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Oil & Gas
Development of Elasto-Plastic NMM-DDA and its Application to the Stability Analysis of Prasat Suor Prat, Angkor
Hashimoto, R. (Kyoto University) | Koyama, T. (Kyoto University) | Kikumoto, M. (Yokohama National University) | Yamada, S. (Waseda University) | Araya, M. (Waseda University) | Iwasaki, Y. (Geo-Research Institute) | Ohnishi, Y. (Kyoto University)
ABSTRACT There are many historic remains in the world and among them many masonry structures are in danger of collapse. To select suitable methods for restoration and preservation, it is greatly important to evaluate the stability of masonry structures considering the interaction between foundation ground and masonry building, and accurate calculation of stress distribution inside the masonry structures is required. In the previous studies, NMM-DDA (coupled umerical anifold ethod and iscontinuous eformation nalysis) one of the discontinuum based numerical methods wasdeveloped to satisfy these requirements and used for the stability analysis of PrasatSuorPrat N1 Tower in the Angkor monuments, Cambodia firstly. However, the original NMM-DDA code treats only elastic bodies (for both DDA blocks and NMM elements) and cannot treatthe failure of soil properly. Hence, in this study, theelasto-perfectly plastic constitutive law was newly introduced to the original NMM-DDA code, and the validitywas checked by performing biaxial test numerically and comparing with analytical solution.The newly developed elasto-plastic NMM-DDA was applied to the stability analysis of PrasatSuorPrat N1 Tower. The simulation results were compared with the on-site observation/investigation and the applicability of elasto-plastic NMM-DDA wasalso discussed.
The JAEA Grouting Test At the Grimsel Test Site: Numerical Simulation of the Grout Injection Process of Silica Sol In Fractured Rock Mass
Koyama, T. (Kyoto University) | Ohnishi, Y. (Kyoto University) | Bruines, P. (Obayashi Corporation) | Tanaka, T. (Obayashi Corporation) | Hasui, A. (KANSO Technos, Co., Ltd) | Katayama, T. (KANSO Technos, Co., Ltd) | Kishi, H. (Japan Atomic Energy Agency (JAEA)) | Kuzuha, Y. (Japan Atomic Energy Agency (JAEA))
Abstract: Grouting, which involves injection of grout material, is commonly used to decrease the hydraulic conductivity of the fractured rock masses and control the groundwater inflow. Since underground facilities were constructed in various geologi-cal conditions, different types of grout material were developed and injected. On the other hand, different types of mixing and injection methods were also developed/ im-proved more effectively and economically. It is also important to evaluate the grout arrival distance and the range of altered hydraulic conductivity after injection. Howev-er, the mechanism of grout injection process has not been clarified sufficiently yet due to complicated chemical and physical processes of grout. In this study, to simulate the grout injection process, the three-dimensional numerical model based on equivalent continuum approach was developed. The viscosity measurements for silica sol and laboratory injection tests using sand column were performed in order to measure the time-dependent viscosity and to investigate the injection mechanism of silica sol. The developed numerical model was applied to the planned in-situ grout injection tests at Grimsel test site, Switzerland. The preliminary simulation was carried out to determine the suitable grout injection pressure and to investigate the arrival distance of silica sol. Simulation results showed that the grout (silica sol) reached 3m and the hydraulic conductivity was decreased in one order around the 1.0โ1.5m from injection hole after injection of 160 minutes. The distribution of grout concentration as well as hydraulic conductivity reduction rate clearly shows the anisotropic infiltration of grout. 1 INTRODUCTION Grouting, which involves injection of grout material, is commonly used to decrease the hydraulic conductivity of the fractured rock masses and control the groundwater inflow. Since underground facilities were constructed in various geological conditions, different types of grout material were developed and injected depending on the geo-logical conditions.
Abstract: Grouting is a widely used method for sealing fractured rock masses around underground structures to reduce or stop groundwater inflow. However, even at pre-sent, the filtration and penetration mechanism of cement-based grout have not been clarified sufficiently yet due to complicated physical and chemical processes of grout, such as pressure-dehydration, consolidation, bleeding, clogging, absorption, sedimen-tation and condensation etc. In this research, to better understand the penetration and filtration mechanism of cement-based grout through rock fractures, a two-dimensional numerical model of coupled Computational Fluid Dynamics and the Distinct Element Method (CFD-DEM) had been developed. By using a direct numerical simulation technique, the interaction between fluid and particles can be evaluated. The simulation results were compared with the laboratory injection test to verify the applicability of the newly developed CFD-DEM code. As a result, the simulation results agree qualitatively well with the actual experi-mental results, and the clogging process during the injection of cement-based grout was successfully reproduced by the CFD-DEM code. Moreover, based on these re-sults, the influence of the water/cement ratio of grout on the filtration and penetration mechanism was investigated in detail. The presented numerical model in this paper gives a better understanding for filtration and penetration mechanism of cement-based grout. 1 INTRODUCTION Grouting is a widely used method for sealing fractured rock masses around under-ground structures to reduce or stop groundwater inflow. One important aspect is the grout penetrability. So far, many experimental studies have been done to detect the penetrability of grout. According to the conventional hypotheses (Gustafson and Stille 1996), the penetration length of cement-based grout depends on the accumulated fric-tion between the grout and the fracture walls. Moreover, the grout penetration stops when the cement grains build a stable arch over a fracture constriction during penetra-tion. This process is known as plug-building or filtration.
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
The JAEA Grouting Test At the Grimsel Test Site: Site Characterization of a Fractured Rockmass And Preparation of DFN Model And Its Equivalent Continuous Porous Media Model
Bruines, P. A. (Obayashi Corporation) | Tanaka, T. (Obayashi Corporation) | Koyama, T. (Kyoto University) | Kishi, H. (Japan Atomic Energy Agency (JAEA)) | Nakanishi, T. (Japan Atomic Energy Agency (JAEA)) | Ohnishi, Y. (Kyoto University)
Abstract: To better understand the grouting process and the effect of grouting on the performance of a nuclear waste repository, the Japanese Atomic Energy Agency (JAEA) has initiated a grouting test carried out in the fractured granite of the Grimsel Test Site (GTS) located in the Swiss Alps. This paper describes the characterization of the rock mass, how the data obtained has been used to make a discrete fracture network (DFN) model and how an up-scaled equivalent continuous porous media (ECPM) model for the purpose of numerical simulation of the grout injection process is generated. Using the optical borehole television (BTV) and hydraulic test data from the boreholes drilled in this project, a number of DFN models have been constructed. The DFN models consist of a stochastic and a deterministic part. The known fractures (from BTV) are included deterministically in the model and their transmissivities have been optimized using the measured hydraulic test results. The distribution of fractures as well as their transmissivities for the stochastic part is based on the distributions extrac-ted from the measured values. The resulting DFN model is then up-scaled using 0.5m cubic blocks to obtain a detailed ECPM model. The generated DFN model and the up-scaled ECPM model was able to reproduce the measured fracture characteristics (e.g. orientation, density) as well as the hydraulic behavior observed in the field (e.g. trans-missivity distribution, anisotropy, heterogeneity) and has proven to be suitable for modeling tracer tests and grouting. 1 INTRODUCTION To better understand the grouting process and the effect of grouting on the perform-ance of a nuclear waste repository, the Japanese Atomic Energy Agency (JAEA) has initiated a grouting test carried out in the fractured granite of the Grimsel Test Site (GTS) located in the Swiss Alps.
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)