The renewal of the area around high-density urban rail transit stations is an important topic for the revitalization of existing urban public spaces.The pedestrian network and the infrastructure around it have a profound impact on the aggregation of passenger flow at rail transit stations.As urban rail transit lines continue to expand across China,a diminishing marginal effect is observed in the incremental passenger flow at various stations.To ensure a more effective alignment between the development intensity,land use nature,public facility density,and passenger flow intensity in urban renewal projects surrounding rail transit stations,and to fully leverage the agglomeration effects of spatial elements within these areas,this paper takes the urban renewal of the surrounding region of the Hi-Tech Central Station in Shenzhen as a case study.Firstly,based on the empirical data of well-functioning passenger flow and station area development intensity,the Gaoxinzhong Station is identified as an arrival-type station among the categories of arrival,departure,and balanced stations.Secondly,the quantitative relationship between the planned passenger flow and anticipated development intensity at the Hi-Tech Central Station is analyzed,revealing that the urban renewal capacity of the station area fails to meet expectations.Finally,a quantitative assessment is conducted on the ground and underground building space capacity,road network structure,and other relevant factors of the surrounding plots around the Hi-Tech Central Station,and a comprehensive evaluation is made of the potential induced passenger flow aggregation capacity of each plot,providing a design basis for achieving the planned capacity.
In order to enhance the stability of the coal mine shaft lifting vessel,the structural form of four-corner guide rails is often used to replace the interrupted part of the end tank passage.However,the current design method of four-corner guide rails is based on the design method of the end tank passage.However,due to the great differences in the structural forms and constraints between four-corner guide rails and the end tank passage,the reliability of the force of four-corner guide rails calculated by referring to the design method of the end tank passage is doubtful.In order to solve this problem,the acceleration time history curve of the four-corner guide rails under loading and unloading conditions is obtained through the field test of the force of the four-corner guide rails.By analyzing the time-history curve,the force of the four-corner guide rails is determined,and its characteristics and influencing factors are proved.After further regression analysis,the calculation method of horizontal force and vertical force of four-corner guide rails of coal mine shaft is established considering the lifting terminal load level.The calculation method based on the field test results is reliable and has important significance for improving the stability,safety and economy of the four-corner guide rails.
Injecting CO2 into underground formations for permanent storage is one of the key technologies for achieving carbon neutrality goals.Wellblock 38 in Wuqi Oilfield is the core area of the first domestic full-process CCUS demonstration project-the Yanchang Petroleum CCUS Demonstration Project,which has been injecting gas since 2014,now for a decade.The study of the migration state of CO2 after injection into the formation and the dynamic changes in the temperature and pressure of the storage layer are crucial for the safety assessment of carbon storage projects.This study,based on core,geological and test data from the CCUS demonstration area in Wuqi Oilfield,utilized the TOUGH2/ECO2N software platform to construct a three-dimensional numerical model to simulate the plume state of CO2 after injection into the formation and its impact on the temperature and pressure system of the formation.The results show that:CO2 tends to migrate to the upper part of the storage layer.In the initial stage of CO2 injection,the temperature around the well decreased sharply from 59.94℃to 48.2℃(a drop of 11.74℃),and the pressure increased from 12.6 MPa to a peak of 15.6 MPa(an increase of 23.81%).However,after 10 years of injection cessation,the temperature gradually returned to near the original value(60.2℃),and the pressure dropped to 12.8MPa(1.59%higher than the initial value).The temperature and pressure changes in the formation were more significant in the initial stage and gradually slowed down,eventually reaching a stable state.The impact of the injected CO2 fluid on the overall temperature and pressure of the formation was relatively limited.This study quantified the temperature and pressure response thresholds for CO2 storage in low-permeability oil reservoirs,revealing the coupling mechanism between the migration of supercritical CO2 and the energy balance of the formation,providing theoretical support for the design of storage schemes and the optimization of monitoring systems in similar reservoirs.
In order to study the mechanical properties and reinforcement mechanism of special-shaped cross-section polypropylene fiber reinforced shotcrete,compressive,splitting tensile,and flexural tests were conducted on benchmark shotcrete and special-shaped cross-section polypropylene fiber reinforced shotcrete,and SEM micro scanning tests were carried out.The results showed that the addition of special-shaped cross-section polypropylene fibers can improve the compressive strength,splitting tensile strength,and flexural strength of sprayed concrete.The most significant improvement was observed when the fiber content was 6 kg/m3,the compressive strength at 1 day,3 days,and 28 days,splitting tensile strength at 28 days,and flexural strength at 28 days were increased by 13.9%,5.8%,5.1%,26.8%,and 8.1%,respectively,compared to the benchmark concrete group.The toughness of sprayed concrete is enhanced by adding special-shaped cross-section polypropylene fibers,and the failure mode changes from brittle to ductile.Special-shaped cross-section polypropylene fibers can reduce the proportion of large pores in the concrete matrix,improve the compactness of the matrix,and reduce the width and number of microcracks at the interface between coarse aggregates and matrix,provide a bridging effect to absorb destructive energy,and enhance the strength and toughness of sprayed concrete.The research results can provide a theoretical basis for the application of special-shaped cross-section polypropylene fiber reinforced shotcrete.
In the process of freezing method construction of underground engineering in Huainan and Huaibei mining areas,the deep frozen soil is subjected to loading and unloading in different directions at the same time,showing a dynamic change from the initial original stress state to the increasing stress on one side and the decreasing stress on the other side.The uneven distribution of stress leads to different stress paths of the soil in front of the working face,so that the soil is in a three-way unequal stress state,which in turn affects its mechanical properties.Based on this,in order to further study the mechanical behavior of frozen soil under true triaxial stress state,this study analyzed the effects of different temperatures,initial stress states,and loading and unloading rates on the strength and deformation characteristics of frozen calcareous clay using a self-developed true triaxial apparatus for frozen soil.The test results show that under the same test conditions,when the loading rate increases from 0.4 mm/min to 0.8 mm/min,the slope of the generalized shear stress q and the generalized shear strain curve γ of the frozen calcareous clay gradually increases,that is,the slope of the stress-strain curve of the frozen calcareous clay increases with the increase of the loading rate,and the peak stress corresponding to the strain softening group also gradually increases.In addition,with the increase of initial stress and loading rate,the stress-strain curve of frozen calcareous clay changes from strain softening to strain hardening as a whole.Under different stress paths,the strengthening effect of loading rate on frozen calcareous clay gradually decreases with the increase of loading rate,and satisfies the power function relationship.Under the same freezing temperature T and loading rate v,the triaxial strength of frozen calcareous clay conforms to the Drucker-Prager criterion in the principal stress space,and the relationship expressions of α and K with freezing temperature T and loading rate v are given respectively.The research results can provide a theoretical basis for deep freezing shaft sinking.
To overcome the limitations of the conventional super-subloading surface constitutive model in capturing soil stress-induced anisotropy and the nonlinear degradation of shear modulus at small strains,this study presents an enhanced model.By incorporating the g(θ)method and integrating classical small-strain stiffness theory,the proposed model offers improved representation of both anisotropic behavior and the nonlinear shear modulus reduction under small-strain conditions.The new model was subsequently applied to predict triaxial shear test results for Shanghai soft clay,Fukakusa clay,and Hefei slightly expansive clay,as well as to simulate the deep excavation of the Huifu Road Station in Hefei Metro.The results demonstrate that the proposed model effectively captures the high initial shear modulus and its nonlinear attenuation under small-strain conditions,unifies the application of four yield criteria(von Mises,Mohr-Coulomb,Matsuoka-Nakai,and Lade-Duncan)to characterize stress-induced anisotropy,and successfully describes both the structural shear-shrinkage softening of soft clay and the shear-dilation softening of overconsolidated soil.The improved model not only effectively characterizes complex mechanical behaviors of natural soil but also accurately predicts deformation patterns of retaining piles during excavation processes.
In geotechnical site investigation,the distance between boreholes often makes the inter-borehole soil layer inferences rely on human experience under conditions of limited in situ tests and sampling.How to conduct intelligent and reliable soil stratigraphic division is a crucial research direction in the current information-oriented development of geotechnical engineering.This paper presents an intelligent soil stratigraphic layer division method by combining Bayesian Compressed Sensing(BCS),Support Vector Machine(SVM)classification,Gaussian Mixture Model(GMM),and Hidden Markov Random Field(HMRF)model.The application flowchart and soil layer division results are presented by taking the Nanjing Yangtze River floodplain ground as an example.The study shows that:BCS can reliably extend the blow count data from standard penetration test(SPT)for subsequent soil layer division;SVM classification can intelligently learn soil boundaries in the two-dimensional space of SPT blow count versus test depth,achieving an initial soil stratigraphic division;based on this,the preliminary optimization of soil layer division can be realized by using the GMM by considering the probability distribution of soil characteristic parameters;finally,the secondary optimization of soil layer division can be realized by using the HMRF model by incorporating spatial correlation constraints(i.e.,adjacent points tending to be the same soil type).Combining the four methods can intelligently and automatically divide soil layers,and can significantly improve the accuracy of overall soil layer division and soil layer boundary identification.
In recent years,the scale and speed of underground space construction have grown rapidly,and the development of deep underground spaces has become increasingly frequent.Under the background of the national spatial planning system,the urban underground space planning of Guangzhou city adheres to the people-centered approach,bottom line thinking,coordinated development,and safety,and explores the system and methods for preparing the underground space planning of super large cities.Firstly,the safety bottom line,resource protection bottom line,and control bottom line range are proposed as areas where underground space is not suitable for construction;Priority should be given to safety and comprehensive resource assessment should be carried out to determine suitable construction areas for underground spaces and general construction areas;To coordinate the comprehensive utilization of underground space,functional composite three-dimensional layering,graded zoning and classification guidance;To achieve deep integration of above ground and underground facilities,infrastructure+is proposed based on the characteristics of underground facilities;To build a safe and resilient underground space,identify disaster risks,classify and stage safety prevention measures,and coordinate above ground and underground disaster prevention and reduction facilities;To improve the efficiency of planning and control,and assist in the sustainable development of underground spaces,it is proposed to strengthen the guarantee mechanism.
In order to explore the causes of subway construction accidents and prevent their occurrence,an analysis was conducted on 18 serious and above subway construction accidents in China from 2001 to 2022.Elements such as individuals,organizations,behaviors,equipment,and environment were extracted from subway construction accidents,and a network of subway construction accident causes was constructed based on this.The complex Network modeling and analysis tool Network X is used to measure network indicators such as node degree,shortest path,and intermediary centrality,combining the measurement results to conduct comparative analysis on key nodes and causal links in networks caused by serious accidents,major accidents,and catastrophic accidents.The results indicate that serious accidents are mainly caused by the superposition of management factors and equipment factors,as well as the superposition of management factors and illegal operation behavior factors.Major accidents are mainly caused by the combination of illegal operations and unfavorable geological conditions.Unfavorable geological conditions are the key factors for improving the level of accidents.Catastrophic accidents are mainly caused by the combination of organizational management factors and illegal operations,among which the lack of preparation of construction plans is the key factor for further escalation of accidents.
In order to explore the optimization of air environment and ventilation design parameters in China's extra-long tunnels,this study first analyzed the statistical data of pollutant emission from motor vehicles in China,combined with literature research,and found that the concentration of NOx in China's tunnels was relatively high,and gradually became the most concerned pollutants in tunnel ventilation.In this study,a field study was carried out in the Yanglin extra-long tunnel in Yunnan.The results show that the peak NO2 concentration exceeds the ventilation design limit by 2.1 times during the test period,and the emission factors of CO,NO2 and PM of gasoline vehicles are 0.79 g/(km·veh),0.04 g/(km·veh)and 10.0 mg/(km·veh),respectively.diesel vehicles are 2.18 g/(km·veh),1.27 g/(km·veh)and 149 mg/(km·veh),respectively.Compared with the pollutant emission values of domestic and foreign tunnel ventilation design standards,it is found that the current standard values in China are too large.According to the measured emission factors,the required air volume is calculated,and the result is more than 50％lower than the required air volume in Guidelines for Design of Ventilation of Highway Tunnel,which is similar to the required air volume in Standard for the Design of Road Tunnels,and the control item of the required air volume is NO2 concentration.The results of this study can provide reference for the calculation of pollutant emission and air demand in tunnel ventilation design in China.
At present,the construction of large-span and super-large-span subway tunnels is increasing.Temporary support is often designed to reduce the span in the construction of those tunnels.However,temporary support needs to be removed before secondary lining is constructed due to the spatial overlap between them.The removal of temporary support is the weak situation,because the original stress balance of the structure will be broken.Improper construction can easily cause safety accidents such as tunnel collapse.In view of the lack of systematic research on the structural mechanical response and safety of the super-large-span tunnel constructed by the double-layer initial support arch-cover method at home and abroad,this paper takes the four-line parallel tunnel of Huahua section of Guangzhou Metro Line 11 as the basis project.Through the combination of theoretical analysis and numerical calculation,the mechanical response and safety of the structure during the dismantling of the tunnel are analyzed from both horizontal and vertical aspects.Finally,a scientific,reasonable,safe,efficient and rapid dismantling scheme was determined,and successfully passed the inspection of on-site construction.The results show that it is feasible to dismantle the super-large-span tunnel in urban soft stratum by using the scheme of'first edge and then middle,and symmetrical demolition in cross direction,first three demolition and one demolition,and then one demolition and one demolition in longitudinal direction',which can provide reference and guidance for subsequent projects.
The underground caverns has the advantages of safe concealment,environmental protection,and land saving.However,due to its enclosed space,pollutants are easily accumulated during construction.Consequently,improving the operation efficiency of the ventilation system and reducing energy consumption during the construction period are the keys to ensuring the safety of personnel and the normal operation of equipment.Taking an underground cavern project as the object,a theoretical calculation is used to determine the frequency conversion control strategy of the cavern fan,and numerical simulation(Fluent)is used to analyze the concentration changes of benzene and dust pollutants in the underground cavern before and after frequency conversion under the pressure ventilation condition,the field environmental quality monitoring data are compared and validated.The results show that:the concentration of pollutants on the longitudinal section of each cavern before and after continuous ventilation frequency conversion increases gradually and then stabilizes.The gradual conservation of pollutant generation and emission rates,with pollutant concentrations at breathing height below the limit values,verifies the effectiveness of the variable frequency strategy.In the construction site,the ventilation dynamic control system is established to realize the variable air volume control.When the axial flow fan maintains an energy-saving rate of around 25％and the jet fan maintains an energy-saving rate of over 60％,the pollutant concentration in the cavern remains within the limit range.This not only ensures the safety of construction personnel but also reduces energy consumption.The study can provide reference for the ventilation frequency conversion design of multi-face construction in underground caverns.
Understanding the resistance coefficient along the tunnel wall is helpful to optimize the ventilation design of tunnel construction and improve the rationality of ventilation scheme.The influence of the height,shape and spacing of rough elements on the resistance coefficient along the tunnel wall is studied.Through the model test and the numerical model,the difference between the empirical formula and the numerical simulation results was explored.The results show that:With the higher height of the rough element on the tunnel wall,the influence on the resistance coefficient along the tunnel wall is less.The shape of rough elements on the tunnel wall has a great influence on the resistance coefficient along the tunnel,and the semi-spherical rough elements have the smallest resistance coefficient along the way.Comparing the calculated results of empirical formula with the numerical simulation results,the difference between them is relatively stable,which is related to the height of rough elements.The correction coefficient α is proposed for the empirical formula,and the corresponding relationship between α and the average roughness height Δ of the wall is α=1.29+0.024 8Δ.
Based on the actual project,a three-dimensional simulation model is constructed to study the deformation and stress characteristics of the special-shaped soil-rock foundation pit excavation of the suspended pile.By adopting bar demolition method,a strength redundancy expression method based on the ultimate bearing capacity of the inner support is proposed,and two inner support importance evaluation indexes of the associated bar and the correlation coefficient are proposed.The findings indicate:(1)Deformation of special-shaped soil-rock foundation pit with the suspended pile mainly concentrates in the upper soil layers,the position of the positive angle and the middle of the longest side of the foundation pit.,achieving a peak value of 17.02 mm.This deformation is linked to the geometric composition and stiffness distribution of the support system itself.Notably,the upper deformation of the supporting structure at the positive corner of the foundation pit is larger,and the influence range is about 2 times that at the negative corner;(2)The strength redundancy based on ultimate bearing capacity can comprehensively and quantitatively evaluate the redundancy of deep foundation pits,where the associated bar can pinpoint which component would be most affected after damage occurs,while the correlation coefficient can,to some extent,reflect critical components within support structures;(3)The redundancy of the inner support based on the ultimate bearing capacity is related to its own load and the arrangement of adjacent support bars.The minimum is 4.18.The associated bar are mainly concentrated in the adjacent bars.In the design of the correlation coefficient,should be optimized to decrease the correlation coefficient of the bar and improve the overall reliability of the support structure.
Before refracturing,due to the long-term injection and production of old wells,the distribution of regional formation pressure shows non-uniform variations.It is urgent to coupling consider this non-uniform stress evolution in the subsequent refracturing.For this purpose,taking the Chang-6 reservoir in the W block of Changqing Oilfield as an example,an in-situ stress evolution model under long-term injection and production of vertical wells is established using the Fast Lagrangian Analysis of Continua.The simulated stress field is then imported into a hydrofracture numerical model based on the discrete lattice method for modeling fracture propagation of refracturing,achieving an integrated simulation of in-situ stress evolution and hydraulic fracturing evolution.The results show that:(1)After the production of well WJ,the pore pressure around this well decreases by about 4 MPa,and the two horizontal principal stresses experience a similar synchronous reduction,but the decreasing magnitude is only about 2.5 MPa.This indicates that production will result in a decrease in the total stress but an increase in the effective stress.(2)Hydraulic fractures tend to propagate towards the depleted area preferentially.The engineering measures,such as slowly injecting fluid or shutting in before refracturing to increase the formation pressure in the depleted area,are recommended on site,thereby avoiding or reducing refracturing fractures extending into these areas.(3)As the injection time increases,the primary growth of refracturing fractures transitions from area expansion to width expansion,indicating that a short-duration,high-volume refracturing should be adopted.On the one hand,maximizing reservoir transformation can be achieved in a short time,on the other hand,increasing the injection rate can promote the even expansion of multiple fractures.
At present,the actual pollutant emissions under slag removal stage have not been fully considered in the ventilation of tunnel construction,greatly increasing the required air volume for tunnel construction and causing huge energy waste.On-site testing of CO concentration and wind speed was conducted based on a certain tunnel,the changes in CO concentration over time under different processes were studied,and the effects of engineering vehicle emissions and fan air supply on the distribution of CO concentration and wind speed in the tunnel were analyzed.The results show that:The CO concentration on the palm face remained basically unchanged within 25 minutes after blasting,about 200 mg/m3;During the slag removal stage,the CO concentration on the palm surface decreases linearly and reaches the standard limit(30 mg/m3)after 90 minutes of ventilation;The actual required air volume for tunnel construction during the slag removal stage is much lower than the standard requirements.As the supply air volume increases,the CO concentration in the return air section decreases exponentially.Based on the research results,an empirical calculation formula for CO concentration in highway tunnel construction ventilation is proposed,which takes into account the coupling effects of CO emissions and supply air volume.
Microwave radiation,as an emerging rock-breaking technology,shows promising applications in assisting mechanical rock fragmentation.To explore the damage mechanisms of microwave radiation on quartz sandstone,this study investigates the variations in uniaxial compressive strength,wave velocity,and macro-microscopic damage characteristics of quartz sandstone under different microwave powers and exposure times.The results indicate that with increasing microwave power and exposure time,the uniaxial compressive strength and elastic modulus exhibit a decreasing trend,while peak strain gradually increases.Both P-wave and S-wave velocities show an overall decline.The damage factor shows an upward trend,and the longer the radiation time,the greater the increase in the damage factor.As microwave power and exposure time increase,the degree of quartz sandstone fragmentation significantly intensifies,resulting in smaller and more numerous fragments.The failure mode shifts from a single shear failure to shear and cleavage along fragile planes.SEM images and fractal dimension(D-value)results indicate that as microwave exposure time increases,the number,length,width,and depth of internal cracks in specimens show an increasing trend,evolving from initial single cracks to superimposed fractures.
Urban underground logistics system is a complex technology and engineering system developed by the cross integration of modern logistics,transportation,vehicle and underground engineering.Based on the concept of the underground logistics system-pipeline-vehicle collaborative design,a set of cargo vehicle design methods for urban underground pipeline logistics is established.Vehicle technology research and design include vehicle scheme research,vehicle structure and new energy function design,vehicle autonomous driving technology design.This paper designs a special cargo vehicle for pipeline logistics,which is a pipe with inner diameter of 3 800 mm and van with exterior dimension length of 5 000 mum,width of 1 500 mum and height of 2 200 mm.The vehicle has automatic driving,high power,long-distance automatic transportation of goods and wireless charging function when the vehicle is driving in the pipeline.The vehicle design adopts the design concept of green,low-carbon,energy saving and integrated application of more new technological innovations.The technical research and design of cargo vehicle conducted in this paper provides a design scheme of cargo vehicle test sample vehicle and a new vehicle design method of underground pipeline logistics for the implementation of commercial urban underground logistics project.
In order to study the dynamic changes and amplitude values of groundwater level in karst mountainous areas,taking the karst mountainous city of Guiyang as an example,selecting daily monitoring data and precipitation data from nine groundwater level dynamic observation points from 2022 to 2023,autocorrelation and cross-correlation analysis are used to analyze the response of groundwater level to precipitation and explore the influence of runoff and drainage conditions and terrain slope on the dynamic changes of groundwater level.The results show that:(1)The groundwater level in the study area is buried at a depth of 1.21～27.68 m,with an annual variation range of 1.54～11.99 m,and there are significant differences in the spatiotemporal distribution of groundwater level dynamics;(2)The relevant analysis results indicate that there is a significant lag in the response of groundwater level to precipitation signals in the study area,with an average lag time of 0～4 days,and it gradually increases from the supply area to the discharge area;(3)The terrain slope is an important factor affecting the amplitude of groundwater level variation in karst mountainous areas.The terrain slope in the study area is positively correlated with the amplitude and variation of groundwater level,with linear goodness of fit(R2)of 0.65 and 0.78,respectively;(4)The depth of groundwater level gradually decreases from the recharge area to the discharge area,and the range of water level changes from the runoff area to the recharge area to the discharge area.
With the global population aging, urban public transportation systems, particularly subway stations, face significant challenges. This paper outlines the basic concepts of age-friendly design for subway stations, analyzes the behavioral characteristics of elderly passengers, and examines their specific needs regarding barrier-free facilities, information signage systems, and station environments. The paper then reviews recent research advancements, including adaptations of facilities for elderly use, integration of smart technologies, and the development of assessment frameworks tailored to age-friendly criteria. Finally, it identifies key challenges in age-friendly renovations, such as insufficient user research, inadequate data analysis, incomplete evaluation systems, a single-scheme verification mechanism and uneven overall development. The paper also outlines future directions in enhancing intelligent systems and evaluation frameworks to better accommodate the needs of elderly passengers and improve their overall travel experience.
