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针对多年冻土区青藏铁路列车荷载振动作用下的动稳定性,通过对北麓河和二道沟三个典型铁路路基横断面振动响应的二分量加速度观测,对比分析客运列车和货运列车引起的路基振动特性和衰减规律,研究不同防护形式路基的列车振动响应。结果表明,路基上的振动作用主要集中在40～80Hz频率范围内;防护形式对路基的列车动力响应有明显影响,热棒加碎石路基动力响应最小,其次为碎石防护路基,未采取任何防护的路基铁轨上的动力响应最大,建议对未采取防护的路基进行防护。分析结论为青藏铁路列车作用下的路基动稳定性评估提供实测依据,对多年冻土区的路基稳定性研究提供参考。 相似文献
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科学合理地分析铁路路基块石层在机车荷载作用下的动力传递机理,对于多年冻土区路基工程稳定性预测有着重要的指导意义,同时对于在青藏高原多年冻土地区建设高坝大库等重要水利工程的动力稳定性分析也具有重要的借鉴作用。通过选取青藏铁路北麓河段典型块石路基结构开展机车通过实时强震动测试,获得了机车通过时的实时加速度数据。在现场测试的基础上,基于有限元分析软件, 运用二维非线性动力响应分析方法对多年冻土区块石路基结构在机车荷载作用下动力传递特性、位移响应特性和应力应变特性进行了数值模拟分析,并通过对比分析素土路基的动力响应特征,科学分析青藏铁路路基块石层在机车荷载作用下的动力传递机理。研究结果表明,块石层的铺设可以有效限制机车荷载产生的加速度向路基深处传递,减小机车振动对路基结构的影响,有助于保护冻土路基的稳定性;块石层的铺设可以较好地减小机车荷载作用下路基的沉降变形,在相同机车荷载作用下块石结构路基的最大沉降量仅为0.9 mm,而素土路基的最大沉降量可达1.9 mm;块石层的铺设可以改变机车荷载作用下路基内部的应力应变状态,使得路基内部最大主应力增大,而最大剪应变幅值、范围均减小。 相似文献
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多年冻土区铁路路基热状况对工程扰动及气候变化的响应 总被引：2，自引：0，他引：2
基于青藏铁路沿线长期地温监测资料,对天然场地及铁路路基下部的浅层地温、多年冻土上限及下伏冻土地温动态变化过程进行对比分析,研究多年冻土区铁路路基热状况对于工程扰动及气候变化的响应过程.监测结果表明,路基修筑后边坡热效应显著,由此导致路基下部多年冻土热状况的不对称分布,必须引起足够的重视.块石路基修筑后,下部多年冻土上限抬升显著,其中阴坡路肩下抬升幅度普遍较阳坡路肩下显著.普通路基修筑后,在年平均地温低于?0.6～?0.7℃的地区下部多年冻土上限有不同程度的抬升,而在年平均地温高于?0.6℃的地区下部冻土上限则出现了一定程度的下降,其中阳坡路肩下降幅显著.受块石层冷却降温作用,低温冻土区块石路基下部浅层冻土地温有明显降温过程,而在高温冻土区这一降温趋势只存在于阴坡路肩下.对于普通路基,多年冻土上限抬升后,浅层冻土地温存在一定的升温过程.对于气候变暖,低温冻土区多年冻土的响应主要集中体现在冻土升温上,而高温冻土区多年冻土的响应则主要表现为冻土上限下降,冻土厚度减小.基于上述监测结果,可将目前青藏铁路路基热状况分为稳定型(低温冻土区块石路基)、亚稳定型(低温冻土区普通路基及高温冻土区块石路基)和不稳定型(高温冻土区普通路基). 相似文献
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基于动三轴试验建立的冻结、融化状态青藏铁路粉质黏土的累积塑性应变模型,考虑路基土体动应力的作用,二次开发适用于青藏铁路高温极不稳定多年冻土区路基长期永久变形的蠕变法则,并在既有的黏弹塑性本构模型将其引入,计算列车荷载作用下青藏铁路路基的永久变形。分析结果显示：（1）列车荷载作用下距离路基顶面不同埋深土体的累积动力永久应变随着等效振次的增加而增加,并且先期的增长速度较快,最终趋于稳定,长期沉降在路基中心处最大,最终在路基距离轨道最远处几乎为零;（2）随着列车速度的增加,路基中心永久变形逐渐增大;（3）随着列车轴重的增加,路基中心永久变形逐渐增大,并且随着埋深的增加,列车轴重对路基永久变形的影响逐渐变小;（4）随着冻结深度的增加,路基表面累积塑性变形呈降低趋势;随着融化深度的增加,路基表面累积永久变形增加。 相似文献
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《中国科学:地球科学》2015,(8)
基于青藏铁路楚玛尔河试验段10年(2003~2013)的地温监测资料,对青藏铁路4种典型路基结构的长期热状况进行了对比分析.结果表明,不同路基结构的长期热状况表现出较大的差异.普通路基与块石基底路基地温场存在明显的不对称分布,表明以上两种路基结构不利于路基的长期热稳定.但块石护坡路基与U型块石路基的地温场分布则表现出了较好的对称性.尽管块石护坡路基下浅层冻土地温存在一定的降温过程,但深层多年冻土却呈现出缓慢升温趋势,显示U型块石路基的热稳定性要优于块石护坡路基.被监测的4种路基结构中,U型块石路基在降低多年冻土温度与提高路基地温场对称性方面表现出了最佳的长期效应.基于青藏铁路10年的监测结果,充分肯定了主动冷却路基设计思路在保护冻土路基长期热稳定性方面的有效性,同时采用冷却路基技术的青藏铁路也达到了时速100 km h?1的设计要求.尽管如此,由于坡向效应所导致的路基左右路肩下的热差异存在于所有监测的路基结构中,但不同结构的热差异幅度不同,并将可能导致路基发生潜在的非均匀性沉降变形,因此需要在后续的维护工程中进行调整. 相似文献
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地温对冻土动力特性及其场地地震动参数的影响 总被引：8，自引：0，他引：8
地温是影响冻土力学性质的重要参数之一。本文基于对2001年11月14日昆仑山口西8．1级大震在多年冻土区所造成的地表变形与地震破坏特征的定量调查结果，通过冻土的振动三轴实验，研究了地温对冻土动本构关系、动弹性模量、阻尼比、动强度等动力特性参数的定量影响规律；进而利用青藏铁路沿线4个冻土剖面和该区50年超越概率分别为63％、10％和2％的场地基岩地震动时程，分析计算了不同地温下冻土场地地震动参数的特征，研究了地温对冻土地面地震位移、速度、加速度和反应谱等的定量影响，为冻土区工程地基、路基以及地下工程震害防御提供了科学依据。 相似文献
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基于轨道结构-路基-地基动力相互作用理论,建立考虑地震-列车移动荷载耦合输入的轨道结构-路基-地基动力学模型,研究高速铁路路基及轨道在耦合荷载作用下的振动响应问题。通过编制DLOAD子程序并与ABAQUS有限元计算程序联立,实现地震荷载与列车移动荷载耦合作用的施加,以高速铁路桩承式路基及自由式路基为研究对象,对地震-列车移动荷载耦合作用下两种路基系统的动力响应进行数值计算并比较两者的振动响应差异。结果表明,耦合荷载对桩承式路基动力响应影响显著,该荷载作用下桩承式路基会发生共振现象,使得桩承式路基中轨道和路基振动位移幅值均大于自由式路基的振动位移幅值;桩承式路基不会影响路基系统的振动频率,但会改变路基系统的振动大小,桩承式路基中轨道X方向加速度、路肩边及路基坡脚处的竖向加速度分别减小6.2%、50%、28.6%。 相似文献
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多年冻土区道路工程病害类型及特征研究 总被引：10，自引：0，他引：10
多年冻土及多年冻土区恶劣的环境给工程构筑物的建设及维护带来了极大的挑战。以青藏工程走廊内的青藏公路、青藏铁路两大道路工程为研究对象,系统论述了其路基工程、桥梁工程、涵洞工程的主要病害类型及分布特征。现场调查显示,青藏公路80%的路基病害由多年冻土融沉所引起,主要表现为严重的不均匀沉降变形和纵向裂缝,且主要发生在高填方路基上。这两种病害与多年冻土地温及含冰量密切相关,地温越高,含冰量越大,病害越为严重。青藏公路桥梁工程的病害主要集中在附属工程及上部结构上,而涵洞工程病害则主要由冻胀、融沉作用、泥石流淤积、冰塞以及施工原因导致。青藏铁路沿线现场监测及调查结果表明,目前铁路路基病害主要为高温冻土区普通路基的（不均匀）沉降变形、纵向裂缝、路桥过渡段沉降变形、风沙灾害及块碎石材料风化引起的冷却路基结构失效等。此外,青藏工程走廊内广泛分布着包括冻胀丘、冰椎、冰幔、热融湖塘等不良冻土地质现象,当上述不良地质现象与工程接近时,会对道路工程的稳定性造成威胁,严重时可导致一些工程病害的发生。 相似文献
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Permafrost along the Qinghai-Tibet Railroad produces the great change under the
influence of climate change, such as the decreasing of permafrost table, the rising of permafrost temperatures, etc. Climate effect on permafrost is the long-term process. Engineering action makes rapidly permafrost the large extent change. On the basis of analyzing the permafrost change under the climate change and engineering action, the thermal regime and spatial distribution of permafrost are predicted for air temperature rising 1℃ and 2℃ after 50 years in this paper. The results show that climate change results in the larger change for the thermal regime and spatial distribution of permafrost. Permafrost change will produce the great effect on the Qinghai-Tibet Railroad engineering, not only resulting in the decreasing of permafrost table beneath the roadbed, but also resulting in thawing settlement due to the thawing of ground ice near permafrost table. The idea of cooling roadbed and active protecting permafrost for the Qinghai-Tibet Railroad engineering could adjust and control the permafrost thermal state, some better methods are provided to ensure the engineering stability in the areas of warm permafrost and high ice content. 相似文献
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Piled embankments, which offer many advantages, are increasingly popular in construction of high-speed railways in China. Although the performance of piled embankment under static loading is well-known, the behavior under the dynamic train load of a high-speed railway is not yet understood. In light of this, a heavily instrumented piled embankment model was set up, and a model test was carried out, in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train. Earth pressure, settlement, strain in the geogrid and pile and excess pore water pressure were measured. The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading. The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase. Accumulated geogrid strain has an increasing tendency after long-term vibration. The closer the embankment edge, the greater the geogrid strain over the subsoil. Strains in the pile were smaller under dynamic train loads, and their distribution was different from that under static loading. At the same elevation, excess pore water pressure under the track slab was greater than that under the embankment shoulder. 相似文献
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Soft ground improvement using piles has increasingly been used as a rapid construction technique for railway and highway embankments over soft soil areas. While most studies conducted so far have addressed only issues of stability and settlement of pile-supported embankments under static loading, very limited attention has been paid to understanding their behaviors under transient loading of moving vehicles. In this study, vibration behaviors of this embankment system under high-speed train passage are investigated through three-dimensional finite element simulation. They include (1) characteristics of the surface wave field at high train speeds, (2) the dependence of vibration amplitude on the train speed and the phenomenon of critical speed, and (3) response at some typical locations in the system when the train moves at the critical speed. The study shows that there are breaks in the simulated wave fronts as transiting between different materials due to the difference in the Rayleigh wave speed among the materials relative to the train speed, and that the increase in train speed is accompanied by the increase in phase shift between the train load and the displacement pattern beneath the load. It is shown that the critical speed of the system is governed by the embankment, instead of the soft soil as commonly observed in previous studies in which the ground is not improved. Namely the vibration amplitude is maximally amplified when the train speed approaches the characteristic Rayleigh wave speed of the embankment material. In addition, the results also suggest that the sloping surfaces on the ballast and embankment along with the piles form a ‘trapping’ effect by which most of the train-induced waves, especially higher-frequency waves, incident to the sloping surfaces are trapped and dissipated within the pile-supported embankment system, and thus significantly reducing vibration amplitudes outside the embankment. 相似文献
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多年冻土场地路基地震响应动应力性状研究 总被引：4，自引：1，他引：3
以青藏铁路工程抗震设计与地震加固为应用背景,基于冻土场地路基的若干典型工况,开展多年冻土场地路基地震响应动应力性状的研究工作。研究表明,与不同的场地地形条件相比,冻土层对路基地震响应动应力的影响更加突出,尤其是含冻土层路基的地震动应力幅值、频率较不含冻土层路基的地震动应力幅值、频率大得多,因而冻土层的存在可能加剧了路基的震害响应。 相似文献
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冻土带是天然气水合物发育的两个重要地质环境之一.青藏高原平均海拔在4000m以上,多年冻土面积约1.4×106km2.本文根据青藏高原冻土层厚度和地温梯度特征,运用天然气水合物的热力学稳定域预测方法,确定中低纬度高海拔区冻土带天然气水合物的产出特征.青藏高原多年冻土带热成因天然气水合物形成的热力学相平衡反映,水合物顶界埋深约27~560m,底界埋深约77~2070m.初步计算表明,青藏高原冻土带水合物天然气资源约1.2×1011~2.4×1014m3.在冻土层越厚、冻土层及冻土层之下沉积层的地温梯度越小的地区,最有利于天然气水合物的发育.气温的季节性变化对天然气水合物影响不大.在全球气温快速上升的背景下,青藏高原天然气水合物将处于失稳状态,天然气水合物顶界下降、底界上升,与冻土带的退化相似,分布区逐渐缩小,最终将完全消失. 相似文献
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This study investigates the behavior of ground vibrations induced by trains moving on embankments using theoretical formulations, finite element analyses, and field experiments. The train-induced vibrations are large at the dominant frequencies of nV/Lc, even though the rail is very rough, where n is a positive integer, V is the train speed, and Lc is the carriage interval. For subsonic train speeds, the train-induced ground vibration is extremely small when the rail is perfectly smooth, but with a minor rail irregularity, the train-induced ground vibration can be significantly increased. However, for supersonic train speeds, the ground vibrations with or without rail irregularities are not very different, and the vibration of the first dominant frequency having the longest wavelength is the most obvious wave. 相似文献
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Alpine cold ecosystem with permafrost environment is quite sensitive to climatic changes and the changes in permafrost can significantly affect the alpine ecosystem. The vegetation coverage, grassland biomass and soil nutrient and texture are selected to indicate the regime of alpine cold ecosystems in the Qinghai-Tibet Plateau. The interactions between alpine ecosystem and permafrost were investigated with the depth of active layer, permafrost thickness and mean annual ground temperature (MAGTs). Based on the statistics model of GPTR for MAGTs and annual air temperatures, an analysis method was developed to analyze the impacts of permafrost changes on the alpine ecosystems. Under the climate change and human engineering activities, the permafrost change and its impacts on alpine ecosystems in the permafrost region between the Kunlun Mountains and the Tanggula Range of Qinghai-Tibet Plateau are studied in this paper. The results showed that the per- mafrost changes have a different influence on different alpine ecosystems. With the increase in the thickness of active layer, the vegetation cover and biomass of the alpine cold meadow exhibit a significant conic reduction, the soil organic matter content of the alpine cold meadow ecosystem shows an exponential decrease, and the surface soil materials become coarse and gravelly. The alpine cold steppe ecosystem, however, seems to have a relatively weak relation to the permafrost environment. Those relationships resulted in the fact that the distribution area of alpine cold meadow decreased by 7.98% and alpine cold swamp decreased by 28.11% under the permafrost environment degradation during recent 15 years. In the future 50 years the alpine cold meadow ecosystems in different geomorphologic units may have different responses to the changes of the permafrost under different climate warming conditions, among them the alpine cold meadow and swamp ecosystem located in the low mountain and plateau area will have a relatively serious degradation. Furthermore, from the angles of grassland coverage and biological production the variation characteristics of high-cold eco- systems in different representative regions and different geomorphologic units under different climatic conditions were quantitatively assessed. In the future, adopting effective measures to protect permafrost is of vital importance to maintaining the stability of permafrost engineering and alpine cold eco- systems in the plateau. 相似文献
18.
青藏铁路重塑冻结粉质黏土动剪切模量试验研究 总被引：3，自引：0，他引：3
通过低温动三轴试验,研究青藏铁路中重塑冻结粉质黏土的动剪切模量的变化规律及其主要因素。研究表明,冻土的最大动剪切模量随负温降低而显著增大,动剪切模量比随轴向荷载单级振次增加而有所增大,随负温降低而降低,随围压增加趋于一致。负温是冻土动力性能的一个极其重要的影响因素,因而寒区工程应引起足够的重视。研究结果对于合理认识冻土动力性能具有一定意义,也为进一步开展多年冻土场地工程地震安全性评价积累部分基础资料。 相似文献
19.
《地震工程与工程振动(英文版)》2015,(3)
A dynamic model test(CL = 4) at different velocities of train,namely different loading frequencies,is carried out to study the dynamic characteristics of a high-speed railway tunnel invert and its foundation soils.Not only are the accelerations,dynamic coefficients,dynamic stresses of the invert and foundation soils emphatically analyzed,their relationship with the velocity of the train are discussed in detail.Through laboratory testing,the attenuation of vibration propagating from up the rails is obtained and the calculation formula of the speed influence coefficient of the tunnel invert is preliminarily established.The depth of the foundation soils influenced by vibration is also determined in this study.It is shown that the responses of the tunnel invert and foundation soils to vibration are slightly increased with the velocity of the train;circumferential stresses in the bottom of the invert are tensile stresses and maximum stresses appear under the foot of the rails;the dynamic soil pressures of the foundation decrease quickly with the distance away from the tunnel invert and an exponential relationship exists between them. 相似文献