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1.
This article presents the settlement of drilled shafts resulting from their structural deformations. Although drilled shafts are widely used as foundations for settlement-sensitive structures such as bridges and high-rise buildings, the structural deformations of drilled shafts are not typically taken into account in the design process. However, if unexpected structural deformations of drilled shafts cause additional settlement to the foundation, the serviceability of the superstructure can be jeopardized. Unfortunately, very few research efforts have been made to quantify the structural deformation of drilled shafts; this needs to be addressed to accurately predict the settlement of drilled shafts. In this study, we investigate the effect of structural deformation on displacement of axially loaded drilled shafts. Finite element analyses were performed to quantify the structural deformation of drilled shafts. The analysis results indicated that the structural deformation of drilled shafts could be quite significant for long drilled shafts. The main factors that affected the structural deformation of drilled shafts were found to be pile length, the material properties of drilled shafts, and the relative humidity of surrounding soil. An approximate equation is proposed to estimate the long-term deformation of drilled shafts.  相似文献   

2.
Long drilled shafts with enlarged bases are generally used to transfer heavy loads from superstructures to the underlying soils. Due to the large slenderness ratio, the load transfer mechanism for these long enlarged base-drilled shafts differs from that of a conventional drilled shaft. This paper presents field-instrumented, full-scale load tests on long drilled shafts longer than 58 m, including one straight and two enlarged base-drilled shafts in marine sediment. The field test results show that compared with straight shafts, the use of an enlarged base increases both toe resistance and shaft resistance. The drilled shafts with enlarged bases have higher load-bearing capacity. The shaft resistance and toe resistance were not simultaneously mobilized. The bottom sediment under the shaft toe has a significant influence on toe resistance and shaft resistance. Shafts having bottom sediment with a relatively large thickness exhibited lower shaft and toe resistance. Thus, the bottom sediment thickness should be strictly controlled.  相似文献   

3.
Abstract

In the field of ocean engineering, anchors are used for several purposes. This article studies the behavior of a helical anchor embedded in soft marine clay under vertical repetitive loading. Helical anchors are simple steel shafts to which one or more helical plates are attached at regular intervals. The tests are conducted on a model helical anchor installed in a soft marine clay bed prepared in a test tank. Repetitive loading is applied using a pneumatic loading arrangement. Different cyclic load ratios and time periods are adopted. In each test, after the application of repetitive loading, poststatic‐pullout tests are conducted to observe the effect of repetitive loading on anchor behavior. From the test results, it is found that, up to a cyclic load ratio of 55%, there is no reduction in capacity. Instead, there seems to be a marginal increase in capacity and reduction in displacement. The reasons for this behavior are explained in terms of induced changes in strength and deformation behavior of marine clay under repetitive load. However, at higher cyclic load ratios, there seems to be reduction in pullout capacity of the anchor, and the reason for this is explained in terms of strain criteria. From this investigation, it can be concluded that the deep anchor is more suitable to a marine environment than a shallow anchor.  相似文献   

4.
Abstract

The Zhanjiang Bay Sea-crossing Tunnel is the first phase of an ambitious plan of the Golden Triangle Economic Zone in southwestern China and passes underneath the deepest artificial shipping channel with the highest level in Asia. The tunnel is a world-record extralong and small-diameter corridor constructed using an uninterrupted single-end shield tunneling method in subsea soft ground under ultrahigh hydraulic pressure for water conveyance. This case study first highlights the engineering challenges of constructing the sea-crossing shield tunnel in subsea soft ground under ultrahigh hydraulic pressure. A series of key techniques are then investigated and some innovations are proposed to address the engineering challenges in the following four key aspects of the sea-crossing shield tunneling process: (a) optimal design of segmental linings; (b) adaptive reformation of the shield machine; (c) structural construction of deep vertical shafts; and (d) supporting techniques of long-distance advancing. On the basis of the field monitoring and numerical analyses, it is concluded that the implemented key techniques ensure the successful management and control of the engineering challenges in terms of optimizing the segmental lining, selecting the shield machine and constructing the vertical working shaft during the sea-crossing shield tunneling process with limited geological investigation data available under submarine conditions.  相似文献   

5.
Abstract

Pile foundation is the most popular option for the foundation of offshore wind turbines. The degradation of stiffness and bearing capacity of pile foundation induced by cyclic loading will be harmful for structure safety. In this article, a modified undrained elastic–plastic model considering the cyclic degradation of clay soil is proposed, and a simplified calculation method (SCM) based on shear displacement method is presented to calculate the axial degradated capacity of a single pile foundation for offshore wind turbines resisting cyclic loadings. The conception of plastic zone thickness Rp is introduced to obtain the function between accumulated plastic strain and displacement of soil around pile side. The axial ultimate capacity of single piles under axial cyclic loading calculated by this simplified analysis have a good consistency with the results from the finite element analysis, which verifies the accuracy and reliability of this method. As an instance, the behavior of pile foundation of an offshore wind farm under cyclic load is studied using the proposed numerical method and SCM. This simplified method may provide valuable reference for engineering design.  相似文献   

6.
The bottom friction beneath random waves is predicted taking into account the effect of seepage flow. This is achieved by using wave friction factors for rough turbulent, smooth turbulent and laminar flow valid for regular waves together with a modified Shields parameter which includes the effect of seepage flow. Examples using data typical to field conditions are included to illustrate the approach. The analytical results can be used to make assessment of seepage effects on the bottom friction based on available wave statistics. Generally, it is recommended that a stochastic approach should be used rather than using the rms values in an otherwise deterministic approach.  相似文献   

7.
Abstract

In this article, the results of an experimental study on the effect of drilling fluid on concrete-soil/rock interface shear strength in the seawater drilling environment are presented. The series of direct shear tests using a purpose-designed shear box with seawater were performed considering different types of drilling fluid and base material, various normal stress levels at the interface, and filtration times. The results indicated that bentonite drilling fluid significantly decreased the concrete-soil/rock interface shear strength while a negligibly small effect was observed for polymer drilling fluid, confirming the findings from the previous studies. It was also observed that the degree of interface shear strength reduction when using bentonite drilling fluid varied with the type of base material as well as the level of normal stress at the interface. The results also confirmed that the groundwater chemistry does not alter governing mechanism of the drilling fluids and the concrete-soil/rock interface interaction and that significant benefit can also be expected when using polymer-based drilling fluid over bentonite in terms of the side resistance of a drilled shaft in seawater drilling environment as well.  相似文献   

8.
Abstract

The instability of the seabed constitutes an important consideration in the planning and design of various offshore facilities. The stresses and the pore water pressure in the sediments, induced by the action of waves during a storm, may cause them to fail, leading to seabed instability. In this article the possible mechanism of such failures are discussed and the conditions necessary for them are formulated through simplified analyses. These provide the combinations of wave, site, and sediment parameters likely to cause instability, which may be used to identify potentially unstable sediments in a given offshore region during a storm. The numerical results are presented in convenient graphical form. Some illustrative field studies are also presented.  相似文献   

9.
Abstract

Ocean waves traveling over soft bottoms attenuate as a result of energy being absorbed by the soft bottom. This wave attenuation is important in the design of offshore facilities. The magnitude of wave attenuation can be predicted with an analytical model that couples wave and seabottom motions and realistically models the nonlinear stress‐strain behavior of soft sediments. An extensive parameter study was performed to develop wave attenuation behavior. Soil and wave characteristics typical of the Mississippi Delta were used for these analysis. Predicted results are compared with field observations, and good agreement is found.  相似文献   

10.
Abstract

This paper describes the results of laboratory tests carried out on model pile shafts in a variety of reconstituted calcareous sands and on silica sand. The factors influencing both the skin friction under static loading and the degradation of skin friction under cyclic loading have been investigated. The grading and crushability of the particles appears to have a significant influence on both, with less favourable performance being found for uniformly graded crushable particles. Relative density and overconsolidation ratio also have some influence.

Under cyclic loading, the amplitude of cyclic displacement and, more specifically, the cyclic slip displacement, influence the extent of cyclic degradation of skin friction.  相似文献   

11.
Abstract

Prediction of salt intrusion length in estuaries is a challenge for managers as well as scientists in this field. Several numerical and empirical models have been developed for the prediction of salt intrusion length in recent decades. However, all these models require large data set on estuary geometry, tide, stratification turbulence which demands experimental cost and time, and which is not always available as in our case. Thus, for reducing the complexity of analysis, a new simple equation was derived to predict the salinity intrusion length using nonlinear multivariable regression in the Bouregreg estuary, Morocco. The equation relates salt intrusion length with freshwater discharge and tidal range using a power law. The salt intrusion length predicted by the developed equation was in good agreement (R2 = 0.72) with that obtained using a numerical salinity transport model (HEC-RAS software “Hydrologic Engineering Center River Analysis System”). This simple formula is completely transparent and practical for Bouregreg estuary, allowing direct assessment of the parameters on the salt intrusion. Therefore, the proposed model can either be used to predict the salt intrusion for a given freshwater discharge and tidal range, or can used as a tool to design the minimum daily discharge to regulate the salt intrusion into the estuary, thereby providing assistance for management plans.  相似文献   

12.
Abstract

The wave‐induced cyclic shear stresses in ocean‐floor sands may cause a progressive buildup of pore water pressure, leading to instability of the bed. This instability may constitute an important consideration in the analysis and design of various offshore engineering facilities. This paper presents a general procedure for the analysis of pore water pressure in the ocean‐floor sands under the action of random waves. Using a simple linear model for the generation of pore water pressure and incorporating the effect of its simultaneous dissipation, a formulation for the expected damage associated with buildup of pore pressure is developed in a stochastic framework. Numerical results of an example analysis are also presented.  相似文献   

13.
Abstract

Based on a new elasto-plastic constitutive model, this paper presents a soil–water coupled numerical prediction of the bearing capacity for shallow foundation constructed on Ballina soft clay for unconsolidated undrained (UU) and consolidated undrained (CU) conditions. This elasto-plastic constitutive Shanghai model has an advantage of describing the mechanical behaviour of over-consolidated and structured soil under different loading and drainage conditions, by using one set of material parameter. In this paper, the Shanghai model used for both UU and CU conditions has the same initial parameters obtained from laboratory test results. The loading conditions and consolidation stages vary based on construction details. The predicted bearing pressure-settlement responses for UU and CU, approves the field observation. The phenomenon of gaining the bearing capacity due to consolidation is captured and explained by the use of soil–water coupled numerical analysis with a new elasto-plastic model. The stress strain behaviour, stress paths and the decay of the structure of elements at different depths presented in this study, reveal the mechanism for the difference between UU and CU conditions to understand the foundation behaviour. Effect of the initial degree of soil structure on the bearing capacity is also addressed. Overall, this approach provides the integrated solution for the shallow foundation design problems under short and long-term loadings.  相似文献   

14.
Abstract

Submarine trenching for pipeline installation in potentially unstable sediments has recently been of increasing concern. Although typical pipeline depths are less than 3 or 4 m, trenching operations generally cause local stress concentrations within the sediments and induce excess pore pressures. The result of these stress concentrations and pore pressure increases may be spreading of submarine slumps that can endanger pipelines or other nearby installations. A simplified analytical approach is described to estimate the extent of slump spreading caused by trenching. It is shown that the spreading potential is affected by many geotechnical characteristics of the sediments in addition to geomorphic processes and the oceanographic regimes governing the area. The primary geotechnical factors that influence spreading include the porepressure parameter Af , the degree of consolidation, the coefficient of earth pressure at rest, and the strength characteristics of the soil. Dimensionless parameters are developed to illustrate graphically the functional relationships among these parameters. A Gulf of Mexico soil profile is used to quantify the spreading phenomenon.  相似文献   

15.
The very purpose of attaching fins to the hull is to reduce the roll motions of a ship. Roll minimization is a requisite for various operations in the seas. The presence of fin system provides enhanced state of stabilization especially when the vessel is performing a fast maneuvering amidst rough environmental disturbance. The fins in turn are activated by electro-hydraulic mechanism based on the in-built intelligence as per control theory like proportional–integral–derivative (PID) or fuzzy logic. As per this paper, fin system is activated using PID control algorithm. A frigate-type warship is considered for the demonstration purpose. Nonlinear roll motions are controlled using active fins. Lift characteristics of the fins in hydrodynamic flow were studied using CFD package fluent.Good amount of reduction in roll amplitude is achieved from various simulations in random sea. The approach can be used for any irregular sea conditions.  相似文献   

16.
The accurate prediction of extreme excursion and mooring force of floating offshore structures due to multi-variete environmental conditions which requires the joint probability analysis of environmental conditions for the worst case situation is still impractical as the processing of large amount of met-ocean data is required. On the other hand, the simplified multiple design criteria (e.g. the N-year wave with associated winds and currents) recommended by API known as traditional method does lead neither to the N-year platform response nor to the N-year mooring force. Therefore, in order to reduce the level of conservatism as well as uncertainties involved in the traditional method the response-based method can be used as a reliable alternative approach. In this paper this method is described. In order to perform the calculations faster using large databases of sea states, Artificial Neural Networks (ANN) is designed and employed. In the paper the response-based method is applied to a 200,000 tdw FPSO and the results are discussed.  相似文献   

17.
ABSTRACT

Water is an important component of many recreational opportunities and New Zealand invests significant resources in recreational water quality (RWQ) monitoring to assess risks to public health. However, monitoring primarily focuses on microbiological hazards and RWQ is considerably broader than this. The goal of this study was to take a comprehensive approach to evaluating RWQ while exploring the potential for greater public involvement in monitoring. A popular river swimming site was co-monitored weekly by volunteers and a council field officer. The attributes monitored–water temperature, visual clarity, benthic cyanobacteria and filamentous periphyton cover, E. coli and rubbish–were identified from a volunteer workshop. There was good concordance between volunteer and council data suggesting that volunteer measurements can be considered reliable. This highlights the potential for volunteers, with professional support, including training and quality assurance, to extend council RWQ surveillance to additional monitoring sites while improving public engagement on water management.  相似文献   

18.
Abstract

A set of time‐averaged sea surface heights at 1° intervals, derived from the adjusted SEASAT altimeter data, and the GEML2 gravity field are used to estimate the long‐wavelength stationary sea surface topography. In order to reduce the leakage of energy in the estimated sea surface topography, the GEML2 field is augmented by the Rapp81 gravity field to generate geoidal undulations with wavelengths consistent with the ones of sea surface heights. These undulations are subtracted from the sea surface heights, and the resulting differences are subjected to filtering in order to recover sea surface topography with minimum wavelengths of 6000 km and an estimated accuracy of 20–25 cm. These estimates agree well with oceanographic and other satellite‐derived results.

The direction of current flow can be computed on a global basis using the spherical harmonic expansion of sea surface topography. This is done not only for the SEASAT/GEML2 estimates, but also using the recent dynamic topography estimates of Levitus. The results of the two solutions are very similar and agree well with the major circulation features of the oceans.  相似文献   

19.
It is well known that the design of submarine pipelines relies on accurate test results for the local buckling collapse of pipes subjected to bending loading. The present paper analyses apparently anomalous values of axial tensile and compressive strains from recent test results in comparison to the values that would be expected on the basis of simple bending theory. This could have important consequences for the efficacy of the design factors derived using these results. The cause of the differences between the strain values obtained in the tests and those expected on the basis of simple bending theory are explained using finite element modelling. The differences result from the type of collars and supports commonly used in bending tests, the effects of which persist for a greater length along the test pipe than has hitherto been assumed. In general, it is pointed out that the application of the simplified engineering theory of bending can be erroneous when ovalisation is imposed or, on the contrary, the boundary conditions of the section are restrained from ovalising deformations. The influence of the D/t ratio is also analysed.The results contribute to the understanding of a crucial limit state for the design of onshore and offshore pipelines.  相似文献   

20.
This paper investigates the properties of thickness extension mode excited by lateral electric field on LiNbO3 by using the extended Christoffel--Bechmann method. It finds that the lateral field excitation coupling factor for a-mode (quasi-extensional mode) reaches its maximum value of 28% on X-cut LiNbO3. The characteristics of a lateral field excitation device made of X-cut LiNbO3 have been investigated and the lateral field excitation device is used for the design of a high frequency ultrasonic transducer. The time and frequency domain pulse/echo response of the LiNbO3 lateral field excitation ultrasonic transducer is analysed with the modified Krimholtz--Leedom--Matthae model and tested using traditional pulse/echo method. A LiNbO3 lateral field excitation ultrasonic transducer with the centre frequency of 33.44 MHz and the --6 dB bandwidth of 33.8% is acquired, which is in good agreement with the results of the Krimholtz--Leedom--Matthae model. Further analysis suggests that the LiNbO3 lateral field excitation device has great potential in the design of broadband high frequency ultrasonic transducers.  相似文献   

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