Large diameter shafts for underground infrastructure

The technique of large diameter shafts for deep excavations was analysed in terms of its basic construction elements, reported literature cases and design methods. The effects of the construction sequence and the geological deposition on the behaviour of the shaft was analysed using 3D finite element models. Induced stresses and displacements on the soil mass were investigated. Three methods to assess the stability of the shaft lining were presented and employed as a post-processing stage of analysis of the models. The results indicated a major influence of the height of the vertical excavation stages on the shaft behaviour, markedly on the induced settlements. The lining analysis also demonstrated the effects of the vertical excavation stages and how different safety assessment methods can produce significantly different results.     

Ways to reduce metal consumption in the construction of sunken shafts

Conclusions 1. A number of positions taken in active documents regulating questions concerning the computation and design of sunken shafts embedded without a thixotropic jacket are highly conditional and require more precise definition. This applies primarily to the computation of wall failure during hang-up of the lower section of the shaft and the soil pressures on circular shafts possessing diameters to 16 m with allowance for their actual curvature.2. The method recommended in the present paper for the design of circular sunken shafts with diameters to 16 m and depths to 10–12 m makes it possible to reduce significantly (by 25–30% on the average) the amount of reinforcement in the upper section of the shaft wall as compared with its consumption for type designs without impairing the strength of the structures.3. It is expedient to disseminate construction experience acquired with lightly reinforced sunken shafts in Vyaz'ma, Leningrad, and Moscow for structures of similar dimensions under various engineering-geologic conditions using the manual of structural solutions and technological schemes for work production developed by the Leningrad Division of the State Institute for the Design and Planning of Beds and Foundations.4. In sinking lightly reinforced shafts, it is necessary to follow especially carefully the conditions set forth in the plan for work production, particularly the excavation of soil in the blade segment, prohibiting their skewing so as to ensure uniform pressure between the shaft walls and ground.Main Administration for Special Foundation Construction. Leningrad Division of the State Institute for the Design and Planning of Beds and Foundations. All-Union Scientific-Research Institute of Hydraulic and Sanitary Engineering. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 8–9, November–December, 1979.     

土压力对软土地基中圆柱型挡土墙的作用

 竖井是过河或海隧道的组成部分,与隧道这样轴向细长的结构相比,竖井在形状上可以有不同的设计。尽管方形有更多的使用空间,但在断面连接处,竖井一般被设计成圆形。此外,在水底或海底进行建筑物施工时,也常采用圆形的沉井作为结构的基础。由于水平面的成拱作用,减小了外部压力而显示其更重要的优点。在进行支撑墙的施工过程中,墙的刚度、施工方法和施工管理对墙的位移具有很大的影响。此外,挡墙的位移发展是可能的,即使增加了刚性的侧向支撑如注浆墙。所以,在开挖过程中由于应力的释放、水平和垂直向的成拱作用,在平面应变条件下圆柱型挡土墙上的土压力是介于静止和主动土压力之间。讨论了无黏性土中圆柱型挡土墙的模型试验,给出土压力的分布和破坏面形状。     

Analysis of lateral earth pressure on a vertical circular shaft considering the 3D arching effect

The lateral earth pressure on a vertical circular shaft is investigated using both experiments and numerical analyses. The study focused on quantifying the magnitude and distribution of the lateral earth pressure, which was measured by considering the three-dimensional arching effect. A framework for determining distribution of the earth pressure based on centrifuge model tests and 2D FE analysis is introduced. The FE modelling techniques and the constitutive relationships of the soil are presented in detail. Parametric analyses showed that the arching effect on the lateral earth pressure is highly dependent on the diameter and height of the shaft, the internal friction angle and the cohesion value of the soil, the end-bearing conditions and the flexural modulus of the shaft. The study found that when the arching effect is considered, the lateral earth pressure on a vertical circular shaft is approximately 80% less than that calculated using Rankine’s theory. The study also found that the arching effect of the soil is more significant for flexible vertical shafts than for rigid vertical shafts embedded in weathered soil.     

盾构法隧道施工引起的土体变形预测

 理论分析表明,不同土质条件下盾构法隧道施工引起的土体移动模型有区别。基于盾构法隧道统一土体移动模型,假定土体不排水,采用N. Loganathan等提出的研究方法,通过对Verriujt计算公式进行修正,推导得到盾构施工过程中由于土体损失引起的土体变形二维解,该方法适用于施工阶段。算例分析表明：所给出方法的计算结果与实测值较吻合,适用于从流塑～坚硬状态的所有黏性土。Loganathan公式只适用于流塑状态的黏性土,当土质较硬时,计算所得到的土体沉降要比实测值小;盾构施工引起的隧道上方土体沉降从地面向下呈非线性增大,在隧道顶部达到最大,离隧道越近,增长越快;隧道周围土体产生向隧道侧的水平位移,从地面向下逐渐增大,在略高于隧道轴线附近达到最大值,再逐渐减小直到0。离隧道越近,土体水平位移越大。     

遮拦叠交效应下地铁盾构掘进引起地层沉降分析

 地铁隧道施工诱发的土体沉降以及临近地下构筑物变形是我国城市轨道交通施工安全控制和风险评估中较为关心的一类施工问题。目前,针对该领域地层沉降的简化理论研究还仅仅针对自由位移场,没有考虑临近既有构筑物的遮拦效应影响。依托上海在建地铁施工工程实践,采用简化理论方法、三维有限元数值模拟方法以及现场监测方法,分析考虑运营隧道遮拦效应影响的土压平衡盾构施工引起的周围土体沉降规律,并与自由位移场条件下盾构施工引起的地层变形进行对比分析;在此基础上,给出地铁盾构复杂叠交穿越引起的临近地铁隧道的变形规律。研究表明,本文提出的简化理论方法和三维有限元数值模拟方法可以较好地模拟遮拦叠交效应下地铁盾构掘进引起的地层沉降变形;临近既有建(构)筑物施工,盾构施工引起的周围土体沉降较大程度地受到遮拦效应影响,与自由位移场条件下的计算结果对比存在较大差别。最后,结合盾构施工监测数据,提出复杂遮拦叠交效应下的盾构叠交施工变形控制技术措施。成果可为合理制定施工场地存在复杂建(构)筑物工况条件的地铁隧道开挖对周围环境保护措施提供一定的理论依据。     

Ground movement induced by parallel EPB tunnels in silty soils

When constructing tunnels with poor geotechnical conditions in densely populated urban areas, there are many challenges including intolerable ground movement, face failure, and potential damage to adjacent structures (i.e., tunnels, piles, and pipelines). Earth pressure balanced (EPB) shields have been widely used to solve these problems. However, tunnel excavation causes release of in situ soil stress, which results in the soil movement. This paper focuses on field measurements of parallel tunnels using EPB shields in silty soils. Specifications on the ground profile, construction procedure, and field monitoring of pore pressure in the soils, ground subsidence, subsurface settlement, and horizontal displacement are reported. During shield advancement, the pore pressures in the soils showed the zigzag-shape distribution along the distance. The settlements indicated upheaval-subsiding behavior in the longitudinal direction. The soil settlement decreased from the crown of the excavation face to the ground surface and to the invert of the excavation face in the transverse direction. Outward horizontal displacements of soils adjacent to the tunnels and inward horizontal displacements of the soils near the ground surface were also observed before the tail injection. The second tunnel excavated rendered a slight squeezing effect on the first tunnel. These satisfactory measurements indicate the effectiveness of the EPB technique in reducing potential damage to adjacent structures.     

顶管施工引起的地面变形计算方法综述

顶管施工会对管道周围的土体产生扰动,引起土体移动。分析了顶管施工引起的地面变形机理,对顶管施工引起的地面变形计算方法的发展概况及研究进展进行了综述,把地面变形计算方法归纳为经验法、理论法、数值法和实测数据分析法,提出了目前该领域研究中需要重点研究的课题和一些新的研究思路。     

Der wassergefüllte Zielschacht – Ein Verfahren zur Beendigung von Schildvortrieben

The ground water balanced reception shaft. A method of shield break out. In the last years shield tunneling activities with closed face below the ground water level have rapidly increased. This is also true for shield diameters about 10 m. The shield break out below the ground water level into shafts requires special concepts and measures to avoid leakage paths. One possible and beneficial concept is the ground water balance method with flooded reception shaft to avoid a hydraulic gradient. Because of the flooding no leakage paths are possible which can cause water inflow and soil erosion.     

Response of clay soil to three-dimensional tunnelling simulation in centrifuge models

Tunnelling-induced ground movements are complicated and investigations into them normally require some simplifications. This paper provides a brief literature review which highlights the advantages of adopting simplifications in physical modelling and addresses some of the deficiencies in the assessment of soil deformation due to a simulated tunnel excavation. A set of centrifuge tests modelling a tunnel heading located at different depths in clay was carried out at 125g. The tunnel was modelled by a semi-circular cavity partly supported by a stiff lining. The unlined tunnel heading was supported by a thin rubber bag supplied with compressed air pressure. Tunnel excavation was simulated by reducing air pressure. The induced ground movements at the subsurface and surface were measured by a 2D image analysis and a new, novel 3D imaging system. The results show that the experiment successfully reproduced key aspects of tunnelling-induced soil deformation in practice. In addition, a new equation to predict horizontal displacements in the longitudinal direction is proposed.     

大断面顶管通道近接穿越下覆既有地铁隧道数值模拟与现场试验

南京某地下步行通道采用非开挖顶管法施工,顶管近距离穿越既有地铁区间隧道及城市主干道。为了保证隧道及主干道安全,施工前建立三维有限元计算模型,模拟施工全过程,预测施工可能引起的隧道及地表变形。根据数值模拟结果提出针对性控制措施,并制定合理的监测方案,分别对隧道竖向位移、水平位移、径向收敛和地表隆沉进行监测。基于监测数据分析隧道及地表变形规律,明确顶管施工期间隧道及地表变形的3个不同发展阶段。研究表明:隧道竖向位移主要表现为隆起,由通道内出土卸荷所引起,工作井基坑开挖对其影响几乎可以忽略;顶管施工过程中,下覆隧道竖向位移先后经历了初始下沉、隆起增强和隆起稳定3个阶段,地表竖向位移先后经历了隆起增强、隆起减弱和沉降3个阶段;同一监测断面内,地表最大沉降位于通道中心轴线上方,距离通道越远沉降越小;采用微欠挖工艺有效控制了隧道最终隆起和地表最终沉降。     

Bodenaustausch als Hilfsmaßnahme beim Schildvortrieb

Total replacement of soil as temporary work at shield driven tunnels. One possible method to build so‐called sealing blocks is the total replacement of soil. This method is safety and economically. With sealing blocks the starting or reception of closed‐type shields in shafts is possible. Because of the steel reinforcement of shaft walls the opening have to be broken manually before the shield drive. In this construction sequence sealing blocks are necessary to secure the stability and the water tightness of water seturated soft ground. They take over the forces from earth and water pressure accruing when the tunnel eye is opened. Sealing blocks consists of plain concrete. Another application of sealing blocks is to create an inspection area for the shield machine. Under difficult ground conditions the block allows to examines and maintaining the face. Sealing blocks are constructed in special excavated construction pits with underwater concrete fill, of rows of overlapping concrete piles or diaphragm wall panels and in sloped excavation pits filled with weak mass concrete. This paper shows some examples of sealing blocks built with the total replacement of soil.     

广东天然气管网西江盾构隧道竖井设计与施工

根据西江盾构隧道始发井和接收井所穿越地层的工程地质和水文地质条件,结合越江盾构隧道竖井内天然气管道安装的特点,通过工程类比和数值计算方法设计了以地下连续墙和喷锚支护与内层衬砌相组合的竖井结构,分析了始发井和接收井在施工期间存在的高风险工况,评价了相应工况下围护结构的安全性,同时提出了适合圆形截面盾构工作竖井的地下连续墙接头型式,总结了西江盾构隧道工作竖井的施工技术,可为类似地质条件下石油天然气管道越江盾构隧道竖井的设计与施工提供参考。     

Structural capacity reduction of drilled shaft foundations due to corrosion in longitudinal bars

Drilled shafts are a common type of deep foundations used to support a wide array of infrastructure facilities such as bridges, high mast lighting, tanks and communication towers. The deep inaccessible subterranean nature and the construction procedures of drilled shafts result in various types of anomalies; most critical of which being necking and voids. This necking or voids translates to loss of concrete cover around the longitudinal bars and its subsequent exposure to the surrounding soil, leading to corrosion. An experimental study using large-scale drilled shaft samples is presented that evaluates the effect of different percentages of rebar corrosion on the axial load capacity of drilled shaft foundations. Results show that the presence of corrosion in the longitudinal bars affects both the strength and buckling capacity of a shaft, and that a 25% necking or void area will result in more than 60% of axial capacity loss of the shaft over a time period of 20 years.     

煤矿斜井井筒过流砂层施工技术研究及应用

流砂层是矿井建设常遇见的不良地层,在含水或动力扰动下具有自流动性,施工不当会引起流砂向临空面流动充填开挖空间将井筒淹没或造成地表大面积塌陷。采用工程地质钻探与地面直流电法勘探技术,确定了流砂层的厚度与含水特征;根据斜井井筒穿越流砂层的垂深,将斜井井筒过流砂层技术方案进行分类研究,提出了斜井井筒过不同厚度流砂层的合理掘进技术;基于理论分析与数值计算,确定了斜井井筒支护结构承受的荷载,提出了斜井井筒过流砂层合理的井壁结构;为评价支护效果,对斜井井筒围岩变形、型钢支架受力、二衬接触应力、衬砌钢筋受力及渗水压力等进行了实时监测,监测结果表明:斜井井筒过流砂层的施工技术方案分类合理,保证了斜井井筒的掘进进度与施工安全;井壁结构安全可靠,保证了斜井井筒围岩与支护结构的稳定。     

Analysis of unlined pressure shafts and tunnels of selected Norwegian hydropower projects

Norwegian hydropower industry has more than 100 years of experiences in constructing more than 4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m (equivalent to almost 10.5 MPa) reached at unlined pressure tunnel of Nye Tyin project. Experiences gained from construction and operation of these unlined pressure shafts and tunnels were the foundation to develop design criteria and principles applied in Norway and some other countries. In addition to the confinement criteria, Norwegian state-of-the-art design principle for unlined pressure shaft and tunnel is that the minor principal stress at the location of unlined pressure shaft or tunnel should be more than the water pressure in the shaft or tunnel. This condition of the minor principal stress is prerequisite for the hydraulic jacking/splitting not to occur through joints and fractures in rock mass. Another common problem in unlined pressure shafts and tunnels is water leakage through hydraulically splitted joints or pre-existing open joints. This article reviews some of the first attempts of the use of unlined pressure shaft and tunnel concepts in Norway, highlights major failure cases and two successful cases of significance, applies Norwegian criteria to the cases and reviews and evaluates triggering factors for failure. This article further evaluates detailed engineering geology of failure cases and also assesses common geological features that could have aggravated the failure. The minor principal stress is investigated and quantified along unlined shaft and tunnel alignment of six selected project cases by using three-dimensional numerical model. Furthermore, conditions of failure through pre-existing open joints by hydraulic jacking and leakage are assessed by using two-dimensional fluid flow analysis. Finally, both favorable and unfavorable ground conditions required for the applicability of Norwegian confinement criteria in locating the unlined pressure shafts and tunnels for geotectonic environment different from that of Norway are highlighted.     

盾构推进引起地表变形及深层土体水平位移分析

 基于弹性力学Mindlin解,考虑刀盘挤土效应产生的切口正面附加压力、软土地层中具有软化特性且不均匀分布的盾壳侧摩阻力、及同步注浆压力引起的地层位移,结合土体损失引起的地层位移,得到盾构施工期间地表竖向位移及深层土体水平位移解答。经与3个工程实测结果进行对比,该方法计算结果与实测数据较为吻合,基本可以反映盾构施工引起的地层位移变化规律。分析结果表明：盾构前方土体在盾构施工作用下产生隆起,其形态基本接近正态分布曲线;较大的注浆压力亦引致地表土体隆起;深层土体在盾构施工期间受到挤压,向远离隧道轴线运动,其最大水平位移量在盾构轴线附近。     

软土地层盾构隧道施工引起的地面隆陷研究

 基于Mindlin解,经数值积分求得盾构掘进时切口附加推力、盾壳对周围土体的摩擦力及同步注浆附加压力引起的地面竖向位移,并以杭州庆春路过江隧道盾构施工引起的地面实测位移对其进行验证。分析结果表明,基于Mindlin解求得的切口附加推力、盾壳摩擦力及同步注浆附加压力引起的地面位移,与地层损失沉降叠加,可用来预测盾构掘进引起的纵向地面隆陷;盾尾同步注浆所致横断面地面隆起符合高斯分布,考虑注浆所致地面隆起后的修正Peck公式,可预测盾构掘进所致地面隆起,并提高地面沉降参数反分析的精度。     

多层地基上轴对称受荷弹性圆板问题

利用弹性圆板与多层地基表面的竖向位移协调条件与光滑接触条件,再由多层地基应力与位移的传递矩阵解,推导出多层地基上轴对称受荷弹性圆板问题的解析解。在此基础上,编制了相应的程序,并进行了数值计算。计算结果表明,园板刚度对弹性圆板的位移以及圆板中心下的竖向应力有着较大的影响。     

Displacement characteristics of high-speed railway tunnel construction in loess ground by using multi-step excavation method

The sequential excavation method (SEM), in which the tunnel face is partitioned into several temporary drifts, can promote face stability and reduce ground displacement. Three-bench seven-step excavation method (TSEM) as a kind of the SEM, which can stabilize the tunnel face but does not require any additional support, has been widely used in loess tunnels with large cross-sections for high-speed railway (HSR) in China. This study focuses on the effects of TSEM on the displacement characteristics for HSR tunnels in loess ground. A series of in-situ tests and numerical simulations were conducted to reveal displacement characteristics and obtain optimal construction approaches for large-span loess tunnels in China. The strata around the loess tunnels have undergone significant settlement either at the arch part or at the ground surface due to loess’s metastable structure especially in the new loess ground. Upper strata above loess tunnels subsided as a whole, and the subsidence developed suddenly and devastatingly. Large residual ground surface settlements still occurred after the ring closure of the primary support even after the application of the upper lining. The best construction approach of TSEM was proposed for its potential to limit surface and subsurface ground displacements, as revealed both by numerical simulation and field monitoring.