Highlight points about foundation and galleries in a gravity dam. Referred book: SK Garg, Irrigation engineering and Hydraulics structures,

1. FOUNDATION TREATMENT
FOR GRAVITY DAM
Prepared By: Shweta Kodihal

2. HOW SHOULD BE THE FOUNDATION
OF DAM.
It must be strong enough and capable to withstand
the pressure exerted on it.
It must withstand the load in both wet and dry
condition.

3. CASE STUDIES.
1) St. Francis dam, California. Height of dam was about 62m high and
210m long. It failed soon after its completion.
Cause of failure: Presence of conglomerate in one abutment. It was
weakened after exposure to moisture from the reservoir.
2) Austin Dam on Colorado river in Texas, year 1900.
Cause of failure: Large cavities had been dissolved in its limestone
foundation.

4. FOUNDATION TREATMENT
1) Preparing the surface
 Remove entire loose soil till bed rock is exposed.
 Stepped final surface to increase frictional resistance against
sliding.
 Faults, seams, or shattered rocks if found should be removed safely.
 Thoroughly cleanse the final foundation surface with wet sand
blasting before concreting for dam section is started.

5. 2) Grouting the foundation
 a) Consolidation grouting: Entire foundation is consolidated by
grouting.
Shallow holes are drilled through the foundation rock. Holes vary
between 10-15m and 5-20m apart.
Mixture of cement and water is forced into holes at low pressure about
30-40N/cm2.
B) Curtain grouting: It helps forming a curtain against seepage through
foundation and reduces uplift pressures.
Deep holes are drilled about 1.2 – 1.5m apart. Holes then with 10-12m
apart are filled with the grout and then the intermediate holes are filled
with varying depth.
Depth of holes may vary 30-40% of total u/s water head.
FOUNDATION TREATMENT

6. GALLERIES FOR GRAVITY
DAM

7. WHAT ARE GALLERIES?
 Galleries are horizontal or sloping openings or passages left on the
body of the dam.
 They run longitudinally (parallel to dam axis) or transversely
(normal to dam axis).
They are provided at various elevations.
All the galleries are interconnected by vertical shafts or staircases or
lifts.
Size of gallery depend on size of dam and function of gallery.
1) Foundation Gallery
2) Inspection Galleries.

8. FOUNDATION GALLERIES
It is provided near the foundation to drain of water which percolates
through the foundation.
It is also called drainage gallery.
It runs longitudinally.
Size varies from 1.5m x 2.2m to 1.8m x 2.4m.
Size should be sufficient enough to accommodate a drilling
machine, grouting machine.

9. INSPECTION GALLERIES
 These galleries serves the purpose of inspection.
 They serve more purpose than just inspection.
They drain of seepage water.
Provide access to dam interior.
Carry cooling pipe during artificial cooling during hydration.
Provide access to outlets like spillway gates, valves etc.

10. THANK YOU