Long-term Slope Stability Research Articles

Seepage and stability analysis of hydraulically anisotropic unsaturated infinite slopes under steady infiltration

An analytical model is derived for predicting the flow field and stability of an unsaturated infinite slope subjected to steady infiltration. The proposed model is novel because it accounts for the hydraulic anisotropy of unsaturated soil. The governing equation for steady-state seepage in an infinite slope is established in terms of matric suction under a constant surface flux boundary condition. On the basis of the available experimental findings on the hydraulic anisotropy behavior of unsaturated soils, the relative hydraulic conductivity for a soil under unsaturated conditions with respect to the soil at saturation is postulated to be a direction-independent scalar. This postulation simplifies the governing equation to a form that is directly solvable via the relative hydraulic conductivity and the saturated hydraulic conductivity tensor. To enable sophisticated applications, an exponential law and a power law that are well established in the unsaturated soil literature are used to relate the relative hydraulic conductivity to the matric suction and the effective degree of saturation, respectively. Closed-form solutions are derived for the matric suction, the flow net (potential function and stream function), and the effective degree of saturation. Analytical solutions are also derived for the soil unit weight and overburden stress. These solutions are incorporated into the unsaturated infinite slope stability formula constructed on a suction stress-based effective stress failure criterion. Hydraulic anisotropy has been shown to directly affect the flow field and the change in matric suction, which, in turn, drastically affects the slope safety factor against shallow landslides. This finding demonstrates that neglecting hydraulic anisotropy can cause a considerable overestimation of the safety factor, resulting in an unsafe slope stability prediction. The proposed model is useful for preliminary evaluation of the long-term stability of unsaturated slopes during wet periods and the antecedent slope conditions for shallow landslide initiation under transient infiltration.

A Study on the Dynamic Response and Deformation of Slopes Supported by Anti-Slide Piles Subjected to Seismic Waves with Different Spectral Characteristics

The long-term stability of slopes in areas with strong earthquakes not only is very important for people’s lives and the safety of property, but also it enables restoration of the ecological environment in the landslide areas, which is very important for sustainable development. The most commonly used seismic-support method, anti-slide piles, provides outstanding seismic performance. However, piles still deform and fail during earthquakes, which can lead to instability of the slope. The dynamic response of a slope reinforced with anti-slide piles is crucial for maintaining the long-term stability of the slope in a strong-earthquake area and, thus, for promoting its sustainable development. However, current research is focused mainly on the stability of the slope, and there have been few studies on the dynamic response of anti-slide piles. For this reason, we have undertaken the present study of a bedding-rock slope supported by a single row of anti-slide piles. By changing the frequency, amplitude, and duration of the input seismic waves, we have systematically explored the influence of their spectral characteristics on the dynamic response of the anti-slide piles and the slope using numerical simulations combined with the wavelet-transform method. Our results show that the spectral characteristics of the seismic waves significantly affect the deformations of the anti-slide piles. Low-frequency and high-amplitude seismic waves have stronger destructive effects on slopes, and high-amplitude seismic waves can generate multi-level sliding surfaces that extend to deeper levels. The low-frequency component of the seismic wave controls the overall deformation of the slope, and the high-frequency component controls the local deformations. An increase in the proportion and duration of low frequencies in seismic waves is the main cause of slope deformation and failure. The present work, thus, provides a useful reference for the design of a slope supported by anti-slide piles in an area with strong earthquakes, as well as for the maintenance of the long-term stability of such a slope, therefore, encouraging the sustainable development of related areas.

Effect of crack depth on the initiation and propagation of crack-induced sliding in a paleosol area on a loess slope: Three-dimensional investigation based on model testing and laser scanning

On the Chinese Loess Plateau (CLP), crack-induced sliding in paleosols triggers retrogressive slope collapse, compromising the long-term stability of loess slopes. Establishing a quantitative relationship between crack depth and slide size is key to elucidating the progressive evolution of crack-induced sliding in paleosols; however, research on this topic is scarce. In this study, a model test was conducted on a paleosol slope subjected to five drying–rainfall cycles. Three-dimensional (3D) laser scanning technology was employed to accurately quantify the variations in crack depth and slide size, and water content sensors were embedded to monitor the preferential flow changes induced by these cracks. Results reveal that crack depth plays a pivotal role in initiating and controlling the propagation of crack-induced sliding in paleosols by influencing the preferential flow capacity through cracks. In the slide initiation stage, a critical crack depth capable of triggering sliding by inducing a sufficiently significant preferential flow and large saturation zones was identified. The depth at which sliding occurs can be expressed as a variable dependent on crack depth based on the single triggering effect of cracking on sliding. Once a crack-induced slide is initiated, the combined action of prior sliding events and current crack propagation accelerates the subsequent sliding in terms of increased size and varying spatial locations by influencing the preferential flow capacity and sliding force values. A comprehensive empirical formula was established to characterize the depth of crack-induced slides, considering the dominant influence of crack depth and slope gradient on sliding development at this stage of slide evolution. Our findings emphasize the pivotal role of crack depth in triggering progressive crack-induced sliding in paleosols, thereby providing valuable insights for soil conservation in paleosol areas on loess slopes on the CLP.

Effects of degraded durability on the long-term stability of in-service slopes with reinforced concreted support structures

Engineering slope stability issues typically exhibit the impact of deteriorating durability on the susceptibility of slopes to failure. A thorough investigation was essential to explore theoretical and experimental aspects of slope durability degradation and its implications on long-term stability. Hence, a durability model was developed to accommodate slope stabilization using reinforced concrete (RC) support structures. This model was grounded in classical durability principles for RC structures. Subsequently, a model test was conducted to compare the responses of a standard slope model with a weakened counterpart subjected to environmental impacts. According to the proposed methodology for slope durability and stability, a case study involving future durability and stability predictions was performed. It was found that the theoretical solutions for the carbonation or neutralization (CN) velocity, depth, and penetration time agreed well with model test results. The slope surface displacements of the weakened slope with deteriorating coefficients between 0.6 and 0.9 were 4 to 8 times those of the standard slope, demonstrating significant degradation in stability. The case study indicated a steady reduction in the safety factor, at a rate of 2.3 to 2.4‰ per year throughout the slope’s service life. Finite-element-based predictions also suggested the potential for corrosion of slope anchor bolts within 20 years and breakage within 30 years, at an average rate of 7.5‰ per year in the ultimate bearing capacity. These findings highlight the need for timely maintenance and reinforcement interventions to ensure the long-term durability of operational slopes.

A Fractional-Order Creep-Damage Model for Carbonaceous Shale Describing Coupled Damage Caused by Rainfall and Blasting

In order to better understand the shear creep behavior of weak interlayers (carbonaceous shale) under the coupling effect of the rainfall dry–wet cycle and blasting vibration, as well as quantitatively characterize the coupled damage of the rainfall dry–wet cycle and blasting vibration, a series of shear creep tests were carried out. The results show that the combined damage of the rainfall dry–wet cycle and blasting vibration greatly intensifies the creep effect of carbonaceous shale, leading to an increase in deceleration creep time, an increase in steady-state creep rate, and a decrease in long-term strength. The coupling damage of the rainfall dry–wet cycle and blasting vibration in carbonaceous shale was quantitatively characterized. Based on the fractional-order theory, a fractional-order creep-damage constitutive model (DNFVP) was established by introducing the Abel dashpot to describe the coupled damage of the rainfall wet–dry cycle and blasting vibration and the nonlinear creep acceleration characteristics. The three-dimensional creep equation of the model was derived. The effectiveness of the DNFVP model was verified through the inversion of model parameters and fitting of experimental data, providing a basis for in-depth research on the long-term stability of high slopes in mines with weak interlayers.

Stability Analysis of Open-Pit Bench Slope under Repeated Heavy Vehicle Loading Based on Stress-Corrosion Model

In the present study, we address an important and increasingly relevant topic in mining safety and efficiency, namely the stability of open-pit bench slopes subjected to daily heavy truck cyclic loading. Specifically, we focus on the stability of Zhahanur open-pit slope (Inner Mongolia region, China) and investigate the potential role of daily heavy truck cyclic loading in bench slope instability. To this end, we incorporate a stress corrosion model into the particle flow code to develop a time-dependent deformation model of the rock. With the established model, we quantitatively analyse the effect of heavy truck cyclic loading on the bench slope stability. Our results support the hypothesis that daily heavy truck loading can cause gradual downward deformation of a rock mass, leading to slope instability. To validate our numerical modelling results, we compare and analyse them with in situ monitoring data. Our study demonstrates the significant impact of daily heavy vehicles on bench slope stability in open-pit mines and provides a practical tool for assessing the long-term stability of open-pit bench slopes and optimising mining operations.

Deep learning–based inverse analysis of GPR data for landslide hazards

In mountainous landscapes, the diverse geotechnical conditions amplify landslide susceptibility. Factors such as precipitation and seismic activity can trigger landslides, while inherent hazards such as voids, fissures, and compaction deficits jeopardize long-term slope stability. Detecting and forecasting these susceptibilities accurately is crucial. In this paper, the time-domain finite-difference approach and the gprMax software are used to conduct forward modeling of landslide susceptibility. An electrical model of subsurface aqueous structures is created, including water-filled and air-filled cavities, fracture zones, and fault lines. The distinctive radar signal responses within these environments are examined, and a dataset of B-scan images associated with their electrical models is constructed. By employing deep learning algorithms and the robust nonlinear mapping ability of convolutional neural networks in the Pix2Pix generative adversarial network, we accelerate the intelligent inversion of the geological radar data on landslide susceptibility. This innovative approach effectively reconstructs hazard models, offering a reliable basis for interpretation of radar signals.

Shear creep characteristics and creep constitutive model of bolted rock joints

The shear creep behavior of bolted rock joints is closely related to the long-term stability of bolt-reinforced high slopes and underground caverns. To investigate the controlling effect of bolts on rock joint shear creep, limestone samples from the Wudongde dam site area in southwest China were collected and processed, and multistep shear creep tests were conducted on both bolted an unbolted rock joints. The results show that the shear creep of bolted rock joints includes the instantaneous strain stage, transient creep stage and steady-state creep stage, yet the accelerating creep typically occurs instantaneously and is unobservable. By comparing the shear creep process of bolted and unbolted rock joints, it is observed that the presence of bolts decelerates the deterioration of joint surfaces, resulting in a shorter duration of transient creep and lower creep rate. Furthermore, the bolt alters the creep failure mode of the rock joint from brittle failure to plastic failure. Based on experimental results, the reinforcement effect of the bolt through joint creep is analyzed, and the stress evolution during creep is divided into three stages, i.e., the stress-compatibility stage, the stress-compensation stage, and the stress-limitation stage. We summarize how the bolt compensates for stress loss caused by joint surface deterioration through increased shear and axial forces, thereby reducing the creep rate and creep deformation of the rock joint. Based on the stress compensation mechanism of the bolt, a B-Q-N (Burgers-shear force Qo-axial force No) creep constitutive model for bolted rock joints is proposed. When the creep behavior of the unbolted rock joint and the anchorage parameters are known, the B-Q-N model can describe the shear creep behavior of bolted rock joints without experimental data for parameter identification, as well verified by our tests.

The Importance of Rock Mass Damage in the Kinematics of Landslides

The stability and kinematics of rock slopes are widely considered to be functions of lithological, structural, and environmental features. Conversely, slope damage features are often overlooked and considered as byproducts of slope deformation. This paper analyzes and discusses the potential role of slope damage, its time-dependent nature, and its control on both the stability of rock slopes and their kinematics. The analysis of several major landslides and unstable slopes, combined with a literature survey, shows that slope damage can play an important role in controlling short- and long-term slope stability. Seasonal and continuously active events cause permanent deformation within the slope due to the accumulation of slope damage features, including rock mass dilation and intact rock fracturing. Rock mass quality, lithology, and scale control the characteristics and complexity of slope damage, as well as the failure mechanism. The authors propose that the role of slope damage in slope kinematics should always be considered in slope stability analysis, and that an integrated characterization–monitoring–numerical modelling approach can enhance our understanding of slope damage, its evolution, and the controlling factors. Finally, it is emphasized that there is currently a lack of guidelines or frameworks for the quantitative assessment and classification of slope damage, which requires a multidisciplinary approach combining rock mechanics, geomorphology, engineering geology, remote sensing, and geophysics.

Experimental study of the influence of wetting and drying cycles on the strength of intact rock samples from a red stratum in the Three Gorges Reservoir area

The influence of wetting and drying cycles (WDC) on the strength weakening of typical rocks in soft and hard interbedded rock masses is vital to comprehend the mechanism of numerous bank slope failures in soft and hard interbedded strata induced by water level fluctuations. How WDC affect the strength of intact rocks in red stratum of the Badong Formation, a typical sliding-prone interbedded stratum in the Three Gorges area, is a topic worthy of comprehensive investigation. In this study, the effects of WDC on the physical and strength parameters of silty mudstone and silty sandstone were examined by performing a series of experiments on a total of 116 rock samples. Models of strength weakening were developed for the two rock types to express the relations between the strength deterioration coefficient (ratio of the weakened and initial value of strength parameters) and the number of WDC. The results indicate that treatment with WDC causes increases in the water absorption rate, and decreases in longitudinal wave velocity, tensile strength, cohesion and internal friction angle for both silty mudstone and silty sandstone samples with the rate of change decreasing with an increasing number of WDC; the variations in physical and strength parameters are larger for silty mudstone compared with silty sandstone; the effects of WDC on tensile strength and cohesion are higher than on internal friction angle for the studied rock types; Intergranular cracks and intragranular cracks were observed to increase with the number of WDC, evolution mode of rock microstructures was proposed, and the main weakening mechanisms induced by WDC was summarized as microcracks growth by mineral expansion and contraction, which weaken the strength of the studied rocks with the impact depending mainly on the mineral contents and microstructures in rocks. Finally, the established strength weakening models were applied in the numerical model to investigate the influence of WDC on the strength of rock mass with silty mudstone and silty sandstone interbedded layers in the Badong Formation. The obtained results provide useful guidance to reasonably evaluate the long-term stability of soft and hard interbedded bank slopes in reservoir area.

Transparent soil model test of a landslide with umbrella-shaped anchors and different slope angles in response to rapid drawdown

Umbrella-shaped anchors, as new stabilizing structures, have been increasingly adopted in engineering practice due to their simple structure, ease of installation, and high load capacity. Reservoir operation, especially during rapid drawdown, affects the long-term stability of reservoir bank slopes as this process affects the stress, seepage and deformation characteristics of the water-level fluctuation (WLF) zone. Thus, the characteristics of the deformation and failure mode of WLF zones reinforced by umbrella-shaped anchors under rapid drawdown conditions are important for the design and construction of anchoring measures. Five slope-anchor scale models based on the Yingpan landslide were established as transparent soil models considering different slope angles and drawdown rates. Displacement, velocity and macroscopic deformation data were obtained using particle image velocimetry (PIV) technology. The results indicated that the deformation process of both reinforced and unreinforced slopes under rapid drawdown conditions could be divided into four phases: initial, shallow sliding, multisliding and stable phases. In the anchor-reinforced models, loss of soil particles occurred when the water level dropped to reach the anchor heads, causing the anchor plates to loosen and slope deformation to accelerate, especially near the lower row of cables. The anchor heads failed first, and progressive slope sliding ensued. Under rapid drawdown conditions, soil liquefaction and subsequent loosening and sliding occurred, generating a far larger zone of accumulation than the zone of collapse. This indicates that soil liquefaction is another important factor of the link between rapid water level drawdown and slope instability causing local collapses. Combining the experimental results and 47 sets of field monitoring data, it could be concluded that the slope stability decreases with increasing slope angle of the WLF zone. This occurs because a higher water level is needed for deformation initiation in the WLF zone in the case of a higher slope angle.

Fractional Catastrophe Model considering the Rheological Properties of Slope Faults

Abstract Fault properties have an important influence on the sliding mode and long-term stability of slopes. In this paper, a cusp catastrophe theoretical model of an open-pit slope is established based on the mechanical model of plane sliding slope instability. The model considers time effects, the rheological properties of fault locking sections, and the strain softening properties of fault softening section. A rheological constitutive model is constructed based on the fractional derivative according to fractional calculus. A slope instability criterion is proposed within catastrophe analysis. The influences of the fault medium length, stiffness ratio, and different orders of the fractional derivative on slope stability are discussed. The critical height and critical safety factor of the dynamic slope instability are derived, and the catastrophe instability time is predicted. The results show that longer softening stages are associated with smaller stiffness ratio values, higher fractional orders, and a greater possibility of slope instability. Slope stability is dynamic under the rheological action of the fault medium.

STUDY ON RHEOLOGICAL CONSTITUTIVE MODEL OF CILILIN VOLCANIC CLAY, INDONESIA IN RELATION TO LONG-TERM SLOPE STABILITY

: Ground movements do not remain constant over time but it is a time-dependent phenomenon in the form of long-term deformations due to in-situ stresses acting all the time on the slope body. Therefore, the time-dependent behavior of soil mass is an important factor that influences long-term slope stability. To understand the long-term slope stability, research on soil rheological characteristics is required so that the time-dependent soil strength reduction can be known. The result of the research will be very useful for the policymaker in disaster mitigation and regional planning. To determine the rheological characteristics of Cililin Volcanic Clay, a laboratory shear creep test was carried out on soil samples taken from the Cililin area, West Java, Indonesia, which is well known as landslide-prone areas. Fifteen undisturbed soil samples were prepared for laboratory shear creep tests. The level of shear stress applied to the shear creep test is 50% - 95% of the peak strength. Then, the soil rheology constitutive models were established which are used to understand the creep behavior of the soil, determine the soil long-term strength, estimate the reduction of soil parameters as a function of time and calculate long-term slope stability. The result shows that the long-term strength of soil is reduced 48.80% from its peak strength after 16 years. The cohesion and internal friction angle reduced from 44.72 kPa and 30.34o become 21.82 kPa and 15.94o, respectively, and the slope safety factor is reduced from 2.16 to 1.04. Rheological modeling also shows that slope stability is a function of time.

Creep constitutive model of siltstone subjected to wet-dry cycles

On the basis of the traditional Nishihara model, a nonlinear viscous pot with strain trigger is connected in series, the nonlinear relationship between creep parameters and the number of wet and dry cycles is established, and a nonlinear creep constitutive model of rock after wet and dry cycles is proposed. The proposed model is used to describe the whole process of the rheological test of siltstone after different drying and wetting cycles, and the parameters of the model are identified. Comparison between the creep data and the model results after different wet and dry cycles shows that the proposed nonlinear creep model can fully describe the creep process of each stage of the siltstone, and fully reflects the rheology of the initial creep, stable creep and nonlinear accelerated creep stages of the siltstone. Results have certain guiding significance for the analysis, evaluation and early warning of the long-term stability of reservoir bank slopes.

SLOPE STABILITY ASSESSMENT OF THE SOUTHWEST OVERALL SLOPE OF THE QAJARAN OPEN-PIT MINE BASED ON THE GSI ROCK MASS CLASSIFICATION SYSTEM

The application of assessing the fracturing quality of rock masses based on the classification system for determining the boundary parameters of the Qajaran open-cast mine slope is substantiated. In the certain geomechanical environment, the long-term slope stability of the south-west wall of Qajaran open-pit mine based on the Geological Strength Index (GSI) classification system is estimated. A comparative analysis between the results with other well-known classification systems, such as MRMR, Q-system and RQD, and the outputs of the proposed GSI system is made. A good agreement between the results obtained from Barton’s Q-system and Hoek’s GSI classification systems is found. It is highly desirable to quantify the rock mass based on 2 and/or more classification systems (e.g. Hoek’s GSI and Barton’s Q-system) to provide much more reliable and reasonable estimates. The stability analysis of Qajaran open-pit overall slope at different scales based on the confirmed lower and upper bounds of the GSI classification system and compared with the results of the accepted stability criteria is performed. It has been shown that when there are limited input data of the jointed rock mass in the current geomechanical environment, it is expedient to use Hoek’s GSI classification system to determine the geometric parameters at different scales at the first development stage of the rock slope designs and estimate the stability of the overall slopes of deep open-pit mines based on Hoek-Brown failure criterion.

Determination of Creep-Induced Displacement of Soil Slopes Based on LEM

The creep of earth slopes is an important challenge of the long-term stability of slopes. This paper develops a limit equilibrium method (LEM)-based analytical approach for calculating the shear displacement of creep-induced failure surface in 2D state for all slices where both force and moment equilibrium equations are simultaneously satisfied as a new research. The relation between shear displacement and creep time is obtained with regard to visco-elastoplastic creep model. The overall safety factor is first calculated for the slip surface using Spencer method. Then, the shear displacements of all slices are obtained based on vertical displacement of crown and using displacement compatibility relation exists between slices. By combining force and moment equilibrium equations and assuming a zero resultant for inter-slice forces, the vertical displacement at crown is determined using visco-elastopastic creep model. A numerical model was developed to calculate slope displacement by the proposed method. Force and moment equilibrium equations are simultaneously satisfied by iteration technique. The proposed method is verified through two numerical examples comparing the new approach and conventional finite element method.

Creep damage properties of sandstone under dry-wet cycles

Rock creep properties can be used to predict the long-term stability in rock engineering. In reservoir bank slopes, sandstones which are frequently used in the bank slope undergoing long-term effects of dry-wet (DW) cycles due to periodic water inundation and drainage may gradually accumulate creep deformation, resulting in rock structure’s damage or even geological hazards such as landslides. To fully investigate the effect of DW cycles on the creep damage properties of sandstone, triaxial creep tests were conducted on saturated sandstone with different DW cycles by using a triaxial rheometer apparatus. The experimental results show that both the instantaneous strain and the stabilized strain increase with the DW cycles. In addition, using the Burgers model, four kinds of functions including an exponentially decreasing function, a linearly decreasing function, a linearly increasing function and an exponentially increasing function were proposed to express the relationships between the shear modulus, viscoelastic parameters of the Burgers model and the deviatoric stress under different DW cycles. Through comparative analysis, it is found that the theoretical curves generated using proposed four kinds of functions are in good agreement with the experimental data. Furthermore, macromorphological and microstructural observations were performed on specimens after various triaxial rheological tests. For samples with small number of DW cycles, approximately X-shaped fracture surfaces were observed in shear failure zones, whereas several shear fractures including obvious axial and horizontal tensile cracks, and flaws were found for samples with relatively large DW cycles due to long-term propagation and evolution of micro-fissures and micro-pores. Furthermore, as the DW cycles increases, the variation in micro-structure of samples after creep failure was summarized into three stages, namely, a stage with good and dense structure, a stage with pore and fissure propagation, and a stage with extensive increase of pores, fissures and loose particles. It is concluded that the combination effect of permeation of water molecules through pores and fissures within sandstone, and the propagation of preexisting pores and fissures owing to the dissolution of mineral particles leads to further deterioration of the mechanical properties of sandstone as the number of DW cycles increases. This study provides a fundamental basis for evaluating the long-term stability of reservoir bank slopes under cyclic fluctuations of water level.

Modelling of thermo-mechanical effects in a rock quarry wall induced by near-surface temperature fluctuations

Mechanical response of rock masses to the periodical fluctuation of surface temperatures is a relevant topic to be focused on for the comprehension of short- to long-term stability of rock slopes continuously stressed by slight yet periodical actions. To better understand how preparatory factors can lead rock masses toward failure, thermal and strain monitoring activities are ongoing in a selected quarry wall, where an experimental test-site was implemented on a jointed rock block. The role of pervasive joints in perturbing the heating-cooling process of the rock mass and their related effects was already output by direct and remote monitoring. For these purposes, FDM numerical modelling was focused on the comprehension and simulation of induced mechanical effects due to cyclical thermal forcings over a simplified 2D half-space. Therefore, the role of rock mass joints on both heat propagation and resulting thermo-mechanical effects was analysed, basing on monitoring data, field experiments and numerical modelling. Numerical results output the role of periodic daily, annual and compound thermal input in inducing irreversible deformation along joints under different rock mass jointing configuration, as a function of the intrinsic period of thermal input and joint attitude. Temperature distribution across joints was also analysed as a possible constraining effect for time and space distribution of yielding. A sensitivity analysis of heat propagation conditions was performed in order to infer the role of joint sets on induced thermo-mechanical strains at the rock block scale. A non-negligible influence on surficial as well as deeper portions of the rock mass was observed, highlighting how near-surface temperature fluctuations can drive the long-term evolution of rock block conditions towards failure.

Time-dependent behavior of saturated silty mudstone under different confining pressures

The long-term stability of rock slopes is greatly affected by the creep behavior of rock mass. This study presents the creep behavior of a saturated silty mudstone that is from the Three Gorges Reservoir in China. Triaxial compression tests and triaxial creep tests were performed on the silty mudstone under different confining pressures. The test results show that the creep behaviors have three stages, namely, the primary creep stage, steady-state stage, and accelerated creep stage when the deviatoric stress is higher than the yield stress of the silty mudstone. The steady-state creep strain rate of the silty mudstone increases with the increment of the axial deviatoric stress. Partial reversals of the axial creep strain curve are found under the confining pressure of 1 MPa and 5 MPa, which may be caused by the expansion of illite minerals after being infiltrated by water in the rock voids. Based on the experimental data of the silty mudstone and the fractional calculus theory, a nonlinear creep model that describes the creep behaviors of the silty mudstone is proposed. The theoretical creep curves obtained from the creep model are in good agreement with the experimental data.

Time-dependence of mechanical behavior of Shikotsu welded tuff at sub-zero temperatures

A series of uniaxial compression and creep tests were performed on dry and wet specimens of Shikotsu welded tuff at −20 °C (−4 °F) to examine the time-dependence of the mechanical behavior of frozen rock. The impact of the water content of the specimens on the time-dependence of mechanical behavior was also investigated. The uniaxial compressive strengths (UCSs) of the frozen wet specimens strongly depended on the loading rate, and were greater than those of the frozen dry specimens at strain rates greater than 4.2 × 10−5 s−1. However, the creep lives of the frozen wet specimens were shorter than those of the frozen dry specimens at stress levels of less than 13.4 MPa (52% of the UCSs of the frozen wet specimens). Deformation behavior induced by pore ice was observed in the frozen wet specimens. The stress–strain behavior transitioned from brittle to ductile as the strain rate increased, and the ratio of the tertiary creep region was relatively larger. The strains of the frozen wet specimens were significantly larger than the frozen dry specimens. These results demonstrated that understanding the time-dependent deformation of frozen rock is crucial for the assessment of the long-term stability of rock slopes in cold regions, as pore ice strongly affected the failure process of the frozen wet specimens.