Mechanical Behavior and Shape Optimization of Lining Structure for Subsea Tunnel Excavated in Weathered Slot

Subsea tunnel lining structures should be designed to sustain the loads transmitted from surrounding ground and groundwater during excavation. Extremely high pore-water pressure reduces the effective strength of the country rock that surrounds a tunnel, thereby lowering the arching effect and stratum stability of the structure. In this paper, the mechanical behavior and shape optimization of the lining structure for the Xiang＇an tunnel excavated in weathered slots are examined. Eight cross sections with different geometric parameters are adopted to study the mechanical behavior and shape optimization of the lining structure. The hyperstatic reaction method is used through finite element analysis software ANSYS. The mechanical behavior of the lining structure is evidently affected by the geometric parameters of crosssectional shape. The minimum safety factor of the lining structure elements is set to be the objective function. The efficient tunnel shape to maximize the minimum safety factor is identified. The minimum safety factor increases significantly after optimization. The optimized cross section significantly improves the mechanical characteristics of the lining structure and effectively reduces its deformation. Force analyses of optimization process and program are conducted parametrically so that the method can be applied to the optimization design of other similar structures. The results obtained from this study enhance our understanding of the mechanical behavior of the lining structure for subsea tunnels. These results are also beneficial to the optimal design of lining structures in general.

Grouting techniques for the unfavorable geological conditions of Xiang'an subsea tunnel in China

One of the major challenges during subsea tunnel construction is to seal the potential water inflow. Thepaper presents a case study of Xiang＇an subsea tunnel in Xiamen, the first subsea tunnel in China. Duringits construction, different grades of weathered geomaterials were encountered, which was the challengingissue for this project. To deal with these unfavorable geological conditions, grouting was adoptedas an important measure for ground treatment. The grouting mechanism is first illustrated by introducinga typical grouting process. Then the site-specific grouting techniques employed in the Xiang＇ansubsea tunnel are elaborated. By using this ground reinforcement technique, the tunneling safety of theXiang＇an subsea tunnel was guaranteed. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Service Life Prediction of Lining Concrete of Subsea Tunnel under Combined Compressive Load and Carbonation

Qingdao Jiaozhou Bay subsea tunnel is the second self-built tunnel in China with the designed service life over 100 years.The durability of lining concrete are one of an important factors to determinate the service life of tunnel.Considering the main environmental loads and mechanical loads of subsea tunnel,the durability properties of lining concrete under combined action of compressive load and carbonation has been studied through the critical compressive load test,accelerated carbonation test,natural carbonation test and capillary suction test.The tests results show that critical compressive load apparently accelerates the carbonation and deteriorates the anti-permeability of concrete.Under the combined action of critical compressive load and carbonation,the durability of lining concrete decreases.Based on the carbonization life criteria and research results,for the high-performance concrete with proposed mix ratio,the predicted service life of lining concrete for Jiaozhou bay subsea tunnel is about 80 years which fails to reach the required service life.It is necessary to adopt other measurements simultaneously to improve the durability of lining concrete.

Durability of Lining Concrete of Subsea Tunnel under Combined Action of Freeze-thaw Cycle and Carbonation

Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete.Under the combined action of freeze-thaw cycle and carbonation,the durability of lining concrete decreases.The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted.For the high performance concrete with proposed mix ratio,the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating.Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.

Characteristics on Seawater Corrosion of Intensely Weathered Surrounding Rock of Subsea Tunnel

Existing studies on the durability of subsea tunnel mainly focus on the concrete deterioration and steel corrosion,while there are few on the infuence of mechanical properties deterioration of surrounding rock on the durability of sub-sea tunnel.To improve the accuracy of long-term stability prediction,seawater corrosion tests of intensely weathered surounding rock of subsea tunnel are car-ried out.In this study,the strength characteristics of remolded samples of inten-sely weathered granite under different seawater concentrations are investigated,the strength attenuation equation under seawater corrosion is established,and the chemical damage evolution equation and model parameters are formulated,The findings provides the basis for analyzing the influence of corosion and weak-ening of surrounding rock on the durability of tunnel within the operation period.

Analysis of Driving Psychological Load in V-Shaped Subsea Tunnels Considering Driver Skin Electrical Signals

To examine the variation law of the driving psychological load in subsea tunnels under different illumination and longitudinal slope conditions,22 drivers were recruited to participate in a real vehicle test in off peak hours under similar traffic conditions,and the skin electric signals of the drivers in the free flow state were collected.Considering the skin conductance level(SCL)as the load characteristic index,the influence of the different illuminance and slope conditions on the drivers’skin electrical signals was analyzed,and a measurement model of the relationship between the uphill and downhill slopes,illuminance and driver’s SCL value was constructed.The results indicate that the illuminance change rate and driver’s SCL are positively correlated.A larger illuminance change rate leads to an increase in the SCL and psychological workload of the driver.The influence of the uphill and downhill slopes on the driver’s SCL value in different areas of the subsea tunnel is considerably different.With the increase in the degree of the uphill and downhill slopes,the driver’s SCL value increases,and the maximum SCL appears in a slope range of 3.5%–4%.Moreover,the SCL of the drivers in the downhill section is higher than that in the uphill section,corresponding to a larger driving psychological load.

大连湾海底隧道透水式接岸结构对水体交换的影响

在大连湾海底隧道工程中首次应用了透水式接岸结构,采用数值模拟的方法计算了大连湾海底隧道接岸结构施工后的流场和水体交换,并与传统的不透水方案计算结果进行了对比分析。研究结果表明:透水式接岸结构方案中水流会产生明显的横跨隧道方向的流动,对隧道两侧的水体交换有改善的作用,更能促进周边水体交换。这种透水结构具有推广应用价值。

波流耦合影响下分层海床隧道周围砂土渗流孔压及液化分析

目前针对波浪作用下海底盾构隧道周围渗流场的既有理论研究一般将衬砌考虑为不透水介质,较少考虑隧道衬砌的渗透性,尤其是较少考虑波浪与海流共同作用对隧道的影响。此外,既有理论一般将海床视为均质且各向同性工况,忽略了实际情况下分层海床的影响。首先,基于波流共同作用下的海床表面的动力边界条件,采用传递-反射矩阵法得到波流共同作用下自由分层海床的孔压响应;其次,采用镜像法建立了由于隧道存在引起的砂土摄动压力控制方程,并利用砂土与衬砌间渗流连续条件获得了该方程的Fourier级数展开解析解;接着,采用叠加原理得到了波流共同作用下分层海床中隧道周围砂土的渗流压力响应及液化判定解答。最后,将理论解析解与数值结果及已有的试验结果进行对比,获得了较好的一致性。此外,针对海床渗透性和隧道衬砌渗透性进行了影响因素分析。结果表明:海流顺流会增大海床中的孔压和液化程度,逆流会减小海床中的孔压并抑制海床的液化,且流速相同时海床对逆流响应的相对差异总体上也大于顺流;当分层海床上层渗透系数较大时(k+s>1×10^(-2)m/s),海床整体孔压较大,且第一次分层处孔压变化明显;当隧道衬砌渗透系数较小时(k+l<1×10^(-6)m/s),隧道对超静孔隙水压在海床内传播“阻挡”效应明显。

特长跨海公路隧道联络烟道间距优化设置研究——以青岛第二海底隧道为例

青岛第二海底隧道通过在隧道的南北线排烟道上纵向间隔设置联络烟道,将南北线烟道联通。由于目前尚无公路隧道设置联络烟道的案例可供参照,为研究联络烟道对公路隧道防排烟效果的影响,亟需明确在不同联络烟道间距下隧道内火灾温度场、烟气蔓延情况、系统阻力等的分布规律,确定最优联络烟道间距。在现有评价指标烟气蔓延长度l_(60)、排烟效率η的基础上提出阻力削减率ξ,构建基于性能化的联络烟道间距优化评估模型;在调研全国各种隧道横通道间距设置配合形式后,采用Fluent软件模拟不同联络烟道间距下的烟流特性及数据。结果表明:1)联络烟道能有效降低排烟系统的阻力;2)随着联络烟道间距的缩短,烟气蔓延长度l_(60)由260 m缩小至180 m,排烟效率η由93.39%提升至97.80%,阻力削减率ξ由15.42%减小至2.20%;3)联络烟道间距为750 m和1500 m混合的设置方式能起到较好的排烟效果,此时继续缩短联络烟道间距对系统排烟能力提升有限。

透水式接岸新结构波浪荷载受力特性研究

采用局部整体波浪物理模型试验,对大连湾海底隧道北接岸透空新结构方案实施后的区域波浪场分布变化以及透水式接岸结构的受力特点进行了研究。试验研究了底部开孔隧道结构在不同水位及波浪组合下水平方向和垂直方向的波浪总力。试验结果表明最大水平力和最大浮托力并未同步出现,水平力大小多与入射波高相关,浮托力波高仅为影响参数之一,水位变化也是重要的影响因素。目前国内对于类似结构的受力研究处于空白状态,相关研究成果可丰富该领域的研究内容,并为这种新型结构的设计提供数据支持。

正断层错动作用下矿山法隧道受力变形机理的模型试验研究

为研究正断层错动作用下矿山法隧道的受力变形机理,以胶州湾第二海底隧道穿越沧口断裂为工程背景,采用自研的大比尺穿越断层隧道结构破坏加载试验装置,针对设置柔性连接变形缝和变形缝间距对隧道结构抗错断效果的影响,开展几何相似比为1∶40的矿山法隧道穿越倾角70°的正断层错动模型试验,对错动试验过程中的隧道变形、应变分布、围岩接触压力和破坏特性等关键指标进行监测,分析获得了正断层错动作用下隧道变形和力学响应规律。研究结果表明:(1)隧道在正断层错动作用下,呈现纵向拉弯+竖向挤压的受荷模式,在下盘邻近断层面处拱顶部位和上盘邻近断层面处仰拱部位出现脱空区;(2)隧道开裂主要以纵向贯通裂缝为主,近断层面处衬砌还出现了部分斜向裂缝和环向裂缝;(3)节段间的连接形式和节段长度不会根本上改变隧道在断层错动作用下的受荷模式和变形模式,但节段间刚度越小,节段长度越小,结构对于地层强制位错的适应性就更好;(4)相比于刚性连接,节段间的柔性连接吸收了大部分地层强制位错,有效降低衬砌节段的荷载和变形,使结构趋于安全。

海底软弱地层浅埋大直径盾构对接开挖面失稳灾变机制研究

为探明对接距离对海底大直径盾构开挖面失稳机制及规律的影响,依托甬舟铁路金塘海底盾构隧道工程,建立考虑渗流的盾构隧道对接有限元模型,研究对接距离L对开挖面失稳机制以及极限支护压力的影响,并基于极限平衡法建立考虑渗流的盾构近距离对接开挖面极限支护压力理论模型。随着对接距离的增大,开挖面失稳形状和极限支护压力的变化可分为3个阶段。1)快速增长阶段(0<L/D≤0.4)(D为隧道直径):该阶段与单个隧道工况区别最明显,失稳区域由楔形体与仓筒组成;此时受对接隧道的阻碍作用最大,且开挖面附近水头场变化剧烈,渗流力占据主要部分。2)缓慢增长阶段(0.4<L/D≤0.7):失稳区域由对数螺旋体与仓筒组成,此时对接隧道的阻碍作用减小,因此极限支护压力在该阶段受对接距离的影响减小,增长缓慢。3)趋于平缓阶段(0.7<L/D≤1.5):失稳区域由对数螺旋体与倒棱台组成,此阶段对接隧道的阻碍作用可忽略不计,极限支护压力、失稳区域形状与非对接情况相近,可视为单个隧道工况。建立的理论模型得出的结果与数值模拟的结果接近,两者误差在10%以内,验证了该模型的可行性。

考虑流固耦合效应的海底隧道地震响应分析

为研究上覆海水影响下海底隧道地震响应规律,考虑衬砌塑性损伤及流固耦合作用,以汕头海底盾构隧道为工程实例,基于ABAQUS软件建立海水-海床-隧道结构体系有限元模型,分析不同地震激励以及不同海水深度条件下海底隧道动力响应及损伤情况。结果表明:1)在只考虑垂直SV波入射时,应力主要集中在隧道拱脚、拱肩部位,海水深度对海底场地水平运动及海底隧道的作用影响很小;2)在只考虑垂直P波入射时,随海水深度增加,上覆海水整体上会抑制海底场地竖向运动,隧道拱腰以下的应力增大更明显;3)考虑P-SV波延时入射时,隧道能量耗散及损伤具有一定的叠加效应,隧道拱脚及拱肩部位应力集中明显,海水深度小于20 m时,隧道断裂能及损伤较小,SV波占主导地位,海水深度大于20 m时,隧道断裂能及损伤会显著增加,P波起主要作用,在海底隧道抗震设计时有必要考虑海水对隧道地震安全的不利影响。

超大直径泥水盾构水中接收关键技术研究——以汕头海湾隧道为例

为解决超大直径泥水盾构在临海富水淤泥、砂层接收洞门的涌水、涌砂、涌泥地层存在的技术难题,以汕头海湾隧道工程超大直径泥水盾构在富水地层采用的接收关键技术为例,分析超大直径与小直径盾构水中接收的区别。基于超大直径盾构接收流程,阐述了超大直径泥水盾构在接收工作中端头加固、接收井封堵墙施工、接收基座施工、单层玻璃纤维筋洞门破除、贯通测量、接收掘进与注浆、洞门封堵等方面的解决方法,从盾构姿态控制、掘进参数控制、注浆控制、管片复紧、洞门临时封堵几个方面对超大直径盾构接收关键技术进行分析;通过采用设置砂浆接收基座为盾构接收提供足够的反力,保证盾构机出洞安全;借助同步注浆和二次注浆封闭补强质量,加强管片复紧,确保盾构隧道结构强度稳定;在最后5环使用多孔特殊环管片,提高注浆效果。然后,通过排水清砂并从上及下逐次施作钢筋骨架加喷射混凝土封堵洞门、降低无封堵洞门暴露时间、确保洞门施工安全等措施,保障水中接收的安全性。

基于等效面积法的三孔并行海底隧道渗流场解析研究

目前对海底隧道渗流场的研究大多基于单孔隧道,考虑到实际工程常采用三孔并行的排布方式,而隧道互相靠近时渗流场会发生干扰,若采用单孔隧道模型其涌水量计算误差可能超过40%。该文对三孔并行海底隧道渗流场进行理论分析,首先分析了理论解析过程中采用等面积法将多心圆形断面简化为圆形断面的合理性;进而提出三孔并行海底隧道渗流场分析模型,以叠加原理为基础,采用镜像法推导出三孔并行海底隧道渗流场解析解,并将公式进行了退化和数值验证。研究结果表明:按照等面积法将多心圆形断面简化为圆形断面分析对隧道总涌水量影响较小;该文解析解具有一定的精度,可以快速预测三孔并行海底隧道涌水量;由于隧道间的泄压作用,三孔并行海底隧道主隧道周边涌水量分布呈现出非对称性。

高铁海底隧道矿山-盾构对接段渗流应力耦合特征研究

矿山法与盾构法水下对接施工是海底隧道修建的关键技术难题,明确渗流-应力耦合特征是隧道对接段建设和运营安全的重要保障。采用有限元软件对现场对接施工方案进行三维数值模拟,基于数值模拟结果,分析了隧道不同施工区段的渗流特征、位移变形和应力变化规律,揭示了隧道矿山-盾构对接段施工对围岩扰动的渗流-应力耦合机制。结果表明:隧道开挖后,围岩中的孔隙水向隧道洞周及开挖面汇集并不断补给,导致孔隙水压力减小,并形成降水漏斗,隧道洞周渗流速度增加,在开挖阶段涌水量较大;受水力梯度影响,拱底处孔隙水压力最大,施工可通过设置排水措施,进行引排泄压;隧道断面开挖时,位移变形产生突变,受开挖面排水泄压影响,在隧道断面开挖前,拱底处产生竖向位移沉降;相较于盾构法,矿山法施工的扰动程度更大,在不同施工段落区段,采用矿山法施工的开挖断面主应力分布一致。研究可为海底隧道矿山法与盾构法水下对接工程安全性评价提供参考。

有限地层三孔并行海底隧道渗流场解析研究

研究目的:目前对海底隧道渗流场的研究大多基于半无限空间的单孔隧道,考虑实际工程常采用三孔并行的排布方式,且实际工程中隧道下方常存在相对不透水层或基岩等不透水边界,本文以渗流力学为基础采用镜像法和竖井理论推导有限厚度地层海底隧道渗流场解析解,将公式进行退化和数值验证,并对不透水边界距离、三孔隧道埋深、间距及注浆参数进行分析。研究结论:(1)隧道下方不透水边界对涌水量影响较大,当不透水边界距隧道中心为25r1时,对涌水量基本没有影响;(2)三孔并行隧道间渗流场存在相互影响,且随隧道间距的增加影响逐渐减弱,当隧道间距大于30r1时,涌水量基本没有影响;(3)三孔并行隧道涌水量随埋深增大呈现出先减小后增大趋势,埋深为2r1时涌水量最小;(4)三孔并行隧道涌水量随注浆圈厚度增大和渗透系数减小而减小,实际工程中应注浆密实度和注浆厚度并重;(5)本研究成果可为相关海底隧道工程的设计与施工提供参考。

潮汐对海底隧道工作面稳定性的影响研究

潮汐作用下水位变化触发海床地层应力的重分布,影响海底隧道施工中工作面围岩的稳定性。以青岛胶州湾第二海底隧道为工程背景,采用多相大变形数值计算方法—物质点法,分析了潮汐作用下水位变化对隧道开挖工作面围岩的破坏响应。通过数值模拟与现场监测数据的对比,验证了物质点法数值模拟方法的可行性。通过模拟196组不同围岩等级下的水位变化,探究海床沉降、围岩变形、塑性破坏区的分布和特征。结果表明:水位降低会增大施工期间隧道工作面的变形;水位变化与不良围岩参数的组合是隧道工作面失稳的关键,并得到了16组诱发工作面大变形失稳的参数组合。

基于AGRU-Trans融合模型的特长海底隧道交通量预测

为了使海底隧道交通管控部门更好地掌握准确的交通数据,给出行者提供更好的交通引导,通过对循环神经网络和Transformer算法的研究,结合GRU与Transformer模型算法优点并加入自注意力机制,提出一种基于AGRU-Trans融合模型的海底隧道交通量预测模型。选取胶州湾海底隧道市南-黄岛交通运行数据,通过AGRU-Trans融合模型与3种基准模型对比发现,LSTM,Transformer,GRU模型的平均绝对误差(MAE)相比AGRU-Trans分别大了31.48%,67.54%,20.57%;均方根误差(RMSE)分别增长了35.63%,38.45%,32.02%。结果表明:AGRU-Trans融合模型的预测结果与真实数据贴合性最好,预测精度均高于基准模型,因此,基于此方法可为胶州湾海底隧道管理部门对车辆进行精细化诱导及管控提供理论参考。

大连湾海底隧道工程中的水工设施文物保护设计

大连湾海底隧道穿过大连市中山区区级不可移动文物达里尼港旧址和大连港附属建筑的区域。为保证工程顺利建设,对海底隧道沿线不可移动文物北防波堤及丙码头开展文物保护设计工作。严格遵守国家文物保护法律法规,保证文物结构安全,恢复文物风貌,保持文物历史格局不变。以此制定了“拆卸、归安”的文物保护设计理念,对北防波堤及丙码头进行局部拆除,完成海底隧道工程后恢复文物原貌。