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Although a number of techniques have been proposed and developed to determine initial stress in rock mass, the determination of initial stress is not an easy task and all suffer from deficiencies and limitations. The main deficiency of established techniques such as over coring method or hydraulic fracturing method which is currently used in Korea is that they are usually expensive and time consuming. This paper presents a guide to determine the resonable initial stress for tunnel design through the analysis of field instrumentation data measured in Korea.
The deflection and deterioration of road surfaces are largely related to the deformation of underlying soils. The American Association of State Highways and Transportation Officials(AASHTO) has adopted use of resilient modulus in the pavement design to represent the deformational characteristics of pavement materials due to repeated loading. Because of the recent interest in the use of resilient modulus for pavement design, it is needed to evaluate on the effects of moisture, soil type, and stress state on resilient modulus. In this paper, resilient characteristics are investigated for subgrade soils gained from road construction sites in Korea. The experimental technique basically follows the method suggested in this study.
Recently, many kinds of huge construction works are being constructed in many places in Korea. Among these projects, especially at the high speed rail construction sites, many bridge foundations are being built with steel pipe pile foundations because much of this construction occurs on low-lying ground and farmlands. Pile foundations are often used for a wide range of buildings, bridges, and other structures. So, piling operations are powerful sources of construction vibrations which may effect surrounding buildings and have detrimental effects on other structures, sensitive devices, processes and people. In recent years, this problem has gained public interest so people desire and require better living environments. And consequently, the high tech equipment necessary for vibration-proofing has been developed. From this point of view, it is desirable to make preliminary analysis to correctly assess potential vibration problems which may arise at the time of pile driving and to provide the valuable data to make an effective counter plan against such ground vibrations. This paper presents the results of measurements of round vibration on the soil surface of high speed railway construction sites caused by pile driving and supply valuable data for selection of a suitable pile driving method in other sites. The levels of vibration and the attenuations with distance of ground vibrations are also considered, together with the criteria and standards for vibration assessment with respect human and animal response as well as building damage.
Reliable evaluation of initial stress in rock mass is an important step in the analysis and design of underground excavations, particularly for analysing the stability of underground structures to prevent failure or collapse of underground openings. This initial stress rolates primary with depth, rock properties, rock conditions and surrounding circumstances etc. In this study the influence factors on initial stress were analysed by numerical experiment, especially with past stress history, topography, formation and joint of rocks, geological structure(fault).
Hyperbolic model has a merit that soil behavior can be predicted simply by representing the relationship of stress-strain and pore water pressure-strain with the hyperbolic function. And this theory has been used significantly not only in the total stress analysis and effective stress analysis, but also in obtaining required constant from the basic triaxial compression test. In this study, we are going to analyze the result that would come out from the isotropic triaxial compression test considering the anisotropic to seize the presence of anisotropic characteristic of soil developed from applying shear force in the remolded weathered mudstone soils. Also, Several constants related to the ratio of strain-pore water pressure and the relationship of stress-strain came out along the anisotropic using the hyperbolic model suggested by Duncan and Chang(1) and Lo(2∼3). Based on which, the relationships of stress-strain and strain-pore water pressure will be predicted and compared to test results. In the test results, anisotropic characteristic by isotropic consolidation did not appear, and the result of prediction by hyperbolic model had been well consistent with the test results. Accordingly, undrained shear behavior of weathered mudstone soils could be predicted by the hyperbolic model sufficiently.
3-D structure is created at the tunnel face in all tunnelling. Accordingly, the ground around the tunnel under construction shows three dimensions deformational behavior due to the transverse and longitudinal arching effects. In order to obtain the realistic results of these the tunnel behavior from the numerical analysis, actual construction measures and their sequence must be taken into account. In particular, the excavation and installation of support and lining are important tunnel construction parameters. Despite these three dimensionalities encountered in tunnelling, a three-dimensional analysis is often not necessary. Instead, a two-dimensional model can be substituted because of the size and complexity associated with a 3-D model and calculation times to perform a 3-D analysis. The simulation of 3-D conditions by a 2-D model requires experience and the understanding of the relationship between theses two models. Load distribution ratio is used to the 2-D analysis for the consideration of the effects of the tunnel advance in three dimensions in Korea. However, constant load distribution ratios have been assigned for 2-D analysis even if the conditions for tunnel design are different. This paper presents the results of the evaluation of load distribution ratios through a three-dimensional tunnel analysis for the different ground formation and compares the cases of load distribution ratios applied actual tunnel design in Korea.
A single particle crushing test was carried out for recycled aggregates from waste concrete while demolishing variousstructures. When the recycled aggregates were used for backfill or road subbase materials, load-displacement and crushingcharacteristics were analyzed. The recycled aggregates with hydrates and aggregates were sorted into 40 mm size (75-40mm) and 20 mm size (40-20 mm). At initial loading, their irregular surface was closed to and then crushed by loadingplate. Such first crushing stage was called ‘Surface crushing'. Further loading, some hydrate was crushed and detachedfrom aggregate, and such process repeated several times. This state is called ‘hydrate crushing'. The final state is called‘aggregate crushing' in which aggregate crushed and following load suddenly dropped down. As the load increased,such crushing cycle is repeated several times. The shapes of aggregates are round or square, and triangle or long shaped. Depending on their shapes and surface conditions, they crushed in different ways. The 63% of aggregates showed morethan 50% load reduction due to aggregate crushing. The 90% load reduction occurred at 15% of aggregates. The 40mm aggregate crushed at maximum load between 3.05-4.38 kN and 70% of crushed aggregates were less than 20 mm. 본 연구에서는 각종 구조물 철거 시 발생하는 폐콘크리트를 파쇄 처리하여 발생한 순환골재를 각종 토공 및 보조기층용에 재활용 시 발생할 수 있는 하중-변위 및 파쇄 특성을 분석하기 위해 단입자 파쇄실험을 실시하였다. 수화물과골재로 구성된 75mm 이하의 순환골재를 40mm 크기(75-40mm 사이)와 20mm 크기(40-20mm 사이)의 골재로 나누어실험하였다. 순환골재에 하중이 증가할 경우 단입자의 파쇄 거동은 불규칙한 표면이 가압판에 밀착되면서 초기에표면이 파쇄되는 ‘표면파쇄(Surface crushing)', 표면파쇄 이후 골재와 수화물이 분리되는 소규모 부분적 파쇄와 균열이반복적으로 발생하는 ‘수화물파쇄(Hydrate crushing)', 수화물파쇄가 단계적으로 반복되다가 최대하중에서 골재가 파쇄되면서 하중이 급격히 감소되는 취성파괴인 ‘골재파쇄(Aggregate crushing)'의 순서로 파쇄 사이클(crushing cycle)이진행되었다. 한편, 하중이 지속적으로 증가함에 따라 이러한 파쇄 사이클은 수 차례 반복되는 경향을 보였다. 순환골재의 형상은 둥글거나 사각형에 가깝거나, 삼각형 또는 길쭉한 형태로 표면상태나 형상에 따라 파쇄 형상이 다르게 나타났다. 골재파쇄(최대 파쇄)에서 취성파괴로 하중이 감소되는 비율인 파쇄하중 감소율은 50% 이상인 경우는 63%정도이며, 90% 이상인 경우도 15% 정도로 나타났다. 40mm 단입자는 최대하중 3.05~4.38kN 정도에서 대부분 파쇄되어 작은 입자로 분리되며, 세립화된 단입자 개수를 기준으로 20mm 이하의 분포비율은 약 70% 정도였다.
In recent years, environmental problems such as noise and ground vibration induced by many kinds of construction and running trains have gained public interest because people desire and require better living life. Running trains are also one of sources of noise and vibrations which may effect adjacent house and have detrimental effects on other structures, sensitive devices and people. Especially domestic animals and fishes are heavily effected from only low levels of vibration. Consequently, the resonable methods for vibration-reducing is adopted. From this point of view, it is desirable to make preliminary analysis to correctly assess potential vibration problems which may arise at the running of train and to provide the valuable data to make an effective counter plan against such ground vibrations. This paper presents the results of measurements of ground vibration on the adjacent soil surface of railway which is running train, and supply valuable data for selection of a suitable vibration-reducing method. The levels of vibration and the attenuations with distance for ground vibrations are also considered.
Recently, many kinds of huge construction works are being constructed in many places in Korea. The use of big construction equipments, pile driving and rock mass blasting accompany with construction are powerful sources of ground vibrations which may effect surrounding buildings and have detrimental effects on other structures, sensitive devices, people and animals. These environmental problems such as noise and ground vibrations induced by construction have gained public interest because people desire better living life. From this point of view, it is desirable to study for assessment potential vibration problems which may arise at the time of construction works and for making an effective counter plan against the ground vibration. In this paper, the program able to simply predict the ground vibration caused by construction works, especially pile driving and rock mass blasting, was developed. And also, the methods for reducing ground vibration using EPS and crashed stone barriers were proposed and the experimental data for reducing effect of vibration of the proposed methods were presented.
Recently, many road construction is being performed in country side to wide the existing small agricultural road. In this case, the road is designed without the exact site investigation because of financial reason of regional government. So in some case, the road is designed on soft soils and has many problems in the process of construction. Especially agricultural road which needs to wide the existing small road overlying on the untreated soft soil is planned without the site investigation. In this case, the enlarged road will have the problems such as excess settlement or shear failure of road. In the process of designing and constructing structures on soft soils, we need to consider whether the soil properties can be economically improved. In this study, a case study was performed for the stability analysis of agricultural road overlying on the untreated soft soil. Soil tests were performed to investigate soft soil properties and plate bearing test was performed to find the bearing capacity of subbase and subgrade. Numerical analysis was also performed to evaluate the stability of new planning road overlying on the untreated soft soil using commercial soft ware which is used to analyze the consolidation settlement. We found that the new planning road overlying on the untreated soft soil has consolidation settlement in excess of the allowable settlement criteria. After evaluating the several methods available for the improvement of the engineering properties of soft clays of this site, the replacement method as safe and economical method was selected and analysed. We conclude that in case of designing new road to wide the existing small agricultural road, site investigation should be necessary and then road have to be designed rationally in according to the site soil conditions.