Initial Stress Measurement Research Articles

Analysis of Äspö Pillar Stability Experiment: Continuous thermo-mechanical model development and calibration

The paper describes an analysis of thermo-mechanical (TM) processes appearing during the Äspö Pillar Stability Experiment (APSE). This analysis is based on finite elements with elasticity, plasticity and damage mechanics models of rock behaviour and some least squares calibration techniques. The main aim is to examine the capability of continuous mechanics models to predict brittle damage behaviour of granite rocks. The performed simulations use an in-house finite element software GEM and self-developed experimental continuum damage MATLAB code. The main contributions are twofold. First, it is an inverse analysis, which is used for (1) verification of an initial stress measurement by back analysis of convergence measurement during construction of the access tunnel and (2) identification of heat transfer rock mass properties by an inverse method based on the known heat sources and temperature measurements. Second, three different hierarchically built models are used to estimate the pillar damage zones, i.e. elastic model with Drucker–Prager strength criterion, elasto-plastic model with the same yield limit and a combination of elasto-plasticity with continuum damage mechanics. The damage mechanics model is also used to simulate uniaxial and triaxial compressive strength tests on the Äspö granite.

わが国で開発・改良された初期地圧測定法の基準化と国際化

The techniques of initial stress measurement were developed and improved in Japan. It is recommended to standardize some dominant methods in domestic market at first, and then encourage related organizations to promote them to international standard, in order to take an advantageous position of the methods in the international market. Currently, stress relief method and hydraulic fracturing method are considered to be valuable and practical methods. The compact conical-ended borehole overcoring method, one of the stress relief methods, was assigned as the standard of the Japanese Geotechnical Society in 2012. In addition, the new committee has been organized recently for standardizing the high stiffness testing method, an improved hydraulic fracturing technique. If international standard methods that are not the method used in Japan were assigned in future, we may be at a disadvantage for international bids. We may lose opportunities to apply our valuable technical resources such as engineers, instruments, established standards, and know-how in international market. And our techniques may become irrelevant in the international market. Our methods havebeen applied in many domestic foundation investigation fields such as construction of underground power plants, nuclear power plants, and large scale tunnels. It is in our best interest to have our techniques become the international standard as we expect an increase of requirement of those techniques in developing countries in future.

幌延地域に分布する珪質岩に対する幾つかの岩盤応力測定法の適用性と推定された応力状態

幌延地域に分布する珪質岩に対する幾つかの岩盤応力測定法の適用性と推定された応力状態

An experimental investigation of thermal prestressing method for continuous composite steel girder bridges

This paper describes an experimental investigation conducted to verify and substantiate the preceding analytical study, which was focused on the development of the thermal prestressing method (TPSM) including the basic concepts of the method and the methodology for numerical analysis of the thermal prestressing effect. The experimental results from this research, especially the initial stress measurement from a prototype bridge, prove that the method can be successfully used for prestressing continuous composite girder structures. Also, the experimental and analytical results exhibit good agreement, which implies that the thermal prestressing effect can be predicted with reasonable accuracy with the previous proposed methodology. It is concluded that the TPSM can be successfully applied to both the design and construction of continuous composite girder structures, and the authors are optimistic about the TPSM becoming an innovative solution for prestressing continuous composite girder bridges.

Safety Management Based on Detection of Possible Rock Bursts by AE Monitoring during Tunnel Excavation

As underground development continues at great depths, the danger of rock bursts will inevitably increase. It is important to consider countermeasures for avoiding rock bursts in underground work. In Japan, rock bursts have actually been experienced during construction of several tunnels, including the Kan-etsu tunnel construction project, during which many rock bursts were observed. Stress analysis of tunnels is performed based on initial stress measurements in the base rock. In addition, AE measurement has been adopted in construction management, allowing safer excavation. Collective analysis of the data obtained has been shown to be effective for safety control during excavation of hard base rock. In this research, initial stress measurements in base rock, secondary stress analysis around a tunnel, and AE measurements are examined. Based on the results of this analysis, it is clear that the generation of rock bursts is related to the presence of geological discontinuities.

Effect of stress on the aluminum-induced crystallization of hydrogenated amorphous silicon films

The effect of stress, resulting from the presence of hydrogen, on the aluminum-induced crystallization of hydrogenated amorphous silicon films was studied. Layered thin films of hydrogenated and unhydrogenated amorphous silicon and aluminum, deposited by sputtering, were used to study this effect. The stress of the deposited films was determined by measuring the radius of curvature of c-Si substrates before and after deposition of the films. It was observed that unhydrogenated amorphous silicon films exhibit a high compressive stress compared with hydrogenated ones. The amount of stress is shown to decrease with increasing hydrogen content. It was also observed that aluminum always provides tensile stress. After the initial stress measurements, all the samples were annealed for 30 min at temperatures between 200 °C and 400 °C. X-ray diffraction was used to determine the crystallinity of the silicon films. The results of the study show that the temperature at which crystallization of amorphous silicon is initiated is lower for films with a lower initial stress.

Theory of Measurement of Initial Stresses, by Stress Release Method for Micropolar Elastic Medium

In this paper, initial stress measurement theory of micropolar elastic medium by stress release method is described. This measurement method uses the circular solid inclusion cell (SI-cell) as the strain sensor. And because of the SI-cell is regard as inclusion embedded in the micropolar elastic medium, measurement theory is derived by use of the solution of the elastic material with a inclusion problem through the correspondence principle between elasticity and couple stress elasticity. The characteristic of this measurement theory is that the radius of an over coring is finite. Several examples are shown by graphical representation and numerical results.

接着層を考慮した埋設型計測器（ＳＩ‐ｃｅｌｌ）による粘弾性岩盤に対する初期応力測定理論

In this paper, the theory of initial stress measurement based on stress release technique for vscoelastic rock with circular solid inclusion cell (SI-cell) is described. And this theory not only uses the complex variable method and the correspondence principle between elasticity and viscoelasticity, but also considers a bonding interface between a rock and SI-cell. In addition, the problem under pure 3-dimensional loadings can be solved as semi-3-dimensional analyses. Several examples are shown by graphical results.

Residual stress states before irradiation in ESS target structural materials

The present work takes place in the framework of the European Spallation Source target research and development program. A wide spectrum of miniaturized, mechanical test specimens of different structural materials were placed into the SINQ target (Paul Scherrer Institute, Villigen, Switzerland) for post-irradiation investigations, including evaluation of the stress fields produced by irradiation using neutron-diffraction techniques. The measurements on irradiated specimens are planned at SINQ using a new diffractometer designed for this purpose. This paper presents initial stress measurements performed at ISIS (Chilton-Didcot, England) and ILL (Grenoble, France) on specimens which were not irradiated, in order to provide the reference residual stress states and validate the experimental procedure. Both experiments give evidence of a tensile stress state around the weld in electron-beam-welded specimens, while the presence of a crack does not seem to introduce high residual stresses into the center of the weld.

Seawater pumped-storage power plant in Okinawa island, Japan

The authors describe the characteristics, problems and treatment of a seawater pumped-storage power plant which is the first high headtype power plant in the world. The authors propose a general geologic investigation program using boreholes for underground projects. The effectiveness of the investigations conducted by EPDC are evaluated before construction of the vertical shaft of the seawater pumped-storage power plant in Okinawa island, Japan. In the investigation stage of the project, no adit was excavated and all geological and geotechnical information about the underground facilities were obtained efficiently from exploration by drill holes including logging and geotechnical tests such as observation by borehole scanner, prospecting by VSP, initial stress measurement by sleeve fracturing method and JFT test.