Key Takeaways & Executive Findings
- •• Depositional environment significantly controls the microstructure and rheological behavior of sedimentary soft rocks, with floodplain lake and sheet sand microfacies exhibiting superior stability due to dense quartz skeletons. • A novel frequency-domain upscaling method integrating the Mori-Tanaka scheme accurately predicts macroscopic viscoelastic properties from nanoindentation creep data. • Riverbed lag and shallow lake mud microfacies show poor rheological performance due to skeleton relaxation and clay-dominated slip, respectively. • The point bar microfacies displays a 'rigid-soft hybrid' behavior, combining high long-term stability with reduced transient stability.
Abstract
Although significant progress has been made in micromechanical characterization and upscaling of homogeneous materials, systematic investigations into deposition-controlled micro–macro rheological relationships in heterogeneous sedimentary soft rocks remain limited, particularly concerning time-dependent viscous parameter upscaling. This study investigates six typical fluvial and lacustrine microfacies from the Ordos Basin, China, including riverbed lag, natural levee, floodplain lake, point bar, sheet sand, and shallow lake mud. Mineral composition and microstructure are characterized, and nanoindentation creep tests quantify viscoelastic properties. A micro–macro upscaling method that transforms the time-domain Burger model into the frequency domain and utilizes three traditional homogenization schemes: dilute approximation, Mori-Tanaka, and self-consistent methods, for comparative estimation of macroscopic rheological parameters is proposed. Microstructural analysis demonstrates distinct fabric patterns controlled by depositional energy. Floodplain lake and sheet sand microfacies show superior rheological stability due to dense quartz skeletons, whereas riverbed lag and shallow lake mud perform poorly, caused by skeleton relaxation and clay-dominated slip, respectively. The point bar microfacies exhibits a ‘rigid-soft hybrid’ behavior, with high long-term stability but reduced transient stability. Comparatively, the frequency-domain upscaling framework developed in this study, incorporating the Mori-Tanaka scheme, demonstrates satisfactory agreement with experimental data, validating its capability to predict macroscopic viscoelastic properties from microstructural features.
1. Introduction
Nowadays, the long-term stability of weak strata in continental sedimentary rocks has become a critical concern due to the rapid advancement of deep coal mining in western China, steep slope stabilization in mountainous regions, and the construction of deeply buried tunnels. Particularly, within the major Jurassic coal-bearing formations of the Ordos Basin, the rheological behavior of rock masses plays a direct role in engineering hazards such as roof collapse, high-level separation layer formation, and water inrush. These phenomena exhibit pronounced time-dependent and nonlinear characteristics, posing significant challenges to underground engineering safety [1–3]. Therefore, systematically clarifying the rheological mechanisms of sedimentary soft rocks is essential for improving the long-term stability of underground structures and advancing disaster prevention technologies.
It is imperative to consider the multiscale nature of rock mechanical behavior to understand these rheological mechanisms. Fig. 1 indicates that observation scales range from the macroscopic (0.1 mm to 1 km), mesoscopic (1–100 nm), and microscopic (0.1–1 nm) levels, down to atomic and subatomic dimensions. Rocks consist of various mineral particles, and their macroscopic mechanical responses are fundamentally governed by microstructural features such as mineral composition, grain morphology, spatial arrangement, and interparticle bonding. Deformation processes including grain boundary sliding, crystal interface creep, and microcrack propagation act in concert to drive time-dependent macroscopic behaviors, ultimately determining the strength, stiffness, and failure modes of soft rock masses [4,5]. Therefore, it is essential to investigate the mechanical response at the microscale, the fundamental scale at which deformation initiates and evolves, to accurately characterize and predict the macroscopic rheological behavior.
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Mengnan Liu, Wei Qiao, Xianggang Cheng, Ruijie Lv, Xiangsheng Meng (2025). Effect of depositional environment differences on micro-macro rheological behavior of sedimentary soft rocks. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.10.006
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Frequently Asked Questions
What is the main objective of this study?
The study aims to systematically investigate the influence of depositional environment differences on the micro-macro rheological behavior of sedimentary soft rocks, and to propose a frequency-domain upscaling method for predicting macroscopic viscoelastic properties from microstructural features.
Which microfacies were analyzed in the Ordos Basin?
Six typical fluvial and lacustrine microfacies were analyzed: riverbed lag, natural levee, floodplain lake, point bar, sheet sand, and shallow lake mud.
What methods were used to characterize the rocks?
Mineral composition and microstructure were characterized, and nanoindentation creep tests were performed to quantify viscoelastic properties. Three homogenization schemes (dilute approximation, Mori-Tanaka, and self-consistent) were used for upscaling.
Which microfacies showed the best rheological stability?
Floodplain lake and sheet sand microfacies showed superior rheological stability due to dense quartz skeletons.
How was the proposed upscaling method validated?
The frequency-domain upscaling framework incorporating the Mori-Tanaka scheme demonstrated satisfactory agreement with experimental data, validating its capability to predict macroscopic viscoelastic properties.
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