Environmental Engineering Reference
In-Depth Information
4. Flood discharges: Have high potential to erode, raising questions about the location
and erodibility of discharge areas for the spillway and outlet works.
Table 4.1 is a suggested checklist of geotechnical engineering questions to be answered
during site investigations for dam projects.
4.1.2
Geological questions
Typical geological questions for twelve common geological environments have been dis-
cussed and listed in Chapter 3. The following notes highlight the importance of asking
Table 4.1.
Geotechnical engineering questions.
1. Sources of materials, for the following purposes:
- Earthfill, for the core or other zones;
- Filters;
- Rockfill;
- Rip-rap;
- Concrete aggregates;
- Road Pavements;
For each material: Location of alternative sources, qualities/suitabilities, quantities, methods for
winning and processing. Overburden and waste materials and quantities. Possible use of materials
from required excavations, e.g. spillway, outlet works and dam foundations.
2. Reservoir
-Watertightness;
-Effect on regional groundwaters - Levels or quality;
- Stability of slopes inside and outside of reservoir rim;
-Erodibility of soils - Possibility of turbidity problems;
- Siltation rates and likely location of deposits.
3. Dam
- Location - To suit topographic and geological situations;
- Alternative* sites, for comparison of costs and of geotechnical and other issues;
-Type(s) of dam suited to site(s);
- Depths to suitable foundations for: concrete dam; earthfill; core; filters; rockfill; plinth or grout cap;
- Nature of materials to be excavated, excavation methods, and possible uses of materials;
- Stability of excavations, support and dewatering requirements;
- Permeability, compressibility and erodibility of foundations;
- Foundations treatment(s) required: grouting; drainage; slurry concrete; dental treatment; filter
blanket; other;
- Embankment zones, methods of placement, and of control of quality, moisture and compaction;
- Stability of dam, and dam plus foundation in all situations;
- Monitoring systems: types, siting.
4. Spillway, river diversion works and permanent outlet works
- Location and type;
- Excavation method(s), possible use for excavated materials;
- Stability of excavations, need for temporary/permanent support;
- Channel, need for lining/drainage;
- Need for protection of the discharge area, or for excavation of a stilling basin.
5. Tunnels (for river diversion, spillway, or permanent outlet works)
- Location of sites for portals;
-Tunnel alignment(s);
- Portals, excavation and support methods and final treatment;
-Tunnel excavation, support and final treatment methods.
6. Seismicity of region
- Design earthquake, annual exceedance probability versus ground motion;
- Maximum credible earthquake.
* Alternative sites for the dam and associated structures are usually investigated during Stage 2
(Feasibility and site selection).
