Prediction Model of Abutment Pressure Affected by Far-Field Hard Stratum Based on Elastic Foundation Theory

In view of the three-dimensional dynamic abutment pressure,the influence of the far-field hard stratum(FHS)in deep,thick coal seams is indeterminant.Based on elastic foundation theory,a three-dimensional dynamic prediction model of the abutment pressure was established.Using this model,the dynamic change in the coal seam abutment pressure caused by the movement of the FHS was studied,and a method for determining the dynamic change range of the abutment pressure was developed.The results of the new prediction model of the abutment pressure are slightly higher than the measured values,with an error of 0.51%,which avoids the shortcomings of the results because the Winkler foundation model results are lower than the measured values and have an error of 9.98%.As time progresses,the abutment pressure and its distribution range are affected by the FHS movement,which has the characteristics of gradually increasing dynamic change until the FHS fractures.The peak value of the abutment pressure increases linearly with time,and the influence range increases with time following a power function with an exponent of less than 1.The influence range of the FHS movement on the abutment pressure ahead of the working face,behind the working face,and along the working face is 10 times,25 times,and 17 times the mining thickness,respectively.According to the actual geological parameters,the dynamic change range of the coal seam abutment pressure was determined by drawing an additional stress curve and by determining the threshold value.These research results are of great significance to the partition optimization of the roadway support design of deep,thick coal seams.

REMARKS OF SOME PROBLEMS FOR RECTANGULAR THIN PLATES WITH FREE EDGES ON ELASTIC FOUNDATIONS

For the bending, stability and vibrations of rectangular thin plates with free edges on elastic foundations, in this paper we give a flexural function which exactly satisfies not only all the boundary conditions on free edges but also the conditions at free corner points. Applying energy variation principle, we give equations defining parameters in flexural function, stability equation, frequency equation, and general formulae of minimum critical force and minimum eigenfrequency as well.

A method to Estimate Dynamic Responses of VLFS Based on Multi-Floating-Module Model Connected by Elastic Hinges

Based on the elastic foundation beam theory and the multi-floating-module hydrodynamic theory,a novel method is proposed to estimate the dynamic responses of VLFS(Very Large Floating Structure).In still water,a VLFS can be simplified as an elastic foundation beam model or a multi-floating-module model connected by elastic hinges.According to equivalent displacement of the two models in static analysis,the problem of rotation stiffness of elastic hinges can be solved.Then,based on the potential flow theory,the dynamic responding analysis of multi-floatingmodule model under wave loads can be computed in ANSYS-AQWA software.By assembling the time domain analysis results of each module,the dynamic responses of the VLFS can be obtained.Validation of the method is conducted through a series of comparison calculations,which mainly includes a continuous structure and a three-part structure connected by hinges in regular waves.The results of this paper method show a satisfactory agreement with the experiment and calculation data given in relative references.

Elastic Modulus Limit of Support Layer in Twin-Block Ballastless Track Based on Train Load Effect

The support layer is an important component of twin-block ballastless track. The modulus of the support layer is an important design parameter and must be carefully solved. We studied the bending stress and deformation of track slab and support layer due to train load using the beam-plate finite element model on elastic foundation. The results show that support layer type has great impact on both support layer deformation and the stress on subgrade, but has little impact on the bending stress of either track slab or support layer. The continuous support layer type, and articulated support layer type with shear transfer device at their ends, are recommended. In order to keep the stress in the support layer less than that in track slab, the modulus of the continuous, unit, and articulated types of support layer （ in unit twin-block ballastless track）, and the support layer in continuous twin-block ballastless track, should not be larger than 15, 22, 20.5 and 5 GPa, respectively. In addition, the modulus of the unit-type support layer should not be more than 20 GPa, to ensure the step in support layer remains less than 1 mm.

基于地基梁理论的断层非线性错动下隧道纵向响应研究

为研究走滑断层错动作用下隧道结构的纵向响应,采用Pasternak双参数地基和弹性梁理论,建立穿越多破裂面断层隧道在断层强制位错作用下的纵向响应微分方程,通过数学方法求解获得隧道结构在断层位错作用下的纵向变形、内力响应,并通过模型试验和数值模拟对理论解析模型的有效性进行验证。在此基础上,采用理论解析模型对隧道结构纵向响应的影响因素进行敏感性分析。主要得出以下结论:1)理论解析模型计算得到的隧道纵向变形和弯矩变化趋势与模型试验和数值模拟结果完全一致,但数值上趋于保守;2)断层错动的位移形式和围岩-隧道结构的刚度匹配关系对隧道结构纵向响应的影响较大,应根据具体的断层破碎带形式选择合适的断层错动位移函数;3)随着围岩-隧道结构刚度比的增大,围岩对隧道结构的约束作用随之增大,隧道结构纵向内力集中现象增加,但受断层错动影响的范围减小,在具体工程设计中应结合施工成本、抢通时间等来选择合适的围岩-隧道结构刚度匹配关系。

Linear and nonlinear elastic analysis of closely spaced strip foundations using Pasternak model

In this study, an attempt is made to determine the interaction effect of two closely spaced strip footings using Pasternak model. The study considers small strain problem and has been performed using linear as well as nonlinear elastic analysis to determine the interaction effect of two nearby strip footings. The hyperbolic stress-strain relationship has been considered for the nonlinear elastic analysis. The linear elastic analysis has been carried out by deriving the equations for the interference effect of the footings in the framework of Pasternak model equation; whereas, the nonlinear elastic analysis has been performed using the finite difference method to solve the second order nonlinear differential equation evolved from Pasternak model with proper boundary conditions. Results obtained from the linear and the nonlinear elastic analysis are presented in terms of non-dimensional interaction factors by varying different parameters like width of the foundation, load on the foundation and the depth of the rigid base. Results are suitably compared with the existing values in the literature.

三线盾构隧道渐次掘进扰动影响分析

对于三线并行盾构隧道,后行隧道多次侧穿会对已建先行隧道造成扰动影响.基于Mindlin解,采用两阶段分析法,得到了先行隧道在两次盾构平行跨越下的水平附加位移解析解.与国家科学中心核心创新项目上海硬X射线三线并行盾构隧道现场监测数据进行对比,验证了方法的有效性.对三线隧道水平净距、结构纵向刚度、地层损失率及地层剪切模量进行了影响因素参数分析,研究结果表明:先行隧道在后行隧道平行跨越关键断面下产生的水平附加位移峰值与并行隧道水平距离、隧道结构纵向刚度、地层剪切模量成反比,与地层损失率成正比.研究成果可为合理预测后行隧道侧穿施工对已建先行隧道的影响提供一定的理论依据.

深基坑围护结构受力特性分析

由于计算过程简单、所需参数少,现行基坑规范中均采用的是基于平面应变理论的弹性支点法对基坑围护结构进行设计、计算。根据哈尔滨至牡丹江客运专线明挖段基坑工程现场监测结果,分析围护结构在基坑开挖过程中的受力大小及特征,并将最终实测受力与弹性支点法的计算结果进行对比分析,分别得到围护结构全开挖过程中的实测和规范对应的安全系数Fs。通过对现场实测结果与规范计算结果对比分析,在探讨该地区基坑设计的同时,也希望能为该地区类似基坑围护结构的设计与施工提供一些有用的参考。

高压喷射注浆技术用于高铁桥梁纠偏的可行性分析

我国高铁在长期运营过程中,受周边环境变化及人类工程活动等多种因素影响,部分线路桥梁地段出现了较大的横向偏移,严重影响列车正常安全运营,亟需进行纠偏整治。在分析高压喷射注浆桥梁纠偏原理基础上,建立桥梁纠偏理论计算模型,基于弹性地基梁理论,推导高压喷射注浆纠偏情况下,基桩挠度、转角、弯矩和剪力的微分方程,以及桥墩顶部位移计算解析式;通过对比桥墩顶部位移计算值与线路实际偏移量,分析高压喷射注浆技术用于桥梁纠偏的可行性,并以现场典型工程案例纠偏效果进行验证。研究结果表明:桥墩顶部位移与地层土体地基系数和高压喷射注浆产生的超孔隙水压力有关,当土体地基系数和超孔隙水压力分别取1 MPa/m和80.3 kPa时,桥墩顶部的理论计算位移为81.8 mm,远大于常见运营高铁无砟轨道线路实际偏移量;采用某高铁松江特大桥桥梁纠偏工程中,现场实测超孔隙水压力均值30.4 kPa计算的桥墩顶部位移为6.4~31.0 mm,其均值也大于线路最大偏移量18.2 mm,表明高压喷射注浆技术用于桥梁纠偏理论上可行;纠偏完成后桥梁及轨道结构状态稳定,线路线形平顺,恢复常速运营多年未见异常,理论和实践证明采用高压喷射注浆方式进行桥梁纠偏是一项切实可行的技术措施。

Enhanced elastic beam model with BADS integrated for settlement assessment of immersed tunnels

Excessive settlement may induce structural damage and water leakage in immersed tunnels,seriously threatening the tunnels’safety.However,making accurate assessment of the settlement in immersed tunnels is difficult due to the incomplete knowledge of the geotechnical parameters and the inadequacy of the model itself.This paper proposes an effective method to accurately assess the settlement in immersed tunnels.An enhanced beam on elastic foundation model(E-BEFM)is developed for the settlement assessment,with the Bayesian adaptive direct search algorithm adopted to estimate unknown model parameters based on previous observations.The proposed method is applied to a field case of the Hong Kong–Zhuhai–Macao immersed tunnel.The original BEFM is used for comparison to highlight the better assessment performance of E-BEFM,particularly for joints’differential settlement.Results show that the proposed method can provide accurate predictions of the total settlement,angular distortion(a representation of tubes’relatively differential settlement),and joints’differential settlement,which consequently supports the associated maintenance decision-making and potential risk prevention for immersed tunnels in service.

基于相似理论的复合地基弹性垫层模型试验研究

为了对比分析不同桩型(半刚性桩和柔性桩)、不同垫层材料(砂垫层、碎石垫层、弹性垫层)和垫层厚度对复合地基承载特性的影响,需要开展复合地基室内模型试验研究。在研制模型试验系统、建立符合模型试验要求的模化条件和相关准则的基础上,分析了复合地基的承载特性,引入了弹性垫层模拟实际工况的可行性。结果表明,随着垫层厚度的增大,桩土应力比有所减小,上刺入量会逐渐增大。柔性桩的桩顶面中心点沉降量明显小于半刚性桩,一般差值在10 mm左右;柔性桩的分级加载分界点在60 kPa左右,半刚性桩则在80 kPa左右。弹性垫层相比于砂垫层和碎石垫层,其整体性相对更好,可将原有的“100~200 mm砂垫层+荷载板”改为“小于100 mm的砂粒找平层+弹性垫层+荷载板”,以更好地发挥实际垫层在复合地基的作用。

北疆膨胀土渠道混凝土衬砌结构变形特性研究

为研究北疆膨胀土梯形渠道混凝土衬砌结构变形和内力的变化规律,通过室内试验和数值模拟计算基土膨胀变形量,基于弹性地基梁理论,建立计算混凝土衬砌板变形和内力的力学模型,分析了基土初始含水率为6%、9%、12%、15%的膨胀土渠道运行后混凝土衬砌板变形和内力的变化规律。结果表明,混凝土衬砌板变形和内力值随基土初始含水率的减小而增加,当基土为风干含水率6%时,渠道底板和坡板膨胀变形最大值分别可达到3.48、3.94 cm;当初始含水率一定时,坡脚处膨胀反力最大,渠底板中间位置位移和弯矩最大;渠坡板距坡脚1/3处位移最大,距坡脚1/6处弯矩最大。最后,根据研究结果提出了两种“防渗保湿”工程措施。

带纵向加强肋复合墙体轴心受压荷载分配规律研究

针对带纵向加强肋复合墙体轴心受压下荷载在各承力部件间的分配问题,采用静力竖向承载力试验方法,对三榀1/2比例带纵向加强肋复合墙体进行试验研究,以弹性地基梁理论为基础,提出墙体在竖向荷载作用下的简化力学模型,计算墙体各承力部件承担竖向荷载比例,并与试验结果对比,分析墙体各承力部件的荷载分配规律。结果表明:所建立的墙体简化力学模型合理可行,竖向荷载在墙体各部件中按照轴向刚度进行分配,加载过程中各部件所承担的荷载比例基本不变,边框柱承担大部分竖向荷载,开洞增加了边框柱承担荷载的比例。

桩基支承梁与弹性地基梁承载性能对比研究

桩基支承梁的梁体承载能力由桩基及梁体本身的刚度提供,而弹性地基梁由于梁体下方和两侧土体的影响,其承载能力较桩基支承梁有一定的提升。以长江下游某内河重力式码头的后轨道梁为研究对象,建立二维模型选取轨道梁危险工况并建立轨道梁三维数值模型,对比分析弹性地基梁与桩基支承梁的内力及位移,研究表明弹性地基梁相比于桩基支承梁,最大挠度减小26.4%~35.3%,最大正弯矩减小11.3%~12.4%,桩身最大压应力减小1.8%~45.3%,最大竖向位移减小28.1%~39.0%,弹性地基梁相比于桩基支承梁在相同的受力情况下,梁体以及桩身的内力、应力均有所减小,弹性地基梁的承载能力更强,同时发现土体轨道梁协同受载不仅使得轨道梁及桩基的受力减小,还会影响轨道梁及桩基的应力分布状态。

基于两相积分模型非线性弹性基底上轴向运动纳米梁的自由振动

利用两相非局部积分模型,研究弹性基底上轴向运动纳米梁的线性振动.利用哈密顿原理,得到非局部纳米梁在固定和简支边界条件下梁的积分-微分方程模型.分析各参数对纳米梁的临界速度和固有频率的影响.结果表明梁的临界速度和固有频率在不同边界条件下,会随着非局部参数和几何参数的增大而增加;第一临界速度随着基底弹性系数的增加而减少.

不同计算模型下圆形水池底板内力分析

弹性地基上的底板设计,是水池结构设计的重点和难点。不同的计算模型与实际情况均有出入,计算所得的结果也会不相同,甚至出入较大。本文对两个实际工程中的圆形水池结构,采用有限元分析软件MIDAS GTS NX,分别建立反力直线分布假定模型、Winkler地基模型和弹性半空间地基模型,进行数值模拟计算。通过对底板变形和内力的对比分析,探讨壁板、底板与地基间的相互作用,为圆形水池结构设计提供理论指导。

开挖卸荷引起下卧已建盾构隧道的纵向变形研究

开挖卸荷引起的下卧已建盾构隧道纵向变形是城市基础设施建设面临的热点和难点问题。将已建盾构隧道视为三参数Kerr弹性地基上的无限长梁,采用两阶段法研究基坑开挖卸荷引起下卧盾构隧道的纵向变形。对简化弹性空间法获得的地基参数进行讨论,通过与有限元模拟结果对比确定了合适的Kerr地基模型参数选取,并对Winkler、Pasternak与Kerr 3种地基模型的模拟结果进行了对比。为获得更合理的上方卸荷引起的隧道响应,推导并求解了考虑隧道侧向土体对隧道作用的平衡微分方程,解析结果与有限元结果基本吻合,与工程实例监测数据对比,验证了方法的有效性。研究表明:相对于Winkler与Pasternak模型,Kerr地基模型更具优越性;对通过简化弹性空间法得到的地基参数进行适当修正可以使弹性地基模型的模拟结果更理想;隧道侧向土体对隧道的作用比较显著,应在计算中考虑。

大型原油储罐有限元分析建模的新方法

为了准确计算大型原油储罐的底板应力,提出了一种有限元分析的建模方法.初步分析了弹簧杆模型与弹性地基接触模型的差异,选取接触单元模拟地基-罐底板的相互作用.比较了罐底板上表面径向应力理论解、有限元计算应力结果与实测应力数据的误差,并结合油罐钢筋混凝土环梁和弹性地基的沉降特点,提出将两种地基的沉降量差作为有限元建模的边界条件.通过试算得到了地基的弹性模量和沉降差估算值.结果表明,理论估算结果与基础沉降监测值吻合很好,该方法可以准确地模拟油罐底板的应力,还可以预测在用大型油罐的安全性.

基坑变形预测与周围环境保护

提出了土体本构模型的确定方法及其参数的获取途径。通过分析与推导，表明对于采用三元件模型等描述材料性态的线性粘弹性模型，可通过采用与时问序列相对应的综合弹性模量Ｅｔｉ代替线弹性模量，将其简化为弹性问题的分析，由此建立了基坑变形预测的计算模型。同时依据提出的计算模型所进行的分析，获得了支护方案的优化设计和坑周环境保护措施。

解析型弹性地基Timoshenko梁单元

采用双参数弹性地基模型和Timoshenko深梁模型,建立了弹性地基一般梁挠度控制方程,求解得到了挠度方程解析通解,构建了双参数弹性地基深梁的挠度、截面弯曲转角及剪切角的解析位移形函数。建立了梁模型、梁基模型等两种势能泛函,利用最小势能原理,构造了两个双参数弹性地基深梁单元,给出了单元列式。分析表明:梁模型单元在均布荷载作用下误差为0.221%,非均布荷载作用下误差为0;梁基模型单元在均布荷载作用下误差为0,在两端集中力作用下误差为6.597%,在跨中集中力作用下误差为102.716%;同时,该文提出的双参数Timoshenko梁模型单元不存在剪切闭锁的问题。