01 July 1997
(1) Categories of Load Tests. Load tests that are frequently performed are proof tests without
internal instrumentation which are conducted to only twice the design load. Load tests are also performed to
failure with or without internal instrumentation.
(a) Proof tests do not indicate the ultimate pile capacity and, consequently, the pile can be
designed to support a higher load than necessary. Proof tests are not adequate when the soil strength may
deteriorate over time such as from frequent cyclic loads in some soils. Coral sands, for example, can cause
cementation that can degrade with cyclic loads (see chapter 5).
(b) Piles tested to failure allow the reserve capacity and the allowable load to be evaluated.
The allowable load when a load test is performed is one-half of the ultimate pile capacity.
through which the pile is driven and the end bearing capacity to be measured in the bearing stratum. The
load test results can be used at other locations where the depth of the different soil strata and the bearing
stratum varies, thereby reducing the need for additional load tests.
(2) Selection and Timing of Load Tests. Pile tests are not always practical or economically feasible
under certain circumstances, particularly for deep foundations or remote locations; but, they are technically
desirable for sound and complete engineering practice.
(a) Pile load tests are relatively expensive and may not be justified if the structure has a small
number of piles. An important or complex structure could compensate for the added cost of a pile test
program when the consequences of a failure will be disastrous. Pile tests are necessary and justifiable
when the subsurface data indicate uncertain foundation soils that would compromise the integrity of the
(b) Consideration will be given to the timing of a pile test program in relation to the construction
schedule. Cost estimates and schedules will include resources for site investigation, test data collection, and
design verification. A pile test program by separate contract may be performed for desired subsurface data
and to allow completion of the foundation design prior to award of the construction contract if time and funds
(c) Test piles should be located at strategic positions such as near boundaries of the foundation
and at interior locations to determine the distribution of the driving resistance. Adequate subsurface
investigations and a pile test program should be performed to confirm the design assumptions. The static
load test should be conducted on the pile with the lowest driving resistance. The use of PDA equipment
permits calibration of wave equation analysis and can reduce the number of load tests required to determine
the pile capacity.
(d) The influence of time-dependent strength gain from soil freeze or loss from soil relaxation is
frequently important. Provisions should be considered in contract documents for delays during load testing
and pile driving operations to allow for soil freeze or relaxation effects so that the true pile capacity can be
determined. This requires careful planing and coordination between designers and construction personnel
to prevent any undue impacts and delays.
(3) Axial Load Tests. Axial compressive load tests should be conducted and recorded according to
ASTM D 1143 but can be modified to satisfy project requirements. The Osterberg load test, where the load
cell is placed at the tip of the pile, is useful in situations where a loading frame cannot be constructed.
(a) The standard load test takes the most time and will measure the most consolidation
settlement of any of the load tests; but, none of the load tests will measure all of the consolidation