Landsliding Associated With the Urban Development in the Muscat Area, Sultanate of Oman.

Sultanate of Oman is located on the southeastern edge of the Arabian Gulf area with Muscat being its capital city. Progressive urban development in the capital area has been made on the expense of rocks that are constantly being excavated and cut at steep slopes without paying much attention to their geological properties. A number of slope failures caused by the over-steepening and toe removal have recently been noticed. A quantitative assessment of the slope stability problems has been addressed in this study. The methodology adopted is based on the geological and geotechnical data that were acquired over a period of two years. The trend and the extension in the urban development were obtained by comparing aerial photographs at 1:20,000 scale and SPOT images at 1:25,000 scale. Based on these data sets, detailed geological maps were prepared for the critical zones located in the study area. The engineering design parameters were calculated by sampling the variable rock units. A vigorous geotechnical testing was done to obtain the design properties for shear strength parameters. The results of this study indicate that moderately weathered, rippable metamorphosed units of schistose rocks represent the most hazardous zones. The presence of weak rocks such as claystone, mudstone, shale and siltstone poses slope stability problems because of their low cohesion and the development of tension cracks at the crest of the slopes. The crystalline rocks such as ophiolite, however, are stable in general but may become hazardous in the presence of fractures which daylight the slope faces at number of places along the coastal areas. Plane type failures involving single discontinuity planes are less common. A combination of two or more discontinuities resulting in the wedge type failures are quite common and may aggravate the instability problems in the presence of talc filled fractures. This fact was further confirmed by the stereonet analyses and the joint shear strength data.