scholarly journals Experiment Study of the Failure Mechanism and Evolution Characteristics of Water–Sand Inrush Geo-Hazards

2020 ◽  
Vol 10 (10) ◽  
pp. 3374
Author(s):  
Qi Liu ◽  
Bo Liu
Keyword(s):  
Pipe Flow ◽  
Confining Pressure ◽  
Hydraulic Pressure ◽  
Transition Flow ◽  
Erosion Process ◽  
Seepage Erosion ◽  
Evolution Characteristics ◽  
Water Outflow ◽  
Flow Stage ◽  
Soil Compactness

Water–sand inrush disasters are frequently encountered during underground engineering construction in karst terrain. The objective of this paper is to study the failure mechanism and evolution characteristics of water–sand inrush caused by the instability of filling medium in karst cavity, as well as the impacts of soil compactness, hydraulic pressure and confining pressure on the instability process. In response to this purpose, a stress-controlled seepage test apparatus in consideration of particle loss was designed, and a series of seepage tests were performed correspondingly. The test results indicate that: (1) Based on the nonlinear feature analysis of water-outflow pattern, the water–sand inrush process can be divided into the “slow flow” stage, “transition flow” stage and “pipe flow” stage by Transition Point I, II. (2) The decreasing soil compactness and increasing hydraulic pressure both exponentially facilitate the seepage-erosion process by increasing the particle-erosion ability; the increasing confining pressure extends the “slow flow” stage and shortens the duration of the “transition flow” stage, ultimately advancing the occurrence of the “pipe flow” stage; the existence of critical hydraulic pressure for the seepage-erosion progress is confirmed, the occurrence of the “pipe flow” stage is significantly advanced once the hydraulic pressure over the critical value. (3) The particle loss caused by the seepage-erosion process is the internal mechanism of water–sand inrush, the variation characteristics of water-outflow pattern are crucial external manifestations correspondingly. Therefore, with the monitoring of water-outflow pattern variation tendency as indicators, the critical status of water–sand inrush can be near-real-time identified, which offers experimental foundation for the early warning and forecast of the occurrence of water–sand inrush.

scholarly journals Damage Evolution Characteristics of Rock Salt under Different Stress Conditions

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Chunping Wang ◽  
Jianfeng Liu ◽  
Lu Wang
Keyword(s):  
Tensile Test ◽  
Rock Salt ◽  
Compression Test ◽  
Damage Evolution ◽  
Confining Pressure ◽  
High Energy ◽  
Brazilian Test ◽  
Evolution Characteristics ◽  
Direct Tensile ◽  
Direct Tensile Test

Understanding the damage evolution characteristics of rock material is essential to the long-term stability and safety analysis of the underground facility. In this study, a series of cyclic loading tests under tensile or compressive stresses are conducted to investigate the damage evolution, deformation, peak strength, and failure pattern of rock salt. A special attention is paid on the microcracking process by using a 3D acoustic emission (AE) test system. The laboratory tests show that the damage degree of rock salt under compression is the highest, followed by the damage in the direct tensile test. The lowest value of damage is determined by using the Brazilian test. The damage degrees where the damage rate starts to decrease are about 0.83 in the direct tensile test, about 0.75 in the Brazilian test, and about 0.91 in the compression test. The failure mode of rock salt changes from the tensile mode in the uniaxial compression test to the compression-shear mode in the confined compression test at low confinement. But from the confining pressure of 15 MPa, the rock salt displays great plastic dilatant distortion and without appreciable macroscopic fractures. Accordingly, with increasing confining pressure, the positions where the rapid increase in cumulative AE counts occurs and where the AE event with high energy appears are changed, from the beginning of the test at low confinement to the postpeak stage of the test at high confinement.

scholarly journals The Effect of Confining Pressure and Water Content on Energy Evolution Characteristics of Sandstone under Stepwise Loading and Unloading

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Shuren Wang ◽  
Paul Hagan ◽  
Yanhai Zhao ◽  
Xu Chang ◽  
Ki-Il Song ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Water Content ◽  
Elastic Energy ◽  
Strain Energy ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Loading And Unloading ◽  
Stepwise Loading

To investigate the mechanical properties and energy evolution characteristics of sandstone depending on the water contents and confining pressure, the uniaxial and triaxial tests were conducted. The test results show that the strain energy was stored in the sandstone samples at the prepeak stage, and that is suddenly released when the failure occurred, and energy dissipation is sharply increased at the postpeak stage. The damage and energy dissipation characteristics of the samples are observed clearly under the stepwise loading and unloading process. The critical strain energy and energy dissipation show a clear exponential relationship. The critical elastic energy decreases linearly as the water content increases. As the confining pressure increases, the critical elastic energy of the samples transforms from linear to exponential. The concept of energy enhancement factor is proposed to characterize the strengthening effect induced by the confining pressure on the energy storage capacity of the rock samples. The energy evolution of the sandstone samples is more sensitive to the confining pressure than that of the water content.

scholarly journals Experimental Investigation of the Effects of the Gangue Particle Size on the Evolution Rules of Key Seepage Parameters

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Lihua Wang ◽  
Jixiong Zhang ◽  
Yongqi Wei ◽  
Cunli Zhu ◽  
Gaolei Zhu
Keyword(s):  
Numerical Simulation ◽  
Theoretical Foundation ◽  
Solid Wastes ◽  
Practical Significance ◽  
Ecological Environment ◽  
Hydraulic Pressure ◽  
Filling Materials ◽  
Evolution Characteristics ◽  
Simulation Results ◽  
Seepage Characteristics

In order to deal with solid wastes and protect the fragile ecological environment on the ground, using gangues as the filling materials in the underground goaf can not only achieve favorable waste disposal but also alleviate surface subsidence and protect surface buildings and the ecological environment, with great practical significance and application prospects. During the water seepage process, the evolution rules of inner seepage channels in the bulk filling materials are the theoretical foundation for the realization of water-preserved mining. In order to gain clear knowledge of the seepage characteristics of the bulk filling gangues with different sizes, the evolution rules of some seepage parameters mainly including the displacement, the porosity, and the permeability of gangues and hydraulic pressure were analyzed via COMSOL numerical simulation. The evolution rules of the seepage characteristics of the bulk filling materials with different sizes were revealed by combining the present experimental and numerical results. Moreover, the present seepage experiment was proved to be reliable by comparing with numerical simulation results. This work can provide theoretical foundation for investigating the evolution characteristics of inner seepage paths in the bulk filling materials and selecting appropriate bulk filling materials under different stress and seepage environments.

scholarly journals MECHANICAL PROPERTIES OF SANDSTONE SUBJECTED TO COUPLING OF TEMPERATURE–SEEPAGE–STRESS

10.6036/10055 ◽  
2021 ◽  
Vol 96 (3) ◽  
pp. 309-315
Author(s):  
Lijie Long ◽  
Dongyan Liu ◽  
Dong Wang ◽  
Jin Li
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Rock Mass ◽  
Elastic Modulus ◽  
Plastic Zone ◽  
Residual Strength ◽  
Confining Pressure ◽  
Peak Strength ◽  
Hydraulic Pressure ◽  
Stress Strain

ABSTRACT: The deformation and fracture of rock mass in deep rock mass engineering are affected by the coupling of temperature, seepage, and stress. A test and a calculation model for sandstone under thermal–hydrological–mechanical (THM) coupling were proposed to reveal the mechanical properties of sandstone. The law of coupling for mechanical indicators of sandstone was established by laboratory tests and numerical simulations. The permeability, peak strength, peak strain, residual strength, elastic modulus, plastic deformation area, and stress–strain cloud diagram were analyzed by the steady state seepage method and THM coupling principle, and the accuracy of the model was verified. Results demonstrate that: (1) As the temperature rises and the peak deformation increases, the sample slowly drops to the residual strength level after the peak stress. (2) The main factor that affects peak strength is confining pressure. In the temperature range of 25 °C–50 °C, the maximum peak strength and peak deformation are increased by heating, and the increases in confining pressure and temperature reduce the reduction coefficient of the residual strength. Moreover, the elastic modulus increases with the increase in confining pressure, but it shows a downward trend when the temperature increases. (3) The plastic deformation zone and stress–strain cloud diagram indicated that when the temperature and osmotic pressure increase, the specimen enters the plastic zone earlier, the effective plastic zone increases, the stress increases, and the deformation is intensified. The proposed method provides a certain reference for the permeability and stability evaluation of rock mass under the conditions of “three-high” (high confining pressure, high hydraulic pressure, and high stress) engineering. Keywords: temperature–seepage–stress coupling, sandstone, mechanical properties

Pulsatile pipe flow transition: Flow waveform effects

2018 ◽  
Vol 30 (1) ◽  
pp. 015111 ◽  
Author(s):  
Melissa C. Brindise ◽  
Pavlos P. Vlachos
Keyword(s):  
Pipe Flow ◽  
Flow Transition ◽  
Flow Waveform ◽  
Transition Flow

Assessment of thermal water outflow plume in heterogeneous glaciofluvial deposits: a case study from Julian Alps, Slovenia

2020 ◽  
Author(s):  
Luka Serianz ◽  
Nina Rman ◽  
Mihael Brenčič
Keyword(s):  
Groundwater Flow ◽  
Analytical Model ◽  
Relative Error ◽  
Thermal Water ◽  
Hydraulic Pressure ◽  
Thermal Plume ◽  
Fresh Groundwater ◽  
Planar Source ◽  
Water Outflow

<p>In Alps, a number of thermal springs are known, which represent the outflow of thermal water from low temperature geothermal systems in fractured rocks. Such dynamics is usually characterized with convection flow, derived either by fault intersection or hydrogeological barrier where the thermal water is uprising due to hydraulic pressure imbalance. When the water is uprising due to convection, it is very likely that the mixing processes between the deep thermal component and the shallow fresh groundwater are established. In Bled case study in Slovenia, the thermal water with average temperature of 21.5 °C, which is around 12 °C higher than average annual air temperature, is discharging from fractured carbonate rocks into glacial Quaternary sediments. Since they have relatively higher but heterogeneous permeability, the uprising thermal water drains into these deposits and, consequently, forms thermal plume which is extending parallel to prevailing fresh groundwater flow direction. Knowing the extent of the thermal plume is of crucial importance for sustainable exploration of the geothermal resource, since it provides answers also to the key issues related to its geothermal and hydraulic characteristics and the dynamics of the regional flow of groundwater, including its recharge area. By approximating the thermal water outflow as a planar source (since we assume it springs out from a fault zone), a planar advective heat transport model (PAHM) was used to evaluate its geometry and quantify the rates. Nine scenarios were applied accounting for different dimensions of the heat source. Each scenario was verified by calculating relative error between the analytical model results and measured borehole temperatures. The PAHM proved to be a useful tool in applying heat transfer as a planar source in groundwater flow. Still, it is necessary to consider or to introduce relatively rough assumptions (e.g. simple model geometry) leading to a very conservative approach. The heterogeneity of the medium has a significant influence on the temperature distributions obtained with different simulation scenarios. Therefore, the calculated temperature distribution within a thermal plume is a subject to uncertainty. In addition, some small portion of a relative error can be attributed to Lake Bled, since the thermal plume is extending in the zone of lake water temperature fluctuation influence. Nevertheless, the analytical model can be used as a tool for simulating spatial distribution of the observed values acquired from field measurements and thus more correctly evaluating the average natural conditions.</p>

scholarly journals Engineering Simulation Tests on Multiphase Flow in Middle- and High-Yield Slanted Well Bores

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2591 ◽  
Author(s):  
Dan Qi ◽  
Honglan Zou ◽  
Yunhong Ding ◽  
Wei Luo ◽  
Junzheng Yang
Keyword(s):  
Multiphase Flow ◽  
Prediction Model ◽  
Flow Pattern ◽  
Pipe Flow ◽  
Slug Flow ◽  
High Yield ◽  
Transition Flow ◽  
Liquid Holdup ◽  
Flow Pattern Map ◽  
Flow Pressure

Previous multiphase pipe flow tests have mainly been conducted in horizontal and vertical pipes, with few tests conducted on multiphase pipe flow under different inclined angles. In this study, in light of mid–high yield and highly deviated wells in the Middle East and on the basis of existent multiphase flow pressure research on well bores, multiphase pipe flow tests were conducted under different inclined angles, liquid rates, and gas rates. A pressure prediction model based on Mukherjee model, but with new coefficients and higher accuracy for well bores in the study block, was obtained. It was verified that the newly built pressure drawdown prediction model tallies better with experimental data, with an error of only 11.3%. The effect of inclination, output, and gas rate on the flow pattern, liquid holdup, and friction in the course of multiphase flow were analyzed comprehensively, and six kinds of classical flow regime maps were verified with this model. The results showed that for annular and slug flow, the Mukherjee flow pattern map had a higher accuracy of 100% and 80–100%, respectively. For transition flow, Duns and Ros flow pattern map had a higher accuracy of 46–66%.

Experimental Research of Fine Sandstone Strength and Deformation Characteristics under Different Confining and Hydraulic Pressure

2013 ◽  
Vol 353-356 ◽  
pp. 562-570 ◽  
Author(s):  
Zai Bin Liu
Keyword(s):  
Rock Strength ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Hydraulic Pressure ◽  
Compression Tests ◽  
Exponential Relationship ◽  
Sandstone Rock ◽  
Strength And Deformation

In order to study sandstone rock strength and deformation parameters under pore water pressure conditions, triaxial compression tests of different hydraulic pressure were executed. Fitting equations of fine sandstone confining pressure and hydraulic pressure coupling effects were established. This research show that fine sandstone rock strength increases with confining pressure increases. Rock mass strength and cohesion have negative exponential relationship with hydraulic pressure. When the hydraulic pressure is 3MPa, elasticity and confining pressure fit to logarithmic relationship. Fine sandstone Elasticity modulus decreases with hydraulic pressure increases. Poisson’s ration and hydraulic pressure fit to linear relationship.

scholarly journals Study on Permeability of Soil-Rock Mixture in Water-Blocking Layer of Open-Pit Coal Mine Dump Site

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Boyu Luan ◽  
Wei Zhou ◽  
Xin Meng ◽  
Xiang Lu ◽  
Zhichao Liu
Keyword(s):  
Coal Mine ◽  
Fine Particles ◽  
Confining Pressure ◽  
Rock Block ◽  
Open Pit ◽  
Water Retention Capacity ◽  
Hydraulic Pressure ◽  
Blocking Layer ◽  
Dump Site ◽  
Water Blocking

Constructing a water-blocking layer in the dump sites of an open-pit coal mine is of great significance to improve the water retention capacity of the reclamation area. The permeability law of the water-blocking layer is costly to be analyzed and researched by means of field tests. In this study, the soil-rock mixture samples similar to the water-blocking layer were prepared, and the rock block proportion (RBP) and hydraulic pressure were adopted as test variables to conduct a permeability test, which provided theoretical support for on-site construction. The results show that when the hydraulic pressure is less than the confining pressure, the permeability increases at a steady rate as the rock block proportion increases. When the hydraulic pressure is close to or equal to the confining pressure, penetrating cracks are easily formed between the soil-rock interfaces of the sample with a higher rock block proportion, resulting in a rapid increase in permeability. With the increase of hydraulic pressure, the migration of the internal fine particles in the sample with a rock block proportion of 40% or less leads to the partial cracks closure, which gradually reduces the permeability. The internal structure of the sample with a rock block proportion more than 40% experiences a process in which the permeability decreases with the crack closure to a significant increase due to the penetrating crack formation. In summary, the soil-rock mixture with about 30% rock block proportion is characterized by suitable permeability and stability, which guarantees the construction cost on-site at the same time. In addition, increasing the rolling times of the truck can increase the compaction of the water-blocking layer and reduce the permeability. The roughness and gradation of the rock blocks can improve the permeability and stability of the water-blocking layer.

scholarly journals An Experimental Investigation of the Progressive Failure of Sandstone and Its Energy Evolution Characteristics

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
Yan Chen ◽  
Baohua Guo
Keyword(s):  
Crack Propagation ◽  
Crack Closure ◽  
Progressive Failure ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Confining Pressures ◽  
The Relationship

In this research study, the progressive failure and energy evolution characteristics of sandstone samples with different sizes were explored under uniaxial and triaxial compression conditions. The characteristic stresses and strains were captured using the crack axial strain levels and dissipative energy. The results showed that, with the increase in the ratios of the height to diameter (H/D), the crack closure stresses increased, while the crack damage stresses decreased. However, the levels of both the crack closure stresses and crack damages were observed to increase with the H/D. With increase in the confining pressure, it was found that the crack closure and crack damage stresses increased, while their levels decreased. The strains of the crack closures, peak crack axial, and crack propagation were observed to decrease with the H/D, while the crack closure strain levels increased. Also, the crack propagation strains were observed to increase with the confining pressures, while the crack closure, peak crack axial, and crack closure strain levels decreased. The progress failure of the sandstone samples was also obtained based on the evolution characteristics of the dissipative energy. The relationship between the energy densities during each phase and the H/D was also analyzed. It was determined that, with the increasing of the H/D, the input, elastic, and dissipative energy densities displayed different evolution characteristics. Furthermore, with the increases in the characteristic stresses, the input and elastic energy densities were found to increase. The dissipative energy density displayed a slight increase with the increases in the peak strength, which resulted in variations with regard to the crack closures and crack damage stresses.

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