534 Ground investigations, contracts and pile testing
11.18. Instead of a pair of piles a single pile can be pushed or pulled against a thrust block
(Figure 11.19). Where pushing methods are used restraining devices should be provided to
ensure that the jack and strut assembly does not buckle during the application of load.
Where possible the lateral movement of the pile heads should be measured by dial gauges
mounted on a frame supported independently of the test piles, as shown in Figure 11.19.
This may not be feasible in marine piles since the oscillation of the piles and the structure
supporting the frame in waves and currents may make it impossible to obtain readings with
sufficient accuracy. Measurements made of the curvature of a pile by lowering an incli-
nometer down a tube fixed to the wall of a hollow pile or cast centrally in a solid pile are
helpful in checking the assumptions made on the point of fixity as described in Chapter 6.
Highly accurate electro-levels can be mounted in a probe and lowered down a sleeve cast
into the pile. The slope of the pile at the head can be measured by extending the pile above
ground level by a stiff indicator rod. Dial gauge readings are made at the top and bottom of
this rod. It is also helpful when testing piles in marine structures to make two sets of tests,
applying the load at two different levels, say at the head and just above low water of spring
tides. This provides two sets of curves relating deflections to bending moments.
Figure 11.20Load–deflection curve for cyclic horizontal loading test on pile (some load cycles
omitted for clarity).
10080604020(^0102030)
Horizontal movement of pile head in mm
Horizontal load on pile head mm
40 50
Figure 11.19Testing rig for lateral loading test on single pile.
Test pile
Dial gauge
Support
Load cell
Hydraulic jack
Strut Concrete
thrust block