热力盾构隧道先盾后井施工衬砌接头变形机理与控制

先盾后井是热力盾构隧道建设中一种高效经济的施工工法。结合中国首例大断面热力盾构隧道工程,基于纵向等效连续化模型和弹性地基梁理论,对施工过程中衬砌接头受力特征和变形机理进行了分析,并提出控制措施;然后建立了衬砌接头全断面接触面单元数值模型,对控制效果进行分析和评价;最后通过现场监测,得到了不同施工阶段管片纵向轴力及接缝变形规律。研究结果表明:先盾后井工法施工中,衬砌接头变形分为两个阶段:基坑开挖及管片拆除,其中管片拆除为接头变形的主因,基坑施工中,基底卸荷产生的负弯矩作用于隧道上,导致邻近竖井管片底部轴力减小、环缝张开,拆除基坑内管片时,作用于端头管片的残余盾构推力和螺栓预紧力消失,导致管片纵向轴力进一步衰减,环缝二次张开;根据现场监测结果,提出的对邻近竖井的管片纵向拉紧并复紧连接螺栓,进行混凝土铺底及衬砌背后二次注浆的控制措施能够有效控制轴力损失,减小接头变形,施工中环向接缝最大张开量3.51 mm,满足隧道防水要求;采用全断面接触面单元建立的数值模型可以较为精确地模拟施工中管片接头力学行为,其结果可作为控制效果评价参考依据。     

Wind‐induced internal pressure effect within a novel super‐large cylindrical–conical steel cooling tower

A cylindrical–conical steel cooling tower (SCT) is a new type of very large thin‐walled, flexible structure. This study focused on the wind loads on the internal and outer surfaces of this structure and its wind‐induced responses. First, using the computational fluid dynamics method, the numerical wind tunnel was conducted to simulate a 189‐m‐high cylindrical–conical SCT, Asia's highest cooling tower that is still under construction. This numerical method was validated by comparing the wind pressures across typical cross sections of the tower model's cylindrical and conical segments with known standard curves. Based on this, the features of the airflow around the typical cross sections and its wake were extracted, and the distribution of mean wind loads along the internal and outer surfaces of the cylindrical and conical sections was obtained. Then functions for estimating the internal and outer surfaces shape factors of the cylindrical and conical segments were obtained by fitting to the simulated data. Furthermore, finite element method was used to analyze the static wind‐induced response of the cylindrical–conical SCT under internal pressure, external pressure, or both internal and external pressure. The effect patterns of internal pressures on the wind‐induced responses of the main tube, stiffening trusses, and auxiliary trusses of the tower were derived from the analysis results. Main findings of the research can provide a reference for design of very large cylindrical–conical SCTs for wind resistance in the future.     

护盾式TBM施工隧洞豆砾石吹填过程模拟研究

豆砾石吹填是TBM施工中非常重要的一道工序,研究吹填过程对分析填充层质量和优化吹填工艺具有一定的工程应用价值。借助PFC在离散体研究方面的优势对豆砾石吹入过程进行多方案模拟,并进行豆砾石的受力运动分析,探究填充层内豆砾石的分布特征及其影响因素。结果表明:依次吹填管片环中部80°、上部160°、顶部180°(补吹)吹填孔,填充层呈4段分布,其中0°~45°和75°~135°区间,粒径不同的颗粒分层分布严重,大颗粒分别靠近管片侧和围岩侧,45°~75°区间存在局部颗粒分层分布现象,135°~180°区间存在吹填不密实的问题;分层分布现象受吹入豆砾石颗粒的粒径组合、表面摩擦系数、所受压力大小等因素的影响;通过改变吹填孔位置和新增吹填孔,控制各孔的填充范围,进而降低颗粒在该范围填充完成前受到的压力,再采用阶梯吹填法吹填,能显著缩小分层分布区且使颗粒分布更为规整。吹填孔的填充范围应控制在45°内,但顶部吹填孔易发生堵塞,不宜用做大量颗粒吹填,因此具体部位吹填孔的填充范围需进一步研究。此研究成果可为工程吹填方案设计提供一定的参考。     

Axisymmetric alternating direction explicit scheme for efficient coupled simulation of hydro-mechanical interaction in geotechnical engineering—Application to circular footing and deep tunnel in saturated ground

Explicit solution techniques have been widely used in geotechnical engineering for simulating the coupled hydro-mechanical (H-M) interaction of fluid flow and deformation induced by structures built above and under saturated ground, i.e. circular footing and deep tunnel. However, the technique is only conditionally stable and requires small time steps, portending its inefficiency for simulating large-scale H-M problems. To improve its efficiency, the unconditionally stable alternating direction explicit (ADE) scheme could be used to solve the flow problem. The standard ADE scheme, however, is only moderately accurate and is restricted to uniform grids and plane strain flow conditions. This paper aims to remove these drawbacks by developing a novel high-order ADE scheme capable of solving flow problems in non-uniform grids and under axisymmetric conditions. The new scheme is derived by performing a fourth-order finite difference (FD) approximation to the spatial derivatives of the axisymmetric fluid–diffusion equation in a non-uniform grid configuration. The implicit Crank-Nicolson technique is then applied to the resulting approximation, and the subsequent equation is split into two alternating direction sweeps, giving rise to a new axisymmetric ADE scheme. The pore pressure solutions from the new scheme are then sequentially coupled with an existing geomechanical simulator in the computer code fast Lagrangian analysis of continua (FLAC). This coupling procedure is called the sequentially-explicit coupling technique based on the fourth-order axisymmetric ADE scheme or SEA-4-AXI. Application of SEA-4-AXI for solving axisymmetric consolidation of a circular footing and of advancing tunnel in deep saturated ground shows that SEA-4-AXI reduces computer runtime up to 42%–50% that of FLAC's basic scheme without numerical instability. In addition, it produces high numerical accuracy of the H-M solutions with average percentage difference of only 0.5%–1.8%.     

隧道爆破及车辆荷载耦合作用下公路振动研究

针对隧道下穿环城公路爆破开挖产生的振动效应,同时考虑公路上车辆瞬时荷载耦合作用,运用LS-DYNA分析环城公路的振动规律及响应特征,并与实际监测结果进行对比分析,研究结果表明:(1)公路中部位置的峰值应力为1.7 MPa,大于两边的峰值应力,随着爆破点与路面间水平距离的增大,峰值应力也逐渐增大;(2)在0.015 s到0.02 s这段时间内,振速幅值最大,随后,幅值降低,振动频率变小,振动趋于缓和,数值模拟的结果要普遍小于实际监测的振速峰值;(3)公路左侧振动的位移响应最大,但是公路中部位置会在之后的振动过程中产生二次峰值,造成更大的位移响应。研究可为相似工程设计提供一个参考。     

基于间距折减法浅埋小净距交叉隧道安全性分析

为解决交叉隧道的安全性评定问题,类比边坡工程中的强度折减法,以既有隧道允许的最大沉降值为判据提出交叉间距折减法。应用FLAC^3D软件模拟探究了不同覆土厚度、交叉角度对上部既有隧道的影响规律。当交叉角度为90°,覆土厚度分别为15、20、24、30 m时的临界交叉间距为3、4.5、7、11 m。当覆土厚度为26 m,交叉角度分别为0°、30°、45°、60°、90°时的安全净间距为6.8、7.6、8.9、8.1、7.4 m。结果表明,新建隧道对既有隧道的影响随覆土厚度增加而增大,随交叉角度增大呈现先增大后减小的趋势。为验证方法的合理性,以盘道岭隧道为背景对3种支护方案进行了交叉间距折减检验进行安全性评估。现场监测表明,开挖前进行的管棚支护较好地控制了对上部公路隧道的影响。     

盾构隧道下穿高速铁路站场安全风险评估管理方法

为提高风险评估对工程设计的指导性,本文结合某地铁区间盾构隧道下穿高速铁路站场工程实例,尝试将风险评估、数值模拟和工程设计结合起来形成反馈机制。首先采用安全风险层次-模糊综合评价法(AHP-FE)对工程进行了初步评估,得到了初步的设计阶段风险等级“高度”和主要风险源及排序;然后采用数值模拟方法对盾构下穿铁路站场进行了施工模拟,得到了主要风险源相关指标的预测值,并提出了系列控制措施;在此基础上,再一次采用安全风险模糊评估理论对工程进行风险分析,最后得到设计阶段允许的“中度”风险等级和相应的风险源排序。本文所遵循的风险评估方法和流程可以提高风险评估的准确性和合理性。     

隧道排水系统非对称堵塞对衬砌外水压力的影响

基于目前未见对隧道排水系统非对称堵塞后的衬砌外水压力的变化规律的研究,以重庆中梁山某隧道为研究背景,建立了隧道及其排水系统的简化模型,通过模拟不同长度的排水系统非对称堵塞,研究了隧道衬砌结构受到的水压力的变化规律,并且在隧道工程中进行了现场模拟排水系统堵塞的试验,试验结果与数值模拟可相互印证。研究结果表明:(1) 隧道排水系统单侧堵塞后,堵塞侧二次衬砌背后的水压力在短时间内将上升,然后逐渐下降至稳定,但高于排水系统正常时的水压;(2) 隧道排水系统非对称堵塞长度不断增加时,堵塞侧二次衬砌背后受到的外水压力峰值和稳定值也不断增加;(3) 隧道排水系统非对称堵塞长度不断增加时,注浆加固圈承受的最大水压力绝对值不断在增加,但注浆加固圈分担水压力的能力将逐渐减小。     

基于统计和塑性区的隧道深浅埋划分方法研究

我国现行公路、铁路隧道规范中隧道深浅埋分界深度公式是基于小跨度隧道的统计资料得出的回归公式,该公式对于跨度较大的隧道的适用性存在明显的不足。笔者通过对隧道规范建议的深浅埋分界深度与对应深度的塑性区半径进行回归分析,拟合出了两者之间的关系式;将拟合出来的关系式带入圆形隧道的塑性区理论式中,获得了隧道深浅埋划分深度的新的计算公式。将本文方法计算结果与现场实测资料和模型试验进行对比,验证本文公式的科学合理性。对比结果表明:(1)在大跨度时本文计算结果与统计结果和模型试验结果十分吻合;(2)在小跨度时本文计算结果与规范计算结果十分吻合。因此,本文方法为在围岩等级较低情况下的深浅埋分界深度计算提供了新的思路和计算方法。     

平行双孔水工隧道相互作用的时效解答

地下工程中常遇到流变岩体中双线近距离隧道施工问题。隧道施工位移的预测和控制,特别是新建隧道的施工对既有隧道产生的影响,是工程中面临的重要问题。针对流变岩体中深埋双圆形水工隧道的问题,笔者采用复变函数方法和Laplace变换技术建立了考虑施工过程时黏弹性应力、位移与弹性复位势之间的关系,然后运用黏弹性叠加原理得到了整个施工过程各个阶段围岩应力和位移全量和增量理论解答,并据此进行新建隧道对既有隧道的影响分析。为验证解答的正确性,对一算例进行了有限元解答和理论解答的比对,两者吻合很好。与数值与实验方法相比,本文解答可以较为便利地对岩体应力、位移进行参数分析,进一步可以指导工程的初步设计。