Near to Sarikei Semangoi Mountain, the underlying bedrock is predominantly Shale bedrock. When excavating the hill to build road, studies have to be made on the Shale weathering charateristics and bedding patterns, as Shale rock is known to disintegrate easily upon exposing to weather or water instrusion.
This slope shows how the neatly cut Shale slope will become after 15 years of service. The surface is now littered with broken Shale fragments and debris. It seems to be bulking at the mid-slope too. The slope is quite gentle, probably about 1:2, gentler if including the intermediate bench. The height is about 10m. If you use slope stability analysis, the strength is only about 50N/sq.mm. During investigation, the strength can reach more than 200N/sq.mm.
Slope analysis requires a lot forward looking and judgement, rock and soil will deteriorate with time. Ground water level changes with seasons and time too. What will be the likely strength after 50 years of exposure to weather and rainfall? What is the dipping direction and angle of the Shale bedrock? What is the thickness of the bedding laminations? These are the factors need to be considered.
This Shale Rock is much better than the Shale rock near Roban (20km away) which has been posted earlier, as they have thicker laminations compared to the Roban Shale.
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