A new method of diametrical core deformation analysis for in-situ stress measurements

Funato, Akio; Ito, Takatoshi

doi:10.1016/j.ijrmms.2016.11.002

Cited by 52 publications

(21 citation statements)

References 1 publication

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“…a hydraulic fracturing test nearby the initial location of the core sample, combining that information with the differential stress from DCDA. As for all strain analysis approaches, Young's modulus and Poisson's ratio have to be determined and the rock must meet the requirements of homogeneity, isotropy and linear elasticity (Funato and Ito 2017).…”

Section: Tests On Core Samples In Laboratorymentioning

confidence: 99%

An open-access stress magnitude database for Germany and adjacent regions

Morawietz

Heidbach

Reiter³

et al. 2020

Geotherm Energy

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Knowledge of the crustal stress state is important for the assessment of subsurface stability. In particular, stress magnitudes are essential for the calibration of geomechanical models that estimate a continuous description of the 3-D stress field from pointwise and incomplete stress data. Well established is the World Stress Map Project, a global and publicly available database for stress orientations, but for stress magnitude data only local data collections are available. Herein, we present the first comprehensive and open-access stress magnitude database for Germany and adjacent regions, consisting of 568 data records. In addition, we introduce a quality ranking scheme for stress magnitude data for the first time.

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Section: Tests On Core Samples In Laboratorymentioning

confidence: 99%

An open-access stress magnitude database for Germany and adjacent regions

Morawietz

Heidbach

Reiter³

et al. 2020

Geotherm Energy

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“…In the DCDA, the differential stress in the plane normal to a borehole is estimated from an azimuthal variation in diameter of a boring core sample (Funato and Ito, 2017). It is assumed that the core sample expands elastically in response to a stress relief when the core is cut from the rock mass by boring.…”

Section: Diametrical Core Deformation Analysis (Dcda)mentioning

confidence: 99%

“…The variable 0 represents diameter of the core sample before it expands in response to the stress relief. Since it is impossible to know 0 with such a high accuracy as its expansion (~1 m) in most cases, Funato and Ito (2017) assumed that ( − 0 ) ≪ 0 and that − 0 can be replaced by…”

Section: Diametrical Core Deformation Analysis (Dcda)mentioning

confidence: 99%

In-situ stress around source faults of seismic events in and beneath South African deep gold mines

Yabe¹,

Abe²,

Ito³

et al. 2019

Proceedings of the International Conference on Deep and High Stress Mining

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To demonstrate the possibility of stress measurement at depths of more than 3 km, in-situ stress states were determined around the source faults of three seismic events: a Mw2.2 seismic event at about 3.3 km below surface in Mponeng gold mine, a Mw3.5 seismic event at about 3.5 km below surface in the Savuka gold mine, and the Orkney earthquake (Mw5.5), with its hypocentre about 5 km below surface, beneath the Moab Khotsong gold mine. The Mw2.2 seismic event occurred in a 30 m thick gabbroic dyke that intruded into a host rock of quartzite. A 90 m long borehole was drilled to penetrate its source fault. Borehole breakout and core discing were observed in the host rock and the hanging wall of the source fault, i.e., in the dyke. Diametrical core deformation analysis (DCDA) and deformation rate analysis (DRA) were applied to core samples retrieved from the borehole. The DCDA determines the differential stress in the plane normal to a borehole by measuring the cross-section shape of a core sample, while the DRA reproduces the normal stress in the orientation in which a cyclic loading is applied, i.e., to obtain hysteresis of the stress-strain curves. By integrating these measurements and criteria of the borehole breakout and the core discing, the principal stress states in the host rock, the footwall in the dyke and the hanging wall in the dyke were reproduced. Significant differences were found between the stress states in the footwall and the hanging wall. The Mw3.5 seismic event occurred in a 36 m thick dyke called BV78. A tunnel that was damaged by the seismic event passed through the source region. The compact conicalended borehole overcoring (CCBO) technique was applied at two sites along the tunnel; one site was in an area de-stressed by mining and the other about 10 m from the dyke in an area of increased stress owing to the mining abutment above. DCDA was also applied to the core samples. Three boreholes (Hole A, Hole B and Hole C) that reach an aftershock area in the upper margin of the source fault of the Orkney earthquake (Mw5.5), were drilled by the ICDP-DSeis project (Ogasawara et al, 2019). Since the holes were designed to be drilled in the direction of the maximum compression, borehole breakout or core discing rarely occurred. The DCDA was applied to core samples recovered from Hole A and Hole B. The DRA was also applied to core samples of Hole A. The differential and the normal stresses along Hole A showed a spatial variation that correlates with a variation in lithology and the aftershock distribution.

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“…One of these is the down-sized compact conical-ended borehole overcoring (CCBO) technique, Sugawara and Obara (1999), which enhances the calibration of stress modelling Ogasawara et al (2012Ogasawara et al ( , 2014b; and Hofmann et al (2013), and improves the understanding of stress states in earthquake-prone ground. As Yabe et al (2019) detail, additional core-stress-measurements deformation rate analysis (DRA; Yamamoto, 2009) and diametrical core deformation analysis (DCDA; Funato and Ito, 2017) were carried out on the dyke core samples, resulting in much better constraints on the stress state in the seismogenic zone. The CCBO stress-measurement technique proved the existence of a normal-faulting stress regime at mining horizons.…”

Section: Introductionmentioning

confidence: 99%

2019 status report: Drilling into seismogenic zones of M2.0–M5.5 earthquakes in South African gold mines (DSeis project)

Ogasawara¹,

Liebenberg²,

Rickenbacher³

et al. 2019

Proceedings of the Ninth International Conference on Deep and High Stress Mining

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In 2014, a M5.5 earthquake ruptured the range of depths between 3.5 km and 7 km near Orkney, South Africa. The main and aftershocks were very well monitored in the nearfield by dense, surface, strong motion meters and a dense underground seismic network in the deep gold mines. The mechanism of this M5.5 earthquake was left-lateral strike-slip faulting, differing from typical mining-induced earthquakes with normalfaulting mechanisms on the mining horizons shallower than 3.5 km depth. To understand why such an unusual event took place, the aftershock zone was probed by full-core NQ drilling during 2017-2018, with a total length of about 1.6 km, followed by in-hole geophysical logging, core logging, core testing, and monitoring in the drilled holes. These holes also presented a rare opportunity to investigate deep life. In addition, seismogenic zones of M2-M3 earthquakes were probed on mine horizons that were also very well monitored by acoustic emission networks. This paper reviews the early results of the project.

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A new method of diametrical core deformation analysis for in-situ stress measurements

Cited by 52 publications

References 1 publication

An open-access stress magnitude database for Germany and adjacent regions

An open-access stress magnitude database for Germany and adjacent regions

In-situ stress around source faults of seismic events in and beneath South African deep gold mines

2019 status report: Drilling into seismogenic zones of M2.0–M5.5 earthquakes in South African gold mines (DSeis project)

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