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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).
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.
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.
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.
In this study, basic physical tests and mechanical tests of crushed rock were performed in order to investigate the field application of crushed rock as substitute materials of sand that is commonly being used as foundation and backfill materials of sewer conduit. Particle-size distribution curve of crushed rock is similar to sand and also it is well-graded soil than common sand. Maximum dry unit weight in proctor compaction test for crushed rock is higher than the values of common sand. So we can estimate that the crushed rock has advantages in workability than sand for the backfill compaction after construction of sewer conduit. When we investigate the results of direct shear test and triaxial compression test on the crushed rock, it has a similar value of shear strength parameters to sand at the same stress state and as time goes by, it tends to increase the unconfined compression strength. But, because the strength reaches at the constant value after 6~7 days, we expect that it can absorb the lateral strain of flexible conduit well. All the above experimental results just proves that crushed rock can substitute for sand as backfill materials and foundation of sewer conduit. 본 연구에서는 하수관거의 기초나 뒷채움재로 많이 사용되고 있는 기존의 모래를 대체할 재료로써 석분의 적용가능성을 평가하기 위하여 석분재료에 대한 기본적인 물리적, 역학적인 특성실험을 실시하였다. 석분의 입도분포는 모래보다 더 좋은 상태를 나타내며, 다짐실험 결과도 모래보다 강도특성이 좋은 것으로 나타났다. 이러한 실험결과로부터 하수관거의 기초 및 뒷채움재로써 석분은 현장적용성이 우수한 것으로 평가되며, 이를 뒷받침하기 위하여 직접전단시험, 삼축압축시험을 실시하여 강도특성을 분석한 결과 모래의 경우와 유사한 경향을 나타내었다. 석분의 경우 일축압축강도 특성은 시간이 지남에 따라 점차 증가하는 경향을 보이지만 6~7일 경과 후에는 거의 일정한 값을 보이는 것을 알 수 있었다. 이와 같은 실험결과로부터 석분도 하수관거의 기초 및 뒷채움재로 충분히 활용할 수 있는 재료로 평가되었다.
In this paper, the effect of shear rate on internal friction angle and unconfined compressive strength of non-cemented and cemented sand was investigated. A dry Jumunjin sand was prepared at loose, medium, and dense conditions with a relative density of 40, 60 and 80%. Then, series of direct shear tests were conducted at shear rates of 0.32, 0.64, and 2.54 mm/min. In addition, a cemented sand with cement ratio of 8% and 12% was compacted into a cylindrical specimen with 50 mm in diameter and 100 mm in height. Unconfined compression tests on the cemented sand were performed with various shear rates such as 0.1, 0.5, 1, 5 and 10%/min. Regardless of a degree of cementation, the unconfined compressive strength of the cemented sand and the angle of internal friction of the non-cemented sand tended to increase as the shear rate increased. For the non-cemented sand, the angle of internal friction increased by 4° at maximum as the shear rate increased. The unconfined compressive strength of the cemented sand also increased as the shear rate increased. However, its increasing pattern declined after the standard shear rate (1 mm/min). A discrete element method was also used to analyze the crack initiation and its development for the cemented sand with shear rate. Numerical results of unconfined compressive strength and failure pattern were similar to the experimental results. 본 논문에서는 실내시험 시 재하속도가 미고결 모래의 내부 마찰각 그리고 고결모래의 일축압축강도에 미치는 영향에 대해 연구하였다. 건조상태의 주문진모래를 상대밀도 40%로 느슨하거나, 60%로 중간 정도 및 80%로 조밀한 상태로 제작한 다음 0.32, 0.64, 2.54mm/min의 재하속도로 직접전단시험을 실시하였다. 또한, 주문진모래에 시멘트 8% 및 12%로 다짐한 직경 50mm, 높이 100mm의 고결 공시체를 일축압축시험 시 0.1, 0.5, 1, 5, 10%/min의 재하속도로 압축하였다. 모래의 고결 여부나 정도에 관계없이 재하속도가 증가할수록 내부 마찰각과 일축압축강도는 증가하는 경향을 보였다. 미고결 모래의 경우 재하속도가 증가할수록 최대 4° 까지 내부 마찰각이 증가하였다. 고결 모래의 경우도 일반적으로 재하속도에 따라 일축압축강도가 증가하였으나, 표준 재하속도인 1%/min를 기준으로 증가하는 경향이 감소하였다. 또한, 개별요소법을 이용하여 고결 모래의 재하속도에 따른 균열 발생 및 발달 과정을 분석하였으며, 해석결과 또한 재하속도가 증가함에 따라 강도가 증가하는 경향을 보였으며 강도가 증가할수록 균열이 뚜렷하게 발달하였다.
영상은 획득, 저장 그리고 전송 등의 처리과정에서 다양한 원인에 의해 훼손되며, 이러한 영상을 복원하기 위한 많은 연구가 이루어지고 있다. 일반적으로 AWGN(additive white gaussian noise)에 의해 훼손된 영상을 복원하는 방법으로 평균 필터와 위너 필터가 있으며, 특히 평탄한 영역에서의 노이즈 제거에 평균 필터가 우수하다. 그러나 평균 필터는 영상의 특징을 고려하지 않으므로 에지 성분이 왜곡되어 평활화되는 단점이 있다. 따라서 본 논문에서는 평균 필터와 함께 에지 성분을 보존하면서 대조도 개선에 강한 위너 필터를 사용하여 각각 필터링한 후, 처리된 영상에 가중치를 설정하여 병렬처리하는 영상 복원 방법을 제안하였다. Image is degraded by several causes such as the process of acquisition, storage and transmission. To restore those images, many researches have been continued. Centrally methods to restore degraded image by AWGN(additive white gaussian noise) a.e mean filter and wiener filter. Especially, mean filter is superior in noise reduction of area that is a small change of luminosity. But mean filter brings about the effect smoothing edge components of the image, because it does'nt consider characteristics of the image. So in this paper we propose an image restoration method compounding respective images adding established weights, after filtering with mean filter and powerful wiener filter in both improvement of contrast and preservation of edge components.
This paper present an evaluation of new drilling and blasting method with two different drilling directions for pilot tunnel enlargement using numerical experiment. That is, three dimensional transient dynamic analysis was made to investigate the effect of the ground vibration when blasting was performed at same position using the equivalent single hole charge.
Currently in Korea, the tunnel enlargement process uses the combined method of TBM/NATM with the conventional method. So, it is difficult to get advantages which involved in the combined method. In this study, the new drilling and blasting enlargement excavation method was developed which drills charge holes in a radial direction inside the pilot tunnel. Then holes are drilled in the outer portion of the tunnel section in the same direction as the tunnel axis to prevent overbreak. Next, all charged holes are blasted simultaneously (to be called the "bidirectional method"). This paper presents an evaluation of new drill and method with two different drilling directions for pilot tunnel enlargement through experimental field tests performed on a road tunnel construction site in Seoul area. To evaluate the efficiency of new tunnel enlargement method, field test results were compared with those of conventional drill and blast method.