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A Novel Approach to Surface Strain Measurement for Cylindrical Rock Specimens Under Uniaxial Compression Using Distributed Fibre Optic Sensor Technology
This study proposes a novel approach to surface strain measurement for cylindrical rock specimens subjected to uniaxial compression using distributed fibre optic sensing technology. The capability and accuracy of this approach in measuring the full-field strain distribution of a rock specimen have been verified by a series of uniaxial compressive strength (UCS) tests on cylindrical specimens of aluminium alloy, sandstone, and granite. By analysing the experimental results, this new approach also has the potential of being utilized to detect the potential failure locations and sequence through strain localization zone variations and estimation of the development of crack opening displacement and rock fracturing characteristics during the loading and unloading process. Detailed installation procedures are provided for this study for assistance in the use of this new approach. The boundary issue of fibre measurements is identified, and solved by extending the bonding length of the measuring fibre.
Journal Article
Science experiments with gravity & motion
Features easy and fun science experiments with gravity & motion using household items, no laboratory needed! Each activity includes easy instructions with how-to photos, and short science explanations.
Book
Experimental Study on Shear Characteristics of Filled Joints Anchored by Basalt Fiber-Reinforced Polymer Materials
Filled joints are widely found in natural rock masses and are one of the main factors causing rock mass engineering instability. The use of bolts can effectively control the shear slip of filled joints, research on bolts filled joints in the filling degree, and other key parameters of the influence of the law, to ensure the stability of the engineering rock body is of great significance. This paper presents shear experiments on bolted filled joints of Basalt Fiber-Reinforced Polymer (BFRP) materials with different joint roughness and filling degrees, while acoustic emission technology monitors the shear failure process of the specimens. The results show that the peak shear strength decreases with the increase in filling degree, and the peak shear strength decreases by 23.9% when the filling degree changes from 0 to 2.0 at 4 MPa and J2 conditions, while the normal stress, the Joint Roughness Coefficient (JRC) and the peak shear strength both show a positive correlation. The normal deformation of bolted filled joints exhibits three distinct evolutionary patterns depending on the filling degree, while both JRC and normal stress significantly influence the magnitude of shear dilatancy-shrinkage deformation. The shear resistance of BFRP bolts is mainly reflected in the post-peak plastic stage, and some of the fibers break during its shear deformation to form controlled yielding, with vertical and horizontal deformation controlled within 15.5~22.3 mm and 4.7~6.9 mm, respectively. The Acoustic Emission (AE) results show that the AE events are mainly in the post-peak plasticity stage, and the proportion is about the sum of the proportion of the other two phases, and this proportion increases with the increase in the filling degree.
Journal Article
Investigate the mechanical property of weak interlayers based on micro-RME and AGBM
Weak interlayers are difficult to be measured using the traditional macroscale Rock Mechanics Experiment, which requires intact and standard rock samples. Because the zones of weak interlayers are usually narrow and variable, and the geomaterials in weak interlayers are fragmented and muddy. This work combines the microscale Rock Mechanics Experiment (micro-RME) and Accurate Grain-Based Models (AGBM), in order to investigate the mechanical property of the weak interlayer found during the construction of Sichuan-Tibet Railway. The composition and mechanical property of rock-forming minerals in weak interlayers were tested using micro-RME, TESCAN Integrated Mineral Analyzer and nanoindentation testing. Based on the results of micro-RME, the AGBM was established to achieve the macroscale property of weak interlayers. The influence of weak interlayers on the deformation of surrounding rocks was discussed numerically.
Journal Article
Study on the Mechanical Properties of Natural Gas Hydrate Reservoirs with Multicomponent under Different Engineering Conditions
For wellbore stability issues induced by drilling operations in natural gas hydrate-containing reservoirs, wellbore stability research will focus on the mechanical properties of hydrate reservoirs. According to the content of the research, the response relationship between the hydrate core and the base physical property changes under different engineering parameters is established, and the law of hydrate mechanical property changes with temperature and pressure is studied for various physical properties. According to theoretical research and experimental data, it has been determined that: hydrate core-resolved gas and transverse and longitudinal wave velocity have a positive correlation with saturation and pressure and a negative correlation with temperature; a negative correlation exists between resistivity and saturation. The hydrate core stiffness strength correlates positively with saturation and adversely with temperature. Under the identical strain conditions, when saturation, pore pressure, and temperature increase, the stress of the hydrate grows rapidly; there is a distinct inflection point, and the hydrate does not form above a particular temperature. To prevent the decomposition of hydrates and minimize disasters such as well wall instability and reservoir collapse, it is possible to reduce reservoir in situ temperature and pressure fluctuations in accordance with operational requirements.
Journal Article
Equivalent modeling method of virtual material for flange connection structure based on contact mechanics experiment
It is essential to consider microscopic contact deformation on the joint surface when the dynamic properties of flange connection structure were characterized. In the study, an equivalent modeling method of virtual material based on microscopic contact experiment was proposed. First, the macroscopic model of flange connection structure was established and assembly process was simulated. Several subregions were divided according to the pressure distribution of joint surface. In each subregion, the pressure distribution was approximately uniform. Second, the microtopography of joint surface was measured experimentally, and the fractal parameters were calculated by power spectral density function method. At the same time, the contact mechanics experiment by industrial CT equipment was conducted to accurately measure the actual contact state of joint surface, and the mathematical model of contact pressures and ratios of actual contact area to nominal contact area was established. Next, the contact stiffness of joint surface was calculated based on fractal contact theory and the actual contact area measured by industrial CT equipment. Finally, the parameters of equivalent virtual material were calculated by weighted average of each subregion. In addition, a modal experiment of flange connection structure was conducted to compare with the simulation result. The result shows that the average relative error of natural frequency was 4.69% between experiment and simulation. It verified the accuracy and reliability of the equivalent modeling method of virtual material based on contact mechanics experiment.
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Journal Article
Stability Evaluation of Old Goaf Treated with Grouting Under Building Load
In this paper, stability of overlying strata and grouting entities are determined as the two key factors affecting the stability of old goaf treated with grouting under building load by theoretical analysis, the additional stress influence depth and the grouting entities strength are determined as the two key indexes for the stability of old goaf treated with grouting under building load. Through theoretical analysis and field investigation, the calculation method of the influence depth of the additional stress in the old goaf under the building load is revised, and the calculation formula of the grouting entities strength is confirmed by theoretical analysis and the experimental results. The uniaxial compression and uniaxial creep stability of the grouting entities under dry and saturated conditions are verified by mechanical experiments. And the revised parameter reference value is provided for the calculation formula of the grouting entities strength. Finally, the stability of the grouting reinforcement project in China is verified by numerical simulation.
Journal Article
A Mechanical Model and its Experimental Verification for a Water Injection String in a Highly Deviated Well
Water injection strings in highly deviated wells are subjected to complex forces on the string bore. In this work, a mechanical model is developed for these forces and for those on downhole tools. On the basis of this model, and taking account of the characteristics of the string in different working conditions, a temperature field model and a pressure field model are introduced, and a statically indeterminate structural calculation method is adopted. A force tester for highly deviated wells is developed and used in eight tests on strings in the Jidong Nanpu oilfield making a comparison between the measurements from the tests and the results of calculations using the mechanical model indicates that the mechanical model exhibits high computational accuracy, with the errors at the wellhead being no more than 10%, and that the forces on packers calculated from the model are in accordance with those measured in the tests. Thus, the mechanical model developed in this work is suitable for analyzing the forces on water injection strings and downhole tools in highly deviated wells.
Journal Article