Compaction grouting is used to stabilise and densify comprisable soils, loose or collapsed strata and rubble fills to increase bearing capacity and stabilize sinkholes and subsurface voids. The density of the soil is increased by injecting a stiff mortar under pressure through cased boreholes across the treatment area.
The degree of densification depends on the type of soil treated, secondary and tertiary treatment boreholes might be required to increase effectiveness.
Compaction grouting can also be carried out from an existing basement or locations with limited headroom, and it is possible to drill through hard material to reach the low strength strata beneath for treatment.
Primary cased boreholes are drilled within a predetermined grid pattern across the treatment area. An injection pipe is inserted into the cased boreholes and a stiff mortar-like grout is pumped under pressure (generally 0.5 to 1 Bar/m depth) commencing at the maximum treatment point. As the grout is pumped in, it gradually forms a bulb which displaces the surrounding soil, thereby increasing the relative density of the soil.
The temporary casing is withdrawn in successive stages of 1m and the grouting process repeated leaving a column of overlapping grout bulbs, as the soil is displaced. The grouting process is repeated across the treatment area until the required bearing capacity is achieved.