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1.
浅层沉积物不排水抗剪强度（Su）是深水作业的关键参数之一。为了获取南海神狐海域首次海域天然气水合物试采区W18-19框体的基本工程地质特征，试采工程准备阶段开展了原位孔压静力触探测试（CPTU）及大量的室内实验。本文将主要基于CPTU计算不排水抗剪强度的基本模型，采用微型十字板、电动十字板、袖珍贯入仪及不固结不排水三轴实验，确定该区域不排水抗剪强度的基本模式，并提出适用于南海神狐钙质黏土层的不排水抗剪强度纵向分布规律计算模型，对该区域水合物上覆层的不排水抗剪强度进行预测。 结果表明，基于总锥端阻力、有效锥端阻力、超孔隙压力的模型系数分为13.8、4.2、14.4。综合考虑地层压实效应和含气情况，本文提出的分段函数预测模型与室内结果的一致性较好，可用于工程设计阶段进行工区不排水抗剪强度纵向分布规律的预测。另外，基于有效锥端阻力的不排水抗剪强度经验模型适应于浅层极软-较硬压实的钙质粘土层，基于超孔隙压力的不排水抗剪强度模型适用于较硬-坚硬的不含气层，而基于总锥端阻力的不排水抗剪强度计算模型则适用于坚硬含气的钙质黏土层。本文提出的分段函数模型有效的提高了经验模型在南海神狐水合物赋存区的适用性，计算结果可为工程安全评价提供支撑。 相似文献
2.
鉴于海底浅表层软黏土强度测试精细化程度不足的现状,引入流体测试中的流变仪,对青岛海域海底浅表层软黏土开展多组原状和重塑试样的不排水剪切强度试验,通过对比静力触探和微型十字板测试结果,验证了流变仪测试方法的有效性。基于流变仪试验结果,揭示了海底软黏土原状和重塑状态下不排水剪切破坏模式,探讨了海底软黏土不排水剪切强度和灵敏度随埋深及液性指数的发展演变趋势,评价了软黏土的结构性特征。最后,引入含水率与液限之比对海底浅表层软黏土重塑不排水剪切强度进行了归一化分析,为近海海洋开发活动提供技术支撑。 相似文献
3.
The undrained shear strength normalized by the yield consolidation pressure, su/pc', is presented for four coastal sites: Busan/Gwangyang and Incheon/Gunsan, having the characteristics of high and low plasticity, respectively. The field vane shear strengths, su(FVT), were compared with unconfined compressive strength, qu/2 which has been used as a representative testing method in Korea. Many researchers have suggested that the undrained shear strength normalized by the yield consolidation pressure, su/pc', depends on Ip. However, the undrained shear strength normalized by the yield consolidation pressure, su/pc' is in the range of 0.25–0.35, independently of the plasticity index, Ip except for su/pc' using qu/2 values in the case of soils having a low plasticity, such as Incheon and Gunsan intermediate soils. Bjerrum's correction factor has been commonly applied to evaluate mobilized undrained shear strength using the field vane test in Korea. However, the corrected undrained shear strengths using Bjerrum's correction factor, including Morris and Williams' method, were considerably underestimated for Korean marine clay when compared with the qu/2 values that have been used as the mobilized undrained shear strength for practical design in Korea. 相似文献
4.
An unusually thick and soft clay, which is called Busan clay, has been deposited throughout the Nakdong River estuary, South Korea. Although many reclamation works have been carried out in the area since early 1990s, large- and small-scale slope failures have taken place mostly during the soil placement on the clay. A case history briefly describes failure of a breakwater resulting from overestimation of the undrained strength, obtained from laboratory testing. An attempt has been made to examine the methods for determining the undrained strength from field vane testing. For this, the undrained strengths from field vane testing were obtained using different correction factors and compared with each other at five sites in the area. An alternative correction method applicable especially for Busan clay was found, using a range of corrected strength ratios. Further, relationships between the depositional environment and the undrained strength of the clay have also been investigated. 相似文献
5.
An unusually thick and soft clay, which is called Busan clay, has been deposited throughout the Nakdong River estuary, South Korea. Although many reclamation works have been carried out in the area since early 1990s, large- and small-scale slope failures have taken place mostly during the soil placement on the clay. A case history briefly describes failure of a breakwater resulting from overestimation of the undrained strength, obtained from laboratory testing. An attempt has been made to examine the methods for determining the undrained strength from field vane testing. For this, the undrained strengths from field vane testing were obtained using different correction factors and compared with each other at five sites in the area. An alternative correction method applicable especially for Busan clay was found, using a range of corrected strength ratios. Further, relationships between the depositional environment and the undrained strength of the clay have also been investigated. 相似文献
6.
Undrained strength behaviour of a cemented marine clay under monotonic and cyclic loading 总被引：1，自引：0，他引：1
The paper presents the results of a series of monotonic and cyclic triaxial shear tests carried out to study the influence of the strain effect and load cycles on the undrained shear strength of a cemented marine clay from the East coast of India. The undrained shear strength of Indian coastal marine clay has been established from a detailed shear testing carried out in three phases. Undisturbed soil samples taken out from the seabed were used in the test. In the first part, a comprehensive monotonic shear testing has been carried out under both stress-controlled and strain rate-controlled conditions. In the second phase on identical soil specimen, undrained cyclic shear tests were carried out at various cyclic stress ratios (CSR) and these stress levels are chosen in such a way so that no failure occurred during testing. In the final phase post cyclic monotonic shear testing was conducted to qualitatively evaluate the damage caused by cyclic loading. The monotonic shear test results bring out the influence of cementation that can be detected by the stress-controlled test. The cyclic stress results are analysed in terms of CSR. Further, the results are correlated in terms of stress path. 相似文献
7.
深水土工调查技术和分析方法新进展 总被引：1，自引：0，他引：1
简要介绍了近年来国外在深水土工调查技术和分析方法方面取得的新进展,包括:钻孔取样技术在钻入模式和取样器的多样化和有效组合,从而实现不同水深和不同土类条件下的高质量取样;带孔压测量的圆锥触探试验在测量方法、孔压测量单元设计、探头的小型化和多样化、数据的快速传输以及分析理论方面的进展;减少土样扰动,准确评估粘土不排水抗剪强度的“SHANSEP”室内试验方法及应用。 相似文献
8.
Undrained shear strength is a fundamental parameter for estimating the stability of soft soils. This study explores the relationship between undrained shear strength, void ratio, and shear wave velocity for saturated and normally consolidated clay specimens. The undrained shear strength void ratio-shear wave velocity relationship was correlated to empirically determined parameters of selected marine clay specimens. To verify the proposed relationship between undrained shear strength and shear wave velocity, in situ flat dilatometer tests were used for determining the undrained shear strength, and downhole tests were used to assess the shear wave velocity on a natural soil deposit at various depths. The undrained shear strength estimated from the in situ shear wave velocities was compared to the undrained shear strength obtained in the field. The results show that the inferred undrained shear strength yield similar values and follow the same trends as the in situ undrained shear strength data. This method using shear wave velocity can help to nondestructively estimate the undrained shear strength of soft soils in the field and be used in both on-shore and off-shore geotechnical engineering projects. 相似文献
9.
Havvanur Kılıç Saadet Arzu Berilgen Perihan Biçer Mustafa Yildirim 《Marine Georesources & Geotechnology》2013,31(4):303-323
Istanbul, the largest city in Turkey and one of the major metropolitan areas in the world, cleaned one of its environmentally polluted areas—Golden Horn—by dredging 5 million m3 of the bottom sediments and pumping the resulting sludge to a storage area behind a dam built at an abandoned rock quarry site in Alibey district. The reclamation of the land that formed over the storage area of Golden Horn dredged material is socially and economically very desirable. In this paper, results from experimental studies that are focused on determining the shear strength behavior of the dredge material and undisturbed soil are presented. Slurry consolidometer test, large model tests and small model tests are used to consolidate the dredged soil samples from Halic to simulate the natural consolidation behavior of these soils. Shear strength parameters are determined by laboratory vane tests; unconfined compression tests; undrained-unconsolidated (UU) and consolidated-undrained (CU) triaxial tests on samples that are obtained through in situ undisturbed samples and laboratory model tank and slurry consolidation. Moreover, the effects of fly ash and lime additives on the undrained shear strength were determined by mixing the materials with the dredged clay from Golden Horn during the model experiments conducted in the laboratory. Based on these findings, equations are proposed that govern the relationships between undrained shear strength and water content value. 相似文献
10.
This paper presents a predictive model for undrained penetration of cylinders into soft seafloor soils. The penetration depth will depend on the velocity of the cylinder as it touches down at the seafloor, and the net deceleration of the cylinder as it is acted on by forces of self-weight, soil buoyancy, and soil-shearing resistance. The soil-shearing resistance force increases as a function of penetration depth and, due to the dependence of undrained shear strength on strain rate, penetration velocity. This paper presents finite element (FE) simulations that quantify both effects and form the basis of a simplified soil-resisting force model. Strain-rate effects are modeled within a framework of rate-dependent plasticity, with shearing resistance increasing semilogarithmically with increasing strain rate above a certain threshold strain rate. With all forces acting on the cylinder, estimated penetration depths are predicted from simple equations of motion for a single particle. Comparisons to laboratory tests involving penetration of cylinders into soft reconstituted marine clay show reasonable agreement between model predictions and measurements. 相似文献
11.
海洋粉质粘土在波浪荷载作用后的不排水抗剪强度衰化特性 总被引：3，自引：0，他引：3
通过对南海重塑粉质粘土土样的大量动三轴试验结果分析,得到此种土在波浪荷载作用后不捧水抗剪强度衰化同动载作用引起的动应变幅及平均累积孔压之间的相互关系和预估公式;并通过与超固结土样的静三轴剪切试验结果的比较,发现动、静三轴两种试验结果具有很好的吻合关系。建议可用超固结土样的静三轴剪切试验同时结合部分动三轴试验来预估土样在波浪荷载作用后不排水抗剪强度衰化与平均累积孔压之间的关系。 相似文献
12.
In this study, a stochastic method was applied to investigate if there exists a statistical correlation between values of undrained shear strength at various vertical distances along Golden Horn. Therefore, the undrained shear strength values measured by field vane shear tests at different depths were used to determine the depth dependent variation of the mean value and standard deviation. Futhermore, autocorrelation functions were defined to describe the correlation between values of cu at different depths. The study showed that the applied method might provide a statistical range to estimate the undrained shear strength value at depths where no measurements are undertaken. 相似文献
13.
Zhongnian Yang Xuesen Liu Lei Guo Yuxue Cui Xiuting Su Chao Jia Xianzhang Ling 《海洋学报(英文版)》2022,41(5):136-146
The Huanghe River（Yellow River） Delta has a wide distribution of fine-grained soils. Fluvial alluviation, erosion,and wave loads affect the shoal area, resulting complex physical and mechanical properties to sensitive fine-grained soil located at the river-sea boundary. The cone penetration test（CPT） is a convenient and effective in situ testing method which can accurately identify various soil parameters. Studies on undrained shear strength only roughly determine the fine content（FC） without ma... 相似文献
14.
This paper reports five case histories of jack-up rig installation in layered soil profiles where a dominate feature was a stronger sand layer overlaying a weaker clay layer. In all cases a relatively continuous load-penetration profile was measured during installation of each of the three spudcan foundations. Summary site-investigation data is provided and consisted of mainly torvane, minature vane, unconsolidated undrained triaxial and pocket penetrometer tests for determining undrained shear strength of the clays and blow counts for deriving the relative density of sand. A statistical averaging method recommended in the InSafeJIP guidelines was used to provide the best fit of the undrained shear strength profile in the clay as this then allowed for spudcan load-penetration profiles to be estimated without introduction of user interpretation or bias. Sand properties were taken as provided in the original site-investigation report. Comparisons between load-penetration profiles calculated using the industry-standard ISO guideline, more recently proposed mechanism-based calculation method and three-dimensional large deformation finite element simulations are made with the measured data, leading to valuable insights for practitioners for estimating behaviour of jack-up installations in problematic sand-over-clay soil profiles. 相似文献
15.
Macro-and Micro-Properties of Two Natural Marine Clays in China 总被引：2，自引：0，他引：2
In this paper,macro- and micro- properties of natural marine clay in two different and representative regions of China are investigated in detail.In addition to in-situ tests,soil samples are collected by use of Shelby tubes for laboratory examination in Shanghai and Zhuhai respectively,two coastal cities in China.In the laboratory tests,macro-properties such as consolidation characteristics and undrained shear strength are measured.Moreover,X-ray diffraction test,scanning electron microscope test,and mercury intrusion test are carried out for the investigation of their micro-properties including clay minerals and microstructure.The study shows that:(1) both clays are Holocene series formations,classified as either normal or underconsolidated soils.The initial gradient of the stress-strain curves shows their increase with increasing consolidation pressure;however,the Shanghai and the Zhuhai clays are both structural soils with the latter shown to be more structured than the former.As a result,the Zhuhai clay shows strain softening behavior at low confining pressures,but strain hardening at high pressures.In contrast,the Shanghai clay mainly manifests strain-hardening.(2) An activity ranges from 0.75 to 1.30 for the Shanghai marine clay and from 0.5 to 0.85 for the Zhuhai marine clay.The main clay mineral is illite in the Shanghai clay and kaolinite in the Zhuhai clay.The Zhuhai clay is mainly characterized by a flocculated structure,while the typical Shanghai clay shows a dispersed structure.The porous structure of the Shanghai clay is characterized mainly by large and medium-sized pores,while the Zhuhai clay porous structure is mainly featreed by small and medium-sized pores.The differences in their macro- and micro- properties can he attributed to different sedimentation environments. 相似文献
16.
Guo-Jun Cai Song-Yu Liu Li-yuan Tong Guang-Yin Du 《Marine Georesources & Geotechnology》2013,31(2):91-104
As indicated by the profile of overconsolidation ratio (OCR), the stress history of a soil deposit is one of the dominant factors that influence the engineering behavior of soils. A commonly used method to obtain the parameter is the laboratory oedometer test, which is of low accuracy and time consuming because of inevitable sample disturbance. These difficulties can be overcome by in situ pizeocone penetration test, which provides continuous measurement of cone resistance, sleeve friction, and pore water pressure induced during the penetration. Though many methods have been proposed to estimate the preconsolidation pressure and overconsolidation ratio of clay deposits, their validity still needs to be proved. In this study, existing empirical methods for interpreting stress history of clays through piezocone tests are briefly reviewed. It is shown that regional correlations are valid. Piezocone tests utilizing a Vertek-Hogentogler CPTU truck that have been completed at different sites in the Jiangsu province of China. Existing correlations are compared with these field test data. It is shown that the correlation based on normalized net tip resistance is pretty accurate for determining the overconsolidation ratio of Quaternary clay deposits. 相似文献
17.
The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties (the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed. Finally, a sensitivity analysis on the parameters in the formula was performed. 相似文献
18.
In situ pore-pressure evolution during dynamic CPT measurements in soft sediments of the western Baltic Sea 总被引：1，自引：1，他引：0
We present in situ strength and pore-pressure measurements from 57 dynamic cone penetration tests in sediments of Mecklenburg (n?=?51), Eckernförde (n?=?2) and Gelting (n?=?4) bays, western Baltic Sea, characterised by thick mud layers and partially free microbial gas resulting from the degradation of organic material. In Mecklenburg and Eckernförde bays, sediment sampling by nine gravity cores served sedimentological characterisation, analyses of geotechnical properties, and laboratory shear tests. At selected localities, high-resolution echo-sounder profiles were acquired. Our aim was to deploy a dynamic cone penetrometer (CPT) to infer sediment shear strength and cohesion of the sea bottom as a function of fluid saturation. The results show very variable changes in pore pressure and sediment strength during the CPT deployments. The majority of the CPT measurements (n?=?54) show initially negative pore-pressure values during penetration, and a delayed response towards positive pressures thereafter. This so-called type B pore-pressure signal was recorded in all three bays, and is typically found in soft muds with high water contents and undrained shear strengths of 1.6–6.4 kPa. The type B signal is further affected by displacement of sediment and fluid upon penetration of the lance, skin effects during dynamic profiling, enhanced consolidation and strength of individual horizons, the presence of free gas, and a dilatory response of the sediment. In Mecklenburg Bay, the remaining small number of CPT measurements (n?=?3) show a well-defined peak in both pore pressure and cone resistance during penetration, i.e. an initial marked increase which is followed by exponential pore-pressure decay during dissipation. This so-called type A pore-pressure signal is associated with normally consolidated mud, with indurated clay layers showing significantly higher undrained shear strength (up to 19 kPa). In Eckernförde and Gelting bays pore-pressure response type B is exclusively found, while in Mecklenburg Bay types A and B were detected. Despite the striking similarities in incremental density increase and shear strength behaviour with depth, gas occurrence and subtle variations in the coarse-grained fraction cause distinct pore-pressure curves. Gaseous muds interbedded with silty and sandy layers are most common in the three bays, and the potential effect of free gas (i.e. undersaturated pore space) on in situ strength has to be explored further. 相似文献
19.
Bruce D. Johnson Mark A. Barry Bernard P. Boudreau Peter A. Jumars Kelly M. Dorgan 《Geo-Marine Letters》2012,32(1):39-48
This study reports the first in situ measurements of tensile fracture toughness, K
IC, of soft, surficial, cohesive marine sediments. A newly developed probe continuously measures the stress required to cause
tensile failure in sediments to depths of up to 1 m. Probe measurements are in agreement with standard laboratory methods
of K
IC measurements in both potter’s clay and natural sediments. The data comprise in situ depth profiles from three field sites
in Nova Scotia, Canada. Measured K
IC at two muddy sites (median grain size of 23–50 μm) range from near zero at the sediment surface to >1,800 Pa m1/2 at 0.2 m depth. These profiles also appear to identify the bioturbated/mixed depth. K
IC for a sandy site (>90% sand) is an order of magnitude lower than for the muddy sediments, and reflects the lack of cohesion/adhesion.
A comparison of K
IC, median grain size, and porosity in muddy sediments indicates that consolidation increases fracture strength, whereas inclusion
of sand causes weakening; thus, sand-bearing layers can be easily identified in K
IC profiles. K
IC and vane-measured shear strength correlate strongly, which suggests that the vane measurements should perhaps be interpreted
as shear fracture toughness, rather than shear strength. Comparison of in situ probe-measured values with K
IC of soils and gelatin shows that sediments have a K
IC range intermediate between denser compacted soils and softer, elastic gelatin. 相似文献
20.
海洋井架结构非线性分析 总被引：2，自引：0，他引：2
根据海洋钻井井架实际结构特点,建立弹性基础上的三维有限元模型.按9种工况对某井架的有限元模型进行加载,并且在传统线弹性理论基础上加以改进,考虑非线性P-△效应的影响.应用有限元分析软件StruCAD进行分析计算,给出可靠的计算结果;并且系统分析结构的受力特点和影响因素,得出对于井架这类高耸结构应该考虑P-△效应的影响. 相似文献