Environmental Engineering Reference
In-Depth Information
Figure 3.32.
Enlargement of joints in dense
Category O
limestone (Portland stone) by pure flowing
water (James and Kirkpatrick, 1980, reproduced by permission of the Geological Society).
Table 3.5.
Solution of jointed rock (from Table 3 of James and Kirkpatrick, 1980).
Largest joint aperture (mm)
For stable inlet face
For rate of retreat of
Suggested preventive
retreat
0.1 m/year
measures
Gypsum
0.2
0.3
Grouting
Anhydrite
0.1
0.2
Cut-off - e.g.
cement-bentonite
Halite
0.05
0.05
Cut-off - e.g.
cement-bentonite
Limestone (Category O)
0.5
1.5
Grouting
Note: Values are for pure water; at joint spacing of one per metre and an hydraulic gradient of 0.2.
containing 300 mg/l of dissolved carbon dioxide. They further conclude that if all large
cavities are backfilled with grout or concrete, then cement grouting (which can fill joints
down to about 0.2 mm aperture) should be adequate to prevent progressive solution of
limestone foundations. They point out the need for care in the conducting of Lugeon per-
meability tests and in estimating the apertures of joints from the results of the tests.
Table 3.5 summarises the conclusions of James and Kirkpatrick for preventing progres-
sive solution along joints in all four soluble rock types.
3.7.5
Potential for continuing dissolution of aggregates of carbonate rock particles,
and of permeable carbonate substances (Category O carbonate, in each case)
James and Kirkpatrick (1980) also discuss solution rates in “particulate deposits”. It is
assumed that such deposits might comprise either aggregates of rock fragments (as in
some zones of sheared or crushed rock, or in filter zones) or substances rendered perme-
able by intergranular voids
(
Figure 3.31b
). Using the theoretical models of James and
Lupton (1978), James and Kirkpatrick show that the length of the solution zone depends
mainly on the solution rate constant and the solubility and that other factors such as the