scholarly journals Laboratory Investigation on the Effects of Natural Fracture on Fracture Evolution of Granite Exposed to Freeze-Thaw-Cyclic (FTC) Loads

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Yu Wang ◽  
Xuefeng Yi ◽  
Shaohua Gao ◽  
Hao Liu
Keyword(s):  
Rock Mass ◽  
Natural Fracture ◽  
Natural Fractures ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Fracture Evolution ◽  
Rock Structure ◽  
Type Fracture ◽  
Felicity Effect ◽  
The Stability

The natural fractures in rock mass are susceptible to damage evolution when subjecting to repeated freeze-thaw (F-T) weathering in cold regions, which can lead to the instability of rock engineering and even occurrence of geological hazards. Knowledge of how natural fracture impacts the overall fracture evolution of freeze-thawed rock is important to predict the stability of rock structure. In this work, we reported uniaxial experimental measurements of the changes in strength, deformation, acoustic emission (AE) pattern, and Felicity effect during increasing amplitude stress-cycling conditions on granite. The results show that the change of fracture aperture is related to the fracture openness and filling characteristics, open-type fracture is sensitive to F-T treatment, and its aperture increases faster than the close-type and fill-type fracture. In addition, strength decreases, and the damping characteristics first decrease and then increase with increasing natural fracture volume. AE activities also present different responses during sample deformation. The proportion of AE signals having low-frequency characteristics increases with increasing natural fracture volume, and the shear sliding along natural fracture results in the surge of AE activities. Moreover, the Felicity effect indicates that the Felicity ratio presents a fluctuation decreasing trend, and the preexisting fractures alter the stress memory characteristics of rock. It is suggested that the changes of the geomechanical and AE pattern are the interactions between the natural fracture and the newly stimulated fracture. The testing results are expected to improve the understanding of the influence of natural fractures on rock fracture evolution and can be helpful to predict the stability of rock structures and rock mass in cold regions.

Instability in Himalayan Rock Slope under Recurrent Freeze-Thaw

2020 ◽  
Author(s):  
Sahil Sardana ◽  
Rabindra Kumar Sinha ◽  
Mamta Jaswal ◽  
Amit Kumar Verma ◽  
Trilok Nath Singh
Keyword(s):  
Rock Mass ◽  
Numerical Modelling ◽  
Rock Slope ◽  
Winter Season ◽  
Intact Rock ◽  
Joint Spacing ◽  
Freeze Thaw ◽  
Discontinuity Sets ◽  
Rock Structure ◽  
The Stability

<p>The highways in the Himalayas region have an important concern as these are the only connecting corridors to the nearby land area. Manali-Leh highway is one such important route in India which is interrupted frequently by landslides and rockslides events due to freeze-thaw activity, earthquake, heavy rainfall and anthropogenic activities are major triggering factors. In the freeze-thaw activity, water enters into the cracks in rocks during rainfall, subsequently, it freezes, leads to enlargement of cracks and/or the initiation of new cracks due to the volumetric expansion of ice. In the summer season, the ice melts and water migrates to the newly generated cracks and later freezes in the winter season. This, in turn, weakens the rock structure that leads to the reduction of the rock mass strength which promotes instability in the rock slopes. This study focuses on the stability assessment of rock slope along the highway from Solang Valley in Himachal Pradesh, India. This highway connects the Solang Valley to the south portal of the Rohtang tunnel and provides all-weather connectivity, as the Manali-Leh highway shut down during the winter season due to heavy snowfall.</p><p>An extensive geotechnical survey was carried out on the studied slope and the rock samples were collected from the field. The artificial freeze-thaw environment was created in the laboratory for the rock specimens to account the natural freeze-thaw effect. Laboratory tests were conducted on the rock specimen conditioned with freeze-thaw to determine the physico-mechanical parameters of intact rock prior to the numerical simulation. The results indicate the significant loss in compressive and tensile strength of rock as the number of freeze-thaw cycles increases. A three-dimensional numerical modelling was performed to assess the stability of the rock slope using the Distinct Element Code (3DEC software). Slope geometry was prepared to represent the actual slope and the various discontinuity sets observed at the field was mapped on the model. The behaviour of the discontinuity sets was modelled using a Mohr-Coulomb slip with residual strength. Normal stiffness of the joints was calculated from rock mass deformation modulus, intact rock young’s modulus and joint spacing. Similarly, the shear stiffness was calculated. The results of numerical modelling show that the displacement of blocks increases and the factor of safety of the slope decreases as the number of freeze-thaw cycles increases.</p>

scholarly journals Research on Fracture and Energy Evolution of Rock Containing Natural Fractures under Cyclic Loading Condition

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xueliang Li ◽  
Yu Wang ◽  
Shuo Xu ◽  
Haonan Yang ◽  
Bo Li
Keyword(s):  
Rock Mass ◽  
Cyclic Loading ◽  
Natural Fracture ◽  
Dissipated Energy ◽  
Energy Evolution ◽  
Rock Engineering ◽  
Cyclic Loading Condition ◽  
Freeze Thaw ◽  
Fracture Evolution ◽  
Naturally Fractured

For rock engineering in cold regions, the naturally fractured rock is susceptible to repeated freeze-thaw (F-T) weathering, coupled fatigue conditions of freeze-thaw (F-T), and stress disturbance act on rock mass, which can lead to the instability of rock engineering and even occurrence of geological hazards. Knowledge of how natural fracture affects the overall fracture evolution of freeze-thawed rock is crucial to rock mass stability. Laboratory multilevel cyclic loading tests are conducted to reveal the fatigue behavior and energy evolution for naturally fractured marble, as well as the influence of natural fracture volume on fracture evolution. The test results show that the preexisting natural fracture impacts fatigue strength, lifetime, and energy dissipation. The dissipated energy is correlated to all kinds of natural fracture (i.e., opening-mode, closing-mode, and filling-mode), and it decreases with the increase of the total natural fracture volume. The dissipated energy presents a first slow and then faster pattern as the cycle number grows. Compared with newly formed cracks, the proportion of energy consumed by stimulating natural cracks is smaller.

scholarly journals Influence of Freeze-Thaw Cycles on Acoustic Emission Characteristics of Granite Samples under Triaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhandong Su ◽  
Ke Geng ◽  
Fubiao Zhou ◽  
Jinzhong Sun ◽  
Huayan Yu
Keyword(s):  
Acoustic Emission ◽  
Triaxial Compression ◽  
Peak Frequency ◽  
Dominant Frequency ◽  
P Wave ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Ae Signal ◽  
The Stability ◽  
Granite Samples

Understanding the acoustic emission (AE) characteristics of rocks that have undergone freeze-thaw cycling is of great significance for the use of AE technology to monitor the stability of rock masses in cold regions. A series of freeze-thaw cycling experiments and triaxial compression AE tests of granite samples were performed. The results show that, with an increasing number of freeze-thaw cycles, the P-wave velocity and peak AE intensity of granite show a substantial downward trend. The AE ringing counts during triaxial compression can be divided into three stages: abrupt period, calm period, and failure period. The overall change of the characteristic AE signal of granite samples that underwent different freeze-thaw cycles is the same. The AE signal during the destruction of granite occurs in clear dual dominant frequency bands. The peak frequency increases with increasing load time, and this trend becomes less clear as the number of freeze-thaw cycles increases. Overall, the peak frequency distribution tends to change from high to low with an increasing number of freeze-thaw cycles. The results provide basic data for rock mass stability monitoring and prediction, which is of great significance for engineering construction and management in cold regions.

Integration of outcrop, subsurface, and microseismic interpretation for rock-mass characterization: An example from the Duvernay Formation, Western Canada

2018 ◽  
Vol 6 (4) ◽  
pp. T919-T936 ◽  
Author(s):  
Mason K. MacKay ◽  
David W. Eaton ◽  
Per K. Pedersen ◽  
Christopher R. Clarkson
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Distinct Element ◽  
Integrated Approach ◽  
Natural Fracture ◽  
Western Canada ◽  
Natural Fractures ◽  
Data Set ◽  
Fracture Geometry ◽  
Rock Mass Characterization

Identifying and characterizing geomechanical domains is important for understanding how a reservoir will respond to hydraulic fracturing, including interaction with natural fractures to create new permeable pathways. We have used a rock-mass characterization approach, which describes the mechanical reservoir package by combining parameters of the intact rock, such as brittleness, with inferred geometry and density of natural fractures. Insights from outcrop observations are important to complement the interpretation of fracture geometry and density derived from subsurface data, to give a more complete understanding of natural fracture networks. This integrated approach is applied to a data set from the Duvernay play in Western Canada. A synthetic model of the subsurface reservoir is constructed using data from well logs, cores, and outcrop analogs. Numerical simulation of the response of the artificial rock mass to hydraulic fracturing is performed using a distinct element code. Independent validation of the model is obtained by achieving an agreement between the simulated microseismic response and the observed distribution of microseismicity during hydraulic fracturing.

Simulation on Freeze-Thaw Action in Multi-Cracks in Rock Mass

2014 ◽  
Vol 1049-1050 ◽  
pp. 426-429
Author(s):  
Wen Dong Ji ◽  
Yong Shui Kang ◽  
Xiao Yu An ◽  
Yue Zhao
Keyword(s):  
Rock Mass ◽  
Freezing Point ◽  
Fractured Rock ◽  
Key Factors ◽  
Fractured Rock Mass ◽  
Freeze Thaw ◽  
Factors Influencing ◽  
Field Temperature ◽  
Temperature Filed ◽  
The Stability

Freeze-thaw action in fractured rock mass is discussed. Moist rock exposed to subfreezing temperature would suffer from freeze-thaw deterioration, which would pose serious threat to the stability of geotechnical engineering. Some key factors influencing freeze-thaw action in rock mass is analyzed, such as temperature, freezing rate, freeze-thaw cycles and porosity of the rock. Further more, using the theory of physical chemistry, the freezing point and frozen ratio were derived. Finally, the model of frost crack was built by ANSYS and then imported into FLAC3D by converting procedure. The stress field, temperature filed as well as the normal and shear stress on surface of the cracks were demonstrated. The effect of freezing pressure is reflected in the results.

Research on Modeling Method for Freezing Tunnel with Fractured Surrounding Rock

2012 ◽  
Vol 455-456 ◽  
pp. 1591-1595 ◽  
Author(s):  
Yong Shui Kang ◽  
Quan Sheng Liu ◽  
Kai Shi ◽  
Xiao Yan Liu
Keyword(s):  
Thermal Expansion ◽  
Rock Mass ◽  
Coefficient Of Thermal Expansion ◽  
Geotechnical Engineering ◽  
Continuous Media ◽  
Surrounding Rock ◽  
Modeling Method ◽  
Cold Regions ◽  
Thermal Fields ◽  
The Stability

The modeling method for freezing tunnel with fractured surrounding rock is discussed. Frost weathering of rock in cold regions poses serious threat to the stability of geotechnical engineering. Fracture in the freezing rock plays an important role in the mechanical features of the rock mass. However, most of the previous study on freezing rock considered the rock as continuous media, in which the effects of fracture are not reflected sufficiently. This paper overcomes the above-mentioned insufficient and considers the fracture as an important factor while modeling. The model of frost fracture is built by AutoCAD and then transferred into ANSYS for meshing, and finally imported into FLAC3D for calculating by converting procedure. The method of equivalent coefficient of thermal expansion is used to simulate the expansion of water while freezing. The stress and thermal fields after some steps of calculation are ultimately simulated and the influence of fractures is reflected in the results.

scholarly journals Intelligent Prediction Model of the Triaxial Compressive Strength of Rock Subjected to Freeze-Thaw Cycles Based on a Genetic Algorithm and Artificial Neural Network

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xin Xiong ◽  
Feng Gao ◽  
Keping Zhou ◽  
Yuxu Gao ◽  
Chun Yang
Keyword(s):  
Neural Network ◽  
Genetic Algorithm ◽  
Artificial Neural Network ◽  
Compressive Strength ◽  
Rock Mass ◽  
Ann Model ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Triaxial Compressive Strength ◽  
Artificial Neural

Rock compressive strength is an important mechanical parameter for the design, excavation, and stability analysis of rock mass engineering in cold regions. Accurate and rapid prediction of rock compressive strength has great engineering value in guiding the efficient construction of rock mass engineering in a cold regions. In this study, the prediction of triaxial compressive strength (TCS) for sandstone subjected to freeze-thaw cycles was proposed using a genetic algorithm (GA) and an artificial neural network (ANN). For this purpose, a database including four model inputs, namely, the longitudinal wave velocity, porosity, confining pressure, and number of freeze-thaw cycles, and one output, the TCS of the rock, was established. The structure, initial connection weights, and biases of the ANN were optimized progressively based on GA. After obtaining the optimal GA-ANN model, the performance of the GA-ANN model was compared with that of a simple ANN model. The results revealed that the proposed hybrid GA-ANN model had a higher accuracy in predicting the testing datasets than the simple ANN model: the root mean square error (RMSE), mean absolute error (MAE), and R squared ( R 2 ) were equal to 1.083, 0.893, and 0.993, respectively, for the hybrid GA-ANN model, while the corresponding values were 2.676, 2.153, and 0.952 for the simple ANN model.

Effects of freeze–thaw on the determination and application of parameters of slope rock mass in cold regions

2015 ◽  
Vol 110 ◽  
pp. 32-37 ◽  
Author(s):  
Xuedong Luo ◽  
Nan Jiang ◽  
Xinyu Fan ◽  
Nianfeng Mei ◽  
Hua Luo
Keyword(s):  
Rock Mass ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Slope Rock

scholarly journals Freeze-Thaw Effects on Stability of Open Pit Slope in High-Altitude and Cold Regions

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yong Hong ◽  
Zhushan Shao ◽  
Guangbin Shi ◽  
Yong Dou ◽  
Weiqin Wang ◽  
...  
Keyword(s):  
Rock Mass ◽  
High Altitude ◽  
Coal Mine ◽  
Mining Area ◽  
Open Pit ◽  
Geological Strength Index ◽  
Correction Coefficient ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Thaw Cycle

The cycle of the freeze-thaw action must be taken into account in the stability analysis of an open pit slope in the high-altitude and cold regions, because the natural process of freeze-thaw poses a significant effect on mechanical properties of the rock mass. To achieve this purpose, a linear relationship between the geological strength index (GSI) and the Tianshan slope rock mass rating (TSMR) system is established considering the effect of the freeze-thaw action by introducing a freeze-thaw correction coefficient δ. The GSI value is modified for rock mass in high-altitude and cold regions. The improved Hoek-Brown criterion considers the influences of the freeze-thaw action and steep and gentle slopes. The research outcome is applied in the No. 4 minefield open pit coal mine in the Muli mining area. Numerical calculations are performed by inputting rock mass mechanical parameters obtained in traditional and modified criterions, to discuss the influences of the freeze-thaw action on the stabilities of both the present mining slope and the final slope at the end of the designed mining. The results show that the safety factors of the original slope are 2.33 and 1.67, respectively, while after the modification, they are 2.14 and 1.61, respectively. In terms of the No. 4 minefield open pit coal mine, the slope stability meets the design requirement, although taking the freeze-thaw cycle into account.

scholarly journals A numerical investigation on the performance of hydraulic fracturing in naturally fractured gas reservoirs based on stimulated rock volume

2020 ◽  
Vol 10 (8) ◽  
pp. 3333-3345
Author(s):  
Ali Al-Rubaie ◽  
Hisham Khaled Ben Mahmud
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Natural Fracture ◽  
Shear Stresses ◽  
Individual Element ◽  
Natural Fractures ◽  
Gas Reservoirs ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Naturally Fractured

Abstract All reservoirs are fractured to some degree. Depending on the density, dimension, orientation and the cementation of natural fractures and the location where the hydraulic fracturing is done, preexisting natural fractures can impact hydraulic fracture propagation and the associated flow capacity. Understanding the interactions between hydraulic fracture and natural fractures is crucial in estimating fracture complexity, stimulated reservoir volume, drained reservoir volume and completion efficiency. However, because of the presence of natural fractures with diffuse penetration and different orientations, the operation is complicated in naturally fractured gas reservoirs. For this purpose, two numerical methods are proposed for simulating the hydraulic fracture in a naturally fractured gas reservoir. However, what hydraulic fracture looks like in the subsurface, especially in unconventional reservoirs, remain elusive, and many times, field observations contradict our common beliefs. In this study, the hydraulic fracture model is considered in terms of the state of tensions, on the interaction between the hydraulic fracture and the natural fracture (45°), and the effect of length and height of hydraulic fracture developed and how to distribute induced stress around the well. In order to determine the direction in which the hydraulic fracture is formed strikethrough, the finite difference method and the individual element for numerical solution are used and simulated. The results indicate that the optimum hydraulic fracture time was when the hydraulic fracture is able to connect natural fractures with large streams and connected to the well, and there is a fundamental difference between the tensile and shear opening. The analysis indicates that the growing hydraulic fracture, the tensile and shear stresses applied to the natural fracture.

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