Engineering Properties of Volcanic Tuff from the Western Part of Yemen

This paper deals with a study of the physical and mechanical characteristics of volcanic tuff and ignimbrite from six quarries located at different areas in the western part of Yemen (Manakha, Jahran, Bakhran, Dar Al-Hanash, Abaser and Soraifa). In the region, volcanic tuffs and ignimbrite are locally known by their location names and have been used as solid masonry and cladding stones. All the investigated pyroclastic rocks belong to the Tertiary volcanic. The standard physical and mechanical tests (void ratio, porosity, density, specific gravity, water absorption, uniaxial compressive strength and tensile strength) were carried out on the tuff and ignimbrite samples collected from different parts of the region. Laboratory tests revealed that the void ratio average values range between 0.12 and 0.37, the porosity ranges between 10.57 and 27.12%, the dry density ranges between 1.66 and 2.25 gm/cm3, specific gravity ranges from 1.45 to 1.94, and water absorption ranges from 4.69 to 16.39%. The measured uniaxial compressive strength values range from 24 to 68 MPa, and the tensile strength values range between 4 and 10 MPa. These tuffs and ignimbrites generally are light green, gray, beige, or yellowish in color. With these colors they are favoured for building, coating and decorative stone. This paper concludes that the studied stones have acceptable to good properties as dimension stone. Jahrani and Manakhi tuffs are the best quality, whereas Hanashi ignimbrite is of poorer quality

Slope Stability Assessment and Landslide Susceptibility Map Production of Wadi Dhahr Area, Northwest of Sana’a, Yemen

A slope stability assessment of Wadi Dhahr area, located northwest of Sana’a the capital of Yemen, was carried out in this study. The study area consists of sandstone and volcanic rocks that are deformed by number of faults, joints and basaltic dykes. All the important factors affecting slope stability in the area such as slope angle, slope height, discontinuities measurements, weathering, vegetation cover, rainfall and previous landslides were evaluated. The study was conducted based on the integration of field investigation and satellite image processing. A landslide susceptibility map was produced with the Landslide Possibility Index (LP1) System, and the correlation values were computed between the factors measured and Landslide Possibility Index values. The fractures counted by satellite image were categorised according to their length and zones based on their concentrations. It was found that plain sliding and rockfall are the main modes of failure in the area, while rolling and toppling are rare. Some remedial measures are proposed to protect the slopes where it is needed,  such as the removal of rock overhangs, unstable blocks and trees, and by supporting the toe of slopes and overhanging parts by retaining walls and erecting well sealed drainage conduits. The results will assist in slope management and land use planning in the area