Attenuation Creep Research Articles

The creep characteristics and related evolution of particle morphology for calcareous sand

In the study, the creep characteristics and meso-mechanism of calcareous sand under different stresses are explored through triaxial creep tests. The influence of particle size on calcareous sand creep is also considered. Furthermore, the particularity of calcareous sand creep is revealed by comparing with the creep behavior of silica sand. The results show that during creep, the calcareous sand is more stable than silica sand due to the interlocking of irregular particles. When creep deviatoric stress is small, the creep of calcareous sand is manifested as nonlinear attenuation creep (primary creep), and the creep deformation is smooth without creep failure. With the increase of creep deviatoric stress, the creep deformation is concentrated, resulting in a strain concentration zone similar to the shear band, and the associated creep rate first decreases and then suddenly increases, finally, creep failure occurs. With increasing particle size of calcareous sand, the particle crushing increases, which induces a higher creep deformation, however, the overall creep failure is not generated. During the graded creep of calcareous sand, an obvious creep structural effect is observed, which is temporary and results in a significantly reduction of creep rate. Only after the previous creep structure effect is destroyed by the continuously creep process, the creep response can restore to its original behavior. The meso-behavior is represented by particle morphology, i.e., the fractal dimension and aspect ratio. It is found that both confining pressure and particle size can influence the evolution of particle morphology during creep. With the increase of confining pressure, the fractal dimension of calcareous sand decreases which means that particle grinding is always existent, while the aspect ratio of small-sized calcareous sand after creep decreases first and then stabilizes (slightly increases), suggesting that the overall particle breakage is the main cause of deformation. However, the aspect ratio of large-sized calcareous sand continually decreases, indicating that the main contribution for its deformation is angular cracking. The mesoscopic behavior of silica sand is basically unaffected by creep, and its creep deformation is mainly caused by particle rearrangement.

Effects of shear stress path and roughness on shear creep behavior of marine clay-concrete interface

Floating piles have been widely employed as foundations in coastal regions abounding with marine clay. A growing concern for these floating piles is their long-term performance of bearing capacity. To better understand the time-dependent mechanisms behind the bearing capacity, in this paper a series of shear creep tests was conducted to study the effects of load paths/steps and roughness on shear strain of the marine clay-concrete interface. Four main empirical features were observed from the experimental results. First, the creep process of the marine clay-concrete interface can be largely decomposed into the instantaneous creep stage, the attenuation creep stage and the uniform creep stage. Second, the creep stability time and the shear creep displacement generally increase as the shear stress level increases. Third, the shear displacement rises as the number of loading steps drops under the same shear stress. The fourth feature is that under the shear stress condition, the rougher the interface is, the smaller the shear displacement is. Besides, the load-unloading shear creep tests suggest that: (a) shear creep displacement typically contains both viscoelastic and viscoplastic deformation; and (b) the proportion of unrecoverable plastic deformation increases with increasing shear stress. These tests confirm that the Nishihara model can provide a well-defined description of the shear creep behavior of marine clay-concrete interfaces.

Constructing a three-dimensional creep model for rocks and soils based on memory-dependent derivatives: A theoretical and experimental study

Creep characteristics of rocks directly determine the long-term safety of deep rock mass engineering. In the present proposed framework of memory-dependent (M-D) derivative theory, different M-D elements are constructed and combined to be a memory-dependent derivative creep (MDDC) model with four single elements in this paper. In accordance with the generalized plastic mechanics theory, the one-dimensional MDDC model is extended to a three-dimensional MDDC model. The instantaneous deformation is described by the Hooke body, while the attenuation creep and steady state creep are described by the M-D Kelvin body, and the accelerated creep by the strain-triggered M-D dashpot. The creep test data of sandstone, coal rock, clay, and strongly weathered sandstone are fitted by the MDDC model, Riemann-Liouville type fractional model, Caputo type fractional model, and Burgers model. The results showed that the MDDC model has the highest accuracy and broadest applicability in characterizing the creep of rocks and soils under different stress paths. The MDDC model has a good capacity to describe the creep at the nonlinear accelerated creep stage without detrimentally impacting the memory effect over time. It is thus far more superior to the element combination model and the fractional model.

Experimental Study on Creep Characteristics and Long–Term Strength of Anthracite

Coal pillars from old mines undergo creep, a type of time−dependent deformation. Research on underground engineering stability of coal mines has increasingly focused on long−term strength as an important mechanical index of the creep characteristics of coal pillars. This study performed conventional triaxial compression and triaxial creep tests of anthracite under different confining pressures. The creep law of anthracite and the long−term strength of anthracite was studied according to the test results. The test results demonstrated the following: (1) The conventional elastic modulus and peak strain of anthracite increased exponentially with the confining pressure. (2) Under low stress levels, anthracite exhibited only instantaneous deformation and attenuation creep. In contrast, anthracite exhibited instantaneous deformation, attenuation creep, and steady creep under high stress levels; accelerated creep occurred until failure when the stress reached a particular value. (3) By fitting the steady−state creep rate of anthracite under high stress levels, the functional relationship between axial stress and steady−state creep rate was established, and the threshold of the steady−state creep rate in high−stress−level areas was suggested as the optimum long−term strength of anthracite. (4) The ratio of the long−term strength to instantaneous strength under various confining pressure grades ranged from 70% to 91%.

Experimental research on consolidation creep characteristics and microstructure evolution of soft soil

The influence of creep deformation of soft soil on engineering construction can’t be ignored. In order to deeply understand the macroscopic mechanical properties and the evolution mechanism of soft soil in microscope during consolidation creep, one-dimensional consolidation creep tests and SEM tests of Nansha soft soil were carried out in this paper. Then the image processing was performed by Image J software to obtain the consolidation creep characteristics, microscopic parameters of particles and pores under different loading pressures. The results of experiment and image processing show that 1) The creep process of Nansha soft soil is divided into the initial instantaneous deformation phase, the attenuation creep phase and the stable creep phase. The creep deformation increases with the consolidation creep stress during the three phases. 2) During the creep process, the distance between particles decreases and some particles are gradually broken, the quantity of particles and pores increases but the volume of them decreases. At the same time, the shape of particles and pores changes from nearly round and strip to nearly oval. 3) The consolidation creep stress determines the particles distance and the degree of fragmentation. And this trend is more obvious with the increase of the consolidation creep stress.

Creep Behavior and Its Prediction of Saturated Weakly Cemented Medium-Grained Sandstone under Multiaxial Loadings

Weakly cemented medium-grained sandstone in Ordos mining area of China is widely distributed under phreatic water. The creep behavior of saturated rock is important for the stability of water-resisting strata. In this paper, creep mechanical properties of saturated medium-grained sandstone were studied by triaxial rheological test. The results showed that medium-grained sandstone only shows attenuation creep and stable creep under low stress level, and accelerated creep occurs when axial load reaches about 75% of instantaneous compressive strength. The rock samples exhibit volume dilatancy under most loading levels and finally shear fracture. The failure mechanism is the dislocation separation of mineral particles. Based on the energy dissipation theory, the damage evolution equation was modified and introduced into the Burgers model, which can accurately describe the rheological behavior of saturated medium-grained sandstone. The modified model was used to predict the crack initiation time under different deviatoric stresses, which can provide guidance for early warning of water-resisting rock stability.

Creep Characteristics of Soil in the Sliding Zone of Huangtupo Landslide

The reservoir water level in the Three Gorges Reservoir (TGR) of the Yangtze River is adjusted between 145 m and 175 m throughout the year. The landslide below the reservoir water level bears periodic dynamic seepage pressure on the basis of the original steady-state water pressure. In the process of rising reservoir water levels in particular, the effective stress on the sliding zone soil below the reservoir water level line is reduced, and the sliding zone soil shows an unloading state. In order to study the creep characteristics of landslides in a reservoir area, direct shear creep tests of the sliding zone soil in the Huangtupo landslide in an unloading state were carried out in this study. The test results show that the creep characteristics of the sliding zone soil are obvious. The creep curve of the sliding zone soil presents an attenuation creep stage with low shear stress, which is mainly manifested as an elastic creep. However, with the increase in the shear stress, the creep curve of the sliding zone soil presents a steady creep stage, which is mainly manifested as viscoelastic creep. The nonlinear creep characteristics of the sliding zone soil are related to the creep time, stress level, and soil porosity. The longer the creep time, the greater the stress level and the denser the soil, the more obvious the nonlinear creep characteristics of the sliding zone soil. In this study, the Burgers model was used to fit the creep curve of the sliding zone soil, and the fitting effect was good, which indicates that the Burgers model can sufficiently describe the unloading state creep characteristics of the sliding zone soil in the Huangtupo landslide.

Stress–Strain–Time Description and Analysis of Frozen–Thawed Silty Clay under Low Stress Level

The construction of high-speed railways in cold regions needs to consider the effects of freeze–thaw cycles (FTHs) on the long-term deformation of subgrades. However, at present, research on the creep characteristics of frozen–thawed rocks and soils is not extensive. In the limited studies on frozen–thawed soil creep properties, current research focuses more on high stress–strain–time responses, but for the subgrades, the inner stress is usually low. This paper presents the results of triaxial compression creep tests on remolded, frozen–thawed silty clay sampled in the Yichun-Tieli area and describes its stress–strain–time relationship in an arctan function-based mathematical model. Each creep test condition is studied using three specimens. Frozen–thawed silty clay exhibits attenuation creep under low-level stress. In general, from 4 FTHs to 11 FTHs, the mean elasticity modulus decreases first, and then, increases. The exerted stress is higher than the yield stress; the more FTHs the specimens experience, the more time they need to be deformed stably under the same axial deviatoric stress (ADS). Under the same mean ADS, the mean stable strain of 7 FTHs exceeds the other two FTH conditions and, in general, the mean stable strain of 4 FTHs exceeds 11 FTHs. By dissecting the phenomena, it can be concluded that with FTHs increasing, moisture and voids reconstitute in the process; the elastic strain accounts for most of the total strain and significantly decides the extent of creep deformation; the arctan function-based model is basically able to describe, but not perfectly predict, the stress–strain–time relationship of frozen–thawed silty clay.

Testing the shearing creep of composite geomembranes-cushion interface and its empirical model

An accurate description of composite geomembranes (CGs)–cushion interface behaviour (particularly creep behaviour) is of great importance. This paper presents a creep experiment method for studying the shearing creep characteristics of CGs–cushion interfaces. In this study, natural sand and sandy gravel cushion materials were tested for their creep characteristics with CGs. In the proposed method, the shearing creep curves of CGs–cushion interfaces in multi-stage loading are obtained, and they can be transformed to the creep curve at each specific loading level with Chen’s method. The results show that the power function and modified hyperbolic function exhibit perfect performance in fitting the displacement–stress and displacement–time relationships, respectively. An original empirical creep model for the CGs–cushion interface was established on the basis of these fitting means; it was found to exhibit superior performance in fitting and predicting the attenuation creep curve at each stress level. An accelerating creep model applicable to the accelerating creep phase is presented by using the Kachanov damage factor to reflect the accelerating creep damage to CGs–cushion interface. The study provides enhanced guidance for the engineering design and construction of structures incorporating CGs.

Long‐Term and Short‐Term Creep Characteristic Analysis for HTPB Propellant

AbstractA solid rocket motor is in storage for most of its life cycle, and propellant creep occurs subjected to gravity load. To analyse the creep characteristics of HTPB propellant during long‐term storage, MSC Marc is used to calculate the maximum von Mises stress of the motor under horizontal and vertical storage conditions. Based on the numerical results, the short‐term reciprocating creep test and long‐term creep test are designed and carried out. The results illustrate that the process of propellant creep from deformation to final failure can be divided into four stages: instantaneous deformation stage, attenuation creep stage, steady‐state creep stage and accelerated creep failure stage. When the creep stress level is less than 0.1 MPa, the creep characteristics tend to be stable. When the creep strain exceeds a certain critical value, the propellant will enter the steady‐state creep stage. The damage caused by creep rises with the increase of creep time and stress. When the maximum creep strain is less than 10 %, the creep damage can be fully recovered. The splicing curve of short‐term creep test data is in good agreement with that of long‐term creep test data. A mechanical long‐term creep test method is provided, and the parameters of the modified Burgers model are fitted. The text methods and conclusions can provide a reference for the evaluation of structural integrity and storage life of solid motor.

Numerical Simulation of Non-Stationary Parameter Creep Large Deformation Mechanism of Deep Soft Rock Tunnel

The accelerated creep plays an important role in the disasters of soft-rock tunnels under high stress. However, most of previous studies only involved attenuation creep and uniform creep. Large deformation disasters of soft rock occurred during the tunneling process in the Qianzhou–Sanyangchuan Tunnel, Gusu Province, China. In the paper, we developed the nonlinear generalized Nishihara rheological model with non-stationary parameter creep (NGNRM) to simulate the accelerated creep behaviors of soft rocks under high stress, and implemented it in ABAQUS, to reveal the mechanism of large deformation of soft rock. We proposed the multi-objective back analysis method of surrounding rock mechanical parameters based on the eXtreme Gradient Boosting and the non-dominated sorting genetic algorithm-II. In addition, the orthogonal test design method was used to determine the main parameters affecting the displacement of the tunnel. Using the proposed method, we can evaluate the large deformation mechanism of deep soft rock tunnels, and scientifically determine when to reinforce to prevent a large deformation disaster of the tunnel.

Shear creep mechanical properties and damage model of mudstone in open-pit coal mine

Clarifying the shear creep characteristics of rock and scientifically analyzing its creep deformation law is the key to solving the problem of safe construction and long-term stability analysis of the open-pit coal slope rock mass. Shear creep tests were carried out on mudstone from an open-pit coal mine in Eastern Mongolia to reveal the creep characteristics of mudstone under different normal and shear stresses. Based on the classical Nishihara model, a new composite six-element nonlinear shear creep damage model is established by introducing nonlinear elastomers. Using the least square method, model verification and parameter identification are carried out on the variable test data. At the same time, the influence law of the model parameters on the rock creep deformation is analyzed according to the theoretical curve. The study results showed that the nonlinear shear creeps damage model could better describe the creep characteristics of rock different normal stress and shear stress levels, significantly the non-linear both the strain and time of attenuation creep and accelerated creep. The creep characteristics of the accelerated creep stage described by this model are better than those described by the classical Nishihara model. The model curve is consistent with the changing trend of the experimental data, and the degree of agreement is very high. The correlation coefficients are all above 0.98, which verifies the accuracy and rationality of the model. The influence law of creep parameters is analyzed. The parameters b and c increase nonlinearly with creep. The increase of λ accelerates the process of rock attenuation creep stage; the increase of η10 slows down the progress of rock decay creep stage; with the increase of α, the deformation and creep rate of rock in accelerated creep stage gradually increase. When η2 increases, the deformation in the acceleration stage decreases gradually. The research results can provide important theoretical support for the safe construction and long-term stability analysis of open-pit coal slope rock masses.

Construction of nonlinear creep damage model of frozen sandstone based on fractional-order theory

The frozen wall of a coal mine vertical shaft undergoes creep deformation under long-term load, and excessive deformation induces damage to the frozen wall. The creep behaviour of frozen rock is key in controlling the long-term stability of frozen walls. In this study, Cretaceous saturated frozen sandstone was used as the research object to conduct creep mechanics tests under different confining pressure conditions. Based on the Riemann-Liouville-type integral function, a 6-element frozen sandstone nonlinear creep constitutive equation considering temperature–damage–stress coupling was established and verified by experimental data. The results show that: compared with the rock creep test at 20 °C, the creep process of saturated frozen sandstone also presents an attenuation creep stage, a steady-state creep stage, and an accelerated creep stage. A nonlinear creep damage equation is established based on the fractional-order theory. Comparing the theoretical formula with the experimental data, it was found that the agreement was higher. The research results can provide a theoretical and experimental basis for evaluating creep-induced instability and failure of frozen walls.

Creep damage model of rock with varying-parameter under the step loading and unloading conditions

The creep characteristics of rock under step loading and unloading conditions were investigated in this study. Based on the generalized Burgers model, the total strain of rock was decomposed into elastic, viscoelastic, varying-parameter viscoelastic, and viscoplastic strains considering the damage. The four strains were connected in series to establish a new varying-parameter creep damage model that can characterize the creep characteristics of rock under step loading and unloading conditions as well as identify and verify the model parameters. The study results showed that the varying-parameter creep damage model could better describe the creep characteristics of rock under step loading and unloading conditions, significantly the non-linear both the strain and time of attenuation creep and accelerated creep. The model fitting curve was highly consistent with the experimental data, and the correlation coefficient R2 was greater than 0.98, which thoroughly verified the accuracy and rationality of the model. These findings can provide theoretical support for analyzing the deformation and long-term stability of rock and soil.

A Test Method for Creep Characteristics of Loess Based on the One-Dimensional Consolidator

When the traditional one-dimensional consolidator is used to study the creep characteristics of loess, due to the hoop effect of the ring cutter, only the attenuation creep stage and stable creep stage of loess can be studied, but the accelerated creep stage cannot be presented. In order to avoid the influence of drilling on the creep characteristics of loess, the paper improves the consolidation instrument by drilling holes along the diameter direction in the center of the sample to provide artificial space for soil failure. At the same time, the sample size is increased to ensure that the diameter of the sample is greater than five times of the diameter of the borehole, so as to avoid the influence of drilling on the creep characteristics of loess. The creep characteristics of loess are studied by step loading (vertical pressure at all levels is 125 kPa, 175 Pa, 225 kPa, and 275 kPa), and the whole creep process characteristic curves of loess under different stress conditions are obtained. An endoscope was placed in the hole to observe the deformation and failure characteristics of loess in different stages of creep. This method makes up for the defect that the traditional one-dimensional consolidator cannot obtain the whole process characteristics of loess creep. At the same time, it has the advantages of simple operation, less external influence factors, stronger data reliability, and can directly observe the changes of loess creep soil. It has a beneficial role in promoting the experimental research of loess creep characteristics.

Creep Properties of Expansive Soils under Triaxial Drained Conditions and its Nonlinear Constitutive Model

The creep behaviors of expansive soils play an important role in landslide prediction and long-term stability analysis. In this paper, triaxial drained compression creep tests of expansive soils were conducted on the improved stress-controlled triaxial apparatus. The test results show that only transient deformation and attenuation creep occur with low deviator stress, and the increment of axial strain increases exponentially with deviator stress increasing; while deviator stress reaches a certain value, attenuation creep, steady creep and accelerated creep all occur in a creep curve. Meanwhile, the volumetric strain presents the shear shrinkage characteristic at the initial stage of loading, and the shear shrinkage is small. With the extension of loading time, the volumetric strain gradually varies from shear contraction to dilatancy. When entering the accelerated creep stage, the development rate of volumetric strain increases sharply. Besides, isochronous stress-strain curves of expansive soils indicate that their creep process possesses nonlinear characteristics, and the nonlinear degree is related to creep time and stress level. Imitating the empirical formula of cyclic cumulative deformation of clay, a new nonlinear creep model is presented, which may well describe the creep property of expansive soils. Furthermore, critical failure stress could be obtained based on the proposed creep model. The ratio of the critical failure stress to conventional shear failure stress ranges from 70% to 80%, with average of 75.56%, therefore, critical failure stress may be estimated by conventional triaxial tests with the margin of error 5.5% within.

Study of Creep Mechanical Properties and a Rheological Model of Sandstone under Disturbance Loads

The stress environments of rock masses are complex. To explore the mechanical properties of sandstone under earthquake or disturbance loads, laboratory triaxial creep tests under different disturbance loads were conducted on sandstone from Fuxin, Liaoning Province, China. Given the disturbance load, a creep deformation pattern for sandstone was analyzed, and the influence of the disturbance load on the mechanical properties of rock was considered. Thus, a constitutive model of rock under creep disturbance load was established. The results show that (1) the creep curve can be divided into four stages: attenuation creep, steady creep, disturbance creep, and acceleration creep; the increment of disturbance creep varies for different disturbance loads and the larger the disturbance load, the larger the disturbance creep deformation; (2) with increasing disturbance loads, the long-term strength, failure time, and elastic modulus of sandstone decreases linearly, while the peak strain increases; and (3) considering the influence of the disturbance load and introducing an acceleration element to modify the Nishihara model, a constitutive model describing the whole deformation process of sandstone under creep disturbance load was established. The accuracy of the model was verified by test data and provides a theoretical basis for rock mass stability analysis.

A Time-Dependent Creep Constitutive Model of Deep Surrounding Rock under Temperature-Stress Coupling

In order to study the creep behavior of the surrounding rock of Hengda coal mine in Fuxin under different temperatures, the triaxial creep test of sandstone is carried out by the MTS815.02 test system. The relationship between damage variables and temperature is constructed based on the Weibull distribution of the meso-probability voxel intensity. Aiming at the nonlinear characteristics of rock creep, a nonlinear viscous pot element and a nonlinear spring element are proposed. The two linear viscous pot elements and one linear spring element in the Nishihara model can be replaced separately. Thus, an unsteady parameter creep model is established. The comparison between the Nishihara model curve and the model and the experimental curves in this article has been added to the article. Furthermore, the superiority of this model can be proved. The results show that the established variable-time aging creep model not only can describe the rock attenuation creep and stable creep deformation characteristics but also can make up for the shortcomings of the traditional creep model that cannot describe the accelerated creep characteristics. Moreover, it predicts the development law of creep deformation well. The model is in good agreement with the test curve, which shows the correctness and rationality of the model. It has guiding significance for actual engineering support and prediction of long-term deformation of surrounding rock.

Evaluating the creep characteristics of recycled construction waste materials under saturated and dry condition

The creep deformation characteristics of recycled construction and demolition waste (CDW) filler are important factors affecting its road performance. In this paper, a series of laboratory tests are carried out on CDW filler, including gradation test, compaction test, California bearing ratio (CBR) test, and creep test, and the road performance of different ratios of recycled CDW filler is systematically studied. The mechanical properties of different ratios of CDW materials can meet the requirements of subgrade filler in the specification. Through the creep test, it can be seen that the elastic-plastic deformation speed of CDW material is fast and the duration is short. The creep deformation stage is opposite. Combined with the theoretical analysis, it is found that the t/e-t curve under each stress level has a good linear relationship. The relationship between strain and time is hyperbolic, and the relationship between parameters A, B, and load is a power function. The creep process belongs to attenuation creep, which conforms to the Kelvin model.

Experimental study on creep properties of salt rock under long-period cyclic loading

To study the creep behavior of salt rock under long-period cyclic loading, uniaxial long-period cyclic load creep tests on salt rock specimens under different maximum cycling stresses and periods were carried out. The results indicated that when the maximum cycling stress was greater than 22 MPa, the axial stress-train curve in a single cycle of salt rock could be divided into five stages. When the maximum cycling stress did not exceed 22 MPa and the number of cycles was small, the axial stress-strain curve in a single cycle could still be divided into five stage. However, as the number of cycles increased, stage III gradually disappeared. When a failure occurred, as the number of cycles increased, the maximum creep rate corresponding to the salt rock when it was loaded to the maximum cycling stress showed a trend of “gradually decreasing-basically unchanged-gradually increasing”, and the creep process could be divided into attenuation creep, steady-state creep and accelerated creep stages. When there was no damage, the creep process only included attenuation creep and steady-state creep stages. As the number of cycles increased, the elastic modulus showed a trend of “gradual increase (stage 1)-basically unchanged (stage 2)”. The increment of elastic modulus in stage 1 and the average value of elastic modulus in stage 2 both increased with an increase in the period and the maximum cycling stress. When the maximum cycling stress was the same, there was a critical value for the number of cycles. When the number of cycles did not exceed the critical value, the longer the period, and greater the cumulative irreversible deformation. When the number of cycles exceeded the critical value, the shorter the period, the greater the cumulative irreversible deformation. On the other hand, when the period was the same, the greater the maximum cycling stress, the greater the cumulative irreversible deformation.