Compression Index versus Natural Water Content Relationships for China's Coastal Soft Clays

Yanbin Gao,Zhongqing Chen,David Airey 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.11

A large number of Cc - wn (Cc is the compression index and wn is the natural water content) correlations have been proposed by researchers for different soft clays around the world, but comparisons of these correlations and reasons for differences between them are rarely reported. In this paper the Cc - wn relationships of marine soft clays from eight China’s coastal cities are presented. It is found that the north coast clays have larger slope of the Cc - wn relationships (about 0.02) than the south coast clays (about 0.008). Comparisons with Cc - wn relationships for remoulded clays and structured natural clays reported by other researchers show the importance of accounting for soil structure, and the higher compressibility and higher apparent preconsolidation stresses of the north coast clays, in comparison to the south coast clays, are believed to be associated with chemical bonding and other post-depositional changes. Most of the reported Cc - wn correlations for natural soft clays from around the world have slopes of about 0.011, which are applicable to weakly structured clays. To develop a more widely applicable Cc - wn correlation, the effects of soil structure need to be incorporated.

Numerical modelling of Haarajoki test embankment on soft clays with and without PVDs

Yildiz, Abdulazim,Uysal, Firdevs Techno-Press 2015 Geomechanics & engineering Vol.8 No.5

This paper investigates the time dependent behaviour of Haarajoki test embankment on soft structured clay deposit. Half of the embankment is constructed on an area improved with prefabricated vertical drains, while the other half is constructed on the natural deposit without any ground improvement. To analyse the PVD-improved subsoil, axisymmetric vertical drains were converted into equivalent plane strain conditions using three different approaches. The construction and consolidation of the embankment are analysed with the finite element method using a recently developed anisotropic model for time-dependent behaviour of soft clays. The constitutive model, namely ACM-S accounts for combined effects of plastic anisotropy, interparticle bonding and degradation of bonds and creep. For comparison, the problem is also analysed with isotropic Soft Soil Creep and Modified Cam Clay models. The results of the numerical analyses are compared with the field measurements. The results show that neglecting effects of anisotropy, destructuration and creep may lead to inaccurate predictions of soft clay response. Additionally, the numerical results show that the matching methods accurately predict the consolidation behaviour of the embankment on PVD improved soft clays and provide a useful tool for engineering practice.

서ㆍ남해안 해성점토의 물리ㆍ압축특성 고찰

김상귀(Kim Sangkwi),여규권(Yea Geuguwen),김길수(Kim Kilsu),김홍연(Kim Hongyeon) 한국지반환경공학회 2011 한국지반환경공학회논문집 Vol.12 No.6

국내의 동ㆍ서ㆍ남해안에는 해성점토층이 폭넓게 분포되어 있으며, 해안지역에서 기반시설물을 설계할 때 압축성이 큰 해성점토로 구성된 연약지반의 공학적 특성을 파악하는 일은 매우 중요하다. 본 논문에서는 인천, 목포, 광양 및 부산지역 해성점토의 물리적ㆍ압축특성을 분석하여 각 지역 및 우리나라 서ㆍ남해안 점토특성을 비교하였다. 이를 위하여 114구역 1,471개 샘플의 실험결과를 이용하였다. 비교결과, 인천점토의 경우 중국 황하로부터 유입된 세립실트 및 높은 조수간만의 차로 가장 낮은 소성 및 높은 단위중량을 보였고, 광양점토는 광범위한 준설매립의 영향으로 압축성이 가장 컸다. 그와 비교할 때 목포 및 부산의 경우는 부분적으로 비슷한 수준의 특성을 나타내었다. 목포와 부산점토의 압축지수는 인천에 비하여 2배 이상, 광양점토의 경우는 목포 및 부산에 비해 70% 이상 높게 나타났다. Marine clays are widely distributed in Korean eastern, western and southern coastal areas. Understanding engineering characteristics of the soft ground is very important, whenever civil structures are constructed in those coastal areas. It is because the ground is composed of highly compressible marine clay. In this paper, the physical and compression characteristics of Incheon, Mokpo, Gwangyang and Busan marine clay were analyzed and the characteristics between western and southern coastal marine clays were compared. For this, test results of 1,471 samples from 114 sites were used. As a result, Incheon clay showed the lowest plasticity and the highest unit weight due to influx of silt from the Yellow River and the turn of the tide of Incheon area. However, Gwangyang clay showed highly compressible characteristic due to extensive reclamation. On the other hand, Mokpo and Busan clay showed partially similar levels of characteristics. The compression index of Mokpo and Busan clay was high more than twice in comparison with Incheon clay and that of Gwangyang clay was higher than seventy percents in comparison with Mokpo and Busan clay.

삼각형점토대토기의 등장과 소멸, 무문토기의 종말

이수홍(Soo Hong Lee) 영남고고학회 2023 嶺南考古學 Vol.- No.96

삼각형점토대토기는 최후의 무문토기이다. 영남지역에는 기원전 3세기 말에서 2세기 중엽 사이에 등장한다. 삼각형점 토대 자체는 점토띠를 단단하게 부착시키기 위한 방안으로 원형점토대를 누르는 과정에서 만들어지게 되었다. 삼각형점 토대토기와 공반되는 토기들은 여러 요소가 복합되어 등장하게 되었다. 삼각형점토대토기 문화의 등장은 철기문화의 영 남지역 확산과 관련된다. 삼각형점토대토기 단계에는 토기의 기종과 크기가 다양해진다. 이것은 생업과 조리법이 다양해졌다는 것인데 그만큼 생산력이 증대된 것을 의미한다. 잉여생산물의 증가는 ‘國’ 성립의 배경이 되었으며 이런 사회적 배경이 토기에서 기종과 크기의 다양화로 표출되었다. 기원전 1세기 와질토기가 등장하여 무덤에 부장되는데, 다호리유적에서는 기원후 1세기까지 삼각형점토대토기가 부장 된다. 낙동강하류역의 생활유적에서는 기원후 2세기까지 사용되다가 적갈색 연질토기로 대체된다. 무문토기가 적갈색연 질토기로 대체되는 것이다. 삼각형점토대토기의 시작은 본격적인 철기문화의 시작을 의미한다. 삼각형점토대토기의 종말은 무문토기의 종말이다. 무문토기의 종말은 가내제작, 비전업적 생산체계라는 전통적인 생산체계의 종말을 의미한다. 삼각형점토대토기의 종말 과 연질토기의 등장은 생활토기까지 회전판과 타날기법이라는 새로운 제도술에 의해 제작된다는 것이고, 그것은 구시대 의 종말, 새로운 시대의 개막을 의미한다. Triangular clay-stripe pottery is the last type of plain-pattern. In the Yeongnam region, it appeared at the end third century~middle second century B.C. Triangular clay stripes themselves were made in the process of pressing round ones to solidify the adherence of clay bands. Many different elements made complex appearances in the pottery that accompanied triangular clay-stripe pottery, the emergence of whose culture was related to the spread of the iron culture in the Yeongnam region. Pottery at the stage of triangular clay-stripe pottery became diverse in terms of type and size, which meant that the methods of occupation and cooking also became diverse based on the increased productive capacity. The increase of surplus products became the background of founding a “Kuk(國)”, and this social background was manifested in the diversification of pottery in type and size. In the first century B.C., grey pottery appeared and was buried in tombs. Triangular clay-stripe pottery was buried in tombs at the Daho-ri relic until the first century A.D. It was used at the living relics in the downstream section of the Nakdong River until the second century A.D. and replaced with reddish brown soft pottery. It meant that plain-pattern pottery was replaced with reddish brown soft pottery. The beginning of triangular clay-stripe pottery meant the beginning of the full-blown iron culture. Its end meant the end of plain-pattern pottery, which signified the end of the traditional production system that was home-based and non-full time. The end of triangular clay-stripe pottery and the appearance of soft pottery meant that even life pottery was made in the new ceramic art involving a pottery wheel and the beating technique. It means the end of an old era and the opening of a new era.

Influence of Initial Moisture and Reactive MgO Content on Mechanical and Microstructural Characteristics of Carbonated Reactive Magnesia Treated Soft Clay

Wenhua Liu,Guoqian Hong,Wugang Li,Yi Zhang,Yang Sun 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.5

Soft clay presents many problems in the construction of infrastructures, which can be well solved by using effective solidification materials and technologies. The carbonated reactive magnesia (CRM) comes to the fore for its superiority in energy-saving and high solidification efficiency. Nevertheless, research on the applicability of CRM in soft clay solidifying is limited. In the current study, two major factors, including initial moisture content (w0) and reactive MgO content (Cm), were examined by measuring the unconfined compressive strength (UCS), mass and volume variations, and moisture content variation of CRM-treated soft clay. The intrinsic mechanisms were discussed based on the mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The findings reveal that carbonated specimens with low Cm (≤ 25%) or w0 (≤ 25%) suffer from severe volumetric expansion and cracks, which cause serious reductions in UCS, and the strength of these specimens can be even much lower than that of the uncarbonated ones. Specimens with high Cm and w0 acquire satisfactory strength by carbonation, and the highest UCS can exceed 4 MPa, indicating that the CRM is capable of solidifying soft clay. Water and MgO are both vital for the crystallization of hydrated magnesium carbonates (HMCs), and Cm is also beneficial for restricting volumetric expansion and reducing macropores; while proper w0 is required for the formation and evolution of HMCs, especially the nesquehonite.

An optimum design of on-bottom stability of offshore pipelines on soft clay

유수영,최한석,이승건,도창호,김도균 대한조선학회 2013 International Journal of Naval Architecture and Oc Vol.5 No.4

This paper deals with the dynamic effect of pipeline installation and embedment for the on-bottom stability design of offshore pipelines on soft clay. On-bottom stability analysis of offshore pipelines on soft clay by DNV-RPF109(DNV, 2010) results in very unreasonable pipe embedment and concrete coating thickness. Thus, a new procedure of the on-bottom stability analysis was established considering dynamic effects of pipeline installation and pipe-soil interaction at touchdown point (TDP). This analysis procedure is composed of three steps: global pipeline installation analysis, local analysis at TDP, modified on-bottom stability analysis using DNV-RP-F109. Data obtained from the dynamic pipeline installation analysis were utilized for the finite element analysis (FEA) of the pipeline embedment using the non-linear soil property. From the analysis results of the proposed procedure, an optimum design of onbottom stability of offshore pipeline on soft clay can be achieved. This procedure and result will be useful to assess the on-bottom stability analysis of offshore pipelines on soft clay. The analysis results were justified by an offshore field inspection.

An optimum design of on-bottom stability of offshore pipelines on soft clay

Yu, Su Young,Choi, Han Suk,Lee, Seung Keon,Do, Chang Ho,Kim, Do Kyun The Society of Naval Architects of Korea 2013 International Journal of Naval Architecture and Oc Vol.5 No.4

This paper deals with the dynamic effect of pipeline installation and embedment for the on-bottom stability design of offshore pipelines on soft clay. On-bottom stability analysis of offshore pipelines on soft clay by DNV-RP-F109 (DNV, 2010) results in very unreasonable pipe embedment and concrete coating thickness. Thus, a new procedure of the on-bottom stability analysis was established considering dynamic effects of pipeline installation and pipe-soil interaction at touchdown point (TDP). This analysis procedure is composed of three steps: global pipeline installation analysis, local analysis at TDP, modified on-bottom stability analysis using DNV-RP-F109. Data obtained from the dynamic pipeline installation analysis were utilized for the finite element analysis (FEA) of the pipeline embedment using the non-linear soil property. From the analysis results of the proposed procedure, an optimum design of on-bottom stability of offshore pipeline on soft clay can be achieved. This procedure and result will be useful to assess the on-bottom stability analysis of offshore pipelines on soft clay. The analysis results were justified by an offshore field inspection.

An Egg-Shaped Elastic Viscoplastic Model for Clay: Experimental Investigation and Constitutive Modelling

Pan Ding,Luying Ju,Ri-Qing Xu,Zihai Yan,Mingming Wu,Gangping Zhang 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.5

This paper presents the experimental investigation carried out for evaluation of the rheological behaviours of Hangzhou soft clay, and proposes a three-dimensional elastic viscoplastic model to describe the rheological characteristics under triaxial condition. Firstly, the time-dependent behaviours of Hangzhou soft clay, such as creep and strain rate effects, were observed and discussed based on the analysis of rheological tests. Subsequently, a constitutive model was formulated under the framework of Perzyna’s overstress theory and incorporates other developments, including: 1) A smooth and continuous egg-shaped yield surface, whose shape can change from an ellipse to a teardrop shape, thus providing greater flexibility for better modelling; 2) An equivalent time concept, which enables the model to describe the time-dependent behaviours under different loading paths. By varying the shape parameter, the newly established model can be degenerated into modified Cam-clay (MCC) model or Yin-Graham elastic viscoplastic model. Finally, the model was solved numerically using the fourth-order convergent iterative method combined with the Runge-Kutta method. Comparison of simulation results and experimental data shows that the newly proposed model has an ability to predict creep characteristics and strain rate effects of soft clay.

Improvement of Soft Organic Clay Soil Using Vertical Drains

Walid El Kamash,Kamal Hafez,Mahmoud Zakaria,Azza Moubarak 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.2

The design of foundations based on soft clay is still a very challenging problem. Three experimental cases were performed to examine the action of soft clay: the first case without drains, the second case with sand drains and the third case with prefabricated vertical drains (PVDs). Two-dimensional finite element analysis was carried out using PLAXIS 2D and its findings were compared to previous experimental results where good consistency was found. Parametric study was conducted with a variation in the size, length and diameter of sand drains. The length and spacing of the PVD, the diameter of the smear zone and the permeability of the smear zone were also studied. Results have shown that PVD is preferable to the improvement of soft clay rather than sand drainage systems. The sand drains decreased the time of 90% consolidation by (90.8%) using 50 cm diameter, 2 m spacing and 25 m length, and the PVDs decreased the time of 90% consolidation by (94.4%) using 4 mm × 10 cmdimensions, 2 m spacing and 25 m length. Both sand drains and PVD are effective in decreasing the consolidation time. The results of this paper concluded analytical formula that indicate the percentage of wick drain consolidation.

Amino Silane, Vinyl Silane, TESPD, ZS(TESPD/Zinc Complex) Effects on Carbon Black/Clay Filled Chlorobutyl Rubber(CIIR) Compounds 2 : Effects on Soft Clay/Carbon Black Filled Compounds

Kwang-Jea Kim 한국탄소학회 2009 Carbon Letters Vol.10 No.2

Various silanes, amino silane, vinyl silane, TESPD, and ZS (TESPD/zinc soap complex), are added into chlorinated isobutylene-isoprene copolymer (CIIR)/soft clay/carbon black (CB). The vulcanization characteristics, the processability, and the mechanical properties are measured. In soft clay/CB filled CIIR system, there are no significant changes in Mooney viscosity among compounds. Vinyl silane added compound shows a low extrusion torque. All the silane added compounds shows an increased modulus. The mechanical properties are significantly increased when the S2 is added into CIIR/soft clay/CB compounds.