The plate anchor is widely used because of its good bearing characteristics, but the bearing characteristics are different at different buried depths. In order to study the tensile bearing characteristics of the anchor plate, a self-developed visualized drawing device is used to conduct a drawing model test considering the influences of buried depth and drawing rate. The particle image velocimetry and the digital dynamometer are used to obtain the displacement and shear strain cloud map of packing soil and drawing load of the anchor plate. The results show that the critical buried depth ratio of the anchor plate in dense sand is around four. The drawing process of the shallow-buried anchor plate can be divided into three stages: pre-peak growth, post-peak softening and residual stability. At the pre-peak growth stage, the soil is in local shear failure state, while the soil is in the overall shear failure state at the post-peak softening and residual stability stages. The displacement and shear strain clouds are inverted trapezoidal. The drawing process of the deep-buried anchor plate can be divided into two stages: pre-peak growth stage and post-peak fluctuation stage. In this case, the soil is always in local shear failure, the displacement cloud is in bubble shape distribution, and the shear plane is always in the width of three times of the anchor plate above the anchor plate. The relationship between the dimensionless load and the dimensionless displacement is hyperbolic. This relationship is given and compared with other research results. The shape coefficient-modified Giampa formula can predict the bearing capacity coefficient of the anchor plate well.

Cushion is the key influencing factor to the working performance of composite foundation. Due to the lack of research techniques, the understanding of the working performance of composite foundation cushion needs to be deeply investigated. The hybrid tests was carried out by using the developed hybrid test device and data interaction system, and the whole-component participating test method combining the physical model of the cushion and upper loading with the numerical model of pile-soil foundation was established, which greatly reduced the work of model tests. Using this test method, three groups of hybrid tests with different thickness of cushion were carried out, the working performance of cushion on composite foundation was analyzed, and the mechanism of load transfer, settlement and distribution of friction resistance on pile side were revealed. With the increase of cushion thickness, the load bearing by soil between piles and the relative displacement of piles to soil increased. When the cushion thickness exceeded 200 mm, the pile-soil load bearing ratio tended to be stable.

为增强轨枕的工作性能和减少钢筋混凝土用量,对传统条形轨枕进行结构优化,提出预制装配式X形可调间距轨枕,并对X形轨枕的结构特点、制作流程、轨道维护和钢筋混凝土用量进行分析.同时,建立三维有砟轨道有限元数值模型,对比循环荷载作用下传统轨枕与X形轨枕的竖向、侧向位移和轨枕应力分布.预制装配式X形轨枕由上、下轨枕两部分拼装组成,轨枕间距设计成600,700,800 mm三档,可在自研的X形轨枕制作模具中直接浇筑成形;相同轨枕间距下,铺设X形轨枕每千米混凝土用量相较于Ⅲa型轨枕减少16.7％,钢筋用量减少2.6％;当X形轨枕间距从600 mm增至700,800 mm时,每千米所需铺设的轨枕根数分别减少14.8％和25.5％.模拟结果表明,相较于传统轨枕,采用X形轨枕的轨道竖向沉降减少了5.8％,侧向位移减少了8.4％.新型X形轨枕具有降低道床沉降和促进碳减排的潜能.

开发了可视化土工模型试验箱及模拟隧道开挖地层损失的水囊装置,考虑隧道埋深、隧道与挡土结构水平距离及隧道开挖体积损失3个因素开展了多参数影响模型试验,通过粒子图像测速技术获取填料位移,对地层变形、滑移面演化与地表沉降规律进行分析.结果表明:隧道开挖使隧道上方土体形成三角形集中下沉区域,下沉量随隧道开挖地层损失的增大而增大,地层沉降影响区域随隧道埋深的增大而逐渐扩大,当开挖距离较小时,隧道上方两侧地层向挡墙一侧偏移的现象较为显著.随开挖距离增加,隧道靠近挡土墙一侧滑移面角度变化程度不大,远离挡土结构一侧滑移面角度增大.

桩承式加筋路堤的路堤土拱效应、加筋体张拉膜效应以及桩土地基承载效应之间存在着较为复杂的耦合效应,由于土拱效应随路堤加载与桩间土下沉的演化,目前的计算理论与方法难以真实地评价桩承式路堤荷载调节与沉降稳定的全过程.引入混合试验的技术思路,开发一套阵列式多活动门试验装置及桩土地基混合试验方法,实现加筋垫层路堤物理模型与桩土地基数值模型的适时数据交换,开展9组不同路堤高度与加筋体拉伸模量的参数影响试验.试验结果表明:所建立的混合试验方法能够较好地实现桩承式加筋路堤的全组件参与、全效应耦合工作性能模拟,大大地节省了试验成本和时间,为桩承式加筋路堤的长期承载性能演化以及沉降预测提供了一种新的试验手段.同心圆力学模型能够较为准确地评价路堤的最大土拱效应.当路堤高度较低时,采用拉伸模量较高的加筋体能够提高桩的荷载分担比.采用拉伸模量较高的加筋体,在不同的加筋高度条件下均能够显著地降低桩间土沉降与桩土差异沉降.随着路堤高度的增加,不同加筋体模量试验的桩、土荷载分担比趋于一致,采用地基反力系数法不能可靠地反映桩间土的真实承载机制.

为了从细观力学机理上研究路桥过渡段的劣化规律及其影响因素,采用离散单元(DEM)法生成轨枕与道砟模型,并施加相位荷载,通过多体动力学(MBD)方法建立相互独立的路基弹簧,实现对路桥过渡段中路基刚度变化的模拟,进而建立轨枕-道砟-路基过渡段耦合模型,进行不同路基刚度、列车速度、轴重以及桩基加固下过渡段不均匀沉降研究.结果表明:列车荷载作用下,路桥过渡段中过渡路基区沉降最大,普通路基区次之,桥面路基区最小;当列车车速由94km·h-1增加至281km·h-1、轴重由16t提升至32t时,过渡段不均匀沉降分别增大60.9％和259.4％,轴重的影响更为突出;当列车车速为94km·h-1和轴重为16 t时,采用刚度渐变路基或桩基加固软路基措施后,过渡段各路基区沉降均有减小,过渡段不均匀沉降分别减小56.5％和53.6％,验证了路桥过渡段采用搭板法与桩基加固法的合理性.

以软黏土中桩承桥墩系统为研究对象,分别采用等效理想弹塑性模型和双曲线型滞回本构模型来描述桩承桥墩系统和软土的动力响应行为,系统探究了地震动强度(基岩峰值加速度或基岩峰值速度)、桩身抗弯刚度和桥跨结构质量等因素对不同位置处加速度放大系数及桩基?桥墩系统最大弯矩系数的影响规律.研究发现:当基岩峰值加速度小于0.15g时,软土对地震波的放大效应较为强烈,而当基岩峰值加速度大于0.2g时,软土的阻尼耗能减弱了地震波的震动强度;桥跨结构质量的增加会显著降低桥墩顶部加速度放大系数;由于软土动力特性的非线性和软土?桩基之间相互作用关系的复杂性,桥墩和桩基最大弯矩系数与基岩峰值速度有着强烈的非线性特征,当基岩峰值速度大于0.2 m/s时,桩基?桥墩系统基本进入塑性变形阶段;桩身抗弯刚度和桥跨结构质量分别对桩基和桥墩最大弯矩响应的影响更大,表明桩基和桥墩地震响应分别取决于地震过程中软土的动力作用和上部结构的惯性力作用.

为研究边界条件对循环荷载作用下道砟的力学特性的影响,采用三维扫描技术生成真实形状的道砟颗粒,通过离散元方法模拟单轨枕道砟箱试验.引入侧向周期边界与底部文克勒弹性路基边界以更好地模拟道床的真实受力状态,并与刚性边界道砟箱模拟结果进行对比,探讨侧、竖向边界条件对道床沉降的影响.此外,从细观上分析各边界条件及组合下的道床受力状态,对比周期边界与刚性边界下侧边区域颗粒运动的趋势.研究结果表明:相较于刚性墙边界,周期边界与文克勒弹性路基边界下的道砟沉降量增大、道床弹性模量减小.不同于刚性边界的位移约束,周期边界侧边区域颗粒的位移增大,运动方向更分散,局部孔隙率减小,颗粒平均接触数增大,且平均侧向接触力减少了约41％,表明侧向周期边界处道砟颗粒存在咬合作用且运动方向不受限.在刚性墙模型中引入底部文克勒路基边界后,平均侧向接触力增加了19％,但分布范围没有发生明显变化.针对单轨枕试验的边界条件,考虑侧、竖向边界条件可以更好地模拟道砟的真实受力状态.

为了提高桩土荷载分担比,一些建筑工程桩筏基础下的复合地基采用了加筋垫层,然而加筋垫层复合地基的变形协调与荷载传递的影响还缺乏深入研究.采用自制的二维多活动门试验装置与椭圆钢棒相似土填料,开展了无筋褥垫层随桩间土下沉过程的模型试验,获得了不同垫层厚度下无筋垫层的变形与应力协调特性.在模型试验基础上,采用颗粒离散元DEM数值模拟建立了无筋与加筋垫层数值模型,揭示了有、无加筋条件下的褥垫层工作特性区别,并探讨了褥垫层厚度、桩间净距以及加筋位置等对褥垫层工作特性的影响.结果 表明:当加筋高度距桩顶超过100 mm时,桩土应力比曲线和褥垫层变形均接近未加筋的情况;加筋体设置高度小于100 mm时,下方颗粒垫层的变形协调会受到影响,格栅与下部垫层之间产生脱空现象,从而导致桩土应力比随着桩间土下沉量的增加而出现陡升;陡升段起点对应的桩间土下沉量随着加筋位置的提高而增加,工程中可能会导致复合地基桩体超过承载力而引起复合地基发生破坏.

针对广州南沙区拟建的110 kV保税输变电站站址的深厚淤泥层软土地基处理问题,采用石灰桩复合地基处理方式进行加固.为克服传统石灰桩机械化程度低的缺点,利用开发的扩径石灰桩成套装备与工艺施做了3种不同间距条件下共28根试验桩,通过试验前后钻孔取芯、静力触探以及无侧限抗压强度试验等,对不同桩间距条件的石灰桩复合地基桩间土承载力以及复合地基承载力进行了评估.基于Biot固结理论的有限元方法,对不同间距条件下的石灰桩复合地基沉降规律进行了探讨.验证了扩径石灰桩工艺可行性的同时,也为石灰桩软基处理的设计施工提供依据.

通过数值计算和图像处理技术,再现或预测工程对象的演化过程和发展趋势,为当前工程对象的设计、施工、管理提供指导意见,因此,数值模拟方法已经成为解决岩土工程难题和进行岩土相关科研的一种不可或缺的手段,且逐渐发展成为研究生和高年级本科生的一门必修课程.本文总结了数值模拟在岩土工程实践和科研中的重要性以及当前数值模拟教学存在的问题,创新性提出了一种以"工程问题"为导向,"数值软件+模拟分析"相结合的教学方法,并阐明了本文所提教学方法的内容和实施途径,提升课程教学质量的创新思路、举措、效果及反思,以及推广至相关岩土工程专业课程的应用前景.

为了研究有砟轨道中轨枕结构对道床劣化的影响,通过有限元方法建立三维有砟轨道数值模型,对比分析了在相位循环荷载作用下的传统轨枕与新型X形轨枕的沉降、道床应力分布,探讨了异形轨枕结构对道砟劣化的影响.模拟结果验证了有砟轨道在循环荷载作用下,道砟沉降主要集中在初期压密阶段;轨枕结构对道床工作性能有一定影响,通过比较X形轨枕和传统轨枕下道砟层的竖向以及侧向位移,道砟层与路基交界面处的应力分布状态以及道砟层内部的应力分布状态,发现X形轨枕底部应力峰值减小,道砟层的竖向沉降减少5.8％,侧向变形减少8.4％,表明其对改善道砟受力分布,减少道砟横纵向变形以及缓解道床劣化有一定作用;优化后的X形轨枕结构具有较大道砟接触面积,能更均匀传递上部荷载至道砟层,同时应兼具抗剪、抗侧移能力.研究结果对于优化轨枕结构以减少道砟劣化有一定参考价值.

大量研究表明软弱土与地下结构之间的相互作用效应明显,且会对地震波产生显著的放大效应,从而对建于软弱土地基之中或之上的结构物的抗震表现产生不利影响.以软黏土(以下简称软土)场地桩基桥墩系统为研究对象,采川了一种新型动力本构模型来模拟软土的刚度劣化及滞回阻尼特性,提出了基于等效原则的高效结构弹塑性模拟方法,开展了一系列的三维有限元显式动力分析,系统研究了基岩峰值加速度(PBA)、桩身抗弯刚度、桥梁质量等因素对软土-桩基-桥墩系统地震响应的影响.研究表明:对于所考虑的3组远场地震波,无论结构系统是否进入塑性变形阶段,软土场地桩基桥墩系统的弯矩响应与每一相应因素之间的变化趋势较为一致;即使结构处于弹性变形阶段,由于软土的非线性动力特性及软土-桩基相互动力作用关系的复杂性,桩基桥墩系统的弯矩和弯曲曲率响应随每一因素的变化趋势是非线性的;当结构进入塑性变形阶段,不同组地震波之间桩基桥墩系统的弯曲曲率响应开始产生较大的差异性,表明强震作用下桩基桥墩系统的塑性损伤状态与地震波的频谱分布特性紧密相关;基岩峰值加速度对桩基桥墩系统地震响应的影响最为显著,梁跨结构质量及桩身抗弯刚度依次对桥墩和桩基的地震响应具有相对较大的影响,表明地震过程中上部结构的惯性力和软土-桩基的相互动力作用分别对桥墩和桩基的地震响应起主导作用;此外,研究发现桩身抗弯刚度存在一个临界值,大于该值时,桩身的最大曲率随桩身抗弯刚度的变化而基本保持不变.相关研究发现对评估既有类似软土-桩基-桥墩系统的抗震安全性具有参考价值.

Underground excavations often pass through underground retaining structures on one side or between the structures. In most cases, ground loss will be caused. At present, there are more and more collapses caused by excavation. When the ground loss occurs, the development of earth pressure and ground settlement is the decision basis for structural reinforcement or treatment. To obtain the preliminary rules of disturbance influences of the ground loss, the model test setup and the steel rod analogical soil technology are developed. A trapdoor is used to simulate the stratum loss caused by underground excavation and collapse, and the foundation pit excavation is simplified as the translation of the retaining wall. Considering the ratios of trapdoor depth to width, trapdoor depth to distance and trapdoor depth to side limit width, 15 groups of two-dimensional model tests are carried out. The earth pressure of retaining structures is measured by 18 cantilevered loaders on the retaining plate, and the surface settlement curve is obtained by the particle image velocimetry. The results show that ground loss increases the earth pressure at the upper part of the retaining wall and decreases the earth pressure at the lower part of the retaining wall. After the occurrence of the ground loss, if the adjacent foundation pit continues being excavated, due to the disturbance of the soil, there is no "bin effect" of the decrease of the earth pressure at the bottom of the retaining structures, and the earth pressure distribution when the retaining wall translation reaches the active limit state is in good agreement with the Coulomb’s active earth pressure. Under the influences of the superposition effect of the translation of the retaining wall after the ground loss caused by the adjacent underground excavation, the maximum value of surface settlement and the curvature of curve increase with the increase of trapdoor width, and increase with the decrease of trapdoor distance and side limit width. Due to the use of steel rod analogical soil, the test results mainly reflect the earth pressure and deformation characteristics of the sandy soil.

为了深入探讨桩承式挡墙路堤中的三维土压力分布及变形特性,采用自制的阵列式多活动门装置,选取路堤高度、桩间净距等参数,并考虑桩间土均匀下沉与非均匀下沉的情况,开展10组模型试验.通过粒子图像测速技术对路堤填砂颗粒位移进行监测,采用自制的荷载计与土压力盒量测桩间土、桩顶和挡墙土压力.试验结果表明:路堤变形存在三角扩展和塔形升高2种模式;应力折减比最小值与残余值均随路堤高度的增加而减小,但同时土拱效应衰减(桩间土应力恢复)速度、衰减达到稳定对应的沉降量均增加,非均匀下沉对土拱效应峰值存在削弱作用,但是对土拱效应残余值影响不大;土拱效应发挥导致土压力在桩顶和路堤中部一定高度位置产生集中.三角扩展模式的土拱效应发挥较弱,塔形升高模式中土拱效应在桩间土下沉过程中得以加强并保持了较高的水平.桩承式挡墙路堤三维土压力分布与变形随桩间土下沉演化的研究成果可为桩承式挡墙路堤设计提供参考.

对于桩承式加筋路堤,加筋改变了路堤底面的变形形态,不可避免地将对路堤变形模式与土拱效应产生影响.为了深入分析加筋的影响,利用开发的多沉陷门(Multi-trapdoor)试验装置和椭圆钢棒相似土填料,开展未加筋桩承式路堤试验并得到不同参数组合下存在的3种变形模式,选取3种变形模式的代表性试验,开展相同参数条件下的加筋试验以及4种不同填料高度和3种不同加筋刚度的桩承式加筋路堤试验.通过粒子图像测速技术(PIV)和自制三点式载荷计准确测试得到全场位移及桩顶和桩间土压力.结果 表明:加筋后,未加筋桩承式路堤的三角扩展型和塔形升高型变形模式转化为同心椭圆扩展模式,等沉面模式转化为同心圆等沉模式;2种变形模式之间转化的临界高度为1.5倍桩间净距,但等沉面的高度仅为67％的桩间净距;加筋对土拱效应发挥起到了双重作用,一方面,加筋减小了差异沉降,导致土拱效应发挥程度降低,另一方面,加筋改变了路堤变形模式,为“同心圆”土拱提供了稳定的拱脚,使得土拱效应发挥程度提高;在填料高度低,加筋刚度高的情况下,土拱效应发挥程度进一步降低;而填料高度高,加筋刚度低时,土拱效应达到了充分发挥所需的差异沉降,加筋对土拱效应有提高作用;张拉膜效应发挥程度随加筋刚度增大而提高,且随着桩间土下沉而提高,导致土拱效应减弱.

To study the influences on the earth pressure and ground settlement when the shield tunnel passes through the adjacent underground retaining structures, a self-designed test device is developed, and 15 model tests are carried out taking into account the ratios of tunnel depth to width, side limit width and excavation distance. In the tests, the stratum loss is simulated using the trapdoor settlement. The earth pressures of retaining structures are measured using 18 cantilever load gauges. The particle image velocimetry technique is used to measure the surface settlement. The variations of earth pressure and distribution of surface settlement during excavation under lateral confinement conditions are analyzed. The results show that the earth pressure at the bottom of retaining wall decreases sharply and then increases at a turning point with a certain height when the shield tunnel passes through the adjacent underground retaining structures. The smaller the ratio of depth to width of tunnel, the larger the decrement of the earth pressure at the bottom and the higher the turning point, and the larger the maximum displacement of surface settlement. The larger the ratio of tunnel depth to lateral limit width, the larger the reduction range of earth pressure, and the larger the maximum ground settlement. The greater the ratio of tunnel depth to distance, the greater the influences on earth pressure of retaining structures, and the greater the maximum ground settlement. Two correction coefficients, the maximum surface subsidence C1and the correction coefficient of settlement trough C2, are introduced, and the Peck’s settlement prediction equation is modified. The predictions show good agreement with the measured values of model tests.

Cushion is a key component of composite foundation, which ensures the deformation coordination and rationality of load distribution between soils and piles. However, the mesoscopic working mechanism of the cushion is not well investigated and the design parameters of cushion are mainly determined according to the experience. In order to reveal the coordination mechanism of the cushion, a test apparatus was designed to simulate the working of cushion in the composite foundation. Three visualized plane strain tests were carried out with different heights of the cushion. A series of 2D DEM simulations was conducted with an orthogonal array. Both the model tests and simulation results showed the three similar patterns of deformation which related to the ratio of the cushion height and the net spacing of the piles. Mesoscopic force chain distribution was also analyzed. In addition, a design suggestion of the cushion height was proposed by analyzing. Meanwhile, an index applied to assess the deformation coordination capability was presented. According to the variance analysis and range analysis, it was found that the height of the cushion and the net spacing of the piles were the significant factors which affected the deformation coordination capability. The upper limit value of the index was also explored and proposed to guide the design of cushion.

The magnitude and distribution of earth pressure against retaining wall is a common concern in the design of retaining wall. The distribution of earth pressure on a retaining wall normally presents nonlinear feature under the influence of boundary conditions, friction of wall back, etc. However, the accuracy of several current earth pressure calculation methods considering soil arching effect needs to be verified. In this paper, a series of 2D visual model tests were carried out on a self-developed apparatus measuring the earth pressure of the retaining wall, using test setup and analogical soil that was mixed with elliptical steel rods. The application of analogical soil in collaboration with loadometers to accurately measure the variation of earth pressure can reduce errors in the measurement of lateral pressure using the pressure cell. Two conditions include static condition and active translation model were considered in simulating and measuring the distribution of earth pressure. The results were compared with that of several theoretical methods. Due to impacts of the friction on retaining wall and soil arching effect, both the static and active earth pressure present nonlinear distribution. Meanwhile, the measured static earth pressure is less than theoretical value, while the measured active earth pressure is in good agreement with that of Paik's method. Due to the influence of wall friction, the inclination angle of sliding surfaces is less than that of the theoretical value at the rupture surface. Moreover, inclination of stresses caused by the friction between wall induces the development of arch-shaped slip surfaces.

为研究隧道开挖引起的地表沉降规律,运用PFC2D软件模拟T rapdoor试验,通过沉陷门下沉对双线隧道开挖引起的地表沉降规律及影响因素进行了系统研究.基于休止角试验和单T rap-door模型试验得到数值模型的计算参数,通过开展单T rapdoor数值试验获取地表沉降曲线,拟合得到单线隧道开挖引起的地面沉降Peck公式参数.开展同时开挖的双T rapdoor数值试验,利用单Trapdoor参数叠加得到双线隧道开挖引起的地表沉降预测公式,并与简单叠加公式的拟合结果进行对比.最后进行先后开挖的双Trapdoor数值试验,揭示了隧道间距、埋深和双线隧道开挖顺序对地表沉降的影响规律.结果表明:随着隧道埋深的增加和隧道间距的减小,地表沉降曲线由"W"形态向"V"形态过渡;先后开挖工况下双线隧道引起的地表沉降曲线呈非对称分布,地表沉降量最大值出现在先行隧道一侧,且随着隧道埋深的增加,地表沉降曲线两侧最大值的差异有增加趋势;Peck公式拟合结果与离散单元法(DEM)数值模型和模型试验结果吻合较好,可用于双线隧道开挖引起的地表沉降预测,具有重要的理论指导和工程意义.