scholarly journals Hydromechanical Coupling Characteristics of the Fractured Sandstone under Cyclic Loading-Unloading

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Tong Zhang ◽  
Yang Liu ◽  
Ke Yang ◽  
Ming Tang ◽  
Xiang Yu ◽  
...  
Keyword(s):  
Rock Mass ◽  
Cyclic Loading ◽  
Enhancement Effect ◽  
Single Fracture ◽  
Hydraulic Pressure ◽  
Fracture Permeability ◽  
Confining Stress ◽  
Axial Cyclic Loading ◽  
Residual Strains ◽  
Fractured Sandstone

The mechanical and hydraulic properties of rock mass play a crucial role in underground engineering. To study the effect of hydraulic pressure, confining pressure, and axial cyclic loading-unloading on variation of the deformation and permeability in fractured rock mass, the coupling triaxial experiment of sandstone was conducted. The concept of permeability recovery rate (PRR) and permeability enhancement reduction rate (PERR) was proposed to characterize the change in permeability. The results show that the permeability of fractured sandstone quadratically varies with the change of hydraulic pressure and confining stress. In detail, the permeability decreases with the decrease of hydraulic pressure and increases with the decrease of confining stress, respectively. Compared with the single-fracture permeability, the double-fracture permeability is more sensitive to the change of hydraulic pressure. Furthermore, the permeability of fractured sandstone is more dependent on the hydraulic pressure than the confining stress. With the performance of axial cyclic loading-unloading, the permeability spirals down, and both the axial and radial residual strains quadratically evolve. Following the first axial cyclic loading-unloading, an obvious deformation memory phenomenon characterized by a parallelogram shape in axial stress-strain curves was observed for the sandstone. The cumulative PRR of 85%-95% was maintained in double-fracture sandstone. On the contrary, a fluctuation of cumulative PRR characterized by “V shape” was observed for single-fracture sandstone. The enhancement effect of axial cyclic loading on the permeability was characterized by the decrease of PERR for double-fracture sandstone and increase of PERR with a greater gradient for single-fracture sandstone.

scholarly journals Experimental Study on Seepage Properties of Postpeak Fractured Rocks under Cyclic Loading-Unloading Confining Stress and Axial Stress

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xiaobo Zhang ◽  
Zuhao Xia ◽  
Chi Yao ◽  
Jianhua Yang ◽  
Mingdong Yang
Keyword(s):  
Cyclic Loading ◽  
Permeability Coefficient ◽  
Fractured Rocks ◽  
Axial Stress ◽  
Rock Fracture ◽  
Complex Loading ◽  
Seepage Flow ◽  
Confining Stress ◽  
Fractured Sandstone ◽  
Seepage Properties

Excavation in rock masses always encounters safety problems from rock fracture seepage in water-rich areas, which needs to be paid much attention, especially for fractured rocks under complicated stress state. For this reason, the permeability of fractured sandstone and granite is experimentally investigated under cyclic loading-unloading confining stress and axial stress. The variation of permeability coefficient and seepage flow with increasing and decreasing the confining stress and axial stress are comprehensively analyzed. Results show that the changing patterns of permeability with loading-unloading cycles of confining stress for both fractured sandstone and granite are similar. The permeability is most sensitive to the initial loading-unloading stages. After several loading-unloading cycles, the confining stress has little effect on permeability. The seepage flow decreases as the confining stress is unloaded to the same level in the loading process, indicating a hysteresis effect on the recovery of seepage capacity. The seepage properties under cyclic loading-unloading the axial stress are quite different from those under the confining stress. The permeability of fractured sandstone is most sensitive to the first cycle of loading-unloading of axial stress. The irrecoverable shear slide between fractures under the axial stress causes dilatancy or contraction, which makes the permeability coefficient to consecutively decrease at the subsequent cycles. The permeability of granite first decreases during the first loading of axial stress, while this trend is disordered at the subsequent stages no matter loading or unloading the axial stress. This is because of the accumulation of breakage fragments between fractures, which further disturbs the seepage flow. These findings may be useful for further understanding the seepage properties of fractured granite and sandstone under complex loading-unloading history.

scholarly journals A Finite Element Study on Compressive Resistance Degradation of Square and Circular Steel Braces under Axial Cyclic Loading

2021 ◽  
Vol 11 (13) ◽  
pp. 6094
Author(s):  
Hubdar Hussain ◽  
Xiangyu Gao ◽  
Anqi Shi
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Cyclic Loading ◽  
Slenderness Ratio ◽  
Hysteretic Behavior ◽  
Element Analysis ◽  
Section Shape ◽  
Axial Cyclic Loading ◽  
Global Buckling ◽  
Parametric Studies

In this study, detailed finite element analysis was conducted to examine the seismic performance of square and circular hollow steel braces under axial cyclic loading. Finite element models of braces were constructed using ABAQUS finite element analysis (FEA) software and validated with experimental results from previous papers to expand the specimen’s matrix. The influences of cross-section shape, slenderness ratio, and width/diameter-to-thickness ratio on hysteretic behavior and compressive-tensile strength degradation were studied. Simulation results of parametric studies show that both square and circular hollow braces have a better cyclic performance with smaller slenderness and width/diameter-to-thickness ratios, and their compressive-tensile resistances ratio significantly decreases from cycle to cycle after the occurrence of the global buckling of braces.

Fatigue Failure Model for Composite Laminates under Multi-Axial Cyclic Loading

2000 ◽  
Vol 183-187 ◽  
pp. 945-950 ◽  
Author(s):  
Chong Soo Lee ◽  
W. Hwang ◽  
Hyun Chul Park ◽  
Kyung Seop Han
Keyword(s):  
Cyclic Loading ◽  
Fatigue Failure ◽  
Composite Laminates ◽  
Failure Model ◽  
Axial Cyclic Loading

scholarly journals Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

2018 ◽  
Vol 55 (11) ◽  
pp. 1577-1591 ◽  
Author(s):  
R.M. Buckley ◽  
R.J. Jardine ◽  
S. Kontoe ◽  
B.M. Lehane
Keyword(s):  
Cyclic Loading ◽  
Effective Stress ◽  
Test Site ◽  
Static Tension ◽  
Load Testing ◽  
Stress Regime ◽  
Effective Stresses ◽  
Axial Cyclic Loading ◽  
Tension Testing ◽  
Static And Cyclic Loading

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.

scholarly journals Flow characteristics of fractal fracture with different fractal dimension and different fracture width

2021 ◽  
Vol 25 (6 Part B) ◽  
pp. 4477-4484
Author(s):  
Jun-Jun Liu ◽  
Jing Xie ◽  
Yi-Ting Liu ◽  
Gui-Kang Liu ◽  
Rui-Feng Tang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Rock Mass ◽  
Flow Characteristics ◽  
Fracture Network ◽  
Basic Element ◽  
Single Fracture ◽  
Flow State ◽  
Complex Flow ◽  
Fracture Width ◽  
Fracture Models

Single fracture is the most basic element in complex fracture network of rock mass. Therefore, the study of flow characteristics of single fracture is an important way to reasonably predict the complex flow state in engineering rock mass. In order to study the flow characteristics of fractal single fracture, fracture models with dif?ferent fractal dimension and different fracture width are established in this paper. The results show that: the blocking effect of rough structure on fluid is obviously enhanced under high pressure. In addition, it is weakened and reaches a steady-state with the increase of fracture fractal dimension. The larger the fracture width is, the more obvious the phenomenon is. The hydraulic gradient index tends to 0.5 with the increase of fracture width when fractal dimension is greater than 1.3. It also could tend to 0.5 with the increase of fractal dimension when fracture width is greater than 1 mm.

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