다짐점토의 간극수압 모델에 관한 연구

임희대,박수용 忠南大學校 産業技術硏究所 1995 산업기술연구논문집 Vol.10 No.1

The behavior of an unsaturated soil tested under undrained loading conditions depends on the magnitude of the pore-air and pore-water pressure developed. This paper derives pore pressure parameters that can be utilized in determining the pore pressure response of the compacted clayey materials. Pore pressure parameter expressions are also derived for the pore-water pressures induced as a result of isotropic stress changes and deviator stress changes during undrained loading. The parameters required to computation in the proposed model can be readily determined from the conventional triaxial compression tests. To examine the degree to which the proposed pore pressure model reflects the results of triaxial tests, The back analyses carried out, It is shown from the examination that agreements are generally satisfactory.

Wetting에 의한 필댐 상류측 shell의 거동특성

임희대,백장열,이영섭 충남대학교 산업기술연구소 1999 산업기술연구논문집 Vol.14 No.2

The primary objective of this paper is to see the behavior characteristics of rockfill dam due to wetting. There are many factors which affect the dam failure. One of them is the influence of reservoir filling. Differential movements in dam and foundation develop during reservoir filling, they induced cracking and consequent erosion, and sometimes caused dam failure. One of the major factors contributing to the development of differential movements during reservoir filling is the compression due to wetting which occurs in a wide variety of different types of soils including rockfill. To perform the numerical analysis of dam behavior adequately, the large-scaled triaxial test is needed to consider the effect of wetting on dry and wet rockfill material. But, As the large-scaled triaxial test is high capital cost and not available apparatus for a number of other experiment, it is not applied many case in the country. In this paper, the data of Oroville dam which performed the large-scaled triaxial test is referenced to find out stress-strain curve and hyperbolic parameters on wetting for modeled dam which is not performed the large-scaled triaxial test. So, effect of wetting on modeled dam can be considered for numerical analysis of dam behavior. As a result of numerical analysis, they estimate that horizontal and vertical displacement are increased with the rate of increasing wetting, and shear stress too. Because compression and shear strength is decreased with proceeding wetting. And results of analysis show that load transfer is not affect significantly by the wetting.

Rockfill 댐의 Hydraulic Fracturing에 關한 硏究

임희대,우원재,우상태 忠南大學校 産業技術硏究所 1995 산업기술연구논문집 Vol.10 No.2

The term hydraulic fracturing has been used in the geotechnical engineering literature to describe situations in earth embankment dams where the reservoir water pressure initiates and propagates a cracks. The term has also been used in situations where an existing crack is further widened by the reservoir water pressure. The mechanisms of hydraulic fracturing in the core of rockfill dams that have been proposed to date are quite qualitative and have been postulated in the course of investigations to find the causes of leakage or failures as a results of internal erosion. In this study, the various mechanisms of hydraulic fracturing are outlined and the finite element analyses of 5 representative rockfill dams in Korea were conducted to examine the assumption that hydraulic fracturing occurs in embankment cores when the reservoir water pressure exceeds the total normal stresses. This numerical analyses use the hyperbolic model and its parameters from the conventional triaxial tests. As the results of the analyses, the total normal stresses by FEM exceed the water pressures in most cases which is contray to the fact that the water pressures exceed the total normal stresses by the pressure meters in the case of Soyanggang dam.

Fill Dam의 漏水原因과 遮水에 關한 硏究

임희대,양재석 충남대학교 공업교육연구소 2001 論文集 Vol.24 No.1

In general, leakage of fill dam causes not only fall in economic field in problem of storage efficiency but also collapse of embankment dams. This leakage path can be embankment dams, joining part between embankment dams and foundation ground and foundation ground. Fissure which nearly happens in embankment dams, one of leakage causes of fill dam turned out that load transfer by differential settlement between different core and rip rap with each other is chief cause offerer. This phenomenon turned out to be so dangerous in early containing water. Futhermore, it induces hydraulic fracturing and has considerable influence on stability of embankment dams. Hydraulic fracturing is that fissure happens either in rock mass or internal embankment dams by hydraulic pressure and when dam is filled with water, means that core is torn horizontally by hydraulic pressure. Initial proposed mechanisms of hydraulic fracturing are for the most part supposed things in the process for investigating either leakage or cause of failure by internal erosion and are considerably qualitative but since finite element in moving analysis is used, have begun to be analyzed quantitatively. In this paper, the cause of leakage and the process of occurrence of leakage are examined, and measures which can predict and prevent leakage in advance is presented. Also a impervious method improved is presented after investigation of the methods which have been applied to fill dam to cut off leakage. As an impervious method, grouting after grasping the cause of leakage and flow channel with geophysical investigation is better efficient than only to reinforce part in which erosion or fissure happens.

다짐함수비 變化에 따른 필댐의 擧動分析

임희대,김태곤,이영섭,고근식 충남대학교 산업기술연구소 1999 산업기술연구논문집 Vol.14 No.2

Compaction water content is a key variable which controls fundamental properties of compacted clay (permeability, deformation and strength). There are three conditions in compaction water content (i.e. dry of optimum, optimum and wet of optimum). Actually, soil mass by compaction is unsaturated condition before seepage therefore, soil suction is the key which is able to explain properties of compacted clay. This paper used results from compacted Pittsburg sandy clay tested under UU test condition from Duncan and Seed in order to determine hyperbolic parameters and simulated behavior of Soyanggang dam as a example. As the results of analysis, dry of optimum presents higher strength and smaller displacement. Wet of optimum is sensitive to water content. Both dry and wet of optimum, any hydraulic fracturing potential does not appear. But dry of optimum is close to hydraulic fracturing.

필댐 心壁材料의 分離 및 浸蝕에 關한 硏究

임희대,고부현 忠南大學校 産業技術硏究所 2001 산업기술연구논문집 Vol.16 No.2

Generally piping, or progressive erosion due to concentrated leaks, has caused a larger number of catastrophic failures than any other actions, except overtopping, and many modern techniques of earth dam design and construction have been developed to prevent it. Recent experience indicates that an effect of reservoir filling may lead to the formation of dangerous cracks, and hydraulic fracturing is considered to be a primary cause. The primary objective of this paper is to see the causes of damage, the mechanism of crack, piping or erosion and the possibility of hydraulic fracturing and load transfer in fill dams. The results of this study are summarized as follows: The tendency for dispersion piping is determined by a number of properties of the clay, and the most important properties are ESP and the content of dissolved salts in the seeping water. For the evaluation of a give soil, both the pinhole and pore water salts tests should be made. However, for soils that cannot be easily determined whether they are dispersive or not, only the pinhole test can reliably identify the state of dispersion. As a result of numerical analysis, this paper presents that possibility of hydraulic fracturing and load transfer is increased according to the decrease in wet unit weight, internal friction angle and cohesion. Besides, cracking can be caused by differential settlements or the arching of core material filling in the key trench. This cracking could also result in channels through the key trench fill which would permit rapid internal erosion.

韓國 沿岸에 堆積된 軟弱地盤의 粘土鑛物 分布와 工學的 特性

임희대,문성권 忠南大學校 産業技術硏究所 1997 산업기술연구논문집 Vol.12 No.2

Samples of clay minerals were analyzed using an X-ray diffraction test. Also, the geotechnical properties of the distribution of clay minerals were evaluated after collecting physical and mechanical soil data from Korea Land Corporation, Korea Highway Corporation and the Rural Development Corporation. The results of the X-ray diffraction analysis showed that Korean soft marine clay exists in mixed caly mineral conditions, predominantly illite and muscovite (muscovite causing the formation of illite) existed in all investigated areas. Kaolinite is prevalent in the estuary of the Han River, the estuary of the Kum River, as well as the Asan Bay area. Illite is prevalent in Noksan and Yangsan·Mulkum along the estuary of the Nakdong River. In the estuary of the Han River, montmorillonite is prevalent. These montmorillonites are carried to those areas from the Yellow Sea or they were formed and carried down from China. In order to find out the engineering characteristics based in clay mineral distribution, soil indexes were compared to one another. As a result, the condition of particle size distribution affects the physical and mechanical properties rather than the type of the clay minerals found, because of the small amount of clay minerals detected within Korean marine clay.

중앙심벽형댐의 응력전이에 관한 연구

임희대,임찬수,이성용 忠南大學校 産業技術硏究所 1995 산업기술연구논문집 Vol.10 No.2

Various modes of load transfer may exist in rockfill dams. If the core is softer than the shells, load is transferred from the core onto the shells as a result of greater downward displacement of the core with respect to the shells. But if the core is stiffer than the shells, load transfer occurs from the shells onto the core. In this study, the mechanisms of load transfer in rockfill dams have been outlined and load transfer of Juam main and regulation dam with central core are evaluated by load transfer ratio. The load transfer ratio is defined as the ratio of computed values of major principal stresses in the core to the core overburden stresses. The vertical stresses are determined by the FEM, which use hyperbolic model and incremental method to simulate placement of successive layers of fill. The hyperbolic paramaters for the core was estimated from a series of conventional triaxial tests carried out during construction. From the results of this analyses and its comparison with the values measured by soil pressure meters, it has been shown that significant load transfer from the core to the shells was observed in two dams and that the load transfer ratios predicted are higher than the values measured.

ABUTMENT의 경사가 CORE의 응력-변형률에 미치는 영향

임희대,박수용,우원재 忠南大學校 産業技術硏究所 1995 산업기술연구논문집 Vol.10 No.1

Cracking of core presents a serious hazard resulting in possible leakage and failure. For a realistic evaluation of cracking of core one must take into account irregular steep abutment. The present paper is concerned with the most dangerous transverse movements in the embankment which result from non-uniform settlement along the abutments. In this study, the effect of steepness of abutment has been analyzed for 100m high central trapezodial cores with abutment slopes of 1:0.25, 1:0.5, 1:0.75, and 1:1 respectively. Numerical analysis of longitndinal sections of the embankment has been carried out by the application of finite element method. The nonlinear and stress-dependent stress-strain properties of soil is approximated by using a hyperbolic model. The results of the analyses indicate that there is a decrease of vertical stress due to arching action. This decrease is more for steeper slope than for flatter slope.

海成粘土와 다짐粘土의 透水係數 豫測에 관한 硏究

임희대,이상헌 忠南大學校 産業技術硏究所 1997 산업기술연구논문집 Vol.12 No.2

It is very important for geotechnical engineers to understand properties of coefficient of permeability. The Kozeny-Carman equation is generally used at the present for estimating the coefficient of permeability. Even though the equation proposed by Kozeny-Carman gives fairly good results in estimating of sandy soils. But it is not appropriate for fine-grained soils such as clay. In the case of clayey soils, structure and distribution of particles play and important role in the coefficient of permeability. These structure and distribution are also closely related to specific surface. Large specific surface means that the grain size is very small. Soils possessing large amount of fine grains have a long flow of water. The study comes to the conclusion that the mostly related factor between specific surface and permeability appears to be #200 passing percentage in the case of compacted clays and clay content for marine clay. So new equation is proposed with the two factor in this study. But the developed equation can be used for estimating rough values in the field. That is, it is skeptical to calculate an accurate coefficient of permeability of soils. The other equations proposed until now were considered. But the results of the equations developed by plasticity index or effective grain size are far from the actual value.