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Journal Articles

Rock strength and stress dependence of local flow-path connectivity within faults or fractures; A Preliminary overview of virtual and in-situ hydraulic tests

Ishii, Eiichi; Ozaki, Yusuke; Aoyagi, Kazuhei; Sugawara, Kentaro*

Hydrogeology Journal, 32(8), 23 Pages, 2025/00

This study performed virtual packer tests on modeled single fractures on computer and derived the relationship between flow dimension and mappable indicator, DI, which is defined by the mean stress, groundwater pressure, and rock tensile strength. The greater DI results in the smaller flow area in faults or fractures, subject to fracture-normal closure. Comparing the derived relationship with results from in situ hydraulic tests on natural faults in rock with few fracture-mineral-fillings revealed that flow-path connectivity is high (flow dimension $$geqq$$1.5) when DI was $$<$$2.0 while was low (flow dimension $$leqq$$1.5) when DI was $$geqq$$2.0. This relationship was valid even when DI was varied, or faults were sheared, during injection tests on faults, and even in rock with abundant fracture-mineral-fillings. However, flow-path connectivity in minor fractures far from faults could be also low even when DI was $$<$$2.0 probably due to poor connection to the main fault network or sealing effects of fracture-mineral-fillings. When the permeability of intact rock is high, flow-path connectivity in fractures was high even when DI was $$geqq$$2.0. These findings can be helpful to map the spatial distribution of flow-path connectivity in faults or fractures from limited borehole data.

Journal Articles

Estimation of stress state using measured tunnel convergence in loop galleries excavated in mudstone

Aoyagi, Kazuhei; Sugawara, Kentaro*; Kamemura, Katsumi*; Nago, Makito*

International Journal of Rock Mechanics and Mining Sciences, 178, p.105776_1 - 105776_11, 2024/06

 Times Cited Count:0 Percentile:0.00(Engineering, Geological)

A method for estimating the stress state during the construction of underground facilities such as deep geological disposal repositories is necessary to enhance the reliability of their design, construction, and long-term performance. For this purpose, numerous in situ measurements of variables such as hydraulic fracturing or the stress relief method have been typically performed to estimate the stress state. However, it is difficult in some cases to validate the stress state, particularly in sedimentary rock, because of the variation related to heterogeneous rock masses and topography. This study developed a new method for reliably estimating the in situ stress state of rocks using the measured initial elastic displacement of the loop gallery at 350 m depth in the Horonobe Underground Research Laboratory (URL), Japan. The estimated magnitudes of the maximum and minimum horizontal stresses are 11.25 and 6.25 MPa, respectively, which are similar to the stresses measured using the hydraulic fracturing method performed before excavating the facility. Although the proposed method could only be applied after excavation of the gallery in the studied case, it yielded an estimate of the stress state over a region of hundreds of square meters with high accuracy, as assessed by comparison with measured results. We conclude that the method can be applied to optimizing the design, construction, and performance of large underground facilities, such as deep geological repositories.

Journal Articles

Si-addition contributes to overcoming the strength-ductility trade-off in high-entropy alloys

Wei, D.*; Gong, W.; Tsuru, Tomohito; Lobzenko, I.; Li, X.*; Harjo, S.; Kawasaki, Takuro; Do, H.-S.*; Bae, J. W.*; Wagner, C.*; et al.

International Journal of Plasticity, 159, p.103443_1 - 103443_18, 2022/12

 Times Cited Count:77 Percentile:99.57(Engineering, Mechanical)

Journal Articles

Estimation of in situ stress based on the measurement of convergence during gallery excavation

Aoyagi, Kazuhei; Kamemura, Katsumi*; Sugawara, Kentaro*; Hagihara, Takeshi*

Dai-53-Kai Jiban Kogaku Kenkyu Happyokai Happyo Koenshu (DVD-ROM), p.11 - 12, 2018/07

no abstracts in English

Journal Articles

Development of in situ stress estimation method based on the measured convergence and geological observations

Kamemura, Katsumi*; Aoyagi, Kazuhei; Nago, Makito*; Sugawara, Kentaro*

Dai-45-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.43 - 48, 2018/01

In situ stress state is very important for the design of deep underground facility of high-level radioactive waste disposal repository. This study establishes a practical and effective method for estimating in situ stress state based on the measured convergence and detailed geological observations during gallery excavation. The convergence was measured in various directions of the loop gallery at 350m depth of the Horonobe URL; this allows determination of the stress state corresponding to the rock mass behavior in 120m $$times$$ 200m area. In situ stress state estimated by the back analysis considering existing faults and fractures showed a good agreement with that of estimated from hydraulic fracturing method.

Journal Articles

Development of a back analysis method for the estimation of in situ stress based on the measured convergence in the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Kamemura, Katsumi*; Nago, Makito*; Sugawara, Kentaro*; Matsubara, Makoto*

Proceedings of ITA-AITES World Tunnel Congress 2017 (WTC 2017) (USB Flash Drive), 10 Pages, 2017/06

An in situ stress state is one of the important factors in the design of deep underground facility of high-level radioactive waste disposal repository. This study establishes a practical and effective method for estimating in situ stress state on the basis of the measured convergence during gallery excavation. The convergence was measured in various directions of the loop gallery at 350m depth of the Horonobe Underground Research Laboratory; this allows determination of the stress state corresponding to the rock mass deformation behavior in an approximately 120 m* 200 m area. To estimate in situ stress state around that area, a back analysis method considering the existence of faults and fractures around the gallery was developed. The analyzed results showed a good agreement with the trend of in situ stress state estimated from hydraulic fracturing method.

Journal Articles

Estimation of rock mass stress state based on the convergence measurement result during tunnel excavation

Kamemura, Katsumi*; Aoyagi, Kazuhei; Nago, Makito*; Sugawara, Kentaro*; Matsubara, Makoto*

Dai-14-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), 6 Pages, 2017/01

In the design of deep underground structures such as high-level radioactive waste disposal repositories, the estimation of rock mass stress state is important as well as the estimation of mechanical characteristics of rock mass. This study establishes a practical and effective method for estimating in situ stress based on the convergence measurement results obtained during gallery construction of URL. The convergence was measured in various directions of the URL loop gallery at 350 m depth, and this will allow determination of the stress state over a large area using a back analysis method. In order to improve the accuracy of initial stress estimation, the relationship between convergence measurement results and geological situation of existing fractures were studied. The analysis results show good agreement with the in situ stress state results reported in previous studies and confirm the applicability of the proposed method.

Journal Articles

Estimation of rock mass stress state based on convergence measurement during gallery excavation

Aoyagi, Kazuhei; Nago, Makito*; Kamemura, Katsumi*; Sugawara, Kentaro*

Proceedings of 9th Asian Rock Mechanics Symposium (ARMS-9) (USB Flash Drive), 10 Pages, 2016/10

Journal Articles

Estimation of initial stress based on the convergence measurement result during tunnel excavation

Kamemura, Katsumi*; Fujita, Tomoo; Aoyagi, Kazuhei; Nago, Makito*; Shirase, Mitsuyasu*; Sugawara, Kentaro*

Dai-44-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.109 - 114, 2016/01

How to estimate the initial stress state as well as a mechanical characteristic of rock mass is important in the design of deep underground structures. Some stress measurement methods using borehole, which methodology and evaluation method have been discussed in detail, are carried out if necessary. However, obtained results are often varying widely, so the evaluation of initial stress is difficult. Here, the initial stress state corresponding to the rock mass behavior of about 120m$$times$$200m area is evaluated using the convergence measurement results during tunnel excavation in 350m depth. Analysed result corresponded to that of other method, so the validity of the proposed method was shown.

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