平面应变条件下土工格室加筋垫层的变形分析

将铺设在软土地基上的土工格室加筋垫层看作具有一定刚度的梁板。地基上梁板的变形计算一般以弹理论的文克尔假定为基础。针对文克尔假定中不考虑水平抗力影响的问题,提出了考虑水平抗力的双参数法,并以该法应用于土工格室加筋垫层工法的变形分析。     

软土路基“波浪型”不均匀沉降及其机制分析

在软土地基上修建道路,变形是控制道路质量和正常使用的主要因素。天津东疆港道路建立在经真空预压加固后的吹填土地基上,道路使用3 a后产生了严重的"波浪型"不均匀沉降,严重影响了车辆的行驶及人的生命安全。通过分析软土路基产生波浪变形的机制,提出了道路在建成后产生初始波浪变形,在车辆荷载作用下加剧了这种不均匀沉降的理念;建立了软土路基在波浪变形初值缺陷条件下的力学模型,通过力学分析与计算得出,在初始波浪变形条件下路基波谷受到比波峰大的车辆荷载;路基波峰与波谷处车辆动载大小的不同是加剧地基不均匀沉降变形的原因。提出利用土工格栅的加筋作用可减小不均匀沉降,通过有限元方法分析了该措施的加固效果。     

土工格室加筋土垫层路堤临界高度研究

土工格室能有效减少软土地基上路堤的变形,并增强其稳定性,但对于土工格室加筋土垫层路堤的临界高度还少有研究。采用极限平衡分析方法,假定地基在路堤荷载作用下呈圆弧滑动破坏模式,将格室及其内的填土视为复合体,考虑格室复合体的应力扩散作用和侧向限制作用,提出了路堤临界高度的计算模型,并将该模型值与建立的有限差分模型结果进行对比,然后讨论了格室高度、应力扩散角及格室复合体与地基接触面摩擦系数对路堤临界高度的影响规律。结果表明,理论分析和数值计算结果吻合较好;加筋路堤的临界高度明显大于未加筋路堤的临界高度,并且增加此3种影响因素的取值均能提高路堤的临界高度;同时增强格室的侧向限制作用比提高格室高度和应力扩散角更有利于路堤的稳定。     

双向增强复合地基沉降计算方法研究

将双向增强复合地基中的水平向加筋垫层视为具有一定刚度的地基梁,竖向桩体和桩间土体简化为一系列刚度不同的弹簧,考虑水平加筋垫层上下界面摩阻力的影响,基于Winkler弹性地基梁理论推导出水平加筋体的挠曲变形微分方程,并给出其幂级数半解析解,从而得到了双向增强复合地基在对称荷载作用下的沉降计算方法。通过与常规弹性地基梁法的比较验证了该方法的正确性。该方法可考虑水平加筋体筋材拉力对双向增强复合地基沉降的影响,研究结果表明,水平加筋体的设置有利于减少复合地基的沉降量     

土工格室加筋垫层路堤破坏模式和稳定性评价

采用土工格室加筋垫层提高软土地基上填方路堤的稳定性已得到认可,但其破坏模式和稳定性分析方法仍未取得共识。作者通过室内物理模拟试验,识别软土地基上无筋垫层路堤、土工格栅加筋垫层路堤和土工格室加筋垫层路堤的失效模式,并在此基础上探讨土工格室加筋垫层路堤的稳定性和临界填筑高度分析方法。研究结果表明:软土地基上无筋垫层路堤和土工格栅加筋垫层路堤发生穿过垫层的圆弧滑动破坏;土工格室加筋垫层路堤呈整体破坏模式,滑动面虽呈似圆弧状但未穿过加筋垫层,破裂面在软土地基中形成和发展,而且位置更深。在识别破坏模式的基础上,通过土工格室加筋垫层的工作机理分析,提出了软土地基上土工格室加筋垫层路堤稳定性和临界填筑高度分析方法。     

循环荷载及静载下土工格室加筋路堤模型试验研究

为探究土工格室加筋路堤在循环荷载及静载下的各种性能,利用美国GCTS公司的USTX-2000加载装置进行加载,通过改变加筋层数、格室高度,格室焊距对土工格室加筋路堤进行一系列模型试验。对各种工况下加筋路堤极限承载力、长期循环荷载及固定振次循环荷载后极限承载力的变化进行研究。试验表明,土工格室加筋能显著提高地基极限承载力并能显著减小坡顶和坡中临界破坏时的法向累积变形,在加筋间距一定的情况下,加筋层数增加和格室高度增大均可不同程度提高极限承载力并减小临界破坏时坡顶法向累积变形,格室焊距的减小也可在一定程度提高极限承载力,格室焊距对边坡法向变形影响不大;长期循环荷载下固定间距加筋层数对路堤竖向累积沉降量影响不大,而对边坡坡顶法向累积变形有一定影响,格室高度增大和格室焊距减小均可不同程度减小路堤竖向累积沉降量和坡面法向累积变形;越靠近加载点处,路堤土压力值受加筋影响越显著,加筋提高了土体刚度和密实度,使加筋路堤土压力值较无筋路堤明显增大;对于无筋路堤,改变动载幅值和振次均导致振后极限承载力有不同程度的降低,而对于加筋路堤,当动载幅值≥30 kPa或动载振次≥1 000时,振后极限承载力均有不同程度的提高。     

分级循环荷载下土工格室加筋路堤模型试验研究

目前对土工格室加筋路堤研究主要集中在静载条件下,动载条件下研究的比较少。为研究分级循环荷载下土工格室加筋路堤的力学性能,采用USTX-2000的动力加载装置进行加载,对土工格室加筋路堤在不同加筋层数、格室高度、格室焊距等工况下进行一系列模型试验。对分级循环荷载下路堤的竖向变形和坡面法向变形进行研究,并与固定振幅循环荷载及静载作用下的路堤进行对比分析,研究不同加载方案路堤力学性能的差异性。试验结果表明,土工格室加筋能显著提高路堤承受分级循环荷载的能力和减小竖向累积沉降量,在加筋间距一定的情况下,两层及以上加筋效果比单层加筋效果更显著,格室高度增大和格室焊距减小均可不同程度提高路堤承受分级循环荷载能力并减小竖向累积沉降量;加筋可减小路堤分级循环荷载下的坡面法向变形,格室高度增大和格室焊距减小在分级循环荷载幅值相同时均能减小坡顶和坡中处的法向累积变形;分级循环荷载作用下,当振次≥8 000或幅值≥80 kPa时,路堤竖向累积沉降量超过固定振幅循环荷载,当振次≥9 000或振幅≥90 kPa时,路堤坡顶法向累积变形超过固定振幅循环荷载;分级循环荷载作用下,路堤竖向和坡面法向累积变形均大于静载,加筋可有效减小分级循环荷载和静载作用下坡面法向累积变形差。     

静载作用下土工格栅加筋拓宽路堤土中应力特征试验研究

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。     

浆固碎石桩单桩荷载传递特性研究

浆固碎石桩是加固软土地基的一种新型桩基技术,已成功应用于高速公路和高速铁路等工程软土地基处理。为了研究浆固碎石桩单桩荷载传递机制,假定浆固区压缩模量呈指数分布,应用圆形承载板作用下的半空间体位移的解,对竖向荷载作用下单桩复合地基各部分沉降进行分析,推导出桩轴向压应力、桩侧摩阻力和桩顶沉降计算公式。现场试验实测结果与理论计算结果对比表明,理论计算值与实测值相吻合,验证了理论计算公式的合理性     

土工格室加筋土挡墙静载模型试验研究

土工格室加筋土挡墙因其结构轻巧、稳定性高而具有广阔的工程应用前景，均匀长加筋面板式格室挡墙性能尤为良好，但目前相关的试验研究尚少。以拟建的长加筋面板式土工格室挡墙为对象，开展了竖向分级静载作用下的室内模型试验，对挡墙的变形、墙内竖向应力以及格室加筋层应变进行了测试和分析，探讨了均匀长格室层的加筋作用机制。结果表明：竖向荷载作用下，挡墙上部填土沿水平方向产生了中间大、墙面处小的不均匀沉降，埋于其中的格室加筋层因受弯而产生“网兜”效应，合并格室较强的侧限作用，致使部分竖向应力转化为格室的水平应力，多层格室的水平向转化作用使得挡墙底部的竖向应力明显减小，沉降沿水平方向亦趋于均匀分布。挡墙上部的翘起变形使得加筋层对墙面产生向下的拉力，故墙面竖向位移随荷载的增加而迅速增长；且对墙面产生向内收缩的作用，有效限制了上部墙面的水平位移，0.375H～0.75H(H为总墙高)范围内格室墙面水平位移较大，最大值出现在0.375H高处。加筋层应变沿水平方向的分布形式受填筑高度和荷载的影响较小，竖向荷载作用下均匀长加筋面板式格室挡墙的潜在破裂面的剖面线形为距墙踵一定距离的竖向缓变曲线。该成果可为此类土工格室加...     

Deformation analysis of geocell reinforcement using Winkler model

Geocell reinforcement has been increasingly applied to embankment engineerings. Deformation calculation is one of the major concerns during the design process. Using Winkler foundation model and with consideration of the interface resistance effect, a deformation control differential equation for the geocell reinforced mattress under the vertical symmetric loads is presented in this paper. The corresponding power-series semi analytic solutions for the displacements and the internal forces of geocell reinforcement are also presented. Furthermore, the influence factors such as loads, length and flexural rigidity of geocell reinforcement, coefficient of subgrade reaction and the interface resistance on the stress-deformation characteristic of geocell reinforcement are discussed. Finally, two examples are employed to verify the presented method. This study suggests that the effect of the interface resistance on the deformation of geocell reinforcement should be considered in engineering design.     

Investigation of Flexural Behavior of Geocell Reinforcement Using Three-Layered Beam Model Testing

The study presented in this paper aimed to investigate the flexural behavior of geocell reinforcement by means of three-layered beam model testing. The geocell reinforcement was assumed to be a continuous beam sandwiched between two identical polywood beams. An analytical analysis was conducted to derive the closed-form solution to calculate the deflection of the three-layered beam model. A series of four-point bending tests using dead weights were carried out to test the three-layered beam models. Two geocell products of different dimensions and two types of infill materials, crushed stone and silty sand were tested in this study. Deflections of the layered beam models were measured along with the increment of applied loads. Testing results showed that the geocell reinforcement provides considerable resistance to flexural deformation, especially at higher load levels. The geocell with greater cell height to cell length ratio exhibited overall greater resistance to flexural deflection, especially when crushed stone was used as infill materials. Geocell reinforcements filled by crushed stone showed less flexural deformation than the geocells filled by silty sand. The modulus of the geocell reinforcement was calculated based on the closed-form solution and deflection measurements from the four-point bending tests. Ranges of elastic modulus were presented for the geocell reinforcement filled with compacted crushed stone and silty sand, which can be used as reference values for material property inputs in mechanistic-empirical design of geocell-reinforced pavements.     

Analysis of geocell-reinforced mattress with consideration of horizontal–vertical coupling

Geocell reinforcement has been increasingly applied to road embankment engineering. Deformation calculation is one of the major concerns during the design process. In this paper, the power-series method was employed to investigate the performance of a geocell-reinforced mattress under symmetric loads. The geocell-reinforced mattress was idealized as a beam on a Winkler foundation. In the analysis, the soil–foundation beam interface resistance, related to the horizontal deformation coupling with the vertical deformation, was considered. Semi-analytic solutions were developed to assess the deformations and internal forces of the foundation beam and verified against an existing finite element method [9]. The results of the proposed method were close to the results from the finite element method. Moreover, the effects of various factors, such as height of embankment, horizontal and vertical foundation coefficients, composite elastic modulus and height of geocell-reinforced mattress, on the foundation beam settlement and the tension force within the beam are discussed. It was found that the interface resistance related to the horizontal deformation of the beam has a reduction effect on the embankment settlement, and it is beneficial to reduce the embankment settlement by increasing the beam rigidity and strengthening the subgrade soil body.     

A three-dimensional mechanistic-empirical model for geocell-reinforced unpaved roads

Geocell is a three-dimensional geosynthetic product that was originally developed to confine granular bases and minimize permanent deformation of unpaved roads. Many laboratory and field tests have demonstrated the effectiveness of geocell reinforcement in roadway constructions. However, the lack of a well-established design method that can quantify the benefit of geocell reinforcement has greatly limited the application of geocell in roadways. This paper presents the development of a three-dimensional mechanistic-empirical (M-E) model for geocell-reinforced unpaved roads. The constitutive equation for the tangential resilient modulus of the base material was derived under a general three-dimensional condition. Two analytical models were introduced to estimate the compaction- and repeated load-induced residual stresses in the base layer. These analytical models consider the material properties and construction effects in a rational way thus can be used for various situations. Finally, the proposed M-E model was validated against the test results from four unpaved road sections. Comparisons between the calculated results and the test data show that the three-dimensional M-E model effectively simulated the permanent deformation behavior of geocell-reinforced unpaved roads under a large number of load repetitions, given that the unpaved road was stable under a repeated load.     

条形基础下水平布置纤维增强聚合物筋材地基试验研究

纤维增强聚合物(FRP)具有耐腐蚀、耐水、耐高温、高强度、高弹性模量、质量轻等优点,将其用作加筋材料不仅能显著提高加筋地基的加筋效果,还能有效解决传统加筋材料的耐久性问题。分别对纯砂和5种水平加筋方式进行了加筋地基模型试验,测试了各级荷载下的地基沉降、FRP的应变及土压力数值,并初步探讨了FRP加筋的作用机制。试验结果表明,加筋能显著提高地基承载力和减小地基沉降,特别是双层水平加筋方式的加筋效果更加明显,而锚固件的设置对加筋效果的影响并不大,水平FRP筋材主要起到了土压力扩散作用。     

Effects of base geogrid on geocell-reinforced foundation beds

The effect of a base geogrid layer below the geocell mattress in sand, sand overlying soft clay, and soft clay foundation beds has been studied using a series of laboratory scale load tests. A rigid circular model footing was used to apply static monotonic loading on the foundation beds with and without geocell reinforcement. The model test results show that the provision of an additional layer of planar geogrid at the base of the geocell mattress further increases the performance of the footing in terms of bearing capacity and reduction in surface heave of the foundation bed. It is also observed that the beneficial effect of the base geogrid layer becomes negligible with increasing height of the geocell mattress beyond the influence of the depth of the footing. Strain measurements in the base geogrid layer indicate that it is more effective with the limited heights of the geocell mattress. The earth pressure cells embedded in the subgrade soil provide evidence that when the base geogrid is provided below the geocell mattress, the footing pressure is distributed more uniformly over an extended area.     

Influence of geocell reinforcement on uplift response of belled piles

Piles are frequently used to transfer the heavy compressive loads to strong soil layers located in the depth of bed. In addition, such piles may be subjected to combination of repeated compressive and tensile loads due to earthquake, wind, etc. This paper describes a series of laboratory model tests, at unit gravity, performed on belled pile, embedded in unreinforced and geocell-reinforced beds. The tests were performed to evaluate the beneficial effect of geocell in decreasing the downward and upward displacements and performance improvement of the uplift response of belled pile under repeated compressive and tensile loads. Pile displacements due to fifty load repetitions were recorded. The influence of the height of geocell above the bell of pile, an additional geocell layer at the base of belled pile, and the number of load cycles on pile displacements were investigated. The test results show that the geocell reinforcement reduces the magnitude of the final upward displacement. It also acts as a displacement retardant, and changes the behaviour of belled pile from unstable response condition due to excessive upward pile displacement in unreinforced bed to approximately steady response condition. Therefore, the geocell reinforcement permits higher tensile loads or increased cycling. The efficiency of reinforcement in reducing the maximum upward displacement of the pile (i.e. pull-out resistance) was increased by increasing the height of geocell above the bell of the pile. Furthermore, the comparison showed that a specific improvement in upward and downward displacement and the stability against uplift can be achieved using an additional geocell layer at the base. The geocell reinforcement may reduce the required length of pile shaft, consequently reducing required excavation, backfill, and pile’s material. Simple dimensional analysis showed the need for an increased stiffness of the geosynthetic components in order to match prototype-scale performance similitude.