基于沉降控制的高路堤涵洞纵向调荷技术

为解决高路堤涵洞纵向不均匀沉降所带来的病害问题,基于纵向沉降控制的高路堤涵洞调荷机理,利用有限元软件研究涵洞填土与地基土特性以及不同EPS板参数对涵顶垂直土压力和涵底土体沉降的影响,通过离心模型试验探讨涵洞纵向铺设EPS板对高路堤及涵洞的沉降的影响。通过数值模拟计算,分析不同EPS板模量、铺设范围、厚度以及地基处理范围对高路堤涵洞纵向沉降差减少率的影响。研究结果表明:①填土模量与泊松比对涵顶垂直土压力及涵底土体沉降的影响不显著;②随着地基土模量与泊松比的增加,涵底土体纵向沉降趋于均匀分布;③数值仿真与离心模型试验成果得出,沿涵洞纵向分层铺设EPS板时,涵洞纵向调荷效果最佳;④通过数值模拟计算得到了基于纵向沉降控制的高路堤涵洞调荷设计计算方法。     

Combining EPS geofoam with geocell to reduce buried pipe loads and trench surface rutting

This paper reports full scale experiments, under simulated heavy traffic, of geocell and EPS (expanded polystyrene) geofoam block inclusions to mitigate the pressure on, and deformation of, shallow buried, high density polyethylene (HDPE) flexible pipes while limiting surface settlement of the backfilled trench. Geocell of two pocket sizes and EPS of different widths and thickness are used. Soil surface settlement, pipe deformation and transferred pressure onto the pipe are evaluated under repeated loading. The results show that using EPS may sometimes lead to larger surface settlements but can alleviate pressure onto the pipe and, consequentially, result in lower pipe deformations. This benefit is enhanced by the use of geocell reinforcement, which not only significantly opposes any EPS-induced increase in soil surface settlement, but further reduces the pressure on the pipe and its deformation to within allowable limits. For example, by using EPS geofoam with width 0.3 times, and thickness 1.5 times, pipe diameter simultaneously with geocell reinforcement with a pocket size 110 × 110 mm² soil surface settlement, pipe deformation and transferred pressure around a shallow pipe were respectively, 0.60, 0.52 and 0.46 times those obtained in the fully unreinforced buried pipe system. This would represent a desirable and allowable arrangement.     

Response of pavement foundations incorporating both geocells and expanded polystyrene (EPS) geofoam

The suitability of geocell reinforcement in reducing rut depth, surface settlements and/or pavement cracks during service life of the pavements supported on expanded polystyrene (EPS) geofoam blocks is studied using a series of large-scale cyclic plate load tests plus a number of simplified numerical simulations. It was found that the improvement due to provision of geocell constantly increases as the load cycles increase. The rut depths at the pavement surface significantly decrease due to the increased lateral resistance provided by the geocell in the overlying soil layer, and this compensates the lower competency of the underlying EPS geofoam blocks. The efficiency of geocell reinforcement depends on the amplitude of applied pressure: increasing the amplitude of cyclic pressure increasingly exploits the benefits of the geocell reinforcement. During cyclic loading application, geocells can reduce settlement of the pavement surface by up to 41% compared to an unreinforced case – with even greater reduction as the load cycles increase. Employment of geocell reinforcement substantially decreases the rate of increase in the surface settlement during load repetitions. When very low density EPS geofoam (EPS 10) is used, even though accompanied with overlying reinforced soil of 600 mm thickness, the pavement is incapable of tolerating large cyclic pressures (e.g. 550 kPa). In comparison with the unreinforced case, the resilient modulus is increased by geocell reinforcement by 25%, 34% and 53% for overlying soil thicknesses of 600, 500 and 400 mm, respectively. The improvement due to geocell reinforcement was most pronounced when thinner soil layer was used. The verified three-dimensional numerical modelings assisted in further insight regarding the mechanisms involved. The improvement factors obtained in this study allow a designer to choose appropriate values for a geocell reinforced pavement foundation on EPS geofoam.     

Short- and long-term behavior of EPS geofoam in reduction of lateral earth pressure on rigid retaining wall subjected to surcharge loading

Retaining walls are subjected to dead loads from backfill and adjacent structures, live loads and other loads from the vicinity of the structure. Retaining walls need to withstand earth pressure generated from above mentioned loads satisfactorily throughout their service life. Lateral earth thrust on retaining walls can be minimized by placing a compressible inclusion, such as, EPS geofoam, between the backfill and retaining wall. The present study is aimed at understanding both short- and long-term influence of EPS geofoam on surcharge induced lateral earth pressures on retaining walls through 1-g model studies. Four densities of geofoam in the range of 10–25 kg/m³ and three thicknesses of geofoam in the range of 25–75 mm were used in the present study. Lateral earth pressure at several locations along the height of the wall were monitored using earth pressure cells. Geofoam compression and backfill settlements under the surcharge load were also quantified using image analysis. From the series of model tests, it was observed that with the use of geofoam, lateral earth pressure on retaining wall was reduced under both short- and long-term loading conditions. However, higher reduction was observed under long-term loading.     

过江盾构隧道穿越大堤的地层沉降分析及控制

对杭州庆春路过江盾构隧道施工引起的地表沉降实测数据进行了分析,采用Peck公式对横向地表沉降曲线进行拟合,并对大堤和其他断面地表沉降进行了对比。分析结果表明：盾构在大堤下施工引起的地表沉降更大,原因是盾构施工对周围土体的扰动、大堤结构的复杂性、堤顶车辆对土体施加的循环荷载及降雨等共同作用使堤顶沉降加剧;验证了Peck公式在杭州地区软土地层中预测盾构施工引起地表沉降的适用性,其中地表沉降槽宽度参数K取值范围为0.25～0.31,地层损失率η的取值范围为0.10%～0.34%;结合工程实践,提出了泥水平衡盾构穿越大堤控制地表沉降的措施。     

EPS轻质材料处治桥台跳车的数值分析

基于有限元软件ABAQUS对EPS在桥头填筑中的应用进行数值模拟分析,从计算结果可以看出,相比无处治措施和加土工格栅处治,EPS能显著改善桥背填土的整体强度,减小桥背的竖向沉降,其最大路面竖向变形分别为后者的33.4%和37.7%,并能改善桥台的受力特性,降低桥台的最大应力值。     

A new method for remediation of sandy slopes susceptible to seepage flow using EPS-block geofoam

Using expanded polystyrene (EPS) geofoam (geofoam block) in slope remediation projects has drawn interest from the civil engineering sector for its ease of application and budget saving features. According to design precedence, all slope remediation applications that use geofoam blocks should incorporate permanent drainage systems to prevent instability of the lightweight geofoam blocks due to hydrostatic and seepage pressures. In this study, a new method for slope remediation using geofoam blocks was tested through physical laboratory experiments. For this purpose, a total of 24 lysimeter (dimensions of 60 cm height, 20 cm width, and 200 cm length) experiments (including duplicates) were conducted in which seepage through a geofoam block slope system were generated with three different constant water levels in the water reservoir of the lysimeter. Geofoam blocks (dimensions of 2.5 cm height, 5 cm width, and 15 cm length) were assembled to form embankment type configuration at the toe section of the sandy slopes. This study also included coupled numerical model simulations that were comprised of variably saturated flow modeling and slope stability modeling which could be implemented successfully for the global static failure analysis of the geofoam block slope system comprised of two mediums with different geotechnical characteristics. In addition to global static stability failure analysis, which involved conventional limit equilibrium analysis for the geofoam block slope system, hydrostatic sliding mechanism was investigated which provided insight into using an overburden concept to increase the resistance against horizontal driving forces. Experimental and numerical modeling results showed that the geofoam block slope system was stable even though the phreatic surface was above the bottom of the geofoam block assemblage. For this reason, the embankment type configuration tested in this study can be considered a viable remediation technique where seepage induced deep-seated global stability and hydrostatic sliding failures are a concern.     

3D coupled mechanical and hydraulic modeling of a geosynthetic-reinforced deep mixed column-supported embankment

Numerical studies were conducted to improve the understanding of the behavior of geosynthetic-reinforced column-supported embankments. Due to the complexity of the problem, so far, consolidation process and three-dimensional patterns of columns have not been well simulated in most published numerical studies. As a result, the time-dependant behavior and the serviceability of this system have not been well evaluated. In this study, a three-dimensional coupled mechanical and hydraulic modeling was conducted using FLAC3D to consider consolidation and three-dimensional arrangement of columns. This study was based on a well-documented bridge approach embankment reinforced by a layer of geotextile and supported by deep mixed (DM) columns. The foundation soils including soft clay and silt, the embankment fill, and the deep mixed columns were modeled as linearly elastic-perfectly plastic materials with Mohr–Coulomb failure criteria. The geotextile reinforcement was simulated by geogrid elements incorporated in the FLAC3D software, which can sustain in-plane tensile force only. The staged construction was simulated by building the embankment in lifts. The duration of each lift was the same as the actual construction time plus the lapse time between two consecutive stages. The development of settlement and tension in the geotextile with time is compared with the long-term monitoring data and yields good agreement. The generation and dissipation of excess pore water pressure during and after construction are presented and discussed.     

Performance monitoring of Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) in Louisiana

The Geosynthetic Reinforced Soil (GRS) Integrated Bridge System (IBS) is an alternative design method to the conventional bridge support technology. Closely spaced layers of geosynthetic reinforcement and compacted granular fill material can provide direct bearing support for structural bridge members if designed and constructed properly. This new technology has a number of advantages including reduced construction time and cost, generally fewer construction difficulties, and easier maintenance over the life cycle of the structure. These advantages have led to a significant increase in the rate of construction of GRS-IBS structures in recent years. This paper presents details on the instrumentation plan, short-term behavior monitoring, and experiences gained from the implementation of the first GRS-IBS project in Louisiana. The monitoring program consisted of measuring bridge deformations, settlements, strains along the reinforcement, vertical and horizontal stresses within the abutment, and pore water pressures. In this paper, the performance of instrumentation sensors was evaluated to improve future instrumentation programs. Measurements from the instrumentations also provide valuable information to evaluate the design procedure and the performance of GRS-IBS bridges. The instrumentation readings showed that the magnitude and distribution of strains along the reinforcements vary with depth. The locus of maximum strains in the abutment varied by the surcharge load and time that did not corresponds to the (45+?/2) line, especially after the placement of steel girders. A comparison was made between the measured and theoretical value of thrust forces on the facing wall. The results indicated that the predicted loads by the bin pressure theory were close to the measured loads in the lower level of abutment. However, the bin pressure theory under predicted the thrust loads in the upper layers with reduced reinforcement spacing. In general, the overall performance of the GRS-IBS was within acceptable tolerance in terms of measured strains, stresses, settlements and deformations.     

塑料套管混凝土桩加固公路软土地基现场试验研究

根据某一高速公路塑料套管混凝土桩加固软土地基工程实例,对桩土应力、地表沉降、横向位移、不同深度孔隙水压力进行观测,讨论了塑料套管混凝土桩桩承式路堤的工作机理。结果表明：塑料套管桩加筋路堤的临界高度约为1.26倍桩净距,观测期末,荷载分担比接近89%;桩帽和桩间土最大差异沉降为30 mm左右,且应力集中比随着差异沉降的增大而线性增大;路堤堤脚附近不同深处横向位移随着路堤填筑高度的增加而增加,施工结束时,地表以下2.5 m处横向位移最大,为12.86 mm;横向位移-沉降比和横向位移增加率随着路堤填筑高度的增加逐步减小并趋于稳定,塑料套管混凝土桩加筋路堤系统能够有效防止路堤横向位移的发展和改善路堤的整体稳定性。     

Effectiveness of CFG pile-slab structure on soft soil for supporting high-speed railway embankment

The use of cement-fly ash-gravel (CFG) pile-slab structures is a new effective technique for reducing the settlements of soft foundations in China. A comprehensive research was conducted to investigate the effectiveness of a CFG pile-slab structure-supported embankment of the Beijing-Shanghai high-speed railway in China. Firstly, an analytical method was formulated to calculate the settlements of the CFG pile-slab structure-supported embankment. Secondly, mechanical scaling laws were derived for the proposed testing plan at model scale. Model tests were conducted to quantify and to interpret the settlement distributions. Thirdly, the influence of three key factors (pile length, pile diameter, and slab thickness) for the structural form of the CFG pile-slab structure-supported embankment on the settlement distribution were studied using numerical simulations. The maximum settlements of the CFG pile-slab structure-supported embankment in optimizing the structural form were obtained using the above three research methods and then they were compared with each other. The results show that (1) the settlements obtained by the analytical method, the physical model tests, and the numerical simulations showed good concordance with each other; (2) the settlement-controlling effect of the CFG pile-slab structure was able to meet the requirements of high-speed railway construction; (3) the piles and the soil-bearing capacities of the CFG pile-slab structure-supporting embankment could be fully mobilized because of the “load re-distribution” function of the slab; and (4) the affected area of the engineering load had a depth of more than 18.75?m and a horizontal length of 7.5?m near the toe of the embankment slope.     

塑料排水板处理软基山体填筑施工监测分析

原地表沉降及边桩水平位移速率常作为路基施工中软土地基稳定性监测的控制指标.通过对上海某植物园塑料排水板(PVDs)处理后的软土地基在园林山体填筑过程中的监测数据进行分析,包括原地表沉降、边桩水平位移、边桩竖向位移、孔隙水压力、分层沉降以及深层水平位移,研究适用于园林山体填筑过程中稳定性控制指标及预警值.     

公路桥梁台后路基沉陷处治

公路桥台台后路基沉陷病害,导致台背与构造物连接处的路面出现台阶,严重影响公路的使用功能。通过对G310线牛背至北道公路桥台台后路基沉陷病害的实地调查及处治效果的追踪,分析桥头路基填土高度、填料及压实质量、构造特点、排水功能、汽车荷载等因素对台背路基沉陷的影响,总结砂砾换填、高压注浆及桥头搭板技术的实施及控制方法。     

变桩长与变桩距技术在处理桥头软基中的应用

在软土地基上修建高等级公路时,“桥头跳车问题”是一个技术难题,利用变桩长与变桩距的预制管桩复合地基技术,在桥头软基上设置过渡段,可使堆载排水固结法处理的一般路段与桥头之间的工后沉降平稳过渡,缓解了此两种工法处理路段的沉降差异,并能减小桥头段的纵坡率,利用该技术在杭州湾跨海大桥南岸接线段高速公路试验段的桥头软基处理中效果理想。     

桥头路基路面与搭板一体化结构设计研究

对＂深埋式＂桥头搭板的独立设计和大型工程软件ANSYS的有限元分析进行了研究,提出了深埋式桥头搭板与桥头路基路面一体化结构设计的分析方法,针对由于结构性差异沉降而造成的桥头跳车现象得出了该一体化结构设计的合理性。     

系杆拱桥临时支墩的搭设与预压

结合如东县马西桥工程实例,对系杆拱桥临时支墩的搭设与预压进行了总结和分析。总结了临时支墩的搭设方法、支墩的预压荷载和承载能力的验算。并针对临时支墩的观测点布置、预压方法的选择、预压荷载加载顺序及沉降观测提出了具体的方法和注意事项,详细分析了沉降量的计算和支架的预留高度设置的对应关系,并就临时支墩的实际运用情况进行了总结。     

桥头跳车产生的原因及处理措施

针对台背回填处的跳车问题,就设钢筋混凝土搭板和不设搭板两种情况下过渡段的沉降机理进行了分析,详细介绍了路桥过渡段沉降病害处治的措施,以确保桥涵两端填土和路堤施工质量,更好地解决桥头跳车问题。     

加筋形式对桩承式路堤工作性状影响的试验研究

对无加筋和采用不同加筋材料、加筋层数下桩承式路堤的工作性状进行了三维模型试验研究,侧重分析了桩土应力比、应力折减系数、填土中竖向应力分布、地基沉降等内容。结果表明加筋材料的设置有利于荷载向桩顶的转移,可有效减小沉降,但不同加筋形式下桩承式路堤的工作性状有所不同。使用单层或双层土工布时,路堤的荷载传递机理主要是填土的土拱效应和加筋材料的拉膜效应,但拉膜效应发挥相对较晚。使用双层格栅时,加筋材料与周围砂土形成半刚性平台。单层格栅的作用介于两者之间。试验结果与常规拉膜效应设计方法的对比表明,若假设荷载只由相邻桩间的加筋材料条带承担,计算的拉力将偏大,过于保守。     

高等级公路桥台跳车处置技术

针对普遍存在的高等级公路桥台跳车现象,根据过渡差异沉降、减小路基沉降、控制同步沉降的处理原则,将桥台跳车处置技术分为过渡段设置、地基加固与填料处理、路桥整体设计三大类,总结了各种处置技术的特点,为桥台设计与施工积累了经验。     

Investigation of soil-geosynthetic-structure interaction associated with induced trench installation

The design of subsurface structures associated with transportation and other underground facilities, such as buried pipes and culverts, requires an understanding of soil-structure interaction. Earth loads on these structures are known to be dependent on the installation conditions. To reduce earth pressures acting on buried structures installed under high embankments, the induced trench method has been recommended and applied in practice for several decades. It involves the installation of a compressible material (e.g. EPS geofoam blocks) immediately above the buried structure to mobilize shear strength in the backfill material. A first step towards understanding this complex soil-geosynthetic-structure interaction and accurately modeling the load transfer mechanism is choosing a suitable material model for the geofoam that is capable of simulating compressive testing results. In this study, an experimental investigation is conducted to measure the changes in contact pressure on the walls of a rigid structure buried in granular backfill with an overlying geofoam layer. Validated using the experimental results, finite element analysis is then performed and used to study the role of geofoam density, thickness and location on the load transferred to the buried structure. Conclusions are made regarding the effect of modeling EPS inclusion as a non-linear material and the role of EPS configuration on the earth pressure distribution around the buried structure.