Experience of design of hydrotechnical and bank protection structures on the coast of the baltic sea on the example of the promenad in Svetlogorsk

Company “GEOIZOL Project”

Aleksandrov P.A., chief designer

The most valuable part of the sea resort town is its coastline. In order to develop the recreational potential of Svetlogorsk, it was decided to increase the length of the landscaped coastline of the Baltic Sea. In May 2019, a new 1,240-meter-long promenade, which continued the old one from the sundial to Baltiyskaya Street, opened for pedestrians.

Pic.1 General view of the construction site of the promenade in the city of Svetlogorsk from the Baltiyskaya street

The tasks of the GEOIZOL Project company included updating the previously developed project. The changes affected, first of all, constructive solutions – to increase the stability of the structure.

The architectural concept was determined by the location of the promenade – the smooth curves of the dynamically designed front facade imitate sea waves. Throughout its length, it changes its structure – solid monolithic walls alternate with a surface formed by individual prefabricated reinforced concrete elements. Additional cladding with wooden facade elements with a diameter of 300 mm is provided for at the next stage of the project, after the alluvium of the beach.

Structurally, the promenade is an embankment in the form of a pile trestle, under which the construction of a wave damping chamber is located. The promenade has a pedestrian zone, a bike path and a dedicated lane for the passage of special vehicles.

Pic.2 Principal technical solutions. Incision

In accordance with the architectural solution, the promenade is divided into 5 variants of design schemes according to the types of facade elements. The specifics of the architecture – the complex spatial position of the vertical elements located below the trestle slab – made it difficult to carry out the work. In particular, this concerned the concreting of monolithic walls, curvilinear in plan, having an inclination in different planes. Each element of prefabricated facades was installed at an individual angle, with a uniform step, to embody the smooth line of the structure’s surface, conceived by the architect.

For the construction of the base, driven piles with a section of 35×35 cm and a length of 8 to 11 meters are adopted. The floor slabs of the trestle are beams supported by columns, which are also the main load-bearing structures, and in some areas are elements of the facade.

The structure of the promenade was designed taking into account the pressure of the soil from the back of the structure, which allows the construction of new facilities between the embankment and the slope.

Pic.3 Scheme of promenade structures without piles (finite element model): 1 – lower grillage; 2 – medium grillage; 3 – upper grillage; 4-6 – beams of the promenade slab; 7 – promenade slab; 8 – columns; 9 – ladder structure

The damping chamber perceives the wave load, reduces the speed and the eroding effect of the receding water flows. The constructive solution of the promenade makes it possible to operate the structure without additional protective measures – the alluvium of the beach is provided for by the next stage of the project.

The design of the wave absorber is a monolithic stepped reinforced concrete slab, made along the slope of the embankment, located between two rows of steel sheet piles. The first row – from the side of the sea – prevents soil erosion under the lower grillage. The sheet piling in the back part of the promenade at the interface with the embankment is necessary to ensure the soil impermeability of the structure.

Columns, beams and ceilings are rigidly interconnected and form a single spatial structure. The grappling of the stepped plate of the wave absorber with the grillages and the floor slab is hinged, with the use of elastic gaskets, in order to exclude the transfer of significant forces arising from storm effects to the structure.

Pic.4 General view of the construction site of the promenade

The work was complicated by unfavorable natural and climatic conditions in the construction area. The bank of the Baltic Sea is characterized by a number of processes that negatively affect the bank. Among them are wave action (pressure at the point of maximum wave impact 67.93 kPa), wind loads (probability of storms, including extreme ones, with gusts up to 20-30 m/s), seismicity of the work area up to 6 points. In addition, there were risks of developing slope processes of a high bank slope.

To exclude water impact and reduce the impact of surge phenomena, the project for the production of works provided for the installation of a temporary sheet piling, which was arranged in advance of other works. But even this solution did not completely limit the flow of water to the construction site, which also complicated the work.

The most serious limiting factor for builders was autumn and winter storms. In bad weather, it was impossible to use equipment, primarily cranes, and to carry out construction and installation work.

Additional protection against wave action – backfilling of the dam – was required when constructing a technological road leading to the construction site.

Pic. 5 Stage of installation of the trestle floor slab

The high monolithic parapet of the promenade is provided based on the maximum height of the waves. To prevent water from the wave-damping chamber from entering the pedestrian part of the flyover, semi-permeable drainage pipes of the drainage system are made in the floor slab.

So that the sea element does not spoil the appearance of the building, in order to give an aesthetic appearance and strength characteristics of the facade, the front surfaces were additionally treated with the so-called “water jacket” – a special composition based on cement.

Pic.6 View of the building from the side of the old promenade (sun dial)

The first stage of the promenade construction has been successfully completed. The correctness of the adopted technical solutions was proved by nature – during the three years of operation, severe winter storms did not cause damage to the supporting constructions of the structure. Other stages of the project implementation include the implementation of the pinning of a high bank slope, as well as the installation of larch groins, followed by alluvium of the beach in front of the construction.

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