| چکیده انگلیسی مقاله |
Investigate the relationship between rock hardness and generate debris by modified Selby method (case study Agha - Jari Sandstone) Abstract Debris and rocky hillsides are one of the important and typical land forms in arid and semi- arid regions. In this study, the relation between the hardness of Aghajari sandstone with producing the debris has been surveyed by Selby Method (1981). Selby Method has 6 parameters including: Schmidt Hammer hardness, joint width, joint spacing, continuity joint, orientation of joint toward the slopes, and the degree of weathering. Each parameter is categorized to 5 classes as very loose, loose, medium resistant, resistant, and very resistant. Porosity factor was also added as the sixth factor in the revised method32 samples were collected from 4 transects (each consisted of 8 samples, A to H). Schmidt Hammer Model N and ISRM (1978) standard has been used and Debris landforms were prepared with 1:25000 topographic map, Arc/GIS and surfer software. The results show strong and direct relation between the formation of debris and Schmidt Hammer hardness, weathering and continuity of joint. There are also intermediate relation with conjunction joints and weak relation with joint spacing however no relation with joint width can be seen. Moreover, the layer A (The oldest one) has the lowest resistance and hardness in Aghajari Sand stone. Introduction Relatively, sandstone rocks display landscape features obviously. Debris on the slopes is one of these landscapes, for example rock fall and rock topple are a kind of triggers for create these landscapes. Debris is characteristics of arid and semi-arid region. Geology and climate are the main mechanisms for generate of debris. Weathering, gravity, earthquake, joints and temperature fluctuation are another mechanism. To be used Selby (1980) method, in order to determine the affective factor on debris. Also to determining of resistance rocks, Schmidt rebound hardness (SRH) is so practical. So far In the Geomorphology and geology, More than half a century used of SRH in its researches. In addition to the Selby method, we used of porosity to determine of rock hardness in this paper. The aim of this study is the effect of rock hardness characteristics on generates of debris based on modified Selby method on Agha - Jari sandstone in southwest of Iran (Masjed - Soleyman). Material and methods In this study, In order to obtain samples and estimate of SRH, we took samples along eight layers which are named A to H. Samples A1 to A4 were taken from the oldest layer and samples H1 to H4 belonged to the youngest one. Because the thickness of layers varied from place to place, the sampling interval changes from 50 to 150 meters. Landforms geomorphic map of the study area was prepared by Freehand software via using 1:25,000 topographic maps of Iranian National Survey Organization. Geological data, such as lithology and contacts of the Aghajari sandstone layers, were derived from 1:100,000 geological maps of Geological Survey of Iran. Also we estimate on the field some factors Selby method such as: Width of the joints, the spacing of joints, lateral or vertical continuity of the joints, Orientation of joints with respect to the slopes, State of weathering of the rocks. In following, thin section samples were prepared from fresh rock samples. After preparing thin sections, porosity was determined via point counting by counting 400 points in each sample. Results For understanding the effect of each Selby factors with debris, we comparing all factors to amount of debris on each layer, B, C, D and F have the most debris in throughout layers and A layer don’t any debris. Results showed have directly relationship by increasing between SRH and amount of debris with a high correlation (89%). Another factor showed respectively: Width of the joints: non correlation, the spacing of joints: low correlation (21%), weathering: high correlation (87%), lateral or vertical continuity of the joints: high correlation (83%), Orientation of joints with respect to the slopes: almost high correlation (63%) and porosity with mid correlation (56%). Conclusion Results this paper showed respectively high relationship between debris and Schmidt rebound hardness (SRH), weathering and lateral or vertical continuity of the joints and low relationship between the spacing of joints and non-relationship between widths of the joints. Porosity and Orientation of joints with respect to the slopes have mid relationship with debris. Also A layer (the oldest layer) is weakest layer in through layers. B, C, D, E, G, F layers are resistances and H layer (the youngest) is mid hardness. Kay words: Agha - Jari sandstone, Debris, Selby method, Schmidt rebound hardness (SRH), Rock hardness. |