Three-dimensional stress variation characteristics in deep hard rock of CJPL-Ⅱ project based on in-situ monitoring

In deep hard rock excavation, stress plays a pivotal role in inducing stress-controlled failure. While the impact of excavation-induced stress disturbance on rock failure and tunnel stability has undergone comprehensive examination through laboratory tests and numerical simulations, its validation through insitu stress tests remains unexplored. This study analyzes the three-dimensional stress changes in the surrounding rock at various depths, monitored during the excavation of B2 Lab in China Jinping Underground Laboratory Phase Ⅱ(CJPL-Ⅱ). The investigation delves into the three-dimensional stress variation characteristics in deep hard rock, encompassing stress components and principal stress. The results indicate changes in both the magnitude and direction of the principal stress during tunnel excavation. To quantitatively describe the degree of stress disturbance, a series of stress evaluation indexes are established based on the distances between stress tensors, including the stress disturbance index(SDI), the principal stress magnitude disturbance index(SDIm), and the principal stress direction disturbance index(SDId). The SDI indicates the greatest stress disturbance in the surrounding rock is 4.5 m from the tunnel wall in B2 Lab. SDIm shows that the principal stress magnitude disturbance peaks at2.5 m from the tunnel wall. SDId reveals that the largest change in principal stress direction does not necessarily occur near the tunnel wall but at a specific depth from it. The established relationship between SDI and the depth of the excavation damaged zone(EDZ) can serve as a criterion for determining the depth of the EDZ in deep hard rock engineering. Additionally, it provides a reference for future construction and support considerations.

Influence of stress wave-induced disturbance on ultra-low friction in broken blocks

Deep rock mass tends to be broken into blocks when mining for materials deep below the surface.The rock layer of the roof of the mine can be regarded as a system of blocks of fractured rock mass.When subjected to high ground stress and mining-induced disturbance,the efect of the ultra-low friction of the block system easily becomes apparent,and can induce rock burst and other accidents.By taking the block of rock mass as research object,this study developed a test system for ultra-low friction to experimentally examine its efects on the broken blocks under stress wave-induced disturbance.We used the horizontal displacement of the working block as the characteristic parameter refecting the efect of ultra-low friction,and examine its characteristic laws of horizontal displacement,acceleration,and energy when subjected to the efects of ultra-low friction by changing the frequency and amplitude of the stress wave-induced disturbance.The results show that the frequency of stress wave-induced disturbance is related to the generation of ultra-low friction in the broken block.The frequency of disturbance of the stress wave is within 1–3 Hz,and signifcantly increases the maximum acceleration and horizontal displacement of the broken blocks.The greater the intensity of the stress wave-induced disturbance is,the higher is the degree of block fragmentation,and the more likely are efects of ultra-low friction to occur between the blocks.The greater the intensity of the horizontal impact load is,the higher is the degree of fragmentation of the rock mass,and the easier it is for the efects of ultra-low friction to occur.Stress wave-induced disturbance and horizontal impact are the main causes of sliding instability of the broken blocks.When the dominant frequency of the kinetic energy of the broken block is within 20 Hz,the efects of ultra-low friction are more likely.

Stress-induced trend:the clustering feature of coal mine disasters and earthquakes in China

Nearly half of coal mine disasters in China have been found to occur in clusters or to be accompanied by earthquakes nearby,in which all the disaster types are involved.Stress disturbances seem to exist among mining areas and to be responsible for the observed clustering.The earthquakes accompanied by coal mine disasters may be the vital geophysical evidence for tectonic stress disturbances around mining areas.This paper analyzes all the possible causative factors to demonstrate the authenticity and reliability of the observed phenomena.A quantitative study was performed on the degree of clustering,and space-time distribution curves are obtained.Under the threshold of 100 km,47%of disasters are involved in cluster series and 372 coal mine disasters accompanied by earthquakes.The majority cluster series lasting for 1-2 days correspond well earthquakes nearby,which are speculated to be related to local stress disturbance.While the minority lasting longer than 4 days correspond well with fatal earthquakes,which are speculated to be related to regional stress disturbance.The cluster series possess multiple properties,such as the area,the distance,the related disasters,etc.,and compared with the energy and the magnitude of earthquakes,good correspondences are acquired.It indicates that the cluster series of coal mine disasters and earthquakes are linked with fatal earthquakes and may serve as footprints of regional stress disturbance.Speculations relating to the geological model are made,and five disaster-causing models are examined.To earthquake research and disaster prevention,widely scientific significance is suggested.

Copper pollution decreases the resistance of soil microbial community to subsequent dry–rewetting disturbance

Dry–rewetting（DW） disturbance frequently occurs in soils due to rainfall and irrigation, and the frequency of DW cycles might exert significant influences on soil microbial communities and their mediated functions. However, how microorganisms respond to DW alternations in soils with a history of heavy metal pollution remains largely unknown.Here, soil laboratory microcosms were constructed to explore the impacts of ten DW cycles on the soil microbial communities in two contrasting soils（fluvo-aquic soil and red soil）under three copper concentrations（zero, medium and high）. Results showed that the fluctuations of substrate induced respiration（SIR） decreased with repeated cycles of DW alternation. Furthermore, the resistance values of substrate induced respiration（RS-SIR）were highest in non-copper-stressed（zero） soils. Structural equation model（SEM） analysis ascertained that the shifts of bacterial communities determined the changes of RS-SIR in both soils. The rate of bacterial community variance was significantly lower in noncopper-stressed soil compared to the other two copper-stressed（medium and high） soils,which might lead to the higher RS-SIR in the fluvo-aquic soil. As for the red soil, the substantial increase of the dominant group WPS-2 after DW disturbance might result in the low RS-SIR in the high copper-stressed soil. Moreover, in both soils, the bacterial diversity was highest in non-copper-stressed soils. Our results revealed that initial copper stress could decrease the resistance of soil microbial community structure and function to subsequent DW disturbance.