| With the rapid development of China’s economy and society and the rapid expansion of urban population,municipal pipelines such as water,electricity,gas,communication,and network are increasing year by year,so underground utility tunnels have been widely promoted and applied in a short period of time.At present,the underground utility tunnel has become a major national demand project as important as high-speed rail,water conservancy,and reconstruction of shanty towns,at the same time,it forms a key underground space construction project together with rail engineering and large-scale underground public works.However,the current stage of the utility tunnel project mainly uses traditional reinforced concrete materials combined with cast-in-place,semi-prefabricated,stacked assembly,full-section prefabrication and other processes for the construction of the tunnel body.During this period,a variety of new types of utility tunnel construction machinery have also emerged to replace the traditional scattered and assembled brackets,but there are always problems such as quality,construction period,cost,and pollution.In recent years,the prefabricated corrugated steel utility tunnel has been piloted due to its advantages of strong applicability,light weight,fast construction,low cost,environment friendly,and easy quality control.However,its structure selection,load-bearing deformation characteristics and design calculation methods are immature,and lack of systematic research results,which seriously restricts the popularization of this new type of steel structure.In view of the existing research results,application progress,construction technology and problems of the prefabricated corrugated steel utility tunnel,and this paper,based on a large number of investigations and drawing on the relatively mature results of the current research on corrugated steel pipe culverts for highways,combined with the characteristics of the underground utility tunnel project,a new structure of prefabricated square-arch corrugated steel utility tunnel is proposed.The stress and deformation characteristics and bearing performance of this new structure are systematically studied through comprehensive means including model test,field full-scale test,finite element numerical simulation theoretical analysis,and the influence of foundation soil,backfill soil,section shape,square-arch section parameters and waveform parameters on the performance of utility tunnel structure is analyzed.Finally,the design calculation method is proposed to provide support for the design and engineering application of the new prefabricated square-arch corrugated steel utility tunnel,which is of great significance to improve the overall construction technology level of the underground utility tunnel.The main research results of the paper are as follows:(1)The stress and deformation characteristics and differences of single-cabin corrugated steel utility tunnel with different cross-section shapes are compared and studied through model tests,and the technical advantages of square arched cross-section are demonstrated.The study found that the mechanical characteristics of the utility tunnel with different cross-sectional shapes are quite different.The roof vault stress of the square arched utility tunnel and the tube top stress of the circular utility tunnel only account for 69.2% and 33.1% of the stress at the midpoint of the top plate of the square utility tunnel,respectively.The square section is the most unfavorable section of the underground corrugated steel utility tunnel,and the safety and reliability are poor.The shallow buried small-section cable pipe gallery can be considered for application.The stress distribution of each point in the circumferential direction of the circular utility tunnel is relatively uniform,and the deformation coordination is good,but its space utilization rate is low,and the brackets in the tunnel are difficult to set up.Circular utility tunnel is not suitable for conventional trunk line,but can be used for branch line that transports special single pipeline.The mechanical performance of the square arched utility tunnel is between the square and the circular one,and the space utilization rate is high.It is the preferred section of the trunk tunnel.(2)The model test of the square arched single-cabin corrugated steel utility tunnel under the conditions of different spans,different clear heights and different arch rises was carried out.The study pointed out that the measures to effectively increase the cross-sectional area by increasing the roof span and the clear height of the side plates will cause the roof stress to increase,and the roof stress is more sensitive to the change of rise-span ratio.When the arch rise of the same roof increases,the stress at vault increases but the influence range is limited,and the stress changes outside the vault area are limited.The study also emphasized that factors such as burial depth and waveform parameters should be fully considered in the actual utility tunnel project to further optimize the design of the square arched section.(3)In the square arched three-cabin corrugated steel utility tunnel structure,the roof support conditions have a relatively large influence on its stress,and there is a significant stress concentration phenomenon at the arch springing adjacent to the vertical plate of the cabin.In this paper,it is found through model test research that only under the condition of covering soil of 2.5 m,when the initial stress ratio is 0.25,0.5,and 1,the stress at the arch springing adjacent to the vertical plate on the roof of the large tank is 1.3 times,2.5 times and 3 times the stress at the vault,respectively.And the excessive stress at this position will cause damage to the utility tunnel structure,and reinforcement measures should be taken.The horizontal pressure changes induced by construction operations such as adjacent heaped load and adjacent excavation have a significant impact on the stress and deformation of the square arched three-cabin corrugated steel utility tunnel,especially the horizontal loading under shallow burial conditions and the horizontal unloading conditions under deep burial conditions,in which the horizontal unloading is more likely to cause the strength problem of the top plate and the stability problem of the side plate for the large-span utility tunnel.(4)The full-scale field test of the square arched double-cabin corrugated steel utility tunnel under the real stress state was carried out.High-precision sensing equipment such as distributed optical fiber sensors,fiber grating bolt stress gauges,and total stations were used to obtain the test data of strain of corrugated steel plates,stress of joint bolts,overall settlement,and joint opening of the steel structure.Through the test,the stress and deformation law and bearing characteristics of the square arched double-cabin corrugated steel utility tunnel under the actual backfill loading and the normal service limit load are clarified.The research pointed out that the square arched utility tunnel structure formed by deep-wave corrugated steel plate assembly has excellent bearing performance.The stress of the top plate in each assembly is much greater than that of other components,which controls the comprehensive bearing performance of the tunnel body.The mechanical response of the joint bolts is complex during the whole loading process,which is significantly affected by the loading time,loading sequence,loading method,loading rate,etc.,and is accompanied by fluctuation extremes.However,the overall stress level will gradually decrease with the coordinated deformation between the utility tunnel structure and soil.Optimizing the backfill construction process can effectively improve the stress of the bolts.(5)The refined finite element model of the square arched single-cabin corrugated steel utility tunnel was constructed by the finite element simulation analysis method,and the sensitivity analysis of load-bearing and deformation parameters and structural optimization of the new structure under different influencing factors were carried out.The research shows that the backfill factor has a greater impact on the structure than the foundation soil factor.When the elastic modulus of the foundation soil is doubled,the stress at the vault of the crest section on the outer surface of the roof is only reduced by 6%;when the elastic modulus of the backfill soil increases by 50% and other factors remain unchanged,the stress at the roof vault of the same utility tunnel structure decreases by 14.9%,while the internal friction angle of the backfill soil increases by 40% and other factors remain unchanged,the stress decreases by 22.6%.Therefore,the use of well-graded backfill,layered compaction and other measures can significantly enhance the restraint of the soil around utility tunnel structure and exert the shear resistance of the soil,thereby reducing the external load acting on the structure and helping to improve the bearing capacity and overall stability of the corrugated steel utility tunnel.For the deep-buried corrugated steel utility tunnel,the deep-wave corrugated steel plate is the first choice,and moderately increasing the wave height can reduce the stress of the corrugated steel plate and improve the bearing performance of the tunnel structure.Increasing the plate thickness can effectively reduce the structural deformation,but it needs to be reasonably determined by comprehensively considering the service environment,construction technology,and engineering cost.The research suggests that the corrugation parameters of “large corrugation pitch,deep corrugation depth,and small plate thickness” can be preferentially selected in the design process of the square arched corrugated steel utility tunnel,and optimized on this basis.(6)It is recommended to use the vertical earth pressure calculation formula in the CHBDC specification when designing the structure of square arched corrugated steel utility tunnel.Due to its unique section type and connection characteristics,the earth pressure on different positions of the plate is quite different.According to the test results of this paper,for the square arched single-cabin corrugated steel utility tunnel structure,it is recommended to multiply the influence coefficient f = 1.3 on the basis of the calculation formula in CHBDC specification as the dead-load standard value of the new structure,and for the multi-cabin corrugated steel utility tunnel structure,f = 1.6 is recommended.(7)Combined with the unique cross-sectional characteristics,connection properties and construction technology of the square arched single-cabin corrugated steel utility tunnel,a loadstructure calculation model considering the difference in stiffness of connection point and section shape is proposed,and also the calculation method of the internal force and deformation of the utility tunnel structure is deduced and formed in this paper.Based on the model test as an example,the theoretical calculation value of the proposed method is compared and verified with the test results,and the results show that the stiffness of the section steel flange between corrugated steel plates is 20 times that of the plates.According to the calculation method,the internal force and deformation of the utility tunnel structure is in good agreement with the test results,which fully proves the reliability and effectiveness of the method.It provides theoretical support for the design,deformation prediction and safety assessment for the new steel structure. |
PDF Full Text Request