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1.
In actual engineering, soft clay foundations are in drained or partial drained conditions, it would be useful to establish reasonable constitutive relationship and provide guidance for engineering projects. A hollow cylinder apparatus is used to investigate the anisotropic deformation behavior of natural soft marine clay influenced by intermediate principal stress coefficient b and principal stress direction α. Tests were conducted by maintaining a fixed principal stress direction α relative to the vertical direction, while keeping the intermediate principal stress coefficient b constant. It was found that the anisotropic deformation behavior of natural soft clay is merely influenced by major principal stress direction α, but significantly influenced by intermediate principal stress coefficient b. 相似文献
2.
Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on saturated soft marine clay in the Yangtze estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotorpic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases (or degradation degree increases) significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared to the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does. Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined. 相似文献
3.
An angle exists between the initial static shear stress and cyclic shear stress when embankment and retaining walls are subjected to cyclic loadings. To investigate the influence of this angle on the dynamic properties of marine soft clay, tests were performed on Wenzhou soft clay. When the angle was varied from 0° to 90°, the shear strain and excess pore pressure decreased as θ increased while increased as θ increased from 120° to 180°. Shear strain developed more rapidly when θ was 120°, 150°, or 180° than that when θ was 0°, 30°, or 60°. These results indicate that the number of cycles to failure at the larger angles was greater than at the smaller angles. When θ was 90°, the strain in the x-axis direction increased as the number of cycles increased. The development of the excess pore pressure associated with specimen failure was different for different cyclic shear stress ratios and shearing angles. The effect of θ on the strain and excess pore pressure increased as the cyclic shear stress ratio increased. 相似文献
4.
To investigate cyclic deformation behavior of natural soft marine clay-involved principal stress rotation, a series of undrained tests were conducted by using GDS hollow cylinder apparatus. The principal stress rotates 5000 cycles while the deviator stress was kept at a constant level. The tests results show that the deformation behavior of the tested samples are significantly dependent on cyclic stress ratio (CSR). Furthermore, different type of generation of axial strains occur under different CSRs. With the same CSR, the type of axial strain is different between that considering and ignoring principal stress rotation. When CSR is larger than CSR = 0.42 under principal stress rotation, the axial strain grows rapidly after a few cycles. Compared with the results conducted by cyclic triaxial results, the effect of principal stress rotation on the axial strain is significant. 相似文献
5.
AbstractUnder seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress. 相似文献
6.
AbstractCement soil mixing piles are an effective treatment method for marine soft clay. To investigate the static and dynamic characteristics of the composite soil with cemented soil core, a series of experiments are carried out by using the cyclic simple shear test. The result shows that, the static shear strain showed strain hardening, cemented soil core can improve static shear strength of composite soil, vertical stress can enlarge reinforcement of cemented soil core. The tendency of strain development of composite soil with different area replacement ratios under cyclic loading is the same as that of pure clay, existing critical cyclic stress ratios corresponding to different area replacement ratios. In addition, improving area replacement ratio can increase cyclic strength. At same time, adding of cemented soil core does not change shape of hysteresis curve compared with it for clay either. Moreover, cemented soil core can also obstruct stiffness softening. Through regression analysis of the experimental data, relationship between cyclic number and soil softening index is proved to be linear. The results can give a reference for the dynamic characters of the marine soft clay foundation with cement soil mixing piles. 相似文献
7.
Cyclic vertical-torsional coupling tests were performed on saturated Nanjing fine sand with a relative density of 50% using a hollow cylinder apparatus. The effect of complex initial stress conditions on undrained dynamic strength of saturated Nanjing fine sand was investigated. It is shown that the initial confining pressure, p0, the initial stress ratio, R0, and the initial angle of maximum principal stress direction, α0, have great effects on the characteristics of the dynamic strength of Nanjing fine sand. The dynamic strength increases with p0 and R0, while it decreases with α0. The effect of initial intermediate principal stress parameter b0 on the dynamic strength is slight. 相似文献
8.
The results of one-dimensional compression tests conducted on undisturbed specimens of Jiangsu soft marine clay is presented. Because of its high in situ void ratios and natural water content, Jiangsu soft marine clay displays high values of both the virgin compression index, Cc, and the secondary compression coefficient, Cα. The laboratory data indicates that the value of the ratio Cα/Cc for Jiangsu soft marine clay is constant. However, neither Cα nor Cc are constant: they both depend upon the natural water content (or void ratio) and thus are also dependent on the deformation (or compression) of Jiangsu soft marine clay. Settlement analyses show that the secondary settlement of Jiangsu soft marine clay is a significant component of the field settlement. The concept of a constant value for Cα/Cc is used to predict the secondary settlement of a surcharged embankment founded upon Jiangsu soft marine clay. The predictions are in agreement with the limited post-construction field measurements of the embankment settlement. 相似文献
9.
AbstractIn the coastal area, nearshore and offshore structures have been or will be built in marine soft clay deposits that have experienced long-term cyclic loads. Therefore, the mechanical behavior of marine clay after long-term cyclic loading needs to be investigated. In this research, a series of monotonic and cyclic triaxial tests were carried out to investigate the postcyclic mechanical behavior of the marine soft clay. The postcyclic water pore pressure, shear strength and secant stiffness are discussed by comparing the results with the standard monotonic test (without cyclic loading). It is very interesting that the postcyclic behavior of marine soft clay specimen is similar to the behavior of overconsolidated specimen, that is, the specimen shows apparent overconsolidation behavior after long-term cyclic loading. Then relationship between the overconsolidation ratio and the apparent overconsolidation ratio is established on the basis of the theory of equivalent overconsolidation. Finally, a validation formula is proposed which can predict the postcyclic undrained shear strength of marine soft clay. 相似文献
10.
AbstractThe electrokinetic treatments on high natural moisture content, large compressibility, and low strength dredged marine soil are regarded as an innovative method, but it has not been widely applied due to the difference between theory predictions and realities. To minimize the difference which is resulted from the electric permeability coefficient variations due to pore water drainage and the degree of saturation drops during the electrokinetic treatment of soils, several one-dimensional indoor experiments were conducted with single kaolin clay and natural soft clay. The test results indicate that the electric permeability values conform to the predicted value of Helmholtz–Smoluchowski (H-S) theory under saturated conditions. The permeability for unsaturated soils can be described with relative electric permeability, that is, ke,rel=a(Sr)b. The ranges of fitting parameters are 0.8–1.2 for a and 3–9 for b. The fitting parameters are dependent on the soil type, electric potential gradient, and pore size distribution and so on. The smaller the soil pore size is the more sensitive the permeability coefficient is to the degree of saturation. 相似文献
11.
The behavior of single piles subjected to negative skin friction in soft soil was conducted by analyzing the results from full-scale long-term field measurements and three-dimensional (3D) numerical analyses. A skin friction coefficient (α and β coefficients) of the instrumented piles is back-calculated at different degrees of consolidation (U) of soft marine clay. Back-calculated β-values ranged from 0.15 to 0.35 for clay, and from 0.30 to 0.55 for sand, respectively. In addition, back-calculated α-values ranged from 0.1 to 0.3 for coated pile, and from 0.2 to 0.8 for uncoated pile when undrained shear strength of the soft clay was about 30–60 kPa, respectively. Moreover, this study describes behavior of a pile based on full-coupled 3D finite element (FE) analysis. The appropriate parametric studies needed for verifying the pile-soil interaction with consolidation are presented in this paper. Compared to the results from the measurements, it is shown that the computed results are capable of predicting the pile-soil behavior under consolidation. The major parameters that influence the pile behavior are discussed for different soil-pile conditions. 相似文献
12.
The use of the piezocone penetration test (CPTU) in a geotechnical site investigation offers direct field measurement on stratigraphy and soil behavior. Compared with some traditional investigation methods, such as drilling, sampling and field inspecting method or laboratory test procedures, CPTU can greatly accelerate the field work and hereby reduce corresponding operation cost. The undrained shear strength is a key parameter in estimation of the stability of natural slopes and deformation of embankments in soft clays. This paper provides the measurements of in situ CPTU, field vane testing and laboratory undrained triaxial testing of Lianyungang marine clay in Jiangsu province of China. Based on the literature review of previous interpretation methods, this paper presents a comparison of field vane testing measurements to CPTU interpretation results. The undrained shear strength values from both the field vane tests and cone penetration resistances are lowest at the mid-depths of the marine clay layers, and the excess pore water pressures are highest at the mid-depths of the marine clay layers, indicating that the marine clay layer is underconsolidated. 相似文献
13.
Sheng-Feng Zou Xin-Yu Xie Zhong-Jin Wang Heng-Yu Wang 《Marine Georesources & Geotechnology》2013,31(6):660-670
AbstractThis paper presents a novel elasto-viscoplastic constitutive formulation based on the isotache concepts and the Nishihara model. Incorporating a novel viscoelastic body to include the delay elastic deformation of marine soft clays under the external load, the proposed model is used to evaluate the theories of consolidation-creep coupling, strain rate dependency and stress relaxation of saturated marine soft clays, and hence, the methodology used to determine the parameters of the model is discussed. Ningbo marine soft clay is selected as an example to interpret the determination of the model parameters on a field scale. A series of conventional oedometer tests are conducted as well. Eventually, we utilize the model to simulate several kinds of rheological tests, including one-dimensional (1-D) long-term compression tests on Ningbo marine soft clays, 1-D constant rate of strain (CRS) tests on Batiscan clays and 1-D stress relaxation tests on Hong Kong marine deposits. These findings indicate good agreement between the computational and experimental results, suggesting the given model can provide reliable forecasts for the rheological characteristics of marine soft clays. 相似文献
14.
Palanidoss Subramaniam Mohanachandra Menon Sreenadh Subhadeep Banerjee 《Marine Georesources & Geotechnology》2016,34(7):603-616
The present article discusses the stress–strain behavior and critical state parameters of the dredged Chennai marine clay stabilized with low cement content (2.5–10%). A series of one-dimensional consolidation tests and consolidated undrained tri-axial tests are performed on the cement stabilized dredged Chennai marine clay to evaluate the critical state parameters (λ, κ, M, Г, N) for varying cement contents and curing days. The results show that the slope of the critical state line M increases with an increase in the cement content. The parameter λ for the treated marine clay increases up to a cement content of 7.5% followed by a reduction. The parameter κ decreases with the addition of cement content. Finally, empirical formulations are proposed to predict the critical state parameters as the functions of the cement's contents and curing days. 相似文献
15.
AbstractOne method straightforwardly describing the creep degradation behavior of soft marine clay is proposed and applied to the embankment modeling. Based on the experimental phenomena, the evolution of creep coefficient of soft structured clay is identified comparing with reconstituted clay, and formulated using the creep coefficient of reconstituted clay and a creep-based structure parameter relating to the inter-particle bonding. The contributions of inter-particle bonding and debonding to creep coefficient are thus considered and the creep degradation behavior is then captured straightforwardly. The creep coefficient is extended to 3D and incorporated into a newly developed elasto-viscoplastic model to describe the creep degradation in a direct way. Based on the correlations, the liquid limit is adopted as the viscosity related input parameter. The model is derived using Newton–Raphson algorithm and implemented into a Finite Element code for coupled consolidation analysis. The general applicability on creep degradation of the model is validated by simulating 1D creep, 1D CRS (constant strain rate) and 3D undrained creep tests. Finally, the enhanced model considering creep degradation is applied and validated by simulating one test embankment and one test fill on marine deposited soft sensitive clays. 相似文献
16.
Shen Ruifu Wang Hongjin Zhou Jinxing Zhou Keji
Former graduate student of Tsinghua University now works in Nanjing Hydraulic Research Institute Nanjing
Professor Tsinghua University Beijing
Senior Engineer Tsinghua University Beijing 《中国海洋工程》1994,(4)
- The cyclic rotation of principal stress direction with a constant amplitude is the characteristics of cyclic stress in seabed deposit induced by travelling waves. Presented in the paper are the results obtained from tests simulating the cyclic stress characteristics, with emphasis laid on the buildup of pore water pressure in soil samples. Regression analysis of test data shows that the pore water pressure can be expressed as the function of the number of cycles of cyclic loading, or as the function of generalized shear strain. Using the results thus obtained, the possibility of failure of seabed deposit under cyclic loading induced by travelling waves can be evaluated. The comparison with the results of conventional cyclic torsional shear tests shows that neglect of the effect of the cyclic rotation of the principal stress direction will result in considerable over-estimation of the stability of seabed deposit. 相似文献
17.
Deep marine tight sandstone oil reservoirs are the subject of considerable research around the world. This type of reservoir is difficult to develop due to its low porosity, low permeability, strong heterogeneity and anisotropy. A marine tight sandstone oil reservoir is present in the Silurian strata in the northern Tazhong area of the Tarim Basin, NW China, at a depth of more than 5000 m. The porosity is between 6% and 8%, and the gas permeability is between 0.1 and 1 × 10−3 μm2. The features of this type of reservoir include the poor effects of conventional fracturing modifications and horizontal wells, which can lead to stable and low levels of production after staged fracturing. Here, we conduct a comprehensive evaluation of the mechanical properties of the rock and the in situ stress of the target tight sandstones by using numerous mechanical and acoustic property tests, conducing crustal stress analysis and using data from thin section observations. The dispersion correction technique is used to transform velocity at the experimental high frequency (1 MHz) to velocity at the logging frequency (20 kHz). The logging interpretation models of the transverse wave offset time, mechanical parameters and in situ stress are calculated, and each model represents a high precision prediction. Simulating the in situ stress field of the Silurian strata using a three-dimensional finite element method demonstrates that the average error between the simulation result and the measured value is less than 6%. The planar distribution of each principal stress is mainly controlled by the burial depth and fault distribution. By conducting in situ stress orientation analysis for the target layer via the analysis of paleomagnetism, borehole enlargement, fast shear wave orientation and stress field simulation, we show that the direction of the maximum horizontal stress is N45E. In this paper, a typical and successful comprehensive evaluation of the stress field of the deep tight sandstone oil reservoir is provided. 相似文献
18.
A stress path with continuous rotation of the principal stress direction and continuous alteration of amplitude of deviatoric stress difference under the interaction of wave and earthquake loading was proposed based on the characteristics of the stress path under wave and earthquake loading, respectively. Using a GDS dynamic hollow cylinder apparatus, a series of cyclic triaxial-torsional coupling shear tests were performed on Nanjing saturated fine sand via the stress path mentioned previously under different relative densities, effective initial confining pressures, plastic fines contents, and loading frequencies to study the development of excess pore water pressure (EPWP) of saturated sand under the interaction of wave and earthquake loading. It was found that the development of EPWP follows the trend of fast-steady-mutative-drastic, which is different from that under the cyclic triaxial test or wave loading. The number of cycles causing initial liquefaction (NL) of saturated sand increases remarkably with relative densities. However, the relationships between NL and effective initial confining pressures, plastic fines content, or loading frequencies are more complex. 相似文献
19.
The influence of cyclic loading on the strength and deformation behavior of cemented marine clay has been studied. This marine clay is of recent Pleistocene origin and deposited in a shallow water marine environment. Open pits were dug in sheeted enclosures and from these pits, undisturbed samples were taken for strength testing. A series of standard triaxial shear tests and stress controlled one-way cyclic load tests were conducted at consolidation stress ranges below and above the preconsolidation pressure. For the stress levels below the preconsolidation pressure, the cyclic loading has brought about the collapse of the cementation bond through an increase in strains, and at higher pressure ranges, the soil behaves like typical soft clay. This experiment studied the rate of development of strain and pore water pressure and shows that rate is a function of number of cycles, applied stress, and stress history. In addition, soil degradation during cyclic loading is studied in terms of Degradation Index. Attempt has been made to predict stain, pore water pressure, and degradation index through an empirical model. 相似文献
20.
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