Advanced methods of strengthening the foundations of railway infrastructure

Interview of the Chief Designer of GEOIZOL Project Ivan Bogdanov to the RZD Partner magazine No. 20 (432)

The October issue of the RZD Partner magazine, which is timed to Transport week 2020, contains an interview with the chief designer of GEOIZOL Project, Ivan Bogdanov, where he talks about advanced technologies for strengthening the foundations of railway tracks and engineering protection of infrastructure facilities.

The article is devoted to innovative technologies that can be used in the development of railway infrastructure in key areas of transportation within the framework of a Comprehensive plan for upgrading and expanding the major highways infrastructure (CPMHI). We would like to thank the editorial staff of the RZD Partner magazine for the opportunity to share our experience and give the full text of the interview below.

– Ivan Sergeevich, are there new technologies for the strengthening of the roadbed base, bridge supports, and other railway infrastructure that can be used at Russian Railways facilities?

– It is more correct to talk about advanced modern solutions that are already being used, in particular at infrastructural facilities. There are several technologies that are relevant to Russian Railways. The first is the modification of the foundation soil using columns made of sand or crushed stone, the so-called crushed stone piles, by the method of deep vibration compaction.

This method allows changing the characteristics of the soil in a quality manner: increase strength, drainability, reduce the time of consolidation of the base. The essence of the technology is that wells are formed on the area subject to strengthening with the help of a vibrating float without removing the soil.  Then crushed stone is rammed in. The peculiarity of the technology is that you can improve the base in a short time and at a relatively low cost.

The second method is also about the modification of the soil but using various cement mortars. This refers to the Jet Grouting technology. In this case, depending on the ground conditions, a certain composition of the injection mixture is selected.

Various geosynthetic materials are widely used, primarily for the construction of a flexible foundation frame. They allow forming a stronger foundation of the embankment, distribute the load evenly, and avoid local subsidence. This method is recommended for use in areas with lenses of weak soils or where there is a risk of karst phenomena.

When strengthening embankments, multifunctional geotechnical systems have proven thier worth. In particular, during the pilot project on the Gorky railway, slope reinforcement was carried out by means of dowels using the Geoizol-MP system. The feature of the technology is that drilling and injection of cement mortar go in parallel. This minimizes the risks of such work.

– What is the application of geomembranes and geo-materials on the objects of the Russian Railways? What other solutions can reduce the risk of structural failure under the influence of adverse natural phenomena and improve traffic safety?

– If we are talking about geomembranes, these materials are not used to strengthen structures however, they are used as waterproofing layers or as anti-filtration screens. They reduce the negative impact on the environment and are used in the precincts within the areas where there are risks of accidents and, for example, oil spills. This is a relatively inexpensive material that can be used to prevent an environmental disaster.

Various geomats are used on slopes for anti-erosion protection. They prevent erosion, ravine formation, and other destruction of embankments.

The next group of materials is power geosynthetics. These include one- and two-way geogrids, as well as various nonwoven materials, i.e. dense geotextiles. They perceive the tensile loads that occur at the base of the embankment, and distribute the load from the upper structure of the path over the entire area of the base, preventing uneven precipitation. Besides, they allow reducing the material consumption of embankments.

What solutions are recommended for strengthening structures on unstable soils?

– If we are talking about liquefied thixotropic soils, which are in a static condition have significant strength characteristics, but under the influence of dynamic loads (man-made or seismic) lose their properties quickly and liquate, that is, lose their bearing capacity, then, in my opinion, the most rational solution in this situation is just the use of crushed stone piles. This solution was used, for example, in the construction of the Crimean bridge from the Taman Peninsula.

Crushed stone piles modify the soil and make it non-liquefiable. They remove excess moisture, increase the density of particles, change the ratio of water to particle size, and pore pressure figures.

Moreover, this solution is much more effective than cementation. If one cube of fixed soil requires about a ton of cement, but crushed stone consumption is almost 2 times less (by weight). And at the same time, cement is much more expensive.

Interviewed by Alexander Solntsev

P.S. You can see the publications of Ivan Sergeyevich Bogdanov here.

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