Unless more specific determination of k is done see b

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Unformatted text preview: ases 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 SUBCRADE REACTION ( k ) FOR COHRSIONL.ESS SOILS *MODULUS SOIL CHARACTERISTIC c_--_--_------_~ Relative Density Standard Penetration Test Value ( N) (1) r--------For Dgap, *-_--_-_ For $ttzerged (4) 1.5 1.5 to 4’7 4.7 to 18.0 < 10 10 to 30 30 and Over Dense Moist (3) (2) Loose Medium OF SULIGRADE REACTION ( k ) IN kg/cm3 0.9 0.9 to 29 29 to lo.8 *The above values apply to a square plate 30 x 30 cm or beams 30 cm wide. TABLE 2 MODULUS OF SUBCRADE REACTION ( k ) FOR COHESIVE SOILS SOIL CHARACTERISTIC #--_---,--Consistency (1) -----7 Unconfined Compressive Strength, kg/cm* (2) *MODULUS OF SU~GRADB RENTION ( k,) IN kg/cm” Stifi 1 to 2 Very stiff 2 to 4 Hard 4 and over *The values apply to a square plate 30 x 30 cm. The above values assumption that the average loading intensity does not exceed half the capacity. 12 (3) 2.7 2-7 to 5.4 5.4 to 108 are based on the ultimate bearing IS:2950( PartI)- B-2. FIELD DETERMINATION B-2.1 In cases where the depth of the soil affected by the width of the footing may be considered as isotropic, the’value of k may be determined in accordance with IS : 9214-1979*. The test shall be carried out with a plate of size not less than 30 cm. B-2.2 The average value of k shall be based on a number of plate load tests carried out over the area, the number and location of the tests depending upon the extent and importance of the structure. B-3. LABORATORY DETERMINATION B-3.1 For stratified deposits or deposits with lenses of different materials, evaluation of k from plate load test will be unrealistic and its determination shall be based on laboratory tests [ see IS : 2720 ( Part XI )-1971t and IS : 2720 ( Part Xl1 )-1981$]. B-3.2 In carrying out the test, the continuing cell pressure may be so selected as to be representative of the depth of average stress influence zone (about 0.5 B to B ). B-3.3 The value of k shall be determined from the following relationship: k = 0-65 I2 . -1 .+ -cc B where E, = Modulus of elasticity of soil ( see Appendix A ), fi= Young’s modulus of foundatipn material, p = Poisson’s ratio of soil ( see Appendix A ), and I = Moment of inertia of structure foundation. if determined or of the B-3.4 Im the absence of laboratory test data, appropriate values of E, and p may be determined in accordance with Appendix A and used in B-3.2 for evaluation of k. *Method of determination of subgrade reaction ( k value ) of soils in the field. tMethods of test for soils : Part XI Determination of shear strength parameters of specimen tested in unconsolidated undrained triaxial compression without the measurement of pore water pressure. tMethods of test for soils : Part XII Determinatio’n of shear strength parameters of soil from consolidated undrained triaxial cdrnpression test with measurement of pore water pressure (first revision ). 13 . IS:29SO(PartI)-1981 B-4. CALCULATIONS B-4.1 When the structure is rigid ( see Appendix C ), the average moduhrs of subgrade reaction may also be det...
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