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Buildings and roads on low bearing capacity soils? Leca Keramzyt solution

01 of March '22

We are building more and more. More areas around cities are being transformed into building sites and very quickly go to investors. Often only undeveloped plots of land remain on the market, where so far no one has dared to start construction or there were previously small buildings on them. Land conditions are not always checked before buying an investment site. Sometimes after buying a site for a large investment and it turns out that the soils are of low bearing capacity, and the cost of foundation significantly exceeds the initial budget.

Ways to deal with weak soils

There are several ways to solve this problem. The first way is to replace the soil. It is not always possible or cost-effective, especially when the depth of weak soil ranges from several to several meters. Another way is foundation on piles, columns, etc. Here, too, it is not always possible to start work without problems. In the case of small structures, the cost of preparing platforms for drilling rigs and piling rigs, the cost of transporting equipment and piling itself significantly increases the cost of the investment.

Alternative proven foundation

In recent years, many cubic and road structures have been built on low bearing capacity soils using the principle of relieving the existing soil. Relief can be achieved by laying a lightweight aggregate such as Leca® Geotechnical KERAMZYT 8/10-20 mm. The average bulk weight of this aggregate is 290 kg/m3, and after compaction and under full moisture conditions it does not exceed 500 kg/m3. That is, the fill made of expanded clay is 2-3 times lighter than the native weak-bearing soil. In order to foundation the object on such soils, only part of the weak soil can be removed. The low weight of expanded clay laid on top of peat that has been consolidated over the years makes it possible to add to the load on the subsoil with the construction and use load from the object under construction. In addition, Leca® KERAMZYT is an aggregate that can retain large amounts of rainwater after heavy rains in a short period of time, in order to later successively infiltrate it into the ground. The relief effect is usually used in the foundation of buildings and roads. While drainage properties in the construction of playing fields, green roofs, paths and bicycle roads.

A new path on an existing ditch

Ditches are a typical way of receiving rainwater next to roads. By designing a path on such a ditch, we automatically limit the ability to receive rainwater from the road surface. Can this be at least partially prevented? Yes - if the path is built on a substrate that retains some of the water and infiltrates it after rainfall.

Keramzyt pod

Keramzyt under the path


This type of solution can be to fill the existing enlarged old ditch with lightweight aggregate. If the conditions in the field do not allow other reception of rainwater, then the construction of a path on the so-called "French drain" is sometimes the only possible solution. The essential works consist of:

  • laying geotextile in the widened trench,
  • filling the excavation with Leca® geotechnical keramzite of fraction 8/10-20 mm,
  • compacting the expanded clay,
  • covering the fill with geotextile,
  • laying the water-permeable ballast foundation,
  • laying of water-permeable pavement.

Ścieżka rowerowa

Bicycle path


The water permeability of the substructure and pavement can be replaced by linear drainage directing rainwater to the French drain under the path.
With proper shaping of the slopes, it is possible to collect rainwater from the road, the path and the strip separating the two pavements. The filtration coefficient for 8-20 mm fraction expanded clay fill reaches a value of more than 3.33 cm/s.

Playing fields on expanded clay

On the large area on which sports facilities are built, one may encounter varied soil layering. Interference with such subsoil usually leads to uneven settlement of the running track or playing field slab. Such a situation was encountered by the designers of the sports field in Szczecinek.

Podłoże pod boisko

Substrate for the sports field


A section of the pitch had to be located in the immediate vicinity of the lake, which has been naturally changing the position of its shoreline for many years. On part of the area for the planned stadium, the water left behind a thick layer of organic sediment. If a uniform substructure were used for the entire pitch, the subsidence in this area would be greater than that of the rest of the pitch. Therefore, a mattress about 40 cm thick of Leca® KERAMZIT wrapped in geotextile was laid under a section of the pitch on weak soil. On top of it was laid a substructure of sand, a layer of horticultural soil substrate and a grass surface. The lower substructure load reduced settlement and the pitch slab remained on one level.

Boisko na materacu
z keramzytu

Pitch on a mattress of expanded clay


In many cases, a similar mattress made of Leca® KERAMZITE was placed under the entire pitch slab. This type of solution works especially well in areas with very high groundwater levels or on cohesive soils that prevent natural drainage of rainwater after heavy rains.

Kindergarten on peat

Using the principle of relieving the weak ground, the construction of a kindergarten in Pełczyce, West Pomeranian province, was implemented.

z keramzytu pod stopami

Cushion of expanded clay underfoot


The subsoil was dominated by peat and silt and the groundwater level remained at a depth of 0.7-1.3 meters. After removing part of the weak soil to a depth of only 1.4 m, a "cushion" 0.6 m thick of Leca® KERAMZITE wrapped in geotextile was made. The fill was reinforced from the top with geo-grids, on which the footings and footings of the foundation were made. In order not to overburden the ground between the footings, a 0.7 m thick layer of Leca® KERAMZYU was also laid.

Budynek Przedszkola

Kindergarten building


The groundwater level was temporarily lowered and, after the work was completed, the lower part of the fill was in the zone of these waters. The footings were connected by a reinforced concrete slab, on which the kindergarten building was built.

Roads on lightweight aggregate

Problems with construction on weak soils also occur when building roads and laying utilities. During the past 25 years in Poland, lightweight relieving embankments with Leca® KERAMZYT have been made under roads many times.

keramzytem podłoża pod drogą

Relieving the subsoil under a road with expanded clay


This lightweight aggregate wrapped in geotextile allowed the construction of overruns for the bridge abutments. It relieved pressure on embankments over culverts. It allowed the construction of lightweight embankments for road widenings without adversely affecting existing road structures.
As a rule, construction on expanded clay tends to be easier and cheaper than . In road construction, geotextiles are laid on the prepared leveled ground, and expanded clay is spread on them, which is then compacted in layers about 0.5 m thick with dozers and crawler excavators. The degree of compaction is checked with VSS plates.

Gotowa droga

Finished road


Then the top layer of geotextile is laid and on top of it the classic aggregate substructure and pavement.

Leca® KERAMZYT can be a lightweight, load-bearing relieving fill in many difficult soil conditions. Leca® Polska sp. z o.o. consultants help with the design and implementation of such projects.


For more information, visit the company 'sLECA POLSKA Sp. z o.o. page on thePdA portal.

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