Construction methods · Bored piles and deep foundations

Bentonite and polymer slurry stabilisation

The fluid that keeps a bored hole open: bentonite forms a filter cake on the wall and holds the ground by hydrostatic pressure; polymer slurries do the same with less mud, easier disposal and better concrete bond. Managing the slurry is managing the pile.

How bridges get built · Bored piles and deep foundations · Bentonite and polymer slurry stabilisation

Also called: drilling fluid, bentonite support, polymer slurry

Bentonite and polymer slurry stabilisation — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Mix bentonite (4-6 %) and hydrate, or polymer (0.1-0.3 %); circulate through the hole during drilling.
Test density, viscosity, sand content and pH; desand and recycle; replace before concreting if the sand content exceeds the limit.
Keep the slurry level 1.5-2 m above the groundwater at all times.
Dispose of spent slurry through licensed contractors.

Where it fits

All uncased bored piles and barrettes below the water table; polymer in urban sites with disposal limits.

Where it does not

Bentonite in saline groundwater without conditioning; polymer in very loose gravels.

Plant, pace and money

PlantMixers, tanks, desanders, pumps, testing kit.

ProductivityA slurry plant serves two to four rigs.

CostUSD 20-60 per m3 of slurry; disposal can exceed mixing.

Risks and controls

What goes wrong

Hole collapse from a dropped head, thick filter cake reducing shaft friction, slurry inclusions in the concrete.

Quality assurance

Slurry tests before concreting recorded per pile, level watch, sand content below 4 % (bentonite) or 1 % (polymer).

Examples

Standard on bored piles worldwide; polymers dominate in Hong Kong and Singapore.