Construction of Mankkaanlaaksontie and Seiliniitty street and flood barrier, renovation of Gräsanoja

Project description

Mankkaanlaaksontie will be rebuilt and the street surface will be raised in the section Ring II–Koivu–Mankkaantie. The contract also involves the renovation of the Seiliniitty street and the construction of a flood barrier in the Seiliniitty area. In addition, the contract includes the cleaning and weeding of Gräsanoja and the construction of a new bridge over Gräsanoja. The work area also includes the work on the streets crossing and connected to these streets, to the extent required to connect the structures.

The construction project aims to reuse, where possible, the excavated soil and the materials from demolished buildings. For example, lightweight gravel asphalt used for Mankkaanlaaksontie will Project be utilised in the flood structure. The aim is also to reuse excavated growth platforms in landscaping.

Mankkaanlaaksontie

The contract area will be cleared of vegetation to the extent required for construction and the surface structures of the street and the current street lighting, including posts and bases, will be dismantled. The soil will be strengthened by stabilisation. Gräsanoja's new bridge will be built on steel pipe piles reaching all the way to the rock surface. During construction, traffic will be controlled with arrangements followed in the working hours. A noise barrier will be established on piles. The frame of the noise barrier will consist of steel columns to which a noise barrier cassette used as the wall structure is attached. The facades will be finished with planed larch laths.

Approximately 250 metres of new stormwater drain line will be built and the line built previously will be replaced. Approximately 190 metres of new water main and approximately 50 metres of wastewater sewer will be installed. In addition, the existing water supply and sewerage will be replaced. District heating pipes will be rebuilt in part of the route, because the elevation of the street would leave the pipelines too deep. In some of the ditches, a pile slab will be built to support the pipes. Casing pipes will be installed for the electric and telephone cables.

On the streets, new street lighting will be built, edge restraints of natural stone will be installed and sett paving, dice paving and rubble stones will be installed and the street will be asphalted. In the street green areas, grass or meadow plants will be sown, trees and shrubs will be planted and a few stormwater depressions will be built.

Seiliniitty

The street structures of the Seiliniitty street will be dismantled. 50 metres of new stormwater drain will be built, the wastewater sewer will be renovated and approximately 110 metres of the water main will be renovated. A new wastewater pumping station will be built at the southern end of the Seiliniitty street. A 520 metres long pressure sewer leading from the pumping station will be built by angle drilling. Casing pipes will be installed for electric and communications cables and the district heating pipe. In the Seiliniitty park area, water supply and sewerage will be built and casing pipes will be installed for cables and pipes. Two areas for parallel parking will be built along the street. The street will be asphalted and concrete edge restraints will be installed.

A new flood barrier will be built between the Seiliniitty park and the residential area. The purpose of the flood bank is to protect the residential properties from the floodwaters of Mankkaanpuro/Gräsanoja. From the area between the flood barrier and the residential area, stormwater will be directed to a drainage pipe that will be built through two flood banks. In the event of a flood, the stormwater from the areas inside the flood bank will be directed through the ditch and pump well to be built to a ditch that flows into Mankkaanpuro. The flood bank will be landscaped into a meadow. Trees and shrubs will be planted and grass and meadow plants will be sown in the park area. Lighting will be built on Seiliniitynreitti and Kluuviniitynpolku and the routes will be elevated and they will be surfaced with crushed stone fines. Some benched and rubbish bins will be installed along the routes.

Flood and surface water structures and Gräsanoja

Gräsanoja's renovation measures include cleaning and weeding, paving the channel, adding gravel and removing vegetation as well as constructing settling basins, flood plains, flood canals and stream deflectors. The stream deflectors are tree trunks fixed below the water surface to control the flow of water. The channel will also be supported by pile planking for a distance of about 10 metres. The renovation of the ditch will be carried out in sections and the area being currently worked on will be fenced.

A new channel for Gräsanoja will be built at the allotment gardens. A dam will be built in the old channel. In a normal situation, the dam will direct the water to the new built channel, and when the water floods, the water can flow over the dam to the old channel as well. 

The renovation will begin with measures outside the channel. These include things such as the construction of flood plains so that the extensive vegetation zones in the main channel retain at least some of the solid matter that is released during the work. Outdoor routes may need to be closed during construction. 

More information is available on the planning page Mankkaanlaaksontie, Seiliniitty street and park planning and the page for the flood protection and renovation of Gräsanoja.

Project period: July/2023 - June/2025

Main contractor: GRK Suomi Oy

City developer’s representative: Hannu Lehtikankare