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1.
由岩溶塌陷、隧道开挖等方面引起的土体变形往往会对基础建设和基础结构等造成不均匀沉降、地面塌陷及开裂等危害,确定土体结构顶部松动土压力的分布情况并准确地分析土体变形与土拱效应间关系显得尤为重要。为了揭示土体变形和沉降对结构顶部松动土压力的变化规律,进行了一系列不同H/B的活动门试验（H为地基高度,B为活动门宽度）。基于试验结果,提出以三角形作为力学模型分析不同滑移面时松动土压力的数学模型,考虑了滑移面角度与土体变形及主应力偏转三者之间的关系,分析了滑移面内任意水平微分土条的主应力偏转情况并建立受力平衡微分方程,根据不同滑移面形态下的边界条件求解松动土压力理论公式,与已有试验结果对比验证了理论公式的合理性。通过对滑移面角度、侧向土压力系数和内摩擦角等主要参数进行分析,结果表明：在较小相对位移下（1%～3%）土体应力迅速发生转移和重分布,初始滑移面角度略小于π/4+φ/2（φ为内摩擦角）,随着H/B增大土体应力比缓慢增长最终趋于稳定;地基内封闭三角形滑移面的松动土压力与相对位移及内摩擦角相关;内摩擦角的增加使得土拱效应得到充分发挥,加强了应力转移,降低了土拱应力比;内摩擦角的增大减小了水平向... 相似文献
2.
浅层岩溶土洞塌陷和浅埋隧道施工等时常会引发浅层地基出现局部沉陷,导致地基可能承受不完全土拱效应作用。如何定量分析不完全土拱效应对浅层地基竖向应力的影响尤为重要。统计了国内外浅层活动门试验,将浅层地基滑移面概化为塔形,同时考虑了浅层地基不同深度处土层差异沉降及主应力偏转过程。通过建立主应力偏转角与活动门相对位移之间的数量关系,量化了浅层地基不同深度对应的不完全土拱效应发挥程度,优化了考虑不完全土拱效应的浅层地基竖向应力计算方法。分析了主要参数对不完全土拱效应的影响,结果表明,随着浅层活动门高宽比及相对位移的增大,应力转移量增加,土体有效内摩擦角及滑移面倾角则相反。可为局部沉降作用下的浅层地基竖向应力计算提供理论指导。 相似文献
3.
摩擦型岩土材料土拱效应微观机制颗粒流模拟分析 总被引：2，自引：0，他引：2
利用离散单元计算软件模拟太沙基活动门试验,从散粒体和微观角度研究在摩擦型岩土材料中产生土拱效应时颗粒位移、荷载传递的特点,并进一步研究了颗粒粒径、土体孔隙率、颗粒摩擦系数、活动门宽度以及活动门位移对土拱效应的影响。结果表明：由于土拱的作用,从拱脚往上一定范围内会将拱顶上方的竖向荷载转化成水平荷载并向两侧传递,同时伴随着两侧土体的侧向挤出。伴随活动门的下移,土拱效应在不断调整,增大颗粒粒径、减小孔隙率、增大颗粒摩擦系数、减小活动门宽度,不但可加强土拱效应,而且还能减小土拱效应的影响范围。 相似文献
4.
微型抗滑桩土拱效应空间特征的细观力学分析 总被引：1，自引：0，他引：1
目前研究中大多将土拱效应简化为平面应变问题,而微型抗滑桩由于桩径小,在承担滑坡推力时将发生较大的变形,其土拱效应的产生和发展具有明显的三维空间特征,目前的研究方法难以考虑这一问题。为此采用基于离散单元法的颗粒元程序PFC3D,利用平行黏结模型建立微型抗滑桩进行分析。模拟结果显示,微型抗滑桩系统中土拱主要出现在接近滑面的深部和中部土体中,浅部土体中土拱受到桩身位移的影响无法成型,且桩间以水平土拱为主,桩长和桩身刚度对微型抗滑桩系统的土拱分布影响不大;随着桩间距的增加,土拱的形成受到显著影响。 相似文献
5.
考虑土拱效应的倾斜滑移面间竖向应力研究 总被引：1，自引：0，他引：1
假定两滑移面相互平行,且与水平面呈一定角度?,对滑移面间土体沿竖向取水平薄层作为微分单元体,通过作用在单元体上的水平力和竖向力的平衡条件,基于土体主应力轴旋转理论,得到考虑土拱效应及倾斜角度的倾斜滑移面间竖向应力的理论公式,及对应不同倾斜角度及滑移面-土摩擦角的土侧压力系数。将得到的理论公式与Handy等公式进行比较,验证了该公式的合理性。研究结果表明：对于无黏性土,竖向应力沿深度先近似线性增大,后增加缓慢并逐渐趋于定值。竖向应力随着倾斜角度和滑移面间距的增大而增大,随滑移面-土摩擦角的增大而减小;土侧压力系数随着滑移面-土摩擦角的增大而增大,而随内摩擦角的增大而减小。 相似文献
6.
The traditional theory of soil arching effect was developed on the assumption that stress distribution in the loosening zone is uniform. However, because of the deflection of principal stress' direction, the stress distribution in the loosening zone is actually ununiform. For the evaluation of principal stress axis deflection and stress redistribution, a discrete element method numerical model of trapdoor problem is established for the simulation of soil arching effect. Based on the numerical results, an arc shape of major principal stress trajectory and uniform horizontal stress distribution at the same depth of the loosening zone are adopted. An analytical model is raised to estimate the average loosening earth pressure acting on the trapdoor and stress distribution in the loosening zone at a limit state. In addition, comparison studies are carried out between the predictions of the proposed solutions and discrete element method numerical results as well as available model test results, thereby validating the accuracy of the proposed theoretical model. Both numerical and theoretical results indicate that the vertical stress distribution in the loosening zone is obviously ununiform. The load acting in the middle of loosening zone is transferred toward two sides so that the vertical stress distribution in loosening zone is concave. 相似文献
7.
本文以柿竹园野鸡尾尾矿库为依托,采用有限元方法对其渗流及稳定性进行分析。利用热流与地下水渗流有限元实现环境的相似性,模拟尾矿库的渗流场并进行分析,确定渗流浸润线及水头分布情况;对浸润线上下的土体采用不同的容重,并考虑有效应力参数,建立有限元静力分析模型,并分别从应力、滑移面、塑性区等方面对尾矿库的静力稳定性做了简要分析,同时研究探讨库区水位变化对尾矿库稳定性的影响。结果表明:在给定的计算条件下,野鸡尾尾矿库在渗流下的稳定性良好,具有较高的安全储备,库区水位变化对于该尾矿库稳定性的影响并不大。 相似文献
8.
为明确盾构施工掌子面滑移破坏机制并确定掌子面支护力的合理范围,基于滑移线理论和极限分析上限定理,利用空间离散技术提出了一种盾构施工掌子面三维滑移破裂模型。依据大主应力拱理论计算滑移区顶部竖向土压力值,并以此作为滑移破坏区上部的竖向荷载计算掌子面极限支护力。研究表明,土拱效应显著影响掌子面前方土体竖向应力的大小及分布规律;将本模型与已有研究方法进行比较,验证了本模型获取的掌子面极限支护力极限分析上限解在黏性土地层以及摩擦土地层中的适用性。同时本模型构建的掌子面破坏区域形态更加贴近离心试验结果与数值计算结果。 相似文献
9.
The paper focuses on the behaviour of a model strip footing, resting on a saturated dense sandy soil, subjected to centred
or eccentric vertical loading. Experimental tests, carried out on a small-scale physical model, are able to reproduce effective
stress levels equivalent to those prevailing in prototype problems, thanks to the maintenance of a downward steady-state seepage
in the soil. The test program consists of three series of tests, each corresponding to an imposed value of hydraulic gradient,
and each involving five load eccentricities; one series, in particular, is carried out with still water. Relevant points of
load–settlement curves are related to the evolution of soil-footing collapse mechanism, evidenced by the distortion of some
vertical coloured sand strips. The collapse mechanism is formed either by one or two sliding surfaces, depending on both load
eccentricities and hydraulic gradient values. Significant differences are shown to occur between centred and eccentric loading
footing response. Shear strength parameters obtained from back-analyses carried out on load values recorded at the appearance
of each sliding surface on the free soil surface, in both hypotheses of associated and non-associated flow rule validity,
are adopted to draw, for each test, a theoretical collapse mechanism consisting, in plane strain, of a log-spiral line with
adjacent-end tangents; the obtained theoretical sliding surfaces, in turn, are compared to the experimental ones, showing
that these latter are either stress characteristic or zero-extension lines depending mainly on cumulative footing displacements
and current effective stress level in the soil. 相似文献
10.
The last half-century has witnessed a proliferation in the use of polyvinyl chloride (PVC) pipes in civil engineering applications. However, little physical data are available to date to assess conformance with performance limits of these pipes subjected to events involving localized ground subsidence. In this study, experimental results are generated and evaluated from a series of physical models involving a buried PVC pipe overlying a localized subsiding bedding zone. Ground subsidence was simulated using a precisely controlled trapdoor system positioned at mid-length of the pipe. A technique including the use of a custom-made displacement transducer was developed as part of this study to facilitate collection of continuous deflection profiles along the axis of the pipes. The progressive development of soil arching was also monitored using earth pressure sensors placed on the top, sides, and at several locations beneath the pipe, both within and beyond the zone of ground subsidence. Strains in the external wall of the pipe were also monitored. The results indicate that significant bending developed in the portion of the pipe traversing the subsidence zone, especially at the pipe crown. Beyond this point, radial deflections of the pipe cross section continued to be detected along the pipe length to distances of approximately four pipe diameters. Ground subsidence induced a severe redistribution of the earth pressures measured in the soil mass surrounding the pipe. A significant increase in vertical soil pressures beneath the pipe was captured within a distance of about one pipe diameter outside the subsidence zone. The overall response of the PVC pipe to localized ground subsidence was found to improve with increasing backfill density and decreasing soil confinement.
相似文献11.
地下水渗流对冻土区模型桩力学特性的影响分析 总被引：3，自引：3，他引：0
为了研究冻土区地下水的渗流效应对桩基的荷载传递规律的影响,考虑到桩身轴力、桩侧冻结应力和桩周土温度对桩基承载力均有影响,依据室内模拟试验,分别模拟了无地下水、桩顶水有温度效应、桩底水有温度效应、桩顶水有温度及渗流效应、桩底水有温度及渗流效应5种不同工况下地下水对冻土桩基承载力的影响。试验结果表明：无论是桩顶水还是桩底水,在接近地下水处,同时有温度效应及渗流效应的轴力值变化比仅有温度效应时的小,当地下水为桩底水时加载后的桩轴力小于地下水为桩顶水时的轴力值;桩底水引起的桩侧冻结应力变化幅度比桩顶水大,地下水的温度效应使得部分冻土温度升高而融化,而地下水的渗流效应进一步增大了冻土融化范围,使得桩基力学特性发生改变,进而影响了桩基承载力。 相似文献
12.
土拱效应对考虑拱效应时土压力的计算非常重要,而目前对土拱效应的形成机理认识还不深刻。通过自行设计的室内挡板下落试验对砂土拱效应的问题进行了试验研究。得到了不同的土体埋深情况下,随挡板下移挡板上土体重量、箱内土体的应力和侧压力系数的变化规律。试验结果表明,挡板微小的位移挡板上土体的重量就会快速降低;随着挡板继续下移挡板上土体重量降低的趋势逐渐减缓,认为挡板下移2.5 mm时上部土体达到临界状态;随挡板下移箱底挡板上部中心线上的竖向土压力减小,挡板两侧上部土体的竖向土压力增大;挡板上部中心线上的侧压力系数明显增大。通过土体内的应力变化规律对砂土拱效应的形成机理进行了分析。 相似文献
13.
Granular soils have the inherent ability to develop load transfers in their mass. Mechanisms of load transfers are used as
a basic principle of many civil and geotechnical engineering applications. However, their complexity makes it difficult to
formulate relevant design methods for such works. The trapdoor problem is one of the ways to reproduce load transfers by the
arching effect in a granular layer in non-complex conditions. In addition, many analytical solutions for the prediction of
load transfer mechanisms are based on the trapdoor problem. However, some of the parameters required are still being widely
discussed, in particular the ratio of horizontal stress to vertical stress. For this paper, an experimental device for trapdoor
tests in plane strain conditions was created and several geomaterials were tested. Three phases in the response of the materials
were consistently observed. Each of these phases corresponded to a specific displacement of the trapdoor. A first phase of
high load transfer was observed followed by a transition phase which was followed by a critical phase for which the load transfer
amplitude increased and stabilized. Analytical solutions and experimental values of load transfers were compared. Considerable
differences between the stress ratio needed to fit the experimental data and the stress ratio proposed in the analytical models
were noted. Based on the conclusions of the experimental study, the discrete element method was used to model the same trapdoor
problem. A wide range of granular materials was modeled and tested in the trapdoor problem. The three phases in the response
of the layer were also observed in the numerical modeling. In addition, it was shown that the shear strength of the material
is the key parameter of load transfers: peak shear resistance for the small displacements of the trapdoor and critical shear
strength for the larger displacements. A micro-mechanical analysis showed that the effective stress ratio in the sheared zone
does not vary as much with shear strength. Stress ratios here were again greater than those proposed in the analytical solutions.
Nevertheless, the relevance of the solution of Terzaghi was confirmed as soon as the stress ratio was correctly chosen. 相似文献
14.
土拱效应广泛存在于结构?土相互作用体系中,并不可避免地受到动荷载的影响。为探究循环荷载下土拱的演化过程,开展了循环加载下的活动门试验,结合粒子图像测速法（PIV）,对土拱的结构形态、位移场及竖向应力的变化规律进行了分析。结果表明,初始土拱形成时活动门上方产生三角形脱空区,施加循环荷载后该结构边界逐渐沿竖向延伸并向填土表面发展,位移场影响范围呈扇形向两侧扩大。根据初始差异沉降的不同,土拱的发展演化呈现出最终状态的差异：达到新的稳定状态,或发生失稳破坏。循环荷载下,初始活动门位移较大时土拱更易趋于破坏,表现为脱空区贯通填土表面并形成竖向滑裂面。土拱结构的稳定性受到脱空区土体堆积对其下边界的支撑作用影响。 相似文献
15.
查清地裂缝水文地质情况可以为西安地铁设计和施工提供科学依据。根据西安地铁勘察工作需要,2008年7月～9月选择地裂缝穿过的西安市劳动路小学院内场地首次尝试进行跨地裂缝水文地质专项现场试验。试验内容包括试坑渗水试验、钻孔注水和抽水试验,并以1号抽水井的稳定流抽水试验为典型,研究地裂缝对地下水渗流的影响。采用带1个观测孔的稳定流潜水完整井公式、带2个观测孔的稳定流潜水完整井公式以及潜水完整井水位恢复速度计算公式等3个渗透系数计算方法,得到了地表浅层土体沿地裂缝走向和垂直于地裂缝走向的渗透系数,分析了渗透系数的差异性;最后利用MADIS有限元软件模拟场地内建筑物对地基土施加应力,探讨了建筑物对场地土体的影响。结果表明：利用上述3个公式计算,都得到沿地裂缝方向土体的渗透系数比垂直地裂缝方向的土体稍大;在同一落程中,利用潜水完整井水位恢复速度公式计算得到的渗透系数最大,利用带2个观测孔的稳定流潜水完整井公式计算得到的渗透系数次之,利用带1个观测孔的稳定流潜水完整井公式计算得到的渗透系数最小,这主要是由井损造成的;建筑物对场地土体的影响主要集中在素填土层、黄土层和古土壤层,粉质黏土层以下影响则逐渐减弱,影响深度在18 m左右;由于建筑物长期对地裂缝上盘土体施加荷载,附加应力作用使地基土固结压密,导致地裂缝上盘土体的渗透系数较下盘小。 相似文献
16.
瀑布沟大坝心墙拱效应分析 总被引：2，自引：0，他引：2
在总结前人提出的拱效应系数基础上,对拱效应系数的公式进行了改进,认为拱效应系数应该是实测土压力与上覆土压力和孔隙水压力之和的比值。结合瀑布沟大坝监测资料,用改进的拱效应系数计算公式对大坝心墙拱效应进行计算,并对心墙内拱效应进行动态分析。在施工期,施工工艺是影响大坝心墙拱效应系数的主要因素,填土在仪器埋设以上0～20 m时,拱效应系数较大,随着填土的增加拱效应系数减小,施工期坝体内应力分布在蓄水初期起决定性作用。在蓄水期,心墙上游侧拱效应系数与水位变化呈反相关联,拱效应系数比下游同高程和0+001 m处大;0+001 m处拱效应系数与水位变化呈正相关联,且此处拱效应系数最小;心墙下游处拱效应系数与水位变化呈正关联的关系,在心墙与基岩接触处拱效应系数大于100%。产生这种规律的原因主要有湿化、渗流、水力劈裂作用,三者共同影响,从而导致心墙内应力发生变化。 相似文献
17.
通过室内模型试验测试了桩网结构路基各部分在动静两种荷载下的桩-土应力、格栅拉力,研究了土拱效应的发展演化机制以及土工格栅拉膜效应的发展特点。试验结果表明：桩-土应力以及格栅拉力的分布都是路基横截面方向上大于其纵向延伸方向,这与路基的梯形截面设计相关;空间土拱效应要强于平面土拱效应,空间土拱效应的极限状态出现在桩-土应力比为3.8时,平面土拱效应的极限状态出现在桩-土应力比为2.2时;动荷载下土拱效应较静载有一定的衰减,且静载下土拱效应越强的部位在动载的下衰减程度越大,桩间土压力随振次的发展趋势类似N型,与桩顶土压力的变化趋势正好相反。 相似文献
18.
现有的土拱效应计算方法中,由于采用的计算模型不同,计算结果差异很大。文中克服传统连续介质力学模型的宏观连续性假设,采用二维颗粒流程序（PFC）建立基于模型试验的细观数值分析模型,对桩承式路堤中土体接触力、应力分布、主应力方向、竖向位移进行分析,并比较计算和实测结果,研究土拱效应的荷载传递机制。同时,对不同桩帽、桩间距、填土高度、颗粒大小、摩擦角的情况进行PFC方法的参数敏感性分析。研究结果表明,桩承式路堤桩顶处局部范围可按弹性核考虑;土拱的分布型式受桩帽型式、桩净距、格栅的影响;实际土拱作用的影响范围主要集中在路堤底面以上约1倍桩净距的区域;土拱内部的竖向应力和水平应力均随深度非线性改变,桩土应力比随着荷载水平、土体内摩擦角、颗粒大小的增大而增加。 相似文献
19.
渗流场水头分布计算是进行渗流量和渗流水力坡降计算的基础,准确、有效地求取渗流场水头分布是渗流计算的关键环节。对均质非饱和土体一维稳态流的流动方程进行分析,考虑到渗透系数是与基质吸力相关的函数,通过数学变换,给出了稳定渗流场的解析通式,并基于渗透性函数中的Gardner模型,给出了非饱和土一维稳态流水头垂直分布的解析解。该解析通式表明,均质非饱和土一维稳态流水头垂直分布主要受地表水头、深度和流动率3个因素控制。分别计算了一维稳态蒸发条件下粉土和黏土两种典型土类水头沿垂直方向的分布。计算结果表明：稳态蒸发条件下粉土层和黏土层内的水头分布表现出相似的变化规律,即自地表至地下水位处随着土层深度的增加,水头分布呈现出加速递减的趋势;在相同的蒸发条件下,对于相同深度处的黏土和粉土而言,黏土层内水头更高些;对同一种土类而言,在较大的蒸发状态下同一深度处土层内水头更高。反之,则较低。 相似文献
20.
桩承式路堤土拱形成及荷载传递机制离散元分析 总被引：1，自引：0，他引：1
土拱效应是桩承式路堤中影响荷载传递的关键因素。基于前人的室内模型试验,建立了桩承式路堤离散元（DEM）数值分析模型。基于路堤中应力偏转规律对土拱随桩土相对位移的形成规律进行了分析。在该基础上提出了合理拱轴线土拱模型,并引入荷载传递系数? 对土拱与土拱下方路堤填料间的荷载传递进行量化分析。模拟结果表明,桩土相对位移引起路堤中应力主方向发生偏转并形成虚拟土拱;土拱形态及高度随桩土相对位移的变化而变化,最大拱高约0.8倍桩净间距;? 随土拱高度的增加呈对数关系减小。 相似文献