Uniaxial Compressive Modulus Research Articles

Mixing Ratios and Cementing Mechanism of Similar Silty Mudstone Materials for Model Tests

The similarity model test is one of the important means to study the engineering properties of soft rock. This study aims to develop similar materials for silty mudstone, which has characteristics of low strength and water expansion, based on traditional materials including gypsum, barite powder, clay minerals, and distilled water. The orthogonal design method was used to determine the mixing ratios of the similar materials. The density, uniaxial compressive strength, tensile strength, elastic modulus, and Poisson’s ratio were selected as control indicators of the similar materials. The results show that the water content is the dominant factor for the density, tensile strength, elastic modulus, and Poisson’s ratio of the similar materials of silty mudstone, while the gypsum content is the dominant factor for the uniaxial compressive strength. The physical and mechanical properties of the similar material samples with water content of 19%, barite powder ratio of 32%, and gypsum mass of 250 g show good similarity to those of the raw silty mudstone. The water absorption and expansibility of similar materials with clay mineral ratio of 12% are consistent with those of the raw silty mudstone. The scanning electron microscopy (SEM) observation indicates that the similar material with optimal mixing ratios exhibits a similar microstructure to that of silty mudstone.

Experimental Study of Coal Sample Damage in Acidic Water Environments

We investigated the effects of acidic and circumneutral water on coal samples by uniaxial compression, acoustic emission, and a series of physical tests. In acidic water, the coal samples were damaged, and their ultrasonic velocities decreased, as minerals such as kaolinite and calcite underwent dissolution. When the pH was < 7, the uniaxial compressive strength and elastic modulus decreased, while the duration of the residual strength stage tended to increase. The reactions were stronger at higher H+ concentrations and the number of large pores increased; there was a significant increase in the accumulated acoustic emission counts and maximum average energy near the unstable crack growth stage. The post-peak stage of the coal samples was characterized in the different acidic waters and the failure modes were identified by spectrum analysis. Acidic water damaged the weak areas of coal samples by complex physical and chemical reactions, which made direct tensile failure more likely when the coal samples were loaded.

Experimental Study on the Influence of Moisture Content on the Mechanical Properties of Coal

Water injection in coal seams will lead to the increase of moisture content in coal, which plays an essential role in the physical and mechanical properties of coal. In order to study the influence of moisture content on the mechanical properties of soft media, the forming pressure (20 MPa) and particle size ratio (0-1 mm (50%), 1-2 mm (25%), and 2-3 mm (25%)) during briquette preparation were firstly determined in this paper. Briquettes with different moisture contents (3%, 6%, 9%, 12%, and 15%) were prepared by using self-developed briquettes. Uniaxial and triaxial compression tests were carried out using the RMT-150C rock mechanics test system. The results show that the uniaxial compressive strength and elastic modulus of briquette samples increase first and then decrease with the increase of briquette water, while Poisson’s ratio decreases first and then increases with the increase of briquette water. When the moisture content is around 9%, the maximum uniaxial compressive strength is 0.866 MPa, the maximum elastic modulus is 1.385 GPa, and Poisson’s ratio is at the minimum of 0.259. The compressive strength of briquettes increases with the increase of confining pressure. With the increase of moisture content, the cohesion and internal friction angle of briquettes first increased and then decreased.

Prediction of Uniaxial Compressive Strength and Elastic Modulus of Migmatites by Microstructural Characteristics Using Artificial Neural Networks

Prediction of Uniaxial Compressive Strength and Elastic Modulus of Migmatites by Microstructural Characteristics Using Artificial Neural Networks

Experimental study on the ratio model of similar materials in the simulation test of coal and gas outburst

To obtain the similar materials with specific physical and mechanical parameters and adsorption and desorption indexes used in coal and gas outburst simulation tests, pulverized coal was selected as aggregate, and sodium humate was selected as cementing agent and river sand was selected as auxiliary materials. Based on this, orthogonal tests with 6 factors and 5 levels were designed, and the tests of weighing, uniaxial compression, firmness, adsorption and desorption were carried out. The parameters such as density, uniaxial compressive strength, elastic modulus, firmness coefficient and adsorption–desorption index of similar materials with different ratios were obtained, and the sensitivity of each factor was analyzed by range analysis. The influence of various factors on the similar materials was studied, and the ratio model of similar materials was obtained. The reliability of the model was verified, and a complete method for determining the ratio model of similar materials of outburst coal was put forward. The results show that the density of the similar materials increases with the river sand content, and the uniaxial compressive strength and elastic modulus increase significantly with the pulverized coal ratio and sodium humate content, and the firmness coefficient increases linearly with the pulverized coal ratio. The adsorption constant increases linearly with the sodium humate content, while the adsorption constant b decreases linearly with the sodium humate content. The initial elution rate Δp of similar materials increases at first and then decreases with the increase of sodium humate content.

Mechanical properties and reasonable proportioning of similar materials in physical model test of tunnel lining cracking

Similar materials of surrounding rock and lining suitable for crack of tunnel lining are developed through numerous matching tests according to the numerous theory of geomechanical model test to study the mechanism of crack damage of long-span tunnel lining and the variation rules, such as load and deformation, of physical fields. Similar material of surrounding rock is composed of quartz sand as coarse aggregate, barite powder as fine aggregate, and oil, vaseline, and paraffin as binder. Similar material of lining is based on gypsum and quartz sand, diatomite, fly ash, barite powder, and cement as additives. Physical and mechanical parameters such as uniaxial compressive strength, elastic modulus, and cohesion of materials are controlled through uniaxial compressive, direct shear, and splitting tests. The influence laws of mechanical parameters under various ratios are systematically studied. Test results show that the mechanical parameters of similar material of surrounding rock made of quartz sand, barite powder, and vaseline are stable. The range of variation is moderate, and the fabrication is convenient. The adjustment range of physical and mechanical parameters of similar materials in surrounding rocks is 30.1–52.2 MPa of elastic modulus, 0.23–0.33 MPa of uniaxial compressive strength and 2147–2396 kg/m3 of gravity. In the range of 1.2–2 water paste ratio, gypsum mixture is linearly weakened, and various admixtures strongly influence the mechanical properties of similar materials. Quartz sand as admixture can better replace aggregate in concrete. When the sand content is less than 20%, adding quartz sand into gypsum material can significantly improve the elastic modulus of the material, and the compressive strength changes minimally. When the sand content is more than 20%, the elastic modulus is basically unchanged and the compressive strength gradually decreases. When this similar material is applied to the model test of Fucunchuan tunnel lining crack in the Huangyan Road Capacity Expansion Project, the mechanical and physical properties meet the test requirements. The material can effectively simulate the development and evolution of cracks, provide material basis for obtaining good test results, and serve as a reference for the selection of similar materials for a similar model test.

Mechanical Behaviors of Granite after Thermal Shock with Different Cooling Rates

During the construction of nuclear waste storage facilities, deep drilling, and geothermal energy development, high-temperature rocks are inevitably subjected to thermal shock. The physical and mechanical behaviors of granite treated with different thermal shocks were analyzed by non-destructive (P-wave velocity test) and destructive tests (uniaxial compression test and Brazil splitting test). The results show that the P-wave velocity (VP), uniaxial compressive strength (UCS), elastic modulus (E), and tensile strength (st) of specimens all decrease with the treatment temperature. Compared with air cooling, water cooling causes greater damage to the mechanical properties of granite. Thermal shock induces thermal stress inside the rock due to inhomogeneous expansion of mineral particles and further causes the initiation and propagation of microcracks which alter the mechanical behaviors of granite. Rapid cooling aggravates the damage degree of specimens. The failure pattern gradually transforms from longitudinal fracture to shear failure with temperature. In addition, there is a good fitting relationship between P-wave velocity and mechanical parameters of granite after different temperature treatments, which indicates P-wave velocity can be used to evaluate rock damage and predict rock mechanical parameters. The research results can provide guidance for high-temperature rock engineering.

Effects of Kaolin Addition on Mechanical Properties for Cemented Coal Gangue-Fly Ash Backfill under Uniaxial Loading

In this investigation, six groups of cemented coal gangue-fly ash backfill (CGFB) samples with varying amounts of kaolin (0, 10, 20, 30, 40, and 50%) instead of cement are prepared, and their mechanical properties are analyzed using uniaxial compression, acoustic emission, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The uniaxial compressive strength, peak strain, and elastic modulus of CGFB samples decreased with the kaolin content. The average uniaxial compressive strength, elastic modulus, and peak strain of CGFB samples with 10% amount of kaolin are close to that of CGFB samples with no kaolin. The contribution of kaolin hydration to the strength of CGFB sample is lower than that of cement hydration, and the hydration products such as ettringite and calcium-silicate-hydrate gel decrease, thereby reducing strength, which mainly plays a role in filling pores. The contents of kaolin affect the failure characteristics of CGFB samples, which show tensile failure accompanied by local shear failure, and the failure degree increases with the kaolin content. The porosity of the fracture surface shows a decreasing trend as a whole. When the amount of kaolin instead of cement is 10%, the mechanical properties of CGFB samples are slightly different from those of CGFB samples without kaolin, and CGFB can meet the demand of filling strength. The research results provide a theoretical basis for the application of kaolin admixture in fill mining.

Effect of wetting-drying cycle on hydraulic and mechanical properties of cemented paste backfill of the recycled solid wastes

Cemented paste backfill (CPB) technology is beneficial to the recycling of solid wastes and sustainable development in mines. However, the wetting-drying cycle caused by water intrusion and goaf drainage has a great influence on the waterproof and support performance of CPB. In this study, the hydraulic and mechanical properties of CPB samples under wetting-drying cycles were studied by permeability tests, nuclear magnetic resonance (NMR) tests and uniaxial compression tests. The results show that with the increasing number of wetting-drying cycles, the porosity and permeability of CPB samples increase; the porosity and permeability of CPB samples with small particle size distribution and cementing strength are more sensitive to the increasing number of wetting-drying cycles. During the wetting-drying cycles, the uniaxial compressive strength and elastic modulus of CPB samples gradually deteriorate. This effect is more significant for CPB samples with the smaller particle size distribution and cementing strength. According to the periodic destruction of CPB cemented structures caused by wetting-drying cycles, the deterioration process of mechanical properties of CPB samples can be divided into two stages: initial deterioration stage and re-deterioration stage. The microstructure analysis of CPB samples was used to verify the periodic destruction of the cemented structures. Finally, protective measures of CPB were proposed to ensure the stability of CPB. The CPB with large particle size distribution and cementing strength should be adopted. Besides, the filling rate and the monitoring condition of the goaf can be strengthend to reduce and even avoid wetting-drying cycles.

Estimation Of Mechanical Properties Of Sandstones From Petrographic Characteristics Using Artificial Neural Networks (ANNs)

The accurate determination of strength parameters of rocks such as uniaxial compressive strength (UCS) and elastic modulus (E) using direct and laboratory methods require substantial time and cost. Therefore, the production of predictive relationships and models to forecast the UCS and E is of critical necessity in rock engineering. This study deals with the estimation of UCS and E of sandstones from petrographic characteristics by an artificial neural network (ANN) and multiple regression. For this purpose, 130 core specimens were prepared from sandstones in different locations in Iran. The specimens were tested to determine UCS, E, dry density, and porosity. Also, the petrographic studies including the determination of 11 textural and mineralogy parameters were performed on selected samples. The performance of the ANN model and regression analysis was evaluated using the criteria such as correlation coefficient (R), root mean squared error (RMSE), and variance account for (VAF). According to the ANN results, values of R, RMSE, and VAF were obtained to be 0.925, 0.089, and 97% for UCS and 0.876, 0.094, and 96% for E, respectively. In comparison, for the MLR model, the obtained R, RMSE, and VAF were 0.845, 0.101, and 95% for UCS and 0.797, 0.116, and 93% for E, respectively. A comparison between the findings illustrated that the ANN model was more suitable for forecasting the UCS and E compared with the MLR method.

Acoustic emission characteristics and damage evolution process of layered cemented tailings backfill under uniaxial compression

In order to understand the failure mode, crack evolution and damage constitutive relationship of layered cemented tailings backfill (LCTB), the uniaxial compression test were carried out on four different types of LCTB. Test results show that: (1) The greater the height (h1/H) ratio and the smaller the cement-to-tailings (c/t) ratio, the smaller the uniaxial compressive strength (UCS) and elastic modulus (EM). The LCTB is mainly manifested as tensile failure. (2) The evolution characteristics of acoustic emission (AE) signal show an inverted U-shaped distribution, which first rises and then falls. It can be divided into five stages: quiet period, slow rising period, fast rising period, fast falling period, and slow falling period. (3) A cusp catastrophe model was established to predict the failure of LCTB. The prediction results are accurate. A damage constitutive model of LCTB was constructed. The total damage D of LCTB is composed of the damage value D1 and D2. All damage curves demonstrate an S-shaped distribution, first rising slowly, then rising quickly, and finally rising slowly again and approaching the maximum.

Statistical models for estimating the uniaxial compressive strength and elastic modulus of rocks from different hardness test methods

In engineering projects (dams, tunnels, slope stability) the strength characteristics of the rocks affect the construction operations. It is sometimes difficult, time-consuming, and expensive to evaluate the engineering properties of solid rocks by performing direct tests. For this reason, various laboratory studies have been carried out by many researchers to predict important engineering properties such as uniaxial compressive strength (UCS) and elastic modulus (E) of rocks in a practical way. One of the engineering properties used to estimate UCS-E practically is the hardness of rocks. Hardness tests are easy to apply and non-destructive, and in many of these tests very small specimens are needed. The main objective of this study is to analyze the relations between the UCS-E of the rocks and the various hardness methods (Schmidt hammer hardness, SHH; Shore Scleroscope hardness, SSH; Vickers hardness, HV; Brinell hardness, HB; and Indentation hardness index, IHI). For this purpose, the most appropriate and meaningful relations between hardness tests and UCS-E were determined by simple regression (SR) techniques. Relationships between main engineering properties (UCS, E) and physicomechanical properties were analyzed by multiple regression (MR) techniques using SPSS software. The statistical analyses made revealed the existence of strong correlations between UCS-E and hardness properties of rocks.

Physio-Mechanical Characterization of Rocks

Abstract The present study aims to investigate the physical, petrological, and mechanical properties of ten different types of rocks in the Indian subcontinent, required for the design of structures built in rocks. A comparative assessment is done for the stress-strain response of all the rocks collected under three main categories, e.g., igneous, sedimentary, and metamorphic. The physical properties, e.g., densities and slake durability indices, are determined. The peterological tests are carried out by scanning electron microscope and the X-ray diffraction technique. Mechanical properties, e.g., hardness, uniaxial compressive strength, elastic modulus, and Poisson’s ratio, of the 10 different types of rocks are obtained through static loading at a strain rate of 0.001/s. Lastly, various correlation equations are proposed relating the uniaxial compressive strength, density, elastic modulus, and hardness of the 10 rocks. And the rocks are classified based on the Deere-Miller rock mass classification system.

Experimental Study on Road Base Material of Geopolymer Recycled Concrete

Abstract In order to treat and recycle massive waste concrete, ground waste concrete powder (GWCP) and fly ash (FA) were utilized to produce a geopolymer, a kind of cementitious material. The geopolymer and recycled concrete aggregates (RCAs) were then used to produce geopolymer recycled concrete (GRC), which can be used as a road base material. The feasibility of GRC as a road base material was analyzed by a series of tests, including the mixture ratio test of the geopolymer, road performance test of RCAs, and the tests for mechanical properties of GRC. The test results show that for the geopolymer, the optimum mixture ratio of GWCP to FA was 30/70 (weight/weight), with the concentration of sodium hydroxide (NaOH) solution being 18 mol/L, and the modulus of water glass being 1.5. Except for the slightly large water absorption content, the sludge content, flat and elongated particle content, and the crushing value of RCAs meet the technical requirements for aggregates of road base. The unconfined compressive strength, splitting strength, uniaxial compression modulus, water stability, and dry shrinkage of GRC meet the requirements of the related codes, indicating that it can be used in road base. GRC is not only capable of solving the problems of waste concrete treatment but can also reduce the exploitation of natural stone, the use of cement, and the emission of air pollutants, bringing obvious environmental, economic, and social benefits.

A DEM-Based Approach for Modeling the Damage of Rock Under Freeze–Thaw Cycles

In this study, a new approach based on DEM was developed to simulate the damage of water-rich rock after freeze–thaw cycles. In this way, water-rich rock samples at low temperatures were simplified as rock particles, ice particles, rock–rock contacts, rock–ice contacts, and ice–ice contacts. The volume of the ice particles changed as the temperature changed. The change characteristics were determined by the relationship between the temperature and the unfrozen water content. The developed approach was proven to be effective by comparing the simulation results with the laboratory test results. The physico-mechanical behaviors of water-rich rock samples after freeze–thaw cycles were studied. The results showed that the volume and porosity significantly increased after the freeze–thaw cycles, especially after 15 freeze–thaw cycles, and the increase in the radius was significantly larger than the increase in height. The uniaxial compressive strength, elastic modulus, and peak strain had an exponential reduction as the number of cycles increased. In uniaxial compression tests, the tensile failure rate of the sample after freeze–thaw cycles increased compared with that of the sample without freeze–thaw cycle treatment. With the increase in the number of freeze–thaw cycles, the distribution of cracks in the rock sample was more homogeneous. However, overall, the cracks that formed due to the freeze–thaw cycles were more distributed near the surface of the sample.

Experimental Analysis of the Mechanical Properties and Resistivity of Tectonic Coal Samples with Different Particle Sizes

Because of its weak cementation and abundant pores and cracks, it is difficult to obtain suitable samples of tectonic coal to test its mechanical properties. Therefore, the research and development of coalbed methane drilling and mining technology are restricted. In this study, tectonic coal samples are remodeled with different particle sizes to test the mechanical parameters and loading resistivity. The research results show that the particle size and gradation of tectonic coal significantly impact its uniaxial compressive strength and elastic modulus and affect changes in resistivity. As the converted particle size increases, the uniaxial compressive strength and elastic modulus decrease first and then tend to remain unchanged. The strength of the single-particle gradation coal sample decreases from 0.867 to 0.433 MPa and the elastic modulus decreases from 59.28 to 41.63 MPa with increasing particle size. The change in resistivity of the coal sample increases with increasing particle size, and the degree of resistivity variation decreases during the coal sample failure stage. In composite-particle gradation, the proportion of fine particles in the tectonic coal sample increases from 33% to 80%. Its strength and elastic modulus increase from 0.996 to 1.31 MPa and 83.96 to 125.4 MPa, respectively, and the resistivity change degree decreases. The proportion of medium particles or coarse particles increases, and the sample strength, elastic modulus, and resistivity changes all decrease.

Effects of heating temperature on pore structure evolution of briquette coals

Coal and gas outburst disasters mainly occur in geological structure belts, whose outburst coals are cataclastic, granular, or mylonitic microstructures, and their texture is loose, with mostly broken grain and pieces, so that it they hardly meet the laboratory specimen requirements. Consequently, briquettes are usually prepared at room temperature to study the mechanisms of coal and gas outburst in coal mines. In the present study, we employed a novel method of heating on briquette coal samples to investigate the effect of heating temperature on the strength and pore and fracture structure of briquette coals, and to determine the suitable heating temperature for briquette forming processes. A rock mechanics test system, MTS-815, scanning electron microscopy, nuclear magnetic resonance, and specific surface area and aperture analyzer measurements were used to analyze the mechanical parameters, morphology, and pore size distribution of briquette coal samples at different heating temperatures. The results indicate that the uniaxial compressive strength and elastic modulus of briquette coal first increased and then decreased. The pore size distribution and morphology of the briquette coal samples changed after heating. The smooth intact lamellar shape changed to a rough fractured lamellar shape, and the pores changed from unobvious micropores to observable mesopores and macropores. With an increase in the heating temperature, the transverse relaxation time spectra of the briquette coal samples decreased gradually, and both the porosity of the mesopores and macropores first increased, decreased, and then increased again. The pore diameter distributions of the five tested briquette coal samples had similar pore structures, excluding the sample heated to 600 °C. With an increase in heating temperature, pore volume, specific surface area, and average pore diameter of the briquette coal samples first decreased and then increased. The present study provides a novel method that can be applied in physical simulations aimed at preventing future disasters caused by coal and gas outburst in coal mines.

Micro and macro-structural effects of high temperatures in Prada limestone: Key factors for future fire-intervention protocols in Tres Ponts Tunnel (Spain)

Temperature and cooling methods strongly affect the stability of tunnels drilled in rock masses and so condition interventions for fire emergencies. Samples from two horizontal boreholes drilled in Prada limestone during the design stage of the Tres Ponts Tunnel in the Catalan south Pyrenean zone (Spain) are heated from 105 to 600 °C, and subsequently cooled with air or water to simulate fire extinguishing interventions. Changes in chemical composition and microstructure, physical properties (open porosity, volume, dry total weight, P and S-wave velocity), and mechanical properties (uniaxial compressive strength, elastic modulus, and Poisson’s ratio) are analysed. Rock weakening is observed even at low temperatures (T < 300 °C). The influence of the cooling method appeared at intermediate temperatures of 300-400 °C and open porosity, P and S-wave velocities, and elastic modulus show greater variation for water-cooled samples. A temperature of 500 °C is of paramount importance for ‘Prada’ limestone as it leads to a dramatic increase in porosity and a notable decrease in P and S-wave velocities under both cooling methods. Trans-granular micro-crack progression is observed at 500 °C using scanning electron microscope (SEM), and water-cooled samples show a greater loss in uniaxial compressive strength (UCS), and this is due to micro-crack connections and growing fissures. Thermal damage at 600 °C is also greater when samples are quickly cooled. An ANOVA and a simple regression analysis are performed to discard the influence of the natural location of the borehole samples in the obtained experimental results. Finally, correlations to predict UCS and elastic modulus from volume, open porosity, and P-wave velocity after thermal treatment are proposed using simple exponential and potential functions to help make preliminary decisions after a tunnel fire. These predictive results on the effects of fire on Prada limestone will be considered for the definition of future fire intervention protocols in the Tres Ponts Tunnel.

Experimental study of thermomechanical effects in water-saturated limestones during their deformation

Stability control of elements of stone constructions of various structures is a prerequisite for their safe operation. The use of modern methods of non-destructive diagnostics of the stress-strain state of such constructions is an effective, and in many cases the only way to control it. Studies of thermal radiation accompanying the processes of solid bodies deformation allowed to justify and develop a method that allows to obtain non-contact information about changes in the stress-strain state in various types of geomaterials, including limestones. However, studies of the water saturation influence of rocks on the thermal radiation parameters recorded in this way are currently superficial. Taking into account the water saturation degree of rocks is necessary when monitoring the mechanical condition of stone structures that are in direct contact with water. The main purpose of this work is to study the dependences of changes in the intensity of thermal radiation from the surface of limestone samples with different humidity under conditions of uniaxial compression. The obtained results showed the expected significant decrease in the mechanical properties (uniaxial compressive strength and elastic modulus) of water-saturated samples in comparison with dry ones. At the same time, a significant increase in the intensity of thermal radiation of limestone samples subjected to compression with an increase in their water saturation was recorded, which makes it necessary to take into account the revealed regularity when identifying changes in the stress state of stone structures established according to non-contact IR diagnostics in real conditions.

Mechanical properties, damage evolution, and constitutive model of rock-encased backfill under uniaxial compression

The backfill does not exist independently in the stope, but is in contact with the surrounding rocks to form a combination body to jointly bear pressure. In order to study the joint pressure-bearing mechanism of rock and backfill in the stope, the rock-encased backfill (RB) samples are produced, and the uniaxial compression tests and acoustic emission (AE) monitoring are carried out. The results show that: (1) The encased rock can strengthen the uniaxial compressive strength (UCS) and elastic modulus (EM) of the backfill. The UCS and EM of the RB samples are greatly affected by the cement-tailings (c/t) ratio and radius (r/R) ratio. When the c/t ratio decreases from 1:4 to 1:10, the UCS and EM decrease by about 14% and 29%, respectively; when the r/R ratio increases from 0.2 to 0.8, the UCS and EM decrease by about 63% and 72%, respectively. There is a positive linear function relation between UCS and EM. (2) AE energy release and AE event location characterize the crack growth rate and the crack spatial position of the RB samples respectively. (3) A damage constitutive model of the RB sample is established based on the principle of conservation of energy. The total damage D consists of the damage at the centre of the backfill D1 and the damage in the encased rock D2. All the damage curves are S-shaped. The damage first evolves at the centre of the backfill, then in the encased rock, finally co-evolves, leading to the overall instability and failure, which is mutually verified with the locations of AE events.