A building or structure's soundness starts
with a strong foundation, especially the piles. As a part of
foundation's quality assurance, Maintain Load Test, also known as
Static Load Test is necessary to ensure the pile that was driven
could take the design load of the structure. During this test,
load would be applied on the selected pile and the pile settlement
under the acting load would be recorded. As a common practice,
pile would be loaded up to twice of the working load, which is
regarded as the Test Load of the pile.
Prior testing, the pile head shall be cut off
or built up to the necessary elevation and shall be capped
appropriately to produce a bearing surface perpendicular to the axis
of the pile. The arrangement shall be such that none of the test
load is carried by the ground under the cap.
The test load shall be applied in one of the
following ways
-
By means of a jack which obtains its
reaction from kentledge heavier than the required load;
-
By means of a jack which obtains its
reaction from tension piles or other suitable anchors.
The load shall be measured using a calibrated
load gauge and also a calibrated pressure gauge in the hydraulic
system. The jack and load gauge shall be carefully aligned so that
the load applied is co-axial with the pile. When method (1) is
used, care shall be taken to ensure that the centre of gravity of
the kentledge is on the axis of the pile. The nearest edge of the
crib supporting the kentledge stack shall not be closer than 1.3 m
to the surface of the test pile. Kentledge shall not be used
for testing raked piles. When method (2) is used, all anchor
piles shall be at a distance of at least three (3) pile shaft
diameters from the test pile, centre to centre, and in no case shall
they be less than 2 m from the test pile. If the anchor piles
are to be permanent working piles, their levels shall be
observed during application of the test load to ensure no residual
uplift occurs.
Settlements shall be measured by use of a
reference beam or wire supported independently of the load test
pile, reaction pile or piles supporting reaction loads. Settlements
shall be measured to the nearest 0.1 mm for reference beams or 0.5
mm for reference wires. The reference beam supports shall be located
at least 3 m from the load test pile, reaction pile or piles
supporting reaction loads. The reference beams or wires shall be
protected from the effects of temperature changes.
The Maintained Load Test shall be carried out
as follows unless alternative method specified by the Consultants;
a) The full test load on a pile shall be twice the design load noted
on the
Drawings and it shall be applied in twelve equal decrements. At
least two
hours shall elapse between the addition of each load increment, i.e.
until the rate of settlement is reduced to less than 0.25 mm/hour
and slowing down;
b) The full test load shall be maintained on the pile for at least
48 hours and settlements shall be recorded at intervals of not more
than 12 hours. The test pile shall then be unloaded in four equal
decrements at one-hour intervals until the full load is removed.
Settlement readings shall be made immediately after and before every
load increment is applied or removed.
