In the long-term exploitation of natural gas hydrate, the stress change intensifies the creep effect and leads to the destruction of pore structures, which makes it difficult to predict the permeability of hydrate reservoir. Although permeability is crucial to optimize gas recovery for gas hydrate reservoirs, until now, accurately modeling the permeability of hydrate-bearing clayey-silty sediments during the creep process remains a significant challenge. In this study, by combining the nonlinear fractional-order constitutive model and the Kozeny-Carman (KC) equation, a novel creep model for predicting the permeability of hydrate-bearing clayey-silty sediments has been proposed. In addition, experimental tests have been conducted to validate the derived model. The proposed model is further validated against other available test data. When the yield function F 0, the penetrating damage bands will be generated. Results show that, once the model parameters are determined appropriately by fitting the test data, the model can also be used to predict permeability under any other stress conditions. This study has a certain guiding significance for elucidating the permeability evolution mechanisms of hydrate-bearing clayey-silty sediments during the extraction of marine gas hydrates. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

In the Cangzhou area of China, groundwater over-exploitation has led to serious land subsidence, and the creep deformation of aquitards has been monitored and found to be closely related to the development of land subsidence. The objective of this paper is to develop a computational model to reflect the creep deformation of aquitards in this area. Firstly, creep tests were conducted on clayey soils with burial depths ranging from 65.7 to 121.7 m. The results show that the total strain consists of three parts: instantaneous strain, primary consolidation strain and creep strain. Creep-time curves and isochronous creep stress-strain curves under stepwise loading were obtained by using the Boltzmann superposition principle, and both types of curves were characterized by nonlinearity, and the creep curves as a whole showed a trend of stable development. Secondly, on the basis of analyzing the advantages and disadvantages of the classical rheological models for clayey soils, a nonlinear creep model of NCE_CS that can take into account the influence of primary consolidation is proposed. The model contains five parameters, which can be solved by using genetic algorithm, and then a simple determination method of the parameters is proposed. Finally, by comparing with the test data and the calculation results of four classical creep models, it is confirmed that the NCE_CS model can fit the creep curves better. The NCE_CS model was also successfully used to estimate the creep behavior in another subsidence area located in Renqiu City in northwest of Cangzhou. This study will provide a basis for quantitative calculation of creep of clayey soils in the Cangzhou area.

Numerous incidents and failures of bank slopes are caused by the creep behavior of sliding zone soil. During reservoir regulation, the pore water pressure in the sliding zone undergoes cyclic changes. Under such complex cyclic hydraulic conditions, the creep behavior may differ from that under the monotonic seepage condition, which is still poorly understood. In this paper, the Majiagou landslide in the Three Gorges Reservoir area is taken as a case study. Triaxial creep tests were first carried out to study the creep behavior of the sliding zone soil specimen under cyclic seepage pressure. Then, the nonlinear Burgers creep model was proposed to characterize the observed creep behavior of the sliding zone soil specimen, and the secondary development was performed based on FLAC3D software. Finally, the proposed model was applied to the Majiagou landslide to simulate its deformation under fluctuating reservoir water levels. The following results were obtained: (1) Under low deviatoric stress levels, cyclic seepage pressure causes the creep strain curve to fluctuate significantly. The decrease of seepage pressure leads to a reduction in pore pressure, resulting in a sharp increase in the strain rate of sliding zone soil. (2) The proposed model can well reflect the creep characteristics of sliding zone soil under cyclic seepage pressure. (3) During reservoir operation, the landslide deformation exhibits a step-like growth, and the proposed creep model can effectively simulate the retrogressive deformation characteristics of the Majiagou landslide. The research results provide the theoretical basis for the long-term stability of reservoir landslides under fluctuating water levels.

This study compares how geosynthetics behave under load, under strain, and over time when subjected to confined tensile tests in soil, employing two commonly used mechanisms in research. One test type simulates a reinforced layer, where tensile loads are indirectly applied to the geosynthetic via stresses transferred from the soil. In contrast, the other test applies tensile loads directly to the geosynthetic material using clamps while under soil confinement. The objective is to elucidate how these testing mechanisms might yield differing in-soil tensile characteristics for different geosynthetics. The study involved conducting load-strain-time tests on samples of nonwoven and woven geotextiles, as well as a geogrid, under varying sustained loads over a 120-h period within a sand clay soil providing soil confinement to geosynthetics at different surcharge levels. The results suggest that soil confinement plays a significant role in shaping the load-strain-time behavior of geosynthetics. Furthermore, it was noted that the impact of testing mechanisms on this behavior is contingent upon the type and stiffness of the geosynthetics, as well as their interaction with the confining soil. In general, in-soil tests in which tensile loads are mobilized by geosynthetics and transferred from the soil provide more confident results for better simulating operation conditions. Tests that directly apply tensile loads to the geosynthetic while maintaining stationary soil confinement may yield misleading results, especially for geosynthetics that have poor interaction with the soil.

The effectiveness of load-reduction techniques often diminishes due to creep behavior observed in geomaterials, as loess backfill is used, the load reduction rate of high-filled cut-and-cover tunnels (HFCCTs) after creep will decrease by 10.83%, posing a threat to the long-term stability of deeply buried structures such as HFCCTs. Therefore, a geotechnical solution is crucial to ensuring sustained effectiveness in load-reduction strategies over time. This study utilizes a finite-difference method to examine three promising measures for mitigating creep effects. Our analysis focuses on the time-dependent changes in earth pressure atop the cut-and-cover tunnel (CCT) and the internal distribution of cross-sectional forces, including bending moment, shear force, axial force, and displacement. Results indicate that the creep behavior of load-reduction materials significantly influences the internal force distribution. Furthermore, sustained load reduction is achieved when utilizing low-creep materials like dry sandy gravel as backfill soil, which needs to be borrowed from other sites. Additionally, integrating concrete wedges with load-reduction techniques facilitates a more uniform stress distribution atop CCTs.

The interface creep behavior of the grouted soil anchor subject to varying soil moisture was investigated using the combined incorporation of experimental and data-driven modeling methods to establish an efficient and robust forecasting framework. This study carried out the rapid and creep pullout tests of element anchor specimens at various saturations and then utilized machine learning methods to predict the development of interface creep displacement. The stepwise loading strategy and nonlinear superposition method were combined to generate the interface shear creep curves of the element anchor specimens. A total of 936 data groups of the interface shear displacement were collected with changing soil moisture contents, interface shear time, and interface shearing stress. Next, this study explored the Back Propagation Neural Network (BPNN) and four other machine learning algorithms in predicting the interface creep behavior of the grouted soil anchor under various moisture conditions. As for the hyperparameters, the beetle antennae search (BAS) approach was employed to optimize the BPNN and random forest (RF) models. Finally, the boxplot and Taylor diagrams proved the BASBPNN demonstrated a better performance than BAS-RF in predicting the interface creep behavior. The consequent correlation coefficients ranged from 0.9613 to 0.9805 for BPNN, indicating the accuracy and reliability of the interface creep prediction. A partial dependence plot (PDP) was also introduced to visualize the established machine learning model. The threshold of moisture content near 28.7 % is found to switch the interface shear stress-displacement response from strain-stabilizing to strain-softening behavior and to result in the main moisture-increase-induced interface strength degradation. The soil moisture fluctuation leads to the development of interface shear displacement mainly observed in the early phase of 20 h after the onset of moisture change. The uncovered coupled impact of soil moisture condition and interface shear stress state can provide insights into the evaluation of the time-dependent in-service performance of grouted soil anchors embedded in clayey soils.

To date, few models are available in the literature to consider the creep behavior of geosynthetics when predicting the lateral deformation (delta) of geosynthetics-reinforced soil (GRS) retaining walls. In this study, a general hyperbolic creep model was first introduced to describe the long-term deformation of geosynthetics, which is a function of elapsed time and two empirical parameters a and b. The conventional creep tests with three different tensile loads (P-r) were conducted on two uniaxial geogrids to determine their creep behavior, as well as the a-P-r and b-P-r relationships. The test results show that increasing P-r accelerates the development of creep deformation for both geogrids. Meanwhile, a and b respectively show exponential and negatively linear relationships with P-r, which were confirmed by abundant experimental data available in other studies. Based on the above creep model and relationships, an accurate and reliable analytical model was then proposed for predicting the time-dependent delta of GRS walls with modular block facing, which was further validated using a relevant numerical investigation from the previous literature. Performance evaluation and comparison of the proposed model with six available prediction models were performed. Then a parametric study was carried out to evaluate the effects of wall height, vertical spacing of geogrids, unit weight and internal friction angle of backfills, and factor of safety against pullout on delta at the end of construction and 5 years afterwards. The findings show that the creep effect not only promotes delta but also raises the elevation of the maximum delta along the wall height. Finally, the limitations and application prospects of the proposed model were discussed and analyzed.

The paper is dedicated to developing a comprehensive analysis method of the criteria for defining the compressible thickness critical for estimating long-term settlements in buildings and structures situated on soft soils, focusing on their creep behavior. This study introduces an engineering method grounded on the criterion of soil's undrained condition within the mass, considering both elastic and residual deformations through equivalent creep deformations. Unlike previous methodologies, the proposed method facilitates the assessment of long-term settlements by incorporating creep effects over time, employing undrained shear strength for both normally consolidated and overconsolidated soils. The method enables settlement calculations based on static-sounding data, enhancing predictions' accuracy and reliability. This research endeavors to broaden the application of numerical and analytical calculations in real-world practices, employing elastoviscoplastic soil models to design structures on weak foundations.