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Graduate School of Ajou University Department of Construction and Transportation Engineering 4. Theses(Ph.D)

저소성 실트지반의 부분배수 특성을 고려한 전단강도 평가

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dc.contributor.advisor이상덕-
dc.contributor.author김석조-
dc.date.accessioned2018-11-08T08:11:33Z-
dc.date.available2018-11-08T08:11:33Z-
dc.date.issued2017-02-
dc.identifier.other25001-
dc.identifier.urihttps://dspace.ajou.ac.kr/handle/2018.oak/11462-
dc.description학위논문(박사)--아주대학교 일반대학원 :건설교통공학과,2017. 2-
dc.description.abstract남해안지역의 고소성 점토지반에 대해서는 현재까지 일축압축강도의 절반크기즉, qu/2를 비배수전단강도로 적용하여 설계하였다. 이런 경우에 시료채취시 발생되는 교란효과로 인해 강도가 저평가되지만, 동시에 응력이방성 및 변형률 속도 효과로 인해 강도가 과대평가되므로 상호보완 되고 있다. 따라서, 별도의 보정작업 없이 실내시험에서 얻어진 값을 그대로 설계강도로 적용해 왔다. 반면에 서해안 저소성 실트 지반은 조립분 함유율이 높아서 원지반에서 불교란 시료 채취가 아무리 적절하게 이루어진다 할지라고 시료 내부의 잔류유효응력이 매우 감소하게 되어, 일축압축강도가 현저하게 과소평가되는 경우가 많다. 따라서, 본 연구에서는 저소성 지반에 대해 일축압축시험 및 간이 CU 시험을 실시하여 비배수 전단강도 산정 시험의 적용성을 분석하였으며 , 일련의 실내 및 현장 원위치 시험을 수행하여 완전비배수 및 부분배수 조건 하의 전단강도를 평가하고 비교 분석하였다. 연구 결과, 저소성 실트 지반에서는 경우는 현장 지반과 동일한 조건이 되도록 원위치 유효상재압으로 재압밀시킨 후, 전단시험에서 얻어진 간이 CU 강도, su(scu)의 75%를 설계 비배수 전단강도로 적용하면, 원위치 전단강도를 적절하게 평가할 수 있는 것으로 확인되었다. 또한, 모래 및 실트 함유량이 많은 저소성 지반에 대하여 피에조콘관입시험(CPTU) 데이터 및 강제치환 공법을 이용하여 부분배수 특성을 분석한 결과, 상대적으로 투수성이 커서 표준관입속도(2 cm/s)하에서 콘관입저항력(qt)이 과대하게 평가되어 과압밀비가 크게 산정되는 경향을 보였으며, CPTU 데이터의 50% 이상이 부분배수 상태를 나타내는 Bq < 0.3에 분포하였다. 강제치환 시공과정 중 부분배수 현상으로 인해 원지반의 강도증가 현상이 발생되어 설계 예상 치환깊이와 실측 치환깊이가 달라지기 때문에, 이들이 동일한 값이 되도록 원지반의 지지력에 대해 역해석을 수행한 결과, 소성지수가 감소할수록 내부마찰각이 커지는 경향을 나타내며, 내부마찰각(φ')이 2∼7°의 범위에서 분포하는 것으로 분석되었다.-
dc.description.tableofcontents제 1 장 서 론 1 1.1 연구배경 및 목적 1 1.2 연구내용 및 범위 3 제 2 장 문헌연구 5 2.1 점성토 지반의 비배수 전단강도 특성 5 2.1.1 점성토의 비배수 전단강도로서 일축압축시험(UC)의 적용성 5 2.1.2 저소성 실트 지반에 대한 일축압축시험(UC)의 적용성 11 2.1.3 저소성 실트 지반에 대한 비압밀비배수 삼축시험(UU) 적용성 17 2.1.4 현장 원위치 조건에 부합되는 비배수 전단강도 평가방법 18 2.2 저소성 실트지반의 부분배수 특성 23 2.2.1 흙의 물리적 특성에 의한 부분배수 분석 23 2.2.2 서해안 저소성 실트지반의 물리적특성을 고려한 부분배수 분석 26 2.2.3 피에조콘시험(CPTU)을 이용한 부분배수 분석 28 제 3 장 저소성 실트지반의 비배수 전단강도 평가 34 3.1 물리시험결과 및 원위치 시험에 의한 토질특성 34 3.2 저소성 실트지반에서의 qu/2 강도 및 간이 CU 강도 su(scu) 39 3.3 강도증가율과 연계한 압밀특성 및 간이 CU 시험의 적용성 45 제 4 장 저소성 실트지반의 부분배수 특성 54 4.1 CPTU 데이터를 이용한 부분배수 특성분석 54 4.2 CPTU 데이터를 이용한 부분배수 강도 평가 93 4.3 강제치환 공법에 의한 부분배수 강도 평가 106 제 5 장 저소성 실트 지반의 완전비배수 및 부분배수 조건에서의 안정성 평가 …112 5.1 개요 112 5.2 강제치환공법에 의한 저소성 실트지반의 안정성 평가 114 5.2.1 완전비배수 조건에서의 안정성 평가 114 5.2.2 부분배수 조건에서의 안정성 평가 116 5.3 모래다짐말뚝공법에 의한 저소성 실트지반의 안정성 평가 120 5.3.1 완전비배수 조건에서의 안정성 평가 120 5.3.2 부분배수 조건에서의 안정성 평가 122 제 6 장 결 론 126 참 고 문 헌 129 Abstract 135 List of Figures Fig. 1.1 Research flow chart 4 Fig. 2.1 Hypothetical effective stress path during boring and sampling (Ladd and Lambe, 1963) 5 Fig. 2.2 Strength anisotropy (Tsuchida, 2000) 7 Fig. 2.3 Strength ratio, sue/suc with plasticity index (Tsuchida, 2000) 8 Fig. 2.4 Change in undrained shear strength with strain rate (Tsuchida, 2000) 9 Fig. 2.5 qu/2 from UC test and average strength from recompression triaxial tests for Ishinomaki intermediate soil (suc and sue measured by compression and extension triaxial tests, respectively) (Tanaka et al., 2001) 12 Fig. 2.6 Strain at failure of UC test for Ishinomaki soil (Tanaka et al., 2001) 12 Fig. 2.7 qu/2 from UC test, average strength from recompression triaxial tests and the strength estimated by CPTU for Drammen clay(Tanaka et al., 2001) 13 Fig. 2.8 The relationship between residual effective stress and in-situ effective burden pressure for various regions (all samples collected by Japanese standard sampling method) (Tanaka et al., 2001) 14 Fig. 2.9 Distribution of residual effective stress for Ishinomaki intermediate soil and Drammen clay (Tanaka et al., 2001) 16 Fig. 2.10 The relationship of the plasticity index versus the apparent internal friction angle obtained from UU-test (Ohmaki, 1989) 17 Fig. 2.11 Comparison between su(qu) and su(M.B) (Tsuchida, 2000) 19 Fig. 2.12 Comparison between su(qu) and su(SCU) (Tsuchida, 2000) 21 Fig. 2.13 The relationship between su(M.B) and su(SCU) (Tsuchida, 2000) 22 Fig. 2.14 The relationship between sand contents, plasticity index and consolidation coefficients (Kamei, 1992) 24 Fig. 2.15 Effect of the changed permeability of clayey ground on partially drained behavior (Asaoka, 1989)(continued) 24 Fig. 2.16 Replacement ratio obtained from check boring (Sim, 2015) 29 Fig. 2.17 Cone penetration resistances measured at various penetration velocities for clayey silts (Kim et al., 2006) 30 Fig. 2.18 Cone penetration resistances and excess pore pressure measured at various penetration velocities for clayey silts (Kim et al., 2006) 31 Fig. 2.19 Effect of penetration rate on cone penetration resistance, pore pressure and friction sleeve (Kim et al., 2006) 33 Fig. 3.1 Grain size distribution & Atterberg limits of Hwaseong clayey silt 35 Fig. 3.2 Test results obtained from CPTU at Hwaseong(continued) 37 Fig. 3.3 Comparison of qu/2 and su(scu) strengths for Hwaseong clayey silt 40 Fig. 3.4 Strain at failure of unconfined compression test for Hwaseong clayey silt 41 Fig. 3.5 Volumetric strain under recompression process for Hwaseong clayey silt 42 Fig. 3.6 Comparison of undrained shear strength normalized by yield consolidation pressure for Hwaseong clayey silt 44 Fig. 3.7 Consolidation characteristics for Hwaseong clayey silt(continued) 45 Fig. 3.8 Field vane strength normalized by yield consolidation pressure versus plasticity index (Lasson 1980) 50 Fig. 3.9 Comparison of clay particle content versus plasticity index from five different low-plastic soils 51 Fig. 3.10 Comparison of vane shear strength normalized by yield consolidation pressure for Japanese and Bothkennar clays(Nash et al., 1992, Tanaka, 1994) 52 Fig. 4.1 Grain size distribution and Atterberg limits of Incheon clayey silt (Sim, 2015)(continued) 54 Fig. 4.2 Grain size distribution and Atterberg limits of Hwaseong clayey silt (Fig. 3.1 Re-insertion)(continued) 56 Fig. 4.3 Test results obtained from CPTU at the Incheon site A(Sim, 2015)(continued) 59 Fig. 4.4 Test results obtained from CPTU at the Incheon site B(Sim, 2015) 61 Fig. 4.5 Test results obtained from CPTU at the Incheon site C(Sim, 2015)(continued) 62 Fig. 4.6 Test results obtained from CPTU at the Hwaseong site A(continued) 64 Fig. 4.7 Test results obtained from CPTU at the Hwaseong site B(continued) 65 Fig. 4.8 Test results obtained from CPTU at the Hwaseong site C(continued) 67 Fig. 4.9 Test results obtained from CPTU at the Busan(continued) 69 Fig. 4.10 Comparison of OCR between the oedometer tests and the CPTU using Powell's formula (Incheon)(continued) 72 Fig. 4.11 Comparison of OCR between the oedometer tests and the CPTU using Powell's formula (Hwaseong)(continued) 73 Fig. 4.12 Comparison of OCR between the oedometer tests and the CPTU using Powell's formula (Busan high plastic clay) 75 Fig. 4.13 Pore water pressure effects on measured parameters(Lunne, 1997) 77 Fig. 4.14 Relationship between the in-situ undrained shear strength(suf) obtained by CPTU and the effective overburden pressure() (Incheon)(continued) 79 Fig. 4.15 Relationship between qt-σv0 and su for estimation of Nkt (Hwaseong) (based on site A CPTU data) 81 Fig. 4.16 Relationship between the in-situ undrained shear strength(suf) obtained by CPTU and the effective overburden pressure() (Hwaseong)(continued) 81 Fig. 4.17 Judgment of the drainage conditions at a standard penetration rate, ν=2cm/s based on the CPTU results (Incheon)(continued) 84 Fig. 4.18 Judgment of the drainage conditions at a standard penetration rate, ν=2cm/s based on the CPTU results (Hwaseong)(continued) 86 Fig. 4.19 Judgment of the drainage conditions at a standard penetration rate, ν=2cm/s based on the CPTU results (Busan) 88 Fig. 4.20 Porewater pressure parameter(Bq) obtained from CPTU (Incheon)(continued) 89 Fig. 4.21 Porewater pressure parameter(Bq) obtained from CPTU (Hwaseong)(continued) 90 Fig. 4.22 Porewater pressure parameter(Bq) obtained from CPTU (Busan)(continued) 92 Fig. 4.23 Stress-strain curve & stress path for Incheon clayey silt (depth=14.4m)(continued) 94 Fig. 4.24 Internal friction angles obtained from recompression triaxial tests with depth for Incheon clayey silts 95 Fig. 4.25 Internal angle Ø' for clays of various compositions as reflected in plasticity index 96 Fig. 4.26 Shear strength of Incheon clayey silt under undrained, drained and partially drained conditions (Incheon)(continued) 99 Fig. 4.27 Shear strength of Incheon clayey silt under undrained, drained and partially drained conditions (Hwaseong)(continued) 102 Fig. 4.28 Construction sequences for compulsory replacement method 106 Fig. 4.29 Determination of replacement depth for compulsory replacement method 107 Fig. 4.30 Relationship of the estimated replacement depth in design phase versus the checked depth at completed construction sites with clayey silt 108 Fig. 4.31 Internal friction angles obtained from back analysis when applying compulsory replacement method versus plasticity index(PI) 110 Fig. 5.1 Typical cross section of embankment on marine subsoil(Incheon) 112 Fig. 5.2 Replacement depth estimated by using qu/2 strength based on φ=0 conditions 114 Fig. 5.3 Minimum factor of safety when applying compulsory replacement method (qu/2 strength) 114 Fig. 5.4 Replacement depth estimated by recompression strength based on φ=0 conditions 115 Fig. 5.5 Minimum factor of safety when applying compulsory replacement method (Simple CU test) 115 Fig. 5.6 Estimated replacement depth when applying angles under partially drained conditions 116 Fig. 5.7 Minimum factor of safety when applying angles under partially drained conditions(continued) 118 Fig. 5.8 Subsoil improved replacement ratio of SCP, as=23% when applying qu/2 strength and its minimum factor of safety(continued) 120 Fig. 5.9 Subsoil improved replacement ratio of SCP, as=9.3% when applying simple CU strength and its minimum factor of safety(continued) 121 Fig. 5.10 Subsoil improved replacement ratio of SCP, as=6.1% when applying φ'=3° under partially drained conditions and its minimum factor of safety(continued) 122 Fig. 5.11 Subsoil improved replacement ratio of SCP, as=3.9% when applying φ'=5° under partially drained conditions and its minimum factor of safety(continued) 123 Fig. 5.12 Subsoil improved replacement ratio of SCP, as=1.4% when applying φ'=5° under partially drained conditions and its minimum factor of safety(continued) 124 List of Tables Table. 2.1 Comparison of intermediate soils and low-plastic soils 27 Table. 2.2 Comparison of cone penetration resistances and excess pore pressure with varying penetration velocities 32 Table. 3.1 Characteristics of low-plastic soils 52 Table. 4.1 Soil properties of investigation areas 57 Table. 5.1 Summary of results by each design concept 125-
dc.language.isokor-
dc.publisherThe Graduate School, Ajou University-
dc.rights아주대학교 논문은 저작권에 의해 보호받습니다.-
dc.title저소성 실트지반의 부분배수 특성을 고려한 전단강도 평가-
dc.title.alternativeEvaluation on Shear Strength of Silty Soil with Low Plasticity Focusing on Partial Drainage Characteristics-
dc.typeThesis-
dc.contributor.affiliation아주대학교 일반대학원-
dc.contributor.alternativeNameKim Seok Jo-
dc.contributor.department일반대학원 건설교통공학과-
dc.date.awarded2017. 2-
dc.description.degreeDoctoral-
dc.identifier.localId770731-
dc.identifier.urlhttp://dcoll.ajou.ac.kr:9080/dcollection/jsp/common/DcLoOrgPer.jsp?sItemId=000000025001-
dc.subject.keyword저소성 점토질실트-
dc.subject.keyword간이CU시험-
dc.subject.keyword부분배수특성-
dc.subject.keyword비배수전단강도-
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