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1.
AbstractLiquefaction is a phenomenon developed in loose and saturated layers of sands subjected to dynamic or seismic loading, and often leads to excessive settlement and subsequent failures in structures. Several methods have been proposed to improve soil resistance against liquefaction, among which use of stone columns is one of the most applicable methods. In this research, the effect of stone columns with different geometries and arrangements on the liquefaction behaviour of loose and very loose saturated sands subjected to vibration is investigated using shaking table. Results of the experiments show that when using stone columns in sand layers, the level of maximum settlement is significantly reduced. Further, the presence of stone columns significantly reduces pore water pressure ratio. This further indicates that stone columns have a positive effect and reasonable performance, even in relatively strong earthquakes, provided that the number and cross-section of the columns are sufficient. In addition, stone columns reduce the pore water pressure dissipation time. Moreover, by increasing cross-sectional area and the number of columns, both pore water pressure and settlement decrease. Stone columns in loose sand have a greater effect on the reduction of pore water pressure compared to that of very loose sand. 相似文献
2.
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
3.
The characteristics of dynamic stress in the seabed under wave loading are constant principal stress and continuous rotation of the principal stress direction.Cyclic triaxial-torsional coupling shear tests were performed on saturated silt by the hollow cylinder apparatus under different relative densities,deviator stress ratios and vibration frequencies to study the development of pore water pressure of the saturated silt under wave loading.It was found that the development of pore water pressure follows the trend of "fast～steady～drastic".The turning point from fast to steady stage is not affected by relative density and deviator stress ratio.However,the turning point from steady to drastic stage relies on relative density and deviator stress ratio.The vibration cycle for the liquefaction of saturated silt decreases with increasing deviator stress ratio and increases with relative density.The vibration cycle for the liquefaction of the saturated silt increases with vibration frequency and reaches a peak value,after which it decreases with increasing vibration frequency for the relative density of 70%.But the vibration cycle for the liquefaction of saturated silt increases with vibration frequency for the relative density of 30%.The development of pore water pressure of the saturated silt is influenced by relative density and vibration frequency. 相似文献
4.
The effect of structures on the wave-induced liquefaction potential of seabed sand deposits 总被引：1，自引：0，他引：1
One of the important design considerations for marine structures situated on sand deposits is the potential for instability caused by the development of excess pore pressure as a result of wave loading. A build-up of excess pore pressure may lead to initial liquefaction. The current practice of liquefaction analysis in marine deposits neglects the effects of structures over seabed deposits. However, analyses both in terrestrial and marine deposits have shown that the presence of a structure, depending on the nature of the structure and initial soil conditions, may decrease or increase the liquefaction potential of underlying deposits. In the present study, a wave-induced liquefaction analysis is carried out using mechanisms similar to earthquake-induced liquefaction. The liquefaction potential is first evaluated using wave-induced liquefaction analysis methods for a free field. Then by applying a structure force on the underlying sand deposits, the effect of the structure on the liquefaction potential is evaluated. Results showed that depending on the initial density of the sand deposits and different structures, water depths and wave characteristics, the presence of a structure may increase or decrease the liquefaction potential of the underlying sand deposits. 相似文献
5.
The evaluation of the wave-induced liquefaction potential is particularly important for coastal engineers involved in the design of marine structures. Most previous investigations of the wave-induced liquefaction have been limited to two-dimensional non-breaking waves. In this paper, the integrated three-dimensional poro-elastic model for the wave-seabed interaction proposed by [Zhang, H., Jeng, D.-S., 2005. An integrated three-dimensional model of wave-induced pore pressure and effective stresses in a porous seabed: I. A sloping seabed. Ocean Engineering 32(5/6), 701–729.] is further extended to simulate the seabed liquefaction potential with breaking wave loading. Based on the parametric study, we conclude: (1) the liquefaction depth due to breaking waves is smaller than that of due to non-breaking waves; (2) the degree of saturation significantly affects the wave-induced liquefaction depth, and no liquefaction occurs in full saturated seabed, and (3) soil permeability does not only significantly affect the pore pressure, but also the shear stresses distribution. 相似文献
6.
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
7.
Noureddine Della Ahmed Arab Mostefa Belkhatir 《Marine Georesources & Geotechnology》2013,31(3):218-229
In order to study pore water response and static liquefaction characteristics of silty sand, which has previously experienced liquefaction, two series of monotonic triaxial tests were run on medium dense sand specimens (RD = 50%) at confining pressure of 100 kPa. In the first test series, the influence of the soil saturation under undrained static loading has been studied. It summarizes results of monotonic tests performed on Chlef sand at various values of the Skempton's pore pressure coefficient. Analysis of experimental results gives valuable insights on the effect of soil saturation on sand response to undrained monotonic paths. In the second series of tests, the overconsolidation influence on the resistance to the sands liquefaction has been realized on samples at various values of overconsolidation ratios (OCR). It was found that the increase of overconsolidation ratio (OCR) increases the resistance of sands to liquefaction. 相似文献
8.
Dynamic compaction (DC) has been widely used for a variety of soil types and conditions in coastal area. However, as the ground water table is near the ground surface, a significant increase of pore water pressure is noticed after each impact, which results in local liquefaction and limits further drop effect. Consequently, to obtain effective compaction effects on saturated soils, it is essential for the evaluation of the liquefaction responses of soil medium caused by DC to determine the time delay between the drops and prevent ‘rubbery soil’. In this study, a numerical investigation on the liquefaction responses of saturated granular soils during DC is carried out using a coupled hydro-mechanical model. The developed model considers all the stages of DC involved in impact stage and consolidation stage. A new cap model for simulations of high strain rate behaviors of soils under DC is incorporated in the coupled hydro-mechanical model. Verification of the proposed model is performed against the previous test data and analytical result. Then, a series of parametric studies have been performed to examine the effects of the tamping energy level, hammer radius and permeability on liquefaction responses of saturated granular soils at several stages of DC. The numerical results demonstrate that the dimension of liquefaction zone is driven by the tamping energy level rather than the permeability, and strain rate has a significant effect on soil responses in DC. 相似文献
9.
1 .Ｉｎｔｒｏｄｕｃｔｉｏｎ1ＴｈｉｓｐａｐｅｒｗａｓｆｉｎａｎｃｉａｌｌｙｓｕｐｐｏｒｔｅｄｂｙｔｈｅＮａｔｉｏｎａｌＮａｔｕｒａｌＳｃｉｅｎｃｅＦｏｕｎｄａｔｉｏｎｏｆＣｈｉｎａ (ＧｒａｎｔＮｏ .5 980 90 0 4 ) . Ｃｏｒｒｅｓｐｏｎｄｉｎｇａｕｔｈｏｒ.Ｅ ｍａｉｌ:ｈｌｉｕ @ｊｌｏｎｌｉｎｅ .ｃｏｍ Ｌａｒｇｅｇｒｏｕｎｄｄｅｆｏｒｍａｔｉｏｎｉｎｄｕｃｅｄｂｙｌｉｑｕｅｆａｃｔｉｏｎｄｕｅｔｏｃｙｃｌｉｃｌｏａｄｉｎｇ ,ｓｕｃｈａｓｅａｒｔｈｑｕａｋｅｓｏｒｓｅａｗａｖｅｌｏａｄｉｎｇ ,ｃａ… 相似文献
10.
A seabed instrument called Lancelot has been developed to measure pore pressure characteristics within potentially unstable marine sediment deposits, in any water depth. An estimate of the coefficient of consolidation can be obtained from the sediment pore pressure dissipation response that occurs following penetration into the seabed. This data can be used to calculate the coefficient of hydraulic conductivity, which is useful in analyzing the seepage velocity of pore fluids moving within the sediment mass. Pore-water pressures in excess of the normal hydrostatic profile are detected and used in static and dynamic liquefaction analyses, with a view toward understanding the origin of unusual seabed features such as pockmarks, as well as short-term instability caused by wave loading. An example of static liquefaction due to seepage stress is given for sites in and adjacent to the well-known 1929 Grand Banks debris flow, along with an example of incomplete liquefaction caused by dynamic wave loading within Miramichi Inner Harbor, New Brunswick. The adoption of in situ measurement techniques is shown to produce data of a quality not normally obtainable from recovered core samples, due to pressure relief and sampling disturbance effects. 相似文献
11.
Mohammed Chemmam Mostefa Belkhatir Rachid Bouferra 《Marine Georesources & Geotechnology》2016,34(4):384-394
This article presents a laboratory study of static behavior of silty-sand soils. The objective of this laboratory investigation is to study the effect of initial confining pressures and fines content on the undrained shear strength (known as liquefaction resistance) response, pore pressure, and hydraulic conductivity of sand–silt mixtures. The triaxial tests were conducted on reconstituted saturated silty-sand samples at initial relative density Dr = 15% with fines content ranging from 0 to 50%. All the samples were subjected to a range of initial confining pressures (50, 100, and 200 kPa). The obtained results indicate that the presence of low plastic fines in sand–silt mixture leads to a more compressible soil fabric, and consequently to a significant loss in the soil resistance to liquefaction. The evaluation of the data indicates that the undrained shear strength can be correlated to fines content (Fc), inter-granular void ratio (eg), and excess of pore pressure (Δu). The undrained shear strength decreases with the decrease of saturated hydraulic conductivity and the increase of fines content for all confining pressures under consideration. There is a relatively high degree of correlation between the peak shear strength (qpeak) and the logarithm of the saturated hydraulic conductivity (ksat) for all confining pressures. 相似文献
12.
From this research, overconsolidated undrained and drained behaviors of specimens with high sand content were highly dilatant. According to the comparison results of laboratory tests, the deviator stresses of silty sand were greater than sandy silt due to high sand content under increasing OCRs, and both silty sand and sandy silt were presented strain softening tendency after failure under undrained loading. The pore water pressure increased with increasing fines content under increasing OCRs. Silty sand exhibited more dilatancy and increasing shear strength than sandy silt because pore water pressures of silty sand were lower than sandy silt under higher OCRs. In overconsolidated drained tests, silty sand is higher strength than sandy silt because silty sand has a lower volumetric strain and higher deviator stress than sandy silt under increasing OCRs. As the degree of overconsolidation increased, similar behaviors of silty sand and sandy silt observed that volumetric strain decreased to negative values due to dilatancy effect and low-cohesion under current effective confining pressures. 相似文献
13.
基于广义Biot动力理论和Longuet-Higgins线性叠加模型,构建波浪-海床-管线动态响应的有限元计算模型,求解随机波作用下,多层砂质海床中管线周围土体孔隙水压力和竖向有效应力的分布。采用基于超静孔隙水压力的液化判断准则,得出液化区的最大深度及横向范围,从而判断海床土体液化情况。考虑海洋波浪的随机性,将海床视为多孔介质,海床动态响应计算模型采用u-p模式,孔隙水压力和位移视为场变量。并考虑孔隙水的可压缩性、海床弹性变形、土体速度、土体加速度以及流体速度的影响,忽略孔隙流体惯性作用。参数研究表明:土体渗透系数、饱和度以及有效波高等参数对海床土体孔隙水压力、竖向有效应力和液化区域分布有显著影响。 相似文献
14.
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
15.
A series of model tests were performed on steel- and Perspex-made suction caissons in saturated dense marine sand to explore installation and extraction behaviors. The extractions of the caisson were conducted by applying monotonic loading or by pumping water into the caisson. Responses of suction caissons to pullout rates, aspect ratios, and extraction manners were examined. Test results show that a cone-shaped subsidence region occurs around the suction caisson during the suction-assisted installation. The pullout bearing capacity of the suction caisson in sand is dominated by the loading rate and the loading manner. For the suction caisson subjected to monotonic loading, the maximum bearing capacity is reached at the pullout rate of about 20.0?mm/s. The mobilized vertical displacement corresponding to the pullout capacity increases with increasing the pullout rate. The passive suction beneath the suction caisson lid reaches the maximum value when the pullout bearing capacity is mobilized. In addition, during the suction caisson extracted by pumping water into the caisson, the maximum pore water pressure in the caisson is obtained under the displacement of approximately 0.04 times the caisson diameter. The absolute values of the maximum pore water pressures for the suction caissons approximately equal those of the maximum vertical resistances at the monotonic pullout rate of 5 mm/s. When the vertical displacements of the suction caissons with the aspect ratio of 1.0 and 2.0 reach 0.92 and 1.77 times the caisson diameter, respectively, the seepage failure occurs around the caissons. Using a scaling method, the test results can be used to predict the time length required for the prototype suction caisson to be extracted from the seabed. 相似文献
16.
The central Alborz mountain range, located in northern Iran, neighboring the Caspian Sea and where the two Persia and Eurasia plates meet, is known as a seismologically active area. In this regard, investigation of the behavior of saturated sand deposits located in this area may be of particular interest. Saturated sand deposits are subjected to instabilities owing to liquefaction or volume change due to earthquake shakings. A particular type of saturated sand deposits is Anzali sand which is abundant in Anzali port and other cities located in this area in northern Iran. This type of sand is a representative for most sands found in this area, i.e., the southern coastal line of Caspian Sea. This research is solely focused on the volume change behavior of marine deposits of Anzali area, often characterized as Anzali sand, in terms of the settlement of a model footing located on the surface of the sand by the aid of a transparent laminar shear box apparatus. Effects of a number of factors such as the frequency of the cyclic loading, the initial density of the sand, and the sample preparation method have been investigated. Observations indicated that the density index and the frequency of loading which are proportional to the energy of an earthquake have direct effects on the accumulation and amount of the final settlement of Anzali sand. 相似文献
17.
A series of model tests were conducted on Perspex-made suction caissons in saturated dense marine sand to study the sand plug formation during extraction. Suction caissons were extracted by pullout loading or by pumping air into the suction caisson. Effects of the pullout rates, aspect ratios and loading ways (monotonic or sustained) on the pullout capacity, and plug formation were investigated. It was found that the ultimate pullout capacity of the suction caisson increases with increasing the pullout rate. The sand plug formation under the pullout loading is significantly influenced by the pullout rate and the loading way. When the suction caisson is extracted at a relatively slow rate, the general sand boiling through the sand plug along the inner caisson wall occurs. On the contrary, the local sand boiling will occur at the bottom of the suction caisson subjected to a rapid monotonic loading or a sustained loading. Test results of the suction caisson extracted by pumping air into the caisson show that the pressure in the suction caisson almost follows a linear relationship with the upward displacement. The maximum pressures for suction caissons with aspect ratios of 1.0 and 2.0 during extraction by pumping air into the caisson are 1.70 and 2.27 times the maximum suction required to penetrate the suction caisson into sand. It was found that the sand plug moves downward during extraction by pumping air into the caisson and the variation in the sand plug height is mainly caused by the outflow of the sand particles from the inside of the suction caisson to the outside. When the suction caisson model is extracted under the pullout rate of 2?mm/s (0.28?mm/s for the prototype), the hydraulic gradient along the suction caisson wall increases to the maximum value with increasing the penetration depth and then reduces to zero. On the contrary, when extracted under the pullout rate of 10?mm/s (1.4?mm/s for the prototype), the hydraulic gradient along the suction caisson wall increases with increasing the pullout displacement. When extracted by pumping air into the caisson, the hydraulic gradient reaches the critical value, and at the same time, the seepage failure occurs around the suction caisson tip. 相似文献
18.
Khayra Merabet Ismail Benessalah Mohammed Chemmam 《Marine Georesources & Geotechnology》2020,38(4):461-467
AbstractThe study of the unsaturated soils is a very complex field to which several researches in laboratory and on site are directed these last years. An experimental study aims to quantify the influence of the Skempton coefficient B characterizing the degree of saturation on the behavior of the granular sand to the liquefaction resistance of sand. The study is based on undrained triaxial tests performed on natural Chlef sand carried out at an initial relative density Dr = 50% under a confining pressure of 50, 100 and 200?kPa for Skempton coefficient B?=?10 to 92%. The results of the tests show that an increase of confining pressure leads to an increase of the shear stress of the samples. For the lower value of the degree of saturation results of our findings indicate an increase of the resistance to liquefaction; our results are in good agreement with others observed in several research projects conducted with other sands. The increase of Skempton coefficient B induces an increase of pore water pressure and a decrease of the shear strength. The pore pressure (u) increases with an exponential manner with the increase of the degree of saturation; while the residual shear strength (Rs) decreases with logarithmic manner with the increase of degree of saturation (B). 相似文献
19.
The Interstitial Environment of Sandy Beaches 总被引：1，自引：0，他引：1
Abstract. The interstitial system of sandy beaches is lacunar and has its dimensions defined by the sand granulometry. It can be described by features such as pore size, porosity, permeability, and water content. The most important process occurring in this system, water filtration, is driven by inputs of freshwater from groundwater discharge, and inputs of seawater by tides, wave run-up, and subtidal wave pumping. Reflective beaches have seawater input effected mainly by waves; they filter large water volumes with short residence times. Dissipative beaches display the opposite patterns, slowly filtering small volumes input by tides. Flow patterns and their effects on interstitial climate are described. The water table of the beach moves in response to groundwater discharge, tides, and waves and influences erosion/accretion processes on the beach face: a high water table promotes erosion. A series of moisture zones can be recognised from the dry surface sand at upper tide levels, to permanently saturated sand below the low tide water table, namely: a stratum of dry sand, a stratum of retention, a stratum of resurgence, and stratum of saturation. Interstitial chemistry is briefly described in terms of salinity changes, organic loads, oxygen content, and nutrient cycling. It is concluded that the interstitial environment of sandy beaches spans a continuum between physically and chemically controlled extremes: the former condition occurs on coarse sand reflective beaches, which experience low organic inputs and high filtration rates of large water volumes — resulting in powerful hydrodynamic forces; the latter occurs on dissipative beaches of fine sand, which are subject to high organic inputs and low filtration volumes — resulting in stagnation and steep vertical chemical gradients. Many intermediate situations occur and these are more favourable to interstitial life than either of the extremes. 相似文献
20.
近年来,在各种近海建筑物的建设中,桩基础被越来越广泛地应用。关于海床内桩基各层位对波浪动力响应相位差的研究,国内外学者研究的重点主要集中在海床内各层位孔隙水压力的相位变化。而关于波浪作用下海床各层位土体总压力相位的研究则很少。本研究采用波浪水槽实验,在土床未扰动和土床扰动液化两种工况下,分别施加不同波高的波浪,对底床各层位土体总压力的相位进行对比研究。实验结果表明,当土体未运动时,在渗透性和饱和度均匀的土体中,各层位土体之间不存在相位差。当底床液化后,土体出现显著分层现象,在液化土层和不动土层间存在显著的相位差。此时,总压力振幅呈现先增大后减小的现象,且在床面下-10cm处出现最大值。 相似文献