粉喷桩联合土工格栅加固桥头软基试验研究

软基桥头跳车是目前公路建设中常见的通病之一。通过对实际工程中水泥粉喷桩联合土工格栅处理的桥头软基进行监测与分析认为:填土过程中的应力分配是一个逐渐调整的过程,粉喷桩承受了大部分的上覆荷载,桩土在整个受荷过程中是相互协调共同发挥作用,并能有效减少加固区沉降量与桥台连接处的差异沉降;土工格栅在整个施工过程中,通过调整荷载分配,提高地基的承载力和整体稳定性,从而减少路基沉降;粉喷桩联合土工格栅处理桥头软基的方法对减少侧向位移也是有良好效果的。因此,粉喷桩联合土工格栅是一种良好的软基处理方法,对桥头软基处理,消除桥头跳车病害具有重要指导意义。     

侧向粉喷桩变刚度处治桥头跳车效果研究

为了解决因软土路基不均匀沉降引起的桥头跳车问题,依托G15沈海高速八字桥段工程,提出了侧向粉喷桩变刚度非开挖处治方案,首先采用二维数值模拟得出粉喷桩不同处治深度的影响规律,然后采用三维数值模拟对设计方案进行了分析验证。结果表明:沉降主要发生在淤泥层,随着粉喷桩处治深度的增加,沉降控制效果逐渐变好,当桩长为42 m时,处治深度贯穿整个淤泥层,沉降控制效果最好;侧向粉喷桩较好地约束了路基土体的侧向水平位移,与周围土体形成的复合路基的竖向刚度得到增强,因而在路基沉降控制中能够发挥作用;通过对桥头段进行粉喷桩变刚度处治,使得沉降坡度减小,沿线路方向沉降呈现渐变效果,有效地缓解了桥头跳车问题。     

粉喷桩处理桥头软土地基沉降分析

软土地基上建高速公路，为避免桥台背后工后沉降过大造成“桥头跳”的不利影响，介绍采用粉喷桩加固处理软土地基。阐述了粉喷桩加固机理，并通过有限元软件模拟计算与实测沉降比较，认为总的趋势是吻合的。粉喷桩加固后显著降低了路堤沉降。     

粉喷桩施工质量控制技术及应用

粉喷桩是进行软土地基处理的一种常用施工方法,结合工程实例,在原材料选用、配合比设计的基础上,详细介绍了粉喷桩施工工艺和技术控制要点,通过实践证明,粉喷桩施工质量控制技术成功应用不但提高了地基承载力,而且保证了地基沉降量和稳定性,使桥头跳车现象得以控制。     

粉喷桩在高速公路软基处理中的应用研究

在高速公路软基处理中，粉喷桩复合地基是结构物地基、桥头过渡段等最常用的处理方法。本文通过对大量实际工程的总结和分析，较系统的论述了现阶段粉喷桩在高速公路软基处理应用中存在的不足，并对粉喷桩在高速公路软基处理中常见问题进行剖析，提出了一些防范措施。针对粉喷桩在高速公路软基处理应用中亟待解决的问题，提出了合理的建议。     

沉管灌注筒桩在处理高速公路桥头软基的应用

介绍了杭-宁高速公路长兴段沉管灌注筒桩(简称筒桩)处理高速公路桥头车的试验研究。通过桩身质量检测,高、低应变测试,竖向和水平向静载等试验,证明筒桩的成桩质量可靠。从桩土荷载、孔隙水压力、表面沉降、分层沉降、水平位移等方面对 4 个监测断面进行了观测。综合分析表明,与塑料排水板、粉喷桩等处理方法相比,筒桩处理桥头软基具有技术优越、经济合理等优点。     

CFG桩在处理高速公路软基中的应用

桥头跳车是桥台和路基之间产生差异沉降引起车辆行驶颠簸的一种现象,减缓桥头跳车现象是困扰工程界的一个难题。很多学者对桥头跳车现象产生的机理和解决措施进行了研究,虽然桥头工后沉降过大的问题得到了较好地解决,但是在处理路段与未处理路段衔接处。又产生了新的沉降突变,即所谓的“二次跳车”,选择合适的地基处理方法来处理这个问题,是减缓桥头跳车问题的关键所在^[1-5]。     

软基路基路面施工设计需注意的若干问题

本文结合软基路基路面施工过程中出现的一些问题及工期紧张的实际情况,讨论软基路基预压期的确定、填土速率的控制标准、桥头软基处理和桥台桩基施工、粉喷桩的检测时间和强度控制标准、软基路段路面铺筑和加速浅层软土地基沉降等工程实际问题,提出软基施工中有关的决策应经过科学地论证确定。     

深层搅拌桩在高等级公路软土地基的设计与应用

通过介绍佛山一环南延线高等级公路软土地基加固处理工程设计和施工,阐述了高等级公路采用粉喷桩复合地基加固处理软土地基的设计方法、施工工艺及质检办法,提出在深厚淤泥层上修建高等级公路在设计上应合理确定的主要参数,以及如何通过调整置换率和加固深度达到适应高等级公路沉降过渡要求,从而解决桥头路段"跳车"问题.     

"Y形沉管灌注桩"将有效解决软基处理难题

软土地基处理不当引发的“桥头跳车”是困扰南方许多地区高速公路建设的顽症之一。近日通过浙江省科技厅试验鉴定的“Y形沉管灌注桩”工艺不仅能控制软土地基的沉降,还能大幅度降低造价。目前南方许多地区在高速公路建设的软土地基处理中,都应用预应力管桩、粉喷桩和塑料排水板     

Numerical study of creep effects on settlements and load transfer mechanisms of soft soil improved by deep cement mixed soil columns under embankment load

Deep cement mixed (DCM) soil columns have been widely utilized to improve soft soil to support embankments or seawalls. However, the influence of the time-dependent behavior of the soft soil on the performance of DCM column-supported embankments is not well understood. In this study, the finite element (FE) model was established to investigate the creep effects on settlements and load transfer mechanisms of the soft soil improved by DCM columns under embankment load. Comparisons were conducted for the cases of the soft soil with or without creep. The parametric analysis demonstrated that the area replacement ratio and Young's modulus of the DCM column can largely influence the long-term behaviors of the DCM column-improved composite ground. The numerical results were also compared with the results calculated by German design method (EBGEO) and British design method (BS 8006). Regarding the vertical stress taken by the DCM column, EBGEO method provides a lower limit while BS 8006 method provides an upper limit.     

Displacements of column-supported embankments over soft clay after widening considering soil consolidation and column layout: Numerical analysis

The common challenges for constructing embankments on soft clay include low bearing capacity, large total and differential settlements, and slope instability. Different techniques have been adopted to improve soft clay, such as the use of foundation columns including stone columns, deep mixed columns, and vibro-concrete columns, etc. Due to increased traffic volume, column-supported embankments may be widened to accommodate the traffic capacity need. Adding a new embankment to an existing embankment generates additional stresses and deformations under not only the widened portion but also the existing embankment. Differential settlements between and within the existing embankment and the widened portion may cause pavement distresses. Limited research has been conducted so far to investigate widening of column-supported embankments. In this study, a two-dimensional finite difference numerical method was adopted. This numerical method was first verified against field data and then used for the analysis of widened column-supported embankments over soft clay. The modified Cam-Clay model was used to model the soil under the existing embankment and the widened portion. Mechanically and hydraulically coupled numerical models were created to consider the consolidation of the foundation soil under the existing embankment and the widened portion. Different layouts of foundation columns under the existing embankment and the widened portion were investigated. The numerical results presented in this paper include the vertical and horizontal displacements, the maximum settlements, the transverse gradient changes, and the stress concentration ratios, which depended on column spacing. The columns installed under the connection side slope were most effective in reducing the total and differential settlements, horizontal displacement, and transverse gradient change of the widened embankment.     

Consolidation of soft clay foundation improved by geosynthetic-reinforced granular columns: Numerical evaluation

Soft clays are problematic soils as they present high compressibility and low shear strength. There are several methods for improving in situ conditions of soft clays. Based on the geotechnical problem's geometry and characteristics, the in situ conditions may require reinforcement to restrain instability and construction settlements. Granular columns reinforced by geosynthetic material are widely used to reduce settlements of embankments on soft clays. They also accelerate the consolidation rate by reducing the drainage path's length and increasing the foundation soil's bearing capacity. In this study, the performance of encased and layered granular columns in soft clay is investigated and discussed. The numerical results show the significance of geosynthetic stiffness and the column length on the embankment settlements. Furthermore, the results show that granular columns may play an important role in dissipating the excess pore water pressures and accelerating the consolidation settlements of embankments on soft clays.     

高速公路通道软基低强度混凝土桩处理试验研究

在国内首次采用低强度混凝土桩复合地基加固高速公路通道深厚软土地基,解决通道地基处理中的二次开挖、桥头跳车等问题。介绍了在杭宁高速公路通道地基低强度混凝土桩处理中进行的桩土应力、桩土表面沉降、分层沉降、侧向变形等项目的现场测试成果,并以此对路堤荷载作用下低强度混凝土桩复合地基的性状及其处理效果进行分析。     

软基上住宅建筑的不均匀沉降

本文根据福州火电厂软基上住宅工程的沉降观测资料,结合本地区的工程经验与作者的实践体会,探讨软基上住宅建筑与建筑群出现不均匀沉降的原因及其分布特征,对地基基础设计规范与施工规范的有关规定加以讨论,并总结出一些用以减少住宅建筑不均匀沉降的技术措施。     

Probabilistic analysis of settlements under a pile foundation of a road bridge pylon

The paper addresses the reliability change of a road bridge pile foundation due to the unpredictable increase of settlements in time. The analysis is based on the R?dziński Bridge in Wroc?aw, Poland, its design assumptions, and monitoring results. The bridge foundation rests on a multi-layered subsoil assumed random. The Finite Element model of the subgrade is generated in ZSoil® software. To simplify the probabilistic approach, substitute soil strata stiffness parameters are adopted. Tracing their time decrement allows for a comprehensive definition of the entire foundation over-settlement produced by numerous factors. Preliminary sensitivity analysis of settlements to the stiffness variation properly simplifies the random model. The Serviceability Limit State helps to assess the foundation reliability index, further compared with the condition in the EN 1990:2002/A1:2005 standard. In addition, real-life settlements are also measured in the first year of bridge operation, they are used to calibrate the reliability index assessment. An innovative approach is proposed, where appropriate time-wise fluctuation functions represent the expected settlement increase and the related reliability reduction. These fluctuation functions help to plan the future remedial actions to maintain the initial bridge safety and to indicate the action frequency and scope. Future reliability levels may be extrapolated too. The real-life survey database of settlements makes it possible to validate the results of probabilistic calculations. A dedicated flowchart is devised to support further analysis of a wide structural domain.     

某高速公路桥头路段不同软基处理加固效果分析

高速公路桥头路段由于不均匀沉降带来的问题一直困扰着软土地基高速公路的建设,怎样使得桥头路段的地基处理方式既可以达到沉降控制的目的又可以达到节约建设经费的目的,是桥头路段软基处理的一个难点。基于某高速公路桥头路段现场沉降观测资料针对塑料排水板、水泥搅拌桩、塑料套管桩和预应力管桩处理方式,分别分析了处理深度6,8,13和27m的加固效果,结合每种处理方式在工程中的适用范围和每平方米造价,总结出一定处理深度范围内的桥头路段采用某一种处理方式能够达到加固效果和经济效果。     

混凝土芯砂石桩复合地基技术在处理桥头深厚软基中的应用

针对目前桥头段深厚软基处理方法的缺陷与不足,从控制工后沉降重要理念出发,介绍了混凝土芯砂石桩复合地基技术控制桥头段深厚软基工后沉降的设计思想、施工设备、施工工艺及检测与质量控制方法。该技术特别适合于高含水量、高有机质含量地区对工后沉降有严格要求的深厚软基处理。     

路堤荷载下砼芯水泥土搅拌桩复合地基现场试验研究

针对砼芯水泥土搅拌桩复合地基处理高速公路深厚软土段的工程实例,通过地表沉降、分层沉降、深层水平位移、砼芯荷载以及桩土应力比测试,讨论了砼芯水泥土搅拌桩处理深厚软土地基的加固效果,荷载分布和传递规律。测试结果表明：砼芯水泥土搅拌桩对于路基沉降和水平位移控制效果优于水泥土搅拌桩,且横断面差异沉降较小。复合地基的主要压缩量发生在桩顶至砼芯底端一定范围的土体内,沉降发生深度由砼芯控制。砼芯水泥土搅拌桩上部出现负摩阻力,中性点位于砼芯1/3长度处。桩土应力比为水泥土搅拌的2～3倍,与刚性桩相近,桩体承担大部分路堤荷载。砼芯水泥土搅拌桩复合地基排水通畅,超静孔隙水压力消散迅速。路堤荷载下砼芯水泥土搅拌桩工作特性与载荷板试验下的测试结果有所不同。最后从沉降和承载力控制角度给出了砼芯水泥土搅拌桩复合地基的设计方法     

Analyse numérique et expérimentale du comportement des ouvrages fondés sur un sol mou renforcé par des colonnes ballastées flottantes

This paper work is in the frame of the study about the reduction of settlements in the case of floating columns. The prediction of a settlement remains a prickly problem to which geotechnical engineer is confronted. Experience has shown that structural pathologies are caused by the effects of excessive differential settlements before reaching soil bearing capacity. To palliate this problems in the case of soft and compressible soils, we advocate, as an alternative solution, piles or the reinforcement of the soils with stone columns. This strengthening method, introduced in Algeria in 1999, is economical. However, it does not inihilate settlements but it speeds up the time factor. Numerical modelings by finite element method (FEM) have been carried out through interest into all mechanical and geometrical aspects that are inherent in the meshing of floating stone columns. An analytical formulation of a correction coefficent (μβ) and an abacus of the settlement reduction factor (β) has been suggested. On the other way, the monitoring instrumentation of experimental site since 2008 to 2017 at the level of the harbour lowland of Bejaia has been carried out. It concerns important storage structures fonded on a very compressible ground reinforced by floating stone columns. The records of the settlements at the scale of the structures, according to variable loads recorded in real time, have revealed excessive settlements under the effects of variable stresses from 1 to 3 bars. An exhaustive geological, geotechnical and geomechanical analysis has been carried out for the characterization of the grounds, and numerical modelling by finite element method (FEM) has been carried out. The experimental and numerical investigation of the concerned structures at issue allowed us to confront the results with regard to settlement prediction of an environment reinforced with floating stone columns. The result is a perfect matching in relation to the suggested formula.