An Experimental Study on the M_R Characteristics of Subbase Materials

보조기층재료의 MR 특성에 관한 실험적 연구

The resilient behavior of subbase materials, locally used in Korea. were evaluated in this study by performing laboratory MR tests. The variations of the MR value according to LVDT's location in experiments and moisture conditions, respectively, were evaluated. And, in order to determine the relevant MR characteristics of the prototype materials, laboratory model tests containing smaller particles than those of the prototype were conducted. Based on above results, the relationship of the MR and the bulk stress (${\theta}$) was suggested. The case using internal LVDT. gave much larger $M_R$ value than that using external LVDT, since the external LVDT somewhat overestimates the resilient strain. The measured $M_R$ in damp conditions ($S_r$=40%) was larger than that in wet conditions ($S_r$=70%) by about 10%. The relationship between the $M_R$ and the void ratio was linear according to particle size effect. The relationship of the $M_R$ and the bulk stress (${\theta}$) on subbase materials in damp conditions to be used in Korea could be recommended as $M_R=3960{\cdot}{\theta}^{0.60}$ psi.

본 연구에서는 국내에서 사용되고 있는 보조기층재료에 대해 변형측정정치의 위치 및 포화도에 따른 $M_R$값의 변화양상을 파악하고, 시료내의 입자크기(particle size)에 따른 치수효과(size effect)를 파악하여 적절한 $M_R$ 관계식을 제시하였다. 외부변형측정장치를 사용한 경우의 $M_R$값은 회복변형율을 과대평가 하기 때문에 내부변형측정장치를 사용한 경우보다 작았고, 포화도에 따른 $M_R$값은 wet 상태($S_r$=70%)가 damp 상태 ($S_r$=40%)보다 10% 정도 작게 나타났으며 시편을 구성하는 입자의 치수효과는 과대 입자(oversize particle)를 제거함에 따른 간극비의 변화와 직접적인 관계가 있음을 알 수 있었다. 이와같은 결과를 종합하여 보조기층의 $M_R$ 관계식은 damp 상태의 포화도에서, $M_R=3960{\cdot}{\theta}^{0.60}$ psi.로 제안할 수 있다.