Karst-ALEA: Prevision of karst-related hazards in underground works

• Forschungsstelle: ASTRA SBT
• Projektnummer: FGU2009/003
• Projekttitel Englisch: Karst-ALEA: Prevision of karst-related hazards in underground works

Schlüsselwörter (Englisch)

Tunnels, geological hazards, karst, forecast, groundwater resources

Kurzbeschreibung (Englisch)

Original language is English, i.e. see below

The project will be dedicated to the identification of criteria for the geological and hydrogeological characterisation of a rock mass. A method allowing engineering-geologists to better forecast karst occurrences will be developed. It will concern mainly preliminary studies and project elaboration.

The research project will include three aspects:

1) Formulation of a methodology based on the ongoing SNF research project and selected of appropriate investigation tools.

2) Application tests to real cases allowing to assess the effectiveness of the method and to improve the method (4 existing tunnels);

3) Recommendations making the method accessible for applied situations.

Results of the research will be assembled into a document dedicated to professionals of underground works, providing a method and a series of recommendations adjusted to karst environments and accessible for engineering geologists. This will significantly improve anticipation of karst-related hazards

Projektbeschreibung (Englisch)

Recent tunnel constructions in Switzerland, as well as over the World have shown that karst related uncertainty is a major issue, leading to economic, social, security-related and environmental problems. Many specific problems occur in karst areas, which do not occur in other geological formations.

The main difficulty beyond these problems is the poor predictability of the location and characteristics of karst features (e.g. size of the conduits, phreatic/vadose, sediment filling).

In their present state, the SIA norms 198 and 199 are quite laconic concerning karst problems during tunnel construction. Karst is mainly perceived as a risk specifically linked with some geologic formations, but no method for the risk assessment is provided or recommended. The assessed risk depends thus on the knowledge and the experience of the geologist working for the project. The frequency and importance of the encountered problems, however, prove that the karst related knowledge of the responsible geologists is often too general to allow an optimal evaluation.

The understanding of the spatial distribution of karstic voids significantly progressed along the last two decades. It is now possible to quantify the probability of karst occurrences inside a karst massif by identifying the few inception horizons that guide the karstification in regional scale, reconstructing the hydrogeolgical history and winnowing different speleogenetical zones.

The aim of the present project is to provide a method for the evaluation of the risk of karst occurrences for engineer geologists. The method will include recent scientific research results that need to be transferred towards the needs of applied geology.

The proposed project will enclose three steps:

1) Method formulation: The method will be formulated on the base of a recent SNF project and the scientific literature. It will mainly consist in translating selected aspects of fundamental knowledge of karst into applied recommendations for engineering geology and selecting appropriate investigation tools.

The method will roughly contain the following steps/considerations:

· Identification of lithological horizons (bedding planes), which are susceptible to dissolution processes (i.e. inception horizons);

· Characterization of the actual and the paleo-hydrological conditions;

· Characterization of some parameters of karst conduits: size, degree and nature of infilling (water, sediments);

· Determination of zones with different probability of karst conduit occurrences (“karst risk”).

2) Method validation: The applicability and feasibility of the method will be tested by applying it to real cases (back analysis of 4 existing tunnels).

3) Method improvement and final formulation: Recommendations allowing the method to be applied by engineer geologists will be formulated and discussed with various persons from the practice.

At the end of this project a document will be available, designed for engineer geologists working on underground constructions. Geologists will thus benefit from a practical and applicable method allowing them to better anticipate the occurrences of karst phenomena. The method will also include some general concepts and methods, which will guide geologists on the way to estimate potential groundwater heads and flow regimes in the construction vicinity. The method will also deliver a useful background for engineers who deal with karst occurrences in underground constructions.

Erwartete Erkenntnisse/ Nutzen, Nutzniesser (Englisch)

The project will deliver a method that will synthesise the cutting–edge knowledge of karst science into an applied method which will make it possible to predict the risk to encounter karst conduits in underground works. Such a method does exist neither in Switzerland nor in the rest of the World.

The method will be mainly dedicated to tunnelling but will be also useful for other topics for which the prediction of the position of karst conduits is useful (e.g. ground stability issues, Groundwater management, archaeology, etc.).

The method proposed is novel because no equivalent method does exist anywhere in the World.

Methoden (Englisch)

• ranslating selected aspects of fundamental knowledge of karst into applied recommendations for engineering geology and selecting appropriate investigation tools.
• Formulation of the prediction methodology (some significant steps are already done during the SNF-project).
• Application of the method on cases studies (back-analysis) and interactive improvement of the method workflow.
• Edition of a practical recommendation for tunnel geologists

Spezielle Geräte und Installationen (Englisch)

none.

Allgemeiner Stand der Forschung (Englisch)

The GEOLEP has a long experience in the field of tunnel geology and hydrogeology. In recent years, several dissertations have been published on the subject:

Filipponi M. 2009. Spatial analysis of karst conduit networks and determination of parameters controlling the speleogenesis along preferential lithostratigraphic horizons. – Thesis. Ecole polytechnique fédérale – Lausanne.

Pomian-Srzednicki I. 2001. Calculation of Geological Uncertainties Associated with 3-D Geological Models. – Thesis. Ecole polytechnique fédérale – Lausanne.

Habimana J. 1999. Caractérisation géomécaniques de roches cataclastiques rencontrés dans des ouvrages souterrains alpins. – Thesis. Ecole polytechnique fédérale – Lausanne.

Bürgi C. 1999. Cataclastic fault rocks in underground excavations. A geological characterisation. – Thesis. Ecole polytechnique fédérale – Lausanne.

Maréchal J.C., 1998. Les circulations d’eau dans les massifs cristallins alpins et leurs relations avec les ouvrages souterrains. – Thèse, Ecole polytechnique fédérale – Lausanne.

These works are presented and discussed in various publications. A list is available upon request.

The SISKA is the only institute in Switzerland specialised in the karst environment. It has wide experience in many areas of environmental research. The karst hydrogeology, the karst genesis and 3D visualization of the karst environment are three main competence areas of SISKA. P.-Y. Jeannin, Director, has dozens of publications relating to all these themes. The SISKA was consulted in recent years in connection with problems in karst tunnels, like for example Flims (GR), Engelberg (OW) and Neu-Bois (JU).

Projektziele (Englisch)

Improvement of the risk forecast related to karst in underground works.

Development, editing and production of practical recommendations

Forschungsplan (Englisch)

The proposed project will enclose three steps:

1) Method formulation: The method will be formulated on the base of a recent SNF project and the scientific literature. It will mainly consist in translating selected aspects of fundamental knowledge of karst into applied recommendations for engineering geology.

The method will roughly contain the following steps/considerations:

· Identification of lithological horizons (bedding planes), which are susceptible to dissolution processes (i.e. inception horizons);

· Characterization of the actual and the paleo-hydrological conditions;

· Characterization of some parameters of karst conduits: size, degree and nature of infilling (water, sediments);

· Determination of zones with different probability of karst conduit occurrences (“karst risk”).

Lists of investigation methods and interpretation schemes will be provided for each of these four steps.

2) Method validation: The applicability and feasibility of the method will be tested by applying it to real cases (back analysis of 4 existing tunnels).

3) Method improvement and final formulation: Recommendations allowing the method to be applied by engineer geologists will be formulated and discussed with various persons from the practice

Umsetzung und Anwendungen (Englisch)

The main benefits of the project are as follows:

• Reduction of the "geological risk" linked to karst;

• Proposition of a scientifically founded, normalized and applicable method;

• Reduction of impacts of tunnel construction on the environment.

The application of the proposed method improves the prognosis of karst occurrences in underground constructions. The reduction of risks that is induced will be of benefit for:

· the project owner (better scheduling with respect to deadlines and cost)

· the mandated enterprises (better handling of the situation)

· the workers (reduction of exposition to hazard)

· the users (better scheduling with respect to deadlines and cost)

· the environment (impact reduction)

The proposed method has a good potential to be recognized Worldwide.

Berichtsnummer (Deutsch)

1395

Literatur (Englisch)

A few papers or books do exist, but we could hardly find any syntheses on the prediction of karst voids for underground structures. It is surprising because a lot of experience has been acquired along the increasing number of tunnels drilled over the last 120 years. However, this experience is dispersed in unpublished reports.

The following list gives a literature overview, although most of it does not address the subject directly:

Jefferson I., Rosenbaum M., Edmonds C., Walton N. 2008: Subsidence-collapse: Occurrence, impact and mitigation. - Introduction to a special issue of Quaternary journal of Engineering Geology and Hydrogeology, vol. 41(3), 259-448.

Filipponi M., Jeannin P.-Y. 2006: Is it possible to predict karstified horizons in tunneling? – Austrian Journal of earth sciences, 99: 24-30.

Wang X., Wang M., 2006: Anaylis of the Mechanism of Water Inrush in Karst Tunnels. Proceeding of the Underground Construction and Ground Movement Conference, 66-72.

Waltham T., Bell F., Culshaw M., 2005: Sinkholes and subsidence – Karst and Cavernous Rocks in Engineering Constructions. Springer, 382 p.

Milanovic P. T. 2004: Water resources engineering in karst. - CRC Press, 312 p.

Milanovic P., 2003: Prevention and Remediation in Karst Engineering. Proceedings of the Multidisciplinary Conf. on Sinkholes and the Engineering and Environmental Impacts of Karst, 3-30.

Waltham A.C., Fookes P. G. 2003: Engineering classification of karst ground conditions. Quaternary journal of Engineering Geology and Hydrogeology, vol. 36, 101-118.

Marinos P.G., 2001: Tunnelling and mining in karstic terrain: An engineering challenge. - In: Beck and Herring (eds): Geotechnical and Environmental Applications of Karst Geology and Hydrology, 3-16.

Milanovic P. T. 2000: Geological engineering in karst, dams, Reservoirs, Grouting, Groundwater protection, water tapping, Tunneling. – Zebra Publ. 347 p.

Also some general publications on karst genesis are cited here to frame the speleogenetical background:

Filipponi M., Jeannin P.-Y., Tacher L. 2009: Evidence of inception horizons in karst conduit networks. Geomorphology, 106, 86-99.

Ford D., Williams P. 2007: Karst geomorphology and hydrology. - Unwin Hyman, London, 601 p.

Dreybrodt W., Gabrovsek F., Romanov D., 2005: Processes of Speleogenesis: a modelling approach. Carsologica, ZRC Publishing, Ljubljana, 376 p.

Klimchouk A., Ford D., Palmer A.N., Dreybrodt W. (eds), 2000: Speleogene­sis, evolution of karst aquifers. - National Speleological Society Inc. (publ.), Huntsville, Alabama, USA, 527 p.