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Acta Geotechnica - Prefabricated vertical drains (PVDs) and deep cement mixing (DCM) columns combined ground improvement with a vacuum pressure for embankment construction on soft clay deposits has... 相似文献
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Numerical prediction of the creep behaviour of an unstabilised and a chemically stabilised soft soil
This paper examines the ability of volumetric and deviatoric creep laws associated with constitutive models to simulate the creep behaviour of a soft soil in its natural state or chemically stabilised state. Initially, the models/laws are validated by oedometer and triaxial creep tests, for the stabilised and unstabilised soils. Finally, the long-term behaviour of an embankment built on a soft soil reinforced with deep mixing columns is predicted based on the properties for a curing time of 28 days. The results show that the creep phenomenon should be considered in a long-term analysis of deep mixing columns. 相似文献
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在劲芯水泥土桩承载路堤的工程应用中,芯桩比外桩短的情况比较普遍。但是,人们对短芯劲芯水泥土桩承载路堤的桩体破坏模式和失稳破坏机理的认识较为欠缺,无法合理评价路堤的稳定性。鉴于此,本文通过室内模型试验,开展短芯劲芯水泥土桩承载路堤失稳破坏模式研究。通过监测芯桩导电通路变化、芯桩桩身应变和桩土竖向应力,并结合PIV技术,综合分析桩体渐进式破坏模式和路堤整体失稳规律。研究结果表明,在路堤顶面下,荷载主要由芯桩承担,并随着超载增加,芯桩外桩荷载分担作用减小,但路堤失稳后芯桩仍具有一定荷载分担作用。在路堤失稳破坏过程中,路堤下桩体表现出受压破坏且芯桩底部局部鼓胀破坏,坡面下桩体表现出压弯和拉弯破坏模式,地基滑动面并不完全穿过桩体破坏位置。 相似文献
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水泥土搅拌桩施工扰动评价的一种方法 总被引：2，自引：0，他引：2
水泥土搅拌桩广泛应用于高速公路软土处理工程中,但是在工程实践中发现水泥土搅拌桩施工会对桩周土产生扰动使地基土强度降低从而导致路基路面产生开裂。水泥土搅拌桩这类非挤土桩其施工扰动方面研究比较少,为此展开水泥土搅拌桩施工对桩周土的扰动研究。围绕水泥土搅拌桩施工性状,采用圆孔扩张理论分析了施工过程中桩周土受力,采用Sekiguchi和Ohta（关口-太田）模型计算了桩周土体积应变,根据Hong和Onitsuka扰动度的定义得到了搅拌桩施工桩周土的扰动度变化。结果表明水泥土搅拌桩施工对桩周土的扰动随深度的增大和距桩边距离增大而减小,该分析结果与静力触探现场测试得到的锥尖阻力变化规律一致。 相似文献
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为全面考虑路堤荷载下搅拌桩复合地基的桩土非等应变特性,将路堤、桩体、桩间土及下卧土层整体考虑,在总结前人试验结果基础上提出简化的桩土应力比和桩土差异沉降两阶段模型,改进了现有的桩顶平面处的桩土应力比计算方法。根据实际的应力状态计算桩侧摩阻力,计算桩土荷载分担,进而得到桩体和桩间土沉降。通过各子系统界面处的位移和应力边界条件考虑其相互作用,得到了路堤荷载下搅拌桩复合地基总沉降计算模型。对比淮盐高速公路试验段搅拌桩复合地基的实测沉降、文中模型以及传统复合模量法计算结果,验证了该模型的正确性,结果表明模型计算沉降与实测数据吻合,较常规的复合模量法计算结果更接近实测值。 相似文献
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Increased traffic volume has made it necessary to increase highway capacities by widening embankments and pavements. Adding a new embankment to an existing embankment induces additional stresses and deformations beneath the widened and existing portions of the embankment. Differential settlement may develop between and within the new and existing portions of the embankment, especially over soft soils. This differential settlement often causes pavement distress, such as longitudinal cracks or the drop-off (or sinking) of pavement sections. Different techniques have been adopted to remedy these problems, including the use of foundation columns, such as deep mixed columns, vibro-concrete columns, stone columns, and aggregate piers. However, design procedures for foundation columns constructed for this purpose are not well developed. The analyses of eight cases of column-supported widened embankments and two untreated foundations are presented in this paper. The factors considered include the consolidation of foundation soils under existing embankments and the spacing, region, and modulus of foundation columns. Two-dimensional finite difference software was used after the calibration of the model against a field case study and numerical analyses were conducted to investigate stresses and deformations of the widened embankments over soft soil with or without the remediation of foundation columns. The results presented in this paper include the vertical and the horizontal displacements, the maximum settlements, the transverse gradient change, and the distribution of the additional stresses induced by the widening. Recommendations are made for the design of foundation columns to remedy roadway pavement failure due to widening of embankments. 相似文献
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This work studies the effect of the curing time on the creep behaviour of a stabilised soft soil, using volumetric and deviatoric creep laws associated with constitutive models. Results of unconfined compressive strength tests for several curing times are used to define the time evolution of the mechanical and creep properties. The models/creep laws are validated by oedometer and triaxial creep tests, for 28 and 90 days of curing. The long-term behaviour of an embankment built on a soft soil reinforced with deep mixing columns shows that the effect of curing time decreases the settlement and increases the improvement factor. 相似文献
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《Geomechanics and Geoengineering》2013,8(1):49-55
Stability of levees is critical to the safety of human and structures, especially at high water levels. Levees may fail due to the existence of soft soil foundations or seepage of water through the levees or rapid drawdown. Deep mixing technology has been considered one of the good alternatives to solve foundation and seepage problems while geosynthetics can be used to stabilize slopes during rapid drawdown. Studies have shown that deep mixed columns and geosynthetics can increase the stability of highway embankments over soft soils. In those studies, however, no ponding water exists on either side of the embankment, which is not the case for levees. Experimental studies have shown that deep mixed columns under a combination of vertical and horizontal force could fail due to shear or tension/bending or rotation. A finite difference method, incorporated in the FLAC (Fast Lagrangian Analysis of Continua) Slope software, and a limit equilibrium method (specifically Bishop's method), incorporated in the ReSSA software, were adopted in this study to investigate the stability of the levee with ponding water or under rapid drawdown. In this study, deep mixed columns were installed in continuous wall patterns, which were modeled as 2D deep mixed walls. Geosynthetic layers were modeled using cable elements with grout properties between geosynthetic and soil in the numerical analysis. Mohr-Coulomb failure criteria were used for the levee, the soft soil, and the deep mixed walls. The stability of a levee at different stages (end of construction, average service condition, high water surge, and rapid drawdown from the service condition and the highest water level condition) was examined. The study clearly demonstrated that the deep mixed walls can enhance the stability of the levee by providing shear/moment resistance and hindering seepage through the levee and geosynthetics can enhance the riverside slope stability of the levee by providing tensile resistance to the soil. 相似文献
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The mechanism of bending failure and the magnitude of the bending moment in a column formed by cement deep mixing (CDM) under an embankment load were investigated by a series of three-dimensional (3D) finite element analyses. Based on the numerical results, a design method to consider the bending failure of the CDM column has been established. The usefulness of the proposed methods was verified using the results of two centrifuge model tests of the embankments on the CDM column improved soft model ground model reported in the literature, and the columns had tensile cracks or showed complete failure. 相似文献
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劲芯水泥土桩是一种软土地基处理的新方法,近年来已成功应用于公路、铁路路基处理工程中。然而由于人们对其承载路堤的失稳破坏机制认识不足,无法正确指导设计。采用反映桩体材料破坏后特征的应变软化模型,模拟劲芯水泥土桩承载路堤失稳破坏1g模型试验,通过分析路堤失稳破坏过程中桩体塑性区的开展和桩身受力的变化情况,研究了桩体的破坏顺序及其破坏模式。结果表明：路堤失稳过程中,劲芯水泥土桩并非同时发生破坏,路面正下方桩体首先发生受压破坏,坡面下方桩体自坡脚至坡肩依次发生弯剪破坏;由于桩体的存在,路基中滑动面并非完全穿过桩体破坏位置。基于桩体破坏顺序、破坏模式、受力情况变化,以及荷载传递规律,阐释了劲芯水泥土桩承载路堤渐进式失稳破坏机制。采用现行规范中基于残余强度的柔性桩处理方法,计算的安全系数与试验结果较为接近,但其适用性还需做进一步研究。 相似文献
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The aim of this paper was to determine the ultimate vertical bearing capacity of rectangular rigid footings resting on homogeneous peat stabilized by a group of cement deep mixing (CDM) columns. For this purpose, a series of physical modeling tests involving end-bearing and floating CDM columns were performed. Three length/depth ratios of 0.25, 0.5, and 0.75 and three area improvement ratios of 13.1, 19.6, and 26.2 % were considered. Bearing capacity of the footings was studied using different analytical procedures. The results indicated that compared to unimproved peat, the average ultimate bearing capacity (UBC) improvement of floating and end-bearing CDM columns were 60 and 223 %, respectively. The current study found that simple Brom’s method predicted the UBC of the peat stabilized with floating CDM columns with reasonable accuracy, but underestimated the UBC by up to 25 % in the case of end-bearing CDM columns. Published laboratory experiences of stabilizing soft soils using soil–cement columns were also collated in this paper. 相似文献
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深长变径搅拌桩荷载传递规律的试验研究 总被引：2，自引：0，他引：2
采用一种新型的地基处理方式--变径水泥土搅拌桩,处理了浙江省湖州地区深达20多米的深厚软土地基,通过对载荷试验和桩身应力实测资料的分析,研究了深长变径搅拌桩的承载特性和荷载传递机制。研究表明,受到桩身强度的限制,荷载沿桩身传递限定在一定范围内;由于桩径的变化,桩身应力在变截面处出现了应力集中现象;桩身轴力沿深度逐渐衰减,且在变径位置以上桩体衰减速率较下部快;最大侧摩阻力发生在桩顶附近,在变径处附近由于扩大头端承作用而锐减,但变径位置以下一定深度范围内的桩侧摩阻力得到提高;扩大头端承力随桩顶荷载的增加而逐渐变大,但占总荷载的比例不大,桩侧摩阻力仍提供了大部分的承载力,因此变径水泥土搅拌桩属于有支点端承力的摩擦桩。结合3种不同单桩破坏模式,提出了深长变径搅拌桩的单桩极限承载力计算公式,经过试算发现与现场试验结果相差在10%以内,计算结果可靠,可推广应用于实际工程中。 相似文献
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A multi-column composite foundation is a new concept utilizing different column types with varying lengths and diameters to support the embankment fill and to mobilize the strength and stiffness of the soil at shallow depths. This study presents the results of finite element analyses using the finite element software PLAXIS to investigate the consolidation behavior of a road embankment constructed on a multi-column composite foundation. The finite element results are calibrated for a period of 200 days. The settlement, horizontal displacement, differential settlement, column axial force, and the development and dissipation of excess pore pressure are presented and discussed in detail. It is concluded that a multi-column composite foundation allows a fast rate of consolidation and significantly increases the embankment stability. A multi-column composite foundation formed by CFG–lime columns is more effective than one formed by SC–lime columns. The CFG–lime columns improve the long-term stability of the embankment because the compression modulus of CFG columns is significantly greater than that of SC columns. 相似文献
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在对半挖半填路堤病害及成因分析的基础上,分析了加筋路堤格栅工作机制。通过现场试验,对采用格栅加筋法处理的路堤挖填交界区域进行了原位观测,观测了路堤填土完成时路面沉降、竖向土压力及格栅变形情况。通过建立有限元分析模型,对路堤填筑完成时格栅的拉力及位移进行了分析,并对不同路面荷载和格栅刚度条件下,格栅的拉力与位移进行了计算。结果表明：路堤挖填交界处铺设格栅后,路面局部差异沉降较小。填方区域格栅底部土压力与填土自重应力相当,格栅存在有效加筋长度,在挖填交界面附近产生较大变形和拉力。上层格栅比下层格栅沉降曲线平缓,下层格栅的拉力在交界区域会陡然增大。路面荷载对格栅拉力和位移有一定影响,随埋深增加影响减小,格栅的竖向位移随着荷载增大略有增大,格栅在挖填交界面附近拉力增大。随格栅刚度增大,其拉力也增大,而位移变化很小。 相似文献
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为明确填方路堤荷载下强夯碎石墩的变形特征与其路堤稳定性的内在关联,针对“山地型”软土地区某高速铁路车站高填方路堤的失稳破坏现象,基于现场实测数据和三维数值分析模型,着重研究了不同位置强夯碎石墩墩体的鼓胀变形与侧向弯曲变形规律,并定义墩体鼓胀率和最大侧向弯曲值对其变形特征予以描述。研究结果表明:路堤荷载作用下不同位置的强夯碎石墩发生不同程度的鼓胀变形和侧向弯曲变形,其中鼓胀变形主要由上覆路堤荷载所产生的压缩鼓胀和路堤侧滑所产生的滑动剪切鼓胀所组成,且其最大鼓胀变形区域集中在距桩端1~2倍桩直径范围内;位于强夯碎石墩复合地基潜在滑裂面剪入口附近墩体的鼓胀率最大(0.75%),约为路堤中心处墩体鼓胀率的1.5倍,表明该处以滑动剪切鼓胀变形为主。沿路堤中心线向外不同位置的强夯碎石墩墩体的最大侧向弯曲变形的发展规律近似呈三段线模式,其中潜在滑裂面剪入口附近的17#墩体为其侧向弯曲变形开始陡增的拐点,表明17#与其附近墩体为控制路堤侧向变形与稳定的关键构件。路堤填筑过程中所出现数条裂缝的原因可能在于强夯碎石墩的剪切破坏而致使路堤出现整体滑移所引起的,建议在采用散体材料桩复合地基处治“山地型”软弱地基时,应配合其他加固措施以确保填方路堤的整体稳定性。 相似文献
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为探究荷载作用下软土地基直接拼接拓宽路堤受力和变形特征,利用自行设计制造的模型试验系统,通过改变软土地基差异沉降、土工格栅加铺层数对软土地基高速公路直接拼接路堤进行一系列模型试验,研究各种工况下旧路与新拓宽路堤土中应力变化。试验结果表明,拓宽路堤在荷载作用下新旧路各断面土中竖向应力随着荷载的增大而增大,受路堤填土边坡与下伏地基侧向约束条件的影响,荷载作用下土中竖向应力在填土路堤与地基内沿深度方向呈现先减小、后增大、再减小的分布特征;软土地基拓宽路堤差异沉降对新旧路结合部位土中竖向应力影响较大,土中竖向应力随着差异沉降增大而增大;旧路范围内土中竖向应力受差异沉降的影响不大;在拓宽路堤填土的顶部和底部各布设一层土工格栅加筋层时可明显减小路堤土中竖向应力和路堤沉降：相同荷载作用下对比无加筋路堤,铺设2层土工格栅加筋路堤的顶面沉降最大可以减少62%,土工格栅加筋对软土地基拓宽路堤沉降有较好的控制作用。 相似文献
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高速公路拓宽工程沉降控制复合地基优化设计 总被引：4，自引：0，他引：4
按沉降控制设计理论,结合有关公路设计规范、路面功能性和结构性的要求以及有限元法分析路基差异沉降引起路面附加应力的计算结果,提出了采用工后路基路拱横坡度变化小于等于0.45 %作为软土地基上高速公路拓宽工程的容许新老路基差异沉降控制标准。采用有限元法对佛山-开平高速公路拓宽工程标准断面进行分析,采用不同参数计算出水泥土搅拌桩复合地基的新老路基差异沉降。根据沉降控制标准,优化出既满足新老路基差异沉降控制要求,又效益最优的高速公路拓宽工程软土路基水泥土搅拌桩处理的设计参数,即工程水泥土搅拌桩采用面积置换率为8.9 %(对应桩间距1.6 m),桩长8 m,桩径为0.5 m,水泥掺入比为15 %;实际使用时,考虑桩土存在一定的不协调,可适当提高桩体面积置换率达10.1 %（对应桩间距1.5 m）。 相似文献