Abstract
Wadi Halfa Oolitic Ironstone Formation (WHOIF) covers large areas around Wadi Halfa border town in Northern Sudan. The detrital framework grains of sandstone of WHOIF are composed of sub-angular to sub-rounded quartz grains followed by feldspars, lithic fragments, micas and heavy minerals. The dominant cementing materials are iron oxides, carbonate cement, and some clay minerals. Twelve block samples were carefully selected and collected from six sites to represent different parts of vertical lithofacies sections of the studied formation. The petrographical characteristics of the specimens were first studied and the specimens were then subjected to laboratory tests to determine some of their basic physical and engineering properties. The physical tests constituted unit weight, specific gravity and water absorption. The measured engineering properties included uniaxial compressive strength (UCS) and ultra-sonic pulse velocity (UPV). The UCS and UPV were measured for specimens parallel and perpendicular to the bedding planes of the studied samples. The geotechnical study shows that the UCS values of WHOIF generally range from strong 83.7 MPa to very strong 153.7 MPa for perpendicular direction to bedding planes. Very good statistical correlation coefficient was developed between UCS and UPV. Good correlation was obtained between water absorption, porosity and UPV. These relations indicated that a decrease in void ratio and porosity resulted in an increase in UCS and UPV. An increase in water absorption of sandstone yielded a decrease in ultrasonic pulse velocity and uniaxial compressive strength. Key words: Wadi Halfa Oolitic ironstone formation, lithofacies, uniaxial compressive strength, ultrasonic pulse velocity.
Highlights
The term Nubian Sandstone Formation or Nubian Formation (NF) is applied in the Sudan to those bedded and usually flat-lying sandstones, conglomerates, grits, sandy mudstones and mudstones that rest unconformably on the Basement Complex (Vail, 1978)
The petrographic classification of sandstone samples of Wadi Halfa Oolitic Ironstone Formation according to mineral composition is as follows: quartz arenite 58.3%, sub lithic arenite 16.7% and subarkose 25%
The detrital framework grains of sandstone of Wadi Halfa Oolitic Ironstone Formation (WHOIF) representing an average of 68% of the rock volume and composed of sub angular to sub rounded quartz grains followed by feldspars, lithic fragments, micas and heavy minerals
Summary
The term Nubian Sandstone Formation or Nubian Formation (NF) is applied in the Sudan to those bedded and usually flat-lying sandstones, conglomerates, grits, sandy mudstones and mudstones that rest unconformably on the Basement Complex (Vail, 1978). The present study deals with the geotechnical properties of Wadi Halfa Oolitic Ironstone Formation and attempts to develop correlation equations between the measured geotechnical properties and some simple physical properties of these rocks. The geology of the region of Wadi Halfa is relatively simple It consists of the oldest basement complex rocks of Precambrian age overlain by the Nubian Sandstone Formations (Vail, 1978; Stern et al, 1994). The detrital framework grains of the sandstone of Wadi Halfa Oolitic Ironstone Formation are composed of monocrystalline, polycrystalline quartz grains followed by feldspars, lithic fragments, micas and heavy minerals. The physical property tests performed on the specimens constituted unit weight, specific gravity and water absorption. 12.2 γ, Unit weight; Gs, Specific gravity; W, Water content; e, Void ratio; n, Porosity; WA, Water absorption
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