Environmental Engineering Reference
In-Depth Information
of the hole, by increased take, surface leakage or by monitoring levels of the surface above
the rock being grouted.
It is recommended by Houlsby that grouting is to “refusal” and that the pressure is
maintained for 15 minutes after this to allow time for initial set. Others suggest grouting
until take is less than a certain volume in a 15 minute period, e.g. Water Authority of WA
(1988) specify grouting is to cease when take is less than 30 litres/20 minutes at 700 kPa
or less; 30 litres in 15 minutes at 700-1400 kPa; 30 litres/10 minutes for pressures greater
than 1400 kPa. They also indicate pressures should be maintained until “set” has
occurred. In practice the maximum pressures will have to be determined by careful mon-
itoring as the grouting proceeds.
18.3.7
Monitoring of grouting program
It is absolutely essential that detailed records of the grouting operation are kept. This is
necessary to allow progressive development of the grouting operation, e.g. decision mak-
ing on hole depths, whether closure holes are required or whether grout mixes should be
changed. In most cases, detailed records will also be needed for payment purposes.
Matters recorded should include:
- Hole locations, orientation, depths;
- Stage depths;
-Water pressure test value for each stage prior to grouting, including maximum pressure
used;
-Grout mix(es);
-Grout pressures, takes at for example 15 minutes interval and then in summary;
-Grouting times;
-Leaks, uplift;
-Total grout takes for each stage;
-
Amount of cement in these takes;
-
Cement takes/unit length of hold.
This data will be collected largely by foremen but an engineering geologist should be
involved continuously to interpret the progress of the grouting, relate this to the geotech-
nical model of the foundation and make decisions on closure etc. This will invariably
involve keeping records on sections along and across the grout centreline with geological
data superimposed.
18.3.8
Water pressure testing
Before grouting each stage, a water pressure test should be carried out. This is done using
a method similar to that outlined in Chapter 5, but using a simplified procedure, e.g.
applying only one pressure (100 kPa) for 15 minutes, taking flow quantities at 5, 10 and
15 minutes to estimate the Lugeon value.
18.3.9
Type of cement
Type A (AS1315-1982) portland cement is commonly used (Type I, ASTM) or Type C sul-
phate resistant (Type II) if acid groundwaters warrant, e.g. in some tailings dams. There is
some argument for using Type C as it is marginally finer than Type A and should penetrate
fine fractures more readily.
Deere (1982), Bozovic (1985) and Weaver (1993) indicate that on some South
American, USA and Japanese projects special microfine cements have been manufactured
