The influence of the depth of the ground water table on free field road traffic-induced vibrations

This paper describes the influence of seasonal variations of the ground water table on free field traffic-induced vibrations. The passage of a truck on two types of road unevenness is considered: a joint in a road pavement consisting of concrete plates and a speed bump with a sinusoidal profile. Free field vibrations are computed with a two-step solution procedure, where the computation of the vehicle axle loads is decoupled from the solution of the road–soil interaction problem. The impedance of the soil is calculated using a boundary element method, based on the Green's functions for a dry layer on top of a saturated half-space. It is demonstrated that, in the low-frequency range of interest, wave propagation in the saturated half-space can be modelled with an equivalent single phase medium as an alternative to Biot's poroelastic theory for saturated porous media. The relation between the free field velocity and the depth of the ground water table is dominated by three phenomena: (1) the compressibility of the soil decreases due to the presence of the pore water, (2) the ground water table introduces a layering of the soil which may cause resonance of the dry layer and (3) refracted P-waves in the dry layer interfere with surface waves. If the depth of the ground water table is large with respect to the wavelength of the vibrations in the soil, the response tends to the response of a dry half-space. The average free field velocity is equal to the velocity in the absence of ground water. If the depth of the ground water table is small with respect to the wavelength of the vibrations in the soil, the response tends to the response of a saturated half-space and resonance of the dry layer does not occur. The average free field velocity is smaller than the velocity in the absence of ground water. The interference of refracted P-waves and surface waves causes an additional oscillation of the response as a function of the excitation frequency and the distance between the road and the receiver. Copyright © 2004 John Wiley & Sons, Ltd.     

交通荷载作用下深基坑支护结构稳定性分析

以沈阳华府二期深基坑工程为主要研究对象,研究道路交通荷载对于在建深基坑支护结构的稳定性的影响。通过改变影响基坑稳定性的交通荷载系数及支护结构相关参数,以有限元软件ADINA为计算工具对基坑进行多次数值模拟,得出各参数的改变与支护结构变形之间的关系,并通过与实际现场检测数据进行对比,得到一系列的结论,发现在城市道路交通荷载作用下,主要影响因素为大量交通车辆的运行所产生的静载(包括车辆载重、交通量道路距基坑的距离)与震动产生动载以及基坑本身的自身特性的影响,对基坑支护结构方案的优化有一定的指导意义。     

列车运行对周围地面振动影响的试验研究

针对日益严重的轨道交通引起的环境振动问题,通过对京―广铁路线附近某小区内地面的竖向、横向振动速度和加速度的现场测试,研究了运行列车引起的地面振动及其传播规律。由试验分析可知,列车引起的地面振动速度、加速度振级均随着列车速度的提高和轴重的增加而增大。速度每小时提高10 km时,速度振级和加速度振级均增大约3 dB;车速相同的货车比客车引起的速度振级竖向大10 dB左右,横向大5～15 dB左右;加速度振级竖向大 12 dB,横向大8 dB。钢轨接缝附近地面的振动比无接缝附近的地面振动大,速度振级大2～6 dB。振动随着距振源距离的增大而逐渐减小,竖向振级的衰减过程表现出一定的波动性;横向振级的衰减随距离增大单调减小。     

利用数据场模型评价北京地面沉降交通载荷程度

地面沉降是指地面标高降低的一种缓变地质灾害现象,严重时对城市建设和人民生活会构成威胁。为评价地面沉降交通载荷程度,利用永久散射体干涉测量(PS-InSAR)技术提取北京东部地区沉降信息,利用数据场模型,以地铁站信息和道路节点信息为指标,采用因子贡献权重方法,获取北京地面沉降交通载荷程度分区图。研究结果表明:PS-InSAR方法可以获取区域地面沉降的空间分布趋势,研究区内最大沉降速率达到77.69 mm/a;地面沉降交通高载荷主要分布在北京市朝阳区北部与中部区域,而交通低载荷区域主要位于远离城市重要交通道路和地铁线路不发达乡镇。     

Dynamic responses of a poroelastic half‐space from moving trains caused by vertical track irregularities

The vibrations of railway tracks on a poroelastic half‐space generated by moving trains are investigated through a vehicle–track–ground coupling model. The theoretical model incorporates a vehicle, a track, and a fully saturated poroelastic half‐space soil medium. The source of vibration excitation is divided into two components: the quasi‐static loads and the dynamic loads. The quasi‐static loads are related to the static component of the axle loads, whereas the dynamic loads are due to the dynamic wheel–rail interaction. A linear Hertizian contact spring is introduced between each wheelset and the rail to consider the dynamic loads. Biot's dynamic theory is used to characterize the poroelastic half‐space soil medium. Using the Fourier transform, the governing equations for the track–ground system are solved and the numerical results are presented for a single axle vehicle model. The different dynamic characteristics of the elastic soil medium and the saturated poroelastic medium are investigated. In addition, the different roles of the moving axle loads and the roughness‐induced dynamic loads are identified. It is concluded that the vibration level of the free field off the track predicted by the poroelastic soil medium is smaller than that predicted by the elastic soil medium for vehicle speed below the Rayleigh wave speed of the poroelastic half‐space, whereas it is larger for vehicle speed above the Rayleigh wave speed. The dynamic loads play an important role in the dynamic responses of the track–ground system. Copyright © 2010 John Wiley & Sons, Ltd.     

A combined method to predict the long-term settlements of roads on soft soil under cyclic traffic loadings

In order to investigate the mechanism of the long-term settlement of road on the soft soil, an in situ measurement of a highway in southeast China was conducted during both the construction and post-construction stage. In the theoretical analysis, the long-term settlement of the pavement on thick soft soils was divided into three main components: the consolidation settlement, the creep deformation and the traffic load-induced deformation. The equivalent time line model based on the viscous–elastic–plastic theory was adopted to simulate the road settlement caused by the consolidation and creep of the subsoil. A cyclic strain accumulation model, which was obtained from laboratory tests of soil elements, was adopted to consider the road settlement induced by cyclic traffic loadings. A pavement dynamic response model was used to calculate the dynamic stresses in the subsoil generated by moving traffic loads when the road was open to service. It was found that the equivalent time line model combined with the cyclic strain accumulation model could predict the road settlement accurately at both the construction and post-construction stage. Numerical results showed that the traffic speed had limited effect on the post-construction road settlements for the speed range considered. The post-construction settlement of the road, mainly composed of the traffic-induced settlement and soil creep deformation, could be reduced significantly by increasing the embankment surcharge during the construction stage. The creep component accounted for over 10% of the total post-construction settlement, while the percentage of the creep deformation in total post-construction settlement decreased rapidly as the embankment surcharge increased.     

交通荷载作用下冻土路基动力响应分析

季节冻土区路基在交通荷载作用下的冻胀翻浆病害是一个复杂的热、力相互作用过程,又是一个急需解决的实际工程难题.运用传热学及Biot固结理论建立季节冻土区公路路基的动力分析模型,以季节冻土区典型冻胀翻浆路基为例,分析其工程处理前、后的动力反应特性.结果表明:1)路基温度场的研究表明修筑路基后,在路基及其下部地基中将会产生大片的力学性质极不稳定的高温冻土层;2)路基运营期当交通荷载刚驶入或离开路基计算断面时,路基内的加速度、速度、位移、应力、孔隙水压力均振荡剧烈.但与普通路基相比,防冻胀翻浆路基的碎石层大大削弱了汽车动荷载的冲击振动作用;3)防冻胀翻浆路基中间存在透水层(碎石),减小了路基内的孔隙水压力,与普通路基相比,防冻胀翻浆路基的最大孔隙水压力比减小达30%左右,这对延缓、消除路基病害产生有很大作用.计算理论以及分析结果可为季节冻土区道路的安全运营以及维修提供参考依据.     

Coupled simulation of wave propagation and water flow in soil induced by high‐speed trains

The purpose of this paper is to simulate the coupled dynamic deformation and water flow that occur in saturated soils when subjected to traffic loads, which is a problem with several practical applications. The wave propagation causes vibrations leading to discomfort for passengers and people in the surroundings and increase wear on both the vehicle and road structure. The water flow may cause internal erosion and material transport in the soil. Further, the increased pore water pressure could reduce the bearing capacity of embankments. The saturated soil is modelled as a water‐saturated porous medium. The traffic is modelled as a number of moving wheel contact loads. Dynamic effects are accounted for, which lead to a coupled problem with solid displacements, water velocity and pressure as primary unknowns. A finite element program has been developed to perform simulations. The simulations clearly demonstrate the induced wave propagation and water flow in the soil. The simulation technique is applicable to railway as well as road traffic. Copyright © 2007 John Wiley & Sons, Ltd.     

Efficiency of heavy mass technology in traffic vibration reduction: Experimental and numerical investigation

Vibrations induced by traffic and construction activities cause serious environmental problems. The reduction of the impact of these vibrations on the nearby environment constitutes an important challenge, mainly in urban area. This paper presents both experimental investigation and 3D numerical modeling of the performance of heavy masses technology for scattering the ground vibrations. The efficiency of this method is compared to that of the trench barriers, largely studied in the literature. Analyses show that the heavy mass constitutes an efficient technology for the attenuation of the traffic induced vibrations. The performance of this method depends mainly on the mass weight. An amplitude reduction ratio up to 70% can be reached using this technology.     

交通荷载作用下公路路基工作区深度研究

根据路面不平整实测资料,获得了汽车动荷载的计算模型和参数,并利用此荷载模式来分析公路结构的动力响应。考虑到公路结构的三维分层性状,利用Fourier变换技术和求解层状结构的精确刚度矩阵法,研究了公路结构在移动汽车荷载作用下的动力响应问题。为了方便工程应用,利用Odemark厚度和模量的当量转换公式,将公路结构简化为由路面、路基及地基组成的3层体系,并以此为基础分析了路基动应力的衰减规律,同时重点研究了汽车轴载大小、当量路面厚度及路基模量对路基工作区深度的影响,最后建议了路基工作区深度的定量表达式,研究结果可为公路路基设计提供参考。     

列车运行时由轨道不平顺引起的地基振动研究

采用半解析法研究了列车荷载作用下列车-轨道-饱和地基系统的耦合振动问题。研究模型共分为3部分：车体简化为一个多刚体系统,在车轮与钢轨之间引入线性Hertizian弹簧接触模型模拟轮轨动力相互作用、采用离散轨枕支撑的弹性Euler梁来模拟轨道系统、下卧土体采用多孔饱和半空间模型。列车荷载分为轴重和由轨道不平顺引起的轮轨动力相互作用力。采用Fourier变换分别求解各子系统的控制方程,并通过动力子结构法对各子系统进行耦合。土体在时域内的动力响应通过快速Fourier变换求得。在分析了轮轨动力相互作用力的基础上,研究了轮轨动力作用力和列车轴重作用下饱和地基的动力响应,并分析了轨枕间距和土体渗透系数对饱和地基振动响应的影响。研究表明,轮轨动力作用力对地基远场振动有重要贡献,同时枕木间距对轨道与地基振动响应有较大影响。     

Effect of Geological Conditions on Vibration Characteristics of Ground Due to Subway Tunnel: Field Investigation

Geotechnical and Geological Engineering - Field measurements of the ground vibrations due to subway moving load are carried out in two distinct geological conditions (soft soil ground, granite...     

Calculation of vibration transmission over bedrock using a waveguide finite element model

A finite element method is developed for the study of elastic wave propagation in layered ground environments. The formulation is based on a spectral finite‐element approach using a mixture of high‐order element shape functions and wave solutions. The numerical method provides solutions to vibration transmission on and within layered elastic waveguides. Examples of its use include the theoretical analysis of transmission of vibrations in the vicinity of the surface of the ground. The mathematical model is two dimensional, and the interior of the ground is modelled as an elastic layer overlying a rigid foundation. An analysis of the natural modes of free vibration in a single layer and two layers is presented and compared with known results. In addition the forced response of the layers, for which the surface is assumed to be subjected to a harmonic point force load is shown. These results also include an illustration of the attenuation of surface vibration due to ‘wave impedance blocks’ in the ‘near field’ of the source up to a frequency of 200 Hz for two soil types. Copyright © 2007 John Wiley & Sons, Ltd.     

交通荷载作用下地基中瑞利波的传播特性

瑞利波频谱分析法是一种能有效的测试地基参数的方法,但测试深度较浅.交通荷载产生的波频率低,传播较深,因此利用交通荷载产生的表面波能获的更深土层的参数.根据交通荷载的运动特性和三维波动方程,运用解析方法求得了交通荷载作用下瑞利波的特征方程,并对弥散性和荷载运动对波的传播的影响进行了分析,研究发现对于同一运动速度V,不同频率的波其传播方向不相同.     

Numerical analysis of soil vibrations due to trains moving at critical speed

High-speed train induced vibrations of track structure and underlying soils differ from that induced by low-speed train. Determining the critical speed of train operation remains difficult due to the complex properties of the track, embankment and ground. A dynamic analysis model comprising track, embankment and layered ground was presented based on the two-and-half-dimensional (2.5D) finite elements combining with thin-layer elements to predict vibrations generated by train moving loads. The track structure is modeled as an Euler–Bernoulli beam resting on embankment. The train is treated as a series of moving axle loads; the embankment and ground are modeled by the 2.5D finite elements. The dynamic responses of the track structure and the ground under constant and vibrating moving loads at various speeds are presented. The results show that the critical speed of a train moving on an embankment is higher than the Rayleigh wave velocity of the underlying soil, attributed to the presence of the track structure and the embankment. It is found that the dynamic response of ground induced by moving constant loads is mostly dominated by train speed. While for the moving load with vibration frequency, the ground response is mostly affected by the vibration frequency instead of train speed. Mach effect appears when the train speed exceeds the critical speed of the track–embankment–ground system.     

交通荷载作用下公路软土地基长期沉降的计算

合理预测公路软土地基在交通荷载作用下产生的长期沉降,对公路的设计有着重要的指导作用。基于以往试验规律的分析,提出了一个较为合理地描述软土在长期重复荷载作用下残余变形发展过程的经验模型。通过对上海软土的循环三轴试验的模拟,初步验证了模型的合理性。对于工程边值问题,首先,根据拟静力法将交通荷载视为长期重复作用的静分布力;其次,采用弹性层状体系理论计算交通荷载在地基中引起的附加动应力;最后,将提出的模型用于计算各土层的残余应变,并沿深度对应变积分得到沉降。以日本Saga机场公路为例,说明了公路软土地基沉降的简化计算方法的有效性。     

矩形运动荷载作用下软土地基的三维振动研究

通过引入势函数,并利用Helmholtz原理和Fourier变换技术,研究了运动荷载作用下有限层厚软土地基的振动,考虑了矩形分布荷载作用下振动的三维特性,使得分析更符合工程实际,给出了运动荷载作用下饱和黏弹性地基三维振动的应力、位移和孔隙水压力响应的积分形式解答。利用Fourier数值逆变换进行算例分析,讨论了荷载速度对位移及孔隙水压力分布的影响。结果表明,位移幅值随荷载速度的增加而增大,荷载不同位置处孔隙水压力的分布有很大差异。     

Micro-sequential contour blasting—how does it influence the surrounding rock mass?

The optimal delay time between the contour holes in rock blasting has been studied by theoretical and empirical research in Sweden, regarding ground vibrations, increase in crack frequency, radial crack length and finally overbreak (half cast factor). The model test presented in this paper concerns controlled contour blasting in tunnelling and the full-scale blasts concern tunnelling, road cutting, and dimensional stone quarrying. The results indicate that the microsequential contour blasting technique (contour holes fired in sequence and with a delay in the order of 1–2 ms) is superior to simultaneous initiation both regarding blast-induced ground vibrations and crack frequency increase in the rock mass. Both these evaluation methods reflects the conditions deeper in the remaining rock mass. Simultaneous initiation, however, is superior to micro-sequential contour blasting both regarding the half cast factor and the length of radial cracks emanating from the blastholes. These two parameters are more related to the surface conditions after blasting. The industrial applications of this new knowledge are the use of micro-sequential contour blasting when ground vibrations are of greater concern than the contour, for example, in trench blasting or quarrying in urban areas, and the use of simultaneous initiation when an even rock surface is of high priority.     

Investigation of the channelling effect on pollutants dispersion between adjacent roadway tunnels

The health risks presented by noxious vehicle emissions inside tunnels has been amplified due to the increasing use of roadway tunnels. Particularly, for adjacent roadway tunnels, vehicular emissions from the upstream tunnel can further deteriorate the air quality within the following tunnels. A scale vehicle tunnel model was designed to experimentally modelled the airflow and pollutants dispersion in contiguous roadway tunnels. The channelling effect on pollutants dispersion between adjacent roadway tunnels was studied, and factors such as ventilation speed, open road section length, traffic condition (e.g. car free, car running and traffic congestion) were considered. Pollutants mass flow rate ratio between downstream and upstream tunnels was calculated to evaluate the variation of the entrained pollutants amount. For the car free condition, pollutant can be easily entrained into the downwind tunnel when the gap distance between roadway tunnels decreased. For the car running condition with fixed tunnel gap distance, the traffic speed variation barely changed the pollutants mass flow rate ratio. Furthermore, evident influences on pollutants concentration were observed from continuous congestion and partial congestion. Lastly, numerical simulation using computational fluid dynamics approach was conducted for the car free scenario, and reasonably good agreements were found for pollutants concentration ratio compared with the experimental data. The results yielded from this study further quantified the relationships among different influential factors on the pollutants dispersion between roadway tunnels, and can contribute to an improved tunnel ventilation system design, especially for the downstream tunnel.     

道路行车荷载影响深度分析

提出了黏弹性边界单元有限元模型,用以研究行车荷载在道路中的有效传播深度。通过与Lamb问题的解析解及连盐高速公路实测结果对比分析,验证了数值模型用于研究车辆荷载在道路中引起的动响应具有很好的精度。应用该方法探讨了行车速度、道路各结构层的回弹模量对动响应沿道路深度变化的影响。研究表明,用附加动应力大小作为行车荷载有效传播深度的控制标准不足以反映车辆荷载对道路沉降的影响。尤其对建于软土地基上的道路,建议以竖向动应变作为界定车辆荷载影响深度的控制标准为宜。分析表明,软土地基中行车荷载引起的动响应的影响深度一般在6～10 m范围内,这对地基的设计处理和道路工后沉降的控制具有重要参考意义。