Time-History Dynamic Characteristics of Reinforced Soil-Retaining Walls

Given the complexities of reinforced soil materials’constitutive relationships,this paper compares reinforced soil composite materials to a sliding structure between steel bars and soil and proposes a reinforced soil constitutive model that takes this sliding into account.A finite element dynamic time history calculation software for composite response analysis was created using the Fortran programming language,and time history analysis was performed on reinforced soil retaining walls and gravity retaining walls.The vibration time histories of reinforced soil retaining walls and gravity retaining walls were computed,and the dynamic reactions of the two types of retaining walls to vibration were compared and studied.The dynamic performance of reinforced earth retaining walls was evaluated.

Seismic responses of the steel-strip reinforced soil retaining wall with full-height rigid facing from shaking table test

To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake,while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA(peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally,the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.

Mechanical performance of a double-face reinforced retaining wall in an area disturbed by mining

The application of a double-face reinforced retaining wall during road construction can reduce engineering costs, speed road paving and have a good influence on environment. An ABAQUS numerical model of a double-face reinforced retaining wall was built. The influence of surface subsidence induced by mining was considered. A physical model test was also performed in the laboratory on a reinforced retaining wall. The influence of subsidence induced by mining was observed. The numerical results match measurements in the laboratory very well. The vertical pressure on the base of the retaining wall, the horizontal displacement of the wall and the horizontal soil pressure acting on the wall were analyzed. The differential settlement of the reinforced belt and axial forces in the wall were also studied.

Comparison of Seismic Design Codes between China and the United States for Reinforced Soil Retaining Walls

Because of its excellent seismic performance, reinforced soil retaining walls are increasingly used in civil engineering. Although many countries have published corresponding design codes, the differences between them are still relatively large. Using the FHWA Code and the Code for Seismic Design of Railway Engineering(CSDRE), stability calculations of reinforced soil retaining walls were carried out and the similarities and differences between these two design codes were analyzed. According to the comparative analysis, the following conclusions are drawn: the inertia force, the earth pressure and the tensile force of reinforcements calculated from the CSDRE are less than those from the FHWA Code, and the safety factor calculated from the former is larger. Although the M-O method is recommended to calculate the dynamic earth pressure, the FHWA Code suggests a higher action point as compared to the CSDRE.

Field Measurements and Pullout Tests of Reinforced Earth Retaining Wall

In this paper, field measurements and pullout tests of a new type of reinforced earth retaining wall, which is reinforced by trapezoid concrete blocks connected by steel bar, are described. Field measurements included settlements of the earth fill, tensile forces in the ties and earth pressures on the facing panels during the construction and at completion. Based on the measurements, the following statements can be made: (1) the tensile forces in the ties increased with the height of backfill above the tie and there is a tensile force crest in most ties; (2) at completion, the measured earth pressures along the wall face were between the values of the active earth pressures and the pressures at rest; (3) larger settlements occurred near the face of the wall where a zone of drainage sand and gravel was not compacted properly and smaller settlements occurred in the well-compacted backfill. The results of field pullout tests indicated that the magnitudes of pullout resistances as well as tensile forces induced in the ties were strongly influenced by the relative displacements between the ties and the backfill, and pullout resistances increased with the height of backfill above the ties and the length of ties.

筋材布设方式对加筋土挡墙动力响应的影响

针对目前加筋土挡墙设计和施工中筋材布设方式大多为等长形的问题,提出一种倒梯形的筋材布设方式,并基于挡墙位移分区理论和有限差分Flac^(3D)数值模拟,建立加筋土挡墙三维分析模型,探讨不同峰值加速度下3种加筋土挡墙对位移、水平土压力、筋材拉应力及潜在破裂面的影响。结果表明,随峰值加速度增大,挡墙位移逐渐增大,同一荷载作用下,改变筋材布设方式,侧向水平位移减少9.3%,竖向沉降减少5.3%;3种形式挡墙水平土压力相差不大,最大水平土压力分布在挡墙的中下部;筋材拉应力随峰值加速度的增大,沿墙高从单峰型转化为双峰型分布,最大值位于挡墙中下部;潜在破裂面填土区破裂带的形状与筋材的布设方式有关。所提出的倒梯形筋材布设方式对加筋土挡墙的抗震效果更好,可为施工设计中加筋土挡墙筋材布设提供参考。

台阶级数对加筋土挡墙地震动力响应影响研究

为了优化加筋土挡墙的结构设计,研究了台阶级数对加筋土挡墙抗震性能的影响程度。基于Flac3D软件建立了加筋土挡墙数值模型,探讨了不同地震峰值加速度(peak ground acceleration,PGA)下不同台阶级数加筋土挡墙的侧向位移、竖向沉降、加速度响应和水平土压力的变化规律。结果表明:4 m/s^(2)峰值加速度下,增加台阶级数,侧向位移减小了61.9%,竖向沉降减小了20.5%;PGA放大系数随着台阶级数的增加而增大,其中加筋区PGA放大系数略大于面板处PGA放大系数;1级加筋土挡墙最大水平土压力位于墙脚处,2,3级加筋土挡墙最大水平土压力位于台阶分级处;水平土压力在台阶分级处大于规范计算值。增加台阶级数能够提升加筋土挡墙的抗震性能,可为实际工程中加筋土挡墙的分级设计提供理论参考。

铁路路基挡墙碳减排方案优选及降碳策略研究

铁路路基挡墙在铁路路基全生命周期产生的碳排放不可忽视。为探析不同类型挡墙碳排放水平,选取3种典型挡墙展开研究,提取碳减排最优方案并剖析不同策略组合对其碳排放影响,进而提出碳减排综合策略。首先基于LCA理论,将加筋土挡墙、重力式挡墙及土钉墙全生命周期碳排放分为建材生产、建材运输、施工建造与运营维护4个阶段,基于功能单位,利用碳排放因子法并依据碳排放计算模型测算各类型挡墙各阶段与总碳排放量。研究结果表明,加筋土挡墙因边坡植被固碳能力使其全生命周期表征出固碳效应,且固碳量为197.300 t,重力式挡墙与土钉墙总碳排放量分别为489.344 t和51.834t,故将加筋土挡墙作为碳减排最优方案。然后以加筋土挡墙为研究对象,提取其设计阶段碳排放影响因素,并利用敏感性分析方法识别出其碳排放最敏感的因素为边坡植被类型,其次为挡墙坡度。最后选取百喜草、结缕草、黑麦草3种植被与1∶0.4、1∶0.5、1∶0.6、1∶0.7这4种坡度,分析不同策略组合对加筋土挡墙全生命周期碳排放综合影响。研究表明,对碳汇能力较强的百喜草,降低坡度可提高全生命周期固碳量;对碳汇能力一般的结缕草,避免不利坡度以提高全生命周期固碳量;对碳汇能力较弱的黑麦草,提升坡度可提高挡墙全生命周期固碳量。研究成果可为铁路挡墙降碳设计提供理论依据。

Model test on sand retaining wall reinforced with denti-strip inclusions

In conventional reinforced soil structures,the reinforcements are often laid hori-zontally in the soil.In this paper,a new concept of soil reinforced with denti-strip inclusions was proposed and a series of laboratory model tests were carried out on sand retaining wall reinforced with denti-strip inclusions.Besides the horizontal displacements of the facing,the lateral earth pressures acting on vertical elements were measured.A microscopic measurement was performed to investigate the deformation and progressive failure of the sand within model retaining wall.Based on the image analytical technique,the bearing capability and interaction mechanism of reinforced sand retaining wall were analyzed.The model of the initial shear failure and potential failure surface were also put forward.From the experimental results,it is shown that denti-strip inclusions can increase the bearing capability of retaining wall significantly and restrict the facing displacements efficiently,as compared with conventional horizontal reinforcement.

Shaking table tests on a cantilever retaining wall with reinforced and unreinforced backfill

Physical modelling of cantilever retaining walls with and without backfill reinforcement was conducted on a 1g shaking table to evaluate the mitigation effect of reinforcement on system dynamics(g denotes the acceleration of gravity).The model wall has a height of 1.5 m with a scale ratio of 1/4 and retains dry sand throughout.The input motions are amplified to three levels of input peak base acceleration,0.11g,0.24g,and 0.39g,corresponding to minor,moderate,and major earthquakes,respectively.Investigation of the seismic response of the retaining walls focuses on acceleration and lateral displacement of the wall and backfill,dynamic earth pressures,and tensile load in the reinforcements(modeled by phosphor-bronze strips welded into a mesh).The inclusion of reinforcement has been observed to improve the integrity of the wall-soil system,mitigate vibration-related damage,and reduce the fundamental frequency of a reinforced system.Propagation of acceleration from the base to the upper portion is accompanied by time delay and nonlinear amplification.A reinforced system with a lower acceleration amplification factor than the unreinforced one indicates that reinforcement can reduce the amplification effect of input motion.Under minor and moderate earthquake loadings,reinforcement allows the inertia force and seismic earth pressure to be asynchronous and decreases the seismic earth pressure when inertia forces peak.During major earthquake loading,the wall is displaced horizontally less than the backfill,with soil pushing the wall substantially;the effect of backfill reinforcement has not been fully mobilized.The dynamic earth pressure is large at the top and diminishes toward the bottom.

隧道洞口挡土墙稳定性及其加固技术研究

为研究隧道洞口挡土墙的稳定性,并制定合理的挡土墙加固防护方案,以某隧道横洞为背景,在隧道洞口挡土墙中布置监测点,观测洞口挡土墙的位移及沉降。并通过分析挡土墙失稳的原因,制定采用钢花管灌浆加固、钢筋网片、喷射混凝土等措施加固挡土墙的技术方案。18个监测点被布置在加固后的洞口挡土墙中以观测加固后挡土墙的位移及沉降,对比加固前后的监测结果,加固后洞口挡土墙最危险处位移值和沉降值分别减小86%和64%,挡土墙的位移和沉降的问题得到显著改善,以期为今后类似挡土墙加固防护提供理论参考。

浆砌挡墙外贴挂网混凝土层抗弯试验研究

为保证处置病害浆砌挡墙的施工安全和加固效果,文中提出钢筋混凝土外贴病害浆砌挡墙的加固措施,设计5组抗弯试验(1组为无外贴层,4组为不同厚度外贴层),探究外贴层对浆砌挡墙的加固效果及其作用机理。试验结果表明,加设5~20 cm厚外贴层后,破坏模式由脆性破坏转变为延性破坏,承载力和抗弯刚度显著提升,开裂弯矩提升1.25~5.67倍,极限弯矩增大2.75~13倍。

水平地震作用下双级加筋土挡墙损伤识别研究

因对台阶式加筋土挡墙损伤识别的研究不足,开展了双级加筋土挡墙的大型振动台试验。采用时域识别方法分析了水平地震作用下模型的动力响应特征,阐述了上、下级挡墙自振频率、阻尼比的分布规律,探究了结构损伤程度与自振频率、阻尼比间的对应关系。研究结果表明:加载前上、下级挡墙的自振频率基本一致,阻尼比随墙高的增加而减小;随着加载工况的累积,自振频率逐渐减小,阻尼比逐渐增大。采用数学方法对自振频率和阻尼比分布曲线进行多项式拟合,对比分析可得:当自振频率减小0~15.41%、阻尼比增大0~299.35%时,结构处于基本完好阶段;当自振频率减小15.41%~18.92%、阻尼比增大299.35%~360.07%时,结构处于轻微破坏阶段;当自振频率减小18.92%~21.29%、阻尼比增大360.07%~398.21%时,结构处于中等破坏阶段;当自振频率减小21.29%~29.60%、阻尼比增大398.21%~532.99%时,结构处于毁坏状态。

装配式挡墙箱体集束连接力学性能试验研究

为解决船闸工程现浇施工体系施工效率低、质量不可控等问题,提出将装配式结构应用于船闸挡墙工程,并在此基础上将集束搭接连接应用于装配式挡墙结构。为明确集束连接的力学性能,开展了集束连接局部构件的单向分级加载试验,观察试件破坏特征和裂缝发展规律。试验结果表明:试件破坏模式为小偏心受拉破坏,破坏位置集中在插筋端部较小范围内。研究结果可为船闸挡墙工程集束连接结构的破坏模式分析和受拉承载力计算提供理论支持。

L型加筋土挡墙地震动力响应理论分析

将L型挡墙与加筋土2种柔性支挡结构相结合,充分利用其良好的抗震性能,可用于地震多发区和高烈度区的支挡工程中。研究地震荷载作用下L型加筋土挡墙的破坏机制与动力响应问题。根据第二、第三滑裂面产生条件,提出踵板长度临界系数λ_(cr),以界定长踵板式和短踵板式2种破坏模式。假设填土滑裂面为直线,应用极限分析上限定理,采用Mohr-Coulomb破坏准则,分别建立2种破坏模式下L型加筋土挡墙临界状态方程,推导其地震屈服加速度系数。根据极值原理给出最优解,得到临界屈服加速度系数及其对应的填土滑裂面倾角,分析破坏模式与临界屈服加速度系数受几何参数、物理力学参数和加筋作用的影响。通过算例分析可知:加筋作用可有效地提高L型挡墙的抗震能力,改变其破坏模式;当设计筋材拉伸强度较大时,L型加筋土挡墙只发生长踵板式破坏。

不同面板型式加筋土挡墙振动响应数值分析

以刚/柔组合墙面加筋土挡墙的振动台试验结果为基准,建立刚/柔组合式、模块加返包式、模块式和格宾式面板型式加筋土挡墙的FLAC^(3D)数值模型,研究面板型式对挡墙水平位移、加速度响应及地震土压力分布的影响。结果表明:在静力作用下不同面板型式挡墙的变形模式略有不同;振动作用下,变形大小为组合式<模块加返包式<格宾式<模块式;加筋区内加速度放大系数为组合式>模块加返包式>格宾式>模块式;面板处加速度放大系数均大于加筋区,且面板型式不同,放大规律亦不同;面板型式不同,地震主动土压力非线性分布规律不同;合力作用点位置大多高于M-O方法的H/3,且受加速度幅值影响较小。

模块式空心面板加筋土挡墙面板连接稳定性研究

为揭示预制模块式空心面板加筋土挡墙的面板连接稳定性影响规律,基于极限平衡理论,深入研究了模块式空心面板加筋土挡墙面板连接稳定性。考虑了模块面板的空心率和倾斜角度,计算了筋材连接拉力和面板连接抵抗力,并建立了相应的稳定性分析方法。通过与已有文献结果对比验证了该方法的有效性。进一步对不同因素开展了参数分析。结果表明,增加模块空心率、减小填土内摩擦角和增加加筋间距会降低面板连接稳定性,对挡墙中下部的影响尤为显著;倾斜的加筋土挡墙面板连接稳定性显著降低,对挡墙中上部影响更为显著。

济南华润万象城抗震性能分析与设计

济南华润万象城为一栋结构高度412m的超限高层商业建筑,采用框架-剪力墙结构。结构中同时存在扭转不规则、平面开洞、大跨度结构、大悬挑结构、斜柱、桁架悬挑等多项平面及竖向不规则情况。采用多种计算程序进行了抗震性能分析,其结果均满足既定的抗震性能目标。对复杂商业中的各关键部位设计进行了多方案比选,确定了合理的结构布置和适当的构造措施,取得了良好的效果。

整体现浇面板包裹式加筋土挡墙力学特性研究

为探究整体现浇面板包裹式加筋土挡墙在交通荷载作用下的受力变形特性,以成昆铁路峨米段整体现浇面板包裹式加筋土挡墙为工程背景,利用现场监测数据并运用大型岩土有限元软件midas GTS对整体现浇面板包裹式加筋土挡墙进行了系统研究,实际工程中应适当增加挡墙中部筋带数量,减少加筋间距,增大加筋长度,采用短筋和长筋交替布置的方案,充分发挥筋材的加筋作用,加强挡墙整体稳定性。

预制+现浇组合式面板加筋土挡墙力学特性研究

为了分析预制与现浇组合式面板加筋土挡墙在交通荷载下的力学行为和变形特性,研究依托成昆铁路复线挡墙工程,以成昆铁路某段复合式加筋挡土墙结构为研究对象,通过现场实测和数值模拟结合的方式,对加筋土挡墙的力学特性进行了研究,重点分析了面板变形、墙后土压力、基底及墙顶沉降等分布规律。分析结果表明,实际工程中应适当增加挡墙中部筋带数量,减少加筋间距,增大加筋长度,采用短筋和长筋交替布置的方式,可充分发挥筋材的加筋作用,以加强挡墙整体稳定性。