The study of the physical properties (geophysical methods) of rocks associated with its mechanical properties has recently received lots of attention. Recent studies show that geophysical methods especially the seismic and geoelectric methods are able to estimate the mechanical parameters and recognize their spatial variations, including anisotropy. Meanwhile, electrical and seismic methods are the most used one.Electrical measurement is one of the non-invasive geophysical methods commonly used by engineers working in various fields such as mining, geotechnical, civil, underground engineering as well as oil and gas mineral explorations. This method can be applied both in laboratory and in the field. Numerous scientists have focused on the relation between resistivity and porosity. However, there is a very limited study on the relation between the electrical resistivity and the rock properties apart from porosity.In this paper, changes in the electrical conductivity of rocks during a uniaxial compression test were investigated in laboratory. The uniaxial compressive strength, elastic modulus, and density values of the samples were determined in laboratory. We installed special electrodes on seven nearly saturated core samples in order to measure the resistivity. Core samples had a 52-mm diameter and a 110-mm length. Two-electrode as well as four-electrode arrays were both used in resistivity monitoring in laboratory. Using a four-electrode array minimized the undesirable electrode polarization effects. In the four-electrode array, we used two non-polarizing Ag/AgCl electrodes mounted on the core sample. Our laboratory observations showed that there was not any electrode polarization effect. When we used a two-electrode array, the resistivity changes were less than 5 percent compared to a four-electrode array. In our laboratory investigation, we used different sedimentary core samples including sandstone, fossilioferous limestone and travertine. Maximum resistivity observed for the travertine core sample was less than 12 kohm. During the uniaxial compressive test, deformation measurements were made and the stress–strain curves were plotted. Tangent Young’s modulus values were obtained from stress–strain curves at a stress level equal to 50% of the ultimate uniaxial compressive strength.Sandstone core samples showed a resistivity increase in the whole strain range. On the contrary, the fossiliferous limestone samples (thin section showed that the sample was composed of tiny calcium fossils in a fine aggregate of micrite cementation) showed a resistivity decrease in the whole strain range. Travertine and limestone showed an intermediate behavior (resistivity increased in the lower strain and it decreased in the higher range). In other words, the onset of new crack formation occurs well inside the quasi-linear part of the stress-strain curve. The quasi-linear portion of the stress-strain curve was the result of a competition between closure of one population of cracks, and the growth of new propagation of the existing cracks.Resistivity behavior during a uniaxial compression load is closely related to the pores in the lower strain ranges and then to the new induced fractures in higher strains. Our results showed that the electrical resistivity may be a representative measure of the rock properties. Additionally, the effect of certain minerals on the rock’s resistivity must be taken into account. The results indicated that the rock structure had an important effect on the resistivity behavior during a mechanical loading.

Bedrock unconfined compressive strength (UCS) is a key parameter in designing the geosciences and building related projects comprising both the underground and surface rock structures. Determination of rock UCS using standard laboratory tests is a complicated, expensive, and time-consuming process, which requires fresh core specimens. However, preparing fresh cores is not always possible, especially during the drilling operation in cracked, fractured, and weak rocks. Therefore, some attempts have recently been made to develop the indirect methods, i. e. intelligent predictive models for rock UCS estimation, which require no core preparation and laboratory equipment. This work focuses on the application of new combinations of intelligent techniques including adoptive neuro-fuzzy inference system (ANFIS), genetic algorithm (GA), and particle swarm optimization (PSO) in order to predict rock UCS. These models were constructed based on the collected laboratory datasets upon 93 core specimens ranging from weak to very strong rock types. The proposed hybrid model results were compared with each other, and the real data and multiple regression (MR) results. These comparisons were made using coefficient of correlation, mean of square error, mean of absolute error, and variance account for indices. The comparison results proved that the ANFIS-GA combination had a relatively higher accuracy than the ANFIS-PSO combination, and both had a higher capability than the MR model. Furthermore, the ANFIS-GA and ANFIS-PSO model results were completely in accordance with the UCS laboratory test, and they were more accurate than the previous single/hybrid intelligent models. Lastly, a parametric study of the suggested models showed that the density and Schmidt hammer rebound had the highest influence, and porosity had the lowest influence on the output (UCS).

Measuring of uniaxial compressive strength (UCS) of intact rocks is necessary in many engineering projects. In deep well drilling for petroleum production or exploration drilling in deep tunnels, because depth wells, obtain suitable core samples for UCS test is too extensive and sometimes impossible. Therefore indirect method for UCS determine (for example using rock particles) is common. One of these methods is known as indentation test. In this test an indenter that is hard penetrate in to rock particle which surrounded by resin is used. In this paper, 11 microcrystalline limestone block samples from carbonate Zagros formation outcrops is prepared and UCS test in laboratory is performed. Then cores are crushed and 720 rock particle samples with 2, 3 and 4 millimeters size is prepared. Indentation test with indenter 0.6, 0.8 and 1 millimeters diameter is done and critical transitional force (CTF) for each particles is determined. Empirical equation between UCS and CFT for different samples and indenter with R2³0.78 is suggested. Using multiple regression general equation between UCS, CFT, particle size (D) indenter diameter (I) with R2=0.85 is proposed. Verification of the proposed equations with 135 indentation tests on 3 microcrystalline limestone samples and comparing measuring UCS in laboratory with estimate UCS are evaluated. This comparison showed that 88% they are similar.

Petrophysical and Geomechanical properties of rocks are important parameters in the design of engineering works and classification of rocks for engineering purposes. Recent studies indicate that geophysical methods, especially seismic and electrical, are able to estimate mechanical parameters and recognize spatial variations. In this research, to develop a predictive model for the uniaxial compressive strength (UCS), special electrodes were installed on the saturated core samples and simultaneously, the uniaxial compressive strength test and electric current flowing through the samples was done and variation of electrical resistivity during loading was measured in the laboratory. The results indicated that the structure and texture of rock had an important effect on the resistivity behavior during a mechanical loading.In this study, thirty core samples from the Fault breccias and Bimrocks (Block-in-matrix-rocks), were collected from different locations of Sabzkouh tunnel route in Chahar Mahal and Bakhtiari Provence. Regression analysis showed that there were generally strong correlations between the UCS and Resistivity in the samples having volumetric block proportion (VBP) of 25–75%. Multiple regression equations were derived for the prediction of UCS based on the resistivity and VBP values. The coefficient of determination (R2) and the root mean square error (RMSE) and the geometric mean error ratio (GMER) indices were calculated as 89.13%, 8.683 and 0.911, respectively, to characterize the prediction performance of the MLR model. The statistical test showed that the MLR model was valid and acceptable for predicting UCS.

Determination of uniaxial compressive strength (UCS) of intact rock is an important mechanical parameter required for many engineering projects. In some engineering projects for example well drilling for production petroleum because of more deep well exist limitation for obtain rock core sample and determination UCS. On the other hand determination this parameter is essential in order to analysis well wall stability and wells development program. Because of this, the idea of using drilling cuttings is proposed for determination UCS. In this paper in order to develop relationship between UCS and single compressive strength (SCS) were used from 7 block sample microcrystalline limestone from Asmari formation outcrops. Then UCS test was performed and was determined uniaxial compressive strength. Next these samples were crushed and were prepared 420 single particles. Then SCS for each particle is determined. Since shape of particles effect on particle strength therefore shape of particles has been modified and total particles that used for determination SCS was spherical. In order to study effect size of particle, particles with diameters 2, 3 and 4 millimeter is prepared and determined SCS for each particles. With increase diameter of particle, increase SCS. In order to eliminate effect of size particles is defined variable size and strength and is proposed chart between them. Coefficient of correlation between SCS and UCS is more than 0.91 that present exist good correlation between them.

Abstract: Soil stabilization with cement has for many years been a ground improvement technique for some engineering applications such as construction of stabilized bases under pavements, canal lining and engineered fills. This reliable and simple soil improvement technique can provide great advantages including increasing shear strength parameters and avoiding the use of borrow materials from elsewhere. The compressive strength of artificially cemented soils has been studied by many researchers. On the other hand, using additive fiber, glass, fly ash, silica fume and nano particle in cement stabilization industry has several advantages. There are few studies about the effect of natural zeolite as an additive material on the cemented sand. Natural zeolite, an extender, has been investigated for use as cement and concrete improver by some researchers. In this study, the use of a natural zeolite additive, as a potential improver of cemented sand is investigated. Natural zeolite contains large quantities of reactive SiO2 and Al2O3. Similar to other pozzolanic materials, zeolite substitution can improve the strength of cement by pozzolanic reaction with Ca (OH)2, can prevent undesirable expansion due to alkali- aggregate reaction, reduce the porosity of the blended cement paste and improve the interfacial microstructure properties between the blended cement paste. It has been observed that pozzolanic activity of natural zeolite is higher than that of fly ash but lower than that of silica fume. It was concluded that the clinoptilolite blend decreases the specific gravity of cements. There are several investigations about the relationship between unconfined compressive strength (qu) and voids/cement ratio of cemented sand. However, existing equations based on voids/cement ratio cannot estimate qu values of zeolite cemented sand mixtures properly. In this research, a series of laboratory tests have been performed to investigate the mechanical characteristics of zeolite cemented sand. The effect of zeolite, cement and porosity on behavior is evaluated in term of qu. Therefore, cilinopiolite kind of zeolite, Neka cement type II and Babolsar sand are used in this study. A total number of 144 unconfined compression tests were carried out on 24 combination type of cement and zeolite include different cement percentages 2, 4, 6 and 8 percent of total dry weight of samples and replacement percent’s of 0, 10, 30, 50, 70 and 90 zeolite with cement based on 50, 70 and 85% relative densities in 7 and 28 days curing times. Results show qu and failure properties improvements of cement sand specimens when cement replaced by zeolite at optimum proportions of 30% after 28 days due to pozzolanic reaction. For 28 day curing time, by replacement percentage of 30 zeolite material by cement, the unconfined strength increased 20 to 80% in comparison with cemented samples by increasing shear strain. For higher cement content and less compacted blends, these improvement rates are more. The addition of zeolite to the cement sand mixture can makes increase strain at failure, and reduce brittle behavior. At the end, a power function fits presented to relate qu and zeolite-cement-soil parameters (porosity (n) and voids/ polynomial model of cement and zeolite voids).