减低交通荷载引起地面振动的数值模拟
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摘要
高速铁路和高等级公路是国家重要的基础设施,大力开展交通建设能有效促进国民经济发展,但高速列车及重型卡车的运行会产生振动波,通过土介质传播到周围的工业区和居民区,可能导致一些精密仪器故障、人类感觉不舒适以至于建筑物的破坏。在邻近振源附近设置合理的防护层是防止或减轻这种灾害的重要措施,因此,对于防护结构的材料、布局以及尺寸的研究具有现实指导意义。
现在使用数值模拟方法进行地表列车动力荷载防护的研究并不多,在已有少量文献中对于土介质的模拟多采用理想的弹性模型。本文运用LS-DYNA软件,选用更适合岩土介质的弹塑性模型,对高速列车等交通荷载作用下地面振动及连续墙挡板的防护能力进行三维数值分析,并与现场测试结果进行比较;进一步研究了防护层材料以及防护结构尺寸对于减振效果的影响。其主要研究工作如下:
首先,建立三维几何模型,分别采用弹性材料模型和弹塑性模型,计算了某现场试验,验证了模型设计的合理性。其次,对比研究了无填充壕沟、注水壕沟、不同密度的泡沫填充壕沟以及混凝土桩填充壕沟防护时,地面在高速列车荷载作用下所产生的动力响应。再次,研究了不同列车运行速度产生的地面振动特性,以及在混凝土桩填充壕沟防护下,挡板尺寸对于防护效果及防护范围的影响。结果发现:
①列车运行附近振动较强烈,随着距振源距离的增大,振动明显减弱。在距轨道25m距离内振级较高,应采取有效的隔振减振措施。
②列车运行速度越大,由此产生的振动荷载也随之增大,引发的地面振动效应也增大。而列车运行速度较小时,振级随着距振源距离衰减速度更快。
③无填充壕沟防护层减振效果明显,但在多雨地带易转变成注水壕沟,防护能力有所下降,仍可以有效减低地面的振动效应。EPS泡沫填充壕沟属于质地较软的材料,防护效果较好。密度越小,防护效果越好。质地较硬的材料如混凝土桩填充材料有一定的防护效果,但相比质地较软的材料防护效果较差。
④挡板长度和深度直接影响混凝土减振挡板的防护效果和防护范围,与振动波波长有关,增加减振挡板长度和深度对于一倍波长内的区域的防护效果没有影响,对于一倍波长外的区域,挡板长度每增加0.4倍波长,振级减少量增加4dB;挡板深度每增加0.4倍波长,振级减少量增加6dB,挡板深度对防护效果的影响更为明显,挡板宽度的尺寸主要影响防护范围。
High-speed railways and high-grade roads are important infrastructures for national economy growth. However, the passage massive and high-speed trains may generate ground vibrations, which will propagate through the soil and impinge on surrounding industrial and residential areas, and may cause malfunctioning of some sensitive equipments, discomfort people and damage buildings. It is possible to avoid or mitigate these adverse effects by providing a suitable wave barrier around the vibration sources, and therefore it is of a practicable significance to lead investigations into the material, layout and dimensions of such barrier structures.
Railway traffic induced ground vibration and the isolation project have been a subject with increasing research interests in recent years. In general, a few references on this subject preferred to employ elastic model to simulate soil responses under the traffic dynamic excitation. In this thesis, a more sophisticated elastoplastic model was employed. The ground vibration caused by high-speed train was analyzed with a three-dimensional numerical model by software LS-DYNA. Particularly, barriers which are composed of different materials (open trench, inundated water trench, different density of geofoam in-filled trench, and concrete in-filled trench) and a reinforced concrete pile with different dimensions were numerically analyzed subjected to railway traffic loads. The main research works are as follows:
Firstly, a geometry model was built by LS-DYNA with elastic and elastoplastic material models. The numerical results were compared with in-situ tests to verify this model. Secondly, train-induced ground vibration was respectively investigated without protection barrier and with protection barriers of open trench, in-filled trench. Thirdly, the ground vibration level is studied at different train speeds. Finally, the isolation efficiency of a reinforced concrete pile barrier is comparatively investigated for different dimensions. From these studies, following understandings and conclusions can be made:
①Train speed is the key factor for the ground vibration level. Ground vibration is strong around the railway, and gradually decreases along with the increasing distance from vibration source. The vibration acceleration level is high within the 25m away from the vibration source, which entails effective isolation measures.
②The vibration load increases with promoting train speed, resulting in enhanced ground vibration level. However, the decreasing rate of vibration acceleration level is more rapid in a low train speed.
③Open trench can effectively attenuate ground vibration. For instances, peak acceleration is largely reduced. It may turn to be inundated water trench in rainy area, slightly reducing its attenuation effect. Soft material like geofoam in-filled trench can reduce ground vibration effectively. Hard material like reinforce concrete pile in-filled trench has less isolation effectiveness compared with the soft material.
④Parameter study reveals that barrier length and depth determine the protection zone and the reduction of vibration magnitude, depending on the relative dimensions to vibration wave length. At high train speed condition, the isolation effect is prominent associated with depth rather than width. Within one wave length zone behind the barrier, isolation effect is almost not changed by increasing barrier’s length and depth. At the location far away from one wave length to vibration resources, vibration level decreases 4dB when the barrier length increases 0.4 times wave length. Furthermore, when barrier depth increases by 0.4 times wave length, the vibration level decreases 6dB.
现在使用数值模拟方法进行地表列车动力荷载防护的研究并不多,在已有少量文献中对于土介质的模拟多采用理想的弹性模型。本文运用LS-DYNA软件,选用更适合岩土介质的弹塑性模型,对高速列车等交通荷载作用下地面振动及连续墙挡板的防护能力进行三维数值分析,并与现场测试结果进行比较;进一步研究了防护层材料以及防护结构尺寸对于减振效果的影响。其主要研究工作如下:
首先,建立三维几何模型,分别采用弹性材料模型和弹塑性模型,计算了某现场试验,验证了模型设计的合理性。其次,对比研究了无填充壕沟、注水壕沟、不同密度的泡沫填充壕沟以及混凝土桩填充壕沟防护时,地面在高速列车荷载作用下所产生的动力响应。再次,研究了不同列车运行速度产生的地面振动特性,以及在混凝土桩填充壕沟防护下,挡板尺寸对于防护效果及防护范围的影响。结果发现:
①列车运行附近振动较强烈,随着距振源距离的增大,振动明显减弱。在距轨道25m距离内振级较高,应采取有效的隔振减振措施。
②列车运行速度越大,由此产生的振动荷载也随之增大,引发的地面振动效应也增大。而列车运行速度较小时,振级随着距振源距离衰减速度更快。
③无填充壕沟防护层减振效果明显,但在多雨地带易转变成注水壕沟,防护能力有所下降,仍可以有效减低地面的振动效应。EPS泡沫填充壕沟属于质地较软的材料,防护效果较好。密度越小,防护效果越好。质地较硬的材料如混凝土桩填充材料有一定的防护效果,但相比质地较软的材料防护效果较差。
④挡板长度和深度直接影响混凝土减振挡板的防护效果和防护范围,与振动波波长有关,增加减振挡板长度和深度对于一倍波长内的区域的防护效果没有影响,对于一倍波长外的区域,挡板长度每增加0.4倍波长,振级减少量增加4dB;挡板深度每增加0.4倍波长,振级减少量增加6dB,挡板深度对防护效果的影响更为明显,挡板宽度的尺寸主要影响防护范围。
High-speed railways and high-grade roads are important infrastructures for national economy growth. However, the passage massive and high-speed trains may generate ground vibrations, which will propagate through the soil and impinge on surrounding industrial and residential areas, and may cause malfunctioning of some sensitive equipments, discomfort people and damage buildings. It is possible to avoid or mitigate these adverse effects by providing a suitable wave barrier around the vibration sources, and therefore it is of a practicable significance to lead investigations into the material, layout and dimensions of such barrier structures.
Railway traffic induced ground vibration and the isolation project have been a subject with increasing research interests in recent years. In general, a few references on this subject preferred to employ elastic model to simulate soil responses under the traffic dynamic excitation. In this thesis, a more sophisticated elastoplastic model was employed. The ground vibration caused by high-speed train was analyzed with a three-dimensional numerical model by software LS-DYNA. Particularly, barriers which are composed of different materials (open trench, inundated water trench, different density of geofoam in-filled trench, and concrete in-filled trench) and a reinforced concrete pile with different dimensions were numerically analyzed subjected to railway traffic loads. The main research works are as follows:
Firstly, a geometry model was built by LS-DYNA with elastic and elastoplastic material models. The numerical results were compared with in-situ tests to verify this model. Secondly, train-induced ground vibration was respectively investigated without protection barrier and with protection barriers of open trench, in-filled trench. Thirdly, the ground vibration level is studied at different train speeds. Finally, the isolation efficiency of a reinforced concrete pile barrier is comparatively investigated for different dimensions. From these studies, following understandings and conclusions can be made:
①Train speed is the key factor for the ground vibration level. Ground vibration is strong around the railway, and gradually decreases along with the increasing distance from vibration source. The vibration acceleration level is high within the 25m away from the vibration source, which entails effective isolation measures.
②The vibration load increases with promoting train speed, resulting in enhanced ground vibration level. However, the decreasing rate of vibration acceleration level is more rapid in a low train speed.
③Open trench can effectively attenuate ground vibration. For instances, peak acceleration is largely reduced. It may turn to be inundated water trench in rainy area, slightly reducing its attenuation effect. Soft material like geofoam in-filled trench can reduce ground vibration effectively. Hard material like reinforce concrete pile in-filled trench has less isolation effectiveness compared with the soft material.
④Parameter study reveals that barrier length and depth determine the protection zone and the reduction of vibration magnitude, depending on the relative dimensions to vibration wave length. At high train speed condition, the isolation effect is prominent associated with depth rather than width. Within one wave length zone behind the barrier, isolation effect is almost not changed by increasing barrier’s length and depth. At the location far away from one wave length to vibration resources, vibration level decreases 4dB when the barrier length increases 0.4 times wave length. Furthermore, when barrier depth increases by 0.4 times wave length, the vibration level decreases 6dB.
引文
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[8]和振兴,瞿婉明,杨新文等.列车移动轴荷载作用下的地面振动及隔振研究[J].铁道科学与工程学报,2007,4(5):73-77.
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[2]李保德,谢伟平,李荣.交通荷载所引起的地基振动的研究[J].武汉理工大学学报,2001,3:77-79.
[3] P.Galvin,J.Dominguez.Analysis of ground motion due to moving surface loads induced by high-speed trains [J].Engineering analysis with boundary elements,2007,31:931-941.
[4] G.Lefeuve-Mesgouez,A.Mesgouez.Ground vibration due to a high-speed moving harmonic rectangular load on a poroviscoelastic half-space [J].International Journal of Solids and Structures,2008,45:3353-3374.
[5] X.Sheng,C.J.C.Jones,D.J.Thompson.A theoretical study on the influence of the track on train-induced ground vibration [J].Journal of Sound and Vibration,2004,272:909-936.
[6] M.H.El Naggar,A.G.Chehab.Vibration barriers for shock-producing equipment [J],Canada Geotech.J,2005,42:297-306.
[7]杨先健,高广运,赵丰等.人为地面振动的传播与隔离[C].第四届全国建筑振动学术会议,2004年.
[8]和振兴,瞿婉明,杨新文等.列车移动轴荷载作用下的地面振动及隔振研究[J].铁道科学与工程学报,2007,4(5):73-77.
[9]和振兴,瞿婉明,罗震.地铁列车引起的地面振动[J].西南交通大学学报,2008,43(2):218-222.
[10] J.亨利奇著,熊建国等译.爆炸动力学及其应用[M].科学出版社,1987年.
[11] Bayo E P and Wilson E L.Use of Ritz vectors in wave propagation response [M].Earthquake Eng.Structure Dynamic,1984(12).
[12] Al-Hussaini T.M.,Ahmad S.Design of wave barriers for reduction of horizontal ground vibration [J].Journal of Geotechnical Engineering ASCE,1991,117(4):619-639.
[13]曾根平,范继斌.列车振动对地铁周围环境的影响及减隔振措施[J].现代城市轨道交通,2005,1:44.
[14] M.Adam,O.von Estorff.Reduction of train-induced building vibrations by using open and filled trenches [J].Computers and Structures,2005,83:11-24.
[15] Woods R.D.Screening of surface waves in soils [J].Journal of Soil Mechanics andFoundations Division,ASCE,1968,94(4):951-979.
[16] Hsiao-Hui Hung,Jenny Kuo,Yeong-Bin Yang.Reduction of train-induced vibrations on adjacent buildings [J].Structure engineering and mechanics,2001,11(5):503-518.
[17] Yeong-Bin Yang,Hsiao-Hui Hung.A parametric study of wave barriers for reduction of train-induced vibrations [J].International Journal for Numerical Methods in Engineering,1997,40:3729-3747.
[18] G.Lombaert,G.Degrande,D.Clouteau.Numerical modeling of free field traffic-induced vibration [J].Soil dynamics and earthquake engineering,2000,19:473-488.
[19]梁波,蔡英.不平顺条件下高速铁路路基的动力分析[J].铁道学报,1999,20(2):84-87.
[20]胡宗允,李晶晶.地铁列车荷载分析方法[J].路基工程,2006,5:18-20.
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