Environmental Engineering Reference
In-Depth Information
lower opening where the stem of mixture is included to combine the polluted
grounds and reagents in a closed system. The procedure involves slowly lowering
the cylinder into the ground. The rotation of the blades in the mixture is
accompanied by the introduction of the reagents. The rotating blade movement from
the top downwards, mixes the ground so it reacts. A negative pressure is kept on the
free space in the cylinder to draw all the vapors or dust towards the vapor treatment
system. Once withdrawn, the cylinder is then placed to the side, partially covering
the previous column. The mixture process is repeated until the entire site has been
treated.
On sites where the movement of machines is restricted and where minimal
disturbance is required, “jet mixing” or “jet grouting” with a simple stem is used.
This method involves beating or drilling the stem to the depth required and injecting
liquid cement at very high pressure through horizontal jets. These jets make it
possible to shear the ground hydraulically, producing a uniform ground-purée.
Finally the revolving stem is slowly withdrawn at a carefully controlled speed so
that the jets create an almost cylindrical column of treated ground with a typical
diameter of 0.6-1.5 M. This process must remain specific because of the very fast
reduction in pressure with increasing distance from the origin of the emission. There
are the three general shapes of jet (Figure 15.4); these involve the injection of a
simple fluid (purée), two fluids (purée/air) or three fluids (air/water/purée). Full
details are given by [TAU 92] and [KAU 92].
Figure 15.4
.
Various systems of jet grouting
In the presence of waste-containing organic materials, the process of
solidification can be unsuitable because of mutual interactions between the products
injected and organic compounds present. Oils and greases can simply coat cement,
preventing the reaction between the water and cement. Some organic materials can
be adsorbed on cement surfaces and severely delay the process of hydration. Other
organic materials, mainly the flocculent agents, can disrupt the dispersion of cement
