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1.
AbstractThis article presents a study of liquefaction resistance behaviour of sand using a cyclic triaxial test. The site investigation was performed, and frozen undisturbed specimens were taken from the Izumio site in Osaka, Japan. According to the evidence in 1995 Kobe Earthquake, the first two sand layers are vulnerable to undergo liquefaction. The effect of deviatoric stress on liquefaction resistance was focused on in this study. The excess pore pressure ratio, hysteresis loop, and effective stress path from the cyclic triaxial tests were reported. A multispring element model was employed to simulate the soil behaviour under cyclic loading. The results showed that applied deviatoric stress could influence the liquefaction resistance of sandy soil samples. The plots of the cyclic stress ratio versus the number of cycles to generate liquefaction known as a liquefaction resistance curve can be then constructed and compared with other sands. 相似文献
2.
探讨了应用离散元分析方法求解地震荷载下沉箱和背后填土大变形问题的可能性,开发了能描述沉箱的平面形状及沉箱与土体摩擦特性的矩形单元。并通过简单实例分析了地震时沉箱码头的变形,再现了沉箱码头地震灾害的发生过程,为沉箱在地震情况下的大变形分析提供了一种新途径。比较了两种沉箱模型对分析结果的影响,提出了相应的方法。 相似文献
3.
The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions,and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands.Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model,and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations.Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site.Finally,the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table,and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent. 相似文献
4.
面对通航区很可能发生的船舶抛锚、落物以及沉船等事故造成的危险,使用新型沉箱防护设施对水下生产系统进行安全防护,但目前撞击载荷下沉箱防护设施的安全评估标准并无明确界定。采用有限元方法对水下生产系统沉箱安全防护设施的撞击损伤进行了深入研究,考虑不同落物形状、下落速度、落物质量、碰撞位置对沉箱防护设施撞击损伤的影响。结果表明,锚、长方体落物对沉箱撞击最严重;撞击速度和落物质量与撞击应力成正比;对于非对称开孔的沉箱顶盖,距离开孔较近区域为应力敏感区,受到撞击时撞击应力较大。 相似文献
5.
Chunxia Huang Zhilong Sui Lei Wang Kaifu Liu 《Marine Georesources & Geotechnology》2016,34(3):244-251
The risk of liquefaction and associated ground deformation may be reduced by using various ground-improvement methods, including the stone column technique. To examine the effects of stone columns, a shaking table experimental study using four models (two containing saturated sand and two containing stone column composite foundations) was conducted to measure the development and dissipation of excess pore water pressure and the acceleration response during a simulated earthquake. The test results demonstrate that the effectiveness of stone columns for mitigation of soil liquefaction during an earthquake depends on the following three aspects: (1) the densification of the surrounding soils; (2) drainage along the stone column; and (3) reduction in the total cyclic shear stress of the soil (because the cyclic shear stress is partially shared by the stone column). The first factor (the densification of the surrounding soils) is the most prominent factor among these three. The drainage and re-distribution of the shear stress can only develop fully for sand ground with a considerably higher density; thus, the effectiveness of the last two factors are only significant for dense sand ground. 相似文献
6.
The objective of this paper is to present the effect of sediment characteristics on the dynamic response of sea walls and breakwaters during earthquakes. A finite-difference method is used to calculate the earthquake-induced hydrodynamic pressures of seawater and the pore water in seabed sediment. The water-filled soil mixture is used to model sediment and back-fill soil. The dynamic response of a rigid coastal structure induced by constant ground acceleration is studied, using variable sediment depths and porosity. The dynamic characteristics of the water–embankment–sediment system are investigated, applying four earthquake-records as exciting forces. The result of a quay-walled caisson demonstrates the significance of the seismic-induced dynamic force and the seismic effects should be considered for the design of coastal structures in seismic zone. The damaged wharves of Taichung Port during Chi-Chi earthquake, 21 September 1999 is also reported in the paper. 相似文献
7.
Model tests were conducted to investigate the behaviour of caisson breakwater resting on sand beds subject to impacts due to wave breaking. The centrifuge modelling technique was employed to simulate the prototype stress levels in the foundation soil as the behaviour of sand is highly stress dependent. A wave actuator was developed to simulate the wave-breaking impact loads on the caisson during centrifuge flight. The test results reveal that the vertical and horizontal movements and tilt of the caisson breakwater increase progressively with the number of breaking-wave impacts. The excess pore pressures developed in the foundation sand under non-reversal loading are generally small and appear insignificant. The results of the parametric studies conducted to examine the effects of impact-load pattern, caisson width, rock berm beneath caisson, wave slamming on top slab of caisson and cyclic preloading on the performance of caisson breakwater are also presented. The practical implications of the experimental findings in the present study are also highlighted in this paper. 相似文献
8.
Hiroyoshi Hirai 《Marine Georesources & Geotechnology》2018,36(7):805-817
An investigation was made to present analytical solutions of cyclic response to suction caisson subjected to inclined cyclic loadings in clay using a three-dimensional displacement approach. A model representing the relationship between vertical load and vertical displacement and that between lateral load and lateral displacement along the skirt of suction caisson subjected to cyclic loadings is proposed for overconsolidated clay. For the effect of vertical load on cyclic load capacity of suction caisson, using the Mindlin solution in the case of a vertical point load, the vertical stress of soil under the base of suction caisson is presented. For the stress state of soil beneath the base of suction caisson subjected to cyclic loading, the Mohr–Coulomb failure line and critical state line are presented and the relationship between total stress, effective mean principal stress, stress difference, and pore-pressure is elucidated. The comparison of results predicted by the present method for a suction caisson subjected to cyclic loadings in clay has shown good agreement with those obtained from field tests. Cyclic behavior of clay up to failure is made clear from the relationship between cyclic tensile load, vertical and lateral displacements, and rotation and that between depth, vertical, and lateral pressures. 相似文献
9.
本文用谱分析方法对方柱群墩结构在不规则波作用下的相互影响进行了计算。研究了在不同入射波向时每个方墩的群墩影响系数随墩距变化的规律并与折算圆墩的结果进行了比较。入射波谱采用Ｂｒｅｔｓｃｈｎｅｉｄｅｒ谱。计算结果表明方柱墩群与折算圆柱墩群的群墩影响系数较为接近且随着墩间距的增加趋近于孤立墩情形。 相似文献
10.
为了同时提升消浪效果和节省海岸空间,对低反射防波堤进行改进,提出了一种空间节省型堰式沉箱结构。通过物理模型试验研究了堰式沉箱在规则波作用下的消能机理,然后采用单因子分析法分析了相对淹没深度、波陡和相对波高对反射系数的影响,并且利用SPSS软件对无因次参数进行非线性回归分析得到了反射系数计算公式。结果表明,内堰消浪室可以形成良好的波能耗散机制,随着有效消浪室个数的增多,消浪效果逐渐增强,使得反射系数的最小值和最大值较非透空直立结构分别降低了60%～90%和10%～30%。基于以上研究成果,给出关于特征水位与内堰的相对位置关系的合理建议,并总结了堰式沉箱结构的优化设计要点,对实际工程应用具有一定的指导意义。 相似文献
11.
This paper presents safety evaluations of jetties found on soft clays at Huanghua Port to protect the channel from deposition due to long shore transport. It is likely to be the most critical for the jetties during construction, as far as excess pore water pressure and its effects on the embankment stability are concerned. A rubble mound jetty and a caisson jetty are considered as design alternatives for comparison. Finite element analysis and limit equilibrium analysis are carried out to evaluate the stability of the jetties during construction. For the rubble mound jetty, effective stresses in the soft clays are calculated associated with consolidation, so as to estimate the shear strength increased thereby. With the effective stresses and shear strength, the critical situation of the rubble mound jetty is revealed by the limit equilibrium analysis. For the caisson jetty, wave action is concerned, which is transformed into distributed forces on the caisson. Both the finite element analysis and the limit equilibrium analysis indicate a potential general shear failure of the caisson jetty and the foundation. 相似文献
12.
Caisson foundations are often used in offshore engineering. However, for an optimum design understanding the failure process of a caisson during its installation and the subsequent external loadings is crucial. This paper focuses on the evolving failure of a caisson foundation in sand by advanced numerical modeling. A combined Lagrangian-smoothed particle hydrodynamics method is adopted to deal with the large deformation analysis. The method with parameters are first calibrated and validated by a simulation of cone penetration test in sand. The results of an experimental campaign of a caisson in the same sand are selected and validated for the numerical model. Then, more representative loading combinations are designated for numerical modeling of failure process and mode. Furthermore, three additional caisson dimensions D/d?=?0.5, 1.5, and 2.0 (changing the ratio of caisson diameter D to skirt length d while keeping the same soil-structure surface contact area) are simulated under six representative combined loading paths. Based on that, the influence of caisson dimension to the failure process and mode is investigated. All results are helpful to estimate all possible sliding surfaces under different monotonic combined loading paths for further limit analysis. 相似文献
13.
Side-scan data from the epicentral area of the 1929 Grand Banks earthquake and cores from the resulting turbidite are used to determine a sediment budget for the event. The 1929 turbidite has a volume of about 185 cubic km, which is mostly sand. Features indicating failure on the continental slope are observed only in muddy sediment. A major source of sand in the heads of the fan valleys of the Laurentian Fan is postulated to balance the sediment budget. This sand accumulated proglacially during the Wisconsinan glaciation and probably failed through liquefaction in the 1929 earthquake. 相似文献
14.
15.
Yasaman Jafariavval 《Marine Georesources & Geotechnology》2020,38(2):214-222
AbstractLiquefaction of loose saturated soil deposits is a hazardous type of ground failure occurring under earthquake excitations. Therefore, an accurate estimation of liquefaction potential is extremely important in geotechnical engineering. In the current study, a new model is proposed which estimates the level of strain energy needed for liquefaction initiation. A compiled database containing cyclic tests gathered from previously published works was used to develop new models to predict liquefaction potential. M5′ algorithm was used to find the best correlation between parameters. It was shown that not only the derived formulas are acceptably accurate but also they feature a very simple structure in comparison with available formulas in the literature. The proposed equations are accurate, physically sound and uncomplicated. Furthermore, safety factors were given for different levels of risk, which can be useful for engineering practice. In addition, the influence of different predictors on the liquefaction potential was evaluated and also the significance of input variables was assessed via sensitivity analysis. Finally, a new model was introduced for preliminary estimation of liquefaction potential. 相似文献
16.
L. I. Gonzalez de Vallejo R. Capote L. Cabrera J. M. Insua J. Acosta 《Marine Geophysical Researches》2003,24(1-2):149-160
A series of clastic dikes and tubular vents were identified in southern Tenerife (Canary Islands). These features are the result of seismic liquefaction of a Holocene sand deposit, as the consequence of a high intensity paleoearthquake. The peak ground acceleration (pga) and magnitude of the paleoearthquake generating these liquefaction features were estimated by back calculation analysis. A representative value of 0.30 ± 0.05 g was obtained for the pga. From this, an earthquake intensity of IX was estimated for the liquefaction site. Magnitude bound methods and energy based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M = 6.8. The zone in which the liquefaction structures are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing Holocene materials. Dating of the uplifted sand formation indicates an age of 10,081 ± 933 years, the liquefaction features ranging from this age to 3490 ± 473 years BP. This paleoearthquake was of much greater magnitude than those known historically. Faults with neotectonic activity are significant features that should be borne in mind when assessing the seismic hazards of the Canary Islands, presently considered as low and mainly of volcanic origin. 相似文献
17.
The wave force on a seawater intake structure consisting of a perforated square caisson of 400 mm×400 mm size encircling a vertical suction pipe of 160-mm diameter is investigated using physical model studies. The porosity of caisson was varied from 1.6 to 16.9%. Regular and random waves of wide range of heights and periods were used. It is found that the force ratio (ratio of the force on perforated caisson to the force on caisson with zero percent porosity) reduces to an extent of up to 60% with increase in porosity of the caisson from 1.6 to 16.9%. The force ratio was found to increase with increase in relative wave height and reduces with increase in relative width. Multiple regression analysis of the measured data points was carried out and predictive equations for wave force ratios are obtained both for regular and random waves. The results of this investigation can be used in the hydrodynamic design of perforated caissons, which are widely used as seawater intake structures. 相似文献
18.
It is assumed that the storm wave takes place once a year during the design period, and N histories of storm waves are generated on the basis of wave spectrum corresponding to the N-year design period. The responses of the breakwater to the N histories of storm waves in the N-year design period are calculated by mass-spring-dashpot mode and taken as a set of samples. The failure probability of caisson breakwaters during the design period of N years is obtained by the statistical analysis of many sets of samples. It is the key issue to improve the efficiency of the common Monte Carlo simulation method in the failure probability estimation of caisson breakwaters in the complete life cycle. In this paper, the kernel method of importance sampling, which can greatly increase the efficiency of failure probability calculation of caisson breakwaters, is proposed to estimate the failure probability of caisson breakwaters in the complete life cycle. The effectiveness of the kernel method is investigated by an example. It is indicated that the calculation efficiency of the kernel method is over 10 times the common Monte Carlo simulation method. 相似文献
19.
多消浪室局部开孔沉箱防波堤反射特性的迭代解析研究 总被引：1，自引：0，他引：1
基于势流理论，对多消浪室局部开孔沉箱防波堤的反射特性进行解析研究。研究中采用开孔墙处的二次压力损失边界条件，可以直接考虑波高对于开孔墙处能量损失的影响。利用匹配特征函数展开法和迭代方法得到当前问题的解析解。收敛性验证表明，迭代计算和级数解均具有良好的收敛性。该解析解的计算结果与分区边界元的数值计算结果一致，并且与已有的试验结果符合良好。通过算例分析，研究开孔沉箱防波堤反射系数的主要影响因素。结果表明：与单消浪室开孔沉箱防波堤相比，多消浪室开孔沉箱防波堤可以在更宽的波浪频率范围内保持低反射；增大开孔墙的开孔率，有利于降低多消浪室开孔沉箱防波堤的反射系数；当开孔墙的开孔率沿着入射波方向依次递减时，多消浪室开孔沉箱防波堤的反射系数较小。本文所建立的解析模型简单可靠，可用于工程初步设计中分析开孔沉箱防波堤的水动力性能。 相似文献
20.
Shuwang Yan Jingjing Zhang Jian Chu Zhiliang Huo 《Marine Georesources & Geotechnology》2017,35(3):435-440
Concrete suction caissons have been successfully used as breakwaters or seawalls in recent years. The relative large wall thickness-to-diameter ratio of a concrete caisson can lead to the formation of a full soil heave plug that may cause difficulties in the installation of concrete caisson in clay. One way to overcome this limitation is to use a tampered tip for the caisson wall. An analytical method is proposed in this article to calculate the minimum suction pressure required to penetrate a caisson and the maximum allowable suction pressure that can be applied to avoid too much soil heave plug during the installation of the suction caisson. Four model tests were conducted in normally consolidated clay to study the installation process of a concrete suction caisson with tampered tip and to verify the proposed analytical method. The height of the soil heave plug in the caisson with a tampered tip is observed to be about half of that in the caisson with a flat tip. 相似文献