TIMBER SHORING
1. MATERIALS AND METHODS
1.1 Close timbering shall be done by completely covering the sides of the
trenches and pits generally with short, upright members called 'polling
boards'. These shall be of minimum 25 cm x 4 cm sections generally made
from SAL wood or as directed by COMPANY and also shall conform to local
standards and relevant international construction codes approved by
COMPANY.
1.2 The boards shall generally be placed in position vertically side by side
without any gap on each side of the excavation and shall be secured by
horizontal walling of strong wood at maximum 1.2 metres spacings, strutted
with wooden logs or as directed by COMPANY. The length of the wooden
logs struts shall depend on the width of the trench or pit. If the soil is very
soft and loose, the boards shall be placed horizontally against each side of
the excavation and supported by vertical waling, which in turn shall be
suitably strutted. The lowest boards supporting the sides shall be taken into
the ground and no portion of the vertical side of the trench or pit shall
remain exposed, so as to avoid the earth to slip into the trench. Excavation
Safety shall conform to local standards and relevant international
construction codes approved by COMPANY.
1.3 Timber shoring shall be 'close' or 'open' type depending on the nature of
soil and the depth of pit or trench. The type of shoring shall be as approved
by COMPANY. It shall be the responsibility of CONTRACTOR to take all
necessary steps to prevent the sides of excavations, trenches, pits, etc., from
collapsing.
1.4 Timber shoring may be required to keep the sides of excavations vertical
to ensure safety of adjoining structures or to limit the slope of excavations
or due to space restrictions or for other reasons. Such shoring shall be
carried out, except in an emergency, only under instructions from
COMPANY.
1.5 Installations of shores shall be done from the surface – vertical shores shall
be installed from the surface and first horizontal braces installed just below
the surface. Working persons shall go into the pit or trench only through
ladder long enough to install the next brace or trench jack and shall not use
the horizontal braces/ trench jacks as ladder.
1.6 The withdrawal of the timber shall be done very carefully to prevent
the collapse of the sides of pit or trench. It shall be started at one end
and proceed systematically to the other end. Concrete or masonry shall not
be damaged during the removal of the timber. No claim shall be entertained
for timber which cannot be withdrawn and is lost or buried. Filling of the
trench to the bottom of the horizontal shoring shall be done prior to
withdrawal of shoring to prevent caving in of the sides.
1.7 In the case of ‘open’ timbering, the entire surface of the side of trench or pit
is not required to be covered. The vertical boards of minimum 25cm x 4 cm
sections shall be spaced apart to leave unsupported strips of maximum 50
cm average width. The detailed arrangement, sizes of the timber and the
spacing shall be subject to the approval of COMPANY. In all other respects,
specification for close timbering shall apply to open timbering.
1.8 In case of large pits and open excavations, where shoring is required for
securing safety of adjoining structures or for any other reasons and where
the planking for sides of excavations/pits cannot be strutted against each
other, suitable inclined struts supported on the excavated bed shall be
provided. Load from such struts shall be suitably distributed on the bed to
ensure no yielding of the strut. If COMPANY directs any timbering to be
left-in, keeping in mind the type of construction or any other factor,
CONTRACTOR shall be paid at the scheduled item-rate, for such left-in
timbering.
1.9 Where Ground Water Table exists, continuous dewatering shall be
carried out before timbering the sides and even after timber shoring.
1.10 Design of sizing and spacing of members, walling, struts and wooden logs
shall be carried out as necessary to ensure the stability of excavated sides.
END
