The high percentage of fine-grained sediments (clay and silt) in aggregatesispotentiallydetrimentalto strengthand durabilityof concrete
because they can weaken the bond between the cement paste and the
aggregate particles (Fookes, 1980; Smith and Collis, 2001). Although it
is often assumed that the old fan surfaces have higher percent of finegrained sediments (clay and silt) because they have been subjected to
weathering for longer periods and that the young fan surfaces have
lower percent of silt and clay due to the short term exposure to
weathering, it is not the case in three studied fans. As Table 2 shows,
there is not a meaningful trend in sediment size from old to young
fans or vice versa. In this regard, it should be pointed out that alluvial
fan sediments contain rapid vertical and lateral variations in grain size
(Nilsen, 1982). It has long been recognized that flow diversion and
channel avulsion are frequent processes over the surface of fans