EXCAVATION OF TOWER FOUNDATION PITS:
4.1 While excavating, the earth is cut vertically / tapered / in steps as per the soil conditions at
site to avoid any kind of mishap caused by collapsing of the pit sides during the course of
excavation and foundation work.
4.2 The excavated earth is to be kept at a sufficient distance so that it does not create any
burden on the sides of excavated earth pits.
4.3 During excavation in sandy soil or water bearing strata, and particularly in black cotton soil
where there is every likelihood of collapsing of the sides of the pits, shoring and shuttering
made of wooden planks of sufficient thickness or steel frames of adequate strength to meet
the requirement are to be provided.
4.4 Where water is encountered during excavation, dewatering shall be carried out manually or
by mechanical means or power driven pumps to facilitate excavation and casting of
foundations. The pumps shall be suitable for handling muddy water.
4.5 Excavation in soft rock is done with the help of chisels. Some types of soft rock soils need
to be soaked in water before excavation can be carried out. It is not recommended to use
blasting for excavation in soft rock.
4.6 For excavation in hard rock, blasting can be resorted to. Reference shall be made to
statutory rules for blasting and use of explosives for this purpose. No blasting is permitted
near permanent work or dwellings. At such locations, excavation shall be done by
mechanical methods. To protect persons and animals from injuries and to protect nearby
installations from flying debris, the pits can be covered with steel plates. Blasting shall be
done in a manner such that the pits excavated are as near to the design dimensions as
practicable. Holes are drilled at the base of the excavation for the anchor rods.
4.7 The details of the excavation & the type of soil(s) are entered in the excavation register.
SETTING OF TEMPLATE:
5.1 A stub setting template is a specific tool for a type, design & make of tower. It is a light
rigid steel framework and is used to hold the tower stubs at the correct alignment and slope
during the concreting work. The template is adjustable type which can suit the standard
tower as well as towers with standard extensions.
5.2 After the excavation is completed, the sides of the template are assembled and placed on the
four sides of the location. The sides are then connected together, taking into consideration
the type of tower (normal or with extension) to be erected, to form the shape of the template
with the four corners located in the excavated pits.
5.3 The template is lifted and placed on jacks. Eight jacks are used, two for each corner of the
template. The jacks are supported on sleepers which are placed across the pits so that the
load of the template is distributed away from the excavated pits. The lengths of the sides
and diagonals of the template are measured. These are compared with those given in the
drawing and corrected as required.
5.4 Plumb lines, one in the transverse direction and the other in the longitudinal direction, are
drawn from the peg markings given for the location.
5.5 The template is centred on the location with the help of the plumb lines. The template is
levelled and the height of the base of the template above ground level is kept as given in the
5.6 The lengths of the sides and diagonals of the template are finally checked and corrected if
required. The levelling of the template is also checked and corrected.
5.7 The stubs are then fixed on the legs of the template. The distance between the end of the
stub and the base of the pit is checked with reference to the foundation drawing. If the
distance is less, then the pit is accordingly excavated. In case the distance is more, the extra
excavation is filled with lean concrete of 1 : 4 : 8 mix and allowed to set before further
activities are taken up. NEVER USE SAND TO FILL THE EXTRA EXCAVATION.
5.8 The details of the dimensions & levels of the template are entered in the stub setting