Rock mechanical problems and optimization for the long and deep diversion tunnels at Jinping Ⅱ hydropower station

According to site-specific environments such as high water pressures, high in-situ stresses and strong rockbursts, the design scheme of the long and deep diversion tunnels at Jinping II hydropower station was optimized to ensure construction safety. New drainage tunnels were considered. Furthermore, lining structures and grouting pressures were modified during the excavation of tunnels. The construction scheme was updated dynamically based on the complex geological conditions. For instances, the diversion tunnels were first excavated by drilling and blasting method at the first stage of construction, and then by the combination method of tunnel boring machine （TBM） and drilling and blasting, and finally by drilling and blasting method. Through optimized scheme and updated construction scheme, the excavation of diversion tunnel #1 was successfully completed in June, 2011. This paper summarizes the key issues in rock mechanics associated with the construction of the long and deep diversion tunnels at Jinping II hydropower station. The experiences of design and construction obtained from this project could provide reference to similar projects.

3D Finite Element Analysis of TBM Water Diversion Tunnel Segment Coupled with Seepage Field

In most studies of tunnel boring machine(TBM)tunnelling, the groundwater pressure was not considered, or was simplified and exerted on the boundary of lining structure. Meanwhile, the leakage, which mainly occurs in the segment joints, was often ignored in the relevant studies of TBM tunnelling. Additionally, the geological models in these studies were simplified to different extents, and mostly were simplified as homogenous bodies. Considering the deficiencies above, a 3D refined model of the surrounding rock of a tunnel is firstly established using NURBS-TIN-BRe P hybrid data structure in this paper. Then the seepage field of the surrounding rock considering the leakage in the segment joints is simulated. Finally, the stability of TBM water diversion tunnel is studied coupled with the seepage simulation, to analyze the stress-strain conditions, the axial force and the bending moment of tunnel segment considering the leakage in the segment joints. The results illustrate that the maximum radial displacement, the minimum principal stress, the maximum principal stress and the axial force of segment lining considering the seepage effect are all larger than those disregarding the seepage effect.

Numerical simulation of hydrodynamic characteristics during the diversion closure in a horizontal tunnel

Based on water inrush accident of 1841 working face of Desheng Coal Mine in Wu'an, Hebei province, China, an evaluation model of hydrodynamic characteristics of the project is set up and simulated using Matlab. It is assumed that the pipe flow would transform into seepage flow when the aggregates are plugged into the water inrush channel and the seepage flow would disappear along with grouting process. The simulation results show that the flow velocity will increase with an increase in height of aggregates accumulation body during the aggregates filling process; the maximum seepage velocity occurs on the top of plugging zone; and the water flow decreases with increasing plugging height of water inrush channel. Finally, the field construction results show that the water inrush channel can be plugged effectively by the compacted body prepared with aggregate and cement slurry.

Application of the strength reduction FEM to diversion tunnel plug stability

Firstly,the common design principles for diversion tunnel plug are generalized,and two kinds of numerical analysis methods are discussed.Then the strength reduction FEM is introduced in numerical model analysis and the design steps of the plug's length are illustrated.During the progress to determine the plug's length,the equivalent plastic strain on the potential slip surface is assumed as the flag to tell the failure against sliding,and the plug stability is overall estimated from the plastic zone range and connectivity.

Multiphase Flow Simulations through Tarbela Dam Spillways and Tunnels

Tarbela dam is one of the largest earth filled dam in the world used for power generation and irrigation purposes. Like all reservoirs the sediments inflow in the Tarbela reservoir has resulted in reduction in water storage capacity and is also causing damage to the tunnels, power generating units and ultimately to the plant equipment. This numerical study was performed to predict the flow patterns and characteristics in Tarbela dam. Tunnel 3 and 4 inlets;originally on the bed level were raised in the 3-D model and meshed. Analysis was performed using multiphase flow (water and air) for maximum inflow in the reservoir, i.e., considering summer season and discharging water through different locations, i.e., tunnels and spillways. Pressure, velocities, flow rate and free surface height results obtained were found in good agreement with the analytical and existing results where available. Results show uneven discharge through each gate due to maximum velocity near exits and overall stagnant phenomena of water within the reservoir. Maximum velocity was observed along the spillways outlet. Strong vortex motion was observed near the spillways outlet and tunnel inlets. New design of Tunnel 3 and 4 were suggested to WAPDA in order to decrease the sediment inflow and improvements in design of the spillways were suggested.

Experimental study of drag reduction in flumes and spillway tunnels

Experiments in an open flume model and spillway tunnel model were carried out using drag reduction techniques. Two drag reduction techniques were adopted in the experiments： polymer addition and coating. The drag reduction effect of a polyacrylamide （PAM） solution and dimethyl silicone oil coating were studied in the flume model experiments, and the results were analyzed. Experiments were then carded out with a model of the Xilnodu Hydropower Station, the second largest dam in China. In order to reduce the resistance, the spillway tunnels were internally coated with dimethyl silicone oil. This is the first time that these drag reduction techniques have been applied to so large a hydraulic model. The experimental results show that the coating technique can effectively increase flood discharge. The outlet velocity and the jet trajectory distance are also increased, which enhances the energy dissipation of the spillway tunnel.

Research on the optimal design of spillway tunnel

In order to meet the needs of various tasks of water conservancy project, tunnel excavation under the ground, called hydraulic tunnel. Hydraulic tunnel according to the functions of flood discharge, water diversion, irrigation, water supply, and the construction diversion tunnel of desilting emptying. Nowadays, water conservancy project on flood discharge runnel design requirements more and more high, so the factors taken into account the amount of spillway tunnel engineering, engineering cost, structure design and other factors to evaluate nature of the spillway tunnel is very important. Therefore, in actual construction, of spillway tunnel of optimization design, whether from the economic point of view, or from the point of view of safety and applicability are necessary. This article mainly from the overall layout of flood discharge tunnel, structure design and so on, and then discuss the optimization scheme.

Analysis of the Stability and Mechanical Characteristics of the Jointed Surrounding Rock and Lining Structure of a Deeply Buried Hydraulic Tunnel

On-site monitoring and numerical simulation have been combined to analyze the stability of the jointed surrounding rock and the stress inside the lining structure of a sample deeply buried hydraulic tunnel.We show that the deformation around the tunnel was mainly concentrated in the range 51.37 mm∼66.73 mm,the tunnel circumference was dominated by shear failure,and the maximum plastic zone was about 3.90 m.When the shotcrete treatment was performed immediately after the excavation,the deformation of the surrounding rock was reduced by 58.94%∼76.31%,and the extension of the plastic zone was relatively limited,thereby leading to improvements in terms of the stability of surrounding rock.When the support was provided at different time points,the stress of the surrounding rock in the shallow part of the tunnel was improved everywhere.In the tunnel section with high ground stress and joint development,when 10 cm steel fiber concrete spray layer and 40 cm C25 concrete secondary lining were used,the maximum tensile stress on the lining structure was 0.89 MPa,i.e.,it was less than the tensile strength of concrete,which indicates that the internal force of the lining can meet the overall requirements.

基于不同围岩特性的隧洞衬砌厚度优化分析

基于不同围岩特性的隧洞衬砌厚度优化既能实现安全要求又可以降低工程投资。结合某电站引水隧洞,采用有限元分析法对隧洞在不同围岩特性下的受力情况进行数值模拟,计算分析在不同衬砌厚度下的应力、配筋及裂缝宽度情况,综合考虑安全性和经济性对结果进行分析比较,提出了针对不同围岩特性的隧洞衬砌厚度优化方案。研究结果表明,隧洞衬砌在运行期的应力情况是影响衬砌配筋的关键因素,不同围岩特性下衬砌厚度的选择应充分考虑隧洞衬砌应力、所需配筋及裂缝宽度因素影响,当衬砌达到一定厚度后,所需配筋及裂缝宽度趋于稳定。

岩溶隧洞突涌水灾害风险评价研究

受复杂地质条件的影响,岩溶隧洞在施工过程中极易发生突涌水灾害。为准确评估岩溶隧洞突涌水风险等级,将结构方程模型(SEM)与改进的模糊综合评价法(FCEM)相结合,构建岩溶隧洞突涌水风险评价模型。从地形地貌、气象水文、地层因素、地质构造、岩溶水文地质、施工因素6个方面深入研究;利用SEM确定各指标标准化路径系数并求得其权重,运用改进FCEM法对岩溶隧洞突涌水风险等级进行评价;以滇中引水工程昆呈隧洞为应用实例,利用Crystal Ball软件验证模型的有效性。结果表明:昆呈隧洞有90%的几率处于52~73分值区间范围内(Ⅲ级风险),与现场实际情况一致,表明基于SEM-改进FCEM法构建的岩溶隧洞突涌水风险评价模型具有一定的适用性;其中岩溶水文地质、地质构造、气象水文是该隧洞的主要影响因素,施工中应加强对这几方面的监控和量测,避免发生突涌水灾害。研究成果可为类似岩溶隧洞工程提供参考。

黑河连接洞开挖爆破对黑河引水洞稳定性的影响

鉴于施工支洞与主隧洞交叉段复杂的受力状态及稳定性问题日益引起关注,提出了兼顾考虑现场位差爆破时炸药段位的群孔爆破简化方法,拟定相应的隧洞开挖爆破动力荷载,采用三维动力有限元分析方法,研究了黑河连接洞与黑河引水隧洞交叉施工过程中,连接洞开挖爆破振动对已建引水洞围岩稳定及衬砌结构安全性的影响。结果表明,黑河引水洞衬砌各关键点振动速度随着与爆破荷载距离减小而逐渐增大,最大振速主要发生在交叉口往交叉角为锐角方向17m范围内,衬砌振速在0.733~9.76cm/s之间;爆破的衰减速度较快,在进行爆破时,应考虑爆破点位置以减少多余的处理措施。根据规范要求,仅有1个监测点最大振速略高于最低标准,且超出时间很短,可认为实施八期爆破施工满足要求。

南水北调中线北京段岩体隧洞围岩变形模量分析研究

岩体力学参数是影响地下工程围岩稳定的重要因素,确定合理的岩体变形模量对隧洞设计至关重要。结合南水北调中线北京段西甘池试验洞工程,对岩体进行静载荷试验分析研究,详细介绍试验点岩体的加卸载变形关系曲线,获得西甘池隧洞岩体变形模量参数建议值,为工程设计提供依据,并以期为类似工程的设计和施工提供参考。研究结果表明:试验压力较小时,各试点岩体变形或弹性模量的变化曲线有的升、有的降,试验压力大于0.4 MPa以后,各试点的变形模量和弹性模量逐渐趋于稳定;隧洞围岩变形控制及支护结构设计时,应根据各段围岩的岩性(大理岩、滑石片岩)、结构完整性、节理裂隙的空间展布方式以及发育充填情况等综合考虑,结合工程类比和地质经验最终确定岩体弹性参数的基本代表值。研究的方法和结论可为类似条件下隧洞工程的设计、施工提供参考和借鉴。

导流洞双层进水口优化与传统进水口对比研究

为了研究导流洞双层进水口优化体型后的水力特性,并对其与传统进水口布置进行比较,基于某抽水蓄能电站导流洞的设计参数,采用Fluent软件中的VOF水动力模型进行了三维数值模拟.通过改变竖井宽度,即改变水平洞与竖井进口面积比、去除竖井以及采用常规喇叭口进水口3种方案,对双层进水口进行了比较分析.分析重点包括相对流量、水流弗劳德数、相对压强以及水头损失系数等4个方面的特性.研究结果表明:面积比的变化对双层进水口的流量分配和流速分布产生了显著影响.相比于去除竖井的水平进水口,双层进水口在增加泄流量、降低进水口水头损失方面具有明显优势.在孔流流态下,双层进水口的泄流能力已接近单独采用喇叭口泄洪洞.结果显示,双层进水口的泄流主要以竖井下泄为主.在孔流流态时,双层进水口的泄流受下游泄洪洞断面的控制.其独特优势在于能快速对导流期的水平洞进行封堵,并在运行期间迅速进行泄放洞的改建,以便尽快进入运行状态.

两条轴线平行布置的泄洪洞出口联合消能工布置形式研究

针对芝瑞抽水蓄能电站下水库两条轴线平行布置的泄洪排沙洞,原设计方案出口联合消能工存在消能效果差的问题,通过选用单体正态水工模型,基于水力相似准则进行水工模型试验,对出口联合消能工的布置形式进行研究。试验实测数据表明,最终推荐方案可有效提高消能效率、改善水流流态、优化设计方案,并达到了减少工程投资的目的,有效地解决了轴线平行布置的泄洪洞出口联合消能问题。

抽水蓄能电站无压泄洪洞台阶消能型式研究

基于甘肃某抽水蓄能电站泄洪洞洞内消能设计,探讨在流量及底坡恒定的条件下,台阶尺寸与消能率的相关关系,探寻台阶尺寸的初拟原则,采用现行NB/T 10867-2021《溢洪道设计规范》中跌落流上限及滑行流下限的经验公式(坡角范围为2.86°~59.53°)进行台阶消能流态的初步判别,通过Chanson半经验公式理论计算和CFD数值模拟水工隧洞底板布置不同台阶尺寸对应的消能特性。结果表明:在流量及坡度不变的情况下,台阶尺寸(台阶步长及高度)对消能率的影响有限;台阶尺寸越大,水力要素受流动边界条件影响和扰动越明显;初拟台阶尺寸时,应分析水流掺气点位置及出现掺气均匀流位置随台阶尺寸变化向上游移动的速率,同时结合实际边界条件、便于施工及后期运维等方面综合考虑,台阶高差宜控制在0.20~0.60 m。

硬梁包水电站方变圆大断面隧洞开挖技术

硬梁包水电站引水隧洞进口方变圆大断面洞室开挖通过先进行安全治理、锁口支护、超前预支护等措施后再进入洞段施工,先进行导洞开挖,再利用导洞开挖取得的技术参数和其所揭示的实际地质情况完成扩挖和分段分层开挖,施工时大量采用光爆和预裂爆破技术与工艺,抓住质量关键并严格过程控制,有效地保证了工程控制目标,效果明显,所取得的经验可为类似工程施工借鉴。

基于TBM掘进大数据和特征参数的引水隧洞塌方分析

针对TBM掘进过程中缺乏对围岩质量和塌方风险快捷、精准的预测预警方法,通过对TBM掘进大数据的深入挖掘,结合对实际工程塌方数据的剖析,提出潜在塌方风险的辅助判断依据。首先,对冗杂、连续的原始采集数据进行预处理,获取高质量的分析数据;然后,基于参数的相关性分析提出围岩特征参数的计算方法,并围绕特征参数的合理性和适用性,通过理论推导、室内试验和现场原位掘进试验进行论证;最后,结合实际的TBM塌方案例分析特征参数与围岩地质情况的相关性,提出塌方风险快速判断依据。结果表明:基于TBM掘进数据获取的围岩特征参数在一定程度上反映了围岩质量,其数值与围岩质量正相关,当其数值显著降低、变幅超过69.2%时,当前的掘进循环极大可能存在塌方风险。

浅埋隧道双侧壁导坑法施工数值模拟研究

为准确评价浅埋隧道施工过程的围岩稳定性,利用ANSYS有限元数值分析软件,对沈阳地铁10号线区间浅埋隧道双侧壁导坑法施工进行数值模拟,研究了浅埋隧道施工过程的力学特性及变形规律。结果表明:开挖中上导洞后,围岩位移、应力和支护结构内力显著增大,占整个导洞开挖的50%,且最大位移、应力和支护结构弯矩集中在拱顶、初期支护连接的薄弱处;地表沉降量随时间变化增长趋缓,开挖90 d后趋于稳定,且离开挖面越近,沉降量越大,最大沉降点出现在最先开挖的中上导洞位置;隧道开挖10 d内拱顶下沉较快,随开挖掌子面远离监测点,拱顶沉降速率逐渐减小,开挖顺序对拱顶沉降影响较大,往往先开挖的位置拱顶沉降最大。现场监测结果表明:数值计算与现场监测结果比较吻合,验证了数值分析的合理性。研究成果对浅埋隧道的安全、经济施工具有借鉴意义。

TBM引水隧洞施工模拟管片力学特性影响因素分析

为探究不同影响因素对引水隧洞施工过程管片位移和应力的影响,以榕江-关埠引水隧洞工程典型区间段为例,建立“围岩-管片-内张钢圈”组合结构的三维精细化有限元模型,模拟引水隧洞工程的施工开挖过程,研究隧洞埋深、围岩类型和注浆体刚度3个因素对施工期管片力学特性的影响。结果表明:TBM引水隧洞施工开挖过程中管片位移随着开挖环数增加而逐渐增大,减小隧洞埋深、增强围岩类型(Ⅴ类→Ⅱ类)和增强注浆属性将会降低管片的位移,其最大值分别为1.670 mm、1.406 mm和1.863 mm;管片压应力随开挖环数增加而逐渐增大,拉应力呈先减小后增加的趋势;增大隧洞埋深、降低围岩类型(Ⅱ类→Ⅴ类)和削弱注浆属性将会增加管片的应力,其中管片压应力最大值分别为5.765 MPa、4.833 MPa和6.165 MPa,均满足规范要求。在实际工程中,建议对埋深大和围岩质量差的隧洞工程重点监测,研究结果可为类似的引水隧洞工程提供参考。

敞开式TBM开挖隧洞围岩变形安全评价方法及应用

当TBM开挖隧洞遭遇不良地质条件下的围岩大变形地质灾害时,通常会造成卡机或侵限等风险。开展TBM开挖隧洞围岩变形安全评价工作对降低卡机或侵限等风险具有重要的现实意义。通过分析敞开式TBM开挖隧洞围岩变形特点,建立了敞开式TBM开挖隧洞围岩变形安全评价方法。该方法通过采用三维数值分析和围岩变形现场监测手段,可获得围岩在护盾区间以及出露护盾后的变形,从而实现敞开式TBM开挖隧洞围岩变形安全性判别。在滇中引水工程香炉山隧洞的工程应用表明,所提方法能够有效判别不同支护方案下的围岩变形安全性,从而为敞开式TBM开挖隧洞施工期支护方案实时调整提供依据。