Page 187 - Water Standards
P. 187

completion of the permanent one.
                           2  The water outside powerhouse area should be directly drain⁃
                       aged to beyond the upstream and downstream cofferdams.
                           3  A permanent leakage water sump in the powerhouse should be
                       constructed in advance and acted as the main drainage measure in
                       powerhouse constrction.
                       3   9   4  The layering and blocking division of concrete placement shall
                       meet the following requirements:
                           1  The principle of layering and blocking:
                             1) The layering and blocking shall be done according to the
                                factors of powerhouse structure characteristics, shape and
                                stress, as well as equipment installation. No joints shall
                                be arranged at the stress concentration position and at the
                                weak zones of the structure. The blocked parts shall not be
                                of acute angles and thin slices in the geometric shape. The
                                construction  joints  and  structural  joints  shall  be
                                coordinated each other to avoid weakening the integrity of
                                the structure. Formwork, steel bars, embedded parts,
                                concrete vibrating and the convenience of the second⁃stage
                                concrete placement shall also be considered in layering
                                and blocking.
                             2) The layering thickness shall be decided according to the
                                structure characteristics and temperature control require⁃
                                ments. The layer thickness within foundation restraint
                                zones should be no larger than 2m, and the thickness can
                                be increased up to 2   5m above the restraint zone. For the
                                position with a large heat dissipation surface, the layering
                                thickness can be appropriately increased according to the
                                specific condition, but shall not be larger than 4   0m.
                             3) The size of the blocking are shall be decided according to
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