Page 30 - Building Regulation and Design Guidelines - Structural (Grey Code)

SECTION: 1 GEOTECHNICAL GUIDELINES & REGULATIONS SECTION: 1 GEOTECHNICAL GUIDELINES & REGULATIONS

q) For tension piles designed to resist the uplift forces or end
bearing piles installed from ground level until deep bedrock, the
reinforcement should normally be carried down for the full length.
According to BS 8004 : 1986, Section 7.4.5.3.2
r) The longitudinal reinforcement should extend at least 1.00 m below
the bottom of casing so that movement of the reinforcement during
extraction of casing is minimized. BS 8004 : 1986, Section 7.4.5.4.5
1. Install temporary casing concentric with 2. Drill to the required depth 3. Lower the rebar cage inside
the drilled borehole.
s) A minimum additional allowance of 40 mm should be added to the pile points.
concrete cover recommended in Table 3.4 of BS 8110, Part 1: 1997.
t) Cover spacers may be of pre-formed plastic to be used for the pile.
The spacers should be threaded to lateral stirrups and should be
spaced of not more than 2.0 m with minimum of three to be placed
in each row. One set should be fixed at the pile cut-off level and one
at approximately 1.0 meter from the toe of the cage.
Guide casing
u) For top layers composed of reclaimed/very loose untreated sand,
end bearing in addition to skin friction resistance within the rock 4. Concreting using concrete pump 5. Withdraw the guide casing. 6.Completed pile.
and tremie pipe
socketed length only shall be considered. Lateral spreading forces,
negative skin friction as well as actual reduced lateral stiffness of
pile due to buckling should be investigated.
Fig. (1.37) shows the method statement for continuous flight auger piling
as well as the drilled bored piles. Fig. (1.38): Method Statement for Drilled Bored Piles
1.6.2 POINTS TO BE CHECKED DURING CONSTRUCTION, FIGS. (1.38 & 1.39)
a) If betonite slurry is used, the density should be less than 1.10 g/mL.
The viscosity as measured by the Marsh Cone should be within a
range of 30 to 90 seconds, and the 10 min. gel strength to be in the
range of 1.4 N/m2 to 10 N/m2. The pH value should be maintained
within a range of 9.5 to 12. BS8004: 1986, Section 6.5.3.8.1.
1 Augering
b) The geophysical properties of the bentonite slurry should be re-
established prior to the commencement of concreting operation. A
submersible and circulation pumping system or air lifting system
may be utilized for this purpose.
c) If extensive bentonite slurry loss occurs during drilling, the drilling
Drilled Bored Piles will be stopped immediately. The bore will be backfilled with the
2 Extracting of Auger 3 Installing of
Flights and Injection Steel Reign- excavated material in order to create a plug surrounding the pile
of Cement Mortar forcement
shaft. Re-drilling will then take place. If further fluid loss or shaft
Continuous Flight Auger Piling collapse occurs, the bore will be immediately backfilled with low
strength, lean mix concrete prior to any further excavation taking
Fig. (1.37): Method Statement for Different Types of Bored Piles
place.
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