• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.740-746
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• 2010

Most important characteristics of calcareous sand are the particle angularity and hollow structure. These characteristics lead to the different behavior of calcareous sand compared to siliceous sand. This study performs a series of dilatometer test using calibration chamber, in order to analyze the effect of particle characteristic of calcareous sand on DMT indices. From experimental test, it is observed that the horizontal stress index($K_D$) and dilatometer modulus($E_D$) of calcareous Jeju sand is underestimated compared to siliceous sand. This is because the particle crushing during penetration induces the less contraction of the dilatometer membrane. A slightly smaller influence of particle crushing is reflected in $E_D$ rather than $K_D$, because $P_1$ pressure reflects the deformation characteristics of un-crushed particle relatively well. It is also observed that $K_D$ of Jeju sand is differently influenced by the vertical effective stress compared with that of siliceous sand.

• Geomechanics and Engineering
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• 제3권4호
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• pp.267-284
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• 2011

The aim of the paper is to study the hydro-mechanical behaviour of a tuff and calcareous sand mixture. A first experimental phase was carried out in order to find the optimal mixture. This showed that the material composed of 80% tuff and 20% calcareous sand provides the maximum mechanical strength. The second experimental phase concerns the study of the drying- wetting behaviour of the optimal mixture. Triaxial shear tests in saturated and unsaturated states at constant water content were carried out on samples initially compacted at the MPO. Experimental results let to deduce the parameters necessary for the prediction of the hydro-mechanical behaviour of pavement formulated from tuff and calcareous sand mixtures, related to moisture. This optimal mixture satisfies the regulation rules and hence constitutes a good local eco-material, abundantly available, for the conception of pavements.

• Geomechanics and Engineering
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• 제22권2호
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• pp.173-185
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• 2020

Calcareous soil is originated from marine biogenic sediments and weathering of carbonate rocks. The formation history for calcareous sediment includes complex physical, biological and chemical processes. It is preferably selected as the major fill materials for hydraulic reclamation and artificial island construction. Calcareous sands possess inter pores and complex shape are liable to be damaged at normal working stress level due to its fragile nature. Thus, the engineering properties of calcareous soil are greatly affected by its high compressibility and crushability. A series of triaxial shear tests were performed on calcareous sands derived from South China Sea under different test conditions. The effects of confining pressure, particle size, grading, compactness, drainage condition, and water content on the total amount of particle breakage for calcareous soil were symmetrically investigated. The test results showed that the crushing extent of calcareous sand with full gradation was smaller than that a single particle group under the same test condition. Large grains are cushioned by surrounding small particles and such micro-structure reduces the probability of breakage for well-graded sands. The increasing tendency of particle crushing for calcareous sand with a rise in confining pressure and compactness is confirmed. It is also evident that a rise in water content enhances the amount of particle breakage for calcareous sand. However, varying tendency of particle breakage with grain size is still controversial and requires further examination.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1383-1390
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• 2009

This study conducted a series of drained triaxial test in order to determine the critical state parameters of a high compressible Jeju sand. Jeju sand is classified into mixed sand containing both siliceous and calcareous materials and has high extreme void ratios due to the angularity of grains and the intra-particle voids of hollow particles. It is observed that the behavior of Jeju sand is similar to that of general calcareous sand. The friction angle of Jeju sand at critical state gradually decreases with increasing the mean effective stress. Test result shows that the particle crushing resulted from stress during shear causes the reduction of void ratio at critical state.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.241-252
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• 2010

This study investigates the application of dilatometer test for evaluating the deformation characteristics of granular soil. $K_D$ is the most sensitive to the stress history among CPT and DMT measurements, and $E_D$ and $q_c$ are observed to be similarly affected by the stress history. The coefficient of at-rest earth pressure($K_0$) is an indirect measure evaluating the stress history of granular soil. A relation using only DMT indices provides appropriate prediction of $K_0$ values. Although penetration of dilatometer inevitably induces the failure of cementation bonds, $E_D$ reflects the deformation characteristics of undamaged cementation relatively well. Therefore, a slightly better prediction of M value for cemented sand is achieved by using $E_D$ rather than $q_c$. Because of the weaker particle strength of calcareous sand compared than quartz sand, the majority of sand particles adjacent to dilatometer probe will be crushed during penetration. The particle crushing will induce the less contraction of the dilatometer membrane during penetration, consequently, the smaller $K_D$ and $E_D$ of calcareous sand.

• 대한토목학회논문집
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• 제30권2C호
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• pp.133-140
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• 2010

본 연구에서는 제주해사에 대한 일련의 삼축압축시험을 수행하여 파쇄성이 큰 제주 탄산염 모래의 한계상태정수를 결정하였다. 제주해사는 입자의 모난 정도가 크고 입자표면과 내부에 다수의 공극이 발달되어 전형적인 탄산염 모래의 특성을 보인다. 제주해사는 큰 최대, 최소 간극비와 큰 압축성 때문에 전단 시 압축거동이 지배적이었다. 구속압이 증가할수록 입자가 파쇄되어 제주해사의 첨두마찰각이 다소 감소하였으나, 일반적인 규산염 모래의 마찰각보다는 다소 큰 것이 관찰되었다. 제주해사의 한계상태 마찰각은 평균유효응력이 증가할수록 점차 감소하였으나, 시료의 간극비가 제주해사의 한계상태에 미치는 영향은 미미하였다. 제주해사의 한계상태 정수는 여타의 탄산염 모래와 유사하였으나, 일반적인 규산염 모래보다는 매우 크게 결정되었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1407-1414
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• 2009

In this study, a Jeju sand, which contains both siliceous and calcareous materials, was sampled from a beach in Jeju Island. It is observed that the Jeju sand has high extreme void ratios due to the angularity of grains and the intra-particle voids of hollow particles. From cone penetration test using calibration chamber system, it is found that the cone tip resistance($q_c$)-relative density(Dr)-vertical effective stress(${\sigma_v}'$) relation of Jeju sand almost matches to that of high compressible quartz sand. However, this correlation overestimates the relative density of a coastal sediments in Jeju Island maybe due to the cementation effect of this area. From analysis of the results of cone penetration and SPS tests at a coastal area in Jeju Island, it seems reasonable to assume that the coast of Jeju Island is a natural cemented sediments.

• Geomechanics and Engineering
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• 제28권5호
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• pp.531-546
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• 2022

Ground displacements caused by the construction of overlapping twin shield tunnels with small turning radius are complex, especially under special geological conditions of construction. To investigate the ground displacements caused due to shield machines in the unique calcareous sand layers in Israel for the first time and determine the main factors affecting the ground displacements, field monitoring, laboratory geological analysis, theoretical calculations, and parameter studies were adopted. By using rod extensometers, inclinometers, total stations, and automatic segment-displacement monitors, subsurface tunneling-induced displacement, surface settlement, and displacement of the down-track tunnel segments caused by the construction of an up-track tunnel were analyzed. The up-track tunnel and the down-track tunnel pass through different stratum, resulting in different construction parameters and ground displacements. The laws of variation of thrust and torque, soil pressure in the chamber, excavated soil quantity, synchronous grouting pressure, and grout volume of the two tunnels from parallel to fully overlapping orientations were compared. The thrust and torque of the shield in the fine sand are larger than those in the Kurkar layer, and the grouting amount in fine sand is unstable. According to fuzzy statistics and Gaussian curve fitting of the shield tunneling speed, the tunneling speed in the Kurkar stratum is twice that in the fine-sand stratum.

• 한국지반공학회논문집
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• 제25권11호
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• pp.105-115
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• 2009

본 연구에서는 제주특별자치도 강정항 인근 해역에서 채취한 해사의 기본특성을 분석하고, 실내 챔버시험으로부터 미고결 제주해사의 콘선단저항-상대밀도-연직구속압의 관계를 결정하였다. 또한 현장 표준관입시험, 콘관입시험, Suspension-PS 검층을 수행하여 제주인근 해역 퇴적층의 고결가능성을 평가하였다. 시험결과, 제주해사는 입자의 각진 정도가 크고 입자표면과 내부에 공극이 발달하여 최대, 최소간극비가 큰 탄산염 모래의 특성을 가지고 있었으며, 큰 압축성을 가진 규산염 모래와 유사한 콘선단저항 분포를 나타내었다. 그러나 미고결 제주해사의 $q_c-D_R-{\sigma}_v'$ 관계는 제주인근 해역 퇴적층의 상대밀도를 과대평가하였다. 관입시험(CPT, SPT) 결과와 Suspension-PS 시험에 의한 미소변형전단탄성계수를 비교한 결과, 제주인근 해역의 퇴적층은 고결 가능성이 매우 높은 것으로 확인되었다.

• 한국지역지리학회지
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• 제10권4호
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• pp.851-864
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• 2004

제수도 김녕-월정 해안에 위치한 해안사구는 약 4km의 해안을 따라 내륙으로 약 6km 연장되는 대형 사구이다. 사구의 경계선을 확정하기 위해 항공사진과 랜드샛 영상을 이용한 상세한 지형적인 분석이 이루어 졌으며 질감분석이 효과적임이 밝혀졌다. 또한 두 개의 측선을 따라 해안에서부터 내륙으로 샘플을 습득하고 물리 화학적 분석이 이루어졌다. 현지조사 과정에서 발견된 고토양층은 사구의 발달이 단속적이었음을 말해준다. 제주도의 협재사구에서 이루어진 방사성탄소연대측정 경과는 해안사구가 석회질 퇴적물로 구성되어 있으며 홀로세 후기에 형성된 것임을 보여주고 있다.