Erkundung und Sanierungsstrategien im Erdwärmesonden‐Schadensfall Staufen i. Br.

Abstract

Der Erdwärmesonden‐Schadensfall Staufen i. Br. zeigt in deutlicher Weise Gefährdungen auf, die bei stockwerksübergreifenden Erdwärmesonden‐Bohrungen mit Potenzialunterschieden der angetroffenen Grundwasserstockwerke auftreten können. Durch Grundwasserströmung kam es im Ringraum der Erdwärmesonden‐Bohrungen zu einem Austrag von Abdichtungsmaterial. Dies führte in einer oder mehreren Ringraumabdichtungen zum Misslingen der erforderlichen Stockwerkstrennung. Wasserzutritte in ehemals trockene, quell‐ und schwellfähige Gebirgsabschnitte verursachten das “Gipskeuperquellen”. Diese Wasserzutritte konnten durch schadensbegrenzende Maßnahmen (Nachverpressung der Erdwärmesonden, Dauerabsenkung des Druckwasserspiegels) unterbunden werden. In quellfähiges Gebirge eingedrungenes Wasser lässt sich jedoch weder mit hydraulischen noch anderen Maßnahmen rückgewinnen. Von daher werden die Geländehebungen so lange andauern, bis das eingedrungene Wasser durch den Quell‐/Schwellprozess restlos aufgezehrt ist. Die eingeleiteten schadensbegrenzenden Maßnahmen zeigten Erfolg. Dadurch konnten die maximalen Hebungsgeschwindigkeiten von anfangs 11 mm/Monat auf derzeit ca. 3, 5 mm/Monat reduziert werden. Die Hebungsmessungen seit Herbst 2012 deuten darauf hin, dass die bisher zu beobachtende lineare Prozessverlangsamung nicht unverändert anhält. Durch eine Modellierung wurde deutlich, dass die Pumpmaßnahme zur Vermeidung von erneutem Auftrieb und weiteren Quellvorgängen fortgeführt werden muss.Investigation and remediation strategies for the damaging event caused by failed borehole heat exchanger drillings in Staufen i. Br. The effects of failed borehole heat exchanger drillings in the German town Staufen i. Br. show distinctly the hazards, which can arise from borehole heat exchanger drillings spanning multi groundwater storeys with potential difference of the penetrated groundwater storeys. Groundwater flow induced the discharge of annular sealing in the annulus of the borehole heat exchanger drilling. Under the encountered hydrological boundary conditions, this caused the failure of the required separation of the groundwater storeys in one or more annular sealing. Water influx in previously dry, swellable geological layers caused the so‐called “Gipskeuperquellen” (swelling of the gypsum‐containing Upper Triassic Grabfeld formation). This water influx could be suppressed by damage‐limiting measures (post‐grouting of the borehole heat exchanger, permanent groundwater lowering). It is not possible to reclaim water that ingressed into swellable geological layers neither by hydraulic nor by other measures. Thus, the ground heave will continue until the ingressed water is completely exhausted by the swelling process. The initiated damage‐limiting measures succeed. As a result, the maximum heave rate has decelerated from 11 mm/month at the beginning to currently approximately 3.5 mm/month. Since autumn 2012, the ground heave measurements indicate, that the linear deceleration of the process observed until now does not continue unchanged. By modelling it became clear, that the groundwater pumping has to be continued to avoid more uplift and further swell processes. Experiences from the case Staufen i. Br. show impressively, that a thorough pre‐investigation immediately followed by the initiation of defensive/control measures are absolutely necessary in case of damaging events caused by failed borehole heat exchanger drillings.

Damage event analysis of vertical ground source heat pump systems in Germany

“…The uplift rate was reduced from initially 11.0 to 3.5 mm per month. Since it is not possible to recover penetrated water from sulphate-bearing layers, swelling will stop only when there is no more inflow of groundwater (Ruch and Wirsing 2013). The uplift damaged more than 269 buildings (Sass and Burbaum 2010) In September 2008, two drillings were made for the installation of a vertical GSHP system in Böblingen, a town southwest of the state capital of Stuttgart.…”

Hydro-chemo-mechanical modelling of tunnels in sulfated rocks

“…The swelling-induced damage observed at Pont de Candí and in Staufen and Lochviller (Goldscheider & Bechtel, 2009;Sass & Burbaum, 2010;Ruch & Wirsing, 2013) was triggered by a change in hydrologic conditions. Tunnelling is different because it results in major changes in stress around the excavation.…”

Uncertainty assessment in 3-D geological models of increasing complexity

“…The fault system, kinematically linked to the EMBF, has a releasing bend geometry and today experiences sinistral oblique movement (Behrmann et al, 2003). The major geological units at the site comprise Triassic and Jurassic sedimentary rocks, which are covered by Quaternary sediments of an alluvial plain in the south (Sawatzki and Eichhorn, 1999) (Fig. 1).…”

“…The non-site-specific data category comprises geological data that are generally available from published maps (Sawatzki and Eichhorn, 1999), the literature (Genser, 1958;Groschopf et al, 1981;Schreiner, 1991) and the database of the state geological survey, LGRB. Furthermore, a digital terrain model (DTM) of 1 m grid size is included in the non-site-specific data.…”