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1.
This paper presents a case study of dynamic compaction (DC) on backfill ground for planned oil tanks located at Nanjing Bay. The ultra-high energy DC level of 18,000 kN · m was applied in the area tamping phase of the dynamic compaction. In combination with ground replacement technique by forcing crushed stones into the underlain cohesive layer, the high-compressibility of this layer was properly tackled. The construction techniques and ground improvement mechanisms are introduced and discussed. Field evaluations before and after the dynamic compaction, including surface wave test, plate load test, and soil sampling, showed that the ultra-high energy dynamic compaction in combination with ground replacement achieved much greater improvement depth and ground bearing capacity than conventional DC. Results show that dynamic compaction of 18,000 kN · m combined with ground replacement is of great merit in dealing with backfill ground with weak cohesive content in harbor development. 相似文献
2.
Considering the characteristics of seabed ground in coastal reclamation area, ultra soft clay improvement method by heavy tamping after rockfilling displacement was proposed combined with a case study. The improvement mechanisms of the method can primarily be attributed to rockfilling displacement (RD), dynamic compaction (DC), dynamic replacement (DR) and dynamic replacement and mixing (DRM). For the case study given in this article, heavy tamping construction program was proposed based on field pilot tests. Furthermore, the effectiveness of the proposed ground improvement method was verified through in situ plate load test, sand fill test and the analyses of observed settlement data. Thus, the method of heavy tamping after rockfilling displacement is applicable for the improvement of seabed ground in coastal reclamation area. It is proposed for similar projects that heavy tamping of fills may be performed by layers and correspondingly tamping energy increased to further enhance the improvement effect of DC, DR and DRM. In addition, delayed improvement effect or time effect of soil mass after heavy tamping is still an issue to be further studied. 相似文献
3.
In order to investigate the characteristics of water wave induced liquefaction in highly saturated sand in vertical direction, a one-dimensional model of highly saturated sand to water pressure oscillation is presented based on the two-phase continuous media theory. The development of the effective stresses and the liquefaction thickness are analyzed. It is shown that water pressure oscillating loading affects liquefaction severely and the developing rate of liquefaction increases with the decreasing of the sand strength or the increasing of the loading strength. It is shown also that there is obvious phase lag in the sand column. If the sand permeability is non-uniform, the pore pressure and the strain rise sharply at which the smallest permeability occurs. This solution may explain why the fracture occurs in the sand column in some conditions. 相似文献
4.
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
5.
6.
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
7.
Numerical approach to predict ground displacement caused by installing a horizontal jet grout column
When horizontal jet grouting is conducted in fine-grained soils, the injection of large volumes of fluid with high injection pressure into the ground may cause ground surface upheaval and the lateral movement of subsoil. This paper provides a numerical approach to calculate the ground displacement caused by installing a horizontal column based on determination of the influencing radius of injection pressure and the volumetric expansion strain caused by fluid injection. During the course of this study, the relationship between the influencing radius, column radius, volumetric expansion strain, and jetting parameters is established. The proposed numerical approach is applied to analyze a case history conducted in Shanghai soft soil deposits, which include the monitoring of vertical displacement of the ground surface and lateral displacement of the subsoil during construction. A comparison of the results between the simulated values with the Mohr Coulomb model and field data demonstrates that the numerical approach can yield a reasonable prediction of these field measurements when the influencing radius is six times the radius of the column. The influence range of the horizontal jet grouting activity is also discussed by numerical analysis with respect to two soil models (the Mohr Coulomb model and the hardening soil model). 相似文献
8.
将衬砌分别视为多孔柔性材料和弹性介质,在频率域内研究内水压力作用下饱和分数导数黏弹性土-深埋圆形隧洞多孔柔性或弹性衬砌系统的耦合简谐振动。土体的宏观力学特性采用多孔介质理论来模拟。通过引入与土体体积分数相关的应力系数,利用衬砌和土体界面处位移连续,分别得到饱和黏弹性土和衬砌的位移、应力和孔隙水压力等的解析表达式。在此基础上,分析了多孔柔性衬砌和弹性衬砌结构的差异,并考察了应力系数、渗透系数、分数阶导数本构参数等对系统动力响应的影响,结果表明:多孔柔性衬砌材料条件下系统的动力响应明显大于弹性衬砌材料条件下系统的动力响应;随着分数导数阶数和材料参数比的增加,系统共振效应明显减弱;衬砌边界透水和不透水只是反映边界渗透性的两种极限状态。 相似文献
9.
Soils are classified as sandy soils and clayey soils in most soil classification systems, and appropriate equations are used for practical design, depending on soil type, to represent each soil behavior. Sand-clay mixtures, however, need a special standard to evaluate their specific behaviors since they are categorized as intermediate soils or transitional soils and typically show intermediate properties. In this article, a series of cyclic triaxial tests were conducted on specific sand-fines mixtures with three fine types and various fine contents. The behaviors of various soil mixtures (silica sand with Iwakuni natural clay, Tottori silt, and Kaolin clay) were investigated by considering a concept of granular void ratio expressed in terms of sand structure. The cyclic shear strengths of the soil mixtures were also evaluated by increasing the fine content but no more than the threshold fine content. In the results, the cyclic deviator stress ratio decreased in dense soils whereas it increased in loose soils by increasing the fine content. In addition, a simple equation was proposed to predict the liquefaction resistance of sandy soils by evaluating the cyclic deviator stress ratio with a concept of equivalent granular void ratio. 相似文献
10.
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
11.
Santosh Kumar Yadav Guan-lin Ye Usama Khalid 《Marine Georesources & Geotechnology》2020,38(4):400-416
AbstractBased 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
12.
The failure of marine structures is often attributed to liquefaction in loose sand deposits that are subjected to ocean waves. In this study, a two-dimensional integrated numerical model is developed to characterize the liquefaction behaviours of loosely deposited seabed foundations under various types of ocean waves. In the present model, Reynolds-Averaged Navier–Stokes (RANS) equations are used to simulate the surface wave motion, and Biot's consolidation equations are used to link the solid-pore fluid interactions in a porous medium. A poro-elasto-plastic solution is used to reproduce foundation behaviour under cyclic shearing. Unlike previous investigations, both oscillatory and residual soil responses were considered; they are coupled in an instantaneous approach. Verification of the model results to the previous centrifugal wave tests is carried out, obtaining fairly good agreement. Numerical examples show that foundation behaviour under various types of wave loading, particularly standing waves or a solitary wave, embodies a completely two-dimensional process in terms of residual pore pressure development. The parametric studies demonstrate that liquefaction caused by the build-up of pore pressures is more likely to occur in loosely deposited sand foundations with poor drainage and under large waves. 相似文献
13.
大直径单桩基础是海上风电应用广泛的一种基础形式,严格控制桩基泥面处的位移是保证基础稳定和风机安全运营的关键因素.通过数值方法建立了单桩—海床的三维模型,将可以描述海洋砂土超固结性和结构性的弹塑性本构模型通过UMAT子程序嵌入有限元软件ABAQUS中,桩基承受的波浪荷载通过Morison方程进行计算模拟.针对无波浪荷载、仅作用于海床的波浪荷载、同时作用于桩基和海床的波浪荷载三种情况,分析了海床土的动力响应以及桩基的水平位移之间的差异,探讨了海床土体参数对桩基水平变形的影响.研究结果表明海床土体液化会导致桩基水平变形增加,海床土渗透性、超固结性、结构性对桩基水平位移影响显著,研究成果可为海上风电单桩基础的设计与运维提供参考. 相似文献
14.
The foundations of nearshore and offshore structures are always subjected to long-term cyclic loading which is often a one-way, with low amplitude and a large number of cycles. Hence, the long-term dynamic behaviour of shoreline soils and sediments should be understood to avoid excessive deformation and liquefaction. As one of the most problematic soft soils in Melbourne, Coode Island Silt (CIS) at the northern shoreline of Port Phillip Bay contains a considerable but variable amount of sand. This paper explores the dynamic response of CIS containing different sand content subjected to a large number of cycles. To determine the liquefaction potential, and the effect of sand content on the resilient modulus and permanent strain of CIS, a series of long-term cyclic triaxial tests at a sinusoidal loading frequency of 1 Hz is performed. Based on the test results, it is found that CIS with varying sand content up to 30%, does not liquefy under the cyclic stress ratios and frequency applied in this study. Also, a sand content of 10% causes CIS to degrade more under cyclic loading. In the end, an empirical model to predict the permanent strain of CIS with a variable sand content is calibrated. 相似文献
15.
Marine deposit ground usually need significant improvement before the construction of civil structures in coastal areas due to the poor mechanical properties of soils. Dynamic compaction (DC) is a widely used technique in such projects. In this study, a case history of DC tests in sandy soils with a weak embedded layer is introduced. Two series of DC tests—single point tests and impact zone tests—were applied to test zones with similar geological conditions to investigate the effect of energy level on the depth of improvement (DI). The highest energy used is up to 15000 kN · m. Field measurements were conduct before and after DC in each series to validate the effectiveness of improvement, including crater settlement, excessive pore pressure, and acceleration measurement for single point tests, and the pressure meter and CPT tests for impact zone tests. For single point tests, the effectiveness of improvement increases as the energy level increases to 12000 kN · m. Further increase of compaction energy does not have an effect on settlement, pore pressure, or ground acceleration. For impact zone tests, the energy level does not show a positive correlation with the DI, mainly due to the presence of an embedded weak layer. 相似文献
16.
The objectives of this study are carried out a series of controlled large wave flume experiments using fine-grained sediment from the Huanghe River Delta, exploring the complete sequence of sediment behavior in the bottom boundary layer(BBL) during wave-induced liquefaction. The results show that:(1) The BBL in silty seabed is exposed to a progressive wave, goes through a number of different stages including compaction before liquefaction, sediment liquefaction, and compaction after liquefaction, which determines the range and thickness of BBL.(2) With the introduction of waves, first, the sediment surface has settled by an amount S(S=1–2 cm) in the course of wave loadings with an insufficient accumulation of pore water pressure. And a thin high concentration layer formed the near-bed bottom.(3) Once the liquefaction sets in, the liquefied sediment with an ‘orbital motion' and the sub-liquefied sediment form a two-layer-sediment region. The range of BBL extends downwards and stopped at a certain depth, subsequently, develops upwards with the compaction process. Meanwhile, resuspended sediments diffuse to the upper water column.(4) During the dynamics process of the BBL beneath progressive waves, the re-suspended sediment increment ranked as sediment liquefaction erosion before liquefaction compaction after liquefaction. 相似文献
17.
胜利油田浅海区域海底土层的液化判别方法分析 总被引：2，自引：0，他引：2
针对胜利油田海上石油勘探开发区(埕岛油田)的海底饱和粉土(砂土)液化判别问题,结合工程研究实例,对土层液化判别的各种方法进行对比分析,指出了当前各种方法的局限性和不足,为海底土层的液化判别分析提供了新思路。 相似文献
18.
The use of sand compaction pile or gravel compaction pile is nowadays a common approach for soft ground improvement. In this article, a recycled aggregate porous concrete pile has been developed by replacing natural aggregates with recycled aggregates to overcome issues related to bulging failure or reduced section geometries. Such issues may arise during installation and during the early stages of operation. In addition, the proposed approach utilizes recycled aggregates instead of natural materials. To investigate the applicability of the recycled aggregate porous concrete pile method as a ground improvement technique, a series of laboratory model consolidation tests was performed on soft clay soil reinforced with sand compaction pile, gravel compaction pile, and recycled aggregate porous concrete pile, respectively. The results indicated that the settlement reduction effect of recycled aggregate porous concrete pile was significantly higher than the sand compaction pile and gravel compaction pile methods. The stress sharing ratio from the experimental program showed good agreement with those calculated by elasticity theory. Comparative analyses of the recycled aggregate porous concrete pile versus sand compaction pile and gravel compaction pile approaches, under the same replacement area ratio and surcharge pressure, showed significantly improved consolidation time, settlement reduction, and stress sharing effect. 相似文献
19.
考虑土骨架加速度效应的海床动力反应及其影响因素分析 总被引：2，自引：0，他引：2
由Biot二维广义动力固结理论的形式基本控制方程出发,忽略孔隙流体的加速度,提出了饱和海床动力反应的时域有限元数值解法.联立静力平衡条件和Biot固结方程的退化法所得到的数值解可视为其特例.在比较算例中,退化法得到的超静孔压和有效应力幅值沿海床深度的分布与解析解一致.一般情况下,土骨架的加速度对海床的有效应力和超静孔压影响很小,控制方程可以退化为Biot理论.成层海床上部的粗砂层不会使超静孔压幅值在海床表面下较浅的深度内迅速衰减,难以改变海床的瞬时循环液化深度. 相似文献
20.
Nguyen Ngoc Truc Lena Mihova Toshifumi Mukunoki Duc Minh Do 《Marine Georesources & Geotechnology》2020,38(1):23-39
AbstractThis study conducted a series of laboratory experiments and established numerical models on selected undisturbed soil samples in the Red River Delta (RRD) to determine the effect of change in soils intruded by saline water. The variation in the technical parameters of soils was verified in soils fully saturated by solution of four salt concentrations, that is, 0.0, 9.9, 19.8, and 33.0?g/L. Results show that the content and composition of clay minerals in cohesive soils before and after saline intrusion are unchanged. The same finding is obtained for clay after removing absorbed water layer by using a centrifuge apparatus. The zeta potential and settlement velocity of soils in the RRD increase when salt is added to the saturated solution. Similarly, the deformation of soils increases proportionally with the salt concentrations of that solution. This result is attributed to the linear decrease in deformation modulus. The decrease in modulus versus salinities is nearly consistent for pressure stages from 100 to 400?kPa. The safety factor of bearing capacity also decreases linearly with salinities. The decrease reaches 12.5–16.3% when soils are in the maximum saline solution. All these changes are considered as the degradation of soils in saline media. 相似文献