中铁二院工程集团有限责任公司

Aiming at the many uncertain factors in the large deformation risk assessment of deep lying tunnel in complex mountainous area,this study proposes a novel evaluation methodology for squeezing tunnel large deformations based on combined weighting method and unascertained measure theory.Through systematic investigation of large deformation characteristics in high-stress deep-buried tunnels,an evaluation system comprising seven core indicators was established,including the rock compressive strength,elastic modulus,maximum principal stress,surrounding strength-stress ratio,geological structure,surrounding rock grade,and groundwater.By employing a distance function to integrate the analytic hierarchy process(AHP)with entropy weighting method,it developed a combined subjective-objective weighting model that achieves scientifically validated weight allocation for risk assessment indicators of squeezing tunnel large deformations.Based on unascertained measure theory,this study establishes a risk assessment model for large deformations in squeezing tunnels.The model employs linear single-index measure functions to construct a measurement evaluation matrix,and utilizes confidence criterion for determining deformation risk levels.The model was applied to four representative soft-rock tunnels with large deformations:Yangjiaping Tunnel on the Chengdu-Lanzhou Railway,and Lingdana,Langzhen No.2,and Jiangmula Tunnels on the Southeastern Tibet Railway.Comparative analysis with actual deformation data demonstrated strong agreement between model predictions and field measurements.These results validate the model′s effectiveness and accuracy for risk assessment of large deformations in complex mountainous deep-buried tunnels,establishing a novel approach for such geotechnical evaluations.

Stabilizing pile with rigid platform is a new type of composite stabilizing structure feasibly used to retain high embankment under special conditions,and particularly suitable for the typical embankments on steep terrains in railway engineering.It is mainly composed of upper loaded pile,middle rigid platform and lower inserted pile in the foundation.In order to reveal distribution mode of lateral earth pressure,internal force and displacement characteristics of the retaining structure under external loads,based on typical high embankments in Mile-Mengzi railway engineering in Yunnan province some model tests have been conducted with geometric and gravity similarity ratio of 1∶13 and 1∶1,respectively,and the related numerical simulation and theoretical method are jointly utilized to analyze the problem further.The results show that from the perspective of the relationship between the deformation development of pile-soil system and exerted thrust loads,the development of horizontal displacement of the retaining structure can be divided into three stages:small linear elastic deformation stage under low thrust,elastoplastic deformation stage with small increasing growth rate,and plastic deformation stage with significant increasing growth rate.Distribution curve of lateral earth pressure on the loaded pile-slab wall shows a parabolic pattern with a vertex at the middle-lower part.The earth pressure on the front and the back side of the inserted pile in the foundation generally presents parabolic distribution with small value at the top and big vale at the bottom,big value at the top and small value at the bottom,respectively.The maximum earth pressure on the back side of the inserted pile is located at its top,and the resultant force of the earth pressure on the back side accounts for 24％to 37％of that on the front side.There are zero bending moment and shear force in the middle of the inserted pile.Compared with internal forces at the bottom of the loaded pile,the bending moment and shear force at the top of the inserted pile are significantly reduced by 55％to 60％and 93％to 94％,respectively.The maximum bending moments of the loaded and inserted piles calculated by China railway specification are 16％to 36％and 16％to 23％higher than the experimental values,respectively,which suggests the proposed method in the specification is fairly conservative.Compared with the traditional stabilizing pile with invariable cross section,the bending moment at the top of the inserted pile is reduced by 56％to 63％,which indicates that the new retaining structure can greatly improve the mechanical state of the'fixed segment'of the traditional stabilizing pile,and generally be of remarkable superiority in terms of mechanical performance.

[Objective]Existing urban rail transit turnouts suffer from low lateral crossing speed,which adversely affects turn-back capacity.To enable 8-car A-type metro trains to a-chieve a capacity of 30 pairs per hour in the long term,it is necessary to design a turnout structure scheme that can meet high-speed crossing requirements,with a lateral crossing speed of up to 67 km/h.[Method]The research takes a No.14 turnout with a rail mass specification of 60 kg/m(hereinafter referred to as'No.14 turnout')as research object,and a struc-tural design scheme for the No.14 turnout and its diamond crossing is proposed.Based on current relevant standards and specifications,the turnout conversion calculation theory is em-ployed to perform switch rail conversion calculations for the proposed design scheme.A seamless turnout finite element model is established to conduct static simulation analysis for the design scheme of No.14 seamless turnout.[Result & Conclu-sion]The proposed design scheme meets the required control indicators for turnout conversion force,maximum allowable displacement,and minimum wheel flange groove width.Fur-thermore,the strength of the turnout rails,force transmission components,and longitudinal displacement of movable parts are all compliant with the specifications.

[Objective]Sound barriers are widely used in el-evated sections of urban rail transit.However,studies on their actual noise reduction performance during operation remain limited.Therefore,it is necessary to investigate the noise re-duction effectiveness of vertical noise barriers in real operation conditions and analyze the characteristics and distribution pat-terns of noise.[Method]Using the sound barriers of Ningbo Rail Transit Line 1 as the engineering background,measuring points are placed at different heights(2 m,3 m,and 4m)on vertical sound barriers.Noise levels are monitored as trains passing these points,and the acoustic characteristics such as sound pressure level spectrum and insertion loss are analyzed.[Result & Conclusion]The noise energy generated by train operation is distributed over a broad frequency range,with dominant frequencies between 500 Hz and 800 Hz near the pri-mary noise sources.Within the acoustic shadow zone of the sound barriers,lower measurement points exhibit better noise reduction effects.The sound barriers are more effective at at-tenuating high-frequency noise than low-frequency noise.At a distance of 7.5 m from the track centerline,the average noise reduction values in the acoustic shadow zone for 2 m,3 m,and 4 m high vertical sound barriers are 4.0 dB(A),6.7 dB(A),and 11.1 dB(A),respectively.

[Objective]To achieve cost efficiency and low-carbon transformation in rail transit,the planning,design,and implementation of green and low-carbon urban rail transit sys-tems is investigated.[Method]Aiming at life-cycle sustain-able development,through comprehensive route selection and laying methods optimization(mainly elevated),Shenzhen Metro Line 6 innovatively applies systematic technologies such as comprehensive vibration and noise reduction technology for elevated lines,prefabricated and assembled green construction(such as U-shaped beams and floating plate tracks),distribu-ted photovoltaic power generation,regenerative braking energy feedback,ecological sponge vehicle depot design,intelligent cloud platform and TOD(transit oriented development)model intensive land utilization,etc.,to explore green and low-car-bon planning,design and practice paths.[Result&Conclu-sion]The green and low-carbon technology system of Shen-zhen Metro Line 6 has demonstrated remarkable outcomes:construction costs are reduced by approximately 45％(10.9 billion yuan)compared to a fully underground scheme,with a 2.4 million-ton carbon emission reduction in construction-phase.The operational energy consumption is decreased by 40％(annual electricity savings of 33.6 million kW·h),with accumulated carbon emission reduction of 580 000 tons in 25 years.The annual power generation and energy saving by u-sing photovoltaic and regenerative braking technologies are 6.78 million kW·h;the land development income is expected to reach 30 billion yuan(RMB).This case provides a replica-ble technology integration solution for urban rail transit to a-chieve the carbon peak and carbon neutrality(shorten as"dual carbon")goals,proving that the green,low-carbon and high-quality sustainable development can be collaboratively achieved through systematic innovation.