| Abstract | The rocks between km. 18+000 and 20+200 along the Tak-Mae Sod Highway, Northern Thailand consist of a northwest trending eastward dipping intercalated sequence of biotite microcline gneiss, calc-silicate gneiss, quartz schists and cataclastic granite gneiss. The planar structures include bedding,
schistosity and gneissic layering. Two sets of north-east and north-south trending joints pervade these rocks. Superimposed upon these structures are series of north-south trending high angle normal and reverse faults and the imbricate structures striking parallel to the gneissic layering. The imbricate structures
thrusted the biotite microcline gneiss southwesterly upon each other and up on top of the younger limestone and quartzite. Highway slopes were cut into these rocks and subsequent landslides occurred. Five types of landslides namely rockslides, rockfalls, slumps, earth flows
and debris flows were described. The engineering properties of the major rock types including water absorption, bulk weight, unconfined compressive strength, modulus ratio, cohesion, tangent and secant modulus at 50% ultimate strength, Poisson's ratio, maximum and residual shear strength across the planes of
weakness, internal friction angle were determined together with the field investigations of the orientation and distribution of planes of weakness and
joints, fracture frequencies and rock quality designations. The graphical analyses of slope stability were attempted in the light of these data. It was found that in most places the slopes had adjusted themselves through slope failures to such a degree that most of them are now stable. There are still,
however, three cut slopes where rockslides and rockfalls can occur. The improvements on these slopes can be easily performed by adjusting the slope
angle and/or alignment and clear up the overhanging potential slide block. |