Geoscience Reference
In-Depth Information
extensive damage to old buildings, were limited to 10 mm. Compaction grouting
uses displacement to effect densification of the soil. Highly viscous grout is used.
Large voids as in karstic soil, loose fill (e.g. rubble), etc. can be compacted. Grout
bulbs are formed from an injection point. A sequence of primary, secondary and
tertiary bulb locations is sometimes applied to achieve fuller coverage.
Compensation grouting
In this application, grout slurry is used to fracture the soil thereby effecting
expansion and heave. It can be used to compensate the settlement of a foundation
when a tunnel is being passed below it, or to rectify or reduce differential
settlements of foundations. Elaborate deformation and injection pressure
monitoring and control are required.
Jet grouting
Jet grouting has increasingly become one of the ground improvement
technologies used to address leakage and to provide strength improvement to soils.
The technique of jet grouting uses high pressure/velocity jet fluids to erode the
existing soil and then to mix the cuttings with cement slurry, a binder (at lower
pressure), to form 'soilcrete' (see picture: cement-soil mixer). Excess slurry or
spoil is ejected to the surface. Alternative
methods apply a jet of slurry (single fluid
method) or envelope the water jet by air (triple
fluid method) to enhance erosion. The latter
method is effective in cohesive soil. Not only
are jet grout columns or sheets used for load
carrying, but when applied in overlapping grids,
impermeable seals can be formed, e.g. between
sheet piles to allow the excavation of watertight
spaces, or underground bulwarks for slope
stabilisation. If the native soil is not completely
mixed with slurry, the resulting columns will
have soil inclusions, which can reduce the
strength of the column and/or increase the
permeability of the column. Monitoring and
control are required.
cement-soil mixer
Geo-textiles
Geo-textiles can be used for segregation of layers. Rock-fill being laid on soft
ground to form a road or embankment base can be prevented from punching into
the soil below using a geotextile underlay. It can provide tensile strength.
Horizontal membranes can be used to provide tensile reinforcement and reduce
settlement. It can act as drainage layer, either as a water-conductor or as a filter to
reduce the migration of fine particles into a granular soil drain, or it can act as an
impermeable barrier preventing or controlling the flow of contaminated
groundwater from or in landfill sites. As a tensile support there are two difficulties:
aligning the membrane in the direction of the principal tensile stress, which is
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