An attempt has been made to summarize some of the unique geotechnical problems encountered during construction of a few large man-made islands recently completed off the coast of Osaka Bay, Japan. Large settlements appear to be the most serious problem both during and after construction. Settlements due to consolidation of a thick layer of soft alluvial clay that constitutes seabed seem to virtually cease within a relatively short period of time when vertical drains are installed adequately prior to fill placement. Settlements due to compression of underlying thick diluvial deposits consisting of layers of stiff clays interbedded with coarse-grained soils, however, continue over a prolonged period of time and call for special provisions for structures built on the artificial islands to cope with relatively large future settlements. Although accurate settlement prediction is not possible, it is both technically and economically feasible, nevertheless, to construct large-scale islands. Partjcularly attractive and promising is creation of sizable new areas for various purposes, immediately adjacent to highly-developed, densely-populated cities situated along the coast such as those around Osaka Bay.

When marine clay is hydraulically dredged from seabed and pumped into the pond enclosed by contatinment dykes, marine clay is mixed and flocculated with water and then settled. At this time, the fines will interact with the water to form a Bingham plastic slurry which has non-Newtonian characteristics. The dredged slurry has different physical properties depending on settling locations and settling depths in the pond and has few hundred percent of water content and almost nil of shear strenght. In order to make this condition of the dredged slurry the final formation for public use within a short period, sand spreading method to enhance the support capacity of the dredged slurry is developed. In this paper, the effect of sand mixing into the dredged slurry of this method is analyzed based on reference study, laboratory tests and actual construction results.

Hydraulically filled ground is formed by the settling of soil grains from the mixture of soil grains and water. It was generally known that the settling speed of the soil grains in governed by Stokes low. In the case of clayed dredged material, the shape of soil grains is not round, the surface of the soil grains is relatively large compared to the weight of soil grains and inter-grain ionic force is relatively large compared to the wight of soil grains. By this reason the settling and consolidation behavior of hydraulically filled quite different from that of Stokes law. This study investigated the settling and consolidation behavior of hydraulically filled materials of Yeochon industrial complex by large scale laboratory settling & consolidation container. The test results showed tat actual settling speed of soil grains in quite large compared to that of Stokes law. It was turned out that this phenomenon was due to the aggregation of soil grains. Also, it was truned out that the void ration and water content after the completion of settling process was 8.7 and 322% respectively. The consolidtion settlement of clayey hydraulic fill material was predicated better by "incremental small strain" consolidation concept than classical Terzaghj's consolidation concept (infinitesimal strain).

Recently, by the lack of fill material, the dredg and fill(hydraulic fill) method is commonly used in reclamation projects. Hydraulic fill method dredges the soil and send it with water through the transportation pipe to the site. The intial state of the hydraulic fill material is accordingly the mixture of water and soil skeleton which settles with time forming a new soil layer. The properties of new soil layer is governed the size of the soil skeleton, the flow velocity of mixing water, salt concentration, the distance from the discharge pipe outlet, and other dredging conditions when settling process occur. In this study, the effects of gradation of derdged soil on the deposition properties (with emphasis on the optimum spacing of the discharge pipes) was investigated by field test. It was found that the soft fine graind soil was forme at 350m from the discharge pipe outlet when the dredged material was classified as CL, while the soft fine grained soil was not formed even at the distance farther than 400m from the diacharge pipe outlet when the dredged material was classified as SM.

In characterizing a suspension, heterogenety is included onto the previous characterization using solids concentrations and flocculent characteristics, because of its importance in hydrodynamics. The mechanism of interface formation during the sedimentation of concentrated suspension (thickening) is investigated from a microcosm consisting of four particles in a same plane and a smaller particle below. The critical distances after shich interface forms are calculated as a function of particle size ratio when the small particle is located in the middle of the squre datermined by the large particles. The results shows that the critical separation distance increase as the size ratio approaches to one (homogeneous suspension). This conforms to the trend of existing observations that homogeneous suspensions create the solid-liquid interface at much lower concentration (at al larger separation distance) that the heterogeneous suspensions.

The characteristics of the landfill of coal ash and ironwork wastes are investied by performing the basic geotechnical experiments and groundwater quality analyses in the landfills. The results show that the waste materials themselves have good characteristics that can be used as reclamation materials. However, landfills need either some ground improvement or costly foundation and excavation methods to be used as construction sites, because of the careless management during the period of waste disposal.

The elevation of reclamation work in the coastal area for the industrial complex is determined through the investigation and review of marine conditions, drainage plan and fill materials. The embankment to be constructed with crushed stone on the soft soil should be safe against the wave force, immediate and long term consolidation settlement, overturning and sliding due to self-weight and other forces. Because of lack of fill material from the borrow pit, the soft marine clay to be dredged shall be used as the reclamation material. And Paper Drain Board is used as the improvement method for the deep soft clay strata.

근래 인공섬은 그 수가 많아지고 또 그 크기도 방대해지고 있다. 이 논문은 인공섬의 완성에 앞선 각과정에 대한 제반 문제점들에 대한 지반공학적 분석결과를 포함한다. 최근 인공섬 형성 과정에 사용하는 신공법에 개발되었다. 인공섬의 형성은 단일 공법에 의한 것이 아니고 여러가지 공법의 홍용의한다. 따라서 각 공법에 대한 완벽한 이해는 사업자체의 성공적인 완료와 경제성에 지대한 영향을 준다. 인공섬은 해성퇴적층에 위치하게 된다. 따라서 해성퇴적층의 형성과정, 환경, 퇴적 후의 변화 그리고 지반공학적인 자료가 채취되어야하고 분석되어야 한다. 해성퇴적층에 위치할 인공섬 완료에 필요한 조사, 설계 및 시공에서 반드시 고려되어야 할 과정이 실무자들이 이해하고 사용할수 있는 형식으로 제시되었다. 불완전한 자료, 또 그것에 근거한 설계 및 시공이 줄 수 있는 결과에 관해 기술했다.

The paper presents general engineering properties of soft marine sediments and related geotechnical problems associated with construction of artificial islands. Both of the data from foreing and domestic sources are utilized. The selection of soil improvement methods are also discussed.

Housing lots and area for industrial construction are very serious problem because of narrow country area and high population density of Korea. Especially the form of Pusan is long from north to south. Since the city is surrounded by the sea, traffic trouble and housing lots problem is very serious condition. To solve these problems, Reclamation & Man-made island is needed. So Pusan city is planning for Man-made Island for 2000 year. I will consider about the content of Man-made Island, which is planned by Pusan, and the character of Geotechnical Engineering.

The construction of container terminal at Brani, Singapore required the improvement of soft clay layer having the thickness of about 6.5m, average moisture content of 79.4%, liquid limit of 90.4%, plastic limit of 21.8%, field vane strength of 10 to 25 KPa, pre-consolidation pressure of 225 to 60 KPa and compression index of 0.4 to 1.0. For the improvement of this layer, Colbon drains of 1.3m spacing in triangular pattern were installed to the bottom of the layer and surcharge of more than 11.25m high sand fill was later applied to the treated area. The settlement and lateral displacement of the ground were measured and the speed of surcharge filling was controlled, based on these readings. The removal of surcharge was determinied using the estimated time for the 90% degree of consolidation under the design pressure of 180KPa. The field and laboratory test results show that the soft clay layer has been improved substantially in its strength and consolidation characteristics: increase in strength of about 50KPa and pre-consolidation pressure and decrease in void ratio and compression index.

Assessement of comsolidation characteristics of soft soil is very important in the project of soft soil improvement. In the design step, the consolidation characteristics of soil is determined by the laboratory tests (typically oedometer test), generally. But there is big differences between the condition of laboratory test and the condition of field(in situ). the differences results in the considerable difference between the predicted and measured consolidation behavior. This article analyzed the consolidation data of the "SOFT SOIL IMPROVEMENT PROJECT of the 2nd Namdong Industrial Complex at Inchon". The project was improving the road way net work in the 2nd Namdong Industrial Complex by preloading and sand pile method. Field instrumentation was performed at 10 points which consist of pneumatic piezometers, magnetic probe extensometers, inclinometers and electronic dipmeter. The results showed that there is big difference in the laboratory predicted consolidation behavior and field consolidadion behavior. Also there was big difference in the settlement behavior and pore pressure behavior. This article investigated the above factors by comparing the settlement, pore pressure and strength at different conditions.onditions.

발파공법은 비 점토성 지반의 심층 개량처리에 있어서 경제적이며 실용성 있는 방법이다. 발파에 의한 흙의 다짐효과는 복잡한 과정을 통하여 이루어지며 좋은 결과를 얻기 위해서는 발파 계획에 있어서 동 공법의 작용원리를 잘 이해하고 적용하여야 한다. 본 연구에서는 발파공법에 의한 흙의 다짐효과에 관한 과거의 연구자료를 광범위하게 조사하였다. 지반개량 작용원리에 관련하여 특별한 현상과 증거를 제시하는 실제 사례 자료를 기초로 하여 현재까지 흙의 밀도증가 요인을 설명해 온 개념은 발파에 수반되어 주변 주반에 발생하는 지반거동현상을 설명하기에 부족함이 있음을 지적하였다. 또한 발파지점 부근에 형성되는 액상화 영역과 그 외부 영역에서 각각 발생되는 과인간극수압 및 지반응력상태, 이에 따른 지반침하 형태 그리고 개량지반의 강성 및 강도특성에 관하여 고찰하였다.

This paper reports a case study of dynamic consolidation. The objective of the study is to evaluate the effectiveness of ground improvement at the site for Hyundai Petrochemical Compound constructed at Daesan-Myeon, Seosan-Gun in the western shores of Korea. The site ground was prepared by filling on the existing soft marine deposit which consists of a loose granular soil layer and a medium stiff clay layer. For the stabilization of site ground, the compaction was executed in three different procedures with same pounder weigh, drop height and imprint spacing. The post investigation showed that the object was successfully achieved indicating a significant increase of bearing capacity of the treated ground. In this study the effectiveness of dynamic consolidation is evluated for various factors the applied energy, temping sequences, the radial distance from the imprint location and the depth of bed rock.

This paper reports the application of field tests to weak ground. In this study, field and laboratory tests were performed in the west seashore of KOREA(Ildo, Sore, Kunsan, Youngam). Applied tests are standard penetration test, cone penetration test, dilatometer test, field vane test, unconsolidated undrained test, oedometer test and other fundametal material properties tests. The results of in-situ test are used to estimate soil types and undrained shear strengths of five clay local deposits. SPT results showed low reliability and FVT war also demonstrated the best field test to weak clayey deposits.

In case of construction of the final refuse disposal site on the ground where 20m soft clay layer is deposited, Sand Compaction Pile(SCP) was driven with a view to increase the strength and reduce the settlement when the reclaimed revetment intend to be constructed first in a short time. Field monitoring method is carried out in order to overcome the problems of settlement and stability in the construction of the reclaimed revetment and the assumed problems in the design of composite ground. In this paper the observed data from monitoring sections are analysed, fedback to the desigh and field, and compared with FEM analysis. Conclusions are as follow: in case of 70% replacement the use of modified soilparameters makes the FEM analysis of SCP possible. In case of 27% replacement, n(stress concentration ratio)=0.2-0.3, B(measured settleme reduction coefficient)=0.43 are evalated. Also, horizontal displacement is remarkably happened around the ground.