• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.665-675
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• 2022

The safety problems of giant hydraulic structures such as dams caused by terrorist attacks, earthquakes, and wars often have an important impact on a country's economy and people's livelihood. For the national defense department, timely and effective assessment of damage to or impending damage to dams and other structures is an important issue related to the safety of people's lives and property. In the field of damage assessment and vulnerability analysis, it is usually necessary to give the damage assessment results within a few minutes to determine the physical damage (crack length, crater size, etc.) and functional damage (decreased power generation capacity, dam stability descent, etc.), so that other defense and security departments can take corresponding measures to control potential other hazards. Although traditional numerical calculation methods can accurately calculate the crack length and crater size under certain combat conditions, it usually takes a long time and is not suitable for rapid damage assessment. In order to solve similar problems, this article combines simulation calculation methods with machine learning technology interdisciplinary. First, the common concrete gravity dam shape was selected as the simulation calculation object, and XFEM (Extended Finite Element Method) was used to simulate and calculate 19 cracks with different initial positions. Then, an LSTM (Long-Short Term Memory) machine learning model was established. 15 crack paths were selected as the training set and others were set for test. At last, the LSTM model was trained by the training set, and the prediction results on the crack path were compared with the test set. The results show that this method can be used to predict the crack propagation path rapidly and accurately. In general, this article explores the application of machine learning related technologies in the field of mechanics. It has broad application prospects in the fields of damage assessment and vulnerability analysis.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.4
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• pp.31-49
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• 1989

It is of the most urgent necessity to get hydrological time series of long duration for the establishment of rational design and operation criterion for the Agricultural hydraulic structures. This study was conducted to select best fitted frequency distribution for the monthly runoff and to simulate long series of generated flows by multi-season first order Markov model with comparison of statistical parameters which are derivated from observed and sy- nthetic flows in the five watersheds along Geum river basin. The results summarized through this study are as follows. 1. Both two parameter gamma and two parameter lognormal distribution were judged to be as good fitted distributions for monthly discharge by Kolmogorov-Smirnov method for goodness of fit test in all watersheds. 2. Statistical parameters were obtained from synthetic flows simulated by two parameter gamma distribution were closer to the results from observed flows than those of two para- meter lognormal distribution in all watersheds. 3. In general, fluctuation for the coefficient of variation based on two parameter gamma distribution was shown as more good agreement with the observed flow than that of two parameter lognormal distribution. Especially, coefficient of variation based on two parameter lognormal distribution was quite closer to that of observed flow during June and August in all years. 4. Monthly synthetic flows based on two parameter gamma distribution are considered to give more reasonably good results than those of two parameter lognormal distribution in the multi-season first order Markov model in all watersheds. 5. Synthetic monthly flows with 100 years for eack watershed were sjmulated by multi- season first order Markov model based on two parameter gamma distribution which is ack- nowledged to fit the actual distribution of monthly discharges of watersheds. Simulated sy- nthetic monthly flows may be considered to be contributed to the long series of discharges as an input data for the development of water resources. 6. It is to be desired that generation technique of synthetic flow in this study would be compared with other simulation techniques for the objective time series.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.2
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• pp.37-47
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• 2017

In this study, we analyzed the variability of irrigation water amounts based on the combination of various crops and soil textures using the Irrigation Water Management Model (IWMM). IWMM evaluates the degree of agricultural drought using the Soil Moisture Deficit Index (SMDI). When crops are damaged by the water scarcity under the drought condition indicating that the SMDI values are in negative (SMDI<0), IWMM irrigates appropriate water amounts that can shift the negative SMDI values to "0" to crop fields. To test the IWMM model, we selected the Bandong-ri (BDR) and Jucheon (JC) sites in Gangwon-do and Jeollabuk-do provinces. We derived the soil hydraulic properties using the near-surface data assimilation scheme form the Time Domain Reflectrometry (TDR)-based soil moisture measurements. The daily root zone soil moisture dynamics (R: 0.792/0.588 and RMSE: 0.013/0.018 for BDR/JC) estimated by the derived soil parameters were matched well with the TDR-based measurements for validation. During the long-term (2001~2015) period, IWMM irrigated the minimum water amounts to crop fields, while there were no irrigation events during the rainy days. Also, Sandy Loam (SL) and Silt (Si) soils require more irrigation water amounts than others, while the irrigation water were higher in the order of radish, wheat, soybean, and potato, respectively. Thus, the IWMM model can provide efficient irrigation water amounts to crop fields and be useful for regions at where limited water resources are available.

• Journal of the Korean Geotechnical Society
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• v.25 no.10
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• pp.17-30
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• 2009

Underground construction such as tunneling can induce damages on the surrounding rock mass, due to the stress concentration of in situ stresses and excessive energy input during construction sequence, such as blasting. The developed damage on the rock mass can have substantial influence on the mechanical and hydraulic behaviors of the rock masses around a tunnel. In this study, investigation on the generation of damage around an opening in a jointed rock model under biaxial compression condition was conducted. The joint dip angles employed are 30, 45, and 60 degrees to the horizontal, and the synthetic rock mass was made using early strength cement and water. From the biaxial compression test, initiation and propagation of tensile cracks at norm to the joint angle were found. The propagated tensile cracks eventually developed rock blocks, which were dislodged from the rock mass. Furthermore, the propagation process of the tensile cracks varies with joint angle: lower joint angle model shows more stable and progressive tensile crack propagation. The development of the tensile crack can be explained under the hypothesis that the rock segment encompassed by the joint set is subjected to the developing moment, which can be induced by the geometric irregularity around the opening in the rock model. The experiment results were simulated by using discrete element method PFC 2D. From the simulation, as has been observed from the test, a rock mass with lower joint angle produces wider damage region and rock block by tensile cracks. In addition, a rock model with lower joint angle shows progressive tensile cracks generation around the opening from the investigation of the interacted tensile cracks.

• Journal of Korea Water Resources Association
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• v.41 no.7
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• pp.653-667
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• 2008

The hydraulic model test for the L-type Groynes with "ㄱ" shape were conducted to analyze flow characteristics around these groynes. The results of model tests should be used for the fundamental information to design the L-type Groyne constructed in the field. Main hydraulic factors such as the velocity and thalweg line changes in main channel and separation area were analyzed in this study. The thalweg line is stream line where the maximum velocity occurs, and the separation area is a boundary of main flow and recirculation zone. Model tests with 5 different arm-lengths of the L-type Groynes were conducted changing the velocity. The LSPIV(Large Scale Particle Image Velocimetry) technique was used to measure and analyze the flow variation around the L-type Groynes. The velocity in main channel was increased 1.5 times and there was no effects of different groyne arm-length on the velocity changes. The width of thalweg lines $(T_{CL})$ was changed to $55{\sim}58%$ of chanel width, and the Froude number did not affect on the thalweg line $(T_{CL})$ and separation line $(S_h)$ changes.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.63-72
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• 2005

Rocks are dumped to soft marine ground in order to improve trafficability and construction conditions in the tideland reclamation construction sites. Though this rock layer under earth fill has caused in a serious seepage problems after construction, seepage behaviors of this embankment structure is not correctly investigated. Water flow through rock layers is, in general, known as Non-Darcy's flow. However, the embedded rock layer under earth fill is not known whether its flow is governed by Darcy's or Non-Darcy's law. Therefore, a numerical analysis, laboratory model test and filed investigations were performed for analyzing the those seepage characteristics in this research. Results show that there is significance of $95\%$ of confidence between observed heads and seepage rates, and the calculated ones by SAMTLE which is developed under the assumption that the water flows through the two-layer system obey the Darcy's flow. And after operating the hydraulic gradient(i) of $0.10\~0.55$ upon laboratory model, these seepage characteristics of the embedded rock layer show that Reynolds Numbers are less than 10 and the relationship between these velocities of rock layer(v) and hydraulic gradients(i) is linearly proportional with more than 0.79 of the coefficient of correlation $(R^2)$. And the Reynolds Number of the velocity calculated by the relation of v=ki in the embedded rock layer of OO sea dike is $1\~6$. It shows also laminar flow. Based on these results, it is concluded that the seepage characteristics of embedded rock layer under earth fill can be laminar and Darcy's flow.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.119-127
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• 2006

Granulated Blast Furnace Slag (GBFS) is produced in the manufacture process of pig-iron and shows a similar particle formation to that of natural sea sand and also shows light weight, high shear strength, well permeability, and especially has a latent hydraulic property by which GBFS is solidified with time. Therefore, when GBFS is used as a backfill material of quay or retaining walls, the increase of shear strength induced by the hardening is presumed to reduce the earth pressure and consequently the construction cost of harbor structures decreases. In this study, using the model sand box (50 cm$\times$50 cm$\times$100 cm), the model wall tests were carried out on GBFS and Toyoura standard sand, in which the resultant earth pressure, a wall friction and the earth pressure distribution at the movable wall surface were measured. In the tests, the relative density was set as Dr=25, 55 and 70% and the wall was rotated at the bottom to the active earth pressure side and followed by the passive side. The maximum horizontal displacement at the top of the wall was set as ${\pm}2mm$. By these model test results, it is clarified that the resultant earth pressure obtained by using GBFS is smaller than that of Toyoura sand, especially in the active-earth pressure.

• Tunnel and Underground Space
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• v.28 no.6
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• pp.670-691
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• 2018

This study presents the research results of the BMT(Benchmark Model Test) simulations of the DECOVALEX-2019 project Task B. Task B named 'Fault slip modelling' is aiming at developing a numerical method to predict fault reactivation and the coupled hydro-mechanical behavior of fault. BMT scenario simulations of Task B were conducted to improve each numerical model of participating group by demonstrating the feasibility of reproducing the fault behavior induced by water injection. The BMT simulations consist of seven different conditions depending on injection pressure, fault properties and the hydro-mechanical coupling relations. TOUGH-FLAC simulator was used to reproduce the coupled hydro-mechanical process of fault slip. A coupling module to update the changes in hydrological properties and geometric features of the numerical mesh in the present study. We made modifications to the numerical model developed in Task B Step 1 to consider the changes in compressibility, Permeability and geometric features with hydraulic aperture of fault due to mechanical deformation. The effects of the storativity and transmissivity of the fault on the hydro-mechanical behavior such as the pressure distribution, injection rate, displacement and stress of the fault were examined, and the results of the previous step 1 simulation were updated using the modified numerical model. The simulation results indicate that the developed model can provide a reasonable prediction of the hydro-mechanical behavior related to fault reactivation. The numerical model will be enhanced by continuing interaction and collaboration with other research teams of DECOVALEX-2019 Task B and validated using the field experiment data in a further study.

• Geotechnical Engineering
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• v.9 no.1
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• pp.45-58
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• 1993

Paper drain method is one of the methods used for the improvement of soft clay as hydraulic fill sites or the seaside industrial complex. This method adopts a card board as the drain materials instead of sand piles in sand drain method. In this paper 3 types of drain board are used to fond out the characteristics of consolidation by vacuum consolidation model test. So does the no drain board test. This test causes the reduction of pore water pressure to promote the settlement without change of ground water level. Conclusively, the vacuum consolidation shows 3-dimensional behaviors and pore water pressure reaches a negative value in a short time. In addition, it is expected to have a comparatively good consolidation effect using non -woven board, and vacuum loading results in increasing the shear strength at the bottom and top of call layers.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.117-124
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• 2010

Most of the rivers which exist in nature are not a single river but the network that is composed of several branches and mainstreams. The river network are more complicated than other sigle rivers and streams. Therefore the hydraulic characteristics are sensitively changed by reduction and expansion of the width in the confluence or the variation of the flux. In this paper, the hydraulic characteristics were calculated by the change of the width and length in the confluence and the hydraulic model test. The deposit of confluence emerged at the left bank, right bank and the stagnation sector. As the total flow in the branch have increased, stagnation of the left bank and right bank have decreased. When the width of the downstream have been get smaller from 3 m to 2 m, the deposit of the left bank and right bank and stagnation sector have decreased. But as the eddy flow in the center of the confluence is occurred, the erosion has been increased. The result of this paper can be used as a basic data of water management around the junction and for maintenance on the ground of development of the river.