ENGINEERING GEOLOGY
Year:2020 | Volume:13 | Issue:3|Papers Count:7

Investigation and determination of residual frictional properties of rock joints is important for designing structures on or within the rock masses. Tribometer is a device to measure frictional properties of various types of contacting surfaces. In this research, several direct shear experiments conducted on two types of artificial limestone joints named Onyx marble and Travertine. Two types of surfaces geometry such as rough tensile joint surfaces with standard dimensions (based on ISRM suggested methods) and grinded planar small surfaces with dimensions ranged from 1 cm2 to 25 cm2 were prepared. Direct shear experiments by constant shearing rate and under different normal stresses conducted in CNL boundary condition. Results obtained from the residual state of the shear were gathered and investigate and it found that the residual friction coefficient of limestone rock joints, under almost similar normal stress and shearing rate conditions, remains approximately constant with differing the contact size of the specimens. In addition, under approximately similar stress concentrations in contact regions, the residual shear behavior of rough surfaces with standard dimensions is very similar to that of small planar ground surfaces in limestone joints. Finally, based on findings in this research and some other past researches, it is proposed to apply tribometers for measuring the residual shear strength of rock joints. In this paper, a conceptual design of a tribometer is proposed to develop for measuring residual frictional properties of a point contacts of rock surfaces during 5 to 20 mm shear displacements.

In this research, 2D and 3D synthetic modeling of targets representing common geological structures was carried out using Encom ModelVision. In this regard the effect of factors such as material type, size and dimensions, burial depth and geometrical shape of body as well as survey profiles interspacing on the response of spherical, elliptical and linear magnetic bodies representing geological structures was investigated. The results of synthetic data modeling showed that as expected, magnetic intensity is directly correlated with the size and dimensions of the buried bodies having reverse correlation with the burial depth of the body. Also the magnetic response of bodies containing regular and irregular arbitrary polygons, ellipsoid and vertical cylinder largely follows the geometric shape of the body. According to the effect of survey profiles spacing on the spherical, elliptical and linear bodies, a series of simple linear mathematical relationships with high correlation coefficient between survey profile interspacing and ratio of height to half width of magnetic anomaly were obtained. These relationships can be used in prospecting and preliminary exploration stages. The results of field surveys on the buried metallic pipes at Arak University of Technology campus, revealed that despite the selection of fix small station intervals (1m) and employing appropriate transforms and filters on the data by Geosoft Oasis montaj, overal by reducing the number of profiles the response of the buried metallic pipes, gets wider and weaker so that in some cases the trend of anomalies completely changes and even identification of target type is impossible.

Corrosion is one of the destructive factors that causes a lot of damage to the reinforcement inside the concrete and causes irreparable damage to the economy. Chlorine ion penetration in concrete is one of the most important factors affecting concrete corrosion. Therefore, it is necessary to refine corrosion by identifying the concrete properties using proper methods. In this study, the effect of adding zeolite (0, 10 and 15%) to concrete on the uniaxial compressive strength and penetration rate of chlorine ion in concrete was investigated. According to the tests result performed by adding zeolite at the beginning concrete compressive strength decreases but after 90 days the compressive strength increases and is approximately equal to the strength of control samples. Zeolite also reduces the penetration rate of chlorine ions into concrete by 30% on average (compared to the control sample). Finally, it can be concluded that using 10% zeolite improves the concrete properties.

Brittleness and modulus of toughness are among the most important inherent properties of rock, which are determinative for rock excavation operations. In this study, mechanical properties of granite, granodiorite, dolomite, hornfels and marble were studied in the area of Glass water supply tunnel near the Naghadeh city (NW Iran). The stress-strain curve area and rocks strength properties were applied to calculate 13 brittleness indices and modulus of toughness. Statistic relationships between brittleness indices and toughness of modulus suggest strong correlation between B3 brittleness index (R2= 0. 83 and RMSE= 5. 46 coefficients) and B4 brittleness index (R2= 0. 83 and RMSE= 3. 85) respectively with modulus of toughness. The statistical relationship between modulus of toughness and specific energy indicates a strong correlation (R2= 0. 85). The modulus of toughness and brittleness are useful parameters for estimating specific energy of rock cutting. Since the modulus of toughness increases with specific energy of rock cutting, it enabled us to estimate the specific energy of rock cutting.

The freeze and thaw cycles are one of the most important factors in physical weathering of stones, which substantially can influence the long-term durability and service life of building stones. To evaluate the long-term durability of stones against freeze and thaw cycles, two parameters of decay constant (λ ) and half-life index (N1/2) can be applied. To determine these two parameters, the freeze and thaw test should be done, which is a difficult, time-consuming and expensive process. Therefore, development of indirect models to estimate these two parameters without performing freeze and thaw test can be useful for fast and low-cost evaluation of stones’ long-term durability. In this paper, considering the P-wave velocity (VP) of stones during the freeze and thaw process for 22 types of Iran’ s carbonate building stones, two parameters of λ and N1/2 were determined. Then, based on obtained data and using regression analysis and classification and regression tree (CART) techniques, models were developed to predict these two parameters. The results indicated that the developed models using CART technique have higher accuracy and precision than the regression models. These models are able to present acceptable prediction of λ and N1/2 based on the initial porosity of stone.

Seismic analysis of earth and pebble dams is generally carried out in two quasi-static and dynamic methods. Although the quasi-static method with easy application and simple assumptions provides barrier safety, it can sometimes lead to unsafe and uneconomical results. In the present study, the Riley attenuation rule is used in stress and strain calculations of the Azadi dam and both nonlinear static and dynamic analysis are used. Also, a simple elastoplastic behavior model based on the Mohr-Coulomb criterion in Abaqus software has been used. Comparison of the results showed that in both analyzes the maximum strain of Azadi dam core was above the core and the highest stress occurred during the earthquake in the bottom. Also, dynamic stress is higher than static in σ xx direction 49%, σ xy% 30 direction and σ yy% 28 direction. At the floor level, the maximum crustal stress is 29% higher in the middle level, 68% higher and in the upper level 72% higher than the core.

To identify natural behavior of rocks under the similar moisture conditions, two saturation methods of under atmospheric pressure conditions or vacuum pressure are usually used. In the method of vacuum pressure, the values of vacuum pressure Pvac as well as the time of applying this pressure Tvac are two effective parameters. In this study, the saturation method of rock, especially soluble ones such as gypsum and anhydrite, have been studied. The results of the experiments were analyzed in terms of sensitivity for four parameters of dry vacuum pressure Pvac(dry), wet vacuum pressure Pvac(wet) and the time of applying each one (Tvac(wet), Tvac(dry)). The results showed that by increasing Pvac(wet), the percentage of water absorption has been increased and the samples generally gain more than 95% of their increased weight after 4 days of applying wet vacuum and they can be practically assumed to be saturated. Applying dry vacuum Pvac(dry) before wet vacuum Pvac(wet), increases the weight of most samples after applying Pvac(wet). In case of gypsum-anhydrite rocks, the experiment showed that applying dry pressure equivalent to-0. 5 atmospheres (atm) and to 5 hours (Pvac(wet) =-0. 5 atm, Tvac(dry)) = 5h) propose ideal results.