Construction of lightened embankments and fills

Depending on the technical and economical constraints, expanded clay embankments and fills can be constructed in the following ways:

• Embankments/fills consisting of alternating layers of expanded clay and granular mix (of gravel or rockfill) (Fig. X):

Average density after completion: 600 – 1200 kg/m³.

The thickness of each layer can be varied depending on the design requirements

Spreading sequence (repeated)

• A geotextile separation layer (if required) is laid in contact with the founding ground
• A first layer of expanded clay is laid to a thickness of 20 – 100 cm;
• A geotextile separation layer is laid
• A layer of granular mix is laid to a thickness of at least 10 cm
• The top of the granular mix layer is compacted using a vibrating roller, typically weight 15-50 kN.

The total thickness of each sandwich of clay + granular mix must not exceed 120 cm.

The final layer of granular mix, on which the finishing layers will be placed, must be at least 300 mm thick (suggested thickness: 400 mm).

• Embankments/fills consisting of expanded clay only (Fig. Y):

Average density after completion: 400 – 600 kg/m³

Spreading sequence (repeated)

• A geotextile separation layer (if required) is laid in contact with the founding ground
• Expanded clay is laid to a thickness that is variable depending on the means of compaction used (Fig. z)
• The surface of the expanded clay is compacted directly by multiple passes with a vibrating plate compactor (Typical Weight 50-140 kg, width 50-80 cm, contact stress < 5 kN/m2,frequency 75-100 Hz) or a tracked vehicle (excavator, shovel, bulldozer – Contact stress < 50 kN/m2) The number of passes required will depend on the thickness of the layers and the machine used (Fig. Z).

The most commonly used methods for containing embankments with different “angles of slope” (indicative values) range from reinforced ground at the minimum possible angle of slope (90°) to uncontained material (35 – 40°)

• Embankments/fills in expanded clay bound with cement

Densities ranging from 500 – 800 kg/mc and strengths from 1 – 4 MPa, depending on the type of expanded clay and the quantity of cement used.

To increase the stiffness of fills or embankments or to resolve problems of lateral containment, or to deal with other requirements, they can be constructed using cemented expanded clay (permeable concrete – open pore structure.

Each layer must not be more than 50 cm thick and compaction must be carried out with a plate vibrator.

Cemented expanded clay can be manufactured in various ways:

• Continuous on-site manufacture: expanded clay is delivered to site in tanker trucks equipped with suitable pumping gear. At the same time a cement slurry is manufactured on site using suitable machinery, and continuously injected into the pump hose as the expanded clay is delivered. The mixing takes place at this stage.
• Off-site manufacture in a batching plant, with delivery in concrete mixer trucks.
• On-site mixing using bulk expanded clay and cement (if small quantities are required).
• On-site mixing using bagged premixes (Latermix Cem Classic or Maxi)