Abstract
Haibat Sultan Mountain is a long range with elevation of about 860 m (a.s.l.); the PilaSpi Formation forms its carapace in Koya vicinity, with relief difference of about 300 m from Koisanjaq plain. The PilaSpi Formation consists of well thickly to massively bedded dolostone and dolomitic limestone with thickness of about 120 m in Koya vicinity. The main trend is NW - SE being a limb of Bustana anticline representing part of the southwestern limb, with dip amount that ranges from (15 - 30). On 11th of November 2015 a landslide had occurred after a heavy rainfall along Koya - Dukan main road. The type of the slide was plane sliding due to daylight slope, which was formed after the road cut. The length of the slide area: along the road is 90 m with height of 40 m forming almost a parallelogram shape; the thickness of the slid beds is about 2.5 m. The estimated volume of the slid mass is 9000 m3. The main cause of the landslide is the presence of daylight slope, high slope angle; more than the dip angle, presence of old crack surfaces which are filled by reddish brown clayey residual soil. After the he heavy rain fall, which lasted for 20 hours, the infiltrated rain water in the bedding planes in the well bedded, cracked, and jointed beds has increased the pore pressure and decreased the internal friction angle; therefore, the sliding has occurred. The root of the slid mass is below the base of the paved road; therefore, that part which is above the paved road has slid. The remaining part is highly cracked and partly accumulated in the base of the slid mass. Fortunately, the height of the slid mass is only 40 m and the relief difference between the crown area and the toe area is about 50 m; otherwise the slid mass would be larger than the present slid mass. From the field inspection, it is very clear that the involved area is very unstable and in critical equilibrium. The presence of daylight bedding above the crown area, clayey soil in the fractures and open joints and steep slope all are very favorable conditions for triggering the unstable slope, consequently developing of another landslide with larger mass.
Highlights
On the 11th of November 2015, a landslide had occurred after a heavy rainfall along Koya - Dukan main road, north Iraq, Kurdistan Region, and it will be called Koya Landslide in the current study
The main road was blocked by the slid mass for overnight
To recommend relevant preventative actions that should be considered in order not to trigger the involved area, this is in very critical equilibrium states
Summary
On the 11th of November 2015, a landslide had occurred after a heavy rainfall along Koya - Dukan main road, north Iraq, Kurdistan Region, and it will be called Koya Landslide in the current study. The main road was blocked by the slid mass for overnight. The studied area is located northeast of Koisanjaq town, along the main road between Koisanjaq town and Sulaimaniyah city via Dukan town (Figure 1). It is a mountainous area, located along the southwestern flank of Haibat Sultan Mountain with elevation of about 860 m with relief difference with the center of Koisanjaq town of about 300 m. The main aim of this study is to record the landslide event and describe the details of the slid mass and other parts of the landslide with investigating and discussing the reasons of the sliding. To recommend relevant preventative actions that should be considered in order not to trigger the involved area, this is in very critical equilibrium states
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