Methods of increasing the stability of the foundations of bridge cones

Chief Designer of GEOIZOL Project Ivan Bogdanov spoke at the conference “Russian and foreign technologies for the design and construction of bridge structures”.

In his report, he reviewed methods for increasing the stability of the foundations of bridge cones.

Technical solutions for existing bridges and facilities under construction can be conditionally divided into two groups: strengthening of existing facilities and new construction.

 

Strengthening existing facilities

Measures for strengthening the foundations of the embankments cones may be required as a result of a violent nature (after floods, earthquakes, etc.) or during the development of negative channel processes leading to the destruction of the coastline.

Another option is as part of an overhaul or reconstruction of ramshackle bridges to bring them up to modern standards for carrying capacity.

The last one is especially relevant because of the adopted federal program for the repair and construction of road bridges until 2035, which includes more than 3,900 emergency and pre-emergency facilities.

A variant of the technical solution in this case can be a construction of the tie bolt with pressure plates

Ground anchors are anchored in stable layers, creating a restraining force, and plates create additional pressure (cantledge) on the soil below the foot of the slope with increasing restraining forces for fastening the foundation soil mass.

Simpler version of strengthening the cones and slopes of the embankment is a dowel fastening. In this case, the dowels hold the soil mass, fixing in the underlying stable layers, and the coating system prevents displacements on the surface.

As a coastline protection measure, it is advisable to use a sheet piling. This solution can be used both independently and in combination with the anti-landslide measures described above

 

New construction

Geological conditions must be taken into account in new construction. Often, near the coastline, soils are formed by alluvial deposits: silts, watered clays, etc. A derivative of this problem is the necessity to erect a high embankment at the approaches to bridges in conditions of insufficient carrying capacity of soils.

One of the optimal solutions for improving the characteristics of foundation soils is their modification with “crushed stone piles”. The construction of pillars made of inert materials by the deep vibrocompaction method  increases the strength and deformation properties of the soil.

This solution, for example, was used in the construction of two overpass bridges as part of the construction of the Launch Complex No. 3 of the Central Ring Road (TsKAD).

Jet cementation method (Jet Grouting) can be considered as an alternative solution. It involves the high pressure supply of cement slurry to the estimated depth and mixing it with the soil. As a result, an improvement in the characteristics of the soil mass is achieved.

The issue of erecting high approaches to the bridge in case of insufficient carrying capacity of the foundation can be solved by constructing a light embankment, which is formed from blocks of extruded polystyrene foam (EPS or XPS). The specific gravity of this material is 30 times less than that of sand. Reducing the load on the ground avoids or minimizes additional measures for strengthening the foundation.

This decision was made by the engineers of GEOIZOL Project on the approach to the overpass bridge through Neftyanaya  Street at the 8th stage of the reconstruction of the federal highway A-291 “Tavrida”.

Reducing the load is also possible by constructing a reinforced soil embankment due to its smaller dimensions compared to a standard sand embankment. This makes it possible to avoid or significantly reduce the area of soil solidification measures.

The conference “Russian and foreign technologies for the design and construction of bridge structures”, organized by the International Association of Foundation Contractors, took place on September 21-23, 2021 in Moscow.

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