Water inflow into the pit is a crucial problem in open pit mine operation when it is constructed below the water table. In this work, inflow rate into the pit mine is simulated by using MODFLOW codes. The model is assumed to be an equivalent porous medium and created in step excavation method. The result from the simulated model is verified by comparing with the analytical solution (Thiem-Dupuit assumption). During model creation, it is observed that Grid size plays an important role in inflow prediction. Model started with very finer size of grid and gradually increased the size to determine the effect of grid size on inflow rate. With the larger grid size, MODFLOW can predict inflow rate much better than the smaller one. At the same time, model boundary up to the ROI (Radius of Influence) gives better results. The inflow rate achieved by the simulated model is very close to the analytical solution (Error rate obtained approximately 0.3%). Several precautions are made to achieve a highly efficient result. Sensitivity analysis is also done for the simulated model with factorial design. A full factorial design is made by considering head, conductivity, drawdown, pit length and grid size as influencing factors. Among all these five factors, conductivity acts as the most significant factor, responsible to influence the inflow rate most.
Computer simulation model increases the ability of understanding hydrogeology of an open-pit mine. It also aids fast analyzing various geological properties of underground and open-pit mine. Model helps to reconstruct known groundwater head distributions and flow rates. Model identifies hydrogeologic parameters, which can influence groundwater flow path and helps to predict the future flow paths. When simulating hydraulic flow into an open pit mine in relatively flat landed region, water is supposed to flow into the pit from all directions. To create this situation, a higher head value is assigned at the boundary and a relatively smaller head value is assigned at the pit seepage face to make the flow towards the pit maintaining a standard linear gradient. Fig. 1 represents the 2D mesh of the model area and AA' line passes through the region.
Microseismic activities in the right bank slope of Dagangshan hydropower station occurred during reservoir impoundment. This paper introduces the results of microseismic monitoring, and three-dimensional (3D) finite element analysis is used to explore the microseismic activities and damage mechanisms in the right bank slope during reservoir impoundment. Based on data obtained from microseismic monitoring, a progressive microseismic damage model is proposed and then implemented in 3D finite element analysis. The safety factor of the right bank slope obtained from the 3D finite element analysis that includes the effects of progressive microseismic damage is 1.10, indicating that the slope is stable after reservoir impoundment. The microseismic monitoring system is able to capture the slope disturbance during reservoir impounding in real time and is a powerful tool for qualitatively assessing changes in slope stability over time. The proposed progressive microseismic damage model adequately simulates the changes in the slope during the impoundment process and provides a valuable tool for evaluating slope stability.
Landslides resulted from reservoir impoundment are common to see around the world. Reservoir landslides account for huge property losses and even make damage to people’s life. Commonly, borehole inclinometer, dislocation meter, piezometer, anchor stress gauge and GPS are the main monitoring methods which are used in slopes during reservoir impounding. However, conventional monitoring methods are limited by monitoring facilities layout. Microseismic monitoring can acquire the location, time and magnitude of rock mass fracture. Microseismic monitoring technique has been used in hydraulic and hydroelectric projects in recent years (Xu et al., 2016; Tang et al., 2015; Dai et al., 2017). With the development of computer technique, numerical method is widely used to analyze the slope stability during reservoir impounding. In this paper, microseismic monitoring technique and finite element method are used to analyze the stability of the right bank slope of the Dagangshan hydropower station, which is located in Sichuan Province, China, during reservoir impounding.
Globally there is an increasing pressure to reduce the greenhouse gas emissions and increase the use of renewable sources of energy. The storage of solar heat is a crucial aspect for implementing the solar energy for heating purposes especially in high latitudes, as it is the case in Finland, with sun insolation high in summer and almost negligible in winter when the domestic heating demand is high. To use the solar heating during winter thermal energy storages are required. In this paper, equations representing the single U-tube heat exchanger are implemented in weak form edge elements in COMSOL Multiphysics to dramatically speed up the calculation process for modelling of a borehole storage layout. Borehole seasonal solar heat storage of 6425 m3 volume with 64 boreholes is successfully simulated. After 10 years of operation the simulated borehole pattern recovers 62.8% of the stored seasonal thermal energy and provides 380 MWh of thermal energy for heating in winter.
Globally there is an increasing pressure to reduce the greenhouse gas emissions and increase the use of renewable sources of energy. One of the common applications of renewable energy is the solar heat, where energy from the sun is used to heat up water and space in buildings. The storage of solar heat is a crucial aspect for implementing the solar energy for heating purposes. This is especially important in high latitudes, as it is the case in Finland, where sun insolation is highest in the summer when the heating demand is low and lowest in winter when the demand is high.
Previously the authors concluded that the borehole thermal energy storage (BTES) is recommended method for seasonal solar heat storage for small solar community (Janiszewski et al., 2016). In this paper, the implementation of a weak form edge element is presented with the modelling results of a borehole storage layout using COMSOL Multiphysics® 5.2a software. The models can be used for optimisation of the thermal energy borehole storage concept for a small solar community.
The mechanism of rock fragmentation by disc cutters during tunneling is the key to influencing the TBM (Tunnel Boring Machine) performance. In order to study the characteristics of the rock fragmentation process, various numerical methods were performed to establish the three-dimensional model. In this paper, three disc cutters are regarded as the research object, and accordingly three basic collaborative rock fragmentation patterns are proposed to analyze the collaborative effects of disc cutters on the rock fragmentation process, including the sequential cutting pattern, the inside-out cutting pattern and the outside-in cutting pattern. Also, the numerical models of three 19-inch disc cutters are established using the ABAQUS software, considering three different cutting patterns. The center cutters, the plane cutters and the gauge cutters are all considered in this numerical simulation due to their different rotating radius and installation angles, and the model also takes several different rock types into account to consider the stratum influence. The specific rock parameters are collected from the rock samples in Yinhanjiwei Water Conveyance Project. By means of simulating the rotating cutting motion of three rock fragmentation patterns, the mechanical parameters and the specific energy of the disc cutters are analyzed to obtain the best cutting pattern. The results show that the inside-out pattern is one of the most ideal patterns in rock fragmentation process. Furthermore, the results of simulations are verified by the Linear Cutting Machine tests, and can provide some reasonable suggestions for the optimization of the disc cutters layout design of TBM.
The tunnel boring machine (TBM) has been widely applied to tunnel constructions like the subway, the railway, the highway and the water conservation projects, due to its rapid advance rate, high efficiency, nice tunnel formation, little impact on the surrounding environment and excellent working safety (Zhao, 2007). The TBM tunnel excavation depends on disc cutters which are installed in the cutterhead to cut rocks. The performance prediction and rock fragmentation mechanism by TBM cutters are becoming considerably important issues. Research aims to study the rock fragmentation mechanism of TBM cutters and to instruct the optimization of the layout pattern of TBM cutters.
Frost weathering frequently occurs at high-latitude and alpine regions, as well as in winter season at mid-altitude region. The weathering damages to building stones, surface of structures and cultural heritages, and can form distinguishing geomorphology. In this research, microstructure of rock specimen is analyzed using micro X-ray CT and SEM. Using scanning electron microscope (SEM) images, particle detachment, pore connection and crack propagation/expansion were detected, and porosity is analyzed quantitatively. Using X-ray computed tomography, variation on open/closed porosity, pore size distribution, equivalent diameter and local thickness were analyzed. This research can be applied to construction, resources exploitation, prevention of geological disaster, and preservation of historical monuments in cold regions.
Frost weathering frequently occurs at high-latitude and alpine regions, as well as in winter season at mid-altitude region. The weathering damages to building stones, surface of structures and cultural heritages, and can form distinguishing geomorphology. Although there have been many researches to investigate frost weathering, most researchers have focused on variation on physical properties or on the rock surface. The purpose of this study is to evaluate frost weathering of igneous rocks quantitatively using micro-CT and SEM.
2.1 Sample description
Three types of igneous rock were collected in Korea. Basalt, sampled at Cherwon-gun, Gangwon-do, has vesicular texture with needle-shape plagioclase; Diorite, sampled at Goheung-gun, Jeollanam-do, was coarse-grained rock consisting of plagioclase, olivine, micas, quartz and microcline; and Lapilli tuff, sampled at Hwasun-gun, Jeollanam-do, was fine-grained rock with feldspar, quartz, micas, quartzite fragments, and basaltic fragments.
Arima, H. (Hokkaido University, Sapporo) | Sainoki, A. (Kumamoto University) | Fukuda, D. (Hokkaido University, Sapporo) | Kodama, J. (Hokkaido University, Sapporo) | Fujii, Y. (Hokkaido University, Sapporo) | Murayama, H. (Fujita Corporation, Tokyo) | Niwa, H. (Fujita Corporation, Tokyo) | Okazaki, K. (Civil Engineering Research Institute for Cold Region, Hokkaido)
In Hokkaido prefecture, Japan, a number of road mountain tunnels constructed with conventional support systems are still in use. In one of the tunnels, the progressive damage evolution and large deformation of the tunnel wall were observed. The present study investigates its mechanism and the effectiveness of the conventional support system. In order to simulate the time-dependent behavior of the target tunnel, a variable-compliance-type constitutive equation is employed and implemented into FLAC3D. A 3D numerical model reproducing the actual ground surface topography is constructed. Using the numerical model and constitutive equation, the time-dependent damage evolution and resultant deformational behavior are simulated whilst considering combinations of the conventional support system members, namely steel sets, concrete lining and invert concrete. The analysis results show that concrete invert installation is the most effective measure to suppress and control the damage evolution and deformation of the tunnel wall. The concrete lining is the second effective, alleviating the deformation taking place on the tunnel wall and crown. It is then revealed that steel sets do not significantly contribute to suppressing the damage evolution. The analysis result also indicates that axial stresses originally acting on the steel sets are re-distributed to the concrete lining and invert concrete, proving that the two support members can work more effectively than steel sets in the aspect of controlling the time-dependent damage evolution of the surrounding rock mass.
More than 130 road mountain tunnels using conventional support system are still in use in Hokkaido prefecture, Japan, although NATM has already become common in Japan. In one of the tunnels, crack initiation was observed at the crown on concrete lining during its construction (hereafter, this tunnel is referred to as “target tunnel”). Occurrences of serious deformation on its side wall and concrete lining rupture after completion of the tunnel construction were also reported. It is conjectured that these were caused by the time-dependent expansion of a damage zone within a weak rock formation found in the target tunnel subjected to large horizontal stress. Comprehending the damage evolution process and its mechanism is imperative for stability assessment of not only the target tunnel but also other tunnels using similar conventional support system.
Diaz, Melvin B. (University of Science and Technology, Korea) | Kim, Kwang Yeom (Korea Institute of Civil Engineering and Construction Technology) | Shin, Hyu Soung (Korea Institute of Civil Engineering and Construction Technology)
We present an optimized training and prediction model for Rate of Penetration (ROP) forecasting using on-line artificial neural network (ANN) in real-time. The technique aims to assist decision making on drilling operations by predicting ROP under a given set of drilling conditions. The scenario modeler relies on real time drilling data analysis, and it is capable of handling cumulative information analysis in real time for ROP prediction within the same well, but also can consider drilling data gained from other fields under similar conditions. The real time prediction model has been applied to drilling data coming from a geothermal project of over 4 km depth, located in the Pohang, Republic of Korea. The observed results with respect to data intervals or sections set the basis for further adjustments to the model, and encourages its use in different drilling situations.
ANN have been applied to a wide variety of field research areas that include computer vision, speech recognition, and petroleum engineering (Bilgesu et al., 1997). Especially, in the aforementioned field, ANN have been used for ROP forecast (Gidh et al., 2012). It has been shown that this technique is dependent on the size and accuracy of the input parameters, and in general the more number of data points, the better the results. Its ability to consider more drilling parameters into the model makes it advantageous (Monazami et al., 2012).
During ANN learning phase, a selected group of input parameters are provided to the model and they serve to train the algorithm. Two basic types of learning modes can be mention, On-line and off-line training, and they distinguish from each other basically on the training cases are managed after training (Shin 2001). In on-line training, the provided input parameters are discarded after being processed, however the weights are updated.
Owing to the accumulative manner the drilling data is generated in the field, this work explores the applicability of an artificial neural network with an on-line training mode for ROP prediction especially in subsequent drilling sections within the same well.
The aspect of the change in the liquid permeability of rock using distilled water and brine has been reported to be different from that of using gas according to confining pressure Pc and pore pressure Pp. In this study, as part of the research on CO2 geological storage, the permeability of sandstone was measured using supercritical CO2 which has gas and liquid properties simultaneously, and the effect of Pc and Pp on this permeability was analyzed. For supercritical CO2 to be utilized, the series of non- Darcy flow tests with high flow rate were conducted, and the permeability was estimated through the Forchheimer equation considering an inertial flow. An effective pressure coefficient for permeability was derived experimentally to be applied to the effective pressure law. First, we investigated pressure conditions with identical permeability for plotting the iso-permeability line. From the effective pressure law, the effective pressure coefficient of permeability corresponds to the slope of the iso-permeability line. As a results, upon the confining or pore pressure conditions, varied permeability and effective pressure coefficient indicated. To clarify the variation of the coefficient depending on the pressure conditions, we attempted to drive a second-order effective pressure coefficient for which the interaction between Pc and Pp was considered. The coefficient increased non-linearly as the difference of Pc and Pp decreased, with a maximum of 1.36 being observed. The validity and correlation between the effective pressure with the coefficient and the permeability were examined by applying empirical models of permeability dependent on effective pressure.
Previous studies have demonstrated that the liquid permeability of rock with distilled water and brine is different by variation in the confining pressure Pc and pore pressure Pp (Wei et al., 1986). It is important to acknowledge that the supercritical CO2 (here after scCO2) permeability of rock should be examined by taking account of the properties of the supercritical phase midway between the gas and liquid states.
Xiao, Yong (Southwest Petroleum University, China and University of Utah) | Guo, Jianchun (University of Utah) | Chen, Mengting (Southwest Petroleum University, China) | McLennan, John (University of Utah)
The most important consideration for geothermal energy development in non-hydrothermal scenarios is the use of hydraulic fracturing technology to establish an effective network pathway to conduct fluid from injector(s) to producer(s). The number of interconnected fractures and their deformation of the network pathway becomes an important parameter to characterize effective conductivity in geothermal reservoirs. A coupled hydro-mechanical model is used to study conductivity aperture changes by taking account the effect of fracture deformation. The deformation characteristics described invoke a pre-peak linear elastic constitutive relationship and non-linear elastic-plastic constitutive behavior after the peak stress is reached. Starting with accepted dynamic friction-weakening, a hydraulic aperture concept is superimposed and modifications are suggested to available post-peak elastic-plastic constitutive models. Displacement discontinuity method (DDM) is used to construct a boundary element method, which is able to analyze the induced stress field around the unconnected natural fracture. As a result, the unconnected fracture will be in a new stress zone which includes in-situ stress and induced stress. The Barton criterion is used to judge the stability of the disconnected fractures under the new stress field.
Jeon, Min-Kyung (Korea Advanced Institute of Science and Technology, Daejeon) | kwon, Tae-Hyuk (Korea Advanced Institute of Science and Technology, Daejeon) | Voltolini, Marco (Lawrence Berkeley National Laboratory) | Ajo-Franklin, Jonathan (Lawrence Berkeley National Laboratory)
Geologic carbon storage is one of the promising methods to reduce atmospheric carbon dioxide (CO2) concentration. Successful injection and storing of supercritical CO2 (scCO2) in geologic formations requires prediction of invasion behavior of scCO2 because it determines the efficiency of capillary trapping (or residual trapping). We investigated the invasion behavior of scCO2 in a brine-saturated sandstone using pore network modeling. The pore network was generated by using microCT imageries of a sandstone from the Domengine formation that is considered as a potential candidate site for geologic CO2 storage. Then, scCO2 injection to the brine-saturated pore network was simulated by applying the constant pressure difference between the inlet and outlet. This study presents the distribution of invaded scCO2 in the pore network, followed by the discussion on the residual saturations of scCO2 and brine at various differential pressure.
Pore network modeling have been used to predict microscopic behavior of multi-phase flow in porous media. For geological storage of CO2, understanding and prediction of multi-phase flow behavior of scCO2 is fundamental to predict the efficiency and integrity of CO2 storage because the residual trapping (or capillary trapping) plays a significant role in immobilization of scCO2.
In this study, we investigated the invasion behavior of scCO2 in a brine-saturated sandstone using pore network modeling. While flow experiments with scCO2 appears to be challenging due to high pressure and temperature conditions and low repeatability, two-phase flow simulation using the pore network modeling was performed to explore scCO2 distribution in porous media during and after scCO2 injection. The pore network, which is a network consisting of cylindrical pore throats and spherical pore chambers, was reconstructed by using microCT imageries of a Domengine sandstone. Then, scCO2 injection to the brine-saturated sandstone was simulated by applying the constant pressure difference between the inlet and outlet. The distributions of invaded scCO2 in the pore network were presented, and the discussion on the residual saturations of scCO2 and brine at various differential pressure followed.