Unformatted text preview: ntensity of contact pressure,
least lateral dimension of test plate,
P== Poisson’s ratio,
I, = Influence factor, and
= 0.82 for a square plate.
S= A-2,1.1 The average value of E, shall be based on a number of plate
load tests carried out over the area, the number and location of the tests,
depending upon the extent and importance of the structure. A-2.1.2 Eflect of Size - In granular soils, the value of Es corresponding
to the size of the raft shall be determined as follows: *Method of load test on soils ( second revision ). 10 B - IS : 2950 ( Part I) - 1981
where Bj,BP represent sizes of foundation
modulus determined by the plate load test. and plate and E, is the A-2.2 For stratified deposits or deposits with lenses of different materials,
results of plate load test will be unreliable and static cone penetration tests
may be carried out to determine I&.
A-2.2.1 Static cone penetration tests shall be carried out in accordance
with IS :4968(Part III )-1976”. Several tests shall be carried out at regular
depth intervals up to a depth equal to the width of the raft and the results
plotted to obtain an average value of E,.
A-2.2.2 The value of Es may be determined
ship: from the following relation- E, = 2 Cra
Cud = cone resistance in kgf/cm2.
A-3. LABORATORY DETERMINATION OF Es A-3.1 The value of Esshall be determined by conducting triaxial test in the
laboratory [ see IS : 2720 ( Part XI )-19717 and IS : 2720 ( Part XII )-1981x ]
on samples collected with least disturbances.
A-3.2 In the first phase of the triaxial test, the specimen shall be allowed to
consolidate fully under an all-round confining pressure equal to the vertical
effective overburden stress for the specimen in the field. In the second
phase, after equilibrium has been reached, further drainage shall be prevented and the deviator stress shall be increased from zero value to the magnitude
estimated for the field loading condition. The deviator stress shall then be
reduced to zero and the cycle of loading shall be repeated.
A-3.3 The value of & shall be taken as the tangent modulus at the stress
level equal to one-half the maximum deviator stress applied during the
second cycle of loading. *Method for subsurface sounding for soils : Part III Static cone penetration test
(firsi revision ).
tMethods of test for soils : Part XI Determination of shear strength parameters of a
specimen tested in unconsolidated undrained triaxial compression without the measurement of pore water pressme.
2Methods of test for soils : Part XII Determination of shear strength parameters .of
soils from consolidated undrained triaxial compression test with measurement of pore
water pressure (first revision ).
11 -- _.._i._ - lfb” IS : 2950 ( Part I ) - 1981 APPEND1 XB [Clause 3.1(f)]
DETERMINATION OF MODULUS OF SUBGRADE REACTION B-l. GENERAL
B-l.1 The modulus of subgrade reaction ( k ) as applicable to the case of
load through a plate of size 30 Y 30 cm or beams 30 cm wide on the soil is
given in Table 1 for cohesionless soils and in Table 2 for cohesive soils.
Unless more specific determination of k is done ( see B-2 and B-3 ), these
values may be used for design of raft foundation in c...
View Full Document
- Spring '13
- Geotechnical Engineering, New Delhi, Raft, Contact pressure