Ryota HIRAKAWA

Effects of Cementation and Small Cyclic Shear History on Mechanical Properties of Sand

Hirofumi TOYOTA

It has been widely known that liquefaction resistance is increased by stress history and cementation, which is considered as an important factor causing aging of sand. Therefore, attempts, in which cyclic shear history is applied to the specimen and small amount of cement is added to the specimen, have been carried out to reproduce the aging effects. Results obtained from triaxial tests using long-term consolidated specimens have indicated that the number of cycle to liquefaction was increased in Toyoura sand specimen consolidated longer than 14 days. However, shear wave velocity Vs hardly changed through the consolidation time.
This study mainly focused in cementation and cyclic shear history effects. Shear strength, liquefaction, wave propagation and small deformation properties were examined using the specimens reproducing aging effect to compare the difference of mechanical properties between long-term consolidated specimens and other specimens reproducing aging effects.
Firstly, the liquefaction resistance was confirmed by the cyclic undrained triaxial tests (liquefaction tests). Then, drained triaxial tests under constant p�f condition, bender element (BE) tests and local small strain (LSS) tests were conducted to investigate the influence of aging on mechanical properties of sand.

From those experiments, following conclusions are obtained:
1. The influence of cementation on mechanical properties of sand;
a. Liquefaction resistance was increased from cement content of 0.5%.
b. In shear strength, cohesion increased from cement content of greater than 0.1%. However, internal friction angle hardly changed.
c. From BE and LSS tests, initial shear modulus was increased from cement content of 0.3%.

Those results indicate that soil particle structures are obviously stabilized due to cement adding of greater than 0.5%. Therefore, liquefaction resistance is also increased.

2. The influence of cyclic shear history on mechanical properties of sand;
a. Liquefaction resistance was increased when cyclic shear history of greater than 0.01% axial strain was applied to the specimen
b. In shear strength, cohesion and internal friction angle hardly changed.
c. From BE tests, initial shear modulus was increased when cyclic shear history of greater than 0.005% was applied to the specimen.
d. From LSS tests, expansion of elastic region was observed when cyclic shear history of greater than 0.005% was applied to the specimen.

Those results indicate that when cyclic shear history of greater than 0.05% axial strain, which is greater than original elastic region, is applied to the specimen, its liquefaction resistance is increased because of expansion of elastic region.