Deterioration mechanism and rapid detection of performances of an existing subgrade in southern China

To relieve the increasing traffic load, many early built highways need to be widened or reconstructed. The rapid performance detection to existing subgrades is important to their reasonable evaluation and maximized utilization. Based on five kinds of soils taken from an existing highway in southern China, three commonly detecting methods were used to determine their moisture contents, compaction degrees and resilient moduli. The results showed that the measured moisture contents were greater than the design value, and the compaction degrees decreased sharply compared to the original ones. The moisture and heat exchange produced a decrease in the resilient modulus of plate loading test(PLT) from the standard 60 MPa down to 40 MPa. Afterwards, the portable falling weight deflectometer(PFWD) and dynamic cone penetrometer(DCP) were used to evaluate the subgrade performances. The measured PFWD moduli and the DCP penetration rates were correlated with the resilient moduli of PLT, deflections of the Beckman beam test, compaction degrees and moisture contents. The correlation analysis indicates that both of two methods are suitable in rapid detecting subgrade performances, but PFWD method is more recommended for it has higher accuracy and efficiency.

Settlement patterns of mountainous half-filled and half-cut widened subgrade with retaining wall

The settlement of widened highway subgrade in mountainous area is not only affected by the interaction between new and existing subgrade, but also seriously restricted by the external retaining wall. Based on the practical engineering of half-filled and half-cut widened mountainous highway subgrade with external balance weight retaining wall(BWRW), a sophisticated finite element numerical model is established. The evolution law of subgrade settlement is revealed during the whole process of new subgrade filling and BWRW inclination after construction. The settlement component of subgrade is clarified considering whether the existing pavement continues to be used. The results show that the additional settlement caused by the BWRW inclination after construction cannot be ignored in the widening and reconstruction of mountainous highway subgrade. In addition, pursuant to the comprehensive design of subgrade and pavement, the component of subgrade settlement should be determined according to whether the existing pavement continues to be used, while considering the influence of BWRW inclination after construction. When the existing pavement continues to be used, the settlement of the existing subgrade is caused by the new subgrade filling and the BWRW inclination after construction. On the contrary, the settlement is only caused by the BWRW inclination after construction.

Field monitoring of differential frost heave in widened highway subgrade

In cold regions,the widened subgrade could produce uneven frost heave that is detrimental to the pavement.This study investigates the differential frost heave characteristics in a widened subgrade.The field monitoring system mainly consists of temperature,moisture,and displacement sensors and distributed optical fiber cables for strain measurement.The monitoring results show that the cooling period in the subgrade is longer than the warming period.Water content in the subgrade changes significantly within 0−2 m below the subgrade surface but stabilizes within 2−5 m.The maximum frost heave occurs from February to March.In comparison,the existing subgrade has a longer freezing period and larger heave value,caused by the higher density and water content inside.Water in the existing subgrade migrates into the new one after widening,leading to frost heave reduction in the existing subgrade.Simultaneously,the traffic loads result in the consolidation of the new subgrade,thus reducing the heave value in the second year.In the third year,the water supply from the existing subgrade facilitates the frost heave in the new subgrade.The tensile strain distributions obtained by the distributed optical fiber cables show that the maximum differential frost heave occurs at the joint between the existing and new subgrades.The differential frost heave gradually stabilizes after three years.Finally,an improved frost heave prediction model is developed based on the segregation potential concept and monitoring results.

Current situation and development trend of design methods for subgrade structure of high speed railways

Purpose–This method will become a new development trend in subgrade structure design for high speed railways.Design/methodology/approach–This paper summarizes the structural types and design methods of subgrade bed for high speed railways in China,Japan,France,Germany,the United States and other countries based on the study and analysis of existing literature and combined with the research results and practices of high speed railway subgrade engineering at home and abroad.Findings–It is found that in foreign countries,the layered reinforced structure is generally adopted for the subgrade bed of high speed railways,and the unified double-layer or multi-layer structure is adopted for the surface layer of subgrade bed,while the simple structure is adopted in China;in foreign countries,different inspection parameters are adopted to evaluate the compaction state of fillers according to their respective understanding and practice,while in China,compaction coefficient,subsoil coefficient and dynamic deformation modulus are adopted for such evaluation;in foreign countries,the subgrade top deformation control method,the subgrade bottom deformation control method,the subsurface fill strength control method are mainly adopted in subgrade bed structure design of high speed railways,while in China,dynamic deformation control of subgrade surface and dynamic strain control of subgrade bed bottom layer is adopted in the design.However,the cumulative deformation of subgrade caused by train cyclic vibration load is not considered in the existing design methods.Originality/value–This paper introduces a new subgrade structure design method based on whole-process dynamics analysis that meets subgrade functional requirements and is established on the basis of the existing research at home and abroad on prediction methods for cumulative deformation of subgrade soil.

Stabilized effects of L-S cement-mixed batter pile composite foundation for existed warm frozen soil subgrade

In permafrost regions with warm frozen soil,subgrade thaw-collapse phenomenon commonly occurs,facing thaw collapse problems of the existed frozen soil subgrade,thus it is difficult to use traditional methods such as active cooling and passive protection technology to stabilize the existed warm frozen soil subgrade.This study derives a novel stabilizer method,a long-short(L-S)cement-mixed batter pile composite foundation to stabilize the existed warm frozen soil subgrade.To solve the thawcollapse problems in warm frozen soil subgrade,high water content and large compressibility characteristics were compared between soft soil and warm frozen soils.Theoretical analysis of heat conduction and numerical simulation of finite element model were used to study the freeze–thaw process and evaluate the stabilized effects of the L-S cement-mixed batter piles on the warm frozen soil foundation of the Qinghai-Tibet Highway.Furthermore,the thaw process and mechanical properties of foundation and piles were analyzed by introducing the hydration heat factor in the thermodynamic control equation.The results indicate that the thawing displacement of the existed warm frozen soil subgrade was reduced owing to the“support”and“grasp”effects of the L-S cement-mixed batter piles on the surrounding soil.The composite ground formed by strengthening the warm frozen ground with batter piles could considerably improve the bearing capacity of the existed warm frozen ground,effectively restrain the deformation of the upper embankment,and improve the strength of the ground.The analysis can provide method for the construction design of cement mixing batter pile foundation in cold regions.

支盘桩加固既有填砂路基深层软土的模型试验研究

高速公路改扩建中既有填砂路基深层软土加固时存在路面结构层和施工场地空间限制的问题。首先,提出使用单盘挤扩支盘桩方案进行地基处理,通过挤扩法成盘于桩顶,以期实现不破除路面结构层的情况下达到设置桩顶承台或托板的效果。其次,利用群桩地基物理模型试验模拟一个桩土单元体研究加固方案的承载过程,通过分析桩体、盘体和土体的力学及变形指标研究支盘桩加固既有填砂路堤的承载表现和土体变形特征,最后,考虑土体参数和桩体尺寸推导了既有填砂路基深层软土支盘桩加固方法的二维简化模型。研究结果表明,软土在恒载下桩体轴力和土压力随时间变化调整,原因在于软土的压缩性和砂土的散粒体属性;桩顶轴力总和与恒载大小近似线性正相关,同时支盘直径越大桩顶轴力总和越大、桩承荷载占比越高,试验发现支盘桩加固法的桩承荷载占比约70%。另外,利用所建二维简化模型进行参数分析发现填砂路基中的最小盘间净距与上覆荷载、填砂内摩擦角、深层软土强度指标和支盘桩几何参数相关。

盐渍土既有高速铁路路基压实质量检测

高速铁路路基填料压实标准主要通过压实系数、地基系数、动态变形模量等指标进行控制。对于既有路基,在不破坏路基的条件下,路基内部的控制指标难以有效测试。为评价某海外项目既有路基内部填料压实情况,最大程度减少对既有路基工程的扰动破坏,通过试验段建立了动力触探试验(DPT)锤击数与实测压实系数、地基系数、动态变形模量的拟合关系式,并将其应用于该项目全线路基内部压实质量检测。结果表明:应用该拟合关系式能够避免对既有路基的破坏,节约工期,取得了较好的经济效益。

成南高速公路软土地基高路堤拓宽工程差异沉降及控制标准研究

依托成南高速扩容工程,基于有限元方法,深入研究软土区高填路基拓宽工程差异沉降变化规律及其影响因素,提出适用于成南高速软土区高填拼接路基的差异沉降控制标准.研究表明,施工期在旧路基面会产生向两侧的水平变形和较大的不均匀沉降,极易导致旧路面中心附近产生纵向裂缝;运营期,不同运营时段路基表面累积沉降半幅区呈“勺”状分布,沉降最大值出现在路基拼接处附近,此处的底基层更容易出现拉裂破坏,运营期拼接附近成为路面裂缝的多发区域;填土高度、软基厚度、软土性质对路基面差异沉降影响均非常显著,而新路基模量对差异沉降的影响并不明显;综合考虑路面材料的极限拉应力和疲劳效应组合,对差异沉降控制标准进行了4级分级,以指导工程设计.

新线、帮宽及既有高铁路基系统的沉降及稳定性研究

为指导路基拓宽建设形成新旧路基相互作用系统的设计、分析及评价,以杭台铁路浙江省温岭段新线路基、泡沫混凝土帮宽路基和既有路基系统为工程背景,采用现场监测和有限元仿真相结合的方法,研究该复杂系统的沉降、不均匀沉降和稳定特性。监测表明,新线路基填筑初期,其地基沉降受施工荷载的影响较大,呈现出一定的局部回弹和波动现象;随路基填土厚度增加,该回弹波动逐步减小,仿真沉降与实测沉降最终偏差小于5%。轻质泡沫混凝土帮宽施工期间,既有路基的最大沉降位置逐渐由其路基面中心位置过渡至既有路基与帮宽路基的交接处,且帮宽施工期间既有路基的沉降不足2 mm,其沉降量和沉降速率均远小于报警值。帮宽施工完成后,由于软土层的固结效应,既有路基会经历较长的固结沉降过程,其后续固结沉降占最终沉降的比例可达71.4%。泡沫混凝土帮宽会引起既有路基和帮宽路基产生微量倾斜(倾斜率不足0.05%),不影响既有路基线路和帮宽路基线路的平稳运行及正常排水性能。既有路基和泡沫混凝土帮宽路基的反压护道效应,促使整个路基系统的潜在危险滑动面出现在新线路基的远侧边坡位置。

铁路泡沫轻质土路基挡护结构的优化设计研究

泡沫轻质土在施工场地受限的路基帮宽工程中发挥了独特优势,为进一步优化铁路泡沫轻质土路基挡护结构,在商合杭(商丘—合肥—杭州)铁路肥东站开展工程现场试验,获得了挡护结构的受力特征与变化情况。结果表明:泡沫轻质土浇筑完成后具有良好的自立性及强度,挡护结构所受侧向压力显著降低,挡护结构承受的侧向土压力仅2~5 kPa,土压力系数逐渐减小趋近于0.1,因此泡沫轻质土路基挡护结构主要作用是防止泡沫轻质土的劣化、保护轻质土性能,兼作施工模板,可以根据泡沫轻质土填筑固化前的侧压力和风荷载进行结构优化设计。

拼宽路基水泥搅拌桩加固方案有限元分析方法及应用

预测并控制不均匀沉降是路基拼宽工程需要解决的关键问题。针对新旧路基处理工艺不同、荷载作用历程不同等因素,采用有限元分析等方法,探究适宜的新路基处理工艺、新旧路基共同受力及相互影响机理,对施工期及工后沉降进行预测,提出不均匀沉降控制方案,并成功应用于湖堤大道改扩建工程,为类似工程项目实施提供可借鉴的经验。

高速公路拓宽路基综合防排水方案设计

文章结合实际工程案例,探讨了高速公路拓宽路基综合防排水方案设计。研究结果表明,合理地应用综合防排水技术可显著提高路基的稳定性和耐久性,确保道路安全畅通,通过采取文章提出的联合使用碎石排水和排水渠的方案,优化后路基含水量均值下降幅度约为20.15%,验证了该方法在路基排水方面的改善效果,可为高速公路拓宽改扩建工程提供技术支持,并为我国高速公路建设及运营管理提供有益参考。

软土路基加宽公路工程施工关键技术探讨

在公路建设领域,软土路基占据着重要地位。随着我国经济的持续发展,公众的交通需求不断增加,现有道路已无法充分满足需求,对现有道路进行加宽和改造势在必行。然而,在软土路基加宽过程中,面临着诸多挑战。文章以某高速公路软土路基加宽工程为研究对象,由于该工程采用了高压旋喷桩复合地基,并且有新建软土路基路段,因此文章主要分析高压旋喷桩复合地基施工技术与CFG桩施工技术的应用,以供参考。

双线盾构隧道开挖引起既有铁路路基沉降及盾构掘进参数研究:工程案例

为揭示盾构掘进参数对既有铁路路基沉降的影响规律,本文依托北京地铁16号线丰益桥南站至丰台站双线盾构隧道下穿既有铁路线路工程进行案例分析。将盾构掘进过程分为盾构穿越前、盾构穿越中和盾构穿越后三个阶段。实测数据表明,路基沉降在盾构穿越前逐渐增大,在盾构穿越过程中急剧增大,在盾构穿越后趋于稳定。将盾构管片及时封闭成环,施作补偿注浆、二次注浆,有利于控制路基沉降。此外,盾构掘进参数对控制路基沉降具有至关重要的作用。研究结果表明:盾构掘进速度越快引起的路基沉降越大,继而引起较大的土仓压力,并伴随刀盘扭矩和盾构总推力的骤减;由于盾构过程中出土量易于控制,因此其对路基沉降影响不大;然而,如果同步注浆量控制不当,将导致既有路基向上隆起。本研究为盾构开挖下穿多条既有铁路线路引起的路基变形控制以及盾构掘进参数设置提供参考和指导。

公路路基横断面超高加宽计算及设计

该文主要探究公路路基横断面的超高计算和加宽计算方法,以及路基横断面的设计要点。在公路平曲线超高计算中,重点考虑绕中轴旋转和绕内边轴旋转2种形式下超高值计算方法;在公路平曲线加宽计算中,除计算加宽值外,还考虑直线段与平曲线段过渡区域的渐变率,保证2种路段的流畅衔接。在横断面设计中,要注意填方路基和挖方路基的横断面处理方式存在差异。对于分离式路基,在路堤与路堤、路堤与路堑的拼合处理中,要设置线间沟和边坡,并且合理设计线间沟的宽度,确保分离式路基能够拼合成为整体,减少公路出现贯通裂缝的几率。

市政快速路改扩建工程路基拼宽施工技术研究

市政快速路改扩建面临工期紧、质量要求高、施工难度大等诸多问题。以石家庄市北三环快速路改扩建工程为依托,对路基拼宽构造、地基处理技术、新旧路拼宽技术、土工格栅施工技术进行介绍,以达到提高路基拼宽处施工质量、保障该改扩建工程建设工期、实现工程建设效益最大化目标。

高铁路基小角度跨越既有浅埋隧道工程对策

研究目的:高速铁路以路基形式小角度跨越既有铁路隧道浅埋段,为避免新建铁路路基荷载、施工时机械振动及后期运营等对既有铁路隧道产生不利影响,开展相关研究,评价其影响程度,优化路基结构,提出运营监测方案,对设计施工提出指导性意见,对于保障高铁和既有铁路运营安全具有重要意义。研究结论:(1)研究提出高速铁路跨越既有铁路隧道影响评价方法、控制指标、评价参数;(2)研究开展常规路基设计方案对既有铁路影响分析,结果表明既有铁路隧道结构受力接近限值水平,安全储备不足;(3)研究提出U形槽内浇筑轻质混凝土轻型结构设计方案和静力碾压措施,较常规路基设计方案,对既有铁路隧道衬砌受力影响优化幅度达30%~50%;(4)研究提出包括监测范围、内容、布设要求、频率、预警阈值等的全站仪自动化监测方案;(5)本研究成果可为其他新建铁路跨越既有铁路工程提供借鉴。

试分析高速公路加宽工程路基拼宽病害成因

随着交通量的不断增加,许多高速公路已经不能满足现有的交通需求,因此需要进行加宽工程。然而,在加宽工程中,路基拼宽病害是一个常见的问题,它会对道路的使用性能和安全性产生影响。本文将对高速公路加宽工程路基拼宽病害的成因进行试分析。

G50高速拓宽工程路基处理方案研究

以沪渝高速(G50)拓宽改建工程为实例,对现状路基和拓宽段路基处理方案进行了研究,拓宽段比选了堆载预压、复合地基、泡沫轻质土等三种方案,考虑减少新旧路基的差异沉降、降低处理成本等因素,推荐采用泡沫轻质土处理方案。

高速公路改扩建工程路基拼宽施工技术及监理控制要点分析

文章从高速公路改扩建工程施工重难点入手展开研究,通过深入分析施工技术及监理控制要点,采用案例分析与实践总结方法,如路基原地面处理、路基填筑材料选择等,得出提高路基质量、保障施工安全的有效策略,旨在提升高速公路的通行能力和服务水平。