Page 189 - Water Standards
P. 189

shall be adopted to prevent the construction joint from fur⁃
                                ther extending.
                             8) Adjacent blocks shall rise uniformly. When constructed
                                with step joints, the elevation difference of adjacent
                                blocks shall not be larger than 4-5m usually.
                             9) The side walls and top concrete of spiral cases should not
                                be poured at a time.
                       3   9   5  The construction formworks of reinforced concrete spiral case
                       and tailwater tube shall meet the following requirements:
                           1  Wood forms should be used for spiral case and conical tubes
                       and elbows of the tailwater. The form can be made of steel and wood or
                       other materials for the diverging section of the tailwater tube, but
                       there shall be feasible and detailed measures for the connecting part of
                       the steel and wood forms. The formwork deviation in installation and
                       concrete placement shall be no larger than the pemissible values in
                       Table 3   9   5-1   For the straight section of the tailwater tube after con⁃
                       crete pouring at the bottom plate, concrete, brick or masonry forms
                       can be used instead of steel wood forms. The precast inverted T⁃
                       shaped beams should be used as the roof board of the diverging section
                       of the tailwater tube in case of availabel hoisting condition.
                           2  Wood forms shall be produced in the factory, avoiding expo⁃
                       sure to the sun and rain, and the form length shall be decided accord⁃
                       ing to form size and production capacity, hoisting, transportation,
                       and installation and construction capability. Production of the whole
                       body or in subsections can be adopted, and priority should be given
                       to choosing the former one. The conical body of the spiral case can be
                       produced according to a 1 / 4 circular conical section. The pessible er⁃
                       rors of form production shall meet the form design requirements, and
                       should not be larger than the requirements in Table 3   9   5-2  
                           3  Setting out of the tailwater tube form can be done by a graph⁃
                         1 8 2
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