冻结法凿井需注意问题的探讨

介绍了冻结法凿井的原理,从掘进段高的确定、冻结管的断裂问题、冻结井壁的破裂方面探讨了冻结凿井施工中的问题,并针对性的提出了相应的解决办法,对冻结法凿井施工具有一定的指导意义。     

南京长江四桥北锚碇沉井下沉安全监控研究

南京长江四桥北锚碇沉井长69m,宽58m,高52.8m,是目前世界上平面尺寸最大的超大型沉井。因其施工难度大,故对该沉井排水下沉过程进行安全监控。超大型沉井结构受力的最不利工况是下沉初期即开挖形成仅刃脚支撑的大锅底,有限元分析表明,此时顺桥向和横桥向拉应力最大点均出现在首节钢壳沉井隔墙中跨底部。根据有限元分析结果选取典型截面来监控拉应力变化。沉井下沉曲线表现出慢-快-慢的特点,拉应力曲线则分为上升-峰值-下降-回弹4个阶段。沉井下沉初期,随着开挖面的扩大,隔墙底部所受拉应力也相应增加;下沉中期,通过调整开挖方案能有效降低拉应力,改善结构受力状况;当下沉超过一定深度后,井壁外逐渐增大的土压力会使墙底拉应力减小,结构本体趋于安全;排水下沉到位后的地下水回灌能引起墙底拉应力增大。现场监控表明首节钢壳沉井在下沉过程中有较多的安全储备,监控结果反馈于施工指导保证了下沉的安全高效。     

Geomechanical model test for analysis of surrounding rock behaviours in composite strata

Due to the large differences in physico-mechanical pro perties of composite strata,jamming,head sinking and other serious consequences occur frequently during tunnel boring machine(TBM) excavation.To analyse the stability of surrounding rocks in composite strata under the disturbance of TBM excavation,a geomechanical model test was carried out based on the Lanzhou water supply project.The evolution patterns and distribution characteristics of the strain,stress,and tunnel deformation and fracturing were analysed.The results showed that during TBM excavation in the horizontal composite formations(with upper soft and lower hard layers and with upper hard and lower soft layers),a significant difference in response to the surrounding rocks can be observed.As the strength ratio of the surrounding rocks decreases,the ratio of the maximum strain of the hard rock mass to that of the relatively soft rock mass gradually decreases.The radial stress of the relatively soft rock mass is smaller than that of the hard rock mass in both types of composite strata,indicating that the weak rock mass in the composite formation results in the difference in the mechanical behaviours of the surrounding rocks.The displacement field of the surrounding rocks obtained by the digital speckle correlation method(DSCM) and the macro-fracture morphology after tunnel excavation visually reflected the deformation difference of the composite rock mass.Finally,some suggestions and measures were provided for TBM excavation in composite strata,such as advance geological forecasting and effective monitoring of weak rock masses.     

基坑开挖对下卧地铁隧道的施工影响分析

深圳市桂庙路快速化改造工程前海段下沉式隧道平行上穿已建的地铁11号线隧道,下卧的地铁左线隧道中线与下沉式隧道中线水平间距3.2~6.7 m,顶部距离新建隧道底部9.1~15.0 m。下沉式隧道主体结构全长580 m,采取明挖基坑的方式施工,长距离基坑开挖引起的大范围卸载对下卧地铁隧道产生的影响不容忽视。通过建立三维数值分析模型对基坑施工过程进行模拟,动态地分析了基坑开挖对地铁隧道衬砌内力及变形的影响;在此基础上,提出了"分区、分时、分层、分块"开挖以及采取高压旋喷桩加固地基等施工对策。采取上述施工措施后,地铁隧道实测最大上浮值9.1 mm、最大下沉值5.6 mm,这表明下卧隧道的变形得到了有效控制,该研究成果可为今后类似工程提供一定的参考。     

Discrete element model for performance analysis of cutterhead excavation system of EPB machine

With the aim of probing for design theory of cutterhead excavation system of earth pressure balance (EPB) machine, the parameters representing the system performance are concluded firstly. Then a 3D model for cutterhead excavation system of EPB machine is presented with the discrete element method (DEM) software PFC^3D, which is capable of simulating the tunneling ground in site, the machine structure and the excavation operation. The performance parameters indicating stability of excavation face, soil discharging rate, cutterhead system torque and cutter wear are measured by running the DEM code. The results obtained with the DEM model are accord with situ data. It indicates that the DEM model is a promising method replacing the field experiment to analyze the influences of the structural parameters on system performances, which are essential for structure optimization design of the cutterhead system of EPB machine.     

旋喷桩封底隔断承压水头在沉井中的应用

为避免下伏承压水层的基坑在其开挖过程中产生突涌,常用做法多采用人工降水的方式来降低承压水水头;作为顶管工作竖井的沉井开挖面积小、深度大,当遇下伏承压水时,可预先在底板下方高程以旋喷桩相互搭接形成加固层,从而实现对承压水水头的隔断。文章通过理论分析和工程实例验证了该工法的可行性,不仅缩短沉井施工工期,而且大大减小了工程施工对周边环境的影响,为类似工程提供经验和依据。     

大型沉井结构在施工中下沉量与开挖量的关系

大型沉井结构作为深基础的一种,在施工技术和施工机械不断改进的现在,得到了广泛的应用。传统的经验施工法不仅有一定的盲目性,时滞性,不利于防止突沉和控制终沉。为此,寻求一种下沉量与开挖量关系的方程,可以预测下沉,便于在线控制。     

Numerical simulation of the behaviors of test square for prehistoric earthen sites during archaeological excavation

During the process of archaeological excavation in the regions of Southeast China, collapse of test square usually occurs due to poor site-specific conditions. In this paper, the fast Lagrangian analysis of continua in three dimensions (FLAC3D) is employed to reveal the behaviors of test square. Taking the archaeological works in Liangzhu prehistoric earthen sites as the research background, the paper first introduces the geological setting, excavation procedure and monitoring scheme of the studied test square. Then, the deformation of four sides of the test square is modeled using FLAC3D. By comparison, it shows that the numerical results are consistent with the results from field monitoring. The result suggests that the numerical simulation can be effectively applied to representing the actual behaviors of the test square, which is helpful for determination of excavation scheme and stability evaluation of the test square during archaeological excavation.     

Tunneling in fault zones, Tuzla tunnel, Turkey

The Tuzla tunnel was excavated mainly in fault zones, shale and limestones using the conventional and shielded tunnel boring machine (TBM) methods. Fault zones in shales are brecciated and clayey, while those in limestones are of blocky structure. The rock mass rating, rock mass classification and support systems proposed for fault zones in Tuzla tunnel are insufficient for explaining the deformation and failure mechanisms encountered in the tunnel. In addition, dyke exposures, the fault-collapsed karstic system and groundwater also caused some problems during the excavation of the tunnel. The most important event relevant to fault zones in the Tuzla tunnel was the selection of a TBM. Before the excavation of the tunnel, the rock was determined to be of poor to fair quality. Therefore, tunneling with a TBM in rock of poor to fair quality was thought to be economic. However, during the excavation, fault zones with poor to very poor rock characteristics were encountered along an area comprising 70% of the tunnel length. The fault zones caused jamming of the TBM cutter and deviation from the tunnel alignment. In this respect, tunneling with the TBM method was quite problematic. Geotechnical problems encountered in the fault zones required special measures to be taken in the tunnel. With these measures, excavation and supporting of the tunnel were completed successfully by transforming heterogeneous conditions in the fault zones to homogeneous conditions in the tunnel impact area.     

盾构开仓现场气体检测方法的研究

盾构机在掘进过程中要根据地层地质条件以及刀具磨损情况,进行开仓检查或开仓换刀,以防止刀盘结构遭到破坏。盾构土仓内存在的易燃易爆及有毒有害气体直接影响盾构开仓作业人员的健康安全,甚至可能导致缺氧窒息、有毒有害气体中毒及爆炸等恶性事故。结合福建省地铁隧道盾构法施工的实际情况以及福建省地方性标准《盾构法地铁隧道施工现场气体检测规程》的编制情况,本文论述了地铁隧道盾构开仓及气压作业状态下盾构土仓内气体环境的检测方法及现场检测步骤,以便盾构法隧道施工现场气体检测方法更好地向施工企业推广,为安全施工提供参考。     

Control of the stressed-deformed state of open caissons during their sinking

Conclusions 1. During the sinking of a caisson, the pressure and the deformations of the structure change continually in magnitude, and besides, in many cases, they exceed the values adopted in design.2. Experience with the construction of open caissons of large dimensions in plan indicates that, during sinking, tilting was often observed, when a significant increase occurs in the nonuniformity of pressure.3. By organizing observation of the state of the structure of an open caisson, it is possible to regulate the sinking procedure.4. The accumulation of observed data will make it possible to define more accurately the physical nature of the interaction between open caissons and the surrouding medium during their sinking, and this will promote their more economical and reliable design.Main Directorate of Specialized Industrial Construction Trusts (Glavspetspromstroi). All-Union Scientific-Research Institute of Hydraulic and Sanitary Engineering (VNIIGS). Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 2–4, November–December, 1974.     

南京长江四桥北锚碇沉井首次降排水下沉研究

南京长江四桥北锚碇沉井是目前世界上最大的矩形沉井,长69m,宽58m,高52.8m,其首次降排水下沉需要处理下沉精度、结构安全和附近长江大堤沉降等问题。通过现场开挖控制、应力监控和大堤沉降观测表明,在不同下沉阶段采用不同的开挖策略是能够保证沉井下沉精度的;在沉井下沉前期,开挖方案对结构安全起控制性作用,后期则由于土体对沉井侧壁约束作用的加强,下沉深度越大结构越安全;长江大堤的沉降主要由承压含水层的压缩引起,并且产生的沉降量较小,没有出现安全问题;南京长江四桥北锚碇的首次降排水下沉是非常成功的。     

The effect of machine design parameters on the stability of a roadheader

A “roadheader” excavator has a special set of characteristics among tunnel excavation machines and the determination of the stability states of a roadheader is important for effective and continuous excavation. For roadheaders having equal power, if one is more stable than another, it can respond to higher boom forces. A new computer program was developed to analyze the stability states of roadheaders. The developed method allows analysis for both longitudinal and transverse cutting head type machines either at one point on the excavation face or in terms of the whole face. Values of the four stability states of the roadheader, namely: turning around the vertical axis, turning to the side directions, turning to the back direction and sliding, can be obtained using this program. In this study, the effects of machine design parameters were investigated by applying this method to the stability of a longitudinal type roadheader. The studied machine design parameters are the machine weight, boom length, machine width, track width, distance between the back leg of the machine and the center of gravity, distance between the start of the boom and the center of gravity, distance between the horizontal point and the vertical rotation point of the boom, and the distance between the ground and boom axis when it is parallel to the ground. The effect of the machine design parameters on stability has been illustrated in detail.     

基坑开挖对临近基坑地铁高架结构变形的影响

以苏南地区临近城市轨道交通结构的基坑工程为例,通过三维有限元模拟施工过程,反演适宜模拟该基坑施工过程的计算参数,并在此基础上研究不同开挖距离、基坑规模、开挖深度、基坑数量和施工工序的基坑施工对临近地铁高架结构的影响。结果表明:基坑与结构水平间距小于2H(H为基坑深度)时,结构横向变形发展大于竖向,水平间距为1H时,桥墩水平位移和沉降达到最大;地铁高架桥桥墩附加变形伴随着基坑宽度的增大而迅速增大,当基坑宽度大于8H时,影响迅速减小;基坑开挖深度对基坑中线4 H范围内的桥墩影响最大,尤其是开挖深度超过10m后;多个基坑施工引起的结构变形表现出明显的非线性叠加效应;多基坑施工工序对结构总变形略有影响。     

Energy release process of surrounding rocks of deep tunnels with two excavation methods

Numerical analysis of the total energy release of surrounding rocks excavated by drill-and-blast(D&B) method and tunnel boring machine(TBM) method is presented in the paper.The stability of deep tunnels during excavation in terms of energy release is also discussed.The simulation results reveal that energy release during blasting excavation is a dynamic process.An intense dynamic effect is captured at large excavation footage.The magnitude of energy release during full-face excavation with D&B method is higher than that with TBM method under the same conditions.The energy release rate(ERR) and speed(ERS) also have similar trends.Therefore,the rockbursts in tunnels excavated by D&B method are frequently encountered and more intensive than those by TBM method.Since the space after tunnel face is occupied by the backup system of TBM,prevention and control of rockbursts are more difficult.Thus,rockbursts in tunnels excavated by TBM method with the same intensity are more harmful than those in tunnels by D&B method.Reducing tunneling rate of TBM seems to be a good means to decrease ERR and risk of rockburst.The rockbursts observed during excavation of headrace tunnels at Jinping II hydropower station in West China confirm the analytical results obtained in this paper.     

Design of sequential excavation method for large span urban tunnels in soft ground – Niayesh tunnel

Modern tunnel design and construction requires appropriate techniques and technologies during all phases of a tunnel project. Selecting a suitable excavation procedure for large span urban tunnel projects in soft ground is a key factor for successful construction of the project. The costs and time for tunnel construction are strongly influenced by the choice of the excavation procedure. This research focuses on the selection of excavation method, excavation sequence and optimum trailing distance between different excavation stages in soft ground urban tunnelling. Considering soft ground condition and the big cross section of the Niayesh urban road tunnel project, sequential excavation method (SEM) was selected for tunnel construction. In this phase, Central Diaphragm (CD) and Side wall Drift (SD) methods were proposed for tunnel construction and appropriate method was selected based on its potential to limit surface settlements. Then, different excavation sequences considering side wall drift method were planned and modelled using three dimensional finite element method and optimal excavation sequence was selected. Finally, the trailing distance between different excavation stages were analysed numerically and the optimal distance with minimum surface settlement was determined.     

软土场地不规则深基坑旋喷锚护支撑技术

某工程基坑具有周边环境开阔、开挖范围内土质条件差、基坑平面形状不规则、开挖面积大等特点。对比优选对撑和角撑的结合、环形支撑、锚杆拉撑等支撑形式，大部分区域采用对撑和角撑相结合形式，在沉井位置处加设拉梁板支撑，在对撑和角撑难以布置的区段采用斜向旋喷锚桩作为外拉锚撑，在需严格保护的文物建筑区段，采用布置角撑及拉梁钻孔桩的形式。监测数据表明，基坑水平位移及竖直位移均在设计要求变形控制范围内，且取得了较好经济效益。     

基坑深度、墙体长度、墙体插入深度对高层建筑深基坑开挖变形的影响

利用非线性有限元方法 ,研究了基坑深度、墙体长度以及墙体插入深度对深基坑开挖变形的影响 ,具体研究了墙体侧向挠度、地表沉降和坑底隆起的变化。提出了具有实际工程意义的某一步段下基坑的最大开挖深度、墙体插入深度的有效范围等     

嘉兴污水处理工程高位井施工

嘉兴污水处理工程高位井井体分5节制作,采用水力机械挖土分3次排水下沉法施工。由于采用了大口径井点降水,实现了排水下沉深度达29.35m,创上海地区软土层中沉井排水下沉深度的记录。文章叙述了沉井制作、下沉的全过程。其施工技术可供类似工程参考。     

软岩地层结构下大型调压井沉井法施工技术

本文结合新疆某水电站施工实践，介绍了混凝土沉井技术在松散地层中开挖调压井的施工工艺和施工方法。