Page 170 - Water Standards
P. 170
allowable overbreak amount or overfilling concrete in col⁃
lapsed zones. When a concrete pump is used for pouring
the arch concrete, the additional pressure of pumped con⁃
crete shall be considered in the formwork load calculation.
3) The formwork stripping time shall be in accordance with
the regulations in Article 2 7 6 of this specification. Be⁃
sides, factors like the stability of the surrounding rock,
section shape, span and exterior loads shall be
considered. The time of form stripping can be shortened
appropriately in case of being tested.
7 Concrete placement shall meet the following requirements:
1 ) Placement method. Pumping shall be selected
preferentially for the placement of the concrete for side
and roof arches. The placement of bottom arch concrete
can be done directly by a carrier vehicle or belt convey⁃
or.
2) The pouring of pumped concrete shall be in accordance
with the regulations in Article 2 7 31 of this specifica⁃
tion.
3) When transporting concrete by a belt conveyor, the maxi⁃
mum dip angle shall not exceed the values listed in Ta⁃
ble 3 5 3 For mixing proportion, the sand ratio shall
be appropriately increased, the maximum grain size
should not exceed 80mm, and the cement content can
3
be 50-75kg / m lower than that for pumping. The run⁃
ning speed of the belt conveyor should not be larger
than 1-1 2m/ s.
4) Attention shall be paid to the following items in concrete
placement: the pouring of side arches shall be done
layer by layer, and both sides shall rise symmetrically
1 6 3