Engineering Geological Map of Al Madinah al Munawwarah City, Kingdom of Saudi Arabia

SGS-TR-2012-4 Marwan Saikhan, Gabel Barakati, Abdulkhaleg Doban, Waleed Aklouk, Waleed Kadi, Mohammed Theeban, Ibrahem Al Harthi, Khalid Al Wagdani, Marwan Bokhary, Mohammed Al Hussain, and Abdullah Sabtan
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ABSTRACT


It is needless to stress the importance of Al Madinah al Munawwarah to the Muslim world as it is the second holiest place in Islam and has received great attention from the Muslim leaders throughout history.  As a consequence of the rapid expansion of the city since the mid-1980’s, a number of geotechnical problems have emerged such as previously not-evident building stresses on the soil and significant modification of the hydrologic regime, especially in the central area. In response to the need for a thorough effort to anticipate soil and rock behavior and to recommend proper foundation and/or soil improvement, this study aims to draw for Madinah an engineering geological map, an essential part of city planning. Several field inspections, complete in-situ testing, and surface soil sampling were carried out.  The engineering properties were used to characterize the soils and classify rocks in order to arrive at a zonation based on the system set by the American Association for Engineering Geologists (AAEG). A surface engineering geologic map was prepared at a scale of 1:50,000 and that can be used for many purposes. The recent surface modifications in the soil type due to recent construction and the new boundary between the various geological units were also recognized. The map also contains valuable information that were obtained from extensive soil bore holes and used to construct a database.  On a low, relatively flat ground, the Al Madinah area is underlain by igneous rocks in the north and west, and basaltic flows in the south and east. The surrounding topography controls the intensity and direction of the floods. The soil is related to the rock type, mode of weathering, and the nature of flooding. The main soil type in the upper two meters is silty sand (SM), but variations such as poorly graded sand (SP), and gravel of different types (GW and GM) were also observed in limited scattered lenses. Similar soil distributions at greater depths were also found from the compiled information from previous investigations. A block diagram was constructed to recognize the types and thicknesses of soil laterally and vertically to a depth of about 20 meters.  Geohazards in the area pose significant challenges for the planners and designers. The finer materials (silt and clay) may create foundation problems especially if the clay is expansive. The flood potential, although reduced by the construction of dams, may have some local effects due to the topographic modifications. The hydrological system has changed significantly in the central area, and as a temporary solution, the excess water is pumped from shallow ground depths. Volcanic hazard is a major issue since Al Madinah is at the edge of one of the largest and most active basaltic plateaus.

Al Saikhan, M.M., Al Barakaty, G.Z., Doban, A.S., Al Aklouk, W.A., Gadi, W.K., Al Theeban, M.S., Al Harthi, I.M., Al Wagdani, K.S., Bokhary, M.Y., Alhussain, M.A., and Sabtan, A.A., 2014, Engineering geological map of Al Madinah Al Munawwarah City, Kingdom of Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2012-4, 29 p., 14 figs., 12 tables, 2 apps., 2 pls.