Abstract
A high-resolution microseismic (MS) monitoring system was implemented at the right bank slope of the Dagangshan hydropower station in May 2010 to analyse the slope stability subjected to continuous excavation. The MS monitoring system could real-time capture a large number of seismic events occurring inside the rock slope. The identification and delineation of rock mass damage subject to excavation and consolidation grouting can be conducted based on the analysis of tempospatial distribution of MS events. However, how to qualitatively evaluate the stability of the rock slope by utilizing these MS data remains challenging. A damage model based on MS data was proposed to analyse the rock mass damage, and a 3D finite element method model of the rock slope was also established. The deteriorated mechanical parameters of rock mass were determined according to the model elements considering the effect of MS damage. With this method, we can explore the effect of MS activities, which are caused by rock mass damage subjected to excavation and strength degradation to the dynamic instability of the slope. When the MS damage effect was taken into account, the safety factor of the rock slope was reduced by 0.18 compared to the original rock slope model without considering the effect. The simulated results show that MS activities, which are subjected to excavation unloading, have only a limited effect on the stability of the right bank slope. The proposed method is proven to be a better approach for the dynamical assessment of rock slope stability and will provide valuable references for other similar rock slopes.
Highlights
A high-resolution microseismic (MS) monitoring system was implemented at the right bank slope of the Dagangshan hydropower station in May 2010 to analyse the slope stability subjected to continuous excavation. e MS monitoring system could real-time capture a large number of seismic events occurring inside the rock slope. e identification and delineation of rock mass damage subject to excavation and consolidation grouting can be conducted based on the analysis of tempospatial distribution of MS events
Weakening of the dominant structure plane from the slope top downward during excavation process is the main cause of potential slope instability. e acoustic emissions (AEs) accumulation zone obtained from numerical solution and the distribution of high MS density zone are highly coherent, which showed that the evolution simulation of Dagangshan right bank slope stability under excavation using RFPA3D did match the site monitoring results and established the model foundation of RFPA3D slope stability analysis with MS data feedback
According to the proposed rock mass degradation criterion, the mechanical parameters of the rock mass were modified as inputs to update the properties of elements in the numerical model. e stability of the excavated rock slope was evaluated considering the MS damage effect, which is the contribution to the theory of this study. e following conclusions can be drawn: (1) e spatial distribution of MS delineated the weak geological structures and identified the potential sliding surfaces inside the rock slope. ere may be a risk of deformation on the right bank slope. e main cause of fissures in the rock slope surface was local small block deformation due to the existence of unloading fracture zone XL-316 and fault f231
Summary
Continuous excavation may result in energy unbalance and stress redistribution in the deep rock mass of the rock slope, which will cause the movements of weak structures and slippage of the faults. E monitoring results show that there is a close correlation between MS frequency and its accumulated energy release, which can be used to quantify the extent of damage to rock mass inside the rock slope. Erefore, the MS monitoring system is used to determine the spatial location and magnitude of MS events through seismic wave information and to estimate the development of nonlinear strain regions induced by MS activity. The MS monitoring results can be used for an in-depth analysis of the failure characteristics of the excavated slope
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