Unformatted text preview: Bp
*Method of load test on soils ( second revision ). 10 IS : 2950 (Part I) - 1981
where Bf, Bp represent sizes of foundation and plate and Ep is the
modulus determined by the plate load test.
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 Es.
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 Es.
A-2.2.2 The value of Es may be determined from the following
Es = 2 Ckd
Ckd = cone resistance in kgf/cm2.
A-3. LABORATORY DETERMINATION OF Es
A-3.1 The value of Es shall be determined by conducting triaxial test in
the laboratory [ see IS : 2720 (Part XI)-1971† and IS : 2720 (Part XII)1981‡ ] 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 Es 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 ( first
†Methods 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 pressure.
‡Methods 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 IS : 2950 (Part I) - 1981 APPENDIX B
[ Clause 3.1 (f) ]
DETERMINATION OF MODULUS OF SUBGRADE REACTION
B-1.1 The modulus of subgrade reaction ( k ) as applicable to the case
of load through a plate of size 30 × 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
cases where the depth of the soil affected by the width of the footing
may be considered isotropic and the extrapolation of plate load test
results is valid.
TABLE 1 MODULUS OF SUBGRADE REACTION ( k ) FOR
COHESIONLESS SOILS *MODULUS OF SUBGRADE REACTION
( k ) IN kg/cm3 SOIL CHARACTERISTIC
Density Standard Penetration
Test Value ( N ) For Dry or Moist
State For Submerged
State (1) (2) (3) (4) Loose < 10 1.5 0.9 Medium 10 to 30 1.5 to 4.7 0.9 to 2.9 Dense 30 and Over 4.7 to 18.0 2.9 to 10.8 *The above values apply to a square plate 30 × 30 cm or beams 30 cm wide.
TABLE 2 MODULUS OF SUBGRADE REACTION ( k ) FOR
COHESIVE SOILS SOIL CHARACTERISTIC
Stiff Unconfined Compressive
Strength, kg/cm2 *MODULUS OF SUBGRADE
REACTION ( Ks ) IN kg/cm3 (2) (3) 1 to 2 2.7 Very stiff 2 to 4 2.7 to 5.4 Hard 4 and over 5.4 to 10.8 *The values apply to a square plate 30 × 30 cm. The above values are based on the
assumption that the average loading intensity does not exceed half the ultimate bearing
capacity. 12 IS : 2950 (Part I) - 19...
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This note was uploaded on 03/14/2014 for the course CE 684 taught by Professor Prof.deepankarchoudhury during the Spring '13 term at IIT Bombay.
- Spring '13