Macroscopic Failure Processes at Mines Revealed by Acoustic Emission (AE) Monitoring

Abstract

Mining activity may cause different types of seismicity and rock failure.Typical events include (1) fully induced microearthquakes in close proximity to galleries and human activity due to high-stress concentrations (border fractures) and (2) triggered earthquakes within the rock mass at larger distance to the source of the stress perturbation (inner fractures). Type 1 is important to understand the development of rock bursts and evaluate the stability of the mine. Type 2 may be associated with larger events releasing pre-existing stress and being triggered by stress changes due to the mining operation. They are important to assess the seismic hazard related to mining activity.To analyze these different failure processes, we use a dataset of high-frequency acoustic emission (AE) events monitored in an abandoned salt mine. The process of fracture formation in the rock mass was enhanced by the backfilling of a cavity. Thermal stresses induced by the backfilling operation are modeled with a finite-element approach, and observed AE activity is used to quantify the mechanism of event triggering in terms of a Coulomb failure model.Two observations are outstanding. First, the instantaneous triggering of enhanced activity and the slow growth of an inner fracture in relatively far distance to the backfilled cavity is detected. The structure already showed AE activity before the refilling started and was triggered by traction-like stress transfer. Its AE activity correlates well with the calculated Coulomb stress changes at the beginning of backfilling. Second, the sudden occurrence of a macroscopic, induced border fracture at the backfilled gallery which is oriented in agreement with the acting stress field is observed. Although AE activity at the inner fracture was triggered by tiny Coulomb stress changes, indicating a structure already in critical state, formation of the border fracture required significantly larger stresses, hinting at a previously intact rock volume.Online Material: Figure depicting the variability of the static Coulomb stress changes on the inner fracture for different rake values.

Formation Stages and Evolution Patterns of Structural Fractures in Marine Shale: Case Study of the Lower Silurian Longmaxi Formation in the Changning Area of the Southern Sichuan Basin, China

“…Every time the rock is stressed, the microfracture system corresponding to the stress will be produced in its internal structure. This kind of microfracture is called a Griffith microfracture in tectonic mechanics. − When the rock is under stress, if the stress is less than the stress that produced fractures in the earlier stage, the defects formed will not further expand and the acoustic emission phenomenon will not occur. When the stress reaches or exceeds the previous stress, the acoustic emission (AE) phenomenon will occur, which is the Kaiser effect of rock.…”

Tectonic Fracture Formation and Distribution in Ultradeep Marine Carbonate Gas Reservoirs: A Case Study of the Maokou Formation in the Jiulongshan Gas Field, Sichuan Basin, Southwest China

“…In the 1950s, Kaiser discovered that the AE activity of metal materials has the characteristics of memory and irreversibility, which is called the Kaiser effect. In 1963, Goodman proved that rocks also have the Kaiser effect. , …”

“…In 1963, Goodman proved that rocks also have the Kaiser effect. 34,35 The essence of AE in rock is from the stress expansion of its internal microdefects. Every time that a rock is stressed, a microfracture system corresponding to the stress will be produced in the internal structure of the rock; it is called the Griffith fracture in tectonic mechanics.…”

Исследование Особенностей Процесса Разрушения Соляных Пород Методом Акустической Эмиссии

“…Метод основан на регистрации в массиве упругих волн, возникающих при деформировании и разрушении пород вследствие перераспределения напряжений, вызванного ведением горных работ [2]. Несмотря на успешные примеры использования метода при контроле подземных сооружений в массиве соляных пород [3,4] поиск надежных АЭ-критериев их устойчивого состояния остается актуальным вопросом. В качестве таких критериев могут выступать особенности изменения параметров импульсов АЭ при разрушении соляных пород.…”