We've seen how a wetland was turned in to Sochi's Olympic Village. Let's take that short trip to the Krasnaya Polyana mountain area and see what geologic challenges the engineers faced bringing us the facilities necessary for the alpine and Nordic events. Put it like this: it weren't easy.
The site for the alpine events is the Aibga Ridge on the Roza Khutor Plateau. The Mzymta River flows through the valley below, and the area is dissected by many tributary streams. From the valley floor at 485 meters (1,591 feet) to the ridge top at 1,100 meters (3,608 feet), the slopes can be as gentle as 5-15 or as challenging as 35-40.
The Caucasus Mountains have been rising as the Arabian plate grinds in to the Eurasian plate. They're big: the tallest peak, Mt. Elbrus, measures 5,642 meters (18,510 feet). All that tectonic pressure has uplifted Jurassic argillites, sandstones and limestones, plus quaternary argillite covered with gravelly, clay-filled soils. This is a challenging landscape to build in. Add to the fact the Russians lacked expertise in handling large projects in mountainous areas, the tight deadlines, and the worrisome seismicity, and you can understand why the geologists assessing the areas for the new highway, the bobsled course, and the ski jumps were extremely careful in their analysis.
They performed many shear and seismic tests on samples of the soils the facilities would be built on, taking into account both their dry and wet states. The roadway project was their first, and they were able to refine their techniques on it. They needed to determine ways to stabilize the slopes both above and below the road, preferably with minimal impact on the environment. They ended up cutting much of the road through the argillite bedrock, driving anchors deep into the stone to prevent landsliding. They made the upper slope retaining walls steep and tall in order to secure the road without undue impact on the natural surroundings. Lower slopes requiring reinforcement were also given retaining walls and anchors, and soft soil replaced by broken stone or strengthened by grouting. The road was built with the seismic situation in mind: in the end, the values they chose matched the recommendations of Eurocode 8.
The bobsled and luge track (BLT) was a hairier proposition: not only did they have to deal with significant changes in relief (a 650-800 meter drop), but they had a complicated hydrogeological situation to contend with. The track is located on a lower portion of the Aibga Ridge's northern slope, and it's waterlogged gravelly clay loam all the way. Those soils could be hard, or deformable due to the dampness. And the argillites 16-40 meters down aren't very strong. The track is also close to two fault zones and in a dangerous seismic area. Landslides were a particular concern.
The geologists suggested several different types of retaining walls for the various parts of the track. They went with piles, as these would be able to hold back landslides quite well. To prevent them from bending and breaking under the potential pressure, they could be anchored, buttressed, or simply made larger than usual.
The ski jump areas were similar geologically, but the altitude drops were larger. At least the hydrogeology was a bit simpler. The jumps were located in a 8-10 meter deep cut that increased the chances for landsliding. Piles came to the rescue again, along with retaining walls on piles and soil nails. The proposed reinforcements would divide the slopes into two segments, which would prevent a single, deep-seated landslide of the entire slope.
So far, all the careful analysis and precautions seem to be working, and thanks to the geologists involved, the Olympic events can be held safely.