scholarly journals A Nonlinear Creep Damage Model Considering the Effect of Dry-Wet Cycles of Rocks on Reservoir Bank Slopes

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2396
Author(s):  
Xingang Wang ◽  
Baoqin Lian ◽  
Wenkai Feng
Keyword(s):  
Three Dimensional ◽  
Influential Factor ◽  
Time Dependent ◽  
Secondary Development ◽  
Nonlinear Creep ◽  
Test Results ◽  
Creep Tests ◽  
New Model ◽  
Dependent Behavior ◽  
Rock Creep

Water has a crucial effect on the time-dependent behavior of rocks. The long-term cyclical fluctuations of reservoir water level lead to dry–wet (DW) cycles of rocks on reservoir bank slopes, making this influential factor more complex. To deeply understand the time-dependent behavior of rocks under DW cycles, argillite from the reservoir bank slope of Longtan Hydropower Station was used to perform a series of triaxial creep tests. Subsequently, based on analysis of creep test results after different DW cycles, a damage nonlinear Burgers viscoelastic-plastic (DNBVP) model considering the effect of saturation–dehydration cycles was proposed by introducing a nonlinear viscoplastic body and a damage variable describing DW cycles. Then, the three-dimensional creep equations of the new model were derived and its creep parameters were identified. Comparison between the theoretical curves and the test results shows that the theoretical curves of the DNBVP model were able to describe rock creep tests results after different DW cycles. Furthermore, by comparing classical creep models with the proposed model, it was found that the DNBVP model can accurately reflect the nonlinear characteristics of rocks at the accelerated creep stage. Finally, the sensitivity of the DNBVP model was analyzed and discussed, and three-dimensional central difference expressions necessary for secondary development of the new model were also derived in detail. The proposed new model with secondary development may provide a basis for improving the geotechnical design of reservoir bank slopes and the control of reservoir bank landslides.

Negative creep of soils

2020 ◽  
Vol 57 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Yang-Ping Yao ◽  
Yu-Fei Fang
Keyword(s):  
Three Dimensional ◽  
Yield Function ◽  
Time Dependent ◽  
Flow Rule ◽  
Test Results ◽  
Current Yield ◽  
Compression Tests ◽  
Creep Tests ◽  
Negative Creep ◽  
Over Time

After unloading, the deformation of soils cannot be stable immediately, but continues to expand over time even under constant pressure. In this paper, the expansive deformation over time when effective stress is kept constant is defined as the negative creep, while the compressive creep is described as the positive creep. The division between positive creep and negative creep is named the stable normal compression line (SNCL), on which the stress–strain behaviour of the soil is time-independent. Based on the concept of the SNCL and test results, a new formula for creep is proposed. This formula is simple in form and has less parameters, and both negative creep and positive creep can be well predicted. By incorporating this formula into the current yield function of the unified hardening model, a new time-dependent current yield function is built. Combining the yield function, a flow rule, and transformed stress method, a new three-dimensional time-dependent constitutive model considering both positive and negative creep for clays is derived and presented. The new model is then validated by test results, including multistage loading oedometer tests, triaxial undrained creep tests, and triaxial undrained compression tests at the constant strain rates.

scholarly journals Penetration Grouting Mechanism of Time-Dependent Power-Law Fluid for Reinforcing Loose Gravel Soil

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1391
Author(s):  
Tingting Guo ◽  
Zhiwei Zhang ◽  
Zhiquan Yang ◽  
Yingyan Zhu ◽  
Yi Yang ◽  
...  
Keyword(s):  
Numerical Calculation ◽  
Numerical Simulations ◽  
Power Law ◽  
Three Dimensional ◽  
Time Dependent ◽  
Rheological Parameters ◽  
Power Law Fluid ◽  
Dependent Behavior ◽  
Gravel Soil ◽  
Penetration Grouting

The time-dependent behavior of power-law fluid has a significant influence on the grouting effects of reinforcing loose gravel soil. In this paper, based on basic rheological equations and the time-dependent behavior of rheological parameters (consistency coefficient and rheological index), rheological equations and penetration equations of time-dependent power-law fluid are proposed. Its penetration grouting diffusion mechanism for reinforcing loose gravel soil was then theoretically induced. A set of indoor experimental devices for simulating penetration grouting was designed to simulate the penetration grouting of power-law fluid with different time-dependent behaviors for reinforcing loose gravel soil. Then, relying on the COMSOL Multiphysics platform and Darcy’s law, three-dimensional numerical calculation programs for this mechanism were obtained using secondary-development programming technology. Thus, the numerical simulations of the penetration grouting process of power-law fluid with different time-dependent behaviors for reinforcing loose gravel soil were carried out. This theoretical mechanism was validated by comparing results from theoretical analyses, indoor experiments, and numerical simulations. Research results show that the three-dimensional numerical calculation programs can successfully simulate the penetration diffusion patterns of a time-dependent power-law fluid in loose gravel soil. The theoretical calculation values and numerical simulation values of the diffusion radius obtained from this mechanism are closer to indoor experimental values than those obtained from the penetration grouting diffusion theory of power-law fluid without considering time-dependent behavior. This mechanism can better reflect the penetration grouting diffusion laws of a power-law fluid in loose gravel soil than the theory, which can provide theoretical support and guidance for practical grouting construction.

scholarly journals Mesoscopic time-dependent behavior of rocks based on three-dimensional discrete element grain-based model

2020 ◽  
Vol 121 ◽  
pp. 103472 ◽  
Author(s):  
Teng-Fei Fu ◽  
Tao Xu ◽  
Michael J. Heap ◽  
Philip G. Meredith ◽  
Thomas M. Mitchell
Keyword(s):  
Three Dimensional ◽  
Discrete Element ◽  
Time Dependent ◽  
Dependent Behavior

Development of Time Dependent Stress-Strain Simulation of Clay

2009 ◽  
Vol 25 (1) ◽  
pp. 27-40 ◽  
Author(s):  
C.-Y. Ou ◽  
C.-C. Liu ◽  
C.-K. Chin
Keyword(s):  
Constitutive Law ◽  
Time Dependent ◽  
Soil Behavior ◽  
Creep Tests ◽  
Clay Model ◽  
Model Sets ◽  
Dependent Behavior ◽  
Modified Cam Clay ◽  
Parametric Studies ◽  
Cam Clay

AbstractThe objective of this study is to derive a time dependent effective based constitutive law on the basis of framework of the Modified Cam-Clay model. This model takes into account the anisotropic characteristics and creep behavior, based on the theory of viscoplasticity. The model sets the initial yield surface symmetric to the Ko line for modeling the initial Ko condition. A method is then developed to compute the gyration and expansion of the loading surface to simulate the anisotropic behavior due to the principal stress gyration after shear. The creep or time dependent behavior is considered in the model by adopting Kutter and Sathialingam's model, which was derived from Taylor's secondary consolidation theory and Bjerrum's delayed compression model. Compared with the Modified Cam-Clay model, the model requires five additional parameters to describe the soil behavior. All of the additional parameters can be obtained through conventional soil tests or parametric studies. The model is evaluated through a series of simulation of undrained shear tests and undrained creep tests.

Criteria for defining the required duration of a creep test

2015 ◽  
Vol 52 (7) ◽  
pp. 883-889
Author(s):  
Z. Tomanovic ◽  
B. Miladinovic ◽  
S. Zivaljevic
Keyword(s):  
Creep Test ◽  
Time Dependent ◽  
Rock Properties ◽  
Theoretical Issue ◽  
Plastic State ◽  
Practical Issue ◽  
Compression Tests ◽  
Creep Tests ◽  
Material Parameters ◽  
Rock Creep

Time-dependent behaviour of some types of rocks is of the “creep” type, in particular in underground works, mining works, and in measuring procedures of rock properties. Tests used for defining material parameters or parameters relevant to defining a failure or behaviour of a material in the plastic state are usually of significantly shorter duration than the creep test. The duration of creep tests may vary from several hours to several years depending on the material being tested and the phenomenon that is the subject of the research. The required duration of the creep test, which provides reliable definition of the time-dependent material parameters of the rheological model, is a theoretical but also practical issue. The theoretical issue relates to establishing criteria for defining the required duration of the creep test. The practical issue relates to minimizing the duration of the creep test from which the necessary material parameters of the rock mass are obtained for correct numerical calculations. This paper proposes criteria for defining the required duration of a rock creep test, based on analysis of the results of unconfined uniaxial compression tests performed on marly rock samples.

Time-Dependent Behavior of Diabase and a Nonlinear Creep Model

2013 ◽  
Vol 47 (4) ◽  
pp. 1211-1224 ◽  
Author(s):  
Wendong Yang ◽  
Qiangyong Zhang ◽  
Shucai Li ◽  
Shugang Wang
Keyword(s):  
Time Dependent ◽  
Creep Model ◽  
Nonlinear Creep ◽  
Dependent Behavior

scholarly journals Time-Dependent Behavior of a Circular Symmetrical Tunnel Supported with Rockbolts

Symmetry ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 381 ◽  
Author(s):  
Wei Han ◽  
Gang Wang ◽  
Chuanzheng Liu ◽  
Hengjie Luan ◽  
Ke Wang
Keyword(s):  
Rock Mass ◽  
Initial Stress ◽  
Three Dimensional ◽  
Support Effect ◽  
Time Dependent ◽  
Force Model ◽  
Reinforcement Effect ◽  
Creep Stage ◽  
Burgers Model ◽  
Dependent Behavior

Under the effect of initial stress and excavation disturbance, there exists interaction between rock mass and rockbolt in deeply buried tunnels. In order to fully explore the mechanism of rock mass supported with rockbolts, this article studied the time-dependent behavior of the rock mass supported with discretely mechanically or frictionally coupled (DMFC) rockbolts. The interaction model elastic solutions under distributed force model were analyzed, then the viscoelastic analytical solutions were conducted to describe the rheological properties of the coupling model, and the solutions were acquired by setting the constitutive models of the rockbolt and rock mass in terms of a one-dimensional Kelvin model and a three-dimensional Burgers model based on material properties and dimension. Several examples were performed and the influence of initial stress σ0, the viscosity parameters η1 and η2 of the three-dimensional Burgers model as well as the pre-tension T0 on reinforcement effect were analyzed. According to the proposed model, the smaller η2 is or the larger the pre-tension T0 is, the more effective the support effect. However, when the pre-tension is too large, the support effect is no longer significantly enhanced. In addition, the early reinforcement effect is controlled by the first creep stage in the Burgers model while the ultimate support effect is mainly influenced by the viscosity coefficient of the second creep stage in the Burgers model. This research can provide an important theoretical reference to guide the parameter design of rockbolt reinforcement engineering in a circular symmetrical tunnel.

Faktor yang Berhubungan dengan Penggunaan Partograf dalam Persalinan oleh Bidan Praktik Mandiri

2020 ◽  
Vol 2 (2) ◽  
pp. 72-80
Author(s):  
Niluh Nita Silfia
Keyword(s):  
Total Population ◽  
Sampling Technique ◽  
Population Data ◽  
Statistical Test ◽  
Influential Factor ◽  
Test Results ◽  
Cross Sectional ◽  
Factors Associated ◽  
Survey Results ◽  
Research Criteria

Partographs are guidelines for childbirth observations that will facilitate labor assistants in first identifying emergency cases and complications for mothers and fetuses. Preliminary survey at the Sigi Community Health Sub-Center (Pustu) of the 8 Pustu midwives found two midwives (25%) to complete a complete partograph, six midwives (75%) incomplete. The purpose of this study was to determine the determinant factors associated with the use of partographs in labor. The design of this study used observational analytic methods with a cross-sectional approach. 24 BPM survey results were obtained with 30 samples of midwives who met the research criteria and data completeness. The sampling technique was by the total population. Data analysis used logistic regression. The multivariate analysis results showed that APN training was the most influential factor in the use of partographs in labor by midwives. Statistical test results obtained a POR value of 37.7 (95% CI 12.1 - 60.2). This study suggests that midwives must have APN certificates to be valid in providing services.

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