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Quick Search     Advanced Search MODERN TUNNELLING TECHNOLOGY   2016 Vol.53 Issue.2 Published 2016-04-25 Article 1 On the Limitations of Protodyakonov's Pressure Arch Theory ZHENG Yingren, QIU Chenyu Protodyakonov′s pressure arch theory has been a mechanical basis for the design of tunnels and underground works in China, but it has been questioned to some extent by academic and engineering fields. This paper analyzes the real meanings and formation conditions of a pressure arch using the FEM strength reduction method and a model test, researches the relationships among tunnel span, rock mass strength and pressure arch self-stability, and discusses the failure mechanism of tunnels under different buried depths. The results show that: 1) the pressure arch theory is only applicable to rectangular or gentle-vault tunnels with stable surrounding rocks and a shallow buried depth; 2) a pressure arch will not occur in an arched tunnel; 3) a self-stable pressure arch will not occur under very low rock strength and a too large tunnel span; 4) a pressure arch and tunnel failure will not occur in a tunnel with stable surrounding rock; 5) for a tunnel with a great buried depth, the failure first occurs on both sides, so the pressure arch theory is not applicable 2016 Vol. 53 (2): 1-8 [Abstract] ( 2898 ) [HTML 1KB] [ PDF 3162KB] ( 3044 ) 9 Key Construction Techniques for Urban Underwater Bored Tunnels Considering that underwater tunnels are important river-crossing passages in urban areas at present, and using the construction of the Yingpan road tunnel in Changsha city as an example, some innovative design and construction methods are discussed for urban underwater bored tunnels. A method for determining minimum overburden is put forward based on the consideration of engineering control measures and analysis of the problems with existing methods, by which the minimum overburden is determined to be 11.5 m (more than 5 meters shallower than under existing methods in China and abroad) and the tunnel length is reduced by nearly 400 m accordingly. The water seepage during tunnel operation could be reduced by adopting a “blocking-based limited drainage” principle and adjusting grouting-ring thickness and relevant reinforcement parameters. A shallow-buried large-section underwater tunnel with a depth/span ratio of 0.46 and excavation area of 376 m2 is completed successfully using advance full-face pre-reinforcement, a double-layer primary support, a reasonable excavation section division, and proper construction arrangements. 2016 Vol. 53 (2): 9-16 [Abstract] ( 1700 ) [HTML 1KB] [ PDF 4820KB] ( 2594 ) 17 Development of a Testing Platform for Mechanical Rock Breaking With economic development and the improvement of science and technology, such construction machinery as rock tunnel boring machines, shield machines, raise boring machines, and road headers have been applied unprecedentedly to underground works. Therefore, the testing of mechanical rock breaking has become an indispensable experimental means for construction machines used in underground works and can also guide the design and operation of those machines. This paper introduces a new mechanical rock-breaking testing platform developed by Beijing University of Technology that is designed and manufactured by considering such factors as the influence of high ground stress, cutterhead rotation and rock breaking by multiple cutters at the same time. Meanwhile, other cases such as different rock-breaking tools for different excavation machines and different rock mass structures in a sample box are taken into account, which makes for a realistic simulation of construction conditions onsite for different cutting tools. The testing platform consists of a mechanical system, hydraulic system, automatic control system and data acquisition system. The completed platform has been used for several tests under different cases, and test results proved that this platform meets its design requirements. 2016 Vol. 53 (2): 17-25 [Abstract] ( 2226 ) [HTML 1KB] [ PDF 3145KB] ( 2778 ) 26 Research on Regionalization of Cutting-Tool Wear Conditions in Shield Tunnels of Urban Subways in China The shield tunnelling method has been used as a main construction method for urban rail transit tunnels in China and is credited with the characteristics of construction safety, high ground adaptability and little environmental impact. Cutting-tool wear is one of the common problems during shield tunnelling, and manifests mainly as wear in complex ground and as mud cakes in ground characterized by clay. Research was conducted on cutting-tool wear conditions in shield tunnels of urban subways in China by analyzing and collecting 41 cases of cutting-tool wear both at home and abroad from 2003 to 2013 and based on the geologic survey data of 38 domestic urban subway projects. This study provides a good reference for construction safety and the efficient excavation of future domestic urban rail transit projects. 2016 Vol. 53 (2): 26-34 [Abstract] ( 1408 ) [HTML 1KB] [ PDF 2420KB] ( 2722 ) 35 Influence of Fractal Characteristics of a Surface Karst Landform on Tunnel Construction Based on the characteristics of peak morphological parameters under different stages of karst development and the indicative effect of fractal characteristics of surface karst to the development of underground karst, this paper studies the morphology of ground karst in a karst tunnel area by using morphological parameter statistics and fractal theory, analyzes engineering geological conditions under different development stages and intensities of karst, and proposes relevant measures. Using the Baihushan tunnel in Yunnan as an example, the karst morphology of a tunnel area is determined from early to mature stages through peak morphological parameter statistics, a further analysis of the karst development degree of different strata is performed based on the fractal characteristics of the karst depression and contour line, the underground karst morphology is predicted and rational suggestions concerning tunnel construction are provided. 2016 Vol. 53 (2): 35-43 [Abstract] ( 1437 ) [HTML 1KB] [ PDF 2277KB] ( 2179 ) 44 A Study on the Optimized Adjustment Method of Maglev Gyro Control Traverse under Non-Weighted Measurement in Long and Large Tunnels In the process of setting the traverse control network in a long and large tunnel, an additional surveying gyroscopic azimuth is commonly used to correct the error accumulation of the traverse, and this is an effective method for improving the precision of the traverse control network and ensuring breakthrough of the long tunnels. However, it is hard to objectively assess the quality of the orientation results in every survey time due to the timeliness of the gyroscope north-finding process, therefore, each gyroscopic azimuth is regarded as a steady orientation side or equal precision observation during the traverse adjustment, which is surely unfavorable for the accurate breakthrough of long tunnels. In order to solve this problem, the orientation results of the gyroscope sides are evaluated and an unequal precision principle is proposed for the adjustment optimization of the underground traverse based on the newly self-developed acquisition technology of the maglev gyroscope massive north-finding observation data. Based on actual assessment results and a certain tunnel project, a comparison is made between the unequal precision adjustment optimization method and the conventional equal precision data processing method, which proves that the unequal precision adjustment optimization method can effectively improve the positional accuracy of breakthrough points. 2016 Vol. 53 (2): 44-47 [Abstract] ( 1451 ) [HTML 1KB] [ PDF 1385KB] ( 2288 ) 48 The Practice of Design and Technical Managment in Underground Section A of the KVMRT SBK Metro in Kuala Lumpur, Malaysia In light of the project profile, features and design management flow, this paper describes the optimized design, temporary works design, detailed design and technical management of the underground Section A of the KVMRT SBK Metro in Kuala Lumpur, Malaysia, during the implementation stage. Based on the similarities and differences of EPC project designs in China and abroad, it concludes that design plays an important role in international EPC projects and proposes requirements for the abilities and responsibilities of designers. 2016 Vol. 53 (2): 48-53 [Abstract] ( 1703 ) [HTML 1KB] [ PDF 2086KB] ( 2891 ) 54 Influence of the Tectonic Stress Field on Stress and Deformation Failure Characteristics of a Tunnel's Surrounding Rock Based on the measured geostress of a tunnel and FLAC3D software, stress and deformation failure characteristics of surrounding rock after tunnel excavation were simulated with or without consideration of tectonic stress. The results show that: 1) obvious changes to rock stress occur after tunnel excavation, with stress concentration occurring on the sidewall under no tectonic stress and on the top or bottom of the tunnel under tectonic stress, and the area and degree of the stress concentration under a tectonic stress are significantly greater than that under no tectonic stress; 2) the maximum displacement and influence depth occur on the top and bottom of the tunnel under no tectonic stress while they occur on the sidewall under tectonic stress; 3) the outer boundary of the deformation area is shaped like a vertical butterfly under no tectonic stress while it is shaped like a horizontal butterfly under tectonic stress; 4) the outer boundary of the shear strain increment area is approximately shaped like a vertical ellipse under no tectonic stress while it is shaped like a horizontal ellipse under tectonic stress. The research results have particular significance for the stability analysis and support design of deep buried tunnels in zones with tectonic stress. 2016 Vol. 53 (2): 54-62 [Abstract] ( 1535 ) [HTML 1KB] [ PDF 4272KB] ( 2148 ) 63 Effects of Tunnel Excavation Distrurbance on the Liquefiable Properties of Surrounding Stratum Saturated sand soil liquefaction may cause severe damage to tunnels under seismic loading. Accurately evaluating the liquefaction properties of the strata through which tunnels pass and taking anti-liquefaction measures can effectively reduce the seismic damages to tunnels. Based on the Seed method, a numerical simulation technique is used to analyze the changes to the liquefaction properties of surrounding stratum before and after tunnel excavation. The results show that: excavation disturbance can effectively reduce the liquefaction resistance of a stratum, and the reduction degree of the liquefaction resistance at the bottom is a little bit smaller than that of the haunch; with the increase of distance away from the tunnel excavation center, the influence of tunnel excavation on the liquefaction properties of a stratum decreases; the larger the overburden, the less effect excavation has on the liquefaction properties of the stratum; the influence of the excavation disturbance should be taken into account when the liquefaction properties of a stratum through which a tunnel passes is evaluated. 2016 Vol. 53 (2): 63-69 [Abstract] ( 1390 ) [HTML 1KB] [ PDF 2472KB] ( 2144 ) 70 Study of the Safety Factor for Tunnel Stability Considering the Stress Release Effect The actual deformation of a primary lining is far greater than the elastic deformation of a tunnel, and the plastic deformation occurs later. In this paper, surrounding rock is quantified by taking the primary lining as an elastic-plastic material and adopting the FEM numerical limit analysis method, and the interaction between the rock and lining is studied with a characteristic line method. The results show that the safety factor of the surrounding rock remains unchanged under a small stress release rate, while support efficiency decreases under a stress release rate exceeding a certain value and therefore the safety factor of the surrounding rock is reduced. A method for calculating the safety factor of surrounding rock after a stress release is proposed based on the FEM strength reduction and characteristic line methods, providing a theoretical basis for tunnel design. 2016 Vol. 53 (2): 70-76 [Abstract] ( 1421 ) [HTML 1KB] [ PDF 2850KB] ( 1363 ) 77 Instability Analysis of a Rock-Support Structure System for Tunnelling in Shattered Soft Rock Considering that an earthquake may cause extreme shattering damage to a mountain and result in the instability of a tunnel’s rock-support structure system after excavation, and using a typically unstable section of the Dujiashan tunnel in a seismically active area as an example, the instability mechanism of the rock-support structure system during construction in shattered soft rock was analyzed from the three aspects of the rock’s basic characteristics, structure instability characteristics and inclinations of the fractured structural plane based on field monitoring and numerical analysis.The results show that the soft rocks in meizoseismal areas are characterized by brokenness, looseness, low density and overhanging so that the structural instability after tunnel excavation mainly manifests in the form of shearing collapse on the tunnel vault and haunch; plastic extrusion, shear sliding and combined failure are the main forms of instability; the most unfavorable condition for tunnel construction is when the maximum deformation around the tunnel, structure stress and plastic zone all occur on the fractured structural plane at 45°. 2016 Vol. 53 (2): 77-85 [Abstract] ( 1393 ) [HTML 1KB] [ PDF 4854KB] ( 2002 ) 86 Elastic Complex Variable Theory Based Prediction of Shield Tunnel Surrounding Rock Displacement To reveal the surrounding rock displacement distribution of shield tunnels under different displacement boundary conditions, it simplified it as the second basic problem of elastic semi-infinite plane with a circular hole, and the expression of two complex variable functions [φ(z)] and [ψ(z)] as well as an analytical general formula of the displacement component (u, v) at any point on a rock mass were deduced by combining the elastic complex function theory and five different displacement convergence modes around a tunnel. The displacement distribution rules of surrounding rock under different buried depths and displacement boundary conditions were discussed. Based on the theoretical formula, surface settlement of a certain project was predicted and a comparison between the predicted data and measured data was made. The results show that: when the tunnel radius r0 is 4.0 m, the Poisso ratio μ is 0.3, and the tunnel depth h is 2r0 to 6r0, then the maximum relative surface settlement Δvmax ranges from 0.33 to 1.94, and the influence area induced by surface settlement ranges from 28.7 m to 124.1 m; the buried depth has little influence on the maximum relative horizontal displacement Δumax, which is located near the central horizontal line of a tunnel; in five different modes of displacement convergences, the solution results of two displacement boundary conditions are consistent with the measured surface settlements, and therefore these two theoretical solutions can be used as a foundation of tunnel design and construction. 2016 Vol. 53 (2): 86-94 [Abstract] ( 1449 ) [HTML 1KB] [ PDF 3405KB] ( 2028 ) 95 Numerical Study on the Basic characteristics of Pressure Waves at the Entrances of High Speed Railway Tunnels Although the pressure wave generated at a tunnel entrance is an infrasonic one with an intensity that is usually weaker than that of a micro-pressure wave, it may induce some new environmental problems if train speed is increased in the future. In this paper，a numerical simulation study is conducted regarding the properties of a pressure wave at a tunnel entrance that is generated by a high-speed train CRH3 running into the tunnel by using the finite volume method, the dynamic mesh technique of the arbitrary sliding interface(ASI) method, a PISO algorithm and a SST turbulence model with high Reynolds numbers. The results show that the pressure wave generated at a tunnel entrance is made up of negative and positive pressure pulses emitted from the train head and tail while the train is running into the tunnel, and it has the features of directional propagation and attenuation with an increase of distance. Furthermore, the amplitude of the entrance wave is inversely proportional to the observation distance and proportional to the cube of the train speed. 2016 Vol. 53 (2): 95-100 [Abstract] ( 1312 ) [HTML 1KB] [ PDF 3897KB] ( 1921 ) 101 Influence of the Transient Pressure in a Tunnel on the Speed Increase of Existing Passenger Railway Lines In order to meet the requirements of transport capacity, Chengdu Railway Bureau plans to increase the operating speed of some existing railways, i.e., the speed of the Dachuan-Chengdu railway will be increased from 160 km/h to 200 km/h, and the speed of the Suining-Chengdu railway will be increased from 160 km/h and 200 km/h to 250 km/h. To ensure passenger comfort requirements after the speed-up, a single dimensional characteristic curve method was used to calculate transient pressure inside the train running in the tunnels, and the results were compared with domestic standards to select the vehicle type and verify the proposed speed. The results show that: considering the comfort standard, a CRH2 is recommended as the passenger train, allowing the operation speed of the Dachuan-Chengdu railway and the Suining-Chengdu railway to increase to 200 km/h and 220 km/h respectively; the single-track tunnel plays a controlling roll in the railway speed increase because of its small clearance area, and the passing of two trains should be avoided in the double-track tunnels to minimize the possibility of exceeding the transient pressure standard; in addition to the effects of operation speed and sectional area, more attention should be paid to the sealing property of trains regarding the speed-increase plans, and the principle of “independent dimensioning of every tunnel” should be maintained. 2016 Vol. 53 (2): 101-106 [Abstract] ( 1292 ) [HTML 1KB] [ PDF 3039KB] ( 1982 ) 107 Dynamic Response Analysis of Blasting Excavation for a Tunnel Passing through Faults Considering that fault zones are key areas in tunnel construction due to poor stability of rock masses, and based on ANSYS/LS-DYNA software, a 3D numerical simulation under the blasting load is performed for a tunnel passing through faults；the influences of faults at different locations on the dynamic responses of the surrounding rock are analyzed; the distribution characteristics of the peak values of the rock’s vertical displacements, vertical vibration velocities and maximum principal stresses are summarized; the most unfavorable locations and working conditions, as well as the safe distance between the sidewall and fault, are presented for such a tunnel. 2016 Vol. 53 (2): 107-113 [Abstract] ( 1322 ) [HTML 1KB] [ PDF 3031KB] ( 2076 ) 114 Prediction of Long-Term Settlement Caused by Subway Operation under the Influence of Initial Consolidation Long-term settlement caused by subway operation can be divided into settlement caused by undrained accumulated residual deformation and consolidation settlement caused by cyclic pore pressure dissipation, the former of which is obtained by the layer-wise summation method based on the empirical formula of accumulated plastic deformation and a three-dimensional finite-element model of the foundation soil stress, and the latter of which is obtained by a dynamic triaxial test that simulates pore pressure change rules under different initial consolidation degrees. Through fitting of experimental data, a pore pressure calculation model is established for the Hangzhou soft soil under different consolidation degrees and cyclic loading, and combined with the consolidation settlement calculated by one-dimensional Terzaghi consolidation theory, long-term settlement under cyclic subway traffic loading can be obtained. The results show that settlement caused by residual deformation develops rapidly at the early loading stage, settlement caused by pore pressure dissipation occupies about 30% of the total settlement, and this ratio decreases with the increase of the consolidation degree and tends to be stable after six months. 2016 Vol. 53 (2): 114-120 [Abstract] ( 1372 ) [HTML 1KB] [ PDF 2448KB] ( 2174 ) 121 Monitoring Data Processing, Feedback Analysis and Stability Prediction during Tunnel Construction Based on the characteristics of monitoring data during highway tunnel construction, a monitoring quality evaluation method combining reliability, saturation and deletion is proposed in this paper, by which data interpolation, graduation and extension can be achieved using polynomials, exponential smoothing, various regression functions, etc. In this way, data availability can be improved effectively, and the rationality of prediction for the rock stability can be ensured as well. Additionally, a feedback analysis is carried out for the rock parameters by adopting a modified PSO algorithm, and the rock stability was predicted for later construction by using a 3D elastic-plastic damage incremental variable stiffness iteration method. From a simulation of the construction of the Changshan highway tunnel, it is demonstrated that adopting the above method can not only guarantee construction safety, but also guide the adjustment of the construction scheme and support parameters in time. 2016 Vol. 53 (2): 121-127 [Abstract] ( 1405 ) [HTML 1KB] [ PDF 2047KB] ( 2231 ) 128 Simulation Analysis of the Influences of Construction and Curing Measures on the Early Temperature and Stress of an Immersed Tunnel Considering that construction and curing measures adopted in element prefabrication are the key factors for controlling early temperature cracking of an immersed tunnel, and using the construction of the Shengjiamen immersed tunnel in Zhoushan as an example, this paper analyzes the influences of integral casting, layered casting, curtain curing and water storage curing on the temperature field and stress field of elements during prefabrication based on MIDAS FEA software. The obtained results are compared with the measured ones, showing that: 1) the maximum hydration temperature occurs at the tunnel floor during element prefabrication, with its peak value occurring within 1 or 2 days after casting; 2) the maximum temperature stress occurs at the haunch of the interface between the floor and sidewall, with the value being close to or even greater than the current age tensile strength, which easily causes cracking; 3) layered casting can accelerate heat loss inside the element and curtain curing can reduce the differences of temperature inside and outside of the element, all of which can be used to effectively reduce early temperature stress and cracking risk to the element; 4) water storage curing may cause great temperature differences and is not suitable for the early stage of construction. 2016 Vol. 53 (2): 128-133 [Abstract] ( 1454 ) [HTML 1KB] [ PDF 3308KB] ( 1992 ) 134 Experimental Study on the Influence of Slurry Properties on the Airtightness of the Filter Cakes of Slurry Shields The airtightness of a filter cake is critical concerning face stability during intervention under compressed air pressure in a slurry shield. However, the influence of slurry properties on the airtightness of filter cakes has not been identified, and on-site slurry preparation can become a difficulty that requires attention. Slurries with different properties were prepared by means of changing the additive dosage of CMC, and a self-developed laboratory test system for filter-cake air tightness was adopted to conduct filter-cake formation and airtightness tests. The results indicate that a filter cake has different airtight times at different air pressures and will be broken down by compressed air when the airtight time is over; due to high viscosity induced difficulties of slurry penetrating into the formation, the filter cake becomes thinner and is easily broken down, with its airtight time first increasing and then decreasing with increasing slurry viscosity. With respect to the Nanjing Weisanlu river-crossing tunnel project, it is recommended that the slurry density should be within 1.15~1.20 g/cm3, the CMC additive dosage should be 0.03%~0.1% and the funnel viscosity should be 40~50 s for slurry shield intervention under compressed air pressure in the pebble gravel stratum. 2016 Vol. 53 (2): 134-140 [Abstract] ( 1899 ) [HTML 1KB] [ PDF 2922KB] ( 3370 ) 141 Sensitivity Analysis of Factors Affecting Excavation Face Stability in Slurry Shield Tunnelling The stability of the excavation face in shield tunnelling is governed by factors such as tunnel diameter, buried depth and height of the water head; a sensitivity analysis was conducted regarding these factors using the finite element calculation software Plaxis8.2. The results show that: 1) the more sensitive factors such as internal friction angle [φ], water head heights Hw, buried depth H and tunnel diameter D should be considered as the main reference factors for setting slurry pressure; 2) those factors caused by groundwater, such as seepage force and excess pore water pressure, will change the force condition of the excavation face, so the effects of groundwater must be taken into account while calculating and selecting the support force; 3) a shallow buried depth greatly affects the stability of the excavation face, and with the increase of the buried depth the effect becomes weak; 4) the relationship between the tunnel diameter D and the minimum ultimate supporting pressure on the excavation face is linear. 2016 Vol. 53 (2): 141-147 [Abstract] ( 1448 ) [HTML 1KB] [ PDF 2034KB] ( 2172 ) 148 Breaking Modes of Jointed Rock under a TBM Cutter In this paper, a 2D discrete element model was established for jointed rock to study its breaking modes under a TBM cutter. Two groups of cutting simulation tests were designed under the confining pressure of 0~15 MPa, one of which was taken for the horizontal jointed rocks under double cutters (joint spacing js: 80 mm, 100 mm, 150 mm and 200 mm) and the other of which was taken for the inclined jointed rocks under a single cutter (joint angle α: 15°, 30°, 45° and 60°). The results show that: 1) 8 typical breaking modes were observed during the cutting due to the obvious controlling effect of the confining pressure and joint on crack development; 2) the rock-breaking efficiency of a TBM cutter under confining pressure is poorer than that without confining pressure based on a quantitative analysis of the breaking critical stress, standard penetration rate and crack expansion capacity, and the rock-breaking efficiency of a TBM cutter first increases and then decreases with an increase of joint spacing, but increases on the whole with the increase of joint inclination; 3) the rock-breaking efficiency is relatively high in the case of 150 mm joint spacing and a 45°~60° joint angle; 4) most rock breaking modes obtained by the simulation agree well with the ones given by the experimental observation in the literature. 2016 Vol. 53 (2): 148-156 [Abstract] ( 1325 ) [HTML 1KB] [ PDF 4244KB] ( 1979 ) 157 A Study of the Construction Scheme for Complex Metro Tunnels in Very Thick Self-Weight Collapsible Loess Considering that there is no reference experience in China regarding tunnelling in very thick self-weight collapsible loess, and based on international research of collapsible loess treatment methods and the features of such construction, this paper discusses the limitations of the GB50025-2004 Code for Building Construction in Collapsible Loess Regions as applied in metro tunnel construction; proposes relevant treatment principles and analysis processes for tunnel construction in collapsible loess and researches the corresponding construction schemes by using a metro tunnel in very thick self-weight collapsible loess in Xi’an as an example. Based on the given treatment principles, analysis processes and surrounding environment condition, it is determined that adopting the preferred principle of “alignment bypassing” is an economic and highly feasible method when such a complex tunnel project (including open-cut tunnelling, shallow bored tunnelling and shield tunnelling) will pass through a very thick self-weight collapsible loess stratum. Additionally, the paper also provides some valuable suggestions for treatments and control measures in this context. 2016 Vol. 53 (2): 157-164 [Abstract] ( 1387 ) [HTML 1KB] [ PDF 2010KB] ( 2495 ) 165 The Durability Design of Subsea Bored Tunnel Support Structures under Chloride Corrosion A subsea tunnel suffers the long-term impact of chloride corrosion, and with a required design service life of 100 years or more, many more studies of durability design are needed than for normal tunnels. Current study of subsea tunnel durability focuses on material selection and the mix proportion of reinforced concrete structures. This paper gives a detailed analysis of environmental conditions, relevant code specifications and durability design principles for subsea bored tunnels in chloride environments and proposes the concept of paying equal attention to the durability design and bearing capacity design as well as reserving enough space for later restoration. The analysis shows that high-strength high-performance concrete should be adopted for subsea tunnel linings in order to improve concrete density and to resist seawater corrosion, and the limited groundwater drainage principle should be adopted for mined subsea tunnels to ensure effectiveness of their drainage systems. 2016 Vol. 53 (2): 165-172 [Abstract] ( 1673 ) [HTML 1KB] [ PDF 2026KB] ( 2697 ) 173 Field Dewatering Test for Metro Tunnelling in a Water-Rich Sand Stratum Considering that dewatering is essential for metro construction in water-rich sand strata, and using a typical section of the running tunnel from Hexi Station to Hedong Station as an example, the dewatering effect and its influence on the surrounding environment were researched in a test section in Qingdao based on an analysis of the physical and mechanical properties of the sand stratum, which had a high number of clay particles. The results show that groundwater can be lowered to a level between the invert and sidewall under normal conditions by tube well dewatering, but this will be difficult in a combined rock and soil stratum; lowering the water level of 3.57~4.73 m may cause ground settlement of-5.58~ -10.72 mm; the total ground settlements are -24.93~-75.72 mm, of which the settlement induced by dewatering is 14.15%~24.65%; the total building settlements are -18.37~-7.25 m, of which the settlement induced by dewatering is 17.40%~29.05% (about -5.1~-2.1 mm), showing that dewatering has little effect on the surrounding environment. Compared to construction with no dewatering, adopting tube well dewatering and condulet reinforcement can improve construction efficiency in dry seasons such as autumn and winter while it may induce a wide range of settlements in rainy seasons, which necessitates enhanced reinforcement strength of the stratum. The dewatering effect was also calculated by FLAC3D software, indicating that the calculated results agree well with the tested ones. 2016 Vol. 53 (2): 173-181 [Abstract] ( 1393 ) [HTML 1KB] [ PDF 4380KB] ( 1902 ) 182 Research and Application of a Construction Scheme for a Bored Metro Tunnel Intersection in Shallow Fractured Surrounding Rock Based on the "Structure Priority" Principle Considering that the shallow-bored Zhongshan Park Station on Qingdao Metro line 3, which is located in a downtown area, is characterized by difficult construction, a tight schedule and a high safety level, and aiming at some specific problems—such as large traffic flow on the ground, fractured surrounding rock, shallow overburden, complex section shape of the intersection between the station and air duct, a large free face on both sides and high possibility of stress concentration at the corner point—this paper studies the stress and deformation of the surrounding rock under different working conditions with numerical simulation and field monitoring. A construction scheme is proposed for the bored metro tunnel intersection in the shallow fractured rock based on the “structure priority” principle. The results show that adopting this new scheme, featuring the construction of a ring beam and middle secondary lining for the intersection first and then forming a stable frame structure, can weaken the span effect of large-section construction, control the settlement of the fractured rock, improve the construction speed and ensure the stability of the intersection, which is suitable for the construction of a large-section tunnel intersection in a shallow fractured rock mass. 2016 Vol. 53 (2): 182-189 [Abstract] ( 1435 ) [HTML 1KB] [ PDF 4651KB] ( 2161 ) 190 Analysis of the Features of Typical GPR Images during Tunnel Inspection To improve precision of the interpretation of Ground Penetrating Radar (GPR) images during tunnel inspection and provide interpretation templates for typical images, a 2D forward simulation was carried out regarding such typical detection targets as the tunnel’s reinforcement, steel arch, lattice girder, rock disengagement, cavities, and uncompacted areas based on GPR theory and the finite difference time domain method. The features of the GPR images of these targets are summarized by comparing the simulated results with the measured ones. The results show that the ground penetrating radar can be used to detect reinforcement, steel arches, rock disengagements, cavities and uncompacted areas within tunnels, and the resulting images can be used to provide guidance and reference for later interpretation. 2016 Vol. 53 (2): 190-195 [Abstract] ( 1427 ) [HTML 1KB] [ PDF 2830KB] ( 2159 ) 196 Discussion on Deformation Control of Xianghe Tunnel Parallel Adit in Soft Surrounding Rocks The 10 220 m long Xianghe tunnel, which is classified as one with grade I risk on the railway from Guangtong to Dali, has a parallel adit excavated at the right side of tunnel. During construction severe deformations were usually encountered, especially at the sections of intrusive rock, granite porphyry, diabase, fault breccias and carbonaceous shale since the tunnel passed through nine faults and the lithology changed frequently, rock mass were found to be broken and soft. In this paper, such countermeasures as advance geological forecast, inner contour adjustment from straight wall to curved wall, advance support, ground water drainage, increasing of rock mass strength, primary support and clear spacing between parallel adit and main tunnel were put forward based on analyzing of geological characteristics and influential factors of rock mass deformation, and safe driving of parallel adit in soft rock mass is guaranteed. 2016 Vol. 53 (2): 196-201 [Abstract] ( 1295 ) [HTML 1KB] [ PDF 3138KB] ( 2094 ) 202 Principles of the Shallow Bored Tunnel Method Applied to Chimney Collapse Treatment for a Tunnel in Western China A mountain tunnel in western China that is subject to poor geological conditions, shallow buried depth and unsymmetrical pressure encountered a chimney collapse event caused by inappropriate construction and an unreasonable construction method. During the remediation process, surface sealing was used for loose masses, and advanced reinforcement was also adopted using the forward segmented condulet grouting technique based on the “shallow-buried bored excavation method”. According to the collapse treatment principle of “reinforcing the back non-collapsed section, sealing the rock surface and stabilizing the collapsed rock masses,” steel arches and long anchor bolts were used to reinforce the non-collapsed section to prevent the expansion of the accident. For the collapsed sections, the up-and-down bench + reserved core-soil method was used for ring excavation while heavy support was implemented with small-spacing steel arches. According to the feedback of numerical simulation and on-site monitoring data, all the treatment measures are rational and effective and may provide a reference for treatment in similar projects. 2016 Vol. 53 (2): 202-206 [Abstract] ( 1344 ) [HTML 1KB] [ PDF 2600KB] ( 2202 ) 207 Research on the Key Construction Techniques for an Ultra-Deep Specially-Shaped Diaphragm Wall The innovation and development of construction techniques for underground retaining structures prompts the construction of ultra-deep and specially-shaped diaphragm walls. Based on years of diaphragm wall construction experience and successful construction cases featuring specially-shaped diaphragm walls with extreme depth in Yujiabao, Tianjin, this paper presents the key points of construction techniques for this type of diaphragm wall, i.e., trench construction technology with the combination of a hydraulic grab and reverse circulation drilling rig, an empirical formula of verticality control for a specially-shaped ultra-deep diaphragm wall and the flexible connection method used for the rigid joint of a diaphragm wall. This study expands the scope of application for specially-shaped ultra-deep diaphragm walls. 2016 Vol. 53 (2): 207-212 [Abstract] ( 1376 ) [HTML 1KB] [ PDF 2234KB] ( 2108 ) 213 Guidance and Application of Engineering Geological Analysis for Construction of Tunnels on the Kunming-Nanning Passenger Dedicated Line Insufficient understanding of the characteristics of surrounding rock may cause problems with construction quality and economic losses due to various types of geological structures and the frequent change of rock mass properties during tunnel construction. Based on the construction of tunnels on the Kunming-Nanning passenger dedicated line, this paper discusses the characteristics of surrounding rock under different geological conditions and proposes corresponding measures in light of a comprehensive engineering geological analysis in order to give scientific guidance and ensure construction progress. 2016 Vol. 53 (2): 213-216 [Abstract] ( 1335 ) [HTML 1KB] [ PDF 1306KB] ( 2204 )

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