01 December 2022, Volume 39 Issue 12

    

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  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 0-0.

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ENGINEERING GEOLOGY SURVEY OF TUNNELS
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  Monitoring the Geostress of Rock Mass in Fault Zone Using Hollow-Inclusion Strain Gauge

  HAN Xiao-yu, DONG Zhi-hong, FU Ping, LIU Yuan-kun

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 1-7. https://doi.org/10.11988/ckyyb.20220672

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  The hollow-inclusion(HI) strain gauge is used for the first time to monitor the geostress of rock mass in fault zone. A cloud monitoring system based on half-bridge measurement circuit of Wheatstone bridge was established with the hollow-inclusion strain gauge buried at the depth of 24 m in the large-diameter borehole drilled at appropriate position by using centering device and cement paste grouting method during tunnel excavation. Only the elastic parameters of cement paste and hollow inclusion material were considered to calculate the correction coefficient. The three-dimensional stress increment was calculated after the initial time of strain calculation was determined by analyzing the law of monitoring data. Results showed that, with September 16, 2021 as the initial calculation date, the range of the first principal stress (σ₁) in the fourth and fifth period was 10.3~15.0 MPa with a gentle dip W direction; the second principal stress (σ₂) ranged between 3.1 MPa and 4.6 MPa, with a steep dip angle from NEE direction to SEE direction; the third principal stress (σ₃) varied between 0.2 MPa and 1.8 MPa, and the direction is gentle dip angle near S direction. The components of maximum horizontal principal stress (σ_H) and minimum horizontal principal stress (σ_h) varied from 10.1 MPa to 13.9 MPa, and 0.2 MPa to 1.8 MPa, respectively. The direction of maximum horizontal principal stress (α_H) was nearly EW. The results demonstrate that the initial calculation time determined by analyzing monitoring data is more rational. The stress monitoring of hollow inclusion strain gauge is affected by multiple factors including excavation-caused stress disturbance and one-time stress and deformation adjustment of the monitored segment. The obtained σ_H and α_H are close to in-situ stress test results, and the monitoring result reflects the stress field characteristics of the Longpan-Qiaohou fault zone.
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  Key Technologies of Investigating Xianglushan Tunnel of Central Yunnan Water Diversion Project

  CHEN Chang-sheng, ZHANG Hai-ping, ZHOU Yun, LI Yin-quan, SHI Cun-peng, WANG Wang-sheng

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 8-14. https://doi.org/10.11988/ckyyb.20221085

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  The Central Yunnan Water Diversion Project features extremely complex geological structure background and seismic geological conditions. With a total length of 62.60 km and a maximum buried depth of 1 450 m, Xianglushan tunnel crosses the Hengduan Mountains in northwest Yunnan, the watershed of Jinsha River and Lancang River, and several regional deep faults. It is the longest single tunnel with the largest buried depth in the Central Yunnan Water Diversion Project and is also the most difficult to construct large, deep and super long tunnel with the most complex geological condition in water conservancy projects under construction in China. In view of the major engineering geological problems and the potential risks of groundwater environmental impact, we systematically summarize the key survey technologies including 3S-based geological remote sensing interpretation, magnetotelluric sounding, kilometer-level deep hole exploration and testing, route selection of large deep-buried and super long tunnels in complex karst areas, and numerical simulation of three-dimensional seepage field of groundwater. We also developed some key technologies of advanced geological prediction applicable for large, deep-buried, and long tunnels in complex geological conditions, kilometer-level deep hole geostress testing technology, as well as deep rock hydrogeological parameter testing technology. Such technologies form a whole set of systematic and comprehensive research methods for investigating large buried and super long tunnels.
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  Comprehensive Advanced Geological Prediction Technology for Water-rich Broken Tunnel Segment of Water Transfer Project

  DU Jun, LIAO Jian-du , HAN Cheng-li

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 15-20. https://doi.org/10.11988/ckyyb.20220194

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  To mitigate or even avoid water inrush and collapses caused by tunnels crossing water-rich broken rock mass, a comprehensive advanced prediction system based on geological analysis, TSP (tunnel seismic prediction) method and advanced drilling is proposed. The unfavorable geology is evaluated through geological analysis, and then the TSP method is used to locate the unfavorable geological body in front. Subsequently, advanced drilling is used to predict the location and scale of the unfavorable geological structure after it is confirmed. Two engineering examples of the water-rich fractured segment of the Central Yunnan Water Diversion Project demonstrate that the proposed technology could accurately predict the location and scale of unfavorable geology and water inrush. Corresponding early warning measures and countermeasures can be made in time to reduce the probability of geological disasters such as mud inrush, water inrush, and landslides in the construction process and to ensure the safe construction of the tunnel.
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  Estimation of Mechanical Parameters of Intensively Sandy Dolomite Based on Hoek-Brown Strength Criterion

  DONG Jia-xing, ZHOU Zhi-qiang, WANG Zhi-rong, ZHAO Yi-ran, LI Jian-guo, MU Hong-yuan, ZUO Shu-qiong, ZHAO Yong-chuan

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 21-25. https://doi.org/10.11988/ckyyb.20221010

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  Dolomite sandification is a typical geological problem in Yuxi segment of Central Yunnan Water Diversion Project. Accurate physical and mechanical parameters of sandy dolomite could offer basis for construction and design, and ensure the safety of life and property of construction personnel. Due to broken structure, intensively sandy dolomite is difficult to be made into standard specimens for laboratory test to obtain its mechanical parameters. In view of this, the mechanical parameters of intensively sandy dolomite is estimated by using Hoek-Brown strength criterion based on field investigation and needle penetration test. The estimation results are compared with those of field adit test. Results manifest that Hoek-Brown strength criterion has good application effect in estimating the mechanical parameters of intensively sandy dolomite rock mass because most of the estimated values are within the range of test results. In addition, the recommended values of mechanical parameters of intensively sandy dolomite in the study area are given to support engineering construction.
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  Characteristics and Disaster Model of Inrush Medium in Shizishan Tunnel

  LI Yong, HAO Jun-suo, LIU Jun-feng, ZHAO Ming-fan

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 26-32. https://doi.org/10.11988/ckyyb.20221034

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  The aim of this study is to understand the structural characteristics of unfavorable geological bodies and the mechanism of mud and water inrush in the syncline structure of basalt strata. We investigated into the evolution of water and mud inrush, the disaster-causing geological structure, the basic characteristics of disaster-causing medium, the disaster-causing power and the disaster-inducing mechanism at the core of Wulongba syncline structure in Shizishan tunnel of Central Yunnan Water Diversion Project as a case study. Results demonstrated that the water inrush is resulted from the disintegration, softening and argillization of lower tuff cracks caused by the water storage structure in joint fissure dense zone of the upper syncline structure; 2) the diluted debris flow like water inrush medium carries huge energy while bursting instantaneously; 3) the water and mud inrush disaster is caused jointly by tunnel unloading collapse, groundwater action and stress release. The research finding is of guiding significance for mud and water inrush prevention for tunnels crossing fold structure.
  
  
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  Method of Estimating Surrounding Rock Quality Based on Torque Penetration Index and Neural Network

  WU Fan, ZHANG Yun-pei, KOU Jia-bing, LIU Li-peng, LI Peng-yu

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 33-41. https://doi.org/10.11988/ckyyb.20221039

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  Featured with inferior geological adaptability, TBM (Full Face Rock Tunnel Boring Machine) is prone to cause geological disasters such as jamming and collapses when encountered with unfavorable geological conditions or poor surrounding rock quality, hence affecting construction progress and threatening personnel safety. Through TBM data preprocessing, the original data is first divided into complete driving segments, and the torque penetration index (TPI) is calculated. The quality of surrounding rock is then predicted before boring by using time series method and neural network, and the quality of surrounding rock is judged in the rising segment of boring based on the Gini impurity of TPI. Results demonstrate that TPI well reflects the geological conditions of surrounding rock. TPI can be accurately predicted by using time series method and neural network. The quality of surrounding rock can be well judged by the Gini impurity of TPI.
STABILITY ANALYSIS OF WEAK SURROUNDING ROCK MASSES
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  Large Deformation Characteristics and Control Measures of Chlorite Schist Tunnels: A Case Study on Xianglushan Tunnel of Water Diversion in Central Yunnan

  LIU Hai-ming, CHENG Yuan-deng, WU Yong-hong, ZHANG Yu-ting, DING Wen-yun, WANG Zhong-wei

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 42-48. https://doi.org/10.11988/ckyyb.20221017

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  The aim of this research is to further understand the law of large deformation during the excavation of deep-buried soft rock tunnels. The chlorite schist section of Xianglushan Tunnel under construction of the Central Yunnan Water Diversion Project is taken as a research background. Constitutive models more suitable for soft rock tunnels are compared and analyzed by using FLAC^3D. The effects of controlling large deformation by the excavation method with reserved core soil step (working condition 1), the pilot pit method on one sidewall (working condition 2) and the excavation method with middle partition wall (working condition 3) are compared and analyzed. Results unveil that the maximum settlement of the vault obtained by Hoek-Brown (H-B) strain softening model is greater than that of the ideal elastic-plastic model, and the error with actual settlement is 9.3%. The vault settlement in working conditions 1 and 3 reduced by about 20% compared with that in working condition 2, and the convergence deformation of arch waist and arch wall in working condition 3 is obviously controlled compared with working conditions 1 and 2. From the perspectives of large deformation control effect and plastic zone distribution, the excavation method with middle partition wall (working condition 3) could effectively reduce the deformation of chlorite schist segment of the tunnel.
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  Analysis of Large Deformation and Supporting Force of TBM Tunneling in Soft Rock Section of Water Conveyance Tunnel

  FU Jing, HUANG Shu-ling, AI Kai, ZHANG Yu-ting, QIN Yang

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 49-55. https://doi.org/10.11988/ckyyb.20221033

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  The large deformation of soft rock, which is of obvious creep characteristics, seriously threatens the safe operation of TBM (tunnel boring machine). In this paper we analyze and evaluate the deformation of surrounding rock and the safety of supporting structure in the soft rock TBM tunneling segment of a deep-buried water conveyance tunnel. We also investigate into the creep characteristics of soft rock under high stress conditions and compares the stress states of segment structures supported with different methods. Results demonstrate that the stress state of segment and the safety margin of segment structure can be effectively improved by adopting large cross-sectional expansion excavation in association with a buffer layer consisting pea gravel layer and polyethylene foam plate. We suggest to provide reliable working condition for TBM by selecting suitable expansion excavation section and support method as well as reserving enough space for surrounding rock deformation via targeted rock rheological tests and deformation monitoring for similar deep buried tunnel projects. The research findings offer technical support for smooth tunneling, and also provide reference for the construction of similar ultra-long deep-buried tunnels.
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  Inversion Analysis of Rock Mass Mechanical Parameters and Stability Analysis of Emergency Rescue Section in Adit 5# of Xianglushan Tunnel

  HAN Gang, HUANG Shu-ling, DING Xiu-li, MA Xu-qiang, ZHANG Yu-ting, HE Jun

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 56-61. https://doi.org/10.11988/ckyyb.20221069

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  The 5# adit of Xianglushan tunnel under construction of Central Yunnan Water Diversion Project features complex geological conditions as it crosses active fault zones. Severe water-mud bursting disasters and prominent stability problems of surrounding rock hinder the construction progress and project safety. According to field monitoring and geophysical exploration data, we determined the mechanical parameters of surrounding rock at emergency rescue section by using inversion analysis based on neural network and genetic algorithm; on this basis, we simulated the whole process of construction, excavation, and support, and analysed the surrounding rock stability. Results manifested that the surrounding rock mass of emergency rescue tunnel section of adit 5# was in an overall stable state. Except that the deformation of surrounding rock on the right side of the tunnel section K0+501-513 was relatively large, the deformation of other parts was less than 15 cm in general; the depth of plastic zones was within the range of 2-5 m; and the stress of support structures was at a normal level. The research findings would guide the safe and rapid construction of subsequent tunnel sections of 5# adit or tunnels with similar geological conditions.
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  Method of Designing Pipe Roof Support Parameters for Tunnel in Fault Zone

  CHEN Pei, MA Xu-qiang, LONG Jie, LI Zhan-biao, HUANG Shu-ling

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 62-67. https://doi.org/10.11988/ckyyb.20221087

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  A method of designing the support parameters of pipe roof is proposed to ensure the safe construction of tunnel in fault fracture zone and the stability of surrounding rock of working face. First, the pipe roof is divided into several segments of which one part is taken as effective calculation length. The load of loose fractured rock mass on the pipe roof is calculated based on Terzaghi's theory. The bending moment, deflection, and end-reaction are obtained by simplifying the pipe roof into a beam with both ends fixed and supported. Furthermore, the calculation formulae for the support parameters of pipe roof are derived according to the failure conditions of rock mass and pipe roof. The method is applied to a tunnel in fault zone which has undergone several collapses of working face due to only small duct bracing. The results of the proposed method indicate that small duct bracing is inadequate, while pipe roof support could generate smaller convergence deformation during excavation. The research findings offer reference for the design of support parameters of pipe roof in tunnels constructed in fault zones.
  
  
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  Seepage-Stress Coupling Analysis of Soft Rock Tunnel with Drainage Structure

  BI Fa-jiang, HE Jun, ZHANG Yu-ting, LI Mei, ZHU Xu-mei

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 68-74. https://doi.org/10.11988/ckyyb.20221056

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  The safety of surrounding rock and support structures of deep-buried soft rock tunnel is faced with great challenges under the action of high external water pressure. Drainage structure is a common engineering treatment to alleviate the impact of external water pressure on the surrounding rock and support structure of soft rock tunnel. A simple seepage-stress coupling scheme for tunnel’s surrounding rock-lining structure is first established. The drainage effect of the drainage structures of a deep-buried soft rock tunnel crossing a fault zone is investigated through seepage-stress coupling analysis in construction period and operation period. Under the combined action of grouting ring and drainage structures, the hydraulic gradient near tunnel lining is small while the hydraulic gradient of grouting ring is large. As a result, the grouting ring bears most of the external water load, while the tunnel lining bears a small part of the external water load. In addition, under the deformation compatibility between soft rock and lining, the co-bearing effect between grouting ring and lining is finally formed, which effectively improves the safety of the tunnel in operation period.
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  Creep Characteristics and Modelling of Surrounding Rock of Xianglushan Water Diversion Tunnel

  DU Xue-cai, ZHOU Hui, GUO Peng-yun, LIU Wen-bo, XIE Jing, ZHAO Cheng-wei

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 75-81. https://doi.org/10.11988/ckyyb.20221011

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  Rock mechanics tests and creep tests were performed by using real-time high temperature conventional triaxial test system to probe into the creep characteristics of surrounding rock of water diversion tunnel in central Yunnan Province. On the basis of establishing the rock creep constitutive model, a method for determining the creep parameters is proposed according to the characteristics of creep test curve. The relationship between creep parameters and stress is established by analyzing the variation law of creep parameters under different stress levels. Finally, the modified creep constitutive model is obtained by substituting the expression between each creep parameter and stress into the creep constitutive model. Results demonstrate that the established creep model not only reflects the creep characteristics of decay and stable creep stages accurately, and also overcomes the deficiency of traditional model in describing accelerated creep. Moreover, the creep parameters determined by the proposed method reflect the influence of stress on creep parameters and also the influence of stress state on the regularity of creep deformation.
ADAPTABILITY OF TUNNELS CROSSING ACTIVE FAULTS
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  Structural Safety Monitoring System and Layout Design for Long Distance Tunnel Crossing Active Fault Zone

  ZHANG Yu-ting, WANG Yi-shen, ZHAO Li-peng, HUANG Shu-ling, HE Xiao, LI Jian-he

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 82-89. https://doi.org/10.11988/ckyyb.20221189

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  Long-distance water conveyance tunnel and other line projects will inevitably cross active fault zones, giving rise to the risk of structural deformation and tunnel instability. Reliable structural safety monitoring scheme is a necessary means to effectively monitor the safety state of tunnel and evaluate the adaptability of anti-fault measures. At present,there are few studies related to the structural safety monitoring system of tunnels crossing active fault zone. In view of this,a “five adaptations” principle of monitoring the safety of tunnel crossing active fault zone is put forward: the monitoring should adapt to 1) the current specifications or technical standards, 2) the motion characteristics of active fault zones, 3) the deformation law and failure characteristics of tunnel, 4) the anti-fault measures, and 5) the construction methods of tunnel. With the Xianglushan tunnel of Central Yunnan Water Diversion Project as a case study,the safety monitoring system and layout design based on the “five adaptations” are studied in line with the deformation and failure law under fault creep action. At the cross of Xianglushan tunnel and Lijiang-Jianchuan active fault,surrounding rock deformation and opening of joint should be considered as major monitoring items,and shear compression of joint and compressive strain of concrete should be taken as a basic monitoring content; the intersection area of the affected zone and the fault zone should be the key monitoring area; and dislocation meter, joint meter,strain gauge and pressure gauge should be selected as monitoring instruments. Moreover,the monitoring devices should be installed synchronously with the construction of monitored objects. Such a monitoring system serves as a useful idea for the safety monitoring layout design of tunnels crossing active fault zones
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  Mechanical Behavior of Tunnel Structure Passing Through an Active Fault and Subjected to Fault Rupture

  CUI Zhen, ZHANG Yan-jie, ZHOU Guang-xin, XIE Jing, WANG Yi-shen, YANG Jing-hao

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 90-96. https://doi.org/10.11988/ckyyb.20221045

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  As the key controlling project of long-distance cross-basin water transfer project, water conveyance tunnel plays a significant role in alleviating the regional contradiction between economic layout and water resources distribution. In high seismic intensity areas of southwest China where geological structure is complex and active faults are densely distributed, water conveyance tunnel project inevitably crosses multiple active fault zones. The Xianglushan tunnel of Central Yunnan Water Diversion Project, which crosses the Longpan-Qiaohou fault F10-1, is taken as the research object. The influence of active fault on the anti-dislocation adaptability of the tunnel is evaluated based on the displacement, relative deformation, maximum principal stress, and longitudinal equivalent internal force and other factors of key parts of the tunnel. The effect on reducing the internal force and deformation of lining is also verified via numerical calculation. Results unveil that affected by fault movement dominated by strike-slip, one sidewall of the tunnel is in tension, with a small tensile stress around 5 MPa. The maximum normal and tangential deformation of hinge joint are located in the central section of the fault zone. The adaptive hinge design effectively improves the stress state of lining under dislocation condition. The research findings can be directly applied to the engineering design and construction of water conveyance tunnels crossing active faults, and also provide favorable support for the construction of related engineering tunnels.
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  Creep Characteristics and Dislocation Mode of the West Branch of Longpan-Qiaohou Fault in Xianglushan Tunnel

  ZHOU Hui, ZHAO Hai-tao, LI Jian, ZHAO Cheng-wei, LIU Wen-bo, ZHANG Chuan-qing, WANG Yan-zhang

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 97-104. https://doi.org/10.11988/ckyyb.20221014

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  The aim of this research is to comprehensively understand the dislocation law of creep movement of active faults. The west branch of Longpan-Qiaohou fault zone (F10-1) in Xianglushan tunnel of the Central Yunnan Water Diversion Project is taken as research background. A generalized geological model is established to investigate the dislocation law of F10-1 in the whole service period according to geological condition, rock parameters and mechanical performances. The dislocation deformation characteristics and displacement gradients are analyzed, and the stability of the tunnel is discussed in consideration of width of fracture zone and dip angle of fault. Results reveal that the dislocation patterns of the fault zone are similar, showing a sloping type. Strong dislocation disk presents a translational displacement mode, with displacement mainly occuring in the fractured area of weak rock formation. The displacement of fracture zone increases with the increasing of the service life and the fracture zone width as well as the decreasing of fault’s dip angle. According to the displacement of interface between upper influence zone and fracture zone, a large deformation in the left shoulder socket of the tunnel (except for 30° and 50°) is found. The maximum deformation is located on the left side of the tunnel. The displacement gradient presents a single peak at the fracture zone; the peak of displacement gradient increases with the growth of service life and fault dip, while reduces with the expansion of fracture zone width. The research results offer strong support for the safety construction of Central Yunnan Water Diversion Project.
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  Structural Adaptability of Fenghuangshan Tunnel of Central Yunnan Water Diversion Project to Active Fault Zone

  SI Jian-qiang, WANG Tao, XIANG Tian-bing, JIANG Min

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 105-110. https://doi.org/10.11988/ckyyb.20221049

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  Tunnels account for 92% of the water conveyance structures in Central Yunnan Water Diversion Project. The tunnel line confronts with regional active fault zone and strata with complex geological conditions for multiple times, posing threats to the construction and safe operation of the project. The engineering design case of a tunnel of the Central Yunnan Water Diversion Project crossing active fault zone is taken as research background. The structural type of the tunnel is selected, and the adaptability of tunnel structure to creep deformation and stick-slip deformation of fault zone is investigated via three-dimensional simulation, and the reasonable age of service before overhaul in the operation period of the project is put forward. Results manifest that short lining and wide deformation joint can effectively reduce the structural stress caused by the displacement of regional active fault zone, and prolong the service life of the lining structure. The research findings offer reference for the anti-fault design of tunnels.
HYDRAULIC TESTING AND STRUCTURAL ANALYSIS
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  Seismic Performance of Large-span Inverted Siphon Pipe Bridge Structure

  SHI Chang-zheng, CHENG Chao, WANG Zhi-ming, WU He-gao, HU Yue

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 111-116. https://doi.org/10.11988/ckyyb.20221066

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  The finite element model of a pipe bridge structure with large span inverted siphon including support and expansion joint is established. The structural seismic performance of the pipe bridge is investigated using finit element method by examining the influence of supports, expansion joint and water mass in steel penstock on structural seismic response. The large span arch bridge has a significant amplification effect on seismic wave, and the amplification coefficient is within 2-5. Unidirectional sliding supports constrain the lateral displacement of the steel penstock and keep the deformations of the expansion joints and the sliding distance of the supports both within 10 mm, which are beneficial to the seismic resistance of the structure. However, the supports bear large reaction force in lateral direction, which is unfavorable to the design of the supports. Due to the sliding supports and expansion joints, the steel penstock moves like a rigid body under earthquake. The stress of steel penstock is not much affected; but the supporting ring becomes a weakness as it is subjected to notable bending stress. In addition, the huge water mass in the large-diameter steel penstock should also be considered in calculation as it intensifies the structural dynamic response.
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  Seismic Response of Arch Inverted Siphon under the Excitation of River Valley Differential Earthquake

  JIANG Le-ying, LIAO Yi-hui, WANG Zhi-ming, WU Yong-xin, LI Mei

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 117-121. https://doi.org/10.11988/ckyyb.20221035

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  The seismic performance of large-span water transfer structures has become increasingly prominent with the growing number of water transfer projects in recent years. In this paper, the effect of differential ground motion caused by topographic effects on the seismic response of Longchuanjiang large-span water transfer inverted siphon in Central Yunnan Water Diversion Project is examined by establishing a three-dimensional finite element model with the calculated results of SH wave horizontal incidence, oblique incidence and vertical incidence as ground motion inputs. The results are compared with those under uniform excitation. Results manifest that differential ground motion in consideration of topographic effect has a significant impact on the force and deformation of important structural elements, and different structural components behave differently. The transverse force and deformation of steel pipes, piers and other elements under horizontal incidence is the largest, followed by that under oblique incidence, uniform excitation, and vertical incidence in sequence, while the differential seismic effect causes a reduction in the transverse internal force of the arch ring. The location of structural stiffness change is more sensitive to differential seismic effect. In conclusion, it is necessary to consider the topographic effect and the influence of incidence angle of ground motion in the seismic design of large-span water transmission inverted siphon structures.
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  Hydraulic Model Test on Hydraulic Properties at Inlet and Outlet of Xiazhuang Inverted Siphon

  ZHOU Yong-lin, YANG Qing-yuan, CHENG Zi-bing, HUANG Xiao-yong

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 122-127. https://doi.org/10.11988/ckyyb.20221060

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  Multi-pipe inverted siphon is a common structure in water diversion projects. Outlets are usually kept a bit far away from the inverted siphon to keep the flow stable. However, due to difficulties in construction and land acquisition, the inverted siphon and lateral outlet at Xiazhuang are put together, posing adverse impact on flow pattern at the inlet. Based on physical modelling, a method of replacing pressure-free open channel outlet by pressurized tube outlet is proposed to minimize the impact of lateral outlet releasing and improving the flow pattern. Test reveal water surface oscillation with a maximum amplitude of 1.4 m at three downstream lock chambers under normal conditions. Analysis shows that the oscillation is induced by the vertical dispersion of flow between bulkhead gate shaft and working gate shaft. Arranging separating beam or slab could curb the vertical dispersion of flow, hence alleviating surface oscillation by reducing the amplitude to 0.1 m. Separating beam is recommended in future optimization as it is less costly in both engineering quantity and economy. The research findings offer reference for the design, research and operation management of similar projects.
CONSTRUCTION TECHNOLOGY AND MANAGEMENT
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  Application of Loosening Blasting in Excavation of Thick Deposit of Steep Slope

  YANG Hong-xia, LIAO Jian-du, CAO Yu-min

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 128-133. https://doi.org/10.11988/ckyyb.20220188

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  The slope at the exit of Caijiacun tunnel of Central Yunnan Water Diversion Project is highly difficult to be supported with an excavation height about 38 m, excavation slope ratio of 1∶0.3, and a thickness of collapse deposit reaching 8 m. Having analyzed the merits and shortcomings of inter-hole delay and inter-row delay, we researched the millisecond blasting network with low single sound and low unit consumption in excavating the thick deposit of steep slope. We proposed a loosening blasting technology integrating inter-hole and inter-row delay blasting. The technology integrates the control of explosive charge in hole, the upgrading of charge structure, the optimization of initiation network and external protection. Methods of lengthening and sectional plugging, correcting the charge density of pre-splitting hole line, and reserving rock ridges are put forward. The proposed technology is demonstrated to be of sound loosening blasting effect for the thick deposit of steep slope of Central Yunnan Water Diversion Project with the blasting vibration, flying rock and dust been effectively controlled.
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  Research and Practice on Influence Control of Adjacent Construction of Shallow-buried Tunnel in Urban Area

  XIANG Tian-bing, YANG Xiao-long, YAN Shang-long, SI Jian-qiang

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 134-140. https://doi.org/10.11988/ckyyb.20221037

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  Controlling the influence of shallow-buried tunnel construction has always been a challenge for large-scale water diversion project while passing through or near urban area. A dynamic closed-loop feedback-control method for the whole construction process is proposed. The method includes analysing construction conditions, comparing and selecting construction method, determining design scheme, construction process feedback, and dynamic design optimization. In analysing construction conditions, engineering geological condition and cross relations of buildings as well as other necessary influencing factors should be considered as a whole. Construction method should be determined comprehensively by technical and economic comparison. Deformation prediction and deformation control standard are crucial parts of design scheme. Multi-source information feedback and dynamic design optimization are keys to the influence control of adjacent construction. Passing through over 100 sensitive buildings and other structures, the shallow-buried segment of Central Yunnan Water Diversion Project crossing the urban area of Kunming is featured with extremely complex construction environment. The influence of its construction adjacent to the urban area can be under control in general by using the proposed dynamic closed-loop feedback-control method.
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  Measures and Adaptability of Constructing Tunnel Crossing Compacted Granite under High Geostress

  HAO Jun-suo, YIN Qian, LI Yong, LIU Jun-feng

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 141-146. https://doi.org/10.11988/ckyyb.20221032

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  The Shizishan tunnel of the Central Yunnan Water Diversion Project runs through the fracture structure clamping belt between F_Ⅲ-102 and F₁₆ where the D₁¹ calcareous shale and carbonaceous shale are loosely consolidated under high in-situ stress. Geological analysis shows that the residual high in-situ stress of geological compression structure is the major driving force of the large deformation of tunnel, and the low load-resistance and degraded broken structure is the main internal cause of the instability and deformation of tunnel. Site investigation reveals the damage of tunnel reflected as instability and collapse induced by excavation unloading, extrusion of working face, and severely deformed support. To tackle these problems, we propose a principle of “advance support, fast excavation, fast support, and fast closure” for tunnel construction. We summarize the construction measures applicable to the geological condition: 1) advance support with 15mΦ108 mm large pipe shed by using ST-20 pipe shed drilling rig, and grouting reinforcement of surrounding rock of working face; timely strong support with pressure-relieving anchor rods and long-lock-foot anchor pipes to restrain deformation; dynamic control and informatized construction by strengthening deformation monitoring of surrounding rock. Practice has proved that, for tunnels passing through crushed zone of high geostress, construction measures such as reinforcing the shallow surrounding rock and combining active support and passive support can effectively restrain the deep development and deformation of surrounding rock’s loose circle, hence guaranteeing safe and smooth construction.
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  Deployment Strategy of Optical Transport Network Technology Based on Optical Service Unit in Central Yunnan Water Diversion Project

  FAN Lu-lu, ZHANG Yan-jie, WANG Ling-hang, WANG Ya-ping, LI Yi-bai, HE Miao

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 147-153. https://doi.org/10.11988/ckyyb.20221061

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  Communication transmission network, as the basic network of Smart Central Yunnan Water Diversion Project, plays a fundamental role in intelligent engineering project management. In view of the limitations of common communication system configuration, the OTN (Optical Transport Network) technology based on OSU (Optical Service Unit) is proposed to build the communication transmission network of Smart Central Yunnan Water Diversion Project as a case study. The OTN technology based on OSU is comprehensively and systematically deployed and studied from eight aspects: three network integration, interface type, site, networking mode, service bearing, network protection, docking scheme and intelligent management. The OSU-based OTN technology could effectively solve the complex services of carrying small particle and the high delay caused by excessive mapping levels in traditional transmission network. It also provides a feasible strategy for constructing a safe, practical, intelligent and efficient communication transmission network in the Smart Central Yunnan Water Diversion Project. The research findings are of guiding significance for the practical work of constructing a high-speed, flexible, intelligent, safe and future-oriented transmission network of the Smart Central Yunnan Water Diversion Project, and can also be used for reference for the construction of communication networks in other water diversion projects.
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  Diffusion Characteristics of Clay Splitting Grouting Based on Discrete Element Simulation

  ZHANG Ze-fu, CHENG Yuan-deng, DING Wen-yun, CHEN Pei, ZHANG Yong-ming, NIAN Pei-hong, LIU Hai-ming

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 154-160. https://doi.org/10.11988/ckyyb.20221018

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  The aim of this study is to probe into the reinforcement effect of splitting grouting on clay-rich tunnels from a mesoscopic viewpoint. The entrance segment of Wuzhuangcun tunnel of the Central Yunnan Water Diversion Project is taken as a research background. The PFC^2D model of splitting grouting is established by simulating the interaction between slurry and soil particles in the process of grouting based on the discrete element fluid-solid coupling theory, the plate narrow slit model and the secondary development of Fish language. The influences of grouting time step, grouting pressure, particle size ratio and cohesive strength on the slurry diffusion radius and soil porosity are studied. Results reveal that grouting pressure is the dominant control factor affecting the soil reinforcement effect. With the increase of grouting pressure, the slurry diffusion radius expands continuously and the porosity increases continuously. A smaller distance from the grouting hole results in a smaller influence on porosity. An optimal grouting pressure exists. Moreover, mesoscopic soil parameters have obvious influence on the macroscopic mechanical properties after grouting. With the increase of particle size ratio and cohesive strength, the slurry diffusion radius and porosity reduce significantly. The simulation results are in well agreement with indoor model test result, which verified the correctness of the simulated model.
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  Review on Rockburst Prevention Techniques and Typical Applications in Deep Tunnels

  OUYANG Lin, ZHANG Ru-jiu, LIU Yao-ru, HUANG Qi-shuai, LI Jian-he, PANG Zhi-yong

  Journal of Changjiang River Scientific Research Institute. 2022, 39(12): 161-170. https://doi.org/10.11988/ckyyb.20221050

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  The classification, mechanism, evaluation, prediction methods and prevention principles of rockburst are briefly introduced first. On this basis, active and passive prevention and control techniques for rockburst during deep tunnel construction are summarized. In particular, the mechanism, application scope and prevention effects of such measures are highlighted. The differences of rockburst characteristics between drilling and blasting (D&B) method and tunnel boring machine (TBM) method are analyzed, and the applications of rockburst prevention techniques in typical projects are investigated. Such projects include the diversion tunnel of Jinping II hydropower station, the Qinling tunnel of Hanjiang-to-Weihe River Diversion Project, the diversion tunnel of Neelum-Jhelum (N-J) hydroelectric project in Pakistan and Xianglushan tunnel of the diversion project in Central Yunnan. 1) Active rockburst prevention techniques include borehole stress release, advanced stress relief blasting, pilot tunnels, high-pressure water injection, advanced anchor bolts and pre-stressed anchor bolts; passive prevention techniques include shotcrete-bolt support, steel support and reinforcement mesh (flexible steel wire mesh). 2) Timely closed support and active measures against strong-extremely-strong rockburst are the key points of preventing rockburst induced by D&B method and TBM method, respectively. 3) At present, active and passive measures are combined for the rockburst prevention of large hydraulic tunnels. For active prevention, advance stress release is the dominant measure, while for passive prevention, shotcrete-bolt-mesh combined with steel support is adopted together with the use of fast flexible support. 4) Dynamic prevention, precise quantitative prevention, and more efficient advanced stress release technology and flexible energy absorption support system are research directions in future.