• Geomechanics and Engineering
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• 제28권5호
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• pp.505-520
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• 2022

In recent years, geotextile-encased gravel columns (usually called stone columns) have become a popular method to increasing soil shear strength, decreasing the settlement, acceleration of the rate of consolidation, reducing the liquefaction potential and increasing the bearing capacity of foundations. The behavior of improved loose base-soil with gravel columns under shear loading and the shear stress-horizontal displacement curves got from large scale direct shear test are of great importance in understanding the performance of this method. In the present study, by performing 36 large-scale direct shear tests on sandy base-soil with different fine-content of zero to 30% in both not improved and improved with gravel columns, the effect of the presence of gravel columns in the loose soils were investigated. The results were used to predict the shear stress-horizontal displacement curve of these samples using support vector machines (SVM). Variables such as the non-plastic fine content of base-soil (FC), the area replacement ratio of the gravel column (Arr), the geotextile encasement and the normal stress on the sample were effective factors in the shear stress-horizontal displacement curve of the samples. The training and testing data of the model showed higher power of SVM compared to multilayer perceptron (MLP) neural network in predicting shear stress-horizontal displacement curve. After ensuring the accuracy of the model evaluation, by introducing different samples to the model, the effect of different variables on the maximum shear stress of the samples was investigated. The results showed that by adding a gravel column and increasing the Arr, the friction angle (ϕ) and cohesion (c) of the samples increase. This increase is less in base-soil with more FC, and in a proportion of the same Arr, with increasing FC, internal friction angle and cohesion decreases.

• 터널과지하공간
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• 제25권4호
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• pp.383-396
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• 2015

모래자갈층에서 터널굴착 시 발생하는 지표침하에 의해 지상빌딩에 발생하는 손상도를 분석하였다. 모래자갈층의 두께와 터널까지의 심도는 약 20m이고 터널의 폭과 높이는 각각 12m, 8.6m이다. 터널은 막장전방을 3열의 강관다단그라우팅으로 보강하면서 시공하였다. 터널시공 중에 빌딩주변 36개소에서 지표침하를 계측하였고 이를 이용하여 3차원 지표침하면을 구하고 빌딩의 위치에 따라 처짐비와 수평변형율로 빌딩의 손상도를 평가하였다. 시공 중 계측된 지표침하는 약 1~4mm로 작았고 빌딩은 수평압축변형을 받는 상태가 되어 빌딩에 손상이 발생하지 않았다.

• 한국지형학회지
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• 제25권2호
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• pp.15-29
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• 2018

The sediment transport process in a river reflects the process of geomorphological change in the watershed, influencesthe river bed variation and the river channel migration, and is a parametric phenomenon that exhibits a dynamic self-adjusting process. Sediment load is divided into bedload and suspended load depending on the dominant mechanism. Quantitative sediment load is important information for solving river problems. Because it is difficult and time consuming to measure bedload, compared to that ofsuspended load, data on the sediment transport load and the research required for the gravel-bed rivers are insufficient. This study is to analyze the ratio of the bedload to the total sediment load in gravel-bed rivers. The sediment load ratio in gravel-bed rivers increases with the flow rate per unit width, and the rate of the bedload varies more rapidly than the suspended load. The sediment transport efficiency coefficient has been affected by the ratio of the flow depth to the mean diameter of particles and has been dependent on the shear velocity Reynolds number. So $A^{\ast}$ and $B^{\ast}$ are introduced to compensate for the uncertainties such as bed materials, sediment transport, and flow velocity distribution, and the coefficient of bedload ratio has been presented. For the sediment load data in experimental channels and rivers, A* was 3.1. The dominant variables of $B^{\ast}$ were $u_*d_m/{\nu}$ in the gravel-bed and h/dm in the sand-bed. When $B^{\ast}$ the is the same, in the experimental channels the coefficient of bedload ratio was affected by the bed forms, but in the rivers it was of little difference between the gravel-bed and sand-bed.

• 물과 미래
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• 제10권1호
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• pp.20-24
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• 1977

43,000 shallow water wells have been installed as a part of all weather irrigation water supply project executed during 1969 to 1970 in all over Korea penninsula in order to solve water shortage problem of farming land by developing shallow ground water reserved in unconsolidated materials. But after 3 years later it was reported that 34% of the wells were abandoned by the reasons of artificial and natural defects. 48 wells distributed uniformly in the penninsula are selected to determine their well loss constants, relation between well loss and specific capacity, and tophographic classification of the well loss on the shallow water well. The results show that average well loss consatnt and the value of $CQ^2/S_w$ is ranged from $5.95{\times}10^{-5}\;to\;3.65{\times}10^{-8}Day^2M^{-5}$ and from 35.5% to maximum 68.48% respectvely and that relation between specific capacity and well loss constant can be approximately formulated as $C=0.61S_p2.246$ However this result indicates that most wells installed in this time have too high value of well loss constant $CQ^2/S_w$ in comparison with properly deseigned well. The most favorable and producable water bearing formation among unconsolidated deposits such as sand & gravel, boulderly gravel, clayey boulderly gravel, and sand formation in Korea is sand formation deposited in center of valley.

• Advances in concrete construction
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• 제7권2호
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• pp.97-105
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• 2019

In this paper, the workability and static stability were evaluated using a proposed test method. Workability and static stability represent a key property of self-compacting concrete (SCC) in fresh state. A number of standardized test methods were developed to assess these properties. However, no accelerated test method reliably predicts both workability and static stability of SCC. In the present work, a modified K-slump test method was developed to evaluate workability and static stability of SCC. In order to take implicit mixture variations of SCC constituents that can affect fresh SCC properties, a central composite design was adopted to highlight the effect of gravel to sand ratio (G/S), gravel 3/8 to gravel 8/15 ratio (G1/G2), water to cement ratio (W/C), marble powder to cement ratio (MP/C) and superplasticizer content (SP) on workability measured with slump and flow time (T50) tests and static stability measured with sieve stability test (Pi), segregation test index (SSI), Penetration test (Pd) and the proposed K-slump test (Km). The obtained results show that G/S ratio close to 1 and G1/G2 ratio close to 60% can be considered as optimal values to achieve a good workability while ensuring a sufficient static stability of SCC. Acceptable relationships were obtained between Slump flow, Pi, Pd and Km. Results show that the proposed K-slump test allow to assess both workability and static stability of fresh SCC mixtures.

• Geomechanics and Engineering
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• 제37권4호
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• pp.359-370
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• 2024

The primary goal of this study is to evaluate the migration of fine granular materials into overlying layers under cyclic loading using a modified large-scale triaxial system as a physical model test. Samples prepared for the modified large-scale triaxial system comprised a 60 mm thick gravel layer overlying a 120 mm thick subgrade layer, which could be either tailings or railway sand. A quantitative analysis of the migration of fine granular materials was based on the mass percentage and grain size of migrated materials collected in the gravel. In addition, the cyclic characteristics, i.e., accumulated axial strain and excess pore water pressure, were evaluated. As a result, the total migration rate of the railway sand sample was found to be small. However, the total migration rate of the sample containing tailings in the subgrade layer was much higher than that of the railway sand sample. In addition, the migration analysis revealed that finer tailings particles tended to be migrated into the upper gravel layer easier than coarser tailings particles under cyclic loading. This could be involved in significant increases in excess pore water pressure at the last cycles of the physical model test.

• 한국해안·해양공학회논문집
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• 제23권1호
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• pp.50-56
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• 2011

항만생태계 녹색공간 창출을 위해 우리나라 항만에 분포하는 식물상특성, 환경요인분석, 항만유형분석, 적합종, 최소보존면적산출을 통해 식재모식도를 작성하였다. 50개 조사지역에서 44과 174종의 관속식물이 출현하였으며, 그중 염생식물은 19과 48종이 분포하였다. 우점군락은 통보리사초, 갯그령, 좀보리사초, 갯씀바귀, 순비기나무, 갯메꽃, 해당화, 갯완두, 솔장다리, 우산잔디, 번행초, 칠면초, 해홍나물, 갯잔디, 갈대를 포함하여 15개 군락이 분포하였다. 조사지역에 분포하는 식물군락과 환경요인과의 Canonical Correspondence Analysis(CCA) 결과 Clay marsh, Sand marsh, Sand gravel marsh 유형으로 분류되었다. 생육지 유형별 적합종으로 clay marsh는 칠면초, 갈대, 갯잔디, 해홍나물 sand marsh는 갯그령, 갯씀바귀, 통보리사초, 좀보리사초 sand gravel marsh는 갯메꽃, 순비기나무가 선정되었다. 적합종에 대한 최소보전면적을 산출하고 항만생태계 세부 유형별로 가이드라인과 모식도를 작성하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.747-752
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• 2003

This study was carried out to understand the stratigraphy and depositional environment of clayey soils that distributed in the Gadeok-do area, Kimhae plain (Nakdong estuary). For the study, SPT core sampling and magnetic susceptibility analysis were conducted. Soils in study area is classified into five sedimentary facies ascending order; sand/gravel. clay, sand/gravel, clay, interbedded sand and silty clay. Analysis of magnetic susceptibility for Gadeok-do clayey soil reveals that depositional process and environment can be divided into upper, middle and lower layer, and they are closely related to the sea level change since late Quaternary.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 지반공학 공동 학술발표회
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• pp.510-516
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• 2005

This research aims to verify the stress distribution in soil according to the composition of the soil layer in case of surface loading. For this purpose, loading tests with measurement of stresses in the soil on four kinds of layered model ground in laboratory were performed. Those are (1)homogeneous sand, (2)gravel underlain by sand, (3)sand underlain by clay and (4)gravel underlain by clay. Test results are compared and analysed for the compositions of the soil layers. based on the results obtained, it is found that the larger the difference of the strengths of upper and lower layer is, the smaller the stress in the soil in case of surface loading is.

• 자원환경지질
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• 제11권2호
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• pp.81-88
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• 1978

Nearly 300 bottom sediments and 20 box-cores were sampled from the Asan bay. The central portion of the Asan bay is covered by sand, slightly gravelly sand and gravelly muddy sand. Between the central and marginal zones gravelly mud and slightly gravelly sandy mud are characteristically distributed. The gravel population in the sediments seems to be originated from the rocky bottom on the area near the bay because the gravel is angular and composed of the schist and gneiss. The quartz/feldspar ratio is about 3/2. It is considered to be that the amount of feldspar in this bay is much higher than that of any other areas in the Yellow Sea. This is considerd to be comparatively short distance of transport ion of these sediment from the provenance.