土木工程 建筑 外文翻译 外文文献 英文文献 地铁地表沉降

土木工程 建筑 外文翻译 外文文献 英文文献 地铁地表沉降 外文 原文 少年中国说原文俱舍论原文大医精诚原文注音大学原文和译文对照归藏易原文 Surface settlement predictions for Istanbul Metro tunnels excavated by EPB-TBM S. G. Ercelebi • H. Copur • I. Ocak Abstract In this study, short-term surface settlements are predicted for twin tunnels, which are to be excavated in the chainage of 0 ? 850 to 0 ? 900 m between the Esenler and Kirazl? stations of the Istanbul Metro line, which is 4 km in length. The total length of the excavation line is 21.2 km between Esenler and Basaksehir. Tunnels are excavated by employing two earth pressure balance (EPB) tunnel boring machines (TBMs) that have twin tubes of 6.5 m diameter and with 14 m distance from center to center. The TBM in the right tube follows about 100 m behind the other tube. Segmental lining of 1.4 m length is currently employed as the final support. Settlement predictions are performed with finite element method by using Plaxis finite element program. Excavation, ground support and face support steps in FEM analyses are simulated as applied in the field. Predictions are performed for a typical geological zone, which is considered as critical in terms of surface settlement. Geology in the study area is composed of fill, very stiff clay, dense sand, very dense sand and hard clay, respectively, starting from the surface. In addition to finite element modeling, the surface settlements are also predicted by using semi-theoretical (semi-empirical) and analytical methods. The results indicate that the FE model predicts well the short-term surface settlements for a given volume loss value. The results of semi-theoretical and analytical methods are found to be in good agreement with the FE model. The results of predictions are compared and verified by field measurements. It is suggested that grouting of the excavation void should be performed as fast as possible after excavation of a section as a precaution against surface settlements during excavation. Face pressure of the TBMs should be closely monitored and adjusted for different zones. Keywords Surface settlement prediction _ Finite element method _ Analytical method _ Semi-theoretical method _ EPB-TBM tunneling _ Istanbul Metro Introduction Increasing demand on infrastructures increases attention to shallow soft ground tunneling methods in urbanized areas. Many surface and sub-surface structures make underground construction works very delicate due to the influence of ground deformation, which should be definitely limited/controlled to acceptable levels. Independent of the excavation method, the short- and long-term surface and sub-surface ground deformations should be predicted and remedial precautions against any damage to existing structures planned prior to construction. Tunneling cost substantially increases due to damages to structures resulting from surface settlements, which are above tolerable limits (Bilgin et al. 2009). Basic parameters affecting the ground deformations are ground conditions, technical/environmental parameters and tunneling or construction methods (O’Reilly and New 1982; Arioglu 1992; Karakus and Fowell 2003; Tan and Ranjit 2003; Minguez et al. 2005; Ellis 2005; Suwansawat and Einstein 2006). A thorough study of the ground by site investigations should be performed to find out the physical and mechanical properties of the ground and existence of underground water, as well as deformation characteristics, especially the stiffness. Technical parameters include tunnel depth and geometry, tunnel diameter–line–grade, single or double track lines and neighboring structures. The construction method, which should lead to a safe and economic project, is selected based on site characteristics and technical project constraints and should be planned so that the ground movements are limited to an acceptable level. Excavation method, face support pressure, advance (excavation) rate, stiffness of support system, excavation sequence and ground treatment/improvement have dramatic effects on the ground deformations occurring due to tunneling operations. The primary reason for ground movements above the tunnel, also known as surface settlements, is convergence of the ground into the tunnel after excavation, which changes the in situ stress state of the ground and results in stress relief. Convergence of the ground is also known as ground loss or volume loss. The volume of the settlement on the surface is usually assumed to be equal to the ground (volume) loss inside the tunnel (O’Reilly and New 1982). Ground loss can be classified as radial loss around the tunnel periphery and axial (face) loss at the excavation face (Attewell et al. 1986; Schmidt 1974). The exact ratio of radial and axial volume losses is not fully demonstrated or generalized in any study. However, it is possible to diminish or minimize the face loss in full-face mechanized excavations by applying a face pressure as a slurry of bentonite–water mixture or foam-processed muck. The ground loss is usually more in granular soils than in cohesive soils for similar construction conditions. The width of the settlement trough on both sides of the tunnel axis is wider in the case of cohesive soils, which means lower maximum settlement for the same amount of ground loss. Time dependency of ground behavior and existence of underground water distinguish short- and long-term settlements (Attewell et al. 1986). Short-term settlements occur during or after a few days (mostly a few weeks) of excavation, assuming that undrained soil conditions are dominant. Long-term settlements are mostly due to creep, stress redistribution and consolidation of soil after drainage of the underground water and elimination of pore water pressure inside the soil, and it may take a few months to a few years to reach a stabilized level. In dry soil conditions, the long-term settlements may be considered as very limited. There are mainly three settlement prediction approaches for mechanized tunnel excavations: (1) numerical analysis such as finite element method, (2) analytical method and (3) semi-theoretical (semi-empirical) method. Among them, the numerical approaches are the most reliable ones. However, the results of all methods should be used carefully by an experienced field engineer in designing the stage of an excavation project. In this study, all three prediction methods are employed for a critical zone to predict the short-term maximum surface settlements above the twin tunnels of the chainage between 0 ? 850 and 0 ? 900 m between Esenler and Kirazl? stations of Istanbul Metro line, which is 4 km in length. Plaxis finite element modeling program is used for numerical modeling; the method suggested by Loganathan and Poulos (1998) is used for the analytical solution. A few different semi-theoretical models are also used for predictions. The results are compared and validated by field measurements. Description of the project, site and construction method The first construction phase of Istanbul Metro line was started in 1992 and opened to public in 2000. This line is being extended gradually, as well as new lines are being constructed in other locations. One of these metro lines is the twin line between Esenler and Basaksehir, which is 21.2 km. The excavation of this section has been started in May 2006. Currently, around 1,400 m of excavation has already been completed. The region is highly populated including several story buildings, industrial zones and heavy traffic. Alignment and stations of the metro line between Esenler and Basaksehir is presented in Fig. 1. Totally four earth pressure balance (EPB) tunnel boring machines (TBM) are used for excavation of the tunnels. The metro lines in the study area are excavated by a Herrenknecht EPB-TBM in the right tube and a Lovat EPB-TBM in the left tube. Right tube excavation follows around 100 m behind the left tube. Some of the technical features of the machines are summarized in Table 1. Excavated material is removed by auger (screw conveyor) through the machine to a belt conveyor and than loaded to rail cars for transporting to the portal. Since the excavated ground bears water and includes stability problems, the excavation chamber is pressurized by 300 kPa and conditioned by applying water, foam, bentonite and polymers through the injection ports. Chamber pressure is continuously monitored by pressure sensors inside the chamber and auger. Installation of a segment ring with 1.4-m length (inner diameter of 5.7 m and outer diameter of 6.3 m) and 30-cm thickness is realized by a wing-type vacuum erector. The ring is configured as five segments plus a key segment. After installation of the ring, the excavation restarts and the void between the segment outer perimeter and excavated tunnel perimeter is grouted by300 kPa of pressure through the grout cannels in the trailing shield. This method of construction has been proven to minimize the surface settlements. The study area includes the twin tunnels of the chainage between 0 + 850 and 0 + 900 m, between Esenler and Kirazl? stations. Gungoren Formation of the Miosen age is found in the study area. Laboratory and in situ tests are applied to define the geotechnical features of the formations that the tunnels pass through. The name, thickness and some of the geotechnical properties of the layers are summarized in Table 2 (Ayson 2005). Fill layer of 2.5-m thick consists of sand, clay, gravel and some pieces of masonry. The very stiff clay layer of 4 m is grayish green in color, consisting of gravel and sand. The dense sand layer of 5 m is brown at the upper levels and greenish yellow at the lower levels, consisting of clay, silt and mica. Dense sand of 3 m is greenish yellow and consists of mica. The base layer of the tunnel is hard clay, which is dark green, consisting of shell. The underground water table starts at 4.5 m below the surface. The tunnel axis is 14.5 m below the surface, close to the contact between very dense sand and hard clay. This depth isquite uniform in the chainage between 0 + 850 and 0 + 900 m. Surface settlement prediction with finite element modeling Plaxis finite element code for soil and rock analysis is used to predict the surface settlement. First, the right tube is constructed, and then the left tube 100 m behind the right tube is excavated. This is based on the assumption that ground deformations caused by the excavation of the right tube are stabilized before the excavation of the left tube. The finite element mesh is shown in Fig. 2 using 15 stress point triangular elements. The FEM model consists of 1,838 elements and 15,121 nodes. In FE modeling, the Mohr–Coulomb failure criterion is applied. Staged construction is used in the FE model. Excavation of the soil and the construction of the tunnel lining are carried out in different phases. In the first phase, the soil in front of TBM is excavated, and a support pressure of 300 kPa is applied at the tunnel face to prevent failure at the face. In the first phase, TBM is modeled as shell elements. In the second phase, the tunnel lining is constructed using prefabricated concrete ring segments, which are bolted together within the tunnel boring machine. During the erection of the lining, TBM remains stationary. Once a lining ring has been bolted, excavation is resumed until sufficient soil excavation is carried out for the next lining. The tunnel lining is modeled using volume elements. In the second phase, the lining is activated and TBM shell elements are deactivated. When applying finite element models, volume loss values are usually assumed prior to excavation. In this study, the FEM model is run with the assumption of 0.5, 0.75, 1 and 1.5% volume loss caused by the convergence of the ground into the tunnel after excavation. Figures 3 and 4 show total and vertical deformations after both tubes are constructed. The vertical ground settlement profile after the right tube construction is given in Fig. 5, which is in theshape of a Gaussian curve, and that after construction of both tubes is given in Fig. 6. Figure 7 shows the total deformation vectors. The maximum ground deformations under different volume loss assumptions are summarized in Table 3. Surface settlement prediction with semi-theoretical and analytical methods Semi-theoretical predictions for short-term maximum settlement are performed using the Gaussian curve approach, which is a classical and conventional method. The settlement parameters used in semi-theoretical estimations and notations are presented in Fig. 8. The theoretical settlement (Gaussian) curve is presented as in Eq. 1 (O’Reilly and New 1982): 2x,()2i2 (1) S,Semax where, S is the theoretical settlement (Gauss error function, normal probability curve), Smax is the maximum short-term (initial, undrained) settlement at the tunnel centerline (m), x is the transverse horizontal distance from the tunnel center line (m), and i is the point of inflexion (m). To determine the shape of a settlement curve, it is necessary to predict i and Smax values. There are several suggested methods for prediction of the point of inflexion (i). Estimation of i value in this studyis based on averages of some empirical approaches given in Eqs. 2–6: where, Z0 is the tunnel axis depth (m), 14.5 m in this study, and R is the radius of tunnel, 3.25 m in this study. Equation 3 was suggested by Glossop (O’Reilly and New 1982) for mostly cohesive grounds; Eq. 4 was suggested by O’Reilly and New (1982) for excavation of cohesive grounds by shielded machines; Eq. 5 was suggested by Schmidt (1969) for excavation of clays by shielded machines; Eq. 6 was suggested by Arioglu (1992) for excavation of all types of soils by shielded machines. As a result, the average i value is estimated to be 6.6 m in this study. There are several suggested empirical methods for the prediction of the maximum surface settlement (Smax).Schmidt suggested a model for the estimation of Smax value for a single tunnel in 1969 as given in Eq. 7 (through Arioglu 1992): where, K is the volume loss (%). Arioglu (1992), based on field data, found a good relationship between K and N (stability ratio) for face-pressurized TBM cases as in Eq. 8: where cn is the natural unit weight of the soil (kN/m3), the weighted averages for all the layers, which is 19 kN/m3 in this study; rS is the total surcharge pressure (kPa), assumed to be 20 kPa in this study; rT is TBM face pressure (kPa), which is 300 kPa in this study; and CU is the undrained cohesion of the soil (kPa), the weighted averages for all the layers, which is 50 kPa in this study assuming that CU is equal to SU (undrained shear strength of the soil). All averages are estimated up to very dense sand, excluding hard clay, since the tunnel axis passes around the contact between very dense sand and hard clay. The model yields 17.1 mm of initial maximum surface settlement. Herzog suggested a model for the estimation of Smax value in 1985 as given in Eq. 9 for a single tunnel and Eq. 10 for twin tunnels (through Arioglu 1992): where, E is the elasticity modulus of formation (kPa), the weighted averages for all the layers, which is 30,000 kPa in this study, and a is the distance between the tunnel axes, which is 14 m in this study. The model yields 49.9 and 58.7 mm of initial maximum surface settlements for the right and the left tube tunnel, which is 100 mm behind the right tube, respectively. There are several analytical models for the prediction of short-term maximum surface settlements for shielded tunneling operations (Lee et al. 1992; Loganathan and Poulos 1998; Chi et al. 2001; Chou and Bobet 2002; Park 2004). The method suggested by Loganathan and Poulos (1998) is used in this study. In this method, a theoretical gap parameter (g) is defined based on physical gap in the void, face losses and workmanship value, and then the gap parameter is incorporated to a closed form solution to predict elastoplastic ground deformations. The undrained gap parameter (g) is estimated by Eq. 12: where Gp is the physical gap representing the geometric clearance between the outer skin of the shield and the liner, , is the thickness of the tail shield, d is the clearance required for erection of the liner, U*3D is the equivalent 3D elastoplastic deformation at the tunnel face, and w is a value that takes into account the quality of workmanship. Maximum short-term surface settlement is predicted by theoretical Eq. 13 (Loganathan and Poulos 1998): where, t is undrained Poisson’s ratio, assumed to be of maximum 0.5; g is the gap parameter (m), which is estimated to be 0.0128 m in this study; and x is transverse distance from the tunnel centerline (m) and it is assumed to be 0 m for the maximum surface settlement. The model yields 23.0 mm of undrained maximum surface settlement. Other parameters of settlement such as maximum slope, maximum curvature and so on are not mentioned in this study. Verification of predictions by field measurements and discussion The results of measurements performed on the surface monitoring points, by Istanbul Metropolitan Municipality, are presented in Table 4 for the left and right tubes. As seen, the average maximum surface settlements are around 9.6 mm for the right tube and 14.4 mm for the left tube, which excavates 100 m behind the right tube. The maximum surface settlements measured around 15.2 mm for the right tube and 26.3 mm for the left tube. Higher settlements are expected in the left tube since the previous TBM excavation activities on the right tube overlaps the previous deformation. The effect of the left tube excavation on deformations of the right tube is presented in Fig. 9. As seen, after Lovat TBM in the right tube excavates nearby the surface monitoring point 25, maximum surface settlement reaches at around 9 mm; however, while Herrenknecht TBM in the left tube passes the same point, maximum surface settlement reaches at around 29 mm (Fig. 10). If the construction method applied to the site is considered, long-term (consolidation) settlements are expected to be low, since the tail void is grouted immediately after excavation. The results of predictions mentioned above and observed maximum surface settlements are summarized in Table 5. The methods suggested by Loganathan and Poulos (1998) and Schmidt (1969) connected with Arioglu’s suggestion (1992) can predict the maximum short-term surface settlements only for a single tunnel. Plaxis finite element and Herzog (1985) models can predict deformations for twin tubes. Herzog’s model (1985) yields higher maximum surface settlements than the observed ones. The reason for that is that the database of the model includes both shielded tunnels and NATM (New Austrian Tunneling Method) tunnels, of which surface settlements are usually higher compared to shielded tunnels. Schmidt (1969), along with Arioglu’s suggestion (1992), yields predictions close to observed. Plaxis finite element modeling gives the most realistic results, provided there is correct assumption of volume loss parameter, which is usually difficult to predict. The model provides simulation of excavation, lining, grouting and face pressure in a realistic manner to predict surface and sub-surface settlements. The volume loss parameter is usually assumed to be \1% for excavation with face pressure-balanced tunnel boring machines. The realized volume loss in the site is around 1% for this study. Currently, there is difficulty yet in modeling the deformation behavior of twin tunnels. One of the most impressive studies on this issue was performed by Chapman et al. (2004). However, Chapman’s semi-theoretical method still requires enlargement of the database to improve the suggested model in his paper. Conclusions In this study, three surface settlement prediction methods for mechanized twin tunnel excavations between Esenler and Kirazl? stations of Istanbul Metro Line are applied. Tunnels of 6.5-m diameters with 14-m distance between their centers are excavated by EPM tunnel boring machines. The geologic structure of the area can be classified as soft ground. Settlement predictions are performed by using FE modeling, and semi-theoretical (semi-empirical) and analytical methods. The measured results after tunneling are compared to predicted results. These indicate that the FE model predicts well the short time surface settlements for a given volume loss value. The results of some semi-theoretical and analytical methods are found to be in good agreement with the FE model, whereas some methods overestimate the measured settlements. The FE model predicted the maximum surface settlement as 15.89 mm (1% volume loss) for the right tube, while the measured maximum settlement was 15.20 mm. For the left tube (opened after the right), FE prediction was 24.34 mm, while measured maximum settlement was 26.30 mm. 中文翻译 基于盾构法的Istanbul地铁施工引起的地面沉降预测 摘要 在这项研究中，研究的是双线隧道的短期地面沉降，选取线路里程总长为4km的Istanbul地铁从Esenler站到Kirazl站方向850到900m区间为研究对象。Esenler到Basaksehir站掘进线路总长为21.2km。使用两台刀盘直径为6.5m土压平衡盾构机进行双线掘进，两隧道中心距14m。左隧道先于有隧道100m掘进。使用宽1.4m的管片作为支护。使用Plaxis软件进行沉降的有限元分析。该软件能模拟地下隧道的掘进、支护和掌子面支护等。针对典型的地质特征进行预测，这些特征是决定地面沉降量的关键因素。研究区域的地质构造从地面向下分别为素填土、硬粘土、密实砂、高密砂和硬质粘土。本文不仅使用有限元分析地面沉降，也使用半理论(半经验)和解析模型进行预测。结果表明该FE模型对给定流失值的短期地面沉降预测效果较好。半理论和解析模型得到结果与FE模型得到的结果一致。将预测结果和实际测量值进行对比分析，得到在掘进过程中，灌浆应在管片支护安装到位后尽快进行。刀盘压力应严密监控并及时调整适应不同地质。 Keywords:地面沉降预测;有限元模型;解析 方法 快递客服问题件处理详细方法山木方法pdf计算方法pdf华与华方法下载八字理论方法下载 ;半理论方法;土压平衡盾构机;Istanbul地铁 介绍 随着对基础设施需要的增长，人们对在市区中通过浅埋暗挖修建隧道产生了浓厚兴趣。一些地表和次地表岩土结构的变形使地下工程十分脆弱，这些变形应根据可接受级别得到限制和控制。不论什么掘进方式，短期和长期的地表和次地表层变形都应得到预测，在开挖前要对现有的可能受到破坏的结构采取加固措施。隧道建设成本大量增加主要由于其引起的地面沉降超过了允许值(Bilgin et al. 2009)。 反应地层沉降的基本参数有地质条件、技术/环境参数和隧道掘进或构造方法(O’Reilly and New1982; Arioglu 1992; Karakus and Fowell 2003; Tan andRanjit 2003; Minguez et al. 2005; Ellis 2005; Suwansawatand Einstein 2006)。应该以勘探方式进行详细地质调查，弄清地层的物理和机械性质、地下水分布、地层的变形特征，特别是岩层的刚度。技术参数包括:隧道深度、几何形状、隧道直径、单线还是双线隧道和邻近建筑物情况。施工方法应该是安全经济的，其选择应考虑地质条件、技术条件，同时也要考虑将地层移动控制在可接受的范围内。掘进方式、刀盘面压力、推进速度、支护 系统刚性、掘进后处理和土体处理/改善在掘进过程中对岩土结构的沉降有很大影响。 隧道上方土体移动(地面沉降)的主要原因是在挖掘后土体收敛靠近隧道，由于掘进改变了原来土体的压力平衡状态，导致压力重新分布。土体流失和土体体积流失都认为是土体收敛。地表沉降体积一般假设等于隧道内挖走的土体量(O’Reilly and New 1982)。 土体流失可分为围绕隧道外围径向流失和在掘进面的中心轴面流失(Attewell et al. 1986; Schmidt 1974)。现在实际的径向和轴向体积流失率还不能被完全解释和泛化。但是，能做到的是通过调整刀盘面压力，消除和减少在全断面机械掘进中的掘进面土体损失，如在压力仓加入膨润土与水的混合泥浆或发泡处理的填充物，使其达到平衡等。在相同的施工条件下，颗粒土的土体损失一般大于粘性土。隧道两侧的沉降槽宽度在粘性土 案例 全员育人导师制案例信息技术应用案例心得信息技术教学案例综合实践活动案例我余额宝案例 中较宽，这说明对于相同量的土体流失，粘性土的沉降最大值较小。 基于时变的土体行为和地下水的存在可辨别短期和长期沉降(Attewell et al. 1986)。假设土体为不排水，短期沉降发生在挖掘后的几天(最多几周)内。长期沉降主要原因是蠕变，在地下水排出和土内孔隙水压消失后，土体才压力重分布和固结，这个过程也许要经历几个月或几年时间才能达到稳定。在干土条件下，认为长期沉降很有限。 对于机械隧道掘进主要有三种沉降预测方法:(1)数值分析，如有限元方法;(2)解析方法和(3)半理论(半经验)方法。其中，数值分析是最可靠的。但是对于一个有经验的岩土工程师来说，在掘进项目 设计 领导形象设计圆作业设计ao工艺污水处理厂设计附属工程施工组织设计清扫机器人结构设计 阶段，所有方法分析的结果要认真对待。 在这项研究中，这三个方法都将被使用来预测研究区域的短期最大地表沉降，这个研究区域在4km长的Istanbul地铁从Esenler站到Kirazl站方向850到900m区间的双线掘进隧道的正上方地面。Plaxis有限元建模程序用于数字建模;这个方法由Loganathan和Poulos (1998)提出用作解析解。一些不同的半理论模型也用作预测。结果与实际测量值进行比较，并得到验证。 项目、站点和施工方式概况 Istanbul地铁的一期工程开始于1992年，2000建成向公众开放。该线路一直被延长，同时修建了其他多条新线，其中之一就是总长21.2km的Esenler到Basaksehir站的双线隧道。该线掘进施工始于2006年5月。现在大约完成了1400m隧道挖掘。隧道施工区域上方人口稠密，古建筑多，有工业区而且交通量大。该先的线路和车站如图1所示。 图一 隧道掘进使用四台土压平衡盾构机。研究区域的隧道右线使用Herrenknecht土压平衡盾构机，左线使用Lovat土压平衡盾构机。左隧道掘进面在右隧道后100m。相关机械技术参数如表1所示。 表1土压平衡盾构机的参数 Herrenkencht Lovat 掘进直径 6.500m 6.564m 盾壳外径 6.45m 6.52m 前部盾体 7.68m 9.30m 盾构机长度 80m 65m 总重量 578t 534t 刀盘转速 0-2.5 0-6.0 组驱动功率 963KW 1.622KW 钻土类型 混合地层 混合地层 钻头功率 630KW 900KW 最大扭矩 435tm 445tm 最大推力 54(000KN 32.000KN 开挖掉的土体使用钻孔机(螺旋传送机)穿过机器运送到传送带，然后将土体装入出土车运送到竖井。考虑到开挖后土体承受的水压和稳定性问题，压力舱轴向压力为300KPa,将水、泡沫、膨润土和碎石混合通过洞口进入压力舱。压力舱压力应通过在压力舱和螺旋传送机内的压力传感器得到实时监控。管片环宽1.4m，厚30cm,使用翼型真空拼装机组装。每环由5个 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 片和1个封顶片组成。在管片环安装完成后掘进从新开始，在管片环外与隧道开挖面内之间的空隙通过在盾尾的注浆管以300kPa的压力注浆。这种构建方法可保证最小的地表沉降。 研究区域为双线施工的从Esenler站到Kirazl站方向850到900m区间。其中存中新世的Gungoren构造岩层。使用实验室试验和现场试验的方式确定隧道经过区域在 的地质结构特性。地层名称、厚度和性质如表2所示(Ayson 2005).。填土层厚2.5m，由砂、粘土、沙砾和碎石组成。硬粘土层厚4m，灰绿颜色，由沙砾和砂组成。密砂5m层厚，上层褐色下层绿黄色，由粘土、淤沙和云母石组成。致密砂层厚3m，绿黄色，云母石组成。隧道底部是暗绿色硬质粘土。地下水位在-4.5m处。隧道轴心在地下14.5m处，接近于致密砂与硬质粘土连接层。在里程的850到900m区间内其深度不一。 表2 研究区域的地质条件 33a ,(KN/m),(KN/m)S(kPa)E(kPa),(,)dry构成 厚度 PI(%) 渗透率 nUN30 (cm/s) 素填土 2.5 10 13 20 8.000 19.8 13.8 — 1.0 ,4 硬粘土 4.0 20 85 9 51.000 18.2 12.7 3.3 1.0，10密砂 5.0 36 40 35 24.000 19.0 13.5 — 0.5 致密砂 3.0 64 50 35 30.000 19.5 15.0 — 0.25 ,4 陶土 底层 45 150 12 90.000 18.6 14.0 45 1.0，10基于有限元模型地面表沉降预测 Plaxis有限元分析软件是针对土和岩石的地面沉降预测软件。首先，开挖右隧道，然后左隧道在右隧道开挖100m后开始挖掘。假设由左隧道开挖引起的岩土变化在右隧道开挖时达到稳定。使用15个压力点的三角形元素组成的有限元网格如图2所示。该模型由1838个单元和15121个节点组成，使用Mohr–Coulomb本构模型。 图2 有限元模型 模型开挖采用分步方式。土体挖掘和隧道衬砌构建在模拟的不同阶段实现。第一阶段，在盾构机前方土体被挖掘，然后模拟挖掘机刀盘对掌子面施加300kPa压力，以防止掌子面坍塌。在该阶段盾构机使用壳单元进行模拟。第二阶段，使用预制混凝土管片对隧道进行支护，其拼装在盾构机内完成。在吊装管片时盾构机不动。完成管片安装后，盾构机继续掘进，直到掘进长度可安装下一环管片时停止并安装管片。隧道衬砌使用体积单元进行模拟。在第二阶段内，衬砌单元是活动的，盾构机壳单元是固定的。 当使用有限元模型时，通常假设体积流失先于挖掘。这里，FEM设定了由于在挖掘后土体向隧道收敛的体积流失量率分别为0.5,0.75,1和1.5%。图3和图4显示了两隧道开挖后的总位移和竖向位移。右隧道构建完成后竖向土体沉降轮廓线如图5所示，该曲线与Gaussian曲线形状相同。两隧道施工完成后的竖向土体沉降轮廓线如图6所示。图7显示了总位移向量。 最大土体变形在不同的体积流失率时的地面沉降量如图3所示。 图3 左隧道施工后总体沉降 图4 左隧道施工后竖直沉降 图5 右隧道施工后地面沉降量 图6 两隧道施工后地表沉降量 图7 总地表位移向量 表三盾构法施工引起的最大地面沉降 体积流失 右隧道 左隧道 0.5 12.35 20.22 0.75 14.19 22.43 1.0 15.89 24.34 1.5 18.62 27.49 基于半理论和解析模型的地面沉降分析 对短期沉降最大值半理论预测是基于Gaussian曲线的，该曲线是经典的通常的方法。使用半理论预测沉降的参数如图8所示。 图8 左右隧道施工引起的最大地面沉降 理论沉降曲线公式为1。 2x,()2i2S,Se (1) max 其中，S是理论沉降值(Gauss 误差函数，通常可能曲线)，S是在隧道中心线最max 大短期(初始，非排水)沉降量(m),x是从隧道中心线的横向水平位移(m)，i是隧道切点位置(m)。决定沉降曲线形状，这是预测i和S的必要条件。 max 预测切点位置(i)有一些可建议的方法。在这篇文章中预测i值是通过经验公式2-6完成的。 i，i，i，i1234i, (2) 4 i,0.5Z10 (3) i,0.43Z，1.120 (4) 0.8Z,,0i,R,,32R,, (5) 0.88Z,,0i,0.9R,,42R,, (6) 式中，Z是隧道轴深，Z=14.5m，R是隧道半径，R=3.25m。式3针对大多数的收00 敛土体由Glossop提出(O’Reilly and New 1982);式4针对盾构机掘进后土体的收敛由O’Reilly and New (1982)提出;式5针对盾构机粘土的掘进由Schmidt (1969)提出;式6适合于盾构机在任何土体内的掘进由Arioglu (1992)提出;本文取上述结果的平均值作为估计结果，i=6.6m。 这里提供了几个预测最大地面沉降(S)的经验公式。 max Schmidt在1969年提出了针对单隧道的S值的估计模型如试7所示(through max Arioglu 1992): 2,,R,,S,K0.0125 ,,maxi (7),, 式中，K是体积流失率(%)。 根据现场数据，Arioglu (1992)发现了K与N(稳定率)在使掌子面压力平衡的盾构机掘进时的较好符合关系，如试8所示。 ,,Z，，nasr,,,,,0.26,,CNU0.26,, K,0.87e,0.87e (8) 33 式中是天然土体密度(kN/m),将所有层进行平均，得到平均密度19kN/m;,,nS 是总荷载压力(kPa)，本文估计值为20kPa;是土压平衡盾构机的盘面压力(kPa),,T 取300kPa;是非排水土内聚力(kPa),由于土密度取平均值，假设等于(非排CCSUUU水土体抗剪强度)等于50kPa。由于隧道轴心线穿过密致砂和硬质粘土的接触面，所有平均值的估计取决于密致砂而不是硬质粘土。初始最大地表沉降为17.1mm。 Herzog在1985年提出了估计S值的单隧道和双隧道模型分别如试9和10所示max (through Arioglu 1992): 2,,D,,S,Z，，，0.785,,maxn0s,,iE (9) ,, 2,,D4.71,,S,Z，，，,, ns,,max0，，3i，aE (10),, 式中，E为弹性模量(kPa), 将所有层进行平均，得到的平均弹性模量为30000kPa，a是两盾构隧道轴心距，取14m。在模型中，右线和左线初始最大地面沉降分别为49.9和58.7mm，左线施工断面在右线后100m。 对隧道挖掘引起的地面短期最大沉降值的估计也有解析模型可以使用(Lee et al. 1992; Loganathan and Poulos1998; Chi et al. 2001; Chou and Bobet 2002; Park 2004)。本文使用Loganathan and Poulos (1998)提出的方法。该方法基于实际的空隙、面流失和工程质量定义了一个理论空隙参数(g)，然后该参数被从解析解加入到预测弹塑性土体的变形结果中。非排水的参数(g)使用式12估计。 ,g,G，U，w pD3 (11) G,2,，,式中，G是物理空隙 ，表示盾构机外和衬砌之间的几何净空，,是Pp ,U,盾构机尾部壳厚度，为安装衬砌需要的空间,是在掌子面的等效三维弹塑变形，w3D 是考虑施工质量影响的参数。 最大短期地面沉降使用理论公式13(Loganathan and Poulos 1998)预测。 22，，,,,,，,Z4gRg1.38x20,,,,,，，，S41vRexp ,,2222,,,,，，，，ZxR (13)ZR0,,,,0，， 式中，v是非排水土泊松比，假设为0.5;g是空隙参数(m),取0.0128;x是距隧道中心线的水平距离，假设此处沉降为0m。模型产生23.0mm的非排水最大地面沉降。 其他与沉降相关的参数如最大坡度，最大曲率等本文不研究。 通过实际测量数据验证预测并论证 根据Istanbul市政当局提供的左右隧道的地面沉降监测点监测结果如图4所示。从图中看出，左右两隧道平均最大地面沉降分别约为14.4mm和9.6mm，右隧道在左隧道前100m。左右两隧道最大地面沉降分别约为26.3mm和15.2mm。左隧道可能发生更大沉降，因为在右隧道先期的盾构机掘进行为超覆了前期变形。左隧道开挖对右隧道变形的影响如图9所示。从图中看出，当右线Lovat盾构机通过地面监测点25时，最大地表沉降达到了9mm;然而，当左线的Herrenknecht盾构机通过该点时，地面最大沉降量达到29mm,如图10所示。 表四 在里程为850~900之间的地面监测点测量得到的短期最大地面沉降值 左隧道 右隧道 沉降监测点 沉降最大值(m) 沉降监测点 沉降最大值(m) 14 -0.0093 33 -0.0142 15 -0.0045 34 -0.0101 16 0.0102 35 -0.0084 17 -0.0263 36 -0.0113 18 -0.0235 37 -0.0070 19 -0.0163 38 -0.0065 20 -0.0183 39 -0.0059 21 -0.0200 40 -0.0074 22 -0.0177 41 -0.0152 23 -0.0248 24 -0.0220 25 -0.0089 26 -0.0075 31 -0.0117 32 -0.0152 平均 -0.0144 图9 沉降参数和记号 图10 左隧道施工引起的有隧道地面监测点处的位移 如果该建造方式应用于现场，长期(固结)沉降将很小，因为盾尾空隙在掘进后很快被注浆填满。上述提到的预测结果和观察得到的最大地面沉降如表5总结。 表五 短期最大地表沉降预测与观测值总结 预测模型 最大地表沉降 Plaxis有限元模型(左隧道) 20.22mm(0.5%体积流失) 24.34mm(1%体积流失) Plaxis有限元模型(右隧道) 12.35mm(0.5%体积流失) 15.89mm(1%体积流失) Schmidt(1969)and Ariogiu(1992) 17.1mm Logannathan and Poulos(1998) 23.0mm Herzog(1985),右隧道 49.9mm Herzog(1985),左隧道 58.7mm 实测(右隧道) 平均9.6mm，最大15.2mm 实测(左隧道) 平均14.4mm，最大26.3mm 将Loganathan 、 Poulos(1998) 和Schmidt (1969)提出的方法和Arioglu’s提出的方法相结合仅仅能预测单隧道最大短期地面沉降。Plaxis有限元软件和Herzog (1985)模型能预测双线隧道的变形。 Herzog’s模型(1985)生成了比观测值更大的最大地表沉降。这是因为模型的数据库包括了双盾构隧道和NATM(新奥法)施工的隧道，后者相对于前者有更高的地表沉降。Schmidt (1969)和Arioglu’s (1992)的估计值接近实际测量值。 如果体积流失参数假设正确，Plaxis有限元模拟得到了最接近现实的结果，但是该参数通常难以预测。该模型提供了开挖、衬砌安装、灌浆和掌子面等实际掘进行为来预测地面和次表层土体沉降。由于使用土压平衡盾构机，体积流失参数通常认为小于1%，本文取值为1%。 目前，对双隧道掘进引起的岩土变形行为仍然困难。关于这个问题最著名的研究是 Chapman(2004)进行的。但是，Chapman的半理论方法任然需要扩大数据库来改进本文使用的模型。 结论 本文应用了三种地面沉降预测方法研究了Esenler和Kirazl?站之间的机械化双线施工的Istanbul地铁。隧道直径6.5m，两隧道中心轴间距14m，使用土压平衡盾构机施工。施工区域的地质构造为软土质。 沉降预测是通过FE模拟、半理论(半经验)和解析方法实现的。对隧道开挖后的测量结果与模拟结果相比较，结果表明FE模型预测对给定体积流失值的短时间地面沉降效果很好。一些半理论和解析方法与FE模型预测结果比较接近，但是一些方法得到的沉降量大于实测量。FE模型预测的在右线的最大地面沉降量为15.89mm(1%的体积损失)，实际测量值为15.20mm。对于左线(晚于右线开工)，FE预测的是24.34mm，实际测量值为26.30mm。