The modulus of elasticity is a function of composition of the soil, its void ratio, stress history and loading rate. In granular soils it is a function of the depth of the strata, while in cohesive soil it is markedly influenced by the moisture content. Due to its great sensitivity to sampling disturbance, accurate evaluation of the modulus in the laboratory is extremely difficult. For general cases, therefore, determination of the modulus may be based on field tests (see A-2). Where properly equipped laboratory and sampling facility is available, may be determined in the laboratory (see A-3).
A-2 Field Determination
A-2.1 The value of shall be determined from plate load test in accordance with good practice [6-2(12)].
A-2.1.2 Effect of Size
In granular soils the value of corresponding to the size of the raft shall be determined as follows:
A-3 Laboratory Determination of
A-3.1 The value of shall be determined by conducting triaxial test in the laboratory in accordance with accepted standard [6-2(34)] 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
PART 6 STRUCTURAL DESIGN — SECTION 2 SOILS AND FOUNDATIONS
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.