The issues of boulder in tropically weathered granitic rock masses have
roused a lot of problems and risks to the work performances and design quality in
civil engineering. Although the presence of in situ boulder could be predicted
through several methods and classified in several weathering classification schemes,
the behaviour of tropically weathered in situ boulder is not well understood. The aim
of this study is to establish physical classification and engineering characteristics of
granite boulders and to catalogue the boulders in tropical weathering profile. A total
of 46 panels of granitic profile consist of 88 in situ boulders from five quarry sites
located in Johor, Malaysia were investigated involving several field and laboratory
test programs. The field test programs conducted include geological field mapping,
discontinuity survey and classification of physical characteristics of boulder as well
as its surrounding material in various weathering zones. The physical characteristics
examined include occurrence of boulders in moderately to completely weathered
zone, shape, size and rindlets characteristics from respective weathering zone. The
laboratory test programs involve determination of physico-mechanical properties and
mineralogical analysis. The field study revealed five dominant weathering profiles
with different significant types of weathering zone and occurrence of in situ boulder.
This finding indicated that in situ boulder is the main character in the formation of
heterogeneous zone in weathering profile especially in the moderately weathered
(Zone 3), highly weathered (Zone 4) and completely weathered zone (Zone 5). The
angularity, size and rindlets characteristics of the boulder from moderately to
completely weathering zones significantly differ from each other. Due to these
significant differences, the in situ boulders formed in completely, highly and
moderately weathered zones are classified into three major types, namely Type A,
Type B and Type C, respectively. Boulder Type A is surrounded by double rindlets
zones which classified as inner and outer rindlets, while boulder Type B possess
single rindlets zone which is classified as inner rindlets. On the other hand, boulder
Type C has no rindlets and it is surrounded by joints and fractures. The differences in
physical characteristics of boulders Type A, B and C could be used to predict their
existence in different weathering zones. The result obtained from the laboratory
study revealed the physico-mechanical properties which include dry density,
porosity, durability, strength and permeability of rindlets and saprolites found in
completely weathered zone showed significant variance compared to highly and
moderately weathered zone. In conclusion, the in situ boulders formed in moderately
to completely weathered zones possessed significant variance of physical and
mechanical characteristics which can be used as an indicator in weathering
classification and engineering design purposes
