Estimation of regional stress by FEM for a heterogeneous rock mass with a large fault

Matsuki, Koji*; Nakama, Shigeo; Sato, Toshinori

International Journal of Rock Mechanics and Mining Sciences, 46(1), p.31 - 50, 2009/01

https://doi.org/10.1016/j.ijrmms.2008.03.005

This paper consists of two parts. In Part I, we propose a method for determining regional stress from limited stress data by using a 3D finite element method (FEM) in which we define regional stress for a heterogeneous rock mass composed of different rock bodies and a large fault as a displacement boundary condition that is consistent with the mean trend of in situ stress. This method was applied to a small-scale heterogeneous model with a large planar fault that penetrates the region to clarify the estimation accuracy and the effects of incorrect stiffness of the fault, incomplete stress data, and the assumption that the fault shows partial, but not complete, sliding. The results showed that (1) the method proposed in this study can accurately estimate the stress distribution in the region under consideration except at the bottom when the sliding area of the fault is small, (2) the reproducibility of the given stress indicates that the method can be used to estimate appropriate values of the normal and shear stiffnesses of the fault, and (3) both incomplete stress data and the assumption that the fault does not slide decrease the accuracy of stress estimation while the given stresses are approximately reproduced. In Part II, this method is applied to the Tono area, in Japan.

Evaluation of groundwater flow during excavation of shafts by inversion of tilt data

Nakatani, Katsuya*; Matsuki, Koji*; Arai, Takashi*; Omura, Kazuo*; Takeuchi, Shinji; Arai, Yasushi; Horimoto, Seiki*

Journal of MMIJ, 123(1), p.26 - 32, 2007/01

https://doi.org/10.2473/journalofmmij.123.26

Groundwater flow at the site of MIU (Mizunami Underground Research Laboratory) in the Tono district, Japan, was evaluated by a new inverse method using tilt data measured by four tiltmeters during excavation of shafts. The features of the method are that the fluid volume change per unit volume of rock (dv) is assumed to vary in a quadratic manner with the coordinates in elements within a region of groundwater flow, that the values of dv are set to zero at the boundaries of the region and that the sum of squared second derivatives of dv are adopted as constraining conditions which are weighed and added to a squared error in the tilt. An inverse analysis was performed by assuming three sizes for a whole region of groundwater flow. It was shown that there are three regions where the volume of groundwater decreases and two regions where the volume of groundwater increases regardless of the size of the whole region of groundwater flow and that groundwater came mainly from the sedimentary rocks lying between two faults. The latter is consistent with the previous prediction that these faults have a low permeability and may act as a flow barrier. Furthermore, the results of the inverse analysis predict that there may be other hydrogeological structures which prohibit groundwater flow. Thus, the inverse method proposed by the authors for evaluating groundwater flow from tilt data has proved to be reliable in spite of the assumption that the rock mass is a homogeneous and semi-infinite body.

Study on Improved Procedure for Determination of Three Dimensional Distributions of the Initial Rock Stress (Third Report)

Mizuta, Yoshiaki*; Kaneko, Katsuhiko*; Matsuki, Koji*; Sugawara, Katsuhiko*; Sudo, Shigeaki*

JNC TJ7400 2004-011, 125 Pages, 2004/02

JNC-TJ7400-2004-011.pdf:11.26MB

In the fiscal year of 2003, our committee achieved the following work items during the contract period, from September 3rd, 2003 to February 13th, 2004. The more accurate numerical data with respect to the geological / geometrical conditions including the fault were provided from Tono Geoscience Center and the numerical models by Finite Element Method (FEM), Finite Difference Method (FDM) and Boundary Element Method (BEM) were built taking those strata data into account. For small region modeling by FEM, these layers models, Shoumasama model and Tohnou-Shoumasama model, as well as Thounou Mine model, were constructed, and each strain state at the far field boundary was determined. In order to get better agreement in local stress states with the measured values, a far field strain state was determined to the modified model in which material properties of upper granite and lower granite are different. In intermediate region modeling by FDM, actual strata data was taken into account, whereas strata boundary was assumed to be horizontal in former modeling, and far field stress field was analyzed. Intermediate region modeling by BEM was also carried out and field stress state was determined. In wide region modeling by FEM, the fault was built in the model and fault slip was taken into account, and evaluation of strain state at the far field boundary was carried out for inhomogeneous rock including fault. It was proposed to output three-dimensional distribution of the maximum shear stress coefficients in order to advance three-dimensional modeling. It will make clear effect of shape, scale and property of the fault on stress state characteristic. This report describes minutely the results of the studies mentional above.

None

Sekimoto, Yoshinori*; Yamashita, Shigeru*; Ishijima, Yoji*; Ezaki, Tetsuro*; Matsuki, Koji*

PNC TJ1559 92-002, 112 Pages, 1992/03

PNC-TJ1559-92-002.pdf:2.96MB

None

Evaluation of groundwater flow during excavation of shafts by inversion of tilt data

Matsuki, Koji*; Nakatani, Katsuya*; Arai, Takashi*; Omura, Kazuo*; Takeuchi, Ryuji; Arai, Kiyoshi*; Takeuchi, Shinji

no journal, , 

By using a new method for accurately estimating a change in groundwater volume by an inverse analysis of tilt data, groundwater flow at the site of Mizunami Underground Research Laboratory in the Tono district, Japan, was evaluated during excavation of two shafts, based on tilt data measured by four tiltmeters with a resolution of 10 radians. The method developed in this study reproduced the tilt data accurately, and the results obtained by the inverse analysis showed that heterogeneous flow of groundwater occured during the excavation and groundwater came mainly from sedimentary rocks lying between two faults. The latter is consistent with the previous prediction that these faults have a low permeability and may act as a flow barrier.

Advanced study for determination of three dimensional distributions of the initial rock stresses

Nakama, Shigeo; Sato, Toshinori; Kaneko, Katsuhiko*; Matsuki, Koji*; Sugawara, Katsuhiko*; Mizuta, Yoshiaki*

no journal, , 

no abstracts in English

Appricability of the method to estimate hydrogeological structures using a tilt data

Oyama, Takuya; Takeuchi, Ryuji; Saegusa, Hiromitsu; Onoe, Hironori; Matsuki, Koji*

no journal, , 

Authors have been developed the technique for estimating hydrogeological structures, which influence the deep groundwater flow, by an inverse analysis using tilt change by an artificial impact of the underground facility construction. It is possible to complement the data from borehole investigations by using the technique based on the data obtained from surface area. This paper describes the results of evaluation for the applicability of the technique by comparing with the long-term hydraulic monitoring data.