不同含水状态堆积体边坡地震响应特性大型振动台模型试验

堆积体边坡动力响应特性复杂,影响因素众多。已有的大型动三轴试验结果表明,含水状态对堆积体的动剪切模量比与阻尼比有重要影响。针对含水状态这一因素,开展了2组不同含水率的1:12比尺的大型振动台堆积体边坡模型试验,对比分析了其在连续地震荷载序列作用下的加速度响应特性与坡顶位移发展趋势。试验结果表明：2组边坡模型均表现出第一阶自振频率随着加载序列递减、阻尼比随着加载序列增大的现象,但含水率为6.6%时,边坡第1阶自振频率与阻尼比均大于含水率为0.7%的堆积体边坡。堆积体边坡含水率为6.6%时的输入地震动峰值加速度（PGA）放大系数大于堆积体边坡含水率为0.7%时的工况。2组模型坡顶水平响应加速度的傅里叶频谱特征相似,均表现出输入地震波的特征频率越接近模型第1阶自振频率,坡顶水平加速度放大效应越明显,而且从低频侧接近第1阶自振频率的响应比从高频侧接近的要显著。含水率为6.6%的堆积体边坡在多级地震荷载作用下的坡顶永久位移均大于含水率为0.7%的边坡,堆积体边坡含水率为6.6%,坡顶永久位移对输入地震波的频谱特性更敏感。研究结论有助于增强不同含水状态对堆积体边坡动力响应规律影响的认识。     

桩板式抗滑挡墙地震响应的振动台试验研究

汶川地震路基震害调查表明,在顺层或堆积体边坡中的桩板式抗滑挡墙具有良好的抗震性能。为了更好地了解该结构的抗震性能和优化抗震设计方法,以大型振动台模型试验为手段对其进行研究。为明确地震作用下桩板式抗滑挡墙的地震响应特性,试验采用缩尺的卧龙台站实测地震波对模型激励。试验结果揭示了土压力沿桩身分布规律、桩体位移和边坡岩土体加速度的地震响应特征。研究表明,地震土压力沿桩身呈非线性分布,竖向地震荷载对水平加速度有放大效果。所以,双向加载时的地震土压力比水平单向加载时大,但二者差距在地震基本烈度VII、VIII度区域不显著。滑坡推力、滑床对桩的土体抗力和桩身位移均与输入地震动峰值加速度成正比,即随着地震动峰值加速度的增加,加速度放大比增大;滑动面材料剪切强度折减,滑坡推力、土体抗力和抗身位移均增大,且增大速率加快。此外,结合试验成果,建议了桩板式抗滑挡墙设计时地震综合影响系数Cz的合理取值,对应地震基本烈度VII、VIII、IX度区分别为0.2、0.35、0.4。试验结果有助于揭示该结构抗震机制,也为其抗震设计提供了可靠依据。     

液化场地桩基桥梁震害响应大型振动台模型试验研究

采用大型振动台进行液化场地桩基桥梁震害响应模型试验,很好再现了自然地震触发场地液化及结构破坏的各种宏观现象。0.15gEl Centro波输入下,上部砂层局部液化,桩-柱墩加速度主要表现为低频反应,桩动应变幅值自下而上很快增大、到达地表则大幅度减小。0.5gEl Centro波输入下,整个砂层全部液化,桩被折断且加速度也主要表现为低频反应,桩动应变幅值自下而上很快增大、到达地表则大幅度减小。砂层液化与否,对桩-柱墩动力反应影响很大。     

Modulus and damping from shaking table tests of reinforced soil walls

The paper presents rational procedures to estimate normalised shear modulus and damping ratio from measured responses of reinforced soil model walls tested in a 1-g shaking table. Displacement measured at the top of the model walls and input base acceleration time histories are used to produce equivalent hysteretic responses of the model walls. Equivalent hysteretic loops at different strain amplitudes are developed and used to calculate normalised modulus degradation curves and damping ratio for the tested model walls. Model wall responses are also analysed using the single degree of freedom (SDOF) model to determine damping ratio and phase difference, and to verify the validity of SDOF model for application with reinforced soil walls.

Results indicate that the normalised shear modulus significantly decreased at the early stage of the base shaking (i.e. γ_s < 0.03%). For example, about 68% and 80% reductions in shear modulus occurred at γ_s = 0.005% and 0.01% respectively. In addition, a 90% reduction in the normalised shear modulus realised at relatively strong input base acceleration (i.e. for γ_s > 0.03%). Minimum damping ratio of 5% to 10% for both model walls was obtained, increased to 15% to 20% at strain amplitude γ_s = 0.3%, and reached higher values thereafter. Finally, dynamic properties determined from the proposed method are compared with experimental and empirical relationships proposed in literature as well as resonant column test results.     

基于振动台试验的加速度积分位移方法可靠性研究

土体应变变形是土工测试技术的重要难题之一,加速度积分位移是目前动荷载下原位监测和模型试验中认识土体剪应变响应的一种普遍方法,但缺乏验证与可靠性研究。设计砂质边坡?摇臂?质量块振动台模型试验,实测两地震荷载下多组工况的质量块加速度与位移响应时程,探讨了4种代表性方法求解动态、永久位移的可靠性及偏转影响。结果表明,动态位移求解采用高通滤波是一种可靠途径且受积分方式影响较小,各方法在动态位移工况中积分位移与实测相比,峰值平均误差小于等于25%;双拟法积分位移发生严重偏离,与函数形式和处理过程相关。永久位移求解采用高通滤波导致加速度低频成分缺失而无法得到永久位移;双拟法积分位移与实测相比吻合较好,两地震荷载中误差分别为7%和5%;偏转对动态位移求解可靠性影响较小,但对永久位移影响严重,双拟法呈现发散而失真。试验方法与结论,对认识加速度积分位移求取土体剪应变的可靠性和合理选取数据分析方法具有重要科学价值和指导意义。     

A pneumatic shaking table and its application to a liquefaction test on saturated sand

The shaking tables that are used in earthquake engineering are normally driven by hydraulic actuators, which require high maintenance and operation costs. In some studies, when it is only desirable to conduct small-scaled model tests, a pneumatic shaking table can be considered as an alternative to a hydraulic shaking table. This paper describes the design, development, calibration, and performance of a pneumatic shaking table system. It was proved that the pneumatic shaking table can offer satisfactory performances. Using the pneumatic shaking table, a liquefaction test on saturated sand was conducted. During liquefaction, both the stiffness and acceleration response of the ground greatly decreased. In comparison to the sharp increase in excess pore water pressure (EPWP) when liquefaction started, the dissipation process lasted for a much longer time period.     

Dynamic response of a dip slope with multi-slip planes revealed by shaking table tests

This study investigated the effect of internal discontinuity on the dynamic response of a dip slope and evaluated the performance of Newmark’s theory on the sliding of a dip slope with multi-slip planes. A series of shaking table tests were performed under various geometric conditions to explore the dynamic behavior of a dip slope under different external excitations. The test results, including for deformation processes and critical accelerations, under various slope angles, slope sizes, and seismic intensities were examined and further compared with Newmark’s theory. The results of this study are summarized as follows: (1) two types of slope sliding (differential and complete) were determined. (2) Increasing the slope angle and the height of sliding mass tended to shorten the duration of slope deformation. (3) Critical acceleration of the slope increased gradually with increasing peak ground accelerations of input excitations; when the slope height and dip angle increased, the critical acceleration decreased. (4) The triggering time became earlier as the frequency of input excitation increased; the magnitude of sliding mass greatly depended on the amplitude of the input excitation. (5) By comparing critical acceleration between the experimental and theoretical results, Newmark’s theory was determined to overestimate critical acceleration during seismic-induced dip slope failure. This may cause unsafe evaluations, and sliding along existing discontinuities develops more easily in reality.     

特大断面隧道地震动力特性的振动台试验研究

以福州市二环路金鸡山隧道扩建工程为背景,设计制作了特大断面隧道的1/30缩尺模型,并在福州大学土木工程实验中心的双向地震模拟振动台上,完成了21种工况下的模拟地震动试验。对试验数据进行傅立叶分析,发现浅埋条件下特大断面隧道的存在,显著地改变了原场地的动力特性;第一卓越频率主要体现原场地的动力特性,而第二卓越频率主要体现衬砌结构的动力特性。对试验数据进行频响分析,发现地震波自下而上传播至衬砌结构顶部以后,其第二卓越频率附近的频率成分发生了显著增益;其最大增益频率大致等于第二卓越频率。分析特大断面隧道动力特性与输入地震动幅值的关系,发现经历大振幅地震波激励后,衬砌结构上裂缝发展较为显著,其整体刚度明显降低,从而导致第二卓越频率和最大增益频率出现较为明显的下降。基于上述研究成果,进一步提出了特大断面隧道抗震设防的工程建议。     

多点非一致激励下埋地管道多台阵振动台试验方案研究

针对多点非一致激励下埋地管道的破坏特性,首次设计并开展了多点非一致激励下埋地管道的三台阵振动台试验。首先根据试验条件及试验目的,通过专项研究确定了整个模型体系的相似比,设计了适用于长线型地下结构多台阵振动台试验的悬挂式连续体模型箱,确定了传感器的布置位置;其次对模型材料的选取、地震动输入及试验加载方案进行分析设计。最后,利用试验数据分析了模型箱的动力特性及边界效应,结果表明,对多点非一致激励下埋地管道振动台模型试验的设计方案是合理的。该研究为顺利开展多点非一致激励下埋地管道振动台试验奠定了基础,对同类试验也有一定的参考价值。     

Study of shaking table test of seismic subsidence loess landslides induced by the coupling effect of earthquakes and rainfall

Light rain or moderate rain is the most common meteorological event in the rainy season in the loess area of China, so the probability of landslide hazards induced by the coupling effect of earthquakes and rainfall under the condition of light rain or moderate rain is relatively higher than that under heavy rain. To study the dynamic response characteristics and instability mechanism of loess slopes by the coupling effect of earthquakes and rainfall under the conditions of moderate rain and light rain, a low-angle slope model test of a large-scale shaking table after 10 mm of rainfall was carried out. By gradually increasing the dynamic loading, the evolution of the macroscopic deformation and the instability failure mode of the slope model are observed; the temporal and spatial trends of the amplification effect, acceleration spectrum, pore pressure and soil pressure are analyzed; and the failure mechanism of the slope is determined. The results showed that the amplification effect increased along the slope surface upward, and a strong amplification effect appeared at the front of the top of the slope. Because of the stronger dynamic stress action on the upper part of the slope, the immersed soil in the upper part of the slope experienced seismic subsidence deformation, the saturation in the seismic subsidence soil increased, and the water content temporarily increased locally. With the further increase in the loading intensity, a large number of tension cracks were generated in the seismic subsidence area, and water infiltrated down along the cracks and the wetting range expanded under dynamic action. The range of seismic subsidence and cracks further extended to the deep part of the slope. Under the reciprocating action of the subsequent ground motion, the swing amplitude of the soil mass in the seismic subsidence area, which is divided by a large number of cracks in the upper part of the slope, increased further, resulting in the further reduction in the residual strength of the seismic subsidence soil mass located at the crack tip due to the pull and shear action. Finally, under the combined action of gravity and dynamic force, the upper soil mass in the seismic subsidence area dragged the lower soil mass in the seismic subsidence area downward because the sliding force is greater than the residual strength of the soil mass, which induced a seismic subsidence-type loess landslide. Under the coupling effect of earthquakes and rainfall, the instability mode and mechanism of this landslide are significantly different from those of liquefaction-type landslides.

     

锚索框架梁加固平面滑动型边坡地震动力响应

设计并完成了一个缩尺比例为1:20的锚索框架梁加固平面滑动型边坡的振动台试验,通过改变输入地震波类型和峰值,研究了边坡体及支护结构的动力响应特性。试验结果表明：锚固边坡体的整体稳定性较好,地震造成的破坏主要为滑体顶部震碎和无约束坡面岩土体剥蚀、掉块;地震波在经过软弱夹层时存在能量聚集效应,不同地震波下滑体重心处加速度放大系数的差异性随输入地震波峰值的增加而减小;锚索在地震时表现出协同工作的特性,预应力损失最先发生在坡顶,然后向坡体中下部转移;在锚索框架梁的抗震设计时,应考虑边坡体上部的加速度放大效应和锚索预应力损失对边坡整体稳定性的影响。试验结果为合理考虑预应力锚索框架梁的抗震设计提供有益的参考。     

小角度成层倾斜场地动力响应分析的大型振动台试验研究

基于大型振动台试验,研究小角度成层倾斜场地在倾向、走向、垂向、坡面方向、坡面垂直方向上的地震动响应特征,以及地层倾角对场地反应谱的影响规律。试验结果表明：在倾向方向,随着地层倾角的增大,倾斜场地的放大效应增大;在走向方向,当地层倾角小于12.5°时,放大效应强于水平成层场地;在倾向、走向方向,当地层倾角达到12.5°时,场地对反应谱短周期T≤0.1 s部分具有放大作用,对T＞0.1 s的部分具有削弱作用;在垂向方向,随着地层倾角的增加,倾斜场地的放大效应强于水平成层场地;在坡面方向,倾斜场地的放大效应弱于水平成层场地;在坡面垂向方向,倾斜场地的放大效应强于水平成层场地。该研究成果对小角度成层倾斜场地上的建筑物抗震设计具有一定的参考意义。     

砂土地基和粉质黏土地基基坑悬臂开挖离心模型试验

分别开展砂土和粉质黏土两种典型土质条件下基坑悬臂式开挖离心模型试验,详细叙述试验过程中所要解决的关键问题,并提出合理的解决方案。通过对比分析两组试验结果,得到以下结论：非饱和土地基制备中参数控制困难,分层夯实法有待进一步改进,而砂雨法制备的砂土地基参数可控性更好;两组试验的结果有差异,砂土地基试验所呈现的土压力、地基变形、支护弯矩的变化规律更好,因此,岩土离心试验可适当考虑以砂土代替非饱和土;对于采用悬臂式支护结构的基坑,开挖引起的地表沉降曲线在砂土中呈指数型,而在粉质黏土中呈直线型;开挖引起的粉质黏土地基土体位移范围较砂土地基更大;开挖引起的砂土中挡墙弯矩较粉质黏土更大,砂土和粉质黏土中最大弯矩位置都随开挖逐渐下移;在砂土试验中开挖引起主动区土压力各处均减小,而在粉质黏土试验中开挖引起土压力在挡墙底有增大趋势。该基坑工程离心模型试验过程及数据处理方法可为进一步试验提供参考。     

Shaking table tests on slope reinforced by anchored piles under random earthquake ground motions

Acta Geotechnica - Many studies have reported that the seismic responses of slopes and retaining structures are notably different under the effect of multiple seismic waves. Previous experimental...     

How the response spectrum of non-liquefied loose-to-medium sand deposits is affected by the groundwater level

This study examines the water level influence on the seismic response of sand deposits. The seismic ground response of a sand deposit for two cases was computed: groundwater level near the surface and at great depth. The ratio of soil factors computed for both cases evaluates the influence of having the water table near the surface. This parameter is small when the full range of periods is considered, but rises to ∼1.15 when narrowing the range of periods to 0.2–0.6 s, corresponding to the plateau of Eurocode 8 ground type C response spectrum. So, the water level effect is of the same magnitude of the existing soil factor in seismic codes.     

软土场地地铁车站结构地震反应特性振动台模型试验

作为地铁车站结构地震破坏机制大型振动台系列模型试验之一,开展了近、远场强地震动作用下软弱粉质黏土场地框架式地铁车站结构体系的大型振动台模型试验。测试分析了模型地基的加速度、孔压、地表震陷和模型结构的加速度、应变、水平位移反应等。结果表明：地震波在模型地基的传播过程中呈现出自下而上低频增大、高频减小的现象;强地震动作用下模型地基的基频明显降低,呈现出明显的低频聚集（放大）、高频滤波效应;模型地基的孔压比增长较小,在不同特性地震动作用下模型地基孔压比的发展过程存在较大的差异,并显示出显著的空间效应;近、远场地震动作用下模型地下结构的加速度反应存在明显差异,模型地下结构对软土地基地震动加速度反应的影响具有显著的空间效应;模型地下结构相对变形小、未出现明显上浮现象,地震动频谱特性对其侧墙的变形模式和大小存在显著的影响;模型结构中柱为地震损伤最严重部位;模型结构整体损伤情况较轻、处于非破坏状态。     

Development of synthetic soil mixture for experimental shaking table tests on building frames resting on soft soils

In this study, a synthetic soil mixture has been developed and proposed for experimental soil-structure interaction shaking table tests on building frames with shallow foundations resting on soft soil deposits. The proposed mix provides adequate undrained shear strength to mobilise the required shallow foundation bearing capacity underneath the structural model while meeting both criteria of dynamic similarity between the model and the prototype to model soft soils in shaking table tests. To find the most appropriate mixture, different mixes with different proportions of mix components were examined in the soils laboratory. Performing bender element tests, the shear wave velocity of the soil specimens was acquired at different cure ages and the results were examined and compared. Based on the test results, a synthetic clay mixture consisting of kaolinite clay, bentonite, fly ash, lime and water has been proposed for experimental shaking table tests.     

砂箱模型模拟休耕田区以砂桩补注地下水对溶质传输影响

水田在休耕期间蓄水,除了可维持水田原有之生态机能外,亦可增加土壤水分涵养与补注地下水.利用砂箱来模拟休耕田区中打入砂桩以补注地下水时,砂桩存在对灌溉水中之溶质在土壤中传输之影响.由试验结果得知当砂桩贯穿牛踏层时可增加水分入渗速率约40倍,相对的,砂桩亦加速溶质在不同土壤层间之传输速率,尤其在牛踏层下方之土壤为砂层时,其影响更为显著.因此,蓄水过程中需注意水源之品质,以避免土壤与地下水受污染.     

真空预压条件下地下水位和出水量现场测试研究

为研究真空预压期间地下水位和出水量的变化规律,采用研发的新方法对地下水位和出水量开展了现场监测,并对测试结果进行了分析。分析结果表明,真空预压初期加固区内地下水位下降较快,之后处于相对稳定下降状态,停止抽真空后地下水位快速回升。在此期间,加固区外的地下水不断向加固区内渗流补给,形成了一个以加固区为中心一定范围的降水漏斗,直至加固区内外水位趋于动平衡为止。塑料排水板对真空预压条件下地下水位的变化影响显著。真空预压初期平均出水量较大,随后迅速减少并趋于稳定,加固区中央区域出水量要大于边缘区域出水量。     

考虑接缝影响的地下综合管廊振动台模型试验

地下综合管廊属于浅埋狭长型结构,变形缝存在较为普遍,而在地震荷载作用下,其会对地下结构的振动响应产生一定影响,但是目前针对该问题的研究却十分有限。基于振动台模型试验并考虑接缝的影响,开展了不同波形、不同峰值加速度地震波激励下的综合管廊地震响应特征研究,对场地加速度、动土压力以及管廊结构加速度、位移、动应变和弯矩等响应进行了测试和分析。试验结果表明:管廊振动主要受周边土体影响,接缝截面边墙在地震过程中与土体发生脱离,但管廊结构整体性保持良好;管廊接缝在强震下位移较小,不会发生大变形破坏;强震作用下动土压力分布呈非线性特征;接缝截面在地震中受到的弯矩作用小于中部截面,对抗震性能有利。