Drainage Properties of LECA® LWA

Efficient drainage of the structural layers of a road, artificial turf, soil or highway development can prevent loss of load bearing properties caused by water and will provide effective drainage throughout the civil engineering project’s lifetime.

Using free draining LECA® Lightweight Expanded Clay Aggregate as a structural material within a civil engineering development will intercept the percolating water and water rising by capillary action from the sub-formations and direct the rising water away from the upper construction layers to improve load bearing capacity.

Frost damage and loss of load bearing capacity can also be reduced by forming drain trenches filled with LECA® Lightweight Expanded Clay Aggregate, along which the water is guided away. Used within the carriageway drainage, Leca® Lightweight Expanded Clay Aggregate will help filter and increase microbiological breakdown of pollutant run off from fields and highways.

Water drainage system can be difficult when the drain runs across a soft soil site. Leca® Lightweight Expanded Clay Aggregate can be used as a light weight pipe surround to reduce the pressure to the underlying soils and minimize the likelihood of irregular settlement.

The most cost-effective solution is to use the LECA® Lightweight Expanded Clay Aggregate structure to achieve several goals at the same time. For example,LECA® Lightweight Expanded Clay Aggregate is applied as a fill material to reduce the load of the fill structure, but an adequately thick layer of Leca® Lightweight Expanded Clay Aggregate also provides thermal insulation, capillary water break, and drainage of overlaying structural layers, while also improving bearing capacity properties.

The benefits of LECA® Lightweight Expanded Clay Aggregate in areas that usually require deep trenches is especially significant for soft soil conditions, where shallower excavation can reduce or eliminate retaining structures altogether that would otherwise be needed to support a deep trench. In addition, other subgrade reinforcement measures can be reduced or avoided altogether.

In Finland where our Finnish colleagues experience severe freezing conditions, water retention and frost penetration are of prime concern during highway design in an attempt to avoid frost heave and long term maintenance costs. Principles of frost insulation using LECA® Lightweight Expanded Clay Aggregate are shown in Figures 4.7 and 4.8. Along with frost insulation, LECA® Lightweight Expanded Clay Aggregate is used for drainage purposes in the same structure.

Materials used in road construction layers, and the total thickness of these layers can be dimensioned based on their frost and load resistance. Principle design evaluation of frost insulation for road structure is presented in Annex 3.

Annex 3. Calculation of frost heave in road structure

Road frost design considers climate influence via the design frost depth (S), which accounts non-freezing foundation depth depending on the object region.

Design guides of Finnish Transportation Agency uses a coefficient ai to define insulation capacity of a material as related to insulation capacity of sand fill. LECA® Lightweight Expanded Clay Aggregate coefficient ai is 4, when its base depth is at least 0.7 m, maximum dry density at most 400 kg/m3, and when a draining layer at least 0.15 m thick lays below LECA® Lightweight Expanded Clay Aggregate layer.

Road superstructure is designed in such a way that expected frost heave remains within permitted limits, which in turn depend on the road class.  

Frost heave calculation starts with frost heave equalling 0 mm when the thickness of insulating sand superstructure is the same as the design frost depth (S).

Frost heave of subgrade (RNlask) under frost-resistant superstructure can be calculated by Equation 3.1 (Finnish Road Administration 2004).

RNlask = frost heave of subgrade (mm)

S = design frost depth [m]

ai = insulation capacity related to insulation capacity of sand [-]

Ri = frost-resistant layer thickness [mm]

t = subgrade frost expansion [%]

Table 1. Materials relative insulation capacity coefficients (Finnish Road Administration 2004)

1) 100 mm asphalt, 600 mm crushed rock, 300 mm Leca, 150  Drainage course mm

2) 100 mm asphalt, 600 mm crushed rock, 450 mm Sand

3) 100 mm asphalt, 600 mm crushed rock, 1400 mm sand

1. Subgrade frost heave with light gravel subbase layer, S=2,0m and t=6%

1. Subgrade frost heave with sand subbase layer, S=2,0m and t=6%

1. Subgrade frost heave with sand subbase layer, S=2,0m and t=6%