جستجوی مقالات مرتبط با کلیدواژه « مقاومت » در نشریات گروه « زمین شناسی »

Series A of coarse-grained alluvial deposits of Tehran are extended in eastern and north-eastern areas of Tehran. Analyzing and studying of these alluvial deposits from a geological point of view as well as their creation time and general characteristics such as the deposits’ mineral types, their source, and formation conditions, gives a better point of view to geotechnical engineers about exploring their characteristics as well as geotechnical aspects in underground structure design, excavations, and foundation design processes. On the other hand, in order to analyze stability, estimating the factor of safety and the seismic design of these structures, considering their location, which is in Tehran with a high seismic hazard area, the necessity of knowing the exact mechanical and dynamic properties of Tehranchr('39')s alluvium is felt more than ever.

Due to the grain size of Tehran’s coarse-grained alluviums (series A) as well as high level of cementation of them, it is impossible (or maybe so difficult) to make undisturbed samples in order to do experiments. Such that it is excavated 23 boreholes with 30 to 140 meters depth as well as 17 test wells with 20 meters depth in an area which was extended in 10 kilometers in long which were located in Tehran’s No. 13 and No. 14 districts (as it can be seen in Figure 1). During the excavation of the entrance ramp and tunnel of eastern highway of Tehran, in-situ tests have been done in different sequences. Since it was important to investigate real behavior of these alluviums, different in-situ tests such as plate load test, in-situ shear test, pressuremeter test, and downhole test have been done as well as many laboratory and field tests. Furthermore, (1) X-Ray Diffraction (XRD) and (2) X-ray Fluorescence (XRF) as well as (3) Scanning Electron Microscopy (SEM) methods, have been used to explore the type of minerals and those used in cementation.Figure 1. a) Geological plan and the location of boreholes and test wells in the alignment of East Tehran Freeway

Based on the results of XRD tests, it is quite clear that the largest weight percentages of tested samples are lime and silica.Calcium and magnesium levels-as the high-power cations in flocculation process-in soil sample No. 1 (soil with high cementation level) are much more than soil sample No. 2 (soil with moderate cementation level).This is the cause of high cementation level of soil sample No. 1 comparing with soils sample No. 2. A rapid increase in stress level can be seen in in-situ shear test results, in low shear displacements, up to reaching a maximum of τp (peak point) and afterwards reduction in shear stress with softening behavior.  Cohesion and shear strength levels also increase by increasing the depth. According to the plate load tests results, an increase in soil modules changes can be seen in different depths by depth increasing.Large tendencies to increase in volume and dilation can be seen in under shear load cemented soils, after applying a primary compression on them. A brittle behavior with the occurrence of a certain peak can be seen in cemented samples. The significant increase in strength is directly related to the severe dilation rate, which can be seen in cemented samples results.  The shear strength would be decreased, if this cement is broken during the particles’ displacements.The results of downhole tests are shown in Figure 2. According to this figure, it has been explored that Vs,30 is about 600 m/s in moderate cemented soils while it is about 850 m/s in highly cemented soils.  Because of the homogeneity and uniformity of sedimentary deposits, shear wave velocity is increasing due to the higher density of the layers and high level of cementation in both of the soil types. However, this increase is not significant at depths above 25 meters.

Based on the results, cementation level of the eastern coarse-grain-alluvium of Tehran is moderate to high and minerals used in cementation of this type of soil are generally carbonated and especially calcite.Investigating the level of cementation of soil as well as the results of chemical analysis and in-situ tests, it can be found that the strength and deformation parameters of the soil are directly related to the degree of its cementation.Based on the obtained results, the deformation modulus increases by about 25%, the cohesion by about 55% and the shear wave velocity by about 30% with increasing the degree of cementation (Table 1).Increases of these parameters are directly related to depth. However, the cementation level does not significantly affect the internal friction angle of the soil.

In this research relationships between petrological properties and physical and mechanical characteristics have been investigated in three different granitoid rocks' texture. According to field investigations granitoid with coarse, medium and fine texture from three regions respectively Golpaigan (Hasn Robat), Aligudarz (Pir Tak) and Borujerd (Tavan Dasht) were selected and sampled. Laboratory studies on these samples and their thin sections determined mineralogical and petrological composition. According to standard testes some of the physical properties such as porosity and density, and some of the mechanical properties such as point load strength and uniaxial compressive strength were calculated. Then relationship between physical and mechanical properties with petrological characterizes have been studied. This research showed that in these granitoid rocks the effect of the texture type on physical and mechanical properties is greater than mineralogical composition. Also findings showed that the investigation on petrological properties as primary index for evaluation of physical and mechanical properties of granitoid rocks could be done in further studies.

Non-destructive methods such as ultrasonic wave velocity are extensively used for estimating physical and mechanical properties of rock due to the simplicity, economical, fast and harmless nature. Rock constructions have been made worldwide from past to present. Determination of strength of rock constructions such as archeological evidence is not possible using conventional rock strength tests. Developing a cheap, simple, non-destructive, efficient and accurate method to estimate the strength of such constructions can be useful. Rock blocks and constructions have various shapes and sizes. Rock blocks having various shapes and sizes have been prepared from marble, travertine, granite, and limestone and ultrasonic wave velocity at various directions of the blocks dimensions and the uniaxial compressive strength of cylindrical core obtained from the blocks have been measured. The results show that shapes and sizes have no effect on the ultrasonic wave velocity. At the end relationships between uniaxial compressive strength and ultrasonic wave velocity have been determined. The uniaxial compressive strength of blocks and rock constructions can be estimated by the obtained relationships using non-destructive, simple and indeed low cost method of ultrasonic wave velocity.

Salt crystallization is one of the most important weathering agents and may limit the durability of building stones. Salt crystallization induces stresses inside the pores of stones. Consequently, stone durability is closely related to its physical properties and strength. The purpose of this study was to propose a statistical model for estimating stone durability against salt crystallization considering both the physical properties and strength of the stones -utilizing multiple regression. For this purpose, 14 samples of building stones were selected and their mineralogical characteristic, physical properties, and strength (density, porosity, water absorption, uniaxial compressive strength, and Brazilian tensile strength) were determined. Then, the salt crystallization test at a sodium sulfate solution of up to 20 cycles was carried out, and the Dry Weight Loss (DWL) of samples was measured. The durability of each sample was assessed by the percentage of weight loss after the salt crystallization test. The relationships between stone durability and the physical properties and strength of the stones- using simple and multiple regression analyses- were investigated. Moreover, statistical models for estimating stone durability were proposed. These models show that stone durability can be estimated accurately by considering both the physical properties and strength characteristics.

Discontinuities have properties such as orientation، number of set and frequency that can affect the rock strength. Rock specimens having one، two and three cross- sets of discontinuities، various frequencies and orientations of 0، 30، 45، 60 and 90 degrees were prepared. The numbers of rock pieces increased progressively with an increase of frequency and set of discontinuities. As specimens having three sets of discontinuities that one of their sets had four number of parallel discontinuities were consisted 20 rock pieces and they represented jointed rock mass. Joint factor، uniaxial compressive strength and friction angle along the discontinuity surface in direct shear were determined. The uniaxial compressive strength of specimens having one، two and three sets of discontinuities in horizontal and vertical direction was less than the uniaxial compressive strength of intact rock. The uniaxial compressive strength of specimens approached approximately to zero value particularly when the orientation of discontinuities was 60 degrees. This considerable decrease of strength was occurred also for specimens having two and three sets of discontinuities at orientation of 30 degrees. The analysis of results showed that the relationship between ratio of uniaxial compressive strength of jointed specimens to the uniaxial compressive strength of intact rock specimens (anisotropy factor) and joint factor of this research is considerably different with the suggested relationship by Ramamurthy. Properties of discontinuities have altogether essential role on the strength of rock mass.

The main objective of this research is to provide information about the effects of mineralogical characteristics of aggregates on concrete properties. Crushed aggregates were selected with different petrographics from different resources. Aggregates such as, Marble, Dolomite, Tuff, Granite, Genasis, Basalt, Andesite, Lumashele, Sand Stone and Diorite which have different chemical, physical and mechanical properties were used in this study. The results of the study showed that physical and mechanical properties of minerals control properties of concrete and undesirable properties of concrete influenced with which of mineral. Also, the results indicated that aggregates with flaky and elongated minerals subjected to weathering have a great effect on undesirable properties of concretes. The highest uniaxial compressive strength (33 MPa) at 28 curing days was measured in the specimens prepared with dolomite aggregates while the lowest strength (13 MPa) was measured in the specimen prepared with lumashele aggregates at the same age.