Experimental Study of the Creep Disturbance Effect and Acoustic Emission Characteristics of Mudstone with Different Moisture Contents

It is important to have a clear understanding of the creep characteristics of water-rich soft rocks under a dynamic load and the evolution of cracks because soft rock roadways in deep mines are very sensitive to disturbances, and instability and damage can easily occur under the impact of disturbances such as mining and blasting. In this study, a self-developed disturbed creep test bench was used to conduct graded loading creep disturbance tests on mudstone specimens with different moisture contents. The results show that an increase in the moisture content leads to a significant increase in the creep failure strain of mudstone, and the accelerated creep rate is greatly accelerated. Moreover, as the moisture content increases, the type of mudstone creep disturbance failure gradually changes from accelerated creep failure to disturbance failure. By analyzing the acoustic emission (AE) characteristics of the mudstone creep disturbance tests, it was found that the increase in the moisture content greatly weakens the AE count and the accumulated energy. In each stage of disturbance, the AE signals jumped, and the stability was restored at the end of the disturbance. As the load increased, the specimen entered the accelerated creep stage, the AE signal increased exponentially, and the internal cracks expanded rapidly until failure occurred. It is of great significance to carry out creep disturbance experiments and to analyze the evolution of the internal cracks in specimens with different moisture contents to maintain the long-term stability of deep soft rocks.

The Critical Indicator of Red-Bed Soft Rocks in Deterioration Process Induced by Water Basing on Renormalization Group Theory

The internal damage of red-bed soft rock induced by water is pervasive. The accumulation, growth, and localization of damage is a multi-scale process that can lead to significant strength loss in red-bed soft rock. Yet, research on the critical state of deterioration process considering multi-scale failure is limited due to high degree of system freedom. Renormalization group theory is an effective approach to find critical point of phase transition in a disordered system. To apply renormalization group theory in red-bed soft rocks, this article firstly analyzed their microstructures. Then, the granular unit model and stripy unit model are proposed to describe the self-similar characteristics of red-bed soft rocks. The calculation results based on renormalization group theory are consistent with the experimental results. The critical reductions of strength induced by water are 60% in light-yellow silty mudstone and 80% in grey silty mudstone. In addition, the critical state of damage propagation caused by stress is also studied and the analytical solution is derived. Results show that the renormalization group theory can effectively couple the micro damage and strength deterioration which provides guidance to the engineering.

Does Complex Soil Enhance Grain Yield under Cropping System?

Global climate change and the increasing population have increased the difficulties associated with grain production. Several measures have been established to maintain a high crop yield, while preserving or increasing soil health, including biochar application to soil, and producing new complex soil with soil amendment application, e.g., biochar and soft rocks. However, previous studies have focused on the effect of complex soil on a single crop but have not considered crop rotation. In this study, field plots with foxtail millet cultivated for two years under biochar and soft rock application were selected for licorice cultivation to detect the effects of biochar and soft rock application on soil properties and licorice yield. The results showed that the biochar-treated plot had the highest licorice biomass (251.76 g/m2), followed by the combined biochar and soft rock treatment, and that the soft rock and control treatments had the lowest licorice biomass (97.65 g/m2). Plants in biochar-treated plots had the highest liquiritin and glycyrrhizic acid contents, followed by those under soft rock treatment. Soft rocks and biochar increased the soil catalase activity, organic matter, oxalic acid, tartaric acid, formic acid, and available phosphorus (AP). Correlation analysis showed that the licorice biomass was significantly positively correlated with oxalic acid and AP and negatively correlated with soil pH. AP was positively correlated with catalase activity and oxalic acid (p < 0.05) and negatively correlated with soil pH (p < 0.05). Therefore, it can be concluded that the addition of biochar and soft rocks for two years could increase soil organic acid contents (especially that of oxalic acid), which function to reduce soil pH, increase soil AP content, and enhance licorice biomass.