Contents preface (VII) introduction 1—37

16.10. KEYS AND WATER SEALS
Vertical keys in transverse joints [Fig. 16.9 (a)] and horizontal keys in longitudinal joints [Fig. 16.9 (b)] are provided in a dam to increase the shearing resistance between its adjacent concrete blocks. The resulting structure has better stability due to the transfer of load from one block to another through the keys. The keys also increase the percolation distance through the joints and thus reduce water leakage. They also hasten the sealing of the joints with sediment deposits.

558 IRRIGATION AND WATER RESOURCES ENGINEERING
Shear keys provided in longitudinal contraction joints improve the stability of the dam by increasing the resistance to vertical shear.
Contraction joints are sometimes grouted to bind the blocks together so that the structure behaves like a monolithic mass. Even if the stability of the dam does not require the entire mass to act as a monolith, the longitudinal contraction joints must always be grouted so that blocks in a transverse row act monolithically.
The opening of the transverse joints between adjacent blocks creates a passage for leakage of water from the reservoir to the downstream face of a dam. To prevent this leakage, seals (Fig. 16.10) are installed in the joints adjacent to the upstream face. Seals in longitudinal and transverse joints are also useful during grouting operations for confining the grout mixture to the joint. The most common type of seal used in concrete dams has been a metal seal which is embedded in concrete across the joint. In addition, polyvinyl chloride (PVC) seals and rubber seals have also been used.

X

X

Section XX
(a) Vertical keys for	(b) Horizontal keys for
transverse joints	longitudinal joints

Fig. 16.9 Typical keys for joints in gravity dam

(a) Z-type (b) M-type

Fig. 16.10 Metallic water stops in transverse joints

GRAVITY DAMS

559

16.11. GALLERIES
A gallery is an opening within a dam that provides access into or through the dam. These may run either longitudinally or transversely and may be either horizontal or inclined. The following are the common types and uses of galleries (1):
(i) Drainage galleries provide a drainage way for water percolating through the up-stream face or seeping through the foundation.
(ii) Grouting galleries provide space for drilling and grouting the foundation.
(iii) Inspection galleries provide access to the interior of the structure for observing its behaviour after completion.
(iv) Gate galleries (or chambers or vaults) provide access to, and room for, such mechani-cal and electrical equipment as are used for the operation of gates in spillways and outlet works.
(v) Cable galleries provide access through the dam for control cables and/or power ca-bles and related equipment.
(vi) Visitors’ galleries provide access routes for visitors.
Other galleries may be needed in a particular dam to meet special requirements, such as the artificial cooling of concrete blocks, the grouting of contraction joints, and so on.