Soil conditioning of sand for EPB applications: A laboratory research

EPB tunnelling requires the application of soil conditioning to increase its field of applicability particularly for cohesionless soils. Choosing the most suitable conditioning set for the various soils requires the use of a feasible laboratory test which can permit to define the characteristics of the conditioned soils and provide measurable data.A series of tests has been carried out using a laboratory screw conveyor device which was designed for this purpose and which simulates the extraction of the spoil from a pressure chamber in a similar way as in EPB tunnelling.The tested soils were medium-grain sands with varying amounts of silt and the tested conditioned mixtures were obtained with different water contents and amounts of foam. A simple slump test was also used to analyze the global characteristics of the conditioned soils.The test has shown that the proposed laboratory procedure permits a quantitative comparison to be made between different conditioning amounts and agents on the basis of measurable parameters.     

Experimental study of the effect of conditioning on abrasive wear and torque requirement of full face tunneling machines

One of the main operational parameters in pressurized full face soft ground tunneling with machines such as earth pressure balance (EPB) TBMs is soil conditioning. Soil conditioners which are proper foam or conditioning agents, are often injected through the cutterhead or into the cutting chamber to make the muck flowable, lower inner friction between the soil particles, control soil stickiness, prepare the excavated soil to be compressible during the tunneling operation, control the water inflow, reduce the torque on the cutterhead, and lower power and torque of the screw conveyor. Foams can also be used in hard rock tunneling to reduce the wear and torque to replace conventional dust suppression by water sprays. This paper reviews the common practice in soil conditioning and focuses on assessing the influence of the conditioning on tool wear and torque requirement of the machines. Tests performed on many standard type soils and few samples from soft ground tunneling projects around the US on Penn State Soil Abrasion testing device. The results of tests performed in dry, moist and conditioned soil will be discussed and compared in this paper. The preliminary results show that the use of proper soil conditioning can reduce the wear of cutters and machine components by orders of magnitude while it can reduce the torque by over 50%.     

卵石地层土压平衡盾构施工土体改良试验研究

卵石地层摩擦性高,塑流性差,在土压平衡盾构施工过程中遇到了许多困难,通过对其进行土体改良改善土层性能成为不可缺少的辅助施工措施。但是,卵石地层土体改良缺乏系统研究,添加剂配比多依靠工地摸索或工程经验,容易造成添加剂使用不合理,直接影响到盾构施工效率。为此以北京地铁10号线2期隧道区间卵石地层土压平衡盾构施工为案例,进行了一系列土体改良室内试验,研究、评价常用添加剂及改良渣土性能,得到理想改良渣土的添加剂配比参数为泡沫注入比为30%,泥浆注入比为10%,最佳坍落度范围为150～200 mm。利用上述添加剂配比方案进行了盾构掘进试验,显著提高了盾构施工效率。试验结果可为类似地层盾构施工土体改良提供参考。     

土压平衡盾构施工中泡沫改良砂土的试验研究

土压平衡盾构在隧道施工中,特别在地铁区间隧道施工中已经得到广泛应用。土压平衡盾构主要适用于粘性土地层开挖,其在砂土地层的掘进过程中通常会遇到掌子面土压平衡难以形成、螺旋出土器无法正常排土、刀盘扭矩过大及刀具磨损过快等一些问题。最有效的解决方法是使用泡沫等添加剂对土体进行改良,但是目前工程施工现场添加剂的使用尚存在一定的盲目性。文章首先通过自制的试验室发泡装置生产泡沫,并对泡沫的性能与发泡剂溶液浓度的关系进行研究,为有效使用泡沫提供依据,并通过一系列试验研究泡沫对砂土的改良效果,得到适合土压平衡盾构施工的优化泡沫掺入比。     

Pressurised TBM tunnelling in mixed face conditions resulting from tropical weathering of igneous rock

Weathering is a process that turns rock into soil. Deep weathering is prevalent in tropical and sub-tropical areas. The resulting sub-surface conditions can be very onerous for tunnelling, with tunnel drives commonly encountering a significant proportion of mixed face conditions, comprising partly rock and partly soil. Problems that have been encountered have included: inability to maintain the face pressure, ground loss, sinkholes, slow rates of tunnelling, rapid tool wear, damage to tools, mixing arms and other parts of the TBM, very frequent and long interventions, clogging and blow-outs. The nature and extent of the problems on any particular tunnel have depended on the type and design of the TBM, the nature of the rock and the proportion of the tunnel in mixed ground. In Singapore this has resulted in a change from mainly EPB to mainly slurry tunnelling in weathered igneous rock; however, predominantly EPB TBMs have been used in weathered sedimentary rock. Information from EPB and slurry TBM drives is used to illustrate the issues involved.     

Laboratory model tests and field investigations of EPB shield machine tunnelling in soft ground in Shanghai

In the last decades, many studies have been presented by different scholars on the environmental problems induced by the shield tunnelling in soft ground. But it mainly concentrated on ground surface settlement, tunnel surface stability and the influence to existing structures. Among them, little attention was paid to soil disturbance caused by the mismatch of machine’s operation parameters. In order to reveal this inherent relation, a series of laboratory model tests were carried out in the 1/16 scale for a field tunnel in practice where the tunnel had 6.4 m diameter. The tests to simulate earth pressure balance (EPB) shield tunnelling in soft ground were conducted with a microshield machine (0.4 m diameter). Measurements were carried out simultaneously in each test for total jack thrust force, cutting torque, chamber pressure, mucking ratio, ground surface displacement, and earth pressure. Based on the analysis of test results under different overburden ratio, cutterhead aperture ratio and screw rotation speed, the relationships between machine’s operation parameters themselves and its influence on disturbance to surrounding soil mass were discovered. Such discoveries were also verified by the field investigations. These results are useful for engineers and technicians to select suitable and serviceable machine operation parameters and reduce environmental influence at all stages of tunnel construction.     

Machine tunnelling in the twenty-first century

In the coming decades, versatile machines will be developed that will be capable of boring through both hard rock and wet soil conditions. These machines will be able to pass from hard rock through a water-filled fault zone and in a soil tunnel under a river: they will make the transition with ease into a mixed face of rock and boulders. Machines will incorporate state-of-the-art electronics that will give the operator the information needed to maintain a high level of availability and utilization. This will be an important factor in reducing machine tunnelling costs. The new materials that will be used to build cutters will increase cutter life while reducing costs of tunnelling in the hardest rocks. New types of machines will cut non-circular tunnels in hard rock, providing highway and railroad builders the advantage of high-speed machine tunnelling. There will remain for the twenty-first century unlimited opportunities for development to solve difficult tunnelling problems such as undersea tunnels in weak rock conditions. If tunnel owners and builders utilize the resources of the machine developers effectively, technology will be developed rapidly and will dramatically reduce the cost of underground construction.     

Tunnelling through a frequently changing and mixed ground: A case history in Singapore

The Kranji tunnel is part of the Deep Tunnel Sewerage System in Singapore. It is approximately 12.6 km in length. Along the tunnel alignment, all the ground is composed of granite with different weathering grades (from fresh rock to residual soil). The changing ground from hard rock to mixed face and soft ground (and vice versa) at the tunnel level was anticipated. The tunnel depth along the route is between 15 m and 50 m. Two EPB TBMs were deployed at this tunnel with a bored diameter 4.90 m. These machines were designed so that both hard rock and soft ground could be excavated. The cutter head was equipped with a combination of both rippers and disc cutters. During the excavation, it was found that the frequency of the ground change between hard rock and residual soil is much higher than that expected. Due to the frequently changing ground, correspondingly the tunnel boring machine (TBM) operation mode had to be transferred frequently from hard rock tunnelling to transition mode and to earth pressure balance (EPB) close mode. It resulted in great difficulties for the TBM in an optimized operation condition. These difficulties included high cutter wear and flat cutters, tunnel face instability, water inflow at weathering interface, and time delays. In order to overcome these problems and speed up the tunnelling progress, the TBM used in the north drive was modified to attempt the frequently changing ground. The performance of the modified TBM was highly improved. However, the highly abrasive and frequently changing mixed face ground still caused high cutter wear, especially flat cutter wear. These posed many challenges to the equipment and the tunnel crew.     

软土地层土压平衡盾构法施工的模型试验研究

我国沿海地区以及许多内陆城市的地下广泛分布着很深的软黏土沉积层,目前该区域的许多城市都已兴建或正在筹建地铁。为确保在这种软弱地层中能采取与之相适应的盾构工法、减少对周围环境的影响以及降低工程造价,以上海地铁M8线某区间隧道工程为研究背景,采用室内模型试验的方法,进行了土压平衡盾构针对软土地层的适应性试验研究。为此,首先根据相似理论和模型试验方法建立了土体–盾构机器之间的相似系统;随后,针对上海地区特定的软土地层,进行了人工模型土壤的配制和模型试验方法的设计,并利用直径400 mm的模型盾构机模拟直径6340 mm的原型盾构机;最后,进行盾构不同工作参数组合的掘削试验,并记录下试验过程中机器工作参数及土体内应力和变形变化的有关试验结果,通过对试验数据的整理与分析,得出了软土地层中土压平衡盾构法施工的一些有用的规律。     

土压平衡盾构掘进的数学物理模型及各参数间关系研究

为保证开挖面稳定及控制地面沉降,土压平衡盾构掘进时必须合理匹配各施工参数。基于模型试验结果,推导土压平衡盾构的3个基本方程式,进而得到土压平衡盾构2个总平衡方程式,建立土压平衡盾构掘进的数理模型。在此基础上推导总推力、土仓压力、螺旋机转速、掘进速度间关系的数学表达式,利用盾构施工的现场数据验证关系式的正确性。利用现场掘进数据统计刀盘扭矩、刀盘转速、土仓压力间的经验关系式。这些关系对土压平衡盾构设计时的参数选择和匹配有重要的指导意义,可以应用于土压平衡盾构施工时的参数控制。土压平衡盾构掘进的连续性方程为土压平衡盾构掘进时的地面沉降控制提供了新的研究思路。     

Experimental study on working parameters of earth pressure balance shield machine tunneling in soft ground

Deep sedimentary deposits of soft clays are widely distributed in coastal areas as well as many interior major cities in China. In order to study the stratum adaptability of earth pressure balance (EPB) shield machine tunneling in such types of soft ground, model tests of tunneling excavation, using the running tunnel of the Shanghai Metro Line M8 as a background, are carried out with different over burden ratios, opening rates of cutter head, driving speeds and rotation speeds of screw conveyor. Based on the test results, the interrelationships between chamber pressure and mucking efficiency, mucking rate and driving speed, thrust force and torque are obtained. The influences of tunnel depth, opening rate of cutter head and driving speed on thrust force and torque are revealed. Such findings can not only facilitate establishing relationships between shield working parameters and soil properties, but also serve as a guide for the design and construction of shield tunnel in soft ground.     

富水砂性地层盾构渣土改良试验与喷涌防治技术

为解决土压平衡盾构穿越富水砂性地层螺旋输送机喷涌、排渣不畅等难题,基于渣土改良剂的地层适应性规律研发新型化学改良剂并开展相关室内试验.试验结果表明:非离子聚合型泡沫剂可兼备发泡倍数与稳定性能,适当提高泡沫剂浓度Cf能够增大发泡倍率FER和半衰期HT.当cf＞5％时,由于达到临界胶束浓度,FER和HT趋于最大值.透射电镜...     

土压平衡盾构螺旋输送机驱动装置

介绍了土压平衡盾构螺旋输送机的基本结构和功能,描述了国内外不同的螺旋输送机驱动装置,通过分析螺旋输送机实际工作中的受力状况,结合制造维护成本,指出不同螺旋输送机驱动装置的优缺点。     

砂土地层盾构隧道施工对地层扰动的室内掘进试验研究

土压平衡式盾构机在穿越流塑性差、渗透系数大的砂土地层时容易对隧道周围土体产生扰动,导致地表沉降不易控制和作用在衬砌结构上的土压力发生改变。针对地铁盾构隧道穿越砂土地层引起的地层扰动,采用一种能完全反映盾构隧道动态施工全过程的分析方法尤为重要。以城市地铁盾构区间隧道施工采用的土压平衡式盾构机为原型,研制 800 mm土压平衡式模型盾构机,该机主要包括推进机构、掘削机构和出土机构,能实现盾构始发、刀盘切削、螺旋出土、管片拼装等主要功能,以此开展砂土地层中盾构施工的室内掘进试验。试验过程中对盾构掘进引起的地层沉降及衬砌结构上的土压力进行量测,分析地层沉降形态和衬砌结构上土压力的分布形态,同时将试验结果同理论计算、数值分析及现场资料进行对比。研究结果表明,土体性状和盾尾注浆对地层沉降具有重要影响,地层损失是地层发生沉降的主要原因。未注浆情况下盾尾脱环引起的地表沉降值占总沉降值的60%以上,且由于未注浆而增大的地表沉降所占比例为20%～30%,沉降时程曲线具有阶段性和时效性。地表沉降槽宽度系数i与现场测试数据具有一致性。衬砌结构上的土压力分布类似于上下端为长半轴、左右端为短半轴的椭圆形,数值上试验实测值较理论计算值要小。     

砂土地层土压盾构隧道施工掌子面稳定性研究

土压平衡盾构在自稳性较差的砂土地层施工时若仓内支护压力过小可能诱发掌子面失稳,应引起高度重视。采用三维离散元方法分析了砂土地层土压盾构掘进与停机状态下的掌子面稳定性。研究建立了较为精细的土压盾构机模型并引入盾构动态施工过程,充分考虑了刀盘旋转切削土体与面板支撑对掌子面的影响,探讨了刀盘型式、隧道埋深以及刀盘转速等因素对掌子面极限支护压力与失稳区分布的影响规律,并从细观角度解释了砂土地层土压盾构隧道掌子面失稳机理。与既有研究相比,本文考虑了土压盾构动态施工对掌子面稳定性的影响,更加接近工程实际,研究成果可为确保砂土地层土压盾构隧道施工掌子面稳定提供参考。     

裂隙水对节理岩体裂隙扩展影响的CT实时扫描实验研究

采用与CT机配套的加载装置，使用相似材料，对单裂纹含水和不含水的标准试件进行了CT实时监测实验，以观测裂纹扩展的全过程。探讨试件在不同复杂应力状态和原生裂纹处于不同地下水压的情况下，其裂纹的萌生、演化、发展及最终破坏形式。通过在试件中原生裂纹内不注高压水、含有压裂隙水和注水致裂来分别模拟岩体工程中裂隙不受水的影响、受有压水的影响及水压致裂的破坏过程。目的在于探讨3种情况下，岩体的不同破坏形式。从实验结果来看，3种条件下，试件都经历了微裂隙被压密、损伤演化开始、微裂纹扩展贯通、宏观裂纹产生等阶段，但其破坏形式各不相同。说明了在分析岩体结构时要充分考虑地下水的存在状态对工程结构的影响。同时，也为进一步建立岩体结构合理的损伤演化方程、本构关系和研究岩石破坏机理提供了科学依据。     

Feasibility study of tar sands conditioning for earth pressure balance tunnelling

This paper presents the results of laboratory test on the feasibility of soil conditioning for earth pressure balance(EPB) excavation in a tar sand,which is a natural material never studied in this respect.The laboratory test performed is based on a procedure and methods used in previous studies with different types of soils,but for this special complex material,additional tests are also conducted to verify particular properties of the tar sands,such as the tilt test and vane shear test usually used in cohesive materials,and a direct shear test.The laboratory test proves that the test procedure is applicable also to this type of soil and the conditioned material can be considered suitable for EPB excavations,although it is necessary to use a certain percentage of fine elements(filler) to create a material suitable to be mixed with foam.The test results show that the conditioned material fulfils the required standard for an EPB application.     

Rock mechanics for design of Brisbane tunnels and implications of recent thinking in relation to rock mass strength

This paper explores the potential implications of recent thinking in relation to rock mass strength for future tunnelling projects in Brisbane, Australia, particularly as they are constructed within deep horizons where the in situ stress magnitudes is larger. Rock mass failure mechanisms for the current tunnels in Brisbane are generally discontinuity controlled and the potential for stress-induced failure is relatively rare. For the road tunnels which have been constructed in Brisbane over the last 12 years, the strength of the more massive rock masses for continuum analysis has been estimated by the application of the Hoek-Brown (H-B) failure criterion using the geological strength index (GSI) to determine the H-B parameters m_b, s and a. Over the last few years, alternative approaches to estimating rock mass strength for ‘massive to moderately jointed hard rock masses’ have been proposed by others, which are built on the work completed by E. Hoek and E.T. Brown in this area over their joint careers. This paper explores one of these alternative approaches to estimating rock mass strength for one of the geological units (the Brisbane Tuff), which is often encountered in tunnelling projects in Brisbane. The potential implications of these strength forecasts for future tunnelling projects are discussed along with the additional work which will need to be undertaken to confirm the applicability of such alternative strength criteria for this rock mass.     

高应力硬岩地区岩体结构对地下洞室围岩稳定的控制效应研究

官地水电站地下厂房属典型的硬岩地区深埋大型地下洞室群,其重要特点是同时面临高地应力和结构面发育这2个不利条件,实测最大主应力为25～35 MPa,厂区无大的断层和软弱结构面,但错动带和裂隙十分发育。通过对地下洞室群施工过程中出现的围岩局部失稳破坏现象进行全面的分析整理,对三大洞室的岩体结构特征和围岩变形破坏模式进行系统的分析、比较和总结,从而对影响围岩稳定的两大控制因素——地应力和岩体结构对官地地下厂房洞室群围岩稳定的影响程度和方式进行分析和对比。研究表明,由于三大洞室围岩类别以II类为主,岩体结构以块状～次块状结构为主,围岩具有较高的力学强度和强度应力比,从而具有较强的抵抗应力破坏的能力;岩体结构对地下厂房围岩变形与稳定的控制作用较地应力则更为明显,地下洞室群开挖过程中出现的局部失稳或较大变形多与不利方位的结构面直接相关。三大洞室围岩岩体结构特征总体上的相似性非常明确,反映在三大洞室围岩的变形特征和破坏模式上具有很好的统一性。然而,三大洞室的岩体结构特征也存在一定的差异,导致岩体结构影响围岩稳定的方式和程度有所不同。结构面发育造成的另一个不利影响是为坚硬岩体在高地应力条件下产生卸荷时效变形提供了内部条件。因此,在强度应力比较高的硬岩地区,应充分重视岩体结构及其演化对围岩变形和稳定的控制效应。