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1.
ABSTRACT

Geotechnical strata are often treated as horizontally homogeneous for hydromechanical analysis due to the vertical deposition of geological layers; however, such a treatment becomes no longer valid when vertical drilling or construction causes the localized disturbance of subsurface, which would result in radial heterogeneity of geomaterials. This paper presents a poroelastic solution for the saturated multilayered cylinder where multilayer is used to represent radial heterogeneity. After the application of Laplace transform, the governing equations in cylindrical coordinates are derived to obtain the stiffness matrix between stresses, displacements, and pore water pressure. The global matrix is assembled by the boundary conditions and the compatibility of interfaces between adjacent layers. Under time-dependent horizontal compression loads, a parametric study is performed for a cylinder comprised of two layers with distinct properties, and the results show that the load frequency and radial heterogeneity play a significant role in hydromechanical behavior of geomaterials: (1) the time-varying loading can induce a negative pore pressure, and the influence of cyclic loading with a high frequency is limited near the outer surface; (2) the radial heterogeneity due to permeability and compressibility affects the development of pore pressure.  相似文献   

2.
Abstract

The mechanism of local scour under two vibrating pipelines is investigated numerically in this research. A sediment scour model is adopted to estimate the motion of sediment. The general moving objects model, which is dynamically coupled with fluid flow, is set up to simulate the vortex-induced vibration (VIV) of the pipeline. The sediment scour model and pipeline vibration model are verified with the previous experimental results and show good agreement. Then, the coupling effects between the pipeline vibration and the local scour are investigated numerically. The effects of G/D (the ratio of the distance between the two pipelines to the diameter of the pipelines) on the local scour and the VIV of the pipeline are examined. The results indicate that the maximum scour depth under the vibrating pipelines is much larger than the scour depth under the fixed pipelines. Due to the shadowing effect of the upstream pipeline, the maximum scour depth under the upstream pipeline is deeper than that under the downstream pipeline. The pipeline vibration magnitude is closely related to the strength of the vortex that sheds behind the pipeline. The effect of G/D on the shape and strength of the vortices that shed behind the pipelines is significant.  相似文献   

3.
Abstract

In this paper, two analytical models used worldwide to assess salinity variation in alluvial estuaries are applied to the Ashtamudi estuary, a Ramsar site, southwest coast of India; and Bouregreg estuary, in northwest part of Morocco. The estuaries’ bathymetry is described by an exponential function. Both models are quite similar and use a predictive equation for the dispersion in the estuary mouth (D0). The major difference between the two models is the use of the constant value of K?=?0.5 for the Van der Burgh coefficient (K) and the introduction of the correction factor ζ, which is a function of damping (δ) and shape (γ). The performance of these two models was evaluated by comparing their results with field measurements; this revealed that both analytical models apply well to both the estimation of salinity distribution and the prediction of salt intrusion in the Ashtamudi and Bouregreg estuaries (Ashtamudi: RMSE = 0.60–1.22 ppt; Bouregreg: RMSE = 0.92–2.71 ppt). One model agrees more with the field measurements of salinity distribution along the estuaries axis; the second underestimate and overestimate some values of salinity distribution along the estuaries. Possibly, the constant value of K?=?0.5 for the Van der Burgh coefficient (K) has applicability limits for the estuaries under tidal conditions. The specifying of the parameterization may be a field of research.  相似文献   

4.
ABSTRACT

The elastic mechanical response of porous materials under a heat source has many applications in civil engineering and has received considerable attention in the geotechnical literature. In this paper, a Kelvin viscoelastic model is combined with the thermohydromechanical governing equations for marine clay and solved using a numerical inversion of the inverse Laplace transform in the time domain. After validation against existing analytical solutions, numerical parametric studies are conducted to investigate the influence of viscosity on temperature, excess pore pressure, and displacement. It is shown that viscosity has little influence on temperature, a modest influence on displacements, and a quite significant influence on excess pore pressure.  相似文献   

5.
Abstract

In practice, how to quickly improve the bearing capacity of piles in a short time is of great significance. In view of this, a technique of setting grooves and installing PVDs (prefabricated vertical drains) at the surface of the pile is proposed in this investigation to accelerate the consolidation of the surrounding soil. A radial and circular consolidation model is established for permeable piles. The finite cosine transform, finite Weber transform, and discretization method are used to obtain a semi-analytical solution for the consolidation model with a mixed drainage boundary condition at the surface of the pile. The sensitivity of the consolidation process to the strip number and the width of PVDs is discussed. The results show that the technique of installing PVDs in piles could potentially improve the bearing capacity. When the area of drainage channels is fixed, the bearing capacity of permeable piles can be more effectively improved by using a higher strip number of PVDs and a smaller PVD width.  相似文献   

6.
Abstract

Rock drilling is a significant activity widely used in the exploration of marine mineral resources and offshore civil engineering such as marine mining, petroleum and deep-water drilling. The characteristics of size and shape of particles produced during rock drilling influence drilling efficiency and energy consumption. We report a series of drilling experiments on sandstone, limestone and shale to systematically examine particle size distribution and shape and correlate these with original rock structure and composition. Correlations are established via metrics of particle size distribution, average circularity and specific surface area. Impact breakage and contact abrasion of individual particles during rock drilling are the main mechanisms controlling particle size and shape. Impact breakage is controlled by the structural distribution of mineral phases, while contact abrasion is principally related to the hardness of mineral phases. The particle size distribution is affected by the structural distribution of mineral phases. The average circularity of the drilling particles is mainly controlled by the hardness of mineral phases. The specific surface area of rock drilling particles is determined by both structural distribution and hardness of mineral phases – with homogeneous structure and low average hardness of the phases reducing the resulting specific surface area of the drilling products.  相似文献   

7.
Abstract

The deep-water pipeline is the main means of transportation in offshore oil and gas development engineering. The deep-water pipeline may incur lateral global buckling due to the high temperature and pressure that are applied on the pipeline to ensure the contents’ liquidity. With the increasing operating water depth, a higher temperature and pressure are applied to the pipeline, causing large lateral deformation and a large bending moment. Due to the inhomogeneous distribution of the bending moment on the cross-section, different points on the cross-section will deform differently. This kind of deformation causes the cross-section to turn into an oval ring. The cross-section ovalization caused by global buckling was rarely analyzed in former engineering practice since the load is relatively low. With the increase in operation water depth and operation load, the ovality caused by global buckling is noticeable. This article analyzed cross-section ovalization caused by pipeline lateral global buckling with a numerical simulation method. The pipelines with different initial cross-section shapes were simulated, and the influence of several impact factors, including load, pipeline and soil factors on the ovality of the cross-section, were analyzed. The results show that the initial cross-section shape type has little effect on the pipeline ovalization pattern. The initial ovality of the pipeline with an oval ring cross-section shape has little influence on the residual ovality. Among all the factors analyzed in this paper, the pressure difference is the primary factor that should be considered in a pipeline ovalization check.  相似文献   

8.
ABSTRACT

Genypterus blacodes, in terms of its fishing history and local economic importance, is an emblematic species harvested in Chilean Patagonia (41°00’–57°00’S). Most of the current fisheries and biological knowledge of this species come from the open ocean, whereas information about the species in fjords and inner channels is fragmentary. In 2018, two research surveys targeting G. blacodes were conducted in the fjords and inner channels of Chilean Patagonia. A total of 253 pairs of sagittal otoliths were sampled at three different localities, and their contours were modelled using wavelet analysis as a tool for stock discrimination. Contours were compared using canonical analysis, and classification was performed using linear discriminant and Random Forest analyses. The results indicated that the wavelet method is efficient in modelling otolith contours, and the discriminant analyses showed differences among fishing grounds across the latitudinal gradient, thus confirming the hypothesis that G. blacodes conform to at least two separate stock units in Chilean Patagonia. Fishing grounds that were closer in space showed higher levels of misclassification. The discussion focuses on how environmental variables and the geography of fjords shape stock differences and how this information can be used for the sustainable management of G. blacodes.  相似文献   

9.
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10.
Abstract

Quantitative and objective trend analysis of bottom topography in order to detect the tectonic structures has become available by use of the processed Seabeam data. The following two procedures of trend analysis are introduced.

(1) Edge detection procedures in digital image processing are applicable to the analysis of topography for extraction of the lineament of tectonic structures and prediction of the existence of faults based on the digital bathymetric data.

(2) Automatic calculation of water flow using the topographic grid data is used for estimation of not only water flow pattern and volume but also the construction of the ridge or trough axis by calculating the accumulated water volume. This method was also applied to the Seabeam bathymetric data. This is quite useful for detection of offset structures and hidden faults.

These two methods are applied to the topographic data obtained in the North Fiji Basin, which is characterized by active spreading ridges. The regional tectonic structure of the North Fiji Basin was found to be expressed by the topographic trend of the central axis.  相似文献   

11.
Abstract

Geoid heights and vertical deflections derived from satellite radar altimetry contain characteristic signals that may be reproduced and explained by simple models for seamount gravitation acting on the sea surface. Computer algorithms capable of automatic operation and able to detect, approximately locate, and estimate parameters constraining the shape of actual sea‐mounts were written and tested. The computer program which utilized a digital high‐pass filter combined with a roughness sensor was effective in separating the seamount produced geoid undulation/vertical deflection pattern from the remaining data track features, simultaneously detecting and locating along the track such signals. Tests of the algorithm on several SEASAT passes over known bathymetry produced mixed results. Meaningful shape constraints were obtained by matching the geoid anomaly calculated from the seamount model to the actual mean sea level pattern for some seamounts. Results for other seamounts were poor and possible reasons for the failure are discussed. It is concluded that a computerized seamount detection program for radar altimetry data is feasible, but it will have to be more complex than the present one for fully successful operation.  相似文献   

12.
Abstract

Reliability analyses of nail pullout, nail-in-tension, and system reliability of internal limit states are presented for both permanent and temporary soil nails that are designed using default Federal Highway Administration nail load and resistance models within traditional deterministic allowable stress design (ASD) framework. The model uncertainty, correlations between soil strength parameters, between model factor, and nominal load term, and between the two internal limit states, and influence of model factor fittings are all addressed in the analyses. This study provides a general idea of the reliability that is implicitly embedded in current ASD-based soil nail internal limit state designs.  相似文献   

13.
Abstract

This study aims to evaluate the relationship between saturated hydraulic conductivity with particle shape and packing density characteristics of silty sand soils. The article presents a series of hydraulics tests performed on three kinds of sand with different particles shapes (Chlef rounded sand, Fontainebleau sub-rounded sand and Hostun sub-angular sand) mixed with low plastic rounded Chlef silt in the range of 0–30% fines content. The sand–silt mixture samples were tested in the constant-head permeability device at a loose relative density (Dr = 18%) and a constant room temperature (T?=?20?°C). The obtained results indicate that the measured saturated hydraulic conductivity (Ks) correlates very well with the fines content (Fc), packing density in terms of [maximum void ratio “emax,” minimum void ratio “emin,” predicted maximum void ratio “emax”pr and predicted minimum void ratio “emin”pr] and particle shape characteristics ratios in terms of roundness ratio (Rr = Rhs/Rmixture) and sphericity ratio (Sr = Shs/Smixture) of the silty sand materials under consideration. Moreover, the analysis of the available data show a noticeable success in exploring the prediction of the saturated hydraulic conductivity (Ks) based on the particle shape and packing density characteristics (Rr, Sr, emax, and emin) of the studied sand–silt mixture samples.  相似文献   

14.
Abstract

A two‐dimensional, vertically integrated, numerical model has been used to compute the M2 and S2 tidal components for the North Sea. The model has also been applied for simulation of two storm surge situations. The results of the computations are compared with sea level observations from coastal stations, and for one of the simulations a comparison with current measurements is also performed.  相似文献   

15.
M. -C. Huang   《Ocean Engineering》2004,31(7):813-831
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16.
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17.
When a piezocone (CPTU) penetrates the ground, pore pressures are set up due to the stress changes. Pore pressure dissipation occurs in the subsequent consolidation process in a manner dependent on the initial stress distribution. The process of analysis can be used to interpret the consolidation parameters from CPTU data based on strain path approach. For the two approaches to the CPTU analysis, the Houlsby and Teh method used an elastic-plastic model, while the Levadoux and Baligh solution used parameters specifically appropriate for Boston Blue Clay. This article discusses a comparison between the two theoretical predictions and field CPTU measurements deployed in Jiangsu (China) Quaternary clays. The values of the coefficient of consolidation calculated from the two methods are then compared with high-quality laboratory tests. Both theoretical predictions provide good agreement for the shape of the dissipation curve, but the predicted c h values are different and thought should indeed be given to the use of an appropriate value of G/s u.  相似文献   

18.
利用ZooScan图像扫描技术,建立胶州湾浮游动物优势种中华哲水蚤和强壮箭虫体长、面积和体积与干重之间的回归关系.比较了不同季节、不同参数之间的差异.结果表明,不同月份的回归关系之间无显著差异,在三个体型参数中,面积拟合生物量的程度最好,是利用图像方法估算生物量最佳参数.中华哲水蚤和强壮箭虫体型-生物量转换关系可以分别表示为:lgDW=1.611gA+ 1.69,lgDW=1.541gA+l.32.  相似文献   

19.
Abdul Hayir   《Ocean Engineering》2006,33(5-6):654-664
The aim of this study is to present the solutions for the near-field tsunami amplitudes caused by submarine landslumps and slides spreading in two orthogonal directions. A linearized shallow water wave theory is derived. The transform techniques (Fourier and Laplace transform) are used for the solution of Laplace equation. The results show that if the ratio of the velocties is v1/v2=0.1, the numerical results are almost the same as the values obtained for one dimensional movement of the slumps and slides. But, when the ratio of the velocties is v1/v2=1, obtained normalized peak amplitudes, ηmax/ζ0 are smaller than the numerical values for one dimensional solution. It is concluded that normalized peak amplitudes for the models are small because of the interaction of the velocities. Numerical examples are presented for various parameters.  相似文献   

20.
Abstract

This paper presents the results of a laboratory investigation undertaken to study the nature of two submarine carbonate soils from Bombay High off the west coast of India, as well as to study the shear and plasticity behavior of their sand and silt‐clay fractions, respectively. Scanning electron micrographs reveal that the carbonate content in both soils is comprised primarily of nonskeletal particles of various types. X‐ray diffraction and infrared absorption analyses indicate that in one soil the carbonate fraction consists of calcite and aragonite minerals, whereas in the other soil dolomite is also present. The non‐carbonate fraction of both soils is comprised primarily of quartz and feldspar, and also some clay minerals. The nature of the carbonate fraction of the two soils indicates that they were formed by different depositional processes.

During drained triaxial shear the nonskeletal sand grains of both soils exhibit a lower degree of crushing when compared with that of the skeletal carbonate sands, and thus appear to be stronger foundation material.

Although the carbonate contents of the silt‐clay fractions of the two soils are similar, they exhibit markedly different plasticity characteristics . This is probably because of the microlevel cementation produced by carbonate material in one soil.

This study leads one to the conclusion that carbonate content alone should not be treated as a parameter which controls the engineering behavior of submarine soils; the nature and form of carbonate material must also be identified.  相似文献   

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