Green Roof

Landscape with LECA

Leca® Lightweight Expanded Clay Aggregate has been an important ingredient for civil engineers throughout the world in providing the perfect material to solve a variety of engineering issues when developing Green Roofs within a city landscape.

In general, Leca® Lightweight Expanded Clay Aggregate is used to reduce, compensate or prevent settlements, to improve stability of a fill structure or landscape or to decrease soil pressure on a retaining structure produced by backfill. In the same applications, Leca® Lightweight Expanded Clay Aggregate can be used both as drainage intensifying and as moisture retaining for vegetation and also as a frost protection layer.

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Fill Structure Related Load Reduction

A fill structure produces additional loads when it is placed and compacted on a landscape environment; the effects of the additional load are typically most pronounced in the locations of the landscape containing a soft soil subgrade. The load magnitude depends on the fill material density and thickness, and the effect of the additional load produces long term settlement of the landscape embankment or structure. Magnitude of the load affects settlement sensitive soil in proportion of the softness of the soil, with impacts ranging from high total settlement to unacceptably high differential settlement or tilting of the structure. 

Landscape with LECA
Landscape with LECA
Landscape with LECA
Landscape with LECA

By using Leca® Lightweight Expanded Clay Aggregate as a fill material within landscapes, the impact of additional loads produced by the soil layers on the subgrade can be reduced significantly and long term settlements decreased. Differential settlements created by loads or soil conditions can also be compensated with the help of a transitional lightweight structure.

When Leca® Lightweight Expanded Clay Aggregate is applied to reduce settlements for landscapes, the following design aspects shall be taken into account:

  • Properties of the underlying subgrade and its loading history
  • Allowed rate of settlement and differential settlements
  • Designed life time
  • Groundwater and/or perched water level and possible open water level
  • Distance from ground surface to top surface of structure (height of fill layer)
  • Adjacent buildings.

Easing Structural Pressure

It is usual to take in to account geotechnical evaluation during lightweight structure or fill design in which soil parameters and load are accounted for each construction project individually. The lightweight designed structure or fill can entirely or partly compensate additional loads on the subgrade. Partial compensation can be used where settlements have largely occurred, the settlement period after construction is relatively short, or controlled settlements can be accepted. Entire compensation eliminates settlement periods altogether.

When the groundwater or surface water level is high, it can be good practice to partially reduce the weight of the fill structure to ease the pressure on the surrounding area. The structure shall be designed with consideration to buoyancy connected with rising water levels within the structure, a particularly relevant factor for Leca® Lightweight Expanded Clay Aggregate structures located in vicinity of a water body or flood area.

Limited Buoyancy

Leca® Lightweight Expanded Clay Aggregate fill structures are designed to compensate additional loads produced by a fill structure on a subgrade either entirely or partially. Partial compensation can be used when settlements have mostly happened, the settlement period after construction is relatively short, or controlled settlements can be accepted. Additionally, when groundwater or surface water level is high, it is helpful to partially reduce the weight of the fill structure (limited buoyancy).

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