Environmental Engineering Reference
In-Depth Information
completed. The seepage ranges from 16 l/s just after records began to 10 l/s in early
2004. These figures would suggest no deterioration in the curtain, but one should also
consider that:
- The defects in the foundations were probably not great in number and the rock below
the excavated foundation for the core was inherently tight to start with;
- There may have been some “silting up” of the open joints in the rock mass under the
upstream rockfill shoulder.
The grout volume in bags of cement was much higher at the Thomson main dam. A
total of nearly 21,000 bags was put into the curtain and over 100,000 bags in the blan-
ket. About 8-9% of the total went into the river bed and lower 20-30 m of the abutments,
but over 50% was pumped into 70 m of the right abutment. The upper right abutment
was formed by two intersecting landslides and the ground was open to 70-80 m below the
original natural surface.
So far at Thomson the base seepage in the period from 1990 to late 1996, when the
storage was at a continuously high level, was recorded at about 10 l/s. The estimated per-
meability of the foundation is 1-2 Lugeons; during the investigations 100 Lugeon values
were common on the upper right abutment.
It is probably too early to come to any definite conclusions on the grout curtain at
Thomson. To date there has been no measurable deterioration.
Another Snowy Mountains dam, Eucumbene, a 116 m high earthfill dam with limited
rockfill shoulders, seems to have behaved similarly to Talbingo dam. Early records from
1958, first filling, to 1998 show that:
Storage level (RL m)
Head on base of core (m)
Seepage (l/s)
1110
60
13
1143
93
17
1160
110
8
The conclusion on the potential deterioration of the grout curtain would be the same as
drawn from the Talbingo records, although the same two factors noted for Talbingo prob-
ably apply also to Eucumbene.
18.4
CHEMICAL GROUTS IN DAM ENGINEERING
18.4.1
Types of chemical grouts and their properties
There are two distinct types of chemical grouts:
-Group A - colloidal solutions or prepolymers, e.g. silica gel, ligno chrome gel, tannins,
organic or mineral colloids, polyurethane;
-Group B - pure solutions, e.g. acrylamide, phenoplast, aminoplast.
The hydraulic behaviour of these grout types is different:
-Group A - behave as Bingham fluids with an initial shear stress required to mobilize
the grout (as for cement and cement/bentonite grouts);
-Group B - behave as Newtonian fluids - as for water but with a higher viscosity.
Figure 18.23
shows typical flow properties of grouts. Note that the viscosity measured
(in centipoise) is the slope of the graph at any point; the apparent viscosity is the slope of
