Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface.

Earthquake-Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

The range of problems that geotechnical engineers must face is increasing in complexity and scope. Often, complexity arises from the interaction between the soil and the environment – the topic of this lecture. To deal with this type of problem, the classical soil mechanics formulation is progressively generalised in order to incorporate the effects of new phenomena and new variables on soil behaviour. Recent advances in unsaturated soil mechanics are presented first: it is shown that they provide a consistent framework for understanding the engineering behaviour of unsaturated soils, and the effects of suction and moisture changes. Building on those developments, soil behaviour is further explored by considering thermal effects for two opposite cases: high temperatures, associated with the problem of storage and disposal of high-level radioactive waste; and low temperatures in problems of freezing ground. Finally, the lecture examines some issues related to chemical effects on soils and rocks, focusing i...

Soil–environment interactions in geotechnical engineering

Geological disposal is the preferred option for the final storage of high-level nuclear waste and spent nuclear fuel in most countries. The selected host rock may be different in individual national programs for radioactive-waste management and the engineered barrier systems that protect and isolate the waste may also differ, but almost all programs are considering an engineered barrier. Clay is used as a buffer that surrounds and protects the individual waste packages and/or as tunnel seal that seals off the disposal galleries from the shafts leading to the surface.

Bentonite and bentonite/sand mixtures are selected primarily because of their low hydraulic permeability in a saturated state. This ensures that diffusion will be the dominant transport mechanism in the barrier. Another key advantage is the swelling pressure, which ensures a self-sealing ability and closes gaps in the installed barrier and the excavation-damaged zone around the emplacement tunnels. Bentonite is a natural geological material that has been stable over timescales of millions of years and this is important as the barriers need to retain their properties for up to 106 y.

In order to be able to license a final repository for high-level radioactive waste, a solid understanding of how the barriers evolve with time is needed. This understanding is based on scientific knowledge about the processes and boundary conditions acting on the barriers in the repository. These are often divided into thermal, hydraulic, mechanical, and (bio)chemical processes. Examples of areas that need to be evaluated are the evolution of temperature in the repository during the early stage due to the decay heat in the waste, re-saturation of the bentonite blocks installed, build-up of swelling pressure on the containers and the surrounding rock, and degradation of the montmorillonite component in the bentonite. Another important area of development is the engineering aspects: how can the barriers be manufactured, subjected to quality control, and installed?

Geological disposal programs for radioactive waste have generated a large body of information on the safety-relevant properties of clays used as engineered barriers. The major relevant findings of the past 35 y are reviewed here.

The Use of Clay as an Engineered Barrier in Radioactive-Waste Management a Review

Effects of plastic contamination on water evaporation and desiccation cracking in soil

Influencing factors of geometrical structure of surface shrinkage cracks in clayey soils

In the radioactive waste disposal concepts, highly pre-compacted bentonite-sand mixtures are considered as appropriate sealing materials to fill the galleries. Compacted elements of bentonite-sand mixtures are placed adjacent to each others, forming a plug that should limit the transfer of radionuclide. The bentonite has proven to have the capability of retaining radionuclides and the capability of swelling when getting in contact with water and then closing all the voids in the system especially the radial technological void being the gap between the bentonite-sand elements and the host rock. Indeed, when the bentonite-sand elements is emplaced in the gallery, they are first in an unsaturated state and they will start being saturated by the host-rock pore water. They will then start swelling, forming a gel that will close the gap. In this work, such hydration process is experimentally analysed on a small scale. The swelling is analysed by time-lapse photography, its kinetic is also studied by image processing. We can see that the swelling of this material is fast and large, and we can distinguish different states of the material during swelling, starting from the dry centre to the outer boundary. On the other hand, the presence and behaviour of sand grains in the gel formation is evidenced by images as well. The sand grains are found to be covered by bentonite particles and being carried with the bentonite swelling.

Swelling of Highly Compacted Bentonite-Sand Mixtures Used as Sealing Materials in Radioactive Waste Disposal

Water retention properties of Boom clay: A comparison between different experimental techniques

A model to predict the elastic properties of gas hydrate-bearing sediments

Shrinkage of expansive soils may cause serious problems to geotechnical and geo-environmental structures. In this study, the shrinkage behaviour of compacted clay treated with 4% lime was investiga...

Anh Minh Tang

Papers

Swelling of Highly Compacted Bentonite-Sand Mixtures Used as Sealing Materials in Radioactive Waste Disposal

Water retention properties of Boom clay: A comparison between different experimental techniques

A model to predict the elastic properties of gas hydrate-bearing sediments

Shrinkage behaviour of a compacted lime-treated clay

Compression-induced suction change in a compacted expansive clay