Stress characteristics of surrounding rocks for inner water exosmosis in high-pressure hydraulic tunnels

Seepage and stress redistribution are the main factors affecting the stability of surrounding rock in high-pressure hydraulic tunnels.In this work,the effects of the seepage field were firstly simplified as a seepage factor acting on the stress field,and the equilibrium equation of high pressure inner water exosmosis was established based on physical theory.Then,the plane strain theory was used to solve the problem of elasticity,and the analytic expression of surrounding rock stress was obtained.On the basis of criterion of Norway,the influences of seepage,pore water pressure and buried depth on the characteristics of the stress distribution of surrounding rocks were studied.The analyses show that the first water-filling plays a decisive role in the stability of the surrounding rock; the influence of seepage on the stress field around the tunnel is the greatest,and the change of the seepage factor is approximately consistent with the logarithm divergence.With the effects of the rock pore water pressure,the circumferential stress shows the exchange between large and small,but the radial stress does not.Increasing the buried depth can enhance the arching effect of the surrounding rock,thus improving the stability.

Safety estimation of high-pressure hydraulic cylinder using FSI method

Hydraulic cylinder is a primary component of the hydraulic valve systems.The numerical study of hydraulic cylinder to evaluate the stress analysis,the life assessment and the performance of operation characteristics in hydraulic cylinder were described.The calculation of safety factor,fatigue life,piston chamber pressure,rod chamber pressure and the change of velocity of piston with flow time after the beginning of hydraulic cylinder were incorporated.Numerical analysis was performed using the commercial CFD code,ANSYS with unsteady,dynamic mesh model,two-way FSI(fluid-structure interaction)method and k-εturbulent model.The internal pressure in hydraulic cylinder through stress analysis show higher than those of the yield strength.

Ground motion duration effect on responses of hydraulic shallow-buried tunnel under SV-waves excitations

Although intensive research of the influence of ground motion duration on structural cumulative damage has been carried out, the influence of dynamic responses in underground tunnels remains a heated debate. This study attempts to highlight the importance of the ground motion duration effect on hydraulic tunnels subjected to deep-focus earthquakes. In the study, a set of 18 recorded accelerograms with a wide-range of durations were employed. A spectrally equivalent method serves to distinguish the effect of duration from other ground motion features, and then the seismic input model was simulated using SV-wave excitation based on a viscous-spring boundary, which was verified by the time-domain waves analysis method. The nonlinear analysis results demonstrate that the risk of collapse of the hydraulic tunnel is higher under long-duration ground motion than that of short-duration ground motion of the same seismic intensity. In a low intensity earthquake, the ground motion duration has little effect on the damage energy consumption of a hydraulic tunnel lining, but in a high intensity earthquake, dissipation of the damage energy and damage index of concrete shows a nonlinear growth trend accompanied by the increase of ground motion duration, which has a great influence on the deformation and stress of hydraulic tunnels, and correlation analysis shows that the correlation coefficient is greater than 0.8. Therefore, the duration of ground motion should be taken into consideration except for its intensity and frequency content in the design of hydraulic tunnel, and evaluation of seismic risk.

Some Issues on Cement Grouting of Hydraulic Tunnel

Based on the practices of construction supervision to cement grouting at the reservoir emptying and power tunnels of the TSQ stage Ⅰ Hydropower station, some issues on quality control of cement grouting of hydraulic tunnel are discussed, and corresponding suggestions are put forward for revision of current standard (SL62-94). It is regarded that the refilling grouting could not be used for remedying the thickness of concrete lining; the end sealing of refilling grouting section should not be neglected; higher grouting pressure would be used. For the consolidation grouting, grout return pipe should be placed at the grout hole top for pure pressure type grouting; five-grade water cement ratio of grout mix is suggested; a certain standard should be specified for changing the grout to thicker mix by skipping the intermediate grade; the standard for ending the grouting should be relaxed. In current grouting standard, some terms should be complemented for contact grouting of steel penstock and spiral case and for plug grouting of circular-anchor hole.

Fractured rock mass hydraulic fracturing under hydrodynamic and hydrostatic pressure joint action

According to the stress state of the crack surface, crack rock mass can be divided into complex composite tensile-shear fracture and composite compression-shear fracture from the perspective of fracture mechanics. By studying the hydraulic fracturing effect of groundwater on rock fracture, the tangential friction force equation of hydrodynamic pressure to rock fracture is deduced. The hydraulic fracturing of hydrostatic and hydrodynamic pressure to rock fracture is investigated to derive the equation of critical pressure when the hydraulic fracturing effect occurs in the rock fracture. Then, the crack angle that is most prone to hydraulic fracturing is determined. The relationships between crack direction and both lateral pressure coefficient and friction angle of the fracture surface are analyzed. Results show that considering the joint effect of hydrodynamic and hydrostatic pressure, the critical pressure does not vary with the direction of the crack when the surrounding rock stationary lateral pressure coefficient is equal to 1.0. Under composite tensile-shear fracture, the crack parallel to the direction of the main stress is the most prone to hydraulic fracturing. Under compression-shear fracture, the hydrodynamic pressure resulting in the most dangerous crack angle varies at different lateral pressure coefficients; this pressure decreases when the friction angle of the fracture surface increases. By referring to the subway tunnel collapse case, the impact of fractured rock mass hydraulic fracturing generated by hydrostatic and hydrodynamic pressure joint action is calculated and analyzed.

Nonlinear Static and Dynamic Stiffness Characteristics of Support Hydraulic System of TBM

Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key components.The support system,an important part of TBM,is one path through which vibrational energy from the cutter head is transmitted.To reduce the vibration of support systems of TBM during the excavation process,based on the structural features of the support hydraulic system,a nonlinear dynamical model of support hydraulic systems of TBM is established.The influences of the component structure parameters and operating conditions parameters on the stiffness characteristics of the support hydraulic system are analyzed.The analysis results indicate that the static stiffness of the support hydraulic system consists of an increase stage,stable stage and decrease stage.The static stiffness value increases with an increase in the clearances.The pre-compression length of the spring in the relief valve a ects the range of the stable stage of the static stiffness,and it does not a ect the static stiffness value.The dynamic stiffness of the support hydraulic system consists of a U-shape and reverse U-shape.The bottom value of the U-shape increases with the amplitude and frequency of the external force acting on the cylinder body,however,the top value of the reverse U-shape remains constant.This study instructs how to design the support hydraulic system of TBM.

In situ experimental study on TBM excavation with high-pressure water-jet-assisted rock breaking

China’s first high-pressure hydraulically coupled rock-breaking tunnel boring machine(TBM) was designed to overcome the rock breaking problems of TBM in super-hard rock geology, where high-pressure water jet system is configured, including high-flow pump sets, high-pressure rotary joint and high-pressure water jet injection device. In order to investigate the rock breaking performance of high-pressure water-jet-assisted TBM, in situ excavation tests were carried out at the Wan’anxi Water Diversion Project in Longyan, Fujian Province, China, under different water jet pressure and rotational speed. The rock-breaking performance of TBM was analyzed including penetration, cutterhead load, advance rate and field penetration index. The test results show that the adoption of high-pressure water-jet-assisted rock breaking technology can improve the boreability of rock mass, where the TBM penetration increases by 64% under the water jet pressure of 270 MPa. In addition, with the increase of the water jet pressure, the TBM penetration increases and the field penetration index decreases. The auxiliary rock-breaking effect of high-pressure water jet decreases with the increase of cutterhead rotational speed. In the case of the in situ tunneling test parameters of this study, the advance rate is the maximum when the pressure of the high-pressure water jet is 270 MPa and the cutterhead rotational speed is 6 r/min. The technical superiority of high-pressure water-jet-assisted rock breaking technology is highlighted and it provides guidance for the excavation parameter selection of high-pressure hydraulically coupled rock-breaking TBM.

Endurance time history analysis of the seismic behavior and performance assessment of hydro-chemo-mechanical degradation-affected hydraulic tunnels with service time

Subjected to the coupling action of multiple hazards in hydraulic engineering,hydraulic tunnels may be corroded and damaged to varying degrees during their service lives,which will decrease the seismic performance of these structures.However,the research and seismic design of significant hydraulic engineering projects focus on investigating the structural response based on the design material parameters,which may overestimate the seismic capacity of structures during their service lives.In this paper,research is performed to identify the effect of hydro-chemo-mechanical corrosion on the seismic performance of hydraulic tunnels with different burial depths.A plastic damage model of time-varying concrete degradation induced by the hydro-chemo-mechanical effect is first determined and implemented,and the endurance time acceleration records are generated in MATLAB.Then,a study of the endurance time relationship of hydro-chemomechanical corrosion-affected hydraulic tunnels,considering the fluid–structure-surrounding rock interaction systems throughout the service period,is undertaken to directly associate the structural response with the predefined evaluation index.Moreover,this research constructs 3D time-varying fragility surfaces considering the hydro-chemo-mechanical effect and seismic intensity.The results show that the relative displacement of hydro-chemo-mechanical corrosion-affected hydraulic tunnels is larger than that of nonaffected hydraulic tunnels.Hydro-chemo-mechanical effect-induced material deterioration will lead to an increase in the cumulative damage(crack)area and damage degree of hydraulic tunnels.Additionally,the seismic fragility analysis shows that the longer the service time of hydro-chemo-mechanical corrosion-affected hydraulic tunnels,the more likely they are to collapse.Hence,attention should be given to improving the aseismic capacity of hydro-chemo-mechanical corrosion-affected hydraulic tunnels in future seismic design and performance assessments.

Analysis of unlined pressure shafts and tunnels of selected Norwegian hydropower projects

Norwegian hydropower industry has more than 100 years of experiences in constructing more than4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m（equivalent to almost 10.5 MPa） reached at unlined pressure tunnel of Nye Tyin project. Experiences gained from construction and operation of these unlined pressure shafts and tunnels were the foundation to develop design criteria and principles applied in Norway and some other countries. In addition to the confinement criteria, Norwegian state-of-the-art design principle for unlined pressure shaft and tunnel is that the minor principal stress at the location of unlined pressure shaft or tunnel should be more than the water pressure in the shaft or tunnel. This condition of the minor principal stress is prerequisite for the hydraulic jacking/splitting not to occur through joints and fractures in rock mass. Another common problem in unlined pressure shafts and tunnels is water leakage through hydraulically splitted joints or pre-existing open joints. This article reviews some of the first attempts of the use of unlined pressure shaft and tunnel concepts in Norway, highlights major failure cases and two successful cases of significance, applies Norwegian criteria to the cases and reviews and evaluates triggering factors for failure.This article further evaluates detailed engineering geology of failure cases and also assesses common geological features that could have aggravated the failure. The minor principal stress is investigated and quantified along unlined shaft and tunnel alignment of six selected project cases by using threedimensional numerical model. Furthermore, conditions of failure through pre-existing open joints by hydraulic jacking and leakage are assessed by using two-dimensional fluid flow analysis. Finally, both favorable and unfavorable ground conditions required for the applicability of Norwegian confinement criteria in locating the unlined pressure shafts and tunnels for geotectonic environment different from that of Norway are highlighted.

Roughness evaluation in shotcrete-lined water tunnels with invert concrete based on cases from Nepal

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.

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.

Advantages of employing multilevel monitoring wells for design of tunnels subjected to multi-aquifer alluvial

For tunnels being excavated through multiple knowledge of the aquifers’hydraulic head becomes essential for determining groundwater inflow into the tunnel and analyzing its stability,specifically using multilevel monitoring systems.In the multi-aquifer alluvial section of the Glas tunnel(Iran),since the hydraulic head calculations were based on the data obtained from single-piezometer boreholes,the excavation risk was assessed to be at high level and the tunnel seemed to be unstable,thus an incorrect conclusion was derived from the misleading data.To take cost mitigation measures into account,it was necessary to calculate the hydraulic head at tunnel level accurately.By installing nested and clustered wells the mean hydraulic head was measured to be 70 m,significantly different from the 90 m previously determined by boreholes.Considering the updated value,the groundwater inflow and bulkhead load,formerly calculated as 0.65 m^(3)/s and 9.5 bars,were determined to be 0.49 m^(3)/s and 7.5 bars,respectively.

Geostress Measurement for Deep-Buried Long Tunnel through Niba Mountain

In the geostress measurement for Niba Mountain on Ya＇an-Lugu Expressway, results of Kaiser effect tests combined with focal mechanism solution were compared with those obtained by hydraulic fracturing method, both of which are basically coincident. It is shown that the principal stress increases with burial depth ; the maximum principal stress is about 45 MPa, which is larger near fault zones because of stress concentration, and its direction ranges from N20°W to N75°W.

超深勘察钻孔ASR法地应力测试技术应用

宝灵山隧道是某铁路先开段的重难点控制性工程,其中宝灵山DZ-06勘察钻孔深2118.00 m,是该段深度最大的控制性勘察钻孔。在钻孔的2072.53、2084.27 m深度选取合适岩心,采用ASR法(非弹性应变恢复法)开展了地应力测试,并与该钻孔采用水压致裂法获取的地应力结果进行对比,同时验证了ASR法对于估测超深钻孔的三维地应力大小和方向的实用价值。结果表明:在钻孔2072.53~2084.27 m深度范围,ASR法2个测点获取的最大主应力、中间主应力、最小主应力平均值分别为59.70、54.03、30.74 MPa,最大主应力近水平,方向近SN向,说明该区域以水平构造应力为主;ASR法的最大主应力测试结果均值与水压致裂法测试结果回归值一致性很好,最小主应力测试结果均值与水压致裂法测试结果回归值的一致性处于合理范围,两种方法的水平主应力方向测试结果基本一致。

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.

嵌入式可冲洗隧道排水管水力计算模型研究

为解决嵌入式可冲洗隧道排水管物理参数的设计问题,提升隧道排水系统的工作效率,在此应用场景上构建了一种水力计算模型。嵌入式可冲洗隧道排水管不同于“先堵塞,再疏通”的治理思路,其工作方式为定期接入高压水泵,泵送高压水进入冲洗管,在结晶物还未沉积牢固时通过冲洗管上的孔洞冲刷外部排水管壁,达到预防排水管堵塞的目的。基于此场景构建的嵌入式可冲洗隧道排水管水力计算模型,满足水头损失一致的假设,由修正后的伯努利方程、杨海涛水头损失公式和达西-维斯巴赫公式构建冲洗管相邻孔之间的冲洗速度迭代公式,由此计算出各冲洗孔冲洗速度的解析解。理论计算结果表明:冲洗孔水流速度随着沿程水头损失服从严格的速度衰减规律,验证了水力计算模型的合理性。并通过数值模拟分析得出:理论推导结果和数值试验计算结果基本符合一致,对比误差平均值为4.3%;理论推导结果和数值模拟计算结果在管道末尾时差距较大,主要原因是实际流体会在末端形成回流,改变管道内部流场变化,而解析解则是严格遵循沿程水头损失规律。最后,归纳不同工况所需水流的进口速度和进口流量规律:冲洗管进口速度随冲洗孔间距增大而减小,随冲洗孔直径增大而增大;冲洗管进口流量随冲洗孔间距增大而减小,随冲洗孔直径增大而增大。

基于全景展开图像的水工隧洞渗水侵蚀病害快速检测方法研究

为解决水工隧洞尺寸较小、断面形式多变、洞内环境复杂、无信号覆盖给检测图像快速采集带来的难题,研制出一种无信号覆盖下图像实时传输以及适用于不同断面、尺寸下隧洞全断面采集的水工隧洞检测系统,采集重叠率和精度满足三维重建及对自主研发的衬砌展开影像生成器的要求;针对隧洞表观病害传统算法速度慢、精度低等问题,引入DenseNet主干网络和ECA注意力机制对YOLOv5检测算法进行改进,优化特征提取能力;针对单张图像识别难以反映病害整体分布、全景展开图尺寸过大网络难以捕获有效特征等问题,以全景展开图底层图像为种子点,利用方向搜索结合目标检测算法提出一种“段-环-点”的隧洞常见表观病害快速识别算法。现场应用表明:1)相比YOLOv7-tiny、YOLOv8、YOLOv9等模型,改进的YOLOv5模型在mAP和F 1上均有明显提高,可有效提升复杂背景下病害识别与边界定位精度,显著减少误检和漏检现象;2)所提技术适用于圆涵、箱涵等不同类型、尺寸的水工隧洞表观图像快速获取与全景识别,能够用于隧洞表观病害的展示和快速定位,可为病害整治措施的及时制定提供依据。

图像识别技术在水工隧洞收敛变形监测中的应用

基于图像识别技术的水工隧洞收敛变形监测技术,是实现水工隧洞全断面收敛变形简便、易操作的自动化监测的重要手段。在实践应用中,基于图像识别技术实现了靶标自动识别和位移自动测读,测量精度可控制在2 mm之内,通过试验获得了最佳靶标直径和适宜的拍摄距离参数,靶标适宜直径范围为150~250 mm,适宜拍摄距离根据洞径选择3~10 m,并结合某施工期水工隧洞工程进行实际应用,取得了良好的应用效果,可显著减少人工监测工作量,大大提高监测工作效率,研究结果可为隧洞安全监测提供重要参考和技术支撑。

穿越岩溶地区隧洞施工开挖防渗措施研究

穿越岩溶地区隧洞在施工开挖期极易遭遇涌水突泥现象,如何选择合适的防渗措施减少隧洞渗流量一直是热点问题。依托某引调水工程,建立岩溶地区复杂地层三维有限元模型,重点考虑洞顶回填混凝土、洞周注浆圈、混凝土防渗墙3种防渗措施,研究了隧洞开挖过程中孔隙水压力及隧洞渗流量的变化规律,分析了防渗墙和注浆圈渗透系数对渗流特征的影响。结果表明:在本工程中,混凝土防渗墙对隧洞孔隙水压力分布的影响非常大,防渗墙之间水位降低程度明显,而洞周注浆圈对隧洞渗流量的影响最大,施工时要保证注浆圈的质量;孔隙水压力随着与隧洞中心水平距离增加而增加,随着与隧洞中心竖直距离增加呈现先增大后减小的变化趋势;随着注浆圈或防渗墙渗透系数增加,注浆圈或防渗墙区域内的孔压增长速率逐渐降低,隧洞渗流量不断增大。

内水渗漏软化基底对盾构隧洞衬砌管片受力性能的影响分析

水工盾构隧洞在运行过程中存在内水渗漏导致基底软化的风险,基底软化将对隧洞管片受力变形产生影响。依托实际水工盾构隧洞工程,构建了由管片、灌浆体和围岩组成的三维有限元数值模型,针对Ⅴ类围岩条件下因渗漏导致基底均匀和不均匀软化的状况,研究了管片的受力性能变化规律。结果表明:在内外荷载作用下,管片的环向应力、竖向位移和定位销应力均随基底软化深度的增加而增大,均匀软化条件下仰拱管片出现峰值为1.88 MPa的拉应力,存在管片开裂风险;基底软化导致定位销应力增大,而管片竖向位移的变化幅度较小。研究成果可为水工盾构隧洞的安全运行监测提供科学依据。