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1.
Youngcheul Kwon 《Marine Georesources & Geotechnology》2016,34(3):219-233
Difficulties in the prediction of time-distribution of consolidation settlement will be introduced by using the Murayama test embankment case of Japan. In particular, it will be discussed why the prediction of consolidation rate is difficult in multi-layered soil with complex and variable mechanical properties like organic soil or peat. It can be inferred that uncertainties, which are embedded intricately in the consolidation problem as well as given ground condition, would be major causes for consolidation settlement. After that, the author focused on the movement of pore water under the various conditions of hydraulic conductivity in the soils, and how it can affect the time-distribution of the consolidation settlement. For the applied key methodology on the consolidation settlement problem, we propose the hybrid consolidation simulation controlling the movement of pore water with high accuracy and, finally, the aim of this article is to discuss the methodological approaches obtained by the study, including the basic concept and accurate movement of pore water under various conditions of soil layers and hydraulic conductivity. 相似文献
2.
Hongyue Sun Gang Wu Xin Yan Dongfei Wang Zhenlei Wei 《Marine Georesources & Geotechnology》2018,36(8):940-949
Conventional drainage consolidation methods cause significant energy consumption and environmental issues. In this paper, a method combining siphon drainage and surcharge loading is proposed to drain water from soft soil with vertically installed prefabricated vertical drains (PVDs) and a siphon tube. To investigate the availability and effectiveness of this method, a laboratory physical modeling test was conducted to investigate the drainage and consolidation behavior. The laboratory modeling test results of this method were compared with the calculated results of the ideal sand-drained ground consolidation method to clarify the advantages and mechanism of this method. Comparison results show that the pore pressure and settlement in the proposed method developed faster than the calculation results of ideal sand-drained consolidation theory. About 10?m thickness of unsaturated zone can be formed by siphon drainage which produce a surcharge loading effect on the soil below the flow profile. Drainage is a very slow process in soft soil, and siphon drainage can work continually. Siphon drainage combined with surcharge loading is potentially a good alternative to drain water from soft clay economically and environmentally. 相似文献
3.
The paper discusses a new method to put forward to determine the initial pore pressure by extrapolating the last segment of measured pore pressure versus the inverse square root of time scale through incomplete pore pressure dissipation test. For underconsolidated soil, the estimated initial pore pressure is greater than the hydrostatic pore pressure. With the calculation of the initial pore pressure, the status of the consolidation of underconsolidated soil can be evaluated by calculating the apparent degree of consolidation which is defined as excess pore pressure generated by piezocone penetration divided by the difference between the total pore pressure measured by piezocone and in situ hydrostatic pore pressure. The apparent degree of consolidation is less than one as the soil is underconsolidated. The Northern Expressway Connection project of Chongqi Bridge is introduced as an example of practical application. In this case, the studied area is slightly underconsolidated, which is consistent with the results of the laboratory oedometer tests. Finally, compared with overconsolidation ratio (OCR) values from the oedometer tests, a new formula to estimate the OCR of underconsolidated soil using the apparent degree of consolidation was presented. It indicates that the OCR of underconsolidated soil can be proposed directly from partial piezocone dissipation tests. 相似文献
4.
The technique of geotextile tubes used to construct dikes for land reclamation has been widely used. The tubes are usually filled with slun＇y of soil, such as sand, silt or clay. The tensile stress developed in the geotextile during filling the tube is the dominant factor for construction of a safe dike. The existing design methods are good for designing sausage shaped tubes and can not be directly applied for designing fiat tubes, which are commonly used in dike construction. This paper presents a procedure that can detenmine the relatiorrship among the tube size, the pumping pressure, the unit weight of the slurry, and the tensile stress developed in the geotextile during the tube filing. When the tubes are piling up to form the dike, the tubes in the bottom will sustain the load from the weight of the upper ones. A procedure is also developed to calculate the changes of the mechanical and geometrical behavior of the tubes under the load with a similar method. All these approaches have been programmed, which can help dike designers to select the suitable geotextile and determine the profile of the dike. 相似文献
5.
Consolidation occurs in estuarine marine clays for coastal reclamation by dissipation of the excess pore pressure, which is induced by increasing the total overburden stress during conventional mechanical surcharging. The excess pore pressure can be decreased usually by the use of several construction methods such as sand drain and paper drain. Besides the drain methods, vacuum can also be used in the soil mass to consolidate the estuarine marine clays by decreasing the pore pressure as well as increasing the effective stress.The study on vacuum consolidation is devoted so far mainly for laboratory model tests or numerical analysis in Korea. Recently, an instrumentation system was applied to manage the vacuum-applied consolidation on a field, in which a sewage disposal plant was constructed. While vacuum was applied, the behaviors of estuarine marine clays such as the settlement, lateral deformation and pore water pressure have been investigated precisely. The behavior of estuarine marine clays during vacuum-applied consolidation shows some difference from the behavior of estuarine marine clays in the case of conventional preloading. A principal difference is that the lateral deformation corresponding to settlement is smaller than before vacuum application even though the surcharge height has been increased. 相似文献
6.
Pore water and earth pressures acting on retaining structures are investigated using an efficient coastal double-layered excavation model to determine offshore excavation responses to groundwater fluctuations outside foundation pits. Total pore water pressure includes excess pore water pressure (due to groundwater fluctuations) and steady pore water pressure (due to steady seepage) determined using one-dimensional consolidation theory of double-layered soil and one-dimensional steady-state flow theory, respectively. Rankine's active and passive earth pressures are obtained from pore water pressure. This method is applicable to arbitrary groundwater fluctuation conditions. How physical parameters affect pore water pressure is numerically investigated using examples, demonstrating the method's practicality for calculating pore water and earth pressures. 相似文献
7.
8.
Shanwei Ke Peng Wang Xueyue Geng Jun Hai Jinqiang Jin 《Marine Georesources & Geotechnology》2020,38(8):970-979
AbstractCompared with traditional vacuum preloading, air booster vacuum preloading is more effective at strengthening dredged slurry and improving the consolidation process. Although many engineering practices have shown that the pressurized duration has a significant effect on the reinforcement effect, there is no standard available for determining the pressurized duration. In this study, five dredged slurry samples were tested to examine the effect of different pressurized durations on the consolidation. An extensive monitoring system was used to measure the vacuum pressure, pore water pressure, settlement, and water discharge during the test, while the water content and shear strength were measured after the test. The collected monitoring data were comprehensively analyzed to evaluate the reinforcement effect. The results revealed that the pressurization system can be used to reinforce deep dredged slurry and make the whole soil layer more homogeneous. If the pressurized duration is too short, the dissipation of pore water pressure is too little to achieve the pressurization effect. If the pressurized duration is too long, too much gas will be in the soil and enter the vacuum system, which will significantly reduce the vacuum pressure and thus the reinforcement effect. Based on these findings, the optimal pressurized duration was obtained. 相似文献
9.
Vacuum preloading is often used to improve the geotechnical properties of dredged slurry. Although the performance of this method has improved with rapidly developing technology, soil columns usually formed on the drainage boundary induce the decrease of permeability around the boundary, thereby limiting the further development of this method. To address this issue, this paper proposes a method for pretreating the slurry combined with sand prior to vacuum consolidation. This method partially replaces the fine particles with sand to reduce the formation of soil columns. Two groups of vacuum preloading tests were performed to investigate the effect of sand content and sand grain size on the vacuum consolidation of dredged slurry. The test results revealed that for a given sand grain size, increasing the sand content of the sand–slurry mixture increased the pore water drainage and accelerated the dissipation of pore water pressure, thereby increasing the vane shear strength. In contrast, for a constant sand content, the samples containing coarse sand exhibited increased pore water drainage and accelerated dissipation of pore water pressure, thereby increasing the vane shear strength of the soil. 相似文献
10.
Abstract It has been observed that earthquake‐induced settlement depends on the excess pore water pressure accumulated during an earthquake. In particular, in the case where a clay layer is overconsolidated, excess pore water pressure is produced and settlement occurs by dissipation of the excess pore water pressure, which is very large in comparison with the coefficient of secondary compression. Therefore, if the settlement of clay ground induced by secondary compression becomes a serious problem, careful consideration of the earthquake‐induced settlement is needed. In this article, the settlement characteristics of a clay layer induced by cyclic shear are discussed, including the effects of loading period, the threshold shear strain below which no excess pore pressure or no settlement takes place, and the relationships between uniform shear strain cycles and irregular strain‐time histories. Then a calculation procedure for estimating the earthquake‐induced settlement is developed and applied to three soil profile cases, including the clay layers in Mexico City and Osaka Bay in Japan. In the case of a soil profile in Mexico City, settlements of about 0–3 cm are estimated and these values agree reasonably with the leveling results for the Mexico City earthquake of 1985. Furthermore, it is pointed out that the settlement induced by earthquakes is considerably affected by differences in the accelerograms. 相似文献
11.
为了研究黄河口海床沉积物固结过程中电阻率同工程力学性质指标的对应关系,探索海床土体固结过程的新型原位监测技术,本文在黄河刁口流路三角洲叶瓣潮坪上,现场取土配置黄河口快速沉积形成的流体状沉积物和观测研究粉质土海床的固结过程。利用静力触探、十字板剪切试验、孔隙水压力监测等原位土工测试手段,实时测定固结过程中海床土强度变化和孔隙水压力消散过程;同时通过埋置自行研制的环形电极探杆,实时测定海床土固结过程中的电阻率变化。通过对比分析海床土电阻率与工程力学性质指标的同步测定数据发现:黄河口饱和粉土的电阻率与微型贯入试验测得的土体贯入强度,静力触探试验测得的比贯入阻力,十字板剪切试验测得的不排水抗剪强度(峰值强度、残余强度)均呈乘幂关系,且相关性良好;海床沉积物在固结过程中的电阻率与孔隙水压力呈负线性相关性。 相似文献
12.
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
13.
Liang Wang Wei Zhu Jian Xie Lei Li Chunlei Zhang 《Marine Georesources & Geotechnology》2013,31(6):556-566
The shear strength properties of sediments are relevant to many practical problems, including those related to predicting the bearing capacity of the man-made crust lying over dredged disposal sites and those associated with estimating the erosion resistance and the bearing capacity of sediments. In this study, an experimental apparatus and method is developed for sedimentation. This apparatus consists of a settling column, pore measurement apparatus, shear vane apparatus, and multilayer extraction sampling apparatus. The change regulation of interface height, density, excess pore pressure, peak undrained shear strength, residual undrained shear strength, and sensitivity varies before and after the excess pore pressure dissipates to zero in the self-weight consolidation stage. The higher the water content, the greater the particle segregation degree. Particles are mainly segregated in the settling stage, and they are not segregated further in the self-weight consolidation stage. Before excess pore pressure dissipates to zero in the self-weight consolidation stage, shear strength is related to water content, effective stress, and the formed structure of sediments. After excess pore pressure dissipates to zero, peak undrained shear strength is mainly associated with the structure (thixotropy) of sediments. Residual undrained shear strength increases because of the slight decrease in water content. The mechanisms of thixotropy can be expressed as the increase in the original and curing cohesions of sediments with time as determined from microscopic aspects. 相似文献
14.
ABSTRACTThe behavior of loose anisotropically consolidated calcareous sand obtained from an island in the South China Sea was investigated under undrained monotonic and cyclic loading in a hollow cylinder torsional apparatus. The tests were conducted on specimens which consolidated under various initial effective confining pressures and consolidation stress ratios. The monotonic test results show that the failure and phase transformation line are essentially independent of the consolidation conditions, while the initial contractive tendency of the specimens decreases with an increasing consolidation stress ratio. During monotonic loading of the anisotropically consolidated specimens, a same major principal stress direction is observed at the constant stress ratio lines up to the phase transformation line, irrespective of initial effective confining pressure. The cyclic strength of the sand increases with an increasing consolidation stress ratio. Moreover, a pronounced stress dependence is observed in the sand with higher consolidation stress ratio. During cyclic loading, the generated excess pore water pressure presents considerable fluctuations. The normalized terminal excess pore water pressure is described as a function of consolidation stress ratio. The tests show that the particle shape, rather than particle crushing, plays an important role in the monotonic and cyclic behaviors of the calcareous sand. 相似文献
15.
Evaluation of Excess Pore Water Pressure Characteristics in Sand Mat Used for Recycling Dredged Soil
The design of sand mats should be reviewed on the basis of excess pore pressure behavior, which can be obtained by combining the characteristics of soft ground with the permeability of the mats. In this study, a banking model test was performed using dredged sand as the mat material to investigate the hydraulic gradient distribution of sand mats. The results were compared with numerical analysis results utilizing Terzaghi's one-dimensional consolidation equation. The results showed that the pore pressure was influenced by an increase in the amount of settlement at the central part of the sand mat as the height of the embankment increased. The measured decrease of the pressure head due to the residing water pressure in the sand mat was delayed compared to the numerical analysis results. Accordingly, sand mats should be laid to reduce the increased hydraulic gradient at the central part of the embankment. 相似文献
16.
通过青岛保税区地基强夯试验，观测分析了区内海相沉积含砂淤泥质土在夯击能量作用下垂向及水平方向的变形及孔隙水压力产生、消散规律，对区内软土地基可夯性进行评价分析。试验结果对沿海地区淤泥质土加固处理具一定的借鉴意义 相似文献
17.
Qiang Yuan 《Marine Georesources & Geotechnology》2016,34(1):79-86
Based on the vertical equal strain assumption, there are many consolidation theories of soft soil incorporating vertical drains. Because the influence of many factors is often ignored and the flow of the pore water usually happens in three-dimensional directions, analytical solutions could not be accurate enough. Because of the amount of computer storage and the computing time needed, two-dimensional finite element analysis is used to model the stone column improving the soft foundation. The embankment load is transferred to a column because of the soil arching effect. When the embankment is constructed, the settlement accounts for 64% of the total settlement, which shows that the column can reduce the post-construction settlement. The stone column's bulge is confined to a length about one to two times the diameter of the stone column away from its top, and the column at the toe would bears the shear stress to some extent. 相似文献
18.
Note on axisymmetric consolidation of multi-layered poroelastic soils with compressible constituents
In the conventional analysis of Biot’s axisymmetric consolidation, the solid phase and the surrounding fluid were often assumed incompressible for simplicity. Such assumption in soil engineering ignored the effect of compressibility of constituents on the consolidation. In this article, the compressible fluid and solid in soil were taken into account for 3-D consolidation. The pore pressure, the displacements, and the stresses were expressed by two displacement functions, and the Laplace–Hankel transform was applied to set up the stiffness matrix between the generalized displacement and stress. The stiffness matrix consisted of negative exponential functions, ensuring that the computation is efficient and stable. Then the global stiffness matrix is extended by embracing the continuity of the interfaces and boundary conditions of soil base. The relationship between the generalized displacement and stress of the soil base reduces the number of unknowns of the global matrix. Such consideration reduced the number of unknowns of the global matrix and brought in more acceptable boundary conditions where the stiffness and the permeability of semi-infinite soil base can be taken into account. After the inversion of the Laplace–Hankel transform, the real solutions were obtained. The results show that the stiffness and permeability of the soil base can change the development consolidation and that the compressibility of solid particles has a great effect on the settlement in the beginning of consolidation. 相似文献
19.
Vikram Singh 《Marine Georesources & Geotechnology》2018,36(5):505-514
Although the uplift behavior of offshore plate anchors under undrained conditions has been investigated well in the past, studies on the behavior of anchors under long-term sustained loading are in relatively few numbers. The time required for consolidation under sustained load is important because the shear strength of soil changes after dissipation of excess pore pressure. In this paper, small strain finite-element analyses have been performed to investigate the consolidation time history above and beneath strip anchors. The modified cam clay plasticity constitutive model is used for modeling coupled pore fluid stress analysis. The effects of magnitude of preloading with embedment level have been studied. As expected, the FE results have shown that excess pore pressure dissipation time for soil above the anchor increased with the increase in embedment depth and the magnitude of preload. Rapid dissipation of negative excess pore pressure beneath the anchor was observed with increasing embedment depth, if the preload magnitude is equal to or more than 60% of the undrained capacity. Observed consolidation responses are presented as nondimensional design charts and simplified equations for ease of practice. 相似文献
20.
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