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1.
辽河三角洲潮道沉积物为软弱淤泥质土，管桩在波流荷载作用下的弹性变形或振动，可以导致潮道软土强度衰减并发生变形位移，随着悬臂段加长和波流荷载振动作用，下部扮土会自上而下发生液化。简单管桩的抗倾验算可以按照波流力与被动土压力的作用力矩分析，并考虑到海底的冲刷淘空深度。管桩打入下卧高强度粉土时，在保证打入深度的同时，应适当增大管桩的强度，加大管桩自振周期与波浪周期的差值。 相似文献
2.
ABSTRACTWhen dredged soil containing coarse soil is used for the construction of reclaimed ground that is in contact with the surface of seawater, there is a high possibility of the generation of nonuniformly reclaimed ground due to the segregation of fine-grained soil from coarse-grained soil. It is difficult to assume uniform properties of reclaimed ground because the properties are defined and formed by the spontaneously segregating sedimentation. Estimation of the soil’s volume change lacks accuracy if the properties of the reclaimed ground are assumed to be always uniform. Therefore, for pump-dredged reclamation, a predictive study and various experiments are required to estimate the physics and properties of the dredged soil sedimentation. Accordingly, this study demonstrates a modeling test to understand the characteristics of the sedimentary ground using the changing ratio of fraction of the sample passing through a 75-µm sieve. The effect of particle arrangement on hindered settling properties, sedimentation properties, the distribution of water content of sedimentary ground, and physical properties can be determined by the modeling test. The study also suggests the calculation method for the travel distance of the outlet and the volume of input soil based on the experimental results. 相似文献
3.
Calibration chamber tests were conducted on open‐ended model piles driven into dried siliceous sands with different soil conditions in order to clarify the effect of soil conditions on load transfer mechanism in the soil plug. The model pile used in the test series was devised so that the bearing capacity of an open‐ended pile could be measured as three components: outside shaft resistance, plug resistance, and tip resistance. Under the assumption that the unit shaft resistance due to pile‐soil plug interaction varies linearly near the pile tip, the plug resistance was estimated. The plug capacity, which was defined as the plug resistance at ultimate condition, is mainly dependent on the ambient lateral pressure and relative density. The length of wedged plug that transfers the load decreases with the decrease of relative density, but it is independent of the ambient pressure and penetration depth. Under several assumptions, the value of earth pressure coefficient in the soil plug can be calculated. It gradually reduces with increase in the longitudinal distance from the pile tip. At the bottom of the soil plug, it tends to decrease with increase in the penetration depth and relative density, and to increase with the increase of ambient pressure. This may be attributed to (1) the decrease of friction angle as a result of increase in the effective vertical stress, (2) the difference in the dilation degree of the soil plug during driving with ambient pressures, and (3) the difference in compaction degree of soil plug during driving with relative densities. Based on the test results, an empirical equation was suggested to compute the earth pressure coefficient to be used in the calculation of plug capacity using one‐dimensional analysis, and it produces proper plug capacities for all soil conditions. 相似文献
4.
The pile-driving method produces considerable noise and vibrations. Hence, an auger-drilled pile method was developed as a low-noise and -vibration substitute. However, this method does not guarantee the bearing capacity of the pile unless some amount of pile-driving is performed. Therefore, the noise and vibration problems cannot be completely solved. In this study, a prebored screw pile method is proposed to solve these problems. In this method, piles are constructed by the rotary penetration of a screw pile into a prebored hole filled with some cement milk and whose diameter is smaller than that of the screw pile. To determine the shape of the screw pile, laboratory tests with model screw piles were conducted. Also, field load tests were conducted on an actual screw pile fabricated based on the laboratory test result and on a smooth-surfaced pile. In addition, the behavior of the screw pile was estimated by using three-dimensional finite element analysis. The results of the field load test and the numerical simulation showed that the ultimate bearing capacity and the unit skin friction of the screw pile are very superior to those of the smooth-surfaced pile and the cement milk is an important factor in the prebored screw pile method. 相似文献
5.
Mohammed Y. Fattah Bushra S. Zbar Faris S. Mustafa 《Marine Georesources & Geotechnology》2017,35(8):1111-1120
In this study, the dynamic response of pile foundation in dry sandy soil excited by two opposite rotary machines was considered experimentally. A small scale physical model was manufactured to accomplish the experimental work in the laboratory. The physical model consists of two small motors supplied with eccentric mass (0.012?kg) and eccentric distance (20?mm) representing the two opposite rotary machines, an aluminum shaft as the pile, and a steel plate a pile cap. The experimental work was achieved taking the following parameters into considerations: pile embedment depth ratio (L/d, where L is the pile length and d is its diameter) and operating frequency of the rotary machines. All tests were conducted in medium dense fine sandy soil with 60% relative density. Twelve tests were performed to measure the change in load transferred through the pile’s tip to the underlying soil. To predict precisely the dynamic load that will be induced from the rotary machines, a mini load cell with a capacity of 100?kg was mounted between the aluminum plate (the machine base) and the steel plate (pile cap). The results revealed that, before machine operation, the pile tip load was approximately equal to the static load (machine and pile cap), whereas during machines’ operation, the pile tip load decreased for all embedment depth ratios and operating frequencies. This reduction was due to the action of skin friction that was mobilized along the pile during operation, and as a result the factor of safety against pile bearing failure increases. For all operating frequencies and pile lengths, the factor of safety against bearing failure increased during machines’ operation, where the pile tip load became less than its value before starting operation. During operation, the skin friction resistance mobilized along pile length led to decrease the bearing load. 相似文献
6.
AbstractThe 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
7.
海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。 相似文献
8.
AbstractIn this article, the drivability of stepped and tapered offshore piles with the same length and volume has been investigated under hammer blows. To justify the obtained results from field testing and numerical methods, this pile driving procedure has been analyzed and discussed with wave propagation mechanism. It will be shown that tapered pile can be confidently idealized as a number of prismatic segments connected rigidly to each other. This is an interesting finding that fully tapered or stepped piles have a better performance in pile driving and enable users to apply simple one dimensional numerical analysis for simulating pile drivability. 相似文献
9.
针对渤海湾某风电场的海上固定式风机支撑结构,采用适用于大直径单桩结构的PSI曲线模拟桩土相互作用,并采用SACS软件建立支撑结构的动力分析模型。首先对支撑结构进行模态分析;其次考虑海冰结构的随机振动作用模式,根据适用于渤海湾的随机冰力谱构造随机冰载荷时程曲线,基于半耦合的时域方法,采用SACS软件对支撑结构进行冰激振动分析,输出塔筒顶部加速度、单桩基底剪力及倾覆力矩等响应参数的时程曲线和响应功率谱;最后针对冰厚、冰速和海冰强度等海冰参数对支撑结构的冰激振动进行敏感性分析。研究结果表明,在随机振动模式下,冰载荷及结构动力响应对冰厚和海冰强度较为敏感,在进行冰激振动分析时应合理确定冰厚和海冰强度等参数。 相似文献
10.
The problems of ice-induced vibration have been noticed and concerned since the 1960s, but it has not been well resolved. One reason is that the dynamic interaction between ice and structure is so complicated that practical ice force model has not been developed. The recent full-scale tests conducted on jacket platforms in the Bohai Sea presented that ice could cause intense vibrations which endanger the facilities on the deck and make discomfort for the crew. In this paper, the strategy of mitigation of ice-induced offshore structure vibration is discussed. Based on field observations and understanding of the interaction between ice and structure, the absorption mitigation method to suppress ice-induced vibration is presented. The numerical simulations were conducted for a simplified model of platform attached with a Tuned Mass Danlper （TMD） under ice force function and ice force time history. The simulation results show that TMD can fa- vorably reduce ice-induced vibrations, therefore, it can be considered to be an alternative approach to utilize. Finally, the application possibilities of utilizing TMDs on other miniature offshore structures in ice-covered areas of marginal oil fields are discussed. 相似文献
11.
Samuel G. Paikowsky Robert V. Whitman Mohsen M. Baligh 《Marine Georesources & Geotechnology》2013,31(3):213-230
Abstract Open‐pipe piles are widely used for offshore structures. During the initial stage of installation, soil enters the pile at a rate equal to the pile penetration. As penetration continues, the inner soil cylinder may develop sufficient frictional resistance to prevent further soil intrusion, causing the pile to become plugged. The open‐ended pile then assumes the penetration characteristics of a closed‐ended pile. The mode of pile penetration significantly alters the soil‐pile interaction during and after installation. This affects the ultimate static bearing capacity (mainly in granular materials), the time‐dependent pile capacity (in clays), and the dynamic behavior and analysis of the piles. Following a summary demonstrating the effects of pile plugging, a review of the common view of offshore pile plugging is undertaken. The interpretation of plugging by referring to the average plug length has led to the erroneous conclusion that in most piles significant plugging action does not occur. Establishment of an analogy between soil samplers and open‐ended piles enabled correct identification of plugging by referring to the incremental changes in plug length. Examination of case histories of plugging of offshore piles revealed that beyond a certain penetration depth‐to‐diameter ratio, most piles are plugged. 相似文献
12.
Most offshore and coastal structures are supported by pile foundations, which are subjected to large lateral loads due to wind, wave, and water currents. Water currents can induce scouring around piles that reduces lateral capacity and increases lateral deflection of a pile. Current design methods mostly consider the complete removal of soil layers around piles by scouring. In reality, however, scouring creates scour holes at different shapes, sizes, and depths. Their effects on the behavior of laterally loaded piles are not well investigated. A numerical model of a single pile in soft marine clay was first calibrated against field test data without scour. Then several key factors of scour were analyzed, such as the depth, width, and slope of the scour hole and the diameter and head fixity of the pile. The relationships of the ultimate lateral capacity of the single pile with the depth, width, and slope angle of the scour hole were obtained. The numerical results show that the scour depth had more significant influence on the pile lateral capacity than the scour width. In addition, the pile with a free head was more sensitive to scour than the pile with a fixed head. 相似文献
13.
Two types of analytical solutions for waves propagating over an asymmetric trench are derived. One is a long-wave solution and the other is a mild-slope solution, which is applicable to deeper water. The water depth inside the trench varies in proportion to a power of the distance from the center of the trench (which is the deepest water depth point and the origin of x-coordinate in this study). The mild-slope equation is transformed into a second-order ordinary differential equation with variable coefficients based on the longwave assumption [Hunt's, 1979. Direct solution of wave dispersion equation. Journal of Waterway, Port, Coast. and Ocean Engineering 105, 457–459] as approximate solution for wave dispersion. The analytical solutions are then obtained by using the power series technique. The analytical solutions are compared with the numerical solution of the hyperbolic mild-slope equations. After obtaining the analytical solutions under various conditions, the results are analyzed. 相似文献
14.
AbstractIn onshore and offshore fields of ocean engineering, piles are used as foundation systems for various structures. Piles are classified into different types depending on their materials, geometries, and particularly, installation methods, which have advantages or limitations. Companies and engineers have developed a new group of piles, because of necessity to improve their performance in terms of increasing the bearing capacity, reducing impacts of traditional installation procedures, implementing by low- torque power equipment, and utilizing them in widely different ground conditions, including in a marine environment. In the present study, three different models of a new pile with an expander body are introduced to increase the shaft and pile-toe diameters and its self-expansion in the embedment depth under the titles of the Bubble pile (BP), Self-Expanded pile (SEP) and Wing pile (WP). The main subject of this research is to achieve increased bearing capacity, reduced installation effects, and decreased required installation torque. The frustum-confining vessel of Amirkabir University of Technology (FCV-AUT) was employed for this purpose. Up to 14 axial compressive and tensile load tests were carried out on different model piles on sand collected from Anzali shore located on the northern coast of Caspian Sea in Iran, with relative densities of 45% to 50% within FCV-AUT. Comparing the performance of introduced pile with traditional pile corresponding to the same characteristics, the results indicated a significant increase in the axial bearing capacity and reduced disturbance effect of the pile. Also, a lower installation torque of the SE pile was required compared to the helical pile. The test results also demonstrated that the new pile could resist considerable compressive and uplift loads, and could be a possible alternative to traditional piles in the onshore sector. 相似文献
15.
水射流破坏桩内土塞辅助动力沉桩是一种有效处理土塞问题使桩达到标准贯入深度的辅助沉桩方法,而该项技术的关键是水射流对桩内土塞的破坏。借助理论分析、数值模拟和模型实验进行水射流破坏桩内土塞辅助动力沉桩研究。首先进行射流破坏土塞理论分析,定性地说明水射流破坏土塞能力与水射流压力、流量等参数有关;然后对不同形状喷嘴形成的射流的破坏土塞能力进行数值模拟,得到六种喷嘴射流作用下土塞内的最大、最小应力;再通过模型实验对有无射流辅助沉桩的沉桩锤击数进行对比,结果表明水射流辅助沉桩的锤击数少于无射流辅助沉桩的锤击数,说明水射流可用于辅助动力沉桩。最后设计出水射流破坏桩内土塞辅助动力沉桩工艺步骤。 相似文献
16.
Linbo Wu Jianxiu Wang Jie Zhou Tianliang Yang Xuexin Yan Yu Zhao 《Marine Georesources & Geotechnology》2020,38(8):947-969
AbstractShanghai has the largest newly reclaimed area in China’s coastal regions, and dredger fills are universally distributed in reclaimed lands there. Multi-scale geotechnical properties of dredger fills in region-scale (>1?km2), site-scale (1?m2–1?km2), mesoscale (1?cm2–1 m2), and microscale (1?µm2–1?cm2) were studied mainly through cone penetration investigation, borehole investigation, and microscopic inspections. Dredger impact craters, soil structures, and soil textures were investigated qualitatively and quantitatively to identify the dredger fills. Ultimate land subsidence since 1 July 2018 and land subsidence velocity characterized by the land subsidence from 1 July 2018 to 1 January 2019 were evaluated in Shanghai’s typical reclaimed regions. Afterwards, Bayesian network including sixteen variables was proposed for land subsidence risk assessment. Surface subsidence, land subsidence velocity, and comprehensive land subsidence were the most sensitive to data point location and average initial void ratio of underlying strata. These three risk variables were also highly correlated to the thickness of the dredger fill layer and the reclamation time. This finding indicates that variances of the four independent variables (i.e., data point location, average initial void of underlying strata, land reclamation time, and thickness of dredger fill layer) significantly decide variances of the three risk levels. 相似文献
17.
为确保海底爆破施工所诱发的振动不对中华白海豚造成危害,基于量纲分析法对萨道夫斯基经验公式进行修正,建立适用于预测海底爆破质点峰值振动速度的相似准数方程。在此基础上根据现场试验数据进行非线性回归运算,得到相关参数并分析了海底爆破振动强度衰减规律。分析表明:海底爆破质点峰值振速主要由单段装药量、监测点距爆心水平距离、覆盖层厚度及海水深度等因素决定。将参数值分别代入萨氏公式及新建公式计算预测值并进行误差估计,其平均误差分别为20.3%和10.0%,新建公式提高了对质点振速预测的准确性。利用新建公式及超压内安全振速估算保护中华白海豚的安全距离并提出相应的保护措施,为同类工程施工提供理论参考依据。 相似文献
18.
InSAR detection of residual settlement of an ocean reclamation engineering project: a case study of Hong Kong International Airport 总被引：2，自引：1，他引：1
Qing Zhao Hui Lin Wei Gao Howard A. Zebker Albert Chen Kin Yeung 《Journal of Oceanography》2011,67(4):415-426
Man-made land or islands that are reclaimed from the sea are suitable for building airports, harbors, and industry parks for
material transportation because of their broad air and land spaces. However, the reclaimed foundation settlement process is
of public concern, including the continuous impact of ocean processes on its stability. The majority of the buildings and
facilities of Hong Kong International Airport (HKIA) are built on a reclaimed foundation. The reclaimed foundation has been
in residual settlement since completion of the filling project in 1994. In this study, we use persistent scatterer interferometry
(PSI) and ENVISAT (European Satellite) advanced synthetic aperture radar (ASAR) data to detect the residual settlement rates
from 19 April 2006 to 9 January 2008. We use ground truth data to develop empirical correction models for correcting systematic
biases in the ASAR PSI-detected settlement rates. The corrected data follow the Lorentz distribution well, implying that the
residual settlement process is dominated by two modes or categories of settlement rates. The first category represents a relatively
stable state and the second category represents a continuous settlement state. A ground settlement rate map of HKIA shows
that an area of the Passenger Terminal Building and an area of the Southern Runway are two relatively stable areas. There
are two major continuous settlement areas. One covers the airport Midfield. Another is along the coastline, implying that
attention should be paid to impacts of ocean processes on the stability of airport foundations. 相似文献
19.
AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
20.
Based on similarity analyses, a series of experiments have been conducted with a newly established hydro-elastic facility to investigate the transverse vortex-induced vibrations (VIVs) of a submarine pipeline near an erodible sandy seabed under the influence of ocean currents. Typical characteristics of coupling processes between pipe vibration and soil scour in the currents have been summarized for Case I: pipe is laid above seabed and Case II: pipe is partially embedded in seabed on the basis of the experimental observations. Pipe vibration and the corresponding local scour are usually two coupled physical processes leading to an equilibrium state. The influence of initial gap-to-diameter ratio (e0/D) on the interaction between pipe vibration and local scour has been studied. Experimental results show that the critical values of Vr for the initiation of VIVs of the pipe near an erodible sand bed get bigger with decreasing initial gap-to-diameter ratio within the examined range of e0/D (−0.25<e0/D<0.75). The comparison of the pipe vibrations near an erodible soil with those near a rigid boundary and under wall-free conditions indicates that the vibration amplitudes of the pipe near an erodible sand bed are close to the curve fit under wall-free conditions; nevertheless, for the same stability parameter, the maximum amplitudes for the VIV coupled with local scour increase with the increase of initial gap-to-diameter ratio. 相似文献