A Proposal of a Model for the Generation of Weathered Residual Soils

A new fragmentation model, called the GRS (the generation model of weathered residual soils) model, was proposed in this study, This model could identify the formation of a residual soil. This model is based on the phenomena that as the soil was weathered more highly, soil particles were smaller and pores were more expanded simultaneously. The possibility of fragmentation, $P_F,$ which was based on the fractal theory, was introduced in this model. There were some fundamental notions in the GRS model that soil particles were generated as the rock is fragmented, and the fragmentation of the rock was performed step by step. The $P_F,$ of the rock was not constant at each fragmentation steps. As a result of application on the GRS model, there were more residue where $P_{Fi}s$ were small at any particle size. There was a S-shape of PSD curve at the concave shape of $P_{Fi},$ and the PSD curve goes to a gaped graded curve at the convex shape of $P_{Fi}.$ The shape of PSD curve was concave in the case of small $P_{Fi}s.$ The value of $P_{Fi}$ increased with the coefficient of uniformity $(C_u)$ and the fragmentation fractal dimension $(D_r),$ but had no relation with the coefficient of gradation $(C_C)$.

풍화잔류토의 생성모델의 제안

본 연구에서는 풍화잔류토의 생성을 특성화시키는 새로운 분열모델을 제안하였으며, GRS모델이라고 명명하였다. GRS 모델은 풍화가 많이 진행될수록 흙 입자의 크기가 작아지고 흙 속의 간극이 많아진다는 사실에 착안하였으며, 프랙탈 이론으로부터 도출된 $P_F$(분열가능성)로써 풍화잔류토의 생성과정을 표현할 수 있다. 암석이 분열됨으로써 흙 입자들이 생성되며 암석의 분열은 단계별로 진행되지만 각 단계별 분열가능성은 일정하지 않다는 것이 GRS모델의 기본개념이다. GRS모델의 적용성을 검증한 결과, 입자들의 잔류량이 많은 입경에서 $P_{Fi}$(분열단계별 분열가능성)가 작게 산출되었고, 입도분포가 양호할수록 크게 산출되었다. 일반적인 흙에서 나타나는 S자형상의 입도분포곡선은 $P_{Fi}$가 높은 오목형상에서 나타났으며, $P_{Fi}$의 변화형상이 볼록하면서 높은 값을 가질경우에는 빈입도의 입도분포특성을 나타내었다. 전반적으로 $P_{Fi}$가 작은 경우에는 $P_{Fi}$의 변화형상에 관계없이 큰 입자의 잔류량이 많은 오목한 형상의 입도분포곡선을 나타내었다. $P_{Fi}$의 평균값은 균등계수$(C_u)$와 분열프랙탈차원$(D_r)$에 비례하여 증가하였으나, 곡률계수$(C_C)$와는 무관하였다.