Centrifuge experiments for shallow tunnels at active reverse fault intersection

Tunnels extend in large stretches with continuous lengths of up to hundreds of kilometers which are vulnerable to faulting in earthquake-prone areas. Assessing the interaction of soil and tunnel at an intersection with an active fault during an earthquake can be a beneficial guideline for tunnel design engineers. Here, a series of 4 centrifuge tests are planned and tested on continuous tunnels. Dip-slip surface faulting in reverse mechanism of 60-degree is modeled by a fault simulator box in a quasi-static manner. Failure mechanism, progression and locations of damages to the tunnels are assessed through a gradual increase in Permanent Ground Displacement (PGD). The ground surface deformations and strains, fault surface trace, fault scarp and the sinkhole caused by fault movement are observed here. These ground surface deformations are major threats to stability, safety and serviceability of the structures. According to the observations, the modeled tunnels are vulnerable to reverse fault rupture and but the functionality loss is not abrupt, and the tunnel will be able to tolerate some fault displacements. By monitoring the progress of damage states by increasing PGD, the fragility curves corresponding to each damage state were plotted and interpreted in related figures.     

基于经济安全系数比的隧道穿越超浅埋大偏压段方案优化研究

在黄土高原地区,由于沟壑众多,在隧道选线过程中出现了一种最不利的地形条件,即隧道需穿越超浅埋大偏压地段。为了研究其经济、安全、可靠的穿越方案,提出经济安全系数比的概念及计算原理。对隧道穿越超浅埋大偏压段的方案先进行设计,然后采用有限元强度折减法和相关定额计算出各方案的经济安全系数比,并结合数值模拟方法对3种典型穿越方案下的隧道围岩应力、洞室变形和初期支护应力等进行计算分析。经过综合对比,得出按反压法设计的穿越方案最优。该方案既有利于超浅埋大偏压隧道的整体稳定,又有利于减少工程造价。     

Influence of blasting load directions on tunnel stability in fractured rock mass

Tunnels in fractured rock masses are typically damaged by dynamic disturbances from various directions. To investigate the influence of blasting load directions on the stability of a tunnel with a pre-crack nearby, blasting tests were conducted on the physical models of an external crack around a tunnel (ECT) in this study. Failure modes of the tunnels were analysed based on stress wave theory. The Riedel–Hiermaier–Thoma (RHT) material model was employed to perform the numerical simulations on ECT models. Stress distribution around the tunnels and final failure patterns of the tunnels were characterised. The results show that, under blasting loads, the pre-crack propagates and then new cracks initiates on the incident side of the tunnel. These cracks extend towards each other and eventually coalesce. Blasting load directions significantly influence the ultimate failure mode of the tunnel in the fractured rock masses. The new cracks on the shadow side of the tunnel appear at different positions when the blasting stress waves come from various directions. The results are meaningful to the analysis of tunnel stability and optimisation of the tunnel support scheme.     

不同开挖方式对近距离交叠隧道影响模拟研究

研究不同开挖方式对近距离交叠隧道的地层和围岩的影响,揭示不同开挖方式下交叠区围岩及既有隧道衬砌的变形及应力–应变变化规律,为近距离交叠地下工程的变形控制、支护设计和开挖优化设计提供理论依据。通过FLAC3D数值模拟,研究在台阶法、眼镜法、CRD法3种不同开挖方式下交叠区围岩及既有隧道衬砌的变形及应力–应变发展规律、交叠区围岩塑性破坏规律,研究结果如下：(1) 不同开挖方式对交叠隧道施工过程中不同位置的影响程度不同,揭示既有隧道衬砌变形机制演变过程和衬砌破坏的危险点;(2) 根据围岩塑性区发展和隧道衬砌变形量,开挖下部新线隧道时CRD法优于眼镜法和台阶法,CRD法开挖下部隧道时对变形控制效果最好;(3) 新建隧道穿越既有隧道时,比较理想的施工方案为台阶法→CRD法→台阶法;(4) 任何开挖施工方法都会使已建隧道衬砌的4个部位(拱顶、拱脚、直墙边及拱底)承受拉应力,且拱脚处的最大、最小主应力最大,最易发生破坏。     

Model Test and Numerical Analysis Methods in Tunnel Excavation Problem

Tunnels serve various functions such as in subway systems, underground electric power lines, gas pipes, telecommunication lines, water supplies and sewer lines and many other pipelines. The trend of tunnel construction is toward deeper and longer tunnels. In addition, the excavation of tunnels in difficult ground conditions is now not uncommon, though the tunnels themselves are still difficult to construct. Advanced studying methods have been developed for the prediction, monitoring and evaluation of the performance of tunnels and ground. Today, experimental methods and analytical methods are the main approaches used in tunnel studies. In this paper, the present state of tunnel construction and the main study methods are discussed, and the various experimental and analysis methods and their usage are compared. Tunnel excavation is very complex because it involves soils, structure and interaction problems. There is no one perfect studying method, though there are good combinations of numerical analyses and experimental methods which provide the optimum approach for solving tunnel related problems.     

The uplifting behavior of shallow tunnels within the liquefiable soils under cyclic loadings

The liquefaction of soils under earthquake loadings has always been a main concern for geotechnical engineering practices. As an earthquake causes the ground to liquefy, the effective stress and hence the shear strength of the soil decreases sharply, and large deformations happen in the area. This phenomenon occurs only rarely when the liquefaction occurs at a large depth. However, deformations increase extensively when this layer is located in shallow depths near the ground level. In this case super structures and also underground structures may be severely damaged. The tunnels which are constructed in this layer may be affected by the liquefaction as well. In this condition the liquefaction may cause settlement in the ground, deformation in the tunnel shield, buoyancy in the underground buildings, reduction in bearing capacity and increases in lateral spread and pore pressures. In this paper the FLAC software has been used to model the pore pressure changes during earthquakes that lead to soil liquefaction. The studies thus far have been focused on the impact of the soil liquefaction on the tunnels constructed in this area. According to the studies, the buoyancy and uplifting forces due to liquefaction have major effects on the behavior of underground structures. Increasing the soil parameters such as friction angle and damping ratio causes the liquefaction effects on the tunnel to decrease, and increasing the geometric parameters such as tunnel diameter and location depth causes these effects to increase.     

Grouting applications in the Sanliurfa tunnels of GAP, Turkey

The Sanliurfa tunnels are the largest irrigation tunnels in the world. Located in southeastern Anatolia region in Turkey, it is the centerpiece of a project called the Southeastern Anatolia Project (GAP). There is no doubt that the Sanliurfa tunnels system is one of the key structures of the GAP, because of its tunnel length, excavation technique and amount of water carried by the tunnels. Sanliurfa tunnels serve as a model for the tunnels to be constructed in the future because of their excavation, construction and grouting applications. Tunnels require various engineering disciplines to work together. The problems, the applied solutions and the experiences obtained during construction of Sanliurfa tunnels contributed a lot to the tunneling knowledge of scientists and engineers; therefore, it is very important that such information be published. In this paper, excavation techniques, construction methods and characteristic properties of Sanliurfa tunnels have been briefly explained, and grouting applications carried out in tunnels have been discussed in detail.     

Assessment of damage in mountain tunnels due to the Taiwan Chi-Chi Earthquake

Tunnels, being underground structures, have long been assumed to have the ability to sustain earthquakes with little damage. However, investigations of mountain tunnels after the Chi-Chi Earthquake in central Taiwan revealed that many tunnels suffered significant damage to various extents. This work describes the findings of a systematic assessment of damage in the mountain tunnels in Taiwan after the earthquake. It was found that among the 57 tunnels investigated 49 of them were damaged. The damage patterns are summarized based on the characteristics and the distribution of the lining cracks. This systematic investigation, involving geological conditions, design documents, construction and maintenance records of these tunnels, has been conducted to assess the potential factors that may have influence on the various damage patterns and the earthquake loading for tunnels. The results show that the degree of damage is associated with the geological condition and structural arrangement of the tunnel. A tunnel passing through a displaced fault zone will definitely suffer damage. The extent of geological weak zones, distance from the epicenter, and the existence of a slope face are also significant influencing factors. The seismic capacity of the tunnel is influenced by its structural arrangement, type of lining, invert setup, lining reinforcement, and other parameters.     

软土盾构隧道近接施工应力迁移规律研究

在多线叠交隧道空间布置形式下,盾构近距离穿越既有隧道施工对既有隧道的影响主要通过扰动周边的土体,使其应力发生改变,进而影响既有隧道的应力状态。针对外力作用下衬砌和土体两种不同介质进行耦合作用时应力的快速迁移现象,构建了考虑土体流变特性的盾构近接施工应力迁移模型,推导出新建隧道以任一穿越角度施工时,既有隧道和扰动土体在时间域内的应力迁移解析式,并讨论了取值参数的敏感性程度。分析结果可为今后类似多线叠交隧道工程的设计和施工提供理论指导。     

水位和覆土厚度变化对不同形式过江隧道的影响研究

本文结合实际工程的设计参数及地质勘察数据,利用大型有限元软件建立模拟过江隧道开挖的数值模型,分析不同形式过江隧道在不同覆盖层厚度以及不同水位高度下的衬砌应力与隧道拱顶位移的变化规律,为类似工程设计、施工提供参考。     

下穿隧道对既有地铁线路及周边环境影响研究

随着城市地下空间的开发,隧道交叠与穿越案例越来越多,隧道下穿既有线路时往往引发交汇段地表沉降叠加,对既有线路和周边建筑物的安全产生威胁,研究其影响可以有针对性地采取预先加固措施。通过数值模拟试验方法,研究发现当新建隧道下穿既有线路时,后者的衬砌对前者起到了预先加固作用,使得下穿隧道的拱顶沉降比未穿越段较小,但上部隧道的拱顶部位沉降显著加大有必要预先加固。此外先后两次施工的扰动会增大围岩塑性区体积,导致新旧隧道的塑性破坏区相互连通,使得穿越段上方地表的沉降槽仍然表现为显著增大。     

跨海公路隧道岩石覆盖厚度探讨

在特殊的地质环境条件下,建设海底隧道无疑是最安全经济、路线最短的方案。自从1936年第1条海底隧道--日本关门隧道开始建造以来,在世界各地,已有近百条海底隧道相继建设,海底隧道的设计与施工,还有许多技术问题丞待解决。结合我国拟建厦门海底隧道的工程实际,探讨了国内外海峡海底隧道工程的特点及其最小岩石覆盖层厚度的问题;结合世界上已建海底隧道的工程经验,应用经验类比法和数值分析法,研究厦门海底隧道的岩石覆盖厚度。研究成果将对我国未来的海峡海底隧道修建工程有所借鉴。     

Three-dimensional finite difference analysis of shallow sprayed concrete tunnels crossing a reverse fault or a normal fault: A parametric study

Urban tunnels crossing faults are always at the risk of severe damages. In this paper, the effects of a reverse and a normal fault movement on a transversely crossing shallow shotcreted tunnel are investigated by 3D finite difference analysis. After verifying the accuracy of the numerical simulation predictions with the centrifuge physical model results, a parametric study is then conducted. That is, the effects of various parameters such as the sprayed concrete thickness, the geo-mechanical properties of soil, the tunnel depth, and the fault plane dip angle are studied on the displacements of the ground surface and the tunnel structure, and on the plastic strains of the soil mass around tunnel. The results of each case of reverse and normal faulting are independently discussed and then compared with each other. It is obtained that deeper tunnels show greater displacements for both types of faulting.     

全风化岩层中双线盾构上穿近邻地铁隧道影响分析

依托佛莞城际铁路盾构隧道在全风化花岗岩地层中上穿广州地铁七号线工程,针对全风化花岗岩地层致密、渗透系数小及双层四线叠交穿越复杂地层等特点,通过现场监测与三维动态有限元数值模拟手段,解决实际工程中注浆压力合理取值与既有隧道变形控制这两大难题。其中,通过模拟掘进隧道在不同注浆压力值的工况下,对既有隧道动态上浮变形值和地表沉降值的影响关系,进而确定最佳注浆压力值。同时,由于双层四线叠交穿越工况对既有隧道扰动的影响较大,为避免发生管片错台和开裂等危险,结合工程实际提出控制既有隧道变形的措施。研究结果表明：在全风化地层中注浆压力设为0.5MPa时,能合理控制地表沉降与既有隧道变形;穿越施工对既有地铁隧道竖向变形的影响存在“滞后效应”;盾构单线穿越后,既有隧道竖向变形呈现近似单波峰状的正态分布曲线;盾构二次穿越后,曲线形态由近似正态分布曲线向类“M”双波峰形转变,且波峰位置产生约2m的偏移;既有隧道横断面管片最终变形呈“竖鸭蛋”状,其横向椭圆度为1.4‰,竖向椭圆度为0.71‰。针对分析结果,工程中采取合理的压重措施,有效抑制既有隧道的上浮变形,研究成果在隧道穿越类似地层的施工中具有一定的参考价值。     

Determination of the effects of structural properties on tunnel lighting with examples from Turkey

In this work, effects of the structural measures during the construction phase on the tunnel lighting have been studied. The luminance of the access and threshold zones of the tunnel are obtained from the photos taken from the entrances of Gultepe and Diliskelesi Tunnels located on the Istanbul–Ankara TEM motorway in Turkey according to the CIE Publication No. 88. Then the effects of the tunnel surroundings, direction, traffic speed, road pavement and portal design on the tunnel-lighting design-criteria have been investigated by using real tunnel entrance photos taken from certain distances and/or computer generated images. Consequently, it has been explained that significant decreases in the tunnel illumination levels can be achieved by taking the structural measures in tunnels.     

高地应力断层带软岩隧道变形特征与控制措施研究

隧道在穿越断层地带时由高地应力引起的软岩大变形问题是隧道建设施工中难点,给隧道建设的施工与进度带来很大影响。本文结合区域地应力,围岩强度实验等分析柿子园隧道穿越断层地区产生支护结构破坏现象的原因,并对围岩压力,钢架应力,围岩变形进行了现场监测,得到了高地应力软岩大变形引起的支护应力特征与变形特征,提出了控制大变形的技术措施。研究表明,高地应力区软岩隧道穿越断层地带时,由于复杂的构造应力造成隧道结构受力不均,隧道左右两侧围岩压力,支护内力与围岩变形呈现出很大的不对称性。采用优化断面形式、加强初支刚度、非对称预留变形量和锚杆布置等措施可以有效减小隧道结构受力,控制隧道变形。     

基坑工程下已运行地铁区间隧道上抬变形的控制研究与实践

 以上海广场基坑工程下的已建隧道的保护为工程背景, 结合软土基坑隆起变形的残余应力法和软土的卸荷模量, 探索了利用坑内加固和基坑工程的时空效应施工法等措施来控制民用建筑基坑下的已建成隧道的上抬变形。经实践证明,这两种措施的有机结合能成功有效地确保已建隧道的正常运营。该工程为以后同类工程的设计、施工提供了十分宝贵的资料, 有很大的理论与实践意义。     

连拱隧道施工技术初探

随着国家环保措施的逐步加强和完善,隧道工程在公路、铁路建设中所占比例越来越高。大跨度隧道施工难度较大,连拱隧道施工相对安全、结构美观以及相对同等地质条件下的分离式隧道而言具有占地少、投资小等优点。受传统施工方法的制约,连拱隧道多以短隧为主。结合某连拱隧道施工经验,浅谈对连拱隧道施工方法的见解和对连拱隧道质量通病的控制及预防。     

盾构法隧道地表变形影响因素多尺度数值模拟

采用三维非线性有限元数值方法,对上海典型地层中盾构推进过程进行了精细模拟,研究了多几何尺度下盾构外径、隧道埋深及土层力学性质等非施工因素对地表变形的影响。计算结果表明,盾构机外径的尺度效应和隧道埋深对地表变形影响显著;不同尺度下修正剑桥模型中与土性有关的对数硬化模量λ及泊松比μ与地表变形正相关,而临界状态有效应力比M与变形之间的关系不是单调增加或减小的关系。研究成果为软土地区盾构隧道多几何尺度的模型试验和设计施工参数的选取提供了依据。     

上穿公路隧道偶然爆炸对下方供水隧洞影响研究

新建公路隧道从既有供水隧洞上方穿过,在空间上形成交叉隧道,上下隧道最小净距21.5 m,为评价上穿隧道偶然爆炸对下方供水隧洞稳定的影响,应用ANSYS/LS-DYNA对其进行了数值模拟研究。结果表明:当上穿公路隧道油罐车在运输过程中发生爆炸时,下方供水隧洞的拱顶、拱腰对爆炸冲击波的响应较大,最大振动速度约为10.1 cm/s,拱腰和拱底的振动速度分别为8.9 cm/s和3.9 cm/s,拱顶、拱腰部位的最大振动速度大于水工隧洞的安全质点振动速度;此时隧洞最大的动拉应力点位于拱顶,为1.01 MPa,加上隧洞衬砌静态应力(约1.0 MPa),超过了C25砼的抗拉强度设计值1.27 MPa,故油罐车偶然爆炸会造成供水隧洞结构的破坏,影响其稳定性,须采取一定的交通管制措施。