عنوان مقاله [English]
ABSTRACTIn the past two decades the land subsidence and ground failures in Yazd province, especially in Yazd - Ardakan flat area caused many damages and failures in existing roads and structures. The visual appearance of failures are generally: large subsidence in road body in the form of wide and deep cracks, structural failures and cracks in walls and foundations, breakage in water and gas or oil pipe lines, over turning of electrical transmission towers, and appearance of deep cracks and holes in agriculture lands. This research was taken place in Yazd - Ardakan flat after few previous unsatisfactory investigations. In this research a deep borehole and four hand cut holes were drilled and visual investigations throughout the crack distribution indicated that the both external and internal phenomena caused ground failures.
External PhenomenonThe topography maps of Yazd - Ardakan flat area indicate that the ground surface slopes are too small. As the area is arid with fewer rainfalls, rivers and surface water ways can not be created by flow concentrations. In most seasons a few millimeters of rainfall will evaporate or penetrate in ground without surface flow creation. In some cases when a rapid and a dense fall occur, there are no considerable flow ways for extra surface water. Therefore water will rise up in existence of low level grounds, creating natural pools, which their water will find holes to penetrate in ground as concentrated non-controlled flows. Investigations in ground of Yazd - Ardakan flat shows that there are old root holes in many cases which facilitate the concentration flows to underground portions. These flows erode soil and create holes with larger diameters. Due to these erosions, first radial cracks are generated around these holes, and then by extra erosions, circumferential cracks are added perpendicular to radial cracks.
Based on laboratory tests, the ground soil is generally silty soil (0 to 95 percent silt). The silt particles are cemented by clay and salt. The water penetration test at site, showed that the soil permeability is too large compared to laboratory test results. The collapsibility tests in laboratory showed that the soil is collapsible in many cases. Dispersivity tests showed that the soluble salts in particle mid connections can be easily solved and it is enough to collapse soil. Based on the research results, some prevention and treatment methods are proposed. These methods may be described as; constructing artificial water ways, filling the cracks by soil cement mix and finally constructing the low dikes.By determining the failures mechanism, the repair and destruction prevention methods in roads, buildings and installations are proposed in this paper.