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A high seepage-flow velocity represents a potential problem for artificial ground freezing (AGF), as it may hinder the growth of an ice body and the development of a closed ice wall. To avoid such difficulties, careful thermal hydraulic analysis is necessary. This presupposes, of course, that the reliability of the underlying computational models has been verified by means of comparisons with the results of appropriate field tests or physical models. As there are scarcely any results of such tests available in the literature, a new large-scale physical model for AGF under conditions of high seepage-flow velocities has been developed. The present paper documents in detail the experimental set-up, the thermodynamic properties of the soil material, the boundary conditions, and the results of six experiments. These data are valuable as a reliable basis for the evaluation of numerical or analytical prediction models. Additionally, the paper discusses existing closed-form solutions for AGF with and without seepage flow in the light of the experimental results, from the perspective of the refrigeration time and the cooling power required for the merger of a freeze-pipe row.

Sulphatic claystones exhibit a heavily swelling behaviour and are among the most problematic rocks for tunnelling. Their swelling is usually attributed to the transformation of anhydrite to gypsum. The paper questions this simplistic hypothesis through a qualitative discussion of the processes underlying the phenomena that are observed macroscopically, and by identifying a series of fundamental issues that are important from the point of view of tunnel design. At the same time, it provides an overview of ongoing or recent research dealing with the swelling of sulphatic claystones and, more specifically, with the effects of chemical reactions and transport processes, the role of the clay fraction, the pressure dependence of swelling deformations and the possible effects of the seepage flow regime, including evaporation in the unsaturated zone.Sulfathaltige Tonsteine weisen ein besonders starkes Quellverhalten auf und gehören zu den problematischsten Gesteinen beim Tunnelbau. Ihr Quellen wird üblicherweise auf die Umwandlung von Anhydrit zu Gips zurückgeführt. Der vorliegende Aufsatz diskutiert diese vereinfachende Hypothese, indem er die dem makroskopisch beobachtbaren Quellvorgang zugrundeliegenden Prozesse qualitativ behandelt und eine Übersicht über aktuelle Forschungsprojekte vermittelt. Dabei wird eine Reihe von Themen der Grundlagenforschung identifiziert, die auch von praktischer Bedeutung sind. Zu diesen gehören die Fragen nach dem Einfluss der chemischen Reaktions-und Transportvorgänge, der Rolle der Tonfraktion, der Druckabhängigkeit der Quellverformungen und der Bedeutung der Sickerströmung. IntroductionRocks that swell when interacting with water are widely distributed in Switzerland and south-west Germany and have caused serious damage, lengthy operational disruptions and very costly repairs in a number of tunnels. This is particularly true for the anhydritic rocks of the Gypsum Keuper formation. As illustrated by setbacks experienced in two recently constructed tunnels (the Adler tunnel of SBB [1] and the Chienberg tunnel of the Sissach by-pass [2]), claystones containing anhydrite are still among the most problematic rocks in tunnelling today [3] [4]. In purely argillaceous rocks, the swelling behaviour can be traced back to osmosis-driven water uptake, while the dominant mechanism in anhydritic rocks is probably gypsum growth from sulphate solutions (Ca ++ + SO 4 = + 2 H 2 O → CaSO 4 · 2H 2 O).Research on the problem of swelling was triggered in the early 1970's by difficulties encountered in two road tunnels -the Wagenburg tunnel in Germany and the Belchen tunnel in Switzerland. Since then a series of research projects have been carried out which differ with respect to the questions addressed and thus also the methods employed, the scale of the investigation and the scientific disciplines involved. At the microscale, mineralogists have carried out theoretical and experimental studies into the interactions between clay particles, anhydrite and gypsum crystals [5] [6]. The scale of the geological fo...

The proposed Gibraltar Strait tunnel will cross two zones with breccia consisting of a chaotic mixture of blocks and stones embedded in a clay matrix. The breccia is saturated, has a high porosity and exhibits poor mechanical properties in the range between hard soils and weak rocks. The overburden and high in situ pore pressures in combination with the low strength of the breccia may lead to heavy squeezing. The crossing of the breccia zones thus represents one of the key challenges in the construction of the tunnel. In order to improve our understanding of the mechanical behaviour of the breccias, a series of triaxial compressions tests were carried out. Standard rock mechanics test equipment was not adequate for this purpose, because it does not provide pore pressure control, which is important in the case of saturated porous materials. Pore pressure control is routine in soil mechanics tests, but standard soil mechanics equipment allows only for relatively low nominal loads and pressures. In addition, the low hydraulic conductivity of the breccias demands extremely low loading rates and a long test duration. For these reasons, we re-designed several components of the test apparatus to investigate the mechanical behaviour of the breccia by means of consolidated drained and undrained tests. The tests provided important results concerning the strength, volumetric behaviour, consolidation state and hydraulic conductivity of the breccias. The present paper describes the test equipment and procedures, provides an overview of the test results and discusses features of the mechanical behaviour of the breccias which make them qualitatively different from other weak rocks such as kakirites-a typical squeezing rock in alpine tunnelling. The paper also demonstrates the practical importance of the experimental findings for tunnelling in general. More specifically, it investigates the short-term ground response to tunnel excavation from the perspective of elasto-plastic behaviour with the Mohr-Coulomb yield criterion. The computational results indicate that the breccias will probably experience very large deformations already around the advancing tunnel heading, which can be reduced considerably, however, by advance drainage. The analyses additionally show that plastic dilatancy is favourable with respect to the short-term response, thus highlighting the importance of the constitutive model when it comes to theoretical predictions.

The method of artificial ground freezing was employed to ensure stability and waterproofing of the platform and escalator tunnels in the Università station of the Naples underground. The paper presents the temperature histories monitored within the ground during the freezing process. Furthermore, the importance of the mineralogical composition of the ground is discussed and it is shown that the temperatures monitored can be interpreted numerically using the ‘Freeze' code, a thermo-hydraulic software developed at the ETH Zurich. The influence of important parameters, such as the spacing between the freeze pipes, the thermal conductivity of the ground and the time–development of cooling temperatures in the freeze pipes, is investigated and critically discussed in order to gain a better understanding of the thermal behaviour of the ground during artificial freezing with liquid nitrogen. ‘Freeze' software is a powerful tool for analysing field data for cases involving non-constant temperatures within freeze pipes.