AXIAL LOAD TEST PROCEDURES FOR PILE FOUNDATIONS
Presentation
On account of the non-accessibility of solid techniques for evaluating the heap move
instruments among heaps and encompassing soil, or for deciding a definitive limit
of heaps, full-scale load tests are directed. It is a standard practice to lead load tests
in enormous tasks either in the plan stage or during development. The meaning of a
appropriately directed load test is that it outfits the genuine soil obstruction at the site upon
which configuration can be based dependably.
By and by, load tests are all the more ordinarily led to establish that the establishment is
equipped for supporting working burdens with adequate component of wellbeing. In different occasions,
load move attributes are expected to distinguish the component by which burden is
moved to the dirt.
Load tests fluctuate in their method, gear, instrumentation, and burden application
strategy. There are two sorts of tests led for hub kinds of stacking, specifically
pressure tests and pullout (strain) tests. For pressure tests, the heap can be
applied either by adding extra weight or by water powered jacking. Direct use of dead
weight should be possible with cement or steel blocks, water tanks, barricades or some other kind
of loads. Notwithstanding, the utilization of this technique has diminished significantly, and it became
more normal to utilize pressure driven jacks to shift the heap on the test heap, particularly for high
stacking conditions.
EQUIPMENT AND INSTRUMENTATION
The game plan for a hub pressure test is for the most part done utilizing either a dead burden
stage, or a water driven jack with response (or anchor) heaps. The water driven jack with
response heaps course of action (Figure 1) is utilized regularly in load testing. To
limit the impact of stresses moved from the response heaps to the dirt close to the test
shaft, a base distance is expected between the response heaps and the test heap. It is
by and large acknowledged to take into consideration a base separating of 3 response heap widths between
every response heap and the test heap, given that this distance is more noteworthy than 5 ft (Hirany
also, Kulhawy, 1988).
A response shaft is introduced on top of the response heaps. The test heap is stacked by
using a water powered jack that is put on the focal point of the test heap. The applied burden is
estimated with a heap cell set between the water driven jack and the heap or by a strain
measure introduced between the siphon and the jack.
Instruments are basically utilized to keep two sorts of development in load tests. First
is the heap head (butt) development and second are the steady strain estimations
along the heap length. Estimations of the heap head development is fundamental in all heap
tests and is finished by the utilization of dial checks or potentially reviewing frameworks. The steady
strain estimations along the heap length are taken provided that heap move conveyance
not entirely set in stone. Instruments that can be introduced for such estimations are the
telltales (strain poles) and electric strain measures.
A few plans are feasible for directing pullout tests (Hirany and Kulhawy,
1988). Notwithstanding, two plans are more normal than others. In the main arrangement as
shown in Figure 2(a), a water powered jack is situated between a shaft and a response outline
that is moored to the heap by a pressure association (or longitudinal steel rebars). The
response supports can be response heaps or cribbing set at each side of the test heap.
An elective plan is displayed in Figure 2(b) and is different in that the heap is
applied by two pressure driven jacks following up on top of the response upholds. In this arrangement, the
load on the test heap is taken as two times the jacking load. The instruments and estimations
for the pullout tests are like those for pressure load tests.
TESTING METHODOLOGY
Subtleties of various testing methodology can be tracked down in numerous distributions (for example ASTM Dl
143-81, Fuller and Hoy, 1970, Crowther, 1988, Joshi and Sharma, 1987, Hirany and
Kulhawy, 1988). All techniques refered to in the writing are either pressure controlled or straincontrolled.
Controlled-Stress Techniques
Varieties of the controlled-stress techniques are depicted underneath.
Slow Kept up with Burden Test (SML)
In this technique, the heap is stacked in equivalent additions of 25% of the plan load up to
two times the plan load. Every augmentation is kept up with until a settlement of 0.01 in/hr is
reached. The most extreme burden is then held ordinarily for 24 hours and afterward eliminated in
comparable decrements. This sort of test is the ASTM standard method and the most
normal test, particularly in enormous tasks. A normal test endures between 1.5 to 3 days.
Speedy Kept up with Burden Test (QML)
In this technique, 15% of the plan load is added at an at once for 5 minutes. The
most extreme burden is equivalent to multiple times the plan load. At the point when the all out load is reached,
dumping is then finished with four equivalent decrements permitting 5 minutes between every two
decrements. Ordinary season of a heap test can be between 3 to 5 hours.
This strategy enjoys the benefit of being quick however it can't be utilized where the heap is
introduced in layers with critical drag properties since burden might be shed from the
sides to the base without changes in the applied burden (O'Neill and Hawkins, 1982).
Gradual Harmony Test (IE)
This test is a change of the SML test and takes something like 33% of the SML test
length. Albeit the test is quicker, the IE test was accounted for to give comparable
relationships to the SML test (Fellenius, 1975). The IE test is led by applying
augmentations of 15% to 25% of the plan load and keeping up with that heap for around 10
minutes. The heap then, at that point, is permitted to drop (with the expansion in settlement) until it
becomes steady. As of now, harmony between the heap and dislodging is
reached and the following augmentation is applied.
Consistent Time Span Test (CTI)
Stacking utilizing this technique is equivalent to that for the SML methodology. Notwithstanding, each
load is kept up with for precisely 60 minutes. This strategy has a common term of about
10 hours.
Cyclic Test (CYC)
The cyclic test is directed by a progression of stacking and dumping to the most extreme test
load. The pace of stacking can be like that of the SML or CTI systems. This test
can be utilized where there is a need to decide the heap at which creep removals
surpass specific cutoff points. This system is tedious and isn't regularly utilized for
routine burden testing.
Controlled-Strain Strategies
The controlled-strain strategies are partitioned into two classifications:
Consistent Rate Infiltration Test (CRP)
In this test, the heap is made to enter the dirt at a pre-decided consistent rate, while
the heap applied is estimated constantly. Normal rates are 0.03 in/min for firm
soils and 0.06 in/min for granular soils. The test can be acted in under 60 minutes,
however, it requires extraordinary gear and prepared work force.
Consistent Settlement Augmentation Test (CSI)
In this methodology, the heap not entirely set in stone from the heap important to deliver
uniform augmentations of settlement of the heap head. Average settlements are of the
size of 1% of the heap width. The heap addition is shifted to keep up with
the settlement size.
Despite the fact that the sluggish kept up with load test is viewed as the standard method, other
strategies for testing, for example, the QML and CRP have been progressively utilized where
permitted in the nearby construction standards and by and large yield reliable outcomes with the
standard SML test strategy. These other testing methods are suggested as sufficient
testing methods by Fuller and Hoy, 1970 and Reese and O'Neill, 1988.
REFERENCES
American Society for Testing and Materials (1987) “Standard Method for Testing Piles Under Static Axial Compressive Load (Dl 143),” Annual Book of Standards, Vol. 4.08, ASTM, Philadelphia, pp. 237-252.
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