The construction of the power waterway for high-head hydro-power plants is generally one of the most expensive project parts. The costs are especially high when a steel lined tunnel is needed. Extension of concrete lined sections is therefore of special interest and a topic of active research. Extending the usage of concrete lining beyond the usual design practice requires a new design model.

A project investigating this topic will be carried out at UNESCO-IHE and includes one PhD position. This advertisement concerns the PhD position at UNESCO-IHE and the research topic entitled Coupled stress-seepage numerical design of concrete lined pressure tunnels.

Project description
Bearing of internal water pressure by plane concrete lined pressure tunnels is limited by the low tensile strength of concrete. Shrinkage of concrete and cooling of the lining by first filling cause a gap between the concrete lining and surrounding rock mass and therefore the surrounding rock mass cannot be included in the bearing of the internal pressure. Low pressure grouting reconstitutes the contact with the surrounding rock mass and increases the bearing capacity, but still the bearing capacity of plane concrete lining is limited. The bearing capacity of the plane concrete lining can be considerably increased if the surrounding rock mass is radially grouted with high pressure grouting causing so called "pre-stressing" of the final concrete lining. Such a lining system, dependent on the tunnel geometry and rock mass characteristics, can be loaded by internal pressures to approximately 20 bars. This design method (developed by Seeber) is mostly used for plane concrete lined tunnels in Austria and by pressure tunnels around the world designed by Austrian designers.

The high pressure grouting pre-stresses the concrete lining, but also improves the rock mass characteristics; stiffness, strength and especially the tightness. Increase of the rock mass tightness allows for an additional effect that has until now not been used in the design of the lining. Relatively tight rock mass around the concrete lined tunnel reduces water losses and produces external water pressure that, as a contra-pressure, reduces the tensile stresses in the concrete lining. Including the contra-pressure in the design will allow for extended usage, by higher internal water pressures, of the radial grouting method with pre-stressing effect.

The method can be used for design of plane concrete lining in cases where standard Seeber theory reaches its limits. In the case of acceptable rock mass conditions and relatively tight rock mass, the suggested method will extend the applicability of the plane concrete lining with pre-stressing and reduce the length of much more expensive steel lined sections

Information and requirements

• The research will be carried out at the premises of UNESCO-IHE in the Netherlands
• The PhD position is funded with a fellowship in accordance with Dutch NUFFIC regulations (monthly allowance of about € 1190, air travel, health insurance, ancillary expenses and tuition
• Expected starting date is January 2011
• Duration of the project is 4 years
• Candidate must have a masters degree (average mark: 80% or above) in a discipline relevant to the topic, e.g. geotechnical engineering, tunneling, civil engineering, hydro-technical engineering etc.
• Applicants must demonstrate a strong interest and experience in conducting experimental and interdisciplinary research including mathematical modeling
• The applicant should be willing to co-supervise masters students
• The applicant must be proficient in English and have excellent communication and writing skills
• Work experience in or related to tunneling and geotechnical engineering is essential

Application
Application including curriculum vitae, the names and contact details of two referees, a motivation letter and filled PhD application form should be sent per post to the following address before October 1 2010:
Ms Jolanda Boots
Westvest 7
2611 AX Delft
The Netherlands
We intend to contact short-listed candidates by October 15 2010.
Further information can be obtained from Prof. Dr. Miroslav Marence