In most marine reclamation projects, sand fill is placed directly on soft marine seabed soils. The sand particles can easily penetrate into the soft marine soils, and the soft soil can also move into the pore spaces inside the sand at the initial contact interface between the sand and the soft marine soil. In this case, the permeability and the volume of the sand above the initial surface are reduced. To avoid this problem, a geotextile separator is often placed on the surface of the soft marine soils before placing the sand. In this study, a two-dimensional physical model is utilized to study the geotextile separator effects. The initial conditions of a clayey soil, sand fill, and surcharge loading were kept the same in the physical model test with the only difference being that a geotextile separator was either placed on the clay surface or omitted. The settlements of the initial interface were recorded and compared for the two cases without or with the geotextile separator. The particle size distribution of the soils taken across the interface zone for different time durations was then measured, analyzed, and compared. Based on an analysis of the results, the sand percolation depth was 40 mm and fine particle suffusion was apparent when the sand was placed directly on the marine slurry surface without a geotextile separator. However, when a geotextile separator was used sand percolation was avoided, and the fine particle suffusion was effectively diminished. A relative fine particle fraction is defined to illustrate the migration of fine particles from the clay to the sand soils. The fine particle percentages of the Hong Kong Marine Deposits–sand mixtures were calculated for the cases with and without a geotextile separator using an empirical formula and micromechanical modeling to obtain a better understanding of the effects of geotextile separators in practice.
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沿海吹填砂土地基地下水位较高、常含软土夹层,地基处理难度大。为了研究高能级强夯在这类吹填砂土地基上的加固效果,在山东沿海某吹填砂土场地开展6 000和8 000 kN·m能级强夯加固试验。试验结束后分别运用标准贯入试验、静力触探试验、平板载荷试验进行现场检测。通过对比分析了设计要求深度范围内标准贯入试验和静力触探试验,发现夯前夯后标准贯入试验击数和静力触探锥尖试验阻力均明显提升,有效消除了饱和砂土和饱和粉土的液化势;通过平板载荷试验p-s曲线及夯后静力触探锥尖阻力标准值与承载力特征值的关系式,得到夯后砂土地基承载力特征值≥120 kPa,验证了高能级强夯方案的可行性。其次,对软土夹层位置和地下水位高度展开研究,发现软土层会阻碍夯击能传递,减小强夯有效加固深度,且软土层位置不同对强夯加固效果影响程度不同,强夯影响临界范围处存在软土层时,有效加固深度为软土层顶部位置处;对砂土地基进行4 000 kN·m能级强夯试验时,发现未降水强夯后有效加固深度为5 m,降水至地面以下3 m强夯后有效加固深度达到了7 m,提高了加固效果。在高能级强夯研究基础上,对现场吹填砂土地基进行了75万m2的大面积高能级强夯施工,发现处理后地基能够满足建筑用地要求。 相似文献
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本文进行了围堰土料的室内击实,不同压实度下的固结不排水直剪和渗透试验,对围堰在吹填过程中变形进行了现场监测,初步分析了吹填后的沥水特性,提出了几点结论。 相似文献
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采用吹填淤泥作为滩涂围垦填料既能有效解决砂石等理想填料资源的短缺难题,又能避免大量吹填泥弃置所带来的环境负面影响,具有可观经济效益和可持续发展性。但吹填淤泥往往呈流浆或浮泥态,含水率超高,强度低,渗透性差,后续地基处理人员和设备难以直接进场。鉴于此,提出了一种絮凝-固化联合方法处理表层吹淤泥浆形成硬壳层(工作平台)的新思路,并开展室内试验验证了其技术可行性。首先,通过针筒滴定法确定了处理吹填淤泥的絮凝剂(PAM)类型及最佳掺量;然后,通过模型试验模拟了不同配比的絮凝-固化联合处理淤泥浆的絮凝沉积过程,并开展十字板剪切试验测定不同龄期土样的抗剪强度和含水率。结果显示,在同样固化剂掺量情况下,使用絮凝-固化联合处理法代替传统单一水泥固化法,能使试样的不排水抗剪强度至少提高5倍以上,证明了采用絮凝-固化联合方法处理表层吹淤泥浆形成表层工作平台的可行性。 相似文献
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吹填软土由于其物质成分和沉积环境千差万别,决定了其工程性质也差别很大,具有区域性特点。本文以大型沉降柱模拟吹填泥浆自然沉积,对天津滨海新区吹填泥浆静水沉降过程中泥水分界面、含水量、孔隙比变化及其沉积后的相关特性进行了探讨,并对其微观结构特征进行了研究。试验结果分析表明:天津吹填土富含粘土矿物,微结构不稳定。在沉积过程中,颗粒分选明显,各项指标前期变化大,后期趋于稳定,总体工程性质差,难以直接满足工程建设的需要,需进行相应的处理。 相似文献
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以吹填砂为覆盖层的饱和软粘土地基强夯试验研究 总被引：1，自引：0，他引：1
针对某港区工程陆域不同区域的地质条件和工程荷载,进行了不同工艺的强夯试验,对夯坑周围地表变形、土体水平位移以及孔压的增长和消散进行了观测,并对强夯加固效果进行了试验研究。研究表明,采用强夯法加固以吹填砂为覆盖层的饱和软土地基是可行的,有效加固深度可达到6 ~7 m,吹填砂层厚度对有效夯击率和碎石土垫层的作用有显著影响。由于吹填砂层和淤泥质粘土层中的粉细砂薄层有利于孔隙水压力的消散,用强夯法处理该类地基时,如果设计加固深度较小时,可以不设置竖向排水体。通过对试验数据的分析研究,获得强夯法加固该类地基土的最佳强夯参数和施工工艺,并且认为选择强夯施工工艺应考虑吹填砂层厚度。 相似文献
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An equivalent homogeneous continuum theory is developed for modelling discretely drained soil stratum. The model accounts for the local horizontal flow to discrete vertical drains such as wick or sand or stone columns as well as direct vertical drainage of the soil and global horizontal flow due to non-uniform horizontal conditions. Calibration curves for the model are presented for the case of no soil smear due to the drain installation and for the case when smear exists. The model is implemented in both analytical and finite element analyses for those cases where no well resistance is present and when it is of importance. The accuracy and applicability of the model is demonstrated for simple one- and two- layered problems including smear and well resistance. 相似文献
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袋装砂井爆夯法处理软土地基是利用炸药在设置有排水通道的软土中爆炸产生冲击和振动而使土体加固的方法。针对该法进行理论研究,提出了一种将袋装砂井爆夯处理软土地基的三维问题转化为二维平面应变问题的数值模拟方法：袋装砂井转化为等价砂墙;利用等效冲量原理,炮孔爆炸压力则转化为等效压力墙。数值模拟中考虑了土体骨架变形与孔隙水非达西渗流的耦合。对数值模拟的现场试验验证分析表明,沉降数值分析的结果与铁路宁启线软基处理现场测试结果具有很好的可比性。所提出的数值分析方法可模拟袋装砂井爆夯处理软土地基的超静孔隙水压产生和消散以及土体沉降变形的动态过程。 相似文献
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The existence of thick compressible varved clayey silt deposits along the Delaware River presents one major obstacle for design and construction of structures or industrial facilities in this region. To understand the characteristics of this thick weak soil layer and then develop reliable soil parameters for future earthwork design and construction, a comprehensive soil testing program was carried out. The program consisted of both in situ tests [e.g., standard penetration test borings, piezocone penetration test (CPT) soundings, Marchetti flat dilatometer test soundings, seismic shear wave test soundings, CPT pore pressure dissipation tests, and field vane shear tests] and laboratory tests (e.g., soil index tests, consolidation tests, triaxial tests, and chemical tests). Additionally, a field surcharge test program with and without installation of wick drains was carried out to investigate the compressibility of the thick clayey silt deposit and the efficiency of wick drains to help accelerate consolidation. The field and laboratory test results showed that the varved clayey silt deposit was normally consolidated to slightly overconsolidated and moderately to highly compressible. Its physical properties were intermediate between those of Savannah muddy clay and Shanghai soft clay, while much closer to that of Shanghai soft clay. Due to its lamination structure in the horizontal direction, the horizontal consolidation coefficient of the varved clayey silts was significantly greater than that in the vertical direction. The measured undrained shear strength of the varved clay silt almost increased linearly with depth. The installation of wick drains in the thick clayey silt deposits accelerated primary consolidation, but showed no effect on the secondary consolidation under constant loading. The findings obtained from this study will be beneficial for future design and construction of earthworks along the Delaware River. 相似文献
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相对于其他土层,盾构在富水砂层中掘进的风险更大,但目前盾构掘进引起砂层变形的机制并不清楚。依托广州某电力隧道项目,选取一典型富水砂性地层断面对盾构隧道施工引起的地层变形进行高频率、近距离的监测,得到以下几点认识可供类似的工程参考：（1）富水环境下,相对于均质砂层,隧道处于粉砂+粗砂地层组合更容易发生渗透破坏。此情况下,粉砂层在承受更大渗透力同时,又受粗砂层强烈补给供水,非常容易被侵蚀甚至掏空。（2）地层均匀损失与局部集中损失引起地层扰动规律有较大的不同。地层均匀损失时由于拱效应没集中局部损失的强,其扰动范围、地表沉降及水平位移均更大。水平位移最大值的位置与地层损失的非均匀化也密切相关。地层均匀损失时,隧道两边最大水平位移发生在隧道高程范围内;但地层非均匀损失（隧道顶部局部塌落）时,发生最大的水平位移的位置会明显上移。（3）渗透力的作用使得地层扰动范围扩大。（4）地层损失率受注浆影响严重,隧道附近大,地表最小,隧道上方土体呈松散化趋势。 相似文献
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细砂填料改良技术的试验研究 总被引：1，自引：0，他引：1
秦-沈客运专线某标段的路基填料由洁净、均匀而级配不良的细砂组成,为满足《秦-沈线铁路路基施工技术细则》[1]的质量要求,施工单位在对该填料进行大量的改良对比试验基础上,探索出了经济合理的细砂改良技术方案,按此配方及施工工艺完成了数百万方的路基施工填筑任务,为细砂改良积累了大量的技术数据和宝贵经验。通过对细砂填料改良的试验研究,发现了文献[1]的某些规定和检测指标尚须进一步商榷和改进。笔者从理论和实践上对匀粒细砂改良的必要性、文献[1]双指标控制标准等问题提出了质疑,揭示和阐述了匀粒细砂K30值偏小的内在原因和填料强度随填筑深度的变化规律。 相似文献
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排水是岩土体及工程构筑物渗流控制的主要措施之一,其实质是通过在渗流域内形成潜在溢出边界或低水位边界而实现渗流控制的。在排水渗控条件下,渗流场往往具有强烈的边界非线性特征,Signorini型变分不等式方法从理论上为稳定和非稳定排水渗流问题提供了有效的分析方法,但其实际效果还需要得到试验的验证。通过开展含5个排水廊道的排水砂槽模型试验,研究了复杂排水条件下砂土渗流的基本规律,并通过试验数据与数值计算成果的对比分析,论证了Signorini型变分不等式方法的有效性和正确性。试验结果表明,在稳定渗流条件下,排水砂槽上游侧3个排水廊道对渗流控制起主导作用,而下游侧2个廊道则失去排水功能,数值计算与试验成果吻合较好;在非稳定渗流条件下,受测压管精度、砂样均匀性和毛细效应的影响,数值计算与试验成果存在一定偏差,但也较好地揭示了复杂排水条件下砂槽中的非稳定渗流特征。排水砂槽试验结果验证了Signorini型变分不等式方法的有效性和正确性,为复杂排水条件下岩土体及工程构筑物的渗控结构优化设计提供了有效的分析手段。 相似文献
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本文主要介绍拟建于严重液化场区内高层建筑地基处理的研究成果。研究表明:采用袋装砂井处理,能够收到防液化效果,但应注意时间效应;当地震烈度为7°时,对桩基础的高层建筑,只需利用沉桩作用,即可获得较好的抗震加固效果;若袋装砂井与沉桩共同作用进行处理,其抗震加固效果尤为理想,即使当地震烈度达到8°时,也不会产生液化现象。 相似文献
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考虑3种非线性关系的径向排水固结解析解 总被引：1，自引：0，他引：1
大部分砂井及排水板固结解析解理论结合了太沙基一维固结理论, 把土体考虑成线弹性问题, 而研究发现, 软土在等向固结条件下平均有效应力和水平渗透系数与孔隙比成半对数线性关系。同时, 实验表明, 在塑料排水板周围的涂抹区中水平渗透系数成抛物线状分布。因此, 为了充分考虑这些非线性的影响, 推导出了该问题的解析解, 并通过退化验证了该解析解的正确性。同时, 还对参数Cc/Ck和对固结速率的影响进行了分析, 结果表明:当Cc/Ck1时, 固结速率较快; 当Cc/Ck1时, 固结速率较慢; 参数增加, 固结速率逐渐变小。 相似文献
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