| Jet Grouting |
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There are three traditional jet grouting
systems. Selection of the most appropriate system is generally determined
by the in situ soil, the application, and the physical characteristics
of soilcrete (i.e. strength) required for that application. However,
any system can be used for almost any application, provided that
the right design and operating procedures are used.
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Grout is pumped through the rod and
exits the horizontal nozzle(s) in the monitor at high velocity
[approximately 650 ft/sec (200m/sec)]. This energy breaks
down the soil matrix and replaces it with a mixture of grout
slurry and in situ soil (soilcrete). Single fluid jet grouting
is most effective in cohesionless soils.
A two phase internal fluid system is
employed for the separate supply of grout and air down to
different, concentric nozzles. The grout erodes in the same
effect and for the same purpose as with Single Fluid. Erosion
efficiency is increased by shrouding the grout jet with air.
Soilcrete columns with diameters over 3 ft can be achieved
in medium to dense soils, and more than 6 ft in loose soils.
The double fluid system is more effective in cohesive soils
than the single fluid system.
Grout, air and water are pumped through
different lines to the monitor. Coaxial air and high-velocity
water form the erosion medium. Grout emerges at a lower velocity
from separate nozzle(s) below the erosion jet(s). This separates
the erosion process from the grouting process and tends to
yield a higher quality soilcrete. Triple fluid jet grouting
is the most effective system for cohesive soils.
Grout, air and drilling fluid are pumped through separate chambers in the drill string. Upon reaching the design drill depth, jet grouting is initiated with high velocity, coaxial air and grout slurry to erode and mix with the soil, while the pumping of drilling fluid is ceased.
This system uses opposing nozzles and a highly sophisticated jetting monitor specifically designed for focus of the injection media. Using very slow rotation and lift, soilcrete column diameters of 10-16 ft (3-5m) can be achieved.
This is the most effective system for mass stabilization application or where surgical treatment is necessary. |
Jet Grouting
is effective across the widest range of soil types, of any grouting system, including
silts and some clays. Because it is an erosion based system,
soil erodibility plays a major role in predicting geometry,
quality and production. Cohesionless soils are typically more erodible than cohesive soils.
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Since the geometry and physical properties
of the soilcrete are engineered, the degree of improvement can be
readily predicted.
Jet grouting offers an alternative to conventional
grouting, chemical grouting, deep slurry trenching, proprietary
underpinning systems, or the use of compressed air or freezing in
tunneling, etc.
Jet grouting should be considered in any situation
requiring control of underground fluids, or excavation of unstable
soil, whether water-bearing or otherwise.
- Bearing capacity of the system
- Retaining system evaluation for
lateral earth pressures and surcharge loads
- Settlement review
- Strength adequacy of the system
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- What depth is necessary and what
shear strength and geometry of soilcrete will resist the
surcharge, soil and water pressure imposed after excavation?
- Are soil anchors or internal bracing
necessary?
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- What integrity
is possible from interconnected soilcrete elements and how
much water can be tolerated through the soilcrete barrier?
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The operating parameters of air, water and/or grout flow, and pressure, together with monitor rotation and withdrawal speed are selected (following detailed engineering assessment of soil conditions) and are automatically controlled and monitored throughout construction. Reduced flow or increased withdrawal speed produces a smaller soilcrete geometry.
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Theoretically, treatment depth is unlimited, but Jet Grouting has rarely been performed in depths greater than 164 ft (50m).
Treatment can also be pinpointed to a specific strata. The size of the soilcrete mass to be created is determined by the application. The width or diameter of each panel or column is determined during the design stage.
Accurate, detailed and frequent description of soil type, with reasonable assessment of strength or density allows this prediction to be made with confidence. If required, shear and/or tensile reinforcement can be incorporated into the soilcrete.
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The size of the soilcrete mass is determined by the application. The width or diameter of each panel or column is determined during the design stage.
Accurate, detailed and frequent description of soil type, with reasonable assessment of strength or density allows this prediction to be made with confidence.
If required, shear and/or tensile reinforcement can be incorporated into the soilcrete.
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- Nearly all soil types groutable and any cross section of soilcrete possible
- Most effective method of direct underpinning of structures and utilities
- Safest method of underpinning construction
- Ability to work around buried active utilities
- Can be performed in limited workspace
- Specific in situ replacement possible
- Treatment to specific subsurface locations
- Designable strength and permeability
- Only inert components
- No harmful vibrations
- Maintenance-free
- Much faster than alternative methods
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- Sampling of waste materials -- conservative
relative assessment of in situ characteristics
- Core samples
- Daily report forms -- parameters
and procedures of treatment
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