overburden pressure, drill diameter, plate length, overcut, coefficient of friction between the mountains and shield) is analyzed by an extensive parametric study, which related the range of factors mentioned will cover. In order to reduce the computational effort, the developed calculation method must be further optimized. The results are presented in the form of nomograms, which allow for easy determination of the required for the avoidance of jamming of the label feed force or the assessment of risk "sign blocking" and therefore constitute a useful tool for project work in practice.
Work package 4 deals with the factors "Machine Type" and "expansion" in-depth examination. Based on comparative research findings on the pros and cons of different types of machinery and expansion concepts are to be obtained, depending on the tunnel diameter and geotechnical situation. The comparative studies are carried out for typical drilling diameter (corresponding to the cross sections of pilot or safety shafts and tunnels) and for typical "Mountain Falls". The latter will respect (size of convergences) and severity of rock behavior differ preassure hastily speed the mountain (rate of deformation) and defined in terms of a rough classification based on preliminary calculations.
As an example of the complexity and practical relevance of the questions to be e
Funding
Results
The main output of the project is formulation of basic principles for the decision making and provision of design tools for the planning of TBM drives in squeezing ground. The following activities took place:
- Reviewing and uniform description of case histories, which are documented in the literature;
- Improving understanding of the geotechnical and technological interrelationships, representation of the specific hazards and the technical solutions, classification of the relevant influencing factors and structuring of the numerous interactions;
- Creation of nomograms for the simple determination of the necessary thrust force and for the assessment of the shield jamming risk;
- Evaluation of the pros and cons of the different TBM types and tunnel support concepts depends on the tunnel diameter.