Geotechnical Engineering

DHARM

574 GEOTECHNICAL ENGINEERING

(iii) Treatment of the foundation soil...to encourage the occurrence of settlement even

before the construction of the structure, e.g., (a) Dewatering and drainage, (b) Sand

drains and (c) Preloading.

(iv) Provision of plinth beams and lintel beams at plinth level and lintel level in the case

of residential buildings to be founded on weak and compressible strata.

14.9 Plate Load Tests

Perhaps the most direct approach to obtain information on the bearing capacity and the settle-
ment characteristics at a site is to conduct a load test. As tests on prototype foundation are not
practicable in view of the large loading required, the time factor involved and the high cost of
a full-scale test, a short-term model loading test, called the ‘plate load test’ or ‘plate bearing
test’, is usually conducted. This is a semi-direct method since the differences in size between
the test and the structure are to be properly accounted for in arriving at meaningful interpre-
tation of the test results.

The test essentially consists in loading a rigid plate at the foundation level, increasing
the load in arbitrary increments, and determining the settlements corresponding to each load
after the settlement has nearly ceased each time a load increment is applied.

The nature of the load applied may be gravity loading or dead weights on an improvised
platform or reaction loading by using a hydraulic jack. The reaction of the jack load is taken by
a cross beam or a steel truss anchored suitably at both ends. The test set-up with a jack is
shown in Fig. 14.15.

Test plates are usually square or circular, the size ranging from 300 to 750 mm (side or
diameter); the minimum thickness recommended is 25 mm for providing sufficient rigidity. If
the loading set-up is a platform with dead weights, the kentledge may be in the form of sand
bage, scrap iron or ingots or any other convenient heavy material. Jack-loading is superior in
terms of accuracy and uniformity of loading. Settlement of the test plate is measured by means
of at least two or three dial gauges with a least count of 0.02 mm.

Channel

Tie rod Timber

support

Steel girders

Df

Hydraulic

jack

Extension

pipe

Dial gauge

Dp

bp

Section

Df

Angle iron

Anchors

I

Test pit