Deep Mixing Method of soil stabilization using cement as a hardening agent has been widely applied at actual construction sites in recent years. In this method, the effect of cement treatment is generally judged by the unconfined compression test.
This report gives a description of size effect as one of various factors that influence the unconfined compressive strength of cement treated soil. To investigate the size effect, unconfined compression tests were performed on the specimens of various volume with constant slenderness ratio (H/D=2.0) and those of various slenderness ratio with constant diameter (D=40mm).
The effect of tamping methods that influence the unconfined compressive strength was also examined.
As the result, it was found that the unconfined compressive strength, qu, decreased with increasing diameter of specimen under constant slenderness ratio. qu decreased little with increasing slenderness ratio, H/D. E50, the tangent modulus at stress level equal to one-half of qu increased from 200qu kgf/cm2 to 380qu kgf/cm2 for qu with increasing diameter. The unconfined compressive strength, qu2, obtained by tamping a rod bar decreased with decreasing strength, qu1, obtained by dropping on the concrete base. For qu1 less than 15kgf/cm2, qu2/qu1=(0.8∼1.0), and for qu1 greater than 15kgf/cm2, qu2/qu1=1.0 were found.