Strain Range within Linear Elastic Behaviour in Sandy Soils with Inherent Anisotropy

Hirofumi TOYOTA

Recently, the necessity of accurate ground analysis such as seismic response and vibration analysis is becoming higher with the increase of important constructions containing neighboring construction problems. In these analysis, the measurement methods have not been standardized, although various deformation coefficents in the small strain region is needed. In previous studies, inhernt anisotropy was examined using the bender element test (BE test) and the local small strain test (LSS test). The results demonstrated that even Toyoura sand, in which flattness of particles is small, exhibited inhernt anisotropy. In addition, the drainage strength qmax and the angle of sedimentation plane have inverse relation, that is, the qmax decreases when the increases. Although the cyclic loading test was conducted because LSS test the data were scattered in small strain region, stable results couldnt be obtained.
In this study, the main objective is to clarify a strain range exhibiting the linear elastic behaviour in sandy soils with inherent anisotropy by improving the equipments and testing methods.
To increase the accuracy of measurement in small strain region, the base pedestal was tightly fasten on the triaxial plate and the diameter of specimen was slightly reduced. As a result, the scatter of data in small strain region was eliminated from the setting of the base pedestal. The specimen can be easily placed on the base pedestal from specimens diameter change. Thus the accuracy of measurement in small strain region has been improved.
To examine effect of inherent anisotropy, Toyoura sand was used and, the angle of sedimentation plane was set to 0롤22.5롤45롤67.5롤90. After preparing specimens, BE test and LSS test were conducted at effective stress of 150 kPa under drained condition.
The results obtained from the study are summarized as follows:
(1) The initial elastic shear modulus G0 has tendency to increase with the increase of angle of sedimentation plane . This tendency was confirmed by both BE test and LSS test.
(2) The strain range exhibiting linear elastic behaviour obtained from LSS test shows the tendency to decrease with the increase of angle of sedimentation plane .
As described above, even in small flattness of particles like Toyoura sand, the inherent anisotropy was appeared in its mechanical properties. Moreover, the new finding, where the strain range exhibiting linear elastic behavior may be changed by the effect of inherent anisotropy even in the same sand, was obtained.

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