نویسندگان
1 استادیار گروه جغرافیا، دانشگاه تربیت معلّم سبزوار
2 کارشناس ارشد ژئومورفولوژی، دانشگاه تربیت معلّم سبزوار
3 کارشناس ارشد زمینشناسی مهندسی، دانشگاه تربیت مدرّس
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Introduction
Geomorphological Landforms and processes are of the most significant parameters that affect the volume, distribution and quality of construction materials especially aggregates.
Some geomorphological landforms like river beds, river terraces, alluvial fans and taluses have large amounts of weathered rocks and sediments that are appropriate for aggregate exploitation. Geomorphological processes like physical and chemical weathering also affect the quality of aggregates. Aggregates, a type of construction materials, are produced from sand and gravel and weathered bedrock that can be used for concrete, road pavement and other construction purposes. These materials have been weathered, detached from the parent rocks, transported and finally deposited in geomorphological landforms. Study area, Khoramabad catchment in north of town of Khoramabad with a drainage area of 442.19 km2, is part of Zagros Folded Belt. The aim of this research is to evaluate the effect of geomorphological processes and landforms in the formation, distribution and quality of aggregates.
Methodology
The purpose of this research is to evaluate the effect of geomorphological landforms in the distribution of aggregate and to assess the effect of geomorphological processes in the quality of aggregates. To achieve the purpose of this study, at first, Geologic map of the study area at a scale of 1:250000 and the topographic maps at a scale of 1:50000 from Iranian National Geography Organization top sheets were used to derive lithology and DEM of study area. Geomorphological landforms and processes were recognized by Quick bird satellite images. Precise field works and observations also have been carried out for the identification of landforms and processes. To study the quality and strength of study area aggregates, resistance to abrasion (Los Angeles test), uniaxial compressive strength and Impact Value of aggregates have been done.
To determine the aggregate resistance to abrasion, Los Angles test (based on National Standard number 448) of 2 samples (30 kilograms for each sample) of aggregates in old and new river beds was performed. Uniaxial Compressive Strength test has been done based on ASTM D2938 method. Three samples of rack fragments with a dimension of 20 × 20 × 15 centimeters were obtained in talus, old and new alluvial fans. Two cylindrical cores (two-inch) were prepared for each sample and then Compressive Strengths of samples were determined in wet and dry conditions. The aggregate Impact Value test has been done based on sieve No. 8 for 10 samples in taluses, alluvial fans and river beds.
Results and Discussion
Result of this study shows that landforms such as taluses, old and young alluvial fans and old and young river beds have a lot of weathered and crushed materials that can be used as aggregates. Processes of physical weathering such as thermoclastic and cryoclastic processes as well as tectonic joints play an important role in the production of building materials especially in taluses in the base of steep ridges. To study the quality and strength of study area aggregates, resistance to abrasion (Los Angeles test), uniaxial compressive strength, and aggregate Impact Value tests were carried out. Results of Los Angeles test represent that aggregate abrasion of two samples in old and new river beds are 24% and 18% respectively that show rather high quality of aggregates in mentioned landforms.
Uniaxial compressive strength of aggregates for 3 samples in new alluvial fans, old alluvial fans and taluses are respectively 641, 343 and 778 kg/cm2 in dry condition and 495, 249 and 720 kg/cm2 in wet condition.
Results of aggregate Impact Value tests show that mean of this test in taluses, new river beds, old river beds, new alluvial fans and old alluvial fans are 11.05, 11, 11.95, 13.2 and 13.8 percent respectively. Overall results of mentioned tests reveal that geomorphological landforms such as taluses, old and young alluvial fans and old and young river beds have construction materials with appropriate quality. Also, because of more weathering in old alluvial fans, the strength of construction materials of old alluvial fans is weaker than those of new alluvial fan.
Conclusion
Aggregates are produced from sand and gravel and weathered bedrock that can be used for concrete, road pavement and other construction purposes. Location, volume and quality of aggregates are often important for engineers. Results of this study reveal that location and volume of aggregates are efficiently affected by the geomorphological landforms. Aggregate quality and resistance to abrasion are strongly related to geomorphological processes like degree of weathering. For example, because of more weathering in old alluvial fans, the strength and therefore quality of aggregates of old alluvial fans are lower than those of new alluvial fan. Some processes like karstification have negative effect on the aggregate quality because it can result in the formation of voids and cavities in rock fragments. On the other hand, some processes like physical weathering can prepare fresh materials as appropriate aggregates. Thus, geomorphological mapping, identification of landforms and processes, determining the degree of weathering and paleogeomorphological appraisal of areas are of great important in better understanding and exploitation of aggregates.
کلیدواژهها [English]
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