Key Takeaways & Executive Findings
- •• Compressive strength, creep failure stress, and dilatancy stress of sandstone decrease exponentially with increasing water content and increase exponentially with confining pressure. • Lateral creep strain is more significant than axial, and lateral strain enters steady-state creep earlier, with accelerated creep onset occurring earlier laterally under failure stress. • Long-term strength of sandstone shows a negative exponential relationship with water content and a positive exponential relationship with confining pressure, determined via lateral steady-state creep rate. • A novel method for determining long-term strength based on the lateral-to-axial strain ratio (μc) is proposed, independent of water content, aiding in early creep failure prediction.
Abstract
Water is a critical factor affecting the mechanical properties of rocks, leading to their degradation. Understanding the creep mechanical behavior of deep roadway surrounding rock under the influence of underground water is of great significance. Compression and creep experiments on sandstone with varying water contents were conducted using a deep soft rock five-linked rheological experiment system. The experimental conditions, including water content (0%, 0.8%, 1.6%, 2.4% and 3.3%) and confining pressure (0, 6, 9 and 12 MPa), were determined based on pressure-free water absorption tests and in-situ stress measurements. The experimental results show that the compressive strength, creep failure stress, and dilatancy stress of sandstone decrease exponentially with increasing water content, while they increase exponentially with confining pressure. The ratio of lateral to axial instantaneous strain increases nearly linearly with the increase of stress, and the lateral creep strain characteristics of the sample are more significant than the axial ones. The duration of the attenuation creep stage of sandstone decreases with increasing water content and increases with increasing confining pressure. The lateral strain enters the steady-state creep stage before the axial strain, and the onset time of the accelerated creep stage of lateral strain under the failure stress is earlier than that of axial strain. The long-term strength of sandstone was determined based on the lateral steady-state creep rate curve, showing a negative exponential relationship with water content and a positive exponential relationship with confining pressure. A method for determining the long-term strength of rocks based on the ratio of lateral strain to axial strain (μc) is proposed, which is independent of water content. The research results provide a reliable theoretical basis for the analysis of the long-term stability of roadways under the influence of groundwater and the early prediction of creep failure.
1. Introduction
In engineering projects related to mining, hydropower, and petroleum involving rocks, the deformation of surrounding rocks exhibits significant time effects, and the long-term stability of these rock projects is closely related to rock creep [1−3]. Water is one of the most active factors in triggering engineering geological disasters, and rock engineering often exists in a water environment, while the mechanical behavior of rocks differs significantly under dry and saturated conditions [4−6]. The roof and bottom plates of Wanfu Coal Mine’s pump house directly interact with water-bearing strata, exhibiting significant nonlinear large deformation characteristics. The pump house is vital for drainage in the area, with a service life of several decades. High ground stress and deep water increase the risk of damage to surrounding rocks in roadways. Therefore, studying the creep mechanical properties of rocks under different water content states is of great significance for the safe and efficient mining of Wanfu Coal Mine.
Studies have shown that water is an important factor affecting the mechanical properties of rocks, deteriorating their mechanical properties [7, 8]. Water weakens the strength of rocks by increasing the internal stress of rocks and reducing the effective stress [9, 10]. Water also reacts with minerals in the pores of rocks or dissolves minerals in rocks, causing dissolution and weathering of rocks, which reduces their strength [6, 11, 12]. Scholars have also studied the effects of water on the mechanical parameters of rocks. The strength indices of rocks decrease by 60% −90% in the saturated state compared to dry state [13]. As confining pressure increases, both the peak and residual strength of rocks increase, while the effect of water content on various rock parameters lessens with greater confining pressure [11, 14]. DING and TANG [15] found that with increasing water pressure, the peak stress and elastic modulus of saturated rocks increase linearly, while these parameters for dry rocks first decrease and then rise.
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SUN Xiao-ming, JIANG Ming, MIAO Cheng-yu, ZHANG Long-yu, WANG Lei (2025). Creep mechanical properties of sandstones under triaxial compression with different loads and water contents. Journal of Central South University. https://doi.org/10.1007/s11771-025-6078-0
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Frequently Asked Questions
What is the effect of water content on the compressive strength of sandstone?
The compressive strength of sandstone decreases exponentially with increasing water content, as demonstrated in the study.
How does confining pressure influence the creep failure stress of sandstone?
The creep failure stress increases exponentially with confining pressure, indicating that higher confining pressures enhance the rock's resistance to creep failure.
What is the significance of lateral strain in creep analysis?
Lateral strain is more significant than axial strain in creep analysis, as it enters the steady-state creep stage earlier and shows earlier onset of accelerated creep, providing a more sensitive indicator for predicting creep failure.
How is the long-term strength of sandstone determined in this study?
The long-term strength is determined based on the lateral steady-state creep rate curve, showing a negative exponential relationship with water content and a positive exponential relationship with confining pressure.
What is the proposed method for determining long-term strength independent of water content?
The study proposes a method based on the ratio of lateral strain to axial strain (μc), which is independent of water content, offering a reliable approach for long-term strength assessment.
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