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Showing 4 results for Sandstone

Volume 4, Issue 2 (5-2011)

The Alborz dam rock foundation is composed of marl and sandstone. With regard to the proposed plan for the grout curtain in marly rocks (relatively soft and plastic( which is significantly different from the hard and brittle rocks, the boreholes spacing (influence radius slurry), injection pressure (resistance rock), and even the composition and concentration of slurry are important. In the present paper, in order to evaluate the grout curtain of Alborz Dam, emphasis has been placed on two important parameters, namely, the coefficient of permeability and cement take. The results of cement take suggest that the distance between the primary boreholes is long and there is no proper connection between the primary and secondary boreholes. Moreover, grouting results of the fifth and sixth series of grout holes imply that the depth of some of the sixth series of grout holes has not been attained at the water tightening surface. A review of the rate of the cement take - time - pressure graphs and cement take - time graphs on the right abutment indicates that the injection pressure has not been applied in accordance to marly rocks leading to unfavorable phenomenon of opening and closing of joints (hydrojacking). Notably, the check holes results on the right abutment indicate that water tightening at this area has been provided a satisfactory and acceptable job.
Mh Ghobadi, R Babazadeh,
Volume 10, Issue 1 (8-2016)

Strength and durability of sandstones and their influences from natural conditions, are the most important factors which should be considered as engineering materials. In this study, the effect of freeze-thaw and salt crystallization phenomena on strength and durability of upper red formation sandstones collected from southern part of Qazvin province was investigated. Nine specimens of sandstones (specified by A, B, C, CG, S, S1, Tr, Min and Sh) were collected from different part of studied area, then their physical and mechanical characteristics were determined. In order to assessing the effect of freeze-thaw on physical and mechanical characteristics of sandstones, 60 cycles of freeze-thaw test was performed. Also in order to investigate the effect of salt crystallization on strength of studied sandstone, sodium sulphate crystallization test (100% weight solution of Na2SO4) was carried out in 20 cycles. Physical and mechanical characteristics of sandstones such as point load index, Brazilian tensile strength, wave velocity (Vp) and weight loss were computed after different cycles. To evaluate the effect of freeze-thaw and salt crystallization phenomena on durability of sandstones, slake durability test was conducted on specimens subjected to mentioned processes and changes occurred in slake durability index in 15 cycles were investigated. Based on results obtained from current study, it could be concluded that in comparison to freeze-thaw, salt crystallization can considerably reduce the strength and durability of sandstones and deteriorate them. Also it was found that index tests such as point load index, Brazilian tensile strength, wave velocity (Vp) and weight loss can predict the behavior of sandstones in different cycles of freeze-thaw and salt crystallization tests.
Ali Akbar Moomeni, Ming Tao, Alireza Taleb Beydokhti,
Volume 14, Issue 4 (12-2020)

Shallow tunnels have a vital role in urban planning, railway and highway transportation lines. The presence of underground cavities can leads to stress concentration and consequently, instability of the spaces against static and especially dynamic loads. Therefore, the aim of this study was to evaluate the effect of elliptical cavity and its inclination on sandstone rock behavior under compressive static and tensile dynamic loads. In order to evaluate the effect of the cavity under static stress conditions, two groups of intact and hole-bearing sandstone cores with 0, 30, 60, and 90 degrees of hole inclination were prepared and tested under uniaxial compressive loading test. During the test, in addition to the stress recording, damage and deformability of the samples were recorded by using the strain gauge, acoustic emission sensor and camera. Split Hopkinson pressure bar (SHPB) test apparatus was used for doing dynamic loading test. Furthermore, the damage process was recorded using a high-speed camera with 10 micro-seconds interval of frame capability. The obtained results showed that presence of the cavity reduced the rock strength in maximum state (θ=0) up to 55% and in minimum state (θ=90) up to 77% of its initial uniaxial compressive strength. Dynamic tensile loading tests illustrate that the elliptical hole near the free end of sample (reflection boundary of compressive wave to tensile wave) is stable due to locating in superposition area, while the other cavity out of the area with each inclination was undergone to spalling failure. Assessment of failure surface using scanning electron microscope and thin section study indicates that the dominant fracture is grain-boundary type and iron oxide cement has a vital role in developing of this type of fracture.

Mohadeseh Sadeghi, Naser Hafezi Moghads, Mohammad Ghafoori, Mehrdad Amiri, Ali Bashari,
Volume 16, Issue 2 (9-2022)

 The design of underground or terrestrial structures on the rock bed depends on the physical and mechanical properties. Considering the mining method in Tabas coal mine extraction method is long and destructive, the evaluation of the geomechanical properties of the rocks is more necessary. In this research, the characteristics of the rock units of the eastern tunnel No. 3 of Tabas coal Pervadeh mine were investigated. In this study, 3 samples of shale, sandstone and mudstone were examined.  Considering the importance of the subject in this research, new experimental relations have been proposed, and their application shows desirable results. In order to obtain geomechanical characteristics and empirical relationships, physical tests such as porosity, water absorption percentage, unit volume weight, and mechanical properties such as uniaxial compressive strength, point load index, Brazilian tensile strength, direct cutting test, durability and brittleness index were carried out. To achieve the desired objective, the most appropriate relationships are presented using the regression method. Statistical analysis shows good correlation between different parameters in shale, sandstone and mudstone samples.

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