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。

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。

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。

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。

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。

考虑洞间影响的三孔并行海底隧道渗流问题分析

海底隧道渗流场的分析是隧道建设的基本问题,它与隧道围岩稳定性、工程防排水设施的布置密切相关.考虑现有的工程实际,海底隧道常采用"主隧道+服务隧道"的三孔并行方式穿越海峡.以实际工程为背景,建立了不同覆岩厚度下三孔并行海底隧道渗流计算模型,从涌水量、孔隙水压力、渗流速度、注浆参数方面分析了隧道渗流特性.研究结果表明,隧道互相靠近时,渗流场相互影响,无论是采用现行规范中所给出的隧道涌水量计算公式,还是精确解析解公式来预测三孔并行海底隧道主隧道涌水量时均会产生较大误差,将会高估隧道涌水量,最大误差可以达到40%;三孔隧道之间互为"泄压孔",降低了主隧道周边孔隙水压力和渗流速度;注浆作为隧道堵水的关键措施,考虑注浆圈厚度的同时也应该注重注浆的密实性.

广湛客专湛江湾海底隧道工程极限冲刷深度预测

湛江湾是在遂溪河谷基础上经海侵发育起来的潮汐汊道型溺谷海湾,湾内水深大,深槽内水流动力强,水流挟沙力大。基于河道地质条件、泥沙组成及水动力特征,利用水工模型试验手段,预测不利水文条件下隧址河段河床的最大冲刷深度。研究成果表明,以潮为主情况下,隧址河床未产生冲刷;以洪为主情况下,工程河段主槽冲刷后深泓线平面位置无变化,深泓冲深0.00~1.06 m。预测的极限冲刷深度可为过海隧道的科学埋设提供依据。

胶州湾第二海底隧道总体设计方案研究

胶州湾第二海底隧道具有超长、超大、超深、地质复杂、通风排烟困难、疏散救援难度大、两岸接线复杂、建设条件限制多等诸多特点。为了科学、安全、经济地建设胶州湾第二海底隧道,结合项目特点,对超长海底隧道的选址、工法、埋深、断面布置、通风排烟、疏散救援等关键问题进行研究,得出以下主要结论:1)超长海底隧道总体设计应突出地质选线理念,这是降低建设与运营风险、控制投资和保障工期的关键;2)结合具体地质和建设环境条件进行多工法比选、分段选择适宜的施工方法并确定合理埋深,是超长海底隧道总体设计的重要内容;3)胶州湾第二海底隧道海域段采用2条主线隧道+中间服务隧道的布置方式,在海域段主线隧道顶部设置风道,并创新提出2.5段通风方案,利用服务隧道兼作新风通道,解决了超长海底隧道的通风难题;4)隧道两端洞口设置管理中心,在服务隧道洞口设置应急管理站,并利用服务隧道、人行及车行横通道、盾构段疏散楼梯和下层纵向疏散通道组成完善的疏散救援系统,可保障超长海底隧道运营安全。

波浪作用下海底隧道氯离子侵蚀劣化时变分析

浅水区海底隧道处于复杂波动水力环境中,既有理论研究一般只在静水环境中计入氯离子自由扩散对隧道衬砌的侵蚀作用,而较少考虑海洋波浪力对衬砌结构腐蚀的促进作用。首先采用适用于浅水区的Stokes二阶波浪理论确定了海床表面的波浪压力,基于Biot固结理论获得了隧道衬砌周围的水压响应;接着利用改进的Fick第二定律同时考虑水压和浓度梯度驱动下的氯离子扩散,并采用指数型强度劣化模型描述服役时间内衬砌混凝土的劣化效应;最后结合波浪作用下衬砌氯离子侵蚀效应进行了海底隧道衬砌承载力计算,并将理论解析解与数值模型和既有的试验结果进行了对比,获得了较好的一致性。结果表明,忽略动态波浪压力对衬砌混凝土中氯离子渗流的促进作用,将低估衬砌混凝土内部的氯离子扩散速度,随着波浪周期增加,衬砌内部氯离子侵蚀入渗的最大深度明显增大;而不考虑衬砌强度劣化效应会明显高估隧道结构的服役寿命,不利于海底隧道服役期间的安全储备。

地铁隧道过海段复合衬砌参数的敏感性分析

以青岛地铁1号线胶州湾过海隧道为研究背景,选取了影响复合式衬砌外围水压力的9个主要影响因素,在利用Midas有限元数值分析软件的基础上,采用正交试验设计法分析了2种测试水平下这9个因素对水压力折减系数的显著性影响水平。结果表明:影响二次衬砌外围水压力大小的显著性因素为二次衬砌外围半径和围岩渗透系数与二次衬砌渗透系数的比值;影响初期支护外围水压力大小的显著性因素为围岩渗透系数与注浆圈渗透系数的比值、注浆圈厚度、围岩渗透系数与二次衬砌渗透系数的比值及隧道半径。其中,围岩渗透系数与二次衬砌渗透系数的比值对二次衬砌、初期支护的外围水压力均有显著性影响。因此,在海底隧道设计和施工过程中,应重点关注衬砌的渗透性能,注意支护结构的参数设计和选取,以保障海底隧道的顺利开挖及运营安全。