水位下降条件下土坡破坏的离心模型试验研究

水位下降引起土坡破坏的规律机理对于发展稳定性分析方法具有重要意义。研制了离心模型试验中超重力场水位升降模拟设备,进行水位下降条件下黏性土坡变形破坏的离心模型试验。根据试验位移测量结果,基于变形与破坏过程集成分析的思路探讨了土坡破坏机理。水位下降导致土坡发生由坡顶向坡脚的渐进性的错动破坏。水位下降条件下土坡的变形和破坏过程是耦合的。变形局部化发展是导致滑裂面出现的根本原因。滑裂面出现后滑动体内部仍发生显著的变形,并与滑裂面上的错动变形相耦合。     

Centrifuge model test study on micro-pile reinforcement of shallow foundation

Micro-piles are an effective reinforcement measure for existing foundations in practice. A series of centrifuge model tests were conducted on different combinations of shallow foundation and micro-piles to investigate the reinforcement effect of micro-piles. The interaction mechanisms between the shallow foundation and micro-piles were analyzed on the basis of full-field image-based measurements of soil displacement. The micro-piles were proven to provide an effective reinforcement on the shallow foundation by decreasing the settlement, increasing the bearing capacity and making the soil deformation more uniform. The loading induces soil deformation within an area that expands gradually with a similar boundary shape and is widened by the micro-piles. The shallow foundation and micro-piles exhibit a significant nonlinear coupling effect on the bearing ability due to their interaction through the soil with the mechanism summarized with the strengthening effect and weakening effect. The micro-piles have a strengthening effect on the shallow foundation to increase the bearing resistance by constraining the horizontal deformation of the neighboring soil. The shallow foundation has a weakening effect on the micro-piles to decrease the bearing resistance by reducing the pile-soil relative displacement. The weakening effect and strengthening effect play the dominant role in turn as the total resistance increases.     

Centrifuge model test of tunnel face reinforcement by bolting

Typical auxiliary bolting methods were tested using centrifugal models with sandy ground to confirm their strengthening effects on tunnel faces. Face bolting, vertical pre-reinforcement bolting and forepoling were tested separately, in various arrangements. Also, the experimental results were compared with the analytical results by the Distinct Element Method (DEM). Experimental results demonstrate that each bolting technique has an optimum length and arrangement to perform effectively. DEM modeling with a staggered block pattern was used to stimulate the failure states observed in the experiment. The effect of the bolting obtained from the experimental results was also confirmed by numerical simulations.     

Centrifuge modeling of the behaviour of helical piles in cohesive soils from installation and axial loading

Centrifuge modeling offers a viable tool for research in the soil-pile interaction, but this technique has not been used for helical piles in cohesive soils. A centrifuge model test program of helical piles in cohesive soils was carried out to investigate the axial soil-pile interaction and pile failure mechanism. Helical piles were installed while the centrifuge was spinning, which enabled the determination and interpretation of installation torque and pore pressure response of the soil. An analytical model for calculating the installation torque of helical piles screwed into cohesive soils was proposed and verified by test results. The pore pressure response to pile installation was monitored near two piles at two depths. Comparing the measured dissipation curves with the analytical curves for driven piles suggested that the excess pore pressure was primarily induced by the helical pile shaft. The model piles were axially loaded under 20 g condition. The present research may be considered as the first centrifuge test program that measured the axial load distribution along helical piles. The shaft internal loads were recorded using an innovative strain gauging method. The results show that the axial failure modes of helical piles depend on the strength of soil and inter-helix spacing. In general, it may be easier for a stiffer clay to form an inter-helix soil cylinder during axial pile movement.     

Centrifuge modeling of the geotextile reinforced slope subject to drawdown

Geotextile is an effective reinforcement approach of slopes that experiences various loads such as drawdown. The geotextile reinforcement mechanism is essential to effectively evaluate the safety of geotextile-reinforced slopes under drawdown conditions. A series of drawdown centrifuge model tests were performed to investigate the deformation and failure behaviors of slopes reinforced with different geotextile layouts. The deformation and failure of unreinforced and reinforced slopes were compared and the geotextile reinforcement was indicated to significantly increase the safety limit and the ductility, reduce the displacement, and change the failure feature of slopes under drawdown conditions. The slopes exhibited remarkable progressive failure, downward from the slope top, under drawdown conditions. The progressive failure was induced by coupling of deformation localization and local failure based on full-field measurements of displacement of slopes subjected to drawdown. The geotextile reinforced the slope by decreasing and uniformizing the slope deformation by the soil-geotextile interaction. Through geotextile displacement analysis, the geotextile-reinforced slope was divided into the anchoring zone and the restricting zone by a boundary that was independent of the decrease of water level. The geotextile restrained the soil in the anchoring zone and the soil restrained the geotextile in the restricting zone. The reinforcement effect was distinct only when the geotextile was long enough to cross the slip surface of the unreinforced slope under drawdown conditions.     

Shaking table test on underwater slope failure induced by liquefaction

Sand liquefaction is a process in which the excess pore water pressure of saturated sand soils increases and the effective stress of saturated sand decreases under the action of vibration, resulting in the transition of sand soils from the solid state to the liquid state. In this paper, an underwater sand slope model containing the upper sand slope and the bottom non-liquefied clay layer was designed. The whole process of large deformation of flow liquefaction from the solid state to the liquid state was reproduced by the shaking table test and recorded by the high-definition particle image velocimetry (PIV) equipment. Four main influencing factors: the acceleration amplitude of the shaking table, the frequency of the shaking table, the relative density of the sand slope, and the slope ratio of height and width of the sand slope, were considered. During the test, the dynamic response characteristics of acceleration and excess pore water pressure (EPWP) within the underwater sand slope model were monitored and analyzed in the whole deformation process to reveal the mechanism of the sand liquefaction process and the law of development and provide data support for subsequent research.     

风干堆积体边坡地震响应的动力离心模型试验

 堆积体边坡在我国西南地区广泛分布,为深入研究其地震响应规律,设计完成了1∶50比尺的概化边坡离心振动台模型试验,分析4级不同强度地震连续作用下,风干堆积体边坡的加速度响应、边坡变形及其失稳模式。试验结果表明,堆积体边坡水平向PGA放大系数表现出了典型的高程放大效应与趋表放大效应。沿堆积体边坡高程方向,输入地震波频谱特性发生了明显改变,各测点加速度傅里叶谱的卓越频率随PGA增大而降低。考虑竖直向加速度放大效应的影响后,发现合放大系数与水平向夹角随高程有减小的趋势,反映了坡面处发生的波场分裂与波型转换现象。随地震波幅值的增大,水平向与竖直向PGA放大系数均先减小后增大。试验过程中观察发现在地震波加速度峰值达到0.216 g时堆积体边坡开始失稳,坡顶沉降明显,失稳模式以浅层崩滑为主。     

波浪-海床-结构物相互作用离心模型试验及数值模拟

针对波浪-海床-结构物相互作用这一海洋结构物设计中需考虑的重要问题,采用离心模型试验及数值分析模型两种手段进行研究。离心模型试验采用浙江大学自行研制的超重力造波试验装置及ZJU400土工离心机完成,观测到波浪作用下砂质海床内部孔压累积的渐进特性;所采用的数值分析模型基于Biot固结理论,结合可准确描述砂土液化前后力学行为的“交变移动”土体本构模型,可对波浪作用下海床与结构物相互作用及液化现象进行合理模拟。通过与离心模型试验的对比验证该数值模型的有效性,随后利用该模型针对海底埋置管道这一近海区域常见的海工结构物周围土体在波浪作用下的动力响应进行详细分析。结果表明：海底管道的存在会加快管顶及管侧的超静孔隙水压力累积,管道周围土体的弱化及超静孔隙水压力累积导致的额外上浮力两者的耦合作用是海底管道发生上浮的主要原因。     

边坡动力破坏特征的振动台模型试验与数值分析

采用大型振动台模型试验,输入幅值逐级增大的地震波,直到边坡破坏,得到边坡动力破坏特征:上部拉裂缝和下部剪切滑移面形成贯通的破裂面,滑体上监测点位移和加速度响应突变,表明边坡已经发生破坏,且坡顶局部块体在地震作用下发生抛射现象。采用FLAC动力差分软件通过逐渐加大输入地震波幅值,模拟模型边坡振动台试验过程,证实拉裂缝与剪切滑移面贯通是边坡动力破坏的必要条件,位移和加速度响应突变可以作为边坡动力破坏的判据。振动台试验和数值计算在边坡动力破坏三个特征上吻合较好,证明振动台模型试验结果的合理性,也证明数值分析方法的可靠性。     

Evaluation of potential failure of rock slope at the left abutment of Jinsha River Bridge by model test and numerical method

Jinsha River Bridge is located on Tiger Leaping Gorge town, China. The left bank slope composes of moderately thick layer of slate overlain by schistose basalt, and where rocks are controlled by two sets of joint planes. To evaluate the stability of the rock slope under bridge foundation, model test and calculation model based on the geological parameters and the slope stability was simulated and analyzed using Universal Distinct Element Code (UDEC) and Finite Element Mehod (FEM). According to model test, failure mainly initiated at the toe with shear movement along the joint planes, eventually resulting in the sliding along the slope surface and formation of tension crack at the crest of the model. This result coincide with the UDEC model, which shows that slope surface will produce loosening damage and slipping expected along the joint planes under different loading conditions. Moreover, the result of FEM analysis indicates that the rock mass under the main pier has potential shear failure region. So, the bridge foundation should be strengthened to prevent the slope failure under external forces.     

斜坡基底软土桩–网复合地基变形特性离心试验研究

为探究斜坡基底软土–桩网复合地基的变形特性,以沿海铁路线某深厚软土地基断面为原型,开展比尺为1∶100室内离心模型试验。通过对试验数据的整理分析,结果表明:(1)路堤顶部两侧的竖向和横向位移、两侧沉降差在运营期都有明显增长,但竖向和横向位移主要产生于路堤施工阶段,而沉降差基本产生于运营期内;(2)加筋垫层对其下方的地基表层横向位移有明显约束。地基右侧土体的竖向和横向位移关于路堤中心不对称,表现为右侧大于左侧,地基表面呈现出明显偏向斜坡外侧的非对称"沉降盆";(3)斜坡桩和悬浮桩的桩顶竖向和横向位移明显大于平台桩,平台桩潜在破坏模式为弯拉或弯剪破坏,斜坡桩为倾斜破坏,悬浮桩为倾斜+横移破坏;(4)桩发生明显上刺和下刺现象,且淤泥质黏土表现出流体特性发生绕桩横向流动。     

深层搅拌法加固码头软基离心模型试验研究

运用离心模型试验技术对采用深层搅拌法加固码头接岸软基和沉箱码头基础的工作机理和破坏机理开展研究 ,弄清了影响整体稳定性的主要因素 ,得出了不同地基条件、不同着底方式、不同宽度加固体的外部破坏型式和地基整体破坏型式 ,证实了可用朗肯理论计算加固体两侧主、被动土压力。     

Centrifuge model tests of geotextile-reinforced soil embankments during an earthquake

The behavior of geotextile-reinforced embankments during an earthquake was investigated using centrifuge model tests, considering a variety of factors such as gradient of slope, water content of soil, geotextile spacing, and input shaking wave. The geotextile-reinforcement mechanism was revealed on the basis of the observations with comparison of the unreinforced embankment. The geotextile significantly decreases the deformation of the embankment and restricts sliding failure that occurs in the unreinforced embankment during an earthquake. The displacement exhibits an evidently irreversible accumulation with a fluctuation during the earthquake which is significantly dependent on the magnitude of input shaking. The peak strain of the geotextile exhibits a nearly triangular distribution in the vertical direction. The embankment can be divided into two zones, a restricting zone and restricted zone, where the soil and geotextile, respectively, play an active restriction role in the soil-geotextile interaction. The soil restricts the geotextile in the restricting zone, and this restriction is transferred to the restricted zone through the geotextile. The strain magnitude of the geotextile and the horizontal displacement of the geotextile-reinforced embankment decrease with increasing geotextile layers, with decreasing water content of the soil, with decreasing gradient of the slope, and with decreasing amplitude of the earthquake wave.     

砂性地层地震反应离心模型试验研究

介绍了离心模型试验技术在地震工程研究中的应用原理与方法。运用离心模型试验技术 ,研究了砂性地层在地震作用下土层加速度反应、振动超静孔压的产生、消散过程 ,真实地再现了地震时土层液化的主要特性。结果表明离心模型试验技术是研究地层地震反应的有效手段 ,所得结论对进一步开展砂土地震反应与液化机理研究有积极借鉴意义。     

包裹式加筋砂土边坡离心机试验研究与对比分析

利用自主设计的宏细观可视化全程拍摄系统,对包裹式加筋砂土边坡进行了离心机模型试验。研究了20g离心场下包裹式加筋砂土边坡宏观变形模式和力学性状以及筋土界面处细观作用机理和土颗粒运动规律。将离心机试验结果与1g静力模型试验结果进行了对比,分析了不同应力场下加筋边坡变形破坏的宏细观机理。研究结果表明：不同应力场下包裹式加筋砂土边坡破坏模式不同,高应力状态下界面处摩擦咬合力峰值大于筋材拉伸断裂强度,而低应力状态下界面处筋材拉伸断裂强度大于摩擦咬合力峰值。筋土界面处不同的应力状态是影响筋土界面作用方式的重要因素。该研究对进一步认识包裹式加筋砂土边坡破坏机理有积极意义。     

水位骤降对边坡稳定性影响的模型试验及数值模拟研究

自然或人工边坡的稳定性研究是当前岩土工程研究领域的热点问题之一。随着三峡等大型水利设施的兴建和投入使用,水位骤降对边坡稳定性影响也引起人们的广泛关注。通过室内模型试验研究水位骤降引发临水边坡滑坡的原因及失稳模式是经济、便捷的常用方法。本试验模型箱的尺寸为2.5m×1.5m×1.5m(长×宽×高),边坡高度为1.05m。边坡体内埋设了10只土压力盒和7只渗压计,用于测量水位骤降过程中土压力和孔隙水压力的变化情况,记录边坡失稳破坏过程中土体内部的变化过程。同时,利用geo-slope软件模拟边坡失稳破坏的整个过程,并且利用数值模拟的结果与试验结果进行对比分析,解释边坡破坏的机理。试验结果表明:水位骤降对边坡稳定性产生很大影响,水位下降速度越快,边坡沉降也就越大,最后形成明显的位移集中区域;边坡的安全系数分别随着水位高程的减小、水位下降时间的增加出现增加最后趋于稳定;在此土质、坡形条件下的边坡破坏的形态与数值模拟所得8min时滑动面的形态相吻合,据此也用试验验证了数值模拟的可靠性。     

抗滑桩静力与动力破坏离心模型试验对比分析

在探讨边坡中抗滑桩的加固效果时,应该重视混凝土抗滑桩不同条件下破坏规律的研究。采用研制的微混凝土抗滑模型桩,通过动力离心模型试验研究了两种情况下的破坏特点。一种情况是混凝土抗滑桩一侧静力开裂后受地震作用继续开裂至完全断桩,另一种情况是静力条件下稳定的边坡加固桩在地震作用下桩底发生开裂。根据试验观察以及试验结果对比分析了微混凝土抗滑桩在两种不同条件下开裂破坏过程中弯矩分布特点:静力开裂后在地震作用下桩底嵌固约束转化为活动铰约束,其弯矩始终呈抛物线形分布,只是其峰值随时间发生变化;静力条件下稳定的加固桩在地震作用下,其弯矩先有较大增加然后又由于桩底一侧开裂而下降较多,并且小于震前静态弯矩。     

Centrifuge model test on dynamic behavior of group-pile foundation With inclined piles and its numerical simulation

In this paper, dynamic behavior of a grouppile foundation with inclined piles in loose sand has been investigated with centrifuge model tests. The test results are also simulated with elastoplastic dynamic finite element method, in which, not only sectional force of piles, stress of ground, but also deformation of piles are calculated using a three-dimensional elastoplastic dynamic finite element analysis (Code name: DGPILE-3D). The numerical analyses are conducted with a full system in which a superstructure, a pile foundation and surrounding ground are considered together so that interaction between pile foundation and soils can be properly simulated because the nonlinearities of both the pile and the ground are described with suitable constitutive models. Different types of piles, vertical pile or inclined pile, are considered in order to verify the different characteristics of a group pile foundation with inclined piles. The validity of the calculation is verified by the model tests.     

多级拼装悬臂式挡墙地震响应振动台模型试验

多级拼装悬臂式挡墙是一种可用于高填方工程的新型轻型支挡结构.为确定墙-坡系统的地震动力响应特征,进行几何、重度和时间相似比分别为1 ∶ 10,1 ∶ 1和1 ∶ 3.162的三级拼装悬臂墙支挡边坡的水平振动台模型试验.结果表明:坡体加速度沿墙高呈明显的非线性放大效应;墙后静止土压力和动土压力均呈"三峰型"分布模式,各级...     

基于地质力学模型试验综合法的顺层岩质高边坡稳定性研究

针对顺层岩质高边坡稳定性问题,提出降强法与倾斜抬升超载法相结合的地质力学模型综合的试验方法,推导该方法下边坡稳定综合法安全系数表达式,将其应用到白鹤滩左岸顺层岩质高边坡工程实例中,并与FLAC3D强度折减法数值计算结果进行对比。研究结果表明:2种方法得到的边坡变形破坏特征、破坏模式、安全系数均较为接近,说明所提的试验方法和安全系数表达式是合理的;白鹤滩左岸边坡的地质力学模型试验综合法安全系数KSC=1.526~1.575,数值计算得到的稳定安全系数KSS=1.45~1.52;边坡稳定安全的控制性结构面为层间错动带C3–1及其上盘岩体内的软弱结构面,层内错动带LS337上的加固措施是有效的。研究成果对顺层岩质高边坡安全稳定具有重要的工程意义和实用价值。